Technical Tools Used in the Development of
Virginia's Tributary Strategies
VIRGINIA
TRIBUTARY
STRATEGIES
September, 2000
Technical Summary Report
i tinr.-M 1 l.n ĻĻ i .
Prepared by:
Arthur J. Butt, Lewis C. Linker, Jeffrey S. Sweeney, Gary W Shenk,
Richard Batiuk, and Carl Cerco
2^
Chesapeake Bay Program

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Acknowledgements
The authors would like to acknowledge the specific contributions of the following
individuals and Subcommittee members in the preparation of this report:
Bill Brown, Chesapeake Research Consortium, Chesapeake Bay Program Office, Annapolis, MD
Kate Hopkins, University of Maryland Center for Environmental Science, Chesapeake Bay
Program Office, Annapolis, MD
Ping Wang, University of Maryland Center for Environmental Science, Chesapeake Bay
Program Office, Annapolis, MD
Chao-Hsi Chang, Applied Digital Solutions, Chesapeake Bay Program Office, Annapolis, MD
Lori Sprague, U.S. Geological Survey, Richmond, VA
Modeling Subcommittee Members, Chesapeake Bay Program
Model Evaluation Group:
William C. Boicourt, University of Maryland, Cambridge, MD
Kevin Farley, Manhattan College, Riverdale, NY
Wu-Seng Lung, University of Virginia, Charlottesville, VA
Jay L. Taft, Harvard University, Cambridge, MA
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Table of Contents
Introduction 	 1
Section 1: Overview of Airshed, Watershed, and Estuary Models
1.1	Background 		1-1
1.2	Airshed Model 		1-2
1.3	Watershed Model 		1-5
1.4	Estuary Model 		1-9
1.5	Other Diagnostic Tools 		1-14
Section 2: Scenarios
2.1	Overview	 II-1
2.2	Scenario Descriptions 	 II-1
Section 3: Tracer Analysis
3.1	B ackground		Ill -1
3.2	Response to Conservative Dissolved Tracer		Ill -2
3.3	Response to Conservative Particulate Tracer		Ill -7
Section 4: Basin Descriptions with Nutrient and Sediment Loads
4.1	Basin Descriptions		IV-1
4.2	Rappahannock Basin Loads		IV -14
4.3	York Basin Loads 		IV-17
4.4	James Basin Loads 		IV -22
4.5	Eastern Shore Basin Loads 		IV -25
Section 5: Water Quality and Bay Grass Responses
5.1	Overview		V -1
5.2	Rappahannock Basin Water and Habitat Quality		V -7
5.3	York Basin Water and Habitat Quality		V -10
5.4	James Basin Water and Habitat Quality 		V -13
5.5	Eastern Shore Basin Water and Habitat Quality		V -17
5.6	Conclusions and Findings		V -19
Section 6: Small Coastal Basin Monitoring and Modeling
6.1	Background		VI -1
6.2	Small Coastal Basin Monitoring and Modeling		VI -4
6.3	Summary and Conclusions		VI -5
References		R-l
Appendices
Appendix A: Phase IV Chesapeake Bay Watershed Model Documentation 		A-l
Appendix B: Scenario Descriptions 		B-l
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Introduction
Virginia is committed to setting nutrient reduction goals and developing tributary
strategies for the lower Virginia tributaries by legislative statutes and directives of the
Chesapeake Executive Council. To accomplish this Chesapeake Bay Program milestone,
the best science, technical findings, and management tools are being used. The diverse
regional and local stakeholders and partners involved in the goal-setting and tributary
strategy development process were provided with in-depth information of direct
relevance from the best data available to the Bay's scientific and technical community.
This document is a synthesis of the overall findings from modeling results conducted
during the assessment phase of Virginia's Tributary Strategy process.
To initiate the tributary strategy process, a workshop entitled the Virginia Tributary
Technical Synthesis Workshop was held at the Virginia Institute of Marine Science on
March 17-18, 1998. The objective of the workshop was to develop and reach consensus
on status and trends information of various water quality and living resource changes in
the lower Virginia Chesapeake Bay and tributary basins. Data from the first 12 years of
Virginia's Chesapeake Bay Monitoring Program (1985-1996) for the Rappahannock,
York, James, Western and Eastern Shore basins, and lower Chesapeake Bay were
reviewed. A final report entitled Virginia Tributary Basin Specific Profiles: Syntheses of
the Underlying Technical Information Supporting Tributary Strategy Development was
printed in September, 1998.
A second workshop was held on November 20, 1998 to present preliminary model
results from the Chesapeake Bay Estuary Model Package (CBEMP). Results from the
first series of CBEMP ranging scenarios showed environmental responses for each of
Virginia's tributaries under different levels of nutrient and sediment reductions. The
model scenario workshop and subsequent additional scenarios provided Virginia's
Tributary Strategy Technical Review Committee (TRC) members and interested
stakeholders with information needed to set pollutant reduction goals.
This report contains a review of the overall modeling framework, as presented at the
modeling workshop, as well as other models used in the tributary strategy process. In
addition, it includes detailed descriptions of the scenarios, results, and interpretations of
these modeling results. A unique feature of the Virginia Tributary Strategy development
is that, for the first time, qualitative measures of key living resources and habitat needed
to sustain these resources in the lower Bay tributaries, were addressed.
Results and products of the cross-media models of the airshed, watershed, and estuary
were reviewed by Tributary Strategy workgroups of the Rappahannock, York, James, and
Eastern Shore basins. These tributary teams consisted of citizens, local government
leaders, environmental group representatives, and industry representatives. The
workgroups assisted in the interpretation of model results and ultimately, developed
tailored plans for the environmental protection of each tributary, taking into account the
unique characteristics of each basin.
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The plans adopted were innovative, ambitious, and practical. For the first time, air
reductions in the deposition of nitrogen nutrients were considered in the development of
nutrient reduction strategies. Effects of nutrient and sediment loads on key living
resources like SAV were considered for the first time. Each of the lower tributary
strategies contribute to environmental protection of the Chesapeake Bay through local
environmental protection, principally directed at the environmental conditions in each of
the tributaries of each of the lower tributaries.
Additional information on the tributary strategies adopted by the basin workgroups
can be found in each Tributary Strategy available on the web site of the Virginia
Department of Environmental Quality.
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Section 1: Overview of Airshed, Watershed, and Estuary Models
1.1 Background
The cross-media models used in this analysis consist of three models, an airshed model, a
watershed model, and a model of the Chesapeake estuary (Figure 1.1). These models are linked
together so that the output of one simulation provides input data for another. The simulation
period is the ten-year interval from January
1, 1985 to December 31, 1994. These
models have been used by the Chesapeake
Bay Program for more than a decade and
have been refined and upgraded several
times. Application of the cross-media
models assisted in determining tributary
allocations for each of the four lower
Virginia basins; the Rappahannock, York,
James, and Eastern Shore.
A 1992 re-evaluation of pollutant loads
and responses found that, taken as a group,
the four lower basins had relatively little
effect on Chesapeake Bay water quality. A
1992 version of the estuary model
estimated only mainstem water quality. It
could not simulate tributary water quality in sufficient detail for basin allocations in the lower four
catchments. Prompted by the 1992 Executive Council Directive, the Chesapeake Bay Program
and Virginia have worked together over the last six years to develop a detailed model of the lower
Bay and its tributaries. Refinements to the hydrodynamic and water quality model have increased
simulated spatial detail five-fold, mostly in Virginia waters. Capabilities of the model were
expanded to include estimates of key water quality and habitat measurements and their response
to changes in nutrient and sediment loads. As a result, the Virginia tributary teams were provided
with water quality and habitat responses to these pollutant reductions that came from both within
and outside the basin.
Further information on the entire suite of Chesapeake Bay Program models, their
documentation and applications can be found at the following two Web sites:
1)	http://www.chesapeakebay.net/info/model.cfm
2)	http://www.chesapeakebay.net/search/subcommittee.cfm?GROUP_INIT=MODSC&GROUP
_AFFIL=Modeling
Figure 1.1 Cross-Media Models of the Chesapeake
Bay
Regional Acid Deposition Model - RADM
Chesapeake Bay Estuary Modeling Package
t	i	t
Hydrodynamic Model of Bay, tributaries, and continental shelf
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1.2 Airshed Model
The Chesapeake Bay Program airshed model provides estimates of atmospheric deposition
loads of nitrogen. A product of the EPA National Exposure Research Laboratory in Research
Triangle Park, NC, RADM (pronounced "radum"), is an acronym for Regional Acid Deposition
Model. RADM is a three dimensional model which tracks nutrient emissions across the eastern
United States (Dennis, 1996). There are two RADM grids meeting various resolution needs. A
larger grid scale, covering the entire RADM domain, contains about 20,000 square cells of 6400
square kilometers each. A finer grid scale covers the region of the Chesapeake Bay watershed
and has 60,000 cells, each covering 400 square kilometers. The model domain in the vertical is
15 cells deep reaching from ground level to the top of the free troposphere. The depth of the cells
increases with altitude. One of the findings of the RADM is that the Chesapeake Bay "airshed,"
defined as the area accounting for 75% of the watershed deposition, is approximately 5.5 times
the size of the watershed. (Figure 1.2).
RADM is used to drive scenarios associated with reductions in atmospheric deposition of
nitrogen. A base condition of deposition establishes a reference to which other atmospheric
deposition reduction scenarios are compared. As precipitation is the primary forcing function in
the Chesapeake Bay Watershed
Model, great care is taken in
developing this data base. The data
set of daily wet deposition of
nitrate and ammonia is formed
through concentration data from a
regression model and precipitation
data from gauging stations that are
weighted according to a Thiessen
polygon method.
The regression model uses
eleven years (1984-1994) of
National Atmospheric Deposition
Program (NADP) data from fifteen
stations in the Chesapeake
watershed area to determine wet
inorganic nitrogen concentrations.
The regression calculates
concentrations from measured
precipitation amounts, the month of
the year, and latitude.
The concentrations are then
applied to the volume of
precipitation, for each model
segment, to establish daily
Figure 1.2 Chesapeake Bay Airshed Domain
Airshed and Watershed of the
Chesapeake Bay

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) ( k y
Ainihed of the Chesapeake Bay
Watershed of the Qie&apeakje Bay
riastijm United States


+
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deposition of wet nitrate and ammonia. The average precipitation by segment is based on the
spatial distribution of precipitation determined through the Thiessen polygon method. Data used
in this method are from standard NOAA tape files of 178 precipitation stations in the Chesapeake
watershed jurisdictions.
A rate of dry deposition of nitrate is determined for each model segment from average
proportions of wet-to-dry deposition calculated by RADM. The RADM wet-to-dry ratios are
applied to the average wet nitrate deposition of the base data set. The constant dry deposition
and the variable wet deposition rates are input to each Watershed Model segment, including its
non-tidal waters. Overall, dry nitrate deposition does not vary through the base simulation period
of the Watershed Model for each segment, but varies among segments. Dry ammonia inputs are not
accounted for in the model simulation since their magnitudes are unknown.
Atmospheric deposition of wet nitrate and ammonia to water surfaces of the estuary is
determined by applying the same deposition calculated for certain below-fall line Watershed
Model segments, to adjacent regions of the tidal Bay and tidal tributaries. Dry nitrate inputs to
regions in the tidal Bay and tidal tributaries are determined by applying a wet-to-dry ratio of 3.33
to the average wet nitrate deposition for adjacent segments. This wet-to-dry ratio of nitrate is
from monitoring data at an over-water site in the tidal Bay. The constant dry nitrate deposition
rate for the below-fall line WSM segments is used as dry nitrate input to the nearby tidal waters.
Overall, dry nitrate deposition to tidal regions does not vary through the simulation period for
each region, but varies among regions. Dry ammonia is not included in the nitrogen flux to tidal
waters.
Atmospheric deposition of wet organic nitrogen is simulated as a flux only to water surfaces
because it is assumed that inputs and outputs on land surfaces are in balance. Seasonal averages
of measured dissolved organic nitrogen concentrations are applied to the volume of precipitation
for each WSM segment to ascertain deposition of this species to non-tidal waters. Dissolved
organic nitrogen deposition to tidal water regions is the same as that to nearby below-fall line
WSM segments. Dry organic nitrogen deposition is not accounted for in the model simulation
since its magnitude is unknown.
The resultant daily atmospheric deposition to tidal surface waters is input to each cell of the
Chesapeake Bay Estuary Model Package which simulates the hydrology and water and habitat
quality parameters of the tidal Bay and tributaries. Atmospheric deposition to land surfaces and
non-tidal waters of the Chesapeake is accounted for in Watershed Model delivered loads to the
tidal Bay and tidal tributaries.
RADM scenarios account for emission controls and subsequent reduced atmospheric
deposition. RADM determines percent reductions in wet nitrate deposition from the RADM
reference, before 1990 Clean Air Act Amendment controls were in place. It is assumed that the RADM
reference inputs are the same as the calculated base deposition. Seasonally-variable percent
reductions are applied to the nitrate deposition rates of the base data set for each Watershed
Model segment. Wet ammonia deposition remains the same as that of the base since RADM does
not determine ammonia fluxes. Wet-to-dry nitrate ratios associated with the reduction scenarios
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are calculated by RADM for each Watershed Model segment. Dry deposition of nitrate is found
by applying the ratios to the average wet deposition amounts of the scenario.
The RADM results prescribe the loads of wet and dry deposition to the Chesapeake
watershed for the Virginia Tributary Strategy scenarios entitled Full Voluntary Program
Implementation and Limit of Technology (Table 1.1). The established base condition atmospheric
deposition loads were used for all other Virginia Tributary Strategy scenarios.
For the Full Voluntary Program Implementation scenario, atmospheric deposition assumes air
emission controls associated with the "Annual 2010 812 Prospective Projection" air scenario.
This air scenario reflects changes to atmospheric deposition resulting from annual emission
controls on both stationary and mobile sources. Annual levels of emission control are placed on
stationary sources in most of the 37-state RADM/RPM domain, resulting in emissions of no more
than 0.15 lb/mm BTU from utility and large industrial sources. Emission controls placed annually
on mobile sources for this scenario include 1) Tier 1 Light Duty Vehicle emission standards, 2)
Heavy Duty Vehicle 2 gm standard, 3) Phase II Federal Reformulated Gasoline, 4) National Low
Emission Vehicle program, and 5) High and Low Enhanced Inspection and Maintenance (I/M)
and Basic I/M as specified by individual states.
Atmospheric deposition for the Current Limit of Technology scenario assumes that the
maximum practical level of air emission controls are applied year-round in 37 states east of the
Rocky Mountains through the simulation period. Seasonal controls are placed on stationary
sources so that there are emissions of no more than 0.15 lb/mm BTU from utility and large
industrial sources in 37 states or most of the RADM/RPM domain. Annual emission controls on
mobile sources include 1) Tier 1 Light Duty Vehicle and Heavy Duty Vehicle emission standards,
2) Phase II Federal Reformulated Gasoline, 3) National Low Emission Vehicle (NLEV) program,
and 4) High Enhanced Inspection and Maintenance and maximum Low Emission Vehicle benefits
for all counties in the 37-state domain, regardless of ozone attainment.
Table 1.1 Chesapeake Watershed Nitrogen Deposition under Varying Management Schemes for
Controlling Emissions of Nitrogen Atmospheric Deposition Precursors
Scenario
TN Deposition
(millions of kg/year)
Base Condition
204
Full Voluntary Program Implementation/2010 812 Prospective Projection
178
Current Limit of Technology
128
Sources: Chesapeake Bay Program Phase IV Watershed Model and RADM
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1.3 Watershed Model
The Chesapeake Bay Watershed Model has been in continuous operation at the Chesapeake
Bay Program since 1982, and has had many upgrades and refinements since that time. The
version of the Watershed Model used in the Virginia Tributary strategy application, Phase 4.1, is a
comprehensive package for the simulation of watershed hydrology, nutrient and sediment export
from pervious and impervious land uses, and the transport of these loads in rivers and reservoirs.
The model is based on a modular set of computer codes called Hydrologic Simulation Program -
Fortran (HSPF). A slightly modified version of HSPF release 11.1 (Bicknell et al., 1996) is
applied in the watershed simulation. Version 11 is a widely-used public-domain model supported
by the U.S. Environmental Protection Agency (EPA), U.S. Geological Survey (USGS), and U.S.
Army Corps of Engineers (Shenk et al., 1998).
The Watershed Model allows for the integrated simulation of land and soil contaminant runoff
processes with in-stream hydraulic and sediment-chemical interactions. The model takes into
account watershed landuses and application of fertilizers and animal manure; loads from point
sources, atmospheric deposition, onsite wastewater management systems; and best management
practice reduction factors and delivery factors. Land uses, including cropland, pasture, urban
areas, and forests, are simulated on an hourly time-step.
The Watershed Model is designed to simulate nutrient and sediment loads delivered to the
Chesapeake Bay under different management scenarios (Donigian et al., 1994; Linker et al., 1996;
Linker, 1996). The simulation is an overall mass balance of nitrogen and phosphorus in the basin,
so that the ultimate fate of the input nutrients is incorporation into crop or forest plant material,
incorporation into soil, or loss through river runoff. Nitrogen fates may also include volatilization
into the atmosphere and denitrification. Sediment is simulated as eroded material washed off land
surfaces and transported to the tidal Bay. Twelve calendar years (1984-1995) of varying
hydrology are simulated by the Watershed Model although only ten of those years (1985-1994)
are used in this study because of the more limited simulation period of the estuary model.
Scenarios are run on a one-hour time step and results are often aggregated into ten-year-average
annual loads for reporting and comparisons among scenarios. Watershed Model results in the
form of daily flows and nutrient and sediment loads are used as input to the Chesapeake Bay
Estuary Model Package (CBEMP).
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To simulate the delivery of nutrients and sediment to the Bay, the watershed is divided into
eighty-nine major model segments with an average area of 194,000 hectares (Figure 1.3).
Segmentation, based on three tiers of criteria, partitions the watershed into regions of similar
characteristics. The first criterion is
segmentation of similar geographic and
topographic areas, which are further
delineated in terms of soil type, soil moisture
holding capacity, infiltration rates, and
uniformity of slope. The second criterion
involves finer segmentation based on spatial
patterns of rainfall. Each segment has a
bank-full travel time of about 24-72 hours
(Hartigan, 1983). The third criterion used to
delineate segments is based on features of
the river reach. River reaches containing a
reservoir are separated into a reservoir
simulation and a river simulation of the free-
flowing river. For example, the James basin
has eleven model segments including two
that represent reservoirs on the James and
Appomattox. Segmentation generally
became finer with closer proximity to tidal
waters.
Model segments are located so that
segment outlets are as close as possible to
monitoring stations. Water quality and
discharge data are collected from federal and state agencies, universities, and other organizations
that collect information at multiple and single land use sites (Langland et al., 1995; CBP, 1989).
At the interface of the watershed and estuary model domains, model segments are further divided
into 259 sub-segments to accurately deliver flow and nutrient and sediment loads to appropriate
areas of the estuary. The division of basins into multiple segments as well as the use of hourly
time-steps in the simulation greatly improved the accuracy of the model results. Scenario results
are typically reported at the basin level and for ten-year-average annual loads. The use of this
average annual load allows for a mix of wet, dry, and average hydrology years throughout the
basin.
Nutrient loads from the following non-point sources are simulated: conventionally-tilled
cropland, conservation-tilled cropland, cropland in hay, pasture, animal waste areas, forest,
pervious urban land, impervious urban land, atmospheric deposition to non-tidal surface waters,
septic systems, and a mixed-open category that is herbaceous but not part of an agricultural land
use.
Sediment from all pervious land surfaces is simulated using an empirically-based module
which represents sediment export as a function of the amount of detached sediment and the runoff
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Figure 1.3 Watershed Model Segmentation
Major Bitsins of the Chesapeake Bay Watershed

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intensity. Information on land slope and estimated erosion rates were provided by the National
Resources Institute (NRI) database. Delivery of sediment from each land use was calibrated to
the NRI estimates of annual edge-of-field sediment loads calculated by the Universal Soil Loss
Equation.
HSPF 11 allows two types of nutrient export simulation from pervious land. One group of
subroutines simulates nutrient cycling and export mechanistically, using storages of nutrients in
the soil and plant mass and parameters to govern movement between the storages. Another
group of subroutines uses an empirically-based approach, with potency factors for surface runoff
and monthly specified concentrations in the subsurface. Soil characteristics for nutrient
interactions and hydrology (percolation and reserve capacity) are obtained from the SCS Soil
Interpretation Records (USDA).
Nitrogen cycling is simulated in forest using recent research of forest dynamics included in the
mechanistic subroutines for HSPF 11 (Hunsaker, 1994). Forest phosphorus is simulated using the
empirically-based group of subroutines. Crops are modeled using a yield-based nutrient uptake
algorithm for both nitrogen and phosphorus to facilitate the direct simulation of nutrient
management practices. State agricultural engineers provide fertilizer application rates and timing,
crop rotations, and the timing of field operations.
Pasture and pervious urban categories use the mechanistic approach for nitrogen simulation
and the empirically-based method for phosphorus. Impervious urban exports depend on nutrient
storage that is incremented by a daily accumulation factor equal to atmospheric deposition. This
storage is then washed off as a function of the rainfall intensity.
A Chesapeake Bay Program Land Use (CBPLU) database is compiled for the entire
Chesapeake basin. This database is a combination of information from the EPA Environmental
Monitoring and Assessment Program (EMAP), National Oceanic and Atmospheric Administration
(NOAA) Coastal Change Assessment Program (C-CAP), and the USGS Geographic Information
Retrieval and Analysis System (GIRAS). The 1990 EMAP database is the primary source of land
use data.
Detailed information on agricultural lands is gathered from the U.S. Census Bureau series,
Census of Agriculture for 1982, 1987, 1992, and 1997 (Volume 1, Geographic Area Series)
published for each state. Tillage information on a county level is obtained for the conventional
and conservation cropland distribution. Calculations and allocations of the agricultural land
categories of high (conventional) tillage, low (conservation) tillage, pasture, and hay follow
methods described in Chesapeake Bay Watershed Model Land Use and Model Linkages to the
Airshed andEstuarine Models (Hopkins et al., 2000). The non-agricultural land use
classifications of forest, pervious and impervious urban, mixed-open, and water are generally
developed through comparisons of the resultant agricultural land acreage and the CBPLU
database. Hopkins et al. (2000) describes these calculations and allocations in detail.
The final land use category of the Watershed Model is manure acres. This designation allows
for the simulation of high nutrient content runoff from animal operations in unconfined (pasture)
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or confined areas. Manure acres are based on the population of different animal types in the
watershed as given in the U.S. Agricultural Census data. The animal types include beef and dairy
cattle, swine, and three categories of poultry; layers, broilers, and turkeys. The application rates
of manure to agricultural lands are determined by a time-varying manure mass balance as
described in Tracking Best Management Practice Nutrient Reductions in the Chesapeake Bay
Program (1999).
Point source data for the simulation period are obtained from the National Pollution Discharge
Elimination System (NPDES). If no state NPDES data are available, state and year-specific
default data are calculated for each missing parameter and annual estimates of load are based on
flow from the wastewater treatment plant. Septic system loads are also included in the Watershed
Model simulation. Septic system data are compiled using census figures and methodology
suggested in Maizel and Muehlbach (1995).
Each Watershed Model river reach is simulated as completely mixed waters of a fifth- to
seventh- order river with all land uses considered to be in direct hydrologic connection. Of the 44
reaches simulated, the average length is 170 kilometers, the average drainage area is 1900 square
kilometers, and the average time of travel is one day. Seven of the reaches are impounded by
reservoirs.
The 1984-1995 time period is used for calibration of the Watershed Model where simulated
results for stream flows, nutrient and sediment concentrations and loads, and other water quality
parameters are compared to observed data from the tributaries. This calibration was reviewed
and approved by Chesapeake Bay Program Modeling Subcommittee members which consists of
recognized academic experts in the field of modeling and representatives from all Bay Agreement
jurisdictions (PA, MD, VA, and the District of Columbia). Results for the hydrology and water
quality calibration for the Virginia tributaries can be found in Appendices A and B, respectively, in
Chesapeake Bay Watershed Model Application & Calculation of Nutrient & Sediment Loadings.
The results are presented as plots and statistical tables of model results and monitoring data from
calibration stations for the following parameters: flow, temperature, dissolved oxygen (DO), total
suspended sediment, total phosphorus, organic and particulate phosphorus, phosphate, total
nitrogen, nitrate, total ammonia, and organic nitrogen. The appendices also summarize the
accuracy of the calibration.
The Watershed Model provides input information for the Chesapeake Bay Estuary Model
Package. In order to make a linkage between the two models, a more extensive segmentation of
the below-fall line watershed model segments is developed using Geographic Information Systems
(GIS) mapping technology. These sub-segments are wholly contained within the larger
Watershed Model segments and adjoin estuary model grid cells. To accurately load the estuary
model, sub-segment land uses are determined by allocating a calculated proportion of each
segment land use to the sub-segments. After partitioning, the Watershed Model is run with the
new segmentation and land use changes. The simulated flows and nutrient and sediment loads
delivered to adjacent estuary model cells are the inputs to the CBEMP.
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1.4 Estuary Model
The Chesapeake Bay Estuary Model Package (CBEMP) is actually a series of linked models.
A hydrodynamic model simulates the hourly temperatures and movement of water in the Bay. A
eutrophication or water quality model simulates the water and habitat quality response to nutrient
and sediment loads. These loads are inputs from the watershed model as well as from direct
atmospheric deposition to the surface of the Bay, pollutant loads from the ocean interface, and
loads generated by a coupled bottom sediments model. The model package is applied in one
continuous simulation period (1985-1994) to model transport, eutrophication processes, and
sediment-water interactions under various management scenarios designed to analyze the water
quality and living resource responses to load reductions at all points in the Bay. The details of the
development of the hydrodynamic and water quality models and their calibration and sensitivity
are presented in Cerco and Cole (1994), Wang and Johnson (2000), Cerco and Meyers (2000),
Cerco (2000), and Cerco and Moore (2000).
The hydrodynamic and
eutrophication models operate by
dividing the spatial continuum of the
Bay into a grid of discrete cells. The
numerical grid contains 2100 cells
(roughly 1.5 x 3 km) in the surface
plane and one to twenty cells (1.5 to 2
m thick) in the vertical representing a
maximum depth of 30.5 m. The total
number of cells in the grid is about
10,400 (Figure 1.4). The estuary
model has been refined by increasing
the grid in the western tributaries and
in shallow littoral areas and by
extending the grid onto the continental
shelf where input from a global tide
model is employed. Other
improvements involved an extension
of the validation period to include the
time frame of 1985-1994 and the
incorporation of living resource
parameters and processes. The new
computations of zooplankton,
submerged aquatic vegetation, and
benthos compared successfully with
observations aggregated over annual
time scales and at spatial scales on the
order of 100 km2 (Cerco and Meyers,
2000). In addition, a preliminary
investigation of fish bioenergetics
Figure 1.4 Hydrodynamic and Water Quality
Model Grid
Phase IV Chesapeake Bay Watershed Model
Below Fall line Model Subssgments
Chesapeake Bay Water Quality Model Cells
fcx-jrJE jEjrl erg
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modeling is now possible with the CBEMP.
Hydrodynamic Model
The three-dimensional numerical Hydrodynamic Model of the Chesapeake Bay, that provides
transport or water movement to the three-dimensional water quality model, is called CH3D
(Curvilinear Hydrodynamics in 3 Dimensions). It solves conservation equations for water mass,
momentum, salinity, and heat on a boundary-fitted grid in the horizontal plane. The vertical grid
is Cartesian. A finite difference solution scheme is employed such that vertically-averaged
equations are first solved to yield the water surface elevations. These are then utilized in the
computation of the baratropic portion of the horizontal pressure gradient in the internal model.
The Hydrodynamic Model uses a five-minute time step with computations made throughout a
full year. Innovative techniques enable processing of the output to preserve all transport
characteristics while allowing averaging over longer time periods. This technique is instrumental
in allowing the 24-parameter water quality model to run time simulations of several decades on
the bay and its tributaries.
Validation of the Hydrodynamic Model is accomplished by demonstrating its ability to
reproduce observed data over time scales ranging from tidal to seasonal periods. After validation,
the model is applied to simulate Bay hydrodynamics for ten years (1985-1994). These results are
then used to drive the three-dimensional water quality model of the Chesapeake Bay.
Water Quality Model
The central issues in the water quality model (CE-QUAL-ICM) are computations of algal
biomass and dissolved oxygen. Through primary production of carbon, algae provide the energy
required by the ecosystem to function. Excessive primary production is detrimental; however,
since its decomposition in the water and sediments consumes oxygen. Dissolved oxygen is
necessary to support the life functions of higher organisms and is considered an indicator of the
"health" of estuarine system. In order to compute algae and dissolved oxygen, a suite of twenty-
four model state variables is necessary (Tablel.2).
CE-QUAL-ICM treats each cell as a control volume which exchanges material with its
adjacent cells. CE-QUAL-ICM solves, for each volume and for each state variable, a three-
dimensional conservation of mass equation (Cerco and Cole, 1994). The numerous details of the
kinetics portion of the mass-conservation equation for each state variable are described in Cerco
and Cole (1994). In addition, this publication describes the characteristic eutrophication
processes and the mechanisms that influence them. The processes and phenomena relevant to the
water quality model simulation include 1) bottom-water hypoxia, 2) the spring phytoplankton
bloom, 3) nutrient limitations, 4) sediment-water interactions, and 5) nitrogen and phosphorus
budgets.
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Table 1.2 Water Quality State Variables Used in the CBEMP
Temperature
Dissolved organic nitrogen
Salinity
Labile particulate organic nitrogen
Inorganic suspended solids
Refractory particulate organic nitrogen
Diatoms
Total phosphate
Cyanobacteria (blue-green algae)
Dissolved organic phosphorus
Other phytoplankton
Labile particulate organic phosphorus
Dissolved organic carbon
Refractory particulate organic phosphorus
Labile particulate organic carbon
Dissolved oxygen
Refractory particulate organic carbon
Chemical oxygen demand
Ammonium
Dissolved silica
Nitrate
Particulate biogenic silica
Microzooplankton
Mesozooplankton
Over seasonal time scales, sediments are a significant source of dissolved nutrients to the
overlying water column. The role of sediments in the system-wide nutrient budget is especially
important in summer when seasonal low flows diminish riverine nutrient input. In addition, warm
temperatures enhance biological processes in the sediments creating greater sediment oxygen
demand. Bay sediments retain a long-term nutrient load "memory" of several years. In other
words, sediment nutrient fluxes to the water column are determined by organic nutrient inputs
from several previous years. Therefore, the water quality model is coupled directly to a predictive
benthic-sediment model (DiToro et al., 1993). These two models interact at each time step, with
the water quality model delivering settled organic material to the sediment bed, and the benthic-
sediment model calculating the flux of oxygen and nutrients to the water column.
The ultimate aim of eutrophication modeling is to preserve living resources. Usually, the
modeling process involves the simulation of living resource parameters such as dissolved oxygen.
Computed values are compared to living resource standards and a projection is made whether
simulated conditions are beneficial to the resources of interest (e.g. fish, oysters, etc.).
SAV is an important living resource because it provides habitat for biota of economic
importance and helps support the estuarine food chain. The direct simulation of SAV by the
CBEMP accounts for the relationships among grass production, light, and nutrient availability,
allowing for a measurement of the response of SAV to reductions in nutrient and sediment loads.
A thin ribbon of model cells following the 2-meter contour is used to depict the littoral zone for
SAV growth. The SAV component of the model builds upon the concepts established by Wetzel
and Neckles (1986) and Madden and Kemp (1996).
Three state variables are modeled for SAV: shoots, (above-ground biomass), roots (below-
ground biomass), and epiphytes (attached growth to leaves). In addition, three dominant SAV
communities are incorporated in the estuary model based largely on salinity regimes (Moore et al.,
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1999). Within each community, a target species is selected: eelgrass (Zostera marina) for high
salinity, widgeon grass (Ruppia maritima) for moderate salinity, and wild celery (Vallisneria
americana) for tidal fresh. Since SAV production in the Bay and tributaries is largely determined
by light availability (Orth and Moore, 1984; Kemp et al., 1983), a predictive representation of
light attenuation is needed. The computation of light attenuation requires the addition of fixed
solids, or suspended sediment, to the list of model state variables.
In addition to the simulation of SAV as a living resource, three phytoplankton groups are
simulated while zooplankton are separated into two size classes for modeling purposes:
microzooplankton (44-201 microns) and mesozooplankton (> 201 microns). Zooplankton are
selected as a parameter because they are a valuable food source for finfish and to improve the
computation of phytoplankton since zooplankton feed on phytoplankton, detritus, and each other.
Benthos, or bottom-dwelling organisms, are included in the model because they are an
important food source for crabs, finfish, and other economically significant biota and because they
can exert a substantial influence on water quality through their filtering of overlying water (Cohen
et al., 1984; Newell, 1988). Within the estuary model, benthos are divided into deposit feeders
and filter feeders.
The Chesapeake Bay Monitoring Program provides the primary database for the estuary
model calibration and performance evaluation. The program conducts about twenty surveys per
year at approximately 90 stations in the mainstem and five major tributaries. In Virginia waters
alone, over 5.5 million observations were processed for comparison with model results.
Calibration is accomplished by comparing predicted and observed values over the ten years of
simulation
A variety of output formats are used in the calibration assessment including several spatial and
temporal scales. These include ten-year time series plots of water quality and sediment-water
fluxes as shown in Figure 1.5. The monitoring station data represented in this figure is from the
lower estuary of the Rappahannock River (CB Segment LE3). Level 1 represents the surface
layer (or 1 meter below the surface) sample from the Chesapeake Bay Monitoring Program, and
level 2 represents the bottom layer (or 1 meter above the bottom). Chlorophyll was not collected
in the monitoring program from level 2; therefore, there are no bottom observations for this
parameter for calibration or verification.
The CBEMP processes nutrient and sediment loads delivered from the Watershed Model and
nutrient atmospheric deposition to tidal surface waters from the airshed model. In addition, loads
from the ocean interface and from the linked bottom sediments model are incorporated in the
model. The simulation of estuarine hydrology and water and habitat quality parameters and
processes occurs on fifteen-minute time-steps with output generated each ten days. The entire
simulation period is ten years (1985-1994). Seasonal averages for all water and habitat quality
parameters are calculated for each year within this period. Estuary model results from
management scenarios, designed to determine the impact of reduced nutrient and sediment loads,
are often reported as a yearly or seasonal averages of the ten-year simulation.
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Figure 1.5 Calibration results from a monitoring station in the lower estuary Rappahannock River.
VIRGINIA TRIBS, RUN 139 (T3E) 5/24/99
Temperature
LE3 Level 1
Temperature LE3 Surface
Salinity
LE3 "
Level

o

Kj

in

CS

Si

m _
a_


o _

m -

O -
Years
5 e
Years
10
Temperature
LE3 Level 3
Temperature LE3 Bottom
„ * $ o
O -o.
Chlorophyll
LE3 Level 1
Chlorophyll LE3 Surface
Years
4 5 C 7 Š 9 10
Years
Salinity
LE3
Level 1
o_, Salinity LE3 Surface
tr,-<
5
Years
-1
10
Chlorophyll
LE3 Level
o Chlorophyll LE3 Bottom
t I	' -
9 10
1-13

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1.5 Other Diagnostic Tools
While the linked Chesapeake Bay Program models are useful for tributary strategy
development, limitations exist for both the Watershed Model and Estuary Model Package. For
example, the CBEMP does not simulate small coastal basins such as those lining the Eastern
Shore of the Bay and therefore, additional diagnostic tools were needed to estimate the response
of SAV to pollutant loading reductions. The following sections describe these models and how
they were applied.
Tidal Prism Modeling
In order to capture the spatial scales of small coastal basins, additional monitoring data and
finer-scale modeling tools were employed on four target areas: the Piankatank and Poquoson
Creeks on the Western Shore, and the Cherrystone and Hungars Creeks on the Eastern Shore.
Existing monitoring data in these basins was used to test applications of the Tidal Prism Model
(TPM) developed by the Virginia Institute of Marine Science. The modeling effort consisted of
three tasks: 1) pre-calibration simulations to reference basins, 2) calibration/confirmation to
monitoring data and assessment of TPM applications to other basins, and 3) conducting nutrient
reduction scenarios for each of the four catchments. While the TPM did not contain the full
ecosystem (biological) components as the larger CBEMP, it simulated all of the chemical and
physical parameters of the Bay Program estuary model. Results of the TPM application to
Virginia's small coastal basins are described in section IV of this report.
Gallegos Model
The temporal and spatial scales of the CBEMP extend over broad salinity ranges during the
growing season for SAV. A finer-scale tool was needed to define localized impacts of
management pollutant reduction actions on SAV. The Gallegos optical model (1994) was used
for this diagnostic application in Virginia's tributaries (EPA, 1999). It had the unique capability to
compare light attenuation due to measured suspended solids and chlorophyll concentrations. In
other words, the relative importance of these light-limiting parameters on SAV near any
monitoring station was assessed.
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Section 2: Scenarios
2.1 Overview
Models were employed to develop and test various lower tributary management options or
strategies aimed at improving water quality through nutrient and sediment reductions. This
section describes key scenarios used to assess the response of water and habitat quality and living
resource to these load reductions. The major controllable nutrient and/or sediment loads include
those from: 1) fall lines, 2) below-fall lines, 3) point sources, and 4) atmospheric deposition of
nutrients to the tidal Bay water surfaces. All of the scenario results are based on a ten-year
simulation period of varying hydrology in the Chesapeake watershed from 1985 to 1994,
inclusive.
2.2 Scenario Descriptions
The CBEMP framework provided projections of expected water and habitat quality responses
in the mainstem Bay and lower Virginia tributaries under a variety of management options. Five
key scenarios provided the basis of analysis for the lower tributary allocations (Table 2.1). The
full descriptions these and all scenarios can be found in Appendix B.
Table 2.1 Key Scenarios
KEY
SCENARIO
DESCRIPTION
1985 Baseline
Conditions
Represents the conditions of the entire Chesapeake Bay watershed in 1985 with
respect to non-point source, point source, and atmospheric loads. Rationale.
Establishes a reference to which other scenarios will be compared. Also needed to
compare status and trends monitoring data to model results for the Technical
Synthesis.
1996 Progress
Represents the conditions of the entire Chesapeake Bay watershed in 1996 with
respect to non-point source and point source loads. Rationale. This scenario
examines progress in reducing point source and non-point source nutrient and
sediment loads from 1985 to 1996 and represents an estimate of the current water
quality and living resource conditions in the lower tributaries.
Midpoint
1996 Progress -
Full Voluntary
Program
Implementation
This is a derived scenario using point and non-point sources loads for all
Chesapeake Bay basins midway between the 1996 Progress scenario and Full
Voluntary Program Implementation. Reductions vary by major basin.
Atmospheric deposition for this scenario would assimilate these loads from both the
1996 Progress and I'VI'I scenarios. Rationale. This scenario examines tributary
water quality and living resource response midway between a "no further action"
management strategy (1996 Progress) and nutrient and sediment reductions
estimated under a management strategy that achieves maximum reductions under a
voluntary program (FVP1).
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Full Voluntary
Program
Implementation
- FVPI
Rationale. Projects loads under maximum feasible management implementation
using a voluntary program throughout the Chesapeake Bay watershed. It is based on
current technology, expanded program financing, and a maximum of 75% cost share
by states. Time and availability of technical staff are not considered.
Current limit
of Technology
-IOT
Estimates the maximum level of nutrient and sediment reductions given unlimited
resources, unlimited cost share, and 100% landowner participation. A "do
everything, everywhere" policy is applied using current available technologies. Time
and availability of technical staff is not considered. Rationale. This scenario
examines the maximum load reductions of nitrogen, phosphorus, and sediment, and
represents an estimate of the maximum improvement in water quality and living
resource conditions in the lower tributaries.
These scenarios covered the range of nutrient and sediment loads from the maximum loads of
the 1985 Baseline Conditions scenario to the maximum possible controls under existing
technologies estimated by the Current Limit of Technology scenario. Approximations of recent
loads in the lower tributaries are represented by the 1996 Progress scenario. The maximum level
of nutrient and sediment control under a voluntary program is determined by the Full Voluntary
Program Implementation scenario.
More specific management actions directed toward the lower Virginia tributaries were
conducted through a series of five ranging scenarios (Table 2.2 and Appendix B). These
scenarios changed loading conditions in the lower Virginia tributaries while those from the
Potomac River basin and watersheds north of the Potomac were kept at levels established for
their Tributary Strategies. Comparing these scenarios to the equivalent bay-wide scenarios
allowed for the assessment of the impact of lower tributary nutrient and sediment reductions as
compared to the impact from reductions made elsewhere. All of the scenario results are based on
a ten-year simulation period of varying hydrology in the Chesapeake watershed from 1985 to
1994, inclusive. Unless otherwise noted, atmospheric deposition for the ranging scenarios is at
1985 Baseline Conditions.
Table 2.2 Ranging Scenarios
RANGING
SCENARIO
DESCRIPTION
VA 1996 Progress /
Tributary Strategy
Above
Represents non-point source and point source loads with respect to 1996
Progress conditions for Virginia's lower tributaries while the northern
Chesapeake Bay tributaries (Potomac and above) implement Tributary
Strategy load reductions. Rationale. This scenario determines an aspect of
load reductions occurring at different levels in different basins. In this case,
load reduction in the lower Virginia tributaries are relatively less than the load
reductions in the tributaries of the Potomac and above. This scenario develops
estimates of the affect Tributary Strategy load reductions from outside the
lower Virginia tributaries have on water quality and living resources in
Virginia waters.
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VA BNR-BNR
Equivalent /
Tributary Strategy
Above
This is a derived scenario where biological nutrient removal (BNR) is
simulated at above- and below- fall line point sources in Virginia's lower
tributaries. All of Virginia's lower tributaries are at BNR conditions for point
sources except the Rappahannock with BNR only applied to >1 million gallon
per day (mgd) facilities. Point source effluent concentrations of 8.0 mg/L TN
and 2.0 mg/L TP are applied to flows projected to 2000 levels. For facilities
with 1996 discharge TN concentrations less than 8.0 mg/1, the 1996
concentrations are used.
Non-point source loads in the lower tributaries are reduced by basin to the
same (Equivalent) PS:NPS load ratio prior to BNR removal. These non-point
source loads are calculated using the following ratio and solving for BNR non-
point source loads:
1996 Progress PS loads - BNR PS loads = 1996 Progress NPS loads - BNR NPS loads
1996 Progress PS loads - FVPI PS loads 1996 Progress NPS loads - FVPI PS loads
Solids are reduced to a non-point source phosphorus ratio. Northern
Chesapeake Bay tributaries (Potomac and above) are at Tributary Strategy
load levels.
The Watershed Model was not run for this scenario. Instead, point source
delivered loads were calculated by using 1996 transport factors and the edge-
of-stream BNR point sources described above. Rationale. This scenario
examines a moderate point source load reduction and a measure of an
equivalent nutrient reduction from non-point sources.
VA Interim Bay
Agreement /
Tributary Strategy
Above
Nutrient reductions in the lower Virginia tributaries at a 40% interim nutrient
reduction goal while loads in the northern Chesapeake Bay tributaries
(Potomac and above) are at Tributary Strategy levels. Rationale. This
scenario estimates water quality and ecosystem response to controllable loads
in the lower Virginia tributaries set at 40% of 1985 Baseline Conditions.
VA Full Voluntary
Program
Implementation /
Tributary Strategy
Above
Virginia's lower tributaries are at Full Voluntary Program Implementation
load levels and the Northern Chesapeake Bay tributaries (Potomac and above)
are at Tributary Strategy amounts. Atmospheric deposition is at levels of Full
Voluntary Program Implementation in the basins and tidal waters of the lower
Virginia tributaries and at 1985 Baseline Conditions for the Potomac River
basin and watersheds above. Rationale. This scenario determines an aspect of
load reductions occurring at different levels in different basins. In this case,
load reductions in the lower Virginia tributaries are relatively greater than the
load reductions in the tributaries of the Potomac and above.
The final series of scenarios were directed toward reductions within geographic regions of a
tributary or shoreline of the Bay (Table 2.3 and Appendix B). Loads from the Potomac River
basin and tributaries to the north were at Tributary Strategy scenario levels while the lower
Virginia tributaries, or portions of these major tributaries that were not included in the nutrient
and sediment reductions, were held at 1996 Progress amounts. Again, all of the scenario results
are based on a ten-year simulation period of varying hydrology in the Chesapeake watershed from
II- 3

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1985 to 1994, inclusive. Unless otherwise noted, atmospheric deposition for the geographic
management scenarios is at 1985 Baseline Conditions.
Table 2.3 Geographic Management Scenarios
GEOGRAPHIC
MANAGEMENT
SCENARIO
DESCRIPTION
VA Eastern Shore
FVPI /
Tributary Strategy
Above
Eastern Shore VA loads for point sources, non-point sources, and atmospheric
deposition at Full Voluntary Program Implementation levels. All other lower
VA basin loads (Rappahannock, York, James, and Western Shore VA) at 1996
Progress amounts. Northern Chesapeake Bay tributaries (Potomac and above)
at Tributary Strategy loads. Rationale. This scenario determines an aspect of
load reductions occurring at different levels in different basins. In this case,
nutrient and sediment reductions in the Virginia Eastern Shore are relatively
greater than load reductions in all other tributaries.
VA Western Shore
FVPI/
Tributary Strategy
Above
Western Shore VA loads for point sources, non-point sources, and atmospheric
deposition at Full Voluntary Program Implementation levels. All other lower
VA basin loads (Rappahannock, York, James, and Eastern Shore VA) at 1996
Progress amounts. Northern Chesapeake Bay tributaries (Potomac and above)
at Tributary Strategy loads. Rationale. This scenario determines an aspect of
load reductions occurring at different levels in different basins. In this case,
nutrient and sediment reductions in the Virginia Western Shore are relatively
greater than load reductions in all other tributaries.
VA Current LOT
Sediment /
Tributary Strategy
Above
Virginia's lower tributaries at Current Limit of Technology for total suspended
solids (about 33% reduction from 1985 Baseline Conditions). Loads from
point sources, non-point source nutrients, and the atmosphere in the lower
Virginia tributaries are at 1996 Progress levels. Northern Chesapeake Bay
tributaries (Potomac and above) are at Tributary Strategy load levels.
Rationale. This sensitivity scenario examines the relative effect of the most
stringent reductions of suspended sediment loads within the feasible region, with
an estimate of the 1996 level of nitrogen and phosphorus controls.
VA Extreme Sediment
Reduction /
Tributary Strategy
Above
Virginia's lower tributaries are at 40% load reduction of total suspended solids
from 1985 Baseline Conditions. (Pristine sediment load reduction is about
43% from the baseline). Loads from point sources, non-point source nutrients,
and the atmosphere in the lower Virginia tributaries are at 1996 Progress levels.
Northern Chesapeake Bay tributaries (Potomac and above) at Tributary
Strategy load levels. Rationale. This sensitivity scenario examines the relative
effect of sediment reductions outside the feasible region with an estimate of the
current level of control for nitrogen and phosphorus to determine the impact
suspended sediment loads have on lower tributary water quality and living
resources.
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York River
2010 Scenario
This is a Watershed Model scenario developed solely for the York basin. York
point source effluent concentrations at BNR levels of 8.0 mg/1 TN are applied
to year 2000 flows. For facilities with 1996 TN discharge concentrations less
than 8.0 mg/1 and facilities less than 1 mgd, the 1996 concentrations are used.
Point source TP loads in the York apply 1996 concentrations to projected 2000
flows. Year 2000 land uses, septic system loads and animal numbers are
employed while atmospheric deposition is at 1985 Baseline Conditions. The
CBEMP was not run for this scenario. Rationale. This scenario examines non-
point source load reduction potential in 2010 with the implementation of BMPs
assuming land uses, animal numbers, and septic system loads remain at 2000
levels and point source loads are capped at BNR levels. Non-point source loads
in the York are simulated with 2010 projections of BMPs found in Appendix B.
James Above-Fall
Line at BNR-BNR
Equivalent /
Tributary Strategy
Above
Above-fall line James loads at BNR-BNR Equivalent or above-fall line James
point sources at BNR concentrations for TN and TP and 2000 flows. For
facilities in the above-fall line James with 1996 TN concentrations less than
BNR concentrations, the 1996 concentrations are used. Non-point source loads
for the above-fall line James are at a BNR equivalent levels of control. The
Appomattox, below-fall line James, and other VA tributary loads at 1996
Progress. Northern Chesapeake Bay tributaries (Potomac and above) are at
Tributary Strategy load levels. Rationale. This scenario examines the water
quality and living resource response to BNR-BNR Equivalent load reductions in
the above-fall line James.
James Above-Fall
Line, Appomattox, &
Below-Fall Line
Tidal Fresh James at
BNR-BNR Equivalent
/ Tributary Strategy
Above
Loads discharging into the tidal fresh James at levels of BNR-BNR Equivalent.
For facilities discharging into the tidal fresh James with 1996 TN
concentrations less than BNR concentrations, the 1996 concentrations are used.
The James regions discharging below the tidal fresh portion of the James and
other Virginia lower tributaries are set to 1996 Progress loads. Northern
Chesapeake Bay tributaries (Potomac and above) at Tributary Strategy load
levels. Rationale. This scenario examines the water quality and living resource
response to BNR-BNR Equivalent load reductions in regions discharging to the
tidal fresh James.
James Tidal Fresh at
BNR-BNR Equivalent
For Nitrogen /
Tributary Strategy
Above
Loads discharging into the tidal fresh James at levels of BNR-BNR Equivalent
for nitrogen only. James discharging to the tidal fresh region at 1996 Progress
for phosphorus and sediment. For facilities discharging into the tidal fresh
James with 1996 TN concentrations less than BNR concentrations, the 1996
concentrations are used. The James regions discharging below the tidal fresh
portion of the James and other Virginia lower tributaries are set to 1996
Progress loads. Northern Chesapeake Bay tributaries (Potomac and above) are
at Tributary Strategy load levels. Rationale. This scenario examines the water
quality and living resource response to BNR-BNR Equivalent load reductions
for nitrogen only in regions discharging to the tidal fresh James. It quantifies
the importance of nitrogen versus phosphorus controls.
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Section 3 Tracer Analysis
3.1 Background
To better understand the hydrologic interactions of the different tributaries with the mainstem
Bay, a series of tracer scenarios was performed. Tracer analyses are used to visualize the
movement of conservative (or non-reactive) dissolved and particulate materials in the water. The
conservative tracers, similar to non-reactive dyes used in observational studies, are carried and
dispersed by water currents simulated by the Hydrodynamic Model. There are two types of
traces. A dissolved tracer is assumed to be 100% soluble and is used to study the transport of a
soluble pollutant such as nitrogen. A particulate tracer depicts an insoluble constituent, like
suspended sediment or algae, and is associated with a specified settling velocity.
The tracer simulations used the Chesapeake Bay Estuary Model Package, setting all model
constituents to a chemically and biologically non-reactive state. Similar to a dye test, a mass of
tracer was loaded to an area such as a river's head-of-tide. Time-series outputs from the model
showed changing tracer concentrations and movement of tracer particles to illustrate Bay
hydrodynamics and provide information for pollution reduction management decisions. Caution
must be used in the interpretation of tracer results since chemically and biologically active
dissolved and particulate material will behave differently than the assumed inert material. Tracer
analysis; however, allowed for the quantification of large-scale material transport in the Bay.
The dissolved tracers would represent the upper limit of tracer influence since they are non-
settling or would transport further from their source. Particulate conservative tracers were input
in the same manner, but particles had a settling rate of 0.1 m/day or 1.0 m/day, consistent with the
simulated rate of settling for living suspended particles (algae) and inorganic particulate material,
respectively. The particulate tracer with the higher settling velocity would represent the lower
limit of tracer influence since it would transport the least distance from its source. Nutrients and
sediments would most likely behave between the boundaries of the dissolved and particulate
tracer influence.
Dissolved conservative tracers, simulating nutrients, were input continuously at an arbitrary
load of 100,000 kg/year (274 kg/day) at the head-of-tide or fall line of each major basin including
the Susquehanna, Potomac, Rappahannock, York, and James. Figure 3.1 depicts this input load
using the Potomac as an example.
The Hydrodynamic Model uses a time step of five minutes, with an aggregated two-hour time
step output as the driving force for the Water Quality Model. The tracer analyses in the Virginia
tributary studies were conducted for the year 1987, a year of average hydrology. The CBEMP
simulation ran until a steady-state condition existed after three years of repeated 1987
hydrodynamics. Daily concentrations of the tracer were then determined for each of the 10,196
model cells in the tidal Bay (Figure 3.2). Visualizations for the geographically-varying steady-
state tracer concentrations were produced as still images for this report.
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Figure 3.1 Tracer loading of the Potomac River Figure 3.2 Steady-state tracer concentrations
basin at the fall line	after constant loading of the Potomac River
fall line
3.2 Response to Conservative Dissolved Tracer
Tracer runs were carried out on five major
Bay tributaries; the Susquehanna, Potomac,
Rappahannock, York, and James. Figure 3.3
shows the range of possible tracer influence, or
concentrations, on regions of the tidal Bay. The
dark blue shading at the top of the legend
indicates no influence or only trace
concentrations are found in regions after the
estuary model is run to steady-state. The
concentrations at the bottom of the legend,
designated in red, portray a high influence of the
tracer.
Figure 3.3 Dissolved Tracer Influence


~ 0


trace


Low Influence


Moderate Influence


High Influence
The distribution of constant dissolved tracer
loads released from the two largest basins, the Susquehanna and Potomac, are shown in Figure
3.4 and Figure 3.5, respectively. Dissolved tracers from the head-of-tides of these basins were
distributed and mixed throughout the Bay and portions of Virginia's lower tributaries. The
III - 2

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analysis showed low to moderate influence in the lower salinity reaches of Virginia's three main
tributaries. Among the Virginia estuaries, the greatest influence from tracers loaded to the
Susquehanna and Potomac occurred in the mesohaline and polyhaline regions of the
Rappahannock and York while the least effect was in the James. A high influence of the Potomac
tracer is depicted in Virginia waters along the western shore between the mouths of the Potomac
and Rappahannock (Figure 3.5).
Figure 3.4 Influence of Susquehanna Constant	Figure 3.5 Influence of Potomac Constant
Dissolved Tracer	Dissolved Tracer
Constant dissolved inputs from the fall line of the Rappahannock were mostly distributed
throughout this tributary and the western portion of the lower Bay with some significant impact
on Virginia's Eastern Shore (Figure 3.6). The overall influence on the mainstem was much less
than that of the Susquehanna and Potomac tracers. For the York tracer, only trace concentrations
were found in waters north of the York while a low to moderate influence was seen in the lower
James and a high influence south of Mobjack Bay (Figure 3.7). Dissolved tracer inputs from the
James fall line had a negligible impact on the mainstem Bay when compared to sources in the
upper Bay and other Virginia tributaries (Figure 3.8). The mix of geography and Bay currents
delivers most of the James tracer to the coastal ocean.
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Figure 3.6 Influence of Rappahannock	Figure 3.7 Influence of York Constant
Constant Dissolved Tracer	Dissolved Tracer
Figure 3.8 Influence of James Constant
Dissolved Tracer

-------
The relative influence of dissolved tracer loads from the five main tributaries on their tidal
waters was examined. Again, the sources included fall line loads to the Susquehanna, Potomac,
Rappahannock, York, and James River basins. Steady-state concentrations in the estuary model
cells, that resulted from constant fall line loads, were proportionally adjusted according to relative
1987 total nitrogen loads for the different sources. These calculated concentrations were then
compared to assign a percent influence from each source on the major regions of Virginia's tidal
tributaries. With this type of tracer analysis, the influence of the main upper tributary sources on
Virginia waters could be tested and compared to the influence of Virginia tributary sources,
particularly the impacts on the lower portions of Virginia's tributaries. In other words, these
influences generally reflected the overall impact of nitrogen loads from five main Chesapeake
tributaries on water quality in Virginia's estuaries. A summary of the relative influence is found in
Table 3.1 where the column headings indicate the source of the tracer load and the row headings
are the areas of Virginia's tidal tributaries that were affected.
Table 3.1 Dissolved tracer influence on Virginia's lower tributaries using a tracer load equivalent to
the discharged load of nitrogen from each load source
TIDAL REGION
AFFECTED
SOURCE OF TRACER INPUT
Susquehanna
Potomac
Rappahannock
York
James
Rappahannock -
Upper Tidal
1%
0%
99%
0%
0%
Rappahannock -
Middle/Lower
36%
22%
41%
0%
1%
York -
Upper Tidal
4%
2%
0%
94%
0%
York -
Middle/Lower
27%
15%
2%
55%
1%
James -
Upper Tidal
1%
0%
0%
0%
99%
James -
Middle/Lower
15%
9%
1%
2%
73%
The greatest impact of tracer fall line loads at each of Virginia's tributaries was on the upper
tidal regions of the respective tributary. For example, the Rappahannock tidal fresh region was
almost entirely influenced by the tracer released in the Rappahannock. However, the lower tidal
Rappahannock was affected by both in-stream inputs and mainstem Bay processes. In this lower
region, the combined tracer contributions from the mainstem Bay and tributaries to the north was
58% while the effect of the fall line Rappahannock tracer on the lower area was 41%. The
Rappahannock tracer had a slight influence on the lower regions of the York and James.
Throughout the York and in Mobjack Bay, tracer results indicated that loads from the York
fall line had the greatest local influence. More than half of the tracer load impact in the lower
York originated at its head-of-tide. However, loads from other regions, particularly the
III - 5

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Susquehanna and Potomac, were important as outside influences on the lower York and Mobjack
Bay.
The James tidal fresh and mesohaline regions were heavily influenced by the James tracer.
About 73% of the total tracer in the lower James was from the James fall line (Table 3.1).
Among the lower areas of Virginia's tributaries, this region also showed the least impact from
upper Bay loads.
Between the Patuxent River to the north and the Rappahannock River to the south, the
Chesapeake region of CBS straddles the boundary between the upper and lower Bays and
includes the terminus of the southern end of the deep trench (Figure 3 .9). The Susquehanna and
Potomac sources predominated in CB5,
but a slight influence from the lower	Figure 3.9 Chesapeake Bay Estuary Model Segments
tributaries, 4% of the total dissolved tracer
load influence, was seen. This indicates that
the lower tributaries have some impact on
water quality of the mainstem Bay, but the
predominate influence of nutrient reductions
in the lower tributaries are in the lower
tributaries themselves.
To examine the relative influence of
equivalent load reductions in different
tributaries, a separate tracer analysis was
performed. An equal mass of dissolved
tracer load was discharged from each
source to compare the water quality impact
on a pound-per-pound basis. Assuming
load reductions from each tracer source
would be equivalent in cost, this analysis
examined the relative cost effectiveness of
equal load reductions. As can be seen in
Table 3.2, the predominant influence of
tracers from the five key tributaries on
waters in Virginia's tributaries was
estimated to be from local sources.
Chesapeake Bay Model Segments
and Major Rivers

Ļ rtrflWa' Mill.
Ļ QCH'hlifcfaP:
I BtTl v.-
ImiMJlkKJl

III - 6

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Table 3.2 Dissolved tracer influence on Virginia's lower tributaries using an equal tracer load from
each load source
TIDAL REGION
AFFECTED
SOURCE OF TRACER INPUT
Susquehanna
Potomac
Rappahannock
York
James
Rappahannock -
Upper Tidal
0%
0%
100%
0%
0%
Rappahannock -
Middle/Lower
5%
6%
87%
1%
0%
York -
Upper Tidal
0%
0%
0%
100%
0%
York -
Middle/Lower
3%
3%
3%
91%
0%
James -
Upper Tidal
0%
0%
0%
0%
100%
James -
Middle/Lower
4%
5%
5%
8%
78%
Overall, tracer loads from the Potomac basin and tributaries above generally mixed
throughout the Bay. Tracer loads from the lower tributaries had little influence on the Bay, but
had considerable local influence, both within the tributary where the tracer originates and on
adjacent lower tributaries. The tidal fresh and mesohaline portions of each tributary were largely
influenced by above-fall line sources and below-fall line sources that drain directly to the tidal
fresh region. The lower Virginia estuaries were all influenced by loads from the Potomac and
tributaries above, but the greatest single influence was from the basin's own tracer load. Due to
the residual circulation of the Bay, tributaries to the north have a relatively greater influence on
the tributaries to the south, so that the Rappahannock tracer is seen to have a relatively higher
concentration in the lower York than in the lower Potomac.
3.3 Response to a Conservative Particulate Tracer
The influence of conservative particulate tracers were mostly local to the tracer origin.
Particles with a 0.1 m/day settling rate, consistent with an algal settling rate, accumulated almost
entirely within a two segment zone of their input. For example, for the fall line inputs, the
particulate tracer would be found almost entirely within the tributary, with negligible influence on
the mainstem of the Bay. Particles with a settling rate of 1.0 m/day, consistent with inorganic
particulate material, settled primarily within the region of origin. For a fall line discharge, almost
all of the particulate tracer would settle within the tidal fresh region of the tributary.
Ill - 7

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Section 4: Basin Descriptions with Nutrient and Sediment Loads
4.1 Basin Descriptions
Physical Description and Estuarine Characteristics
The lower Chesapeake Bay system consists of the mainstem Bay, three major tributaries on the
western shore (James, York, and Rappahannock) and a number of lesser tributaries and embayments
along the eastern and western shorelines (Figure 4.1). Virginia's lower tributary basins comprise
about 22% of the watershed or about 15,500 square miles. The James/Appomattox basin represents
about 15% of the total watershed and is the third largest source of freshwater to the Chesapeake Bay
after the Susquehanna and Potomac Rivers. The Rappahannock River Basin covers only 4% of the
Bay watershed while the York River Basin contributes another 3% and is represented by both the
Pumunkey and the Mattaponi Rivers (2 and 1%, respectively). The remainder of Chesapeake Bay
drainage area in Virginia consists of the Potomac River Basin and its tributaries, including the
Shenandoah River, which are not discussed in this report.
Virginia's western shore tributaries are classified as partially-mixed coastal plain estuaries.
The tidal range is reported as less than 2 meters. As a result, the tributaries are categorized as
low-energy or microtidal. The depths along the river axes are generally less than 10 meters, but
near the mouth of each river, there are natural deep areas or "holes" more than 20 meters deep.
Rappahannock River Basin
The Rappahannock River Basin is the second largest contributing stream to the Chesapeake
Bay in Virginia, and represents about 7% (-2,600 square miles) of the Commonwealth (Table
4.1). Rappahannock waters flow from the eastern edge of the Blue Ridge physiographic
province through the Piedmont and Coastal Plain physiographic provinces (Figure 4.2). Because
of the high relief, the river produces rapid or "flashy" streamflow peaks during storm events.
The river can carry large loads of sediments and nutrients relative to the size of the basin.
Table 4.1 River Basin Areas
River Basin
Area
(mi2)
Rappahannock
2,680
York
3,000
James
10,240
Eastern Shore
300
Source: Chesapeake Bay Program Phase IV Watershed Model
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Figure 4.1
Lower	Chesapeake
EASTERN SHORE VIRGINIA
JAMES RIVER BASIN
RAPPAHANNOCK RIVER BASIN
YORK RIVER BASIN
Location of the
Lower Virginia Sub-Basins
of the Chesapeake Bay Watershed
it
Chesapeake Bay Program
30	0
30
60 Miles
A
Map Date: June 12,2000
Map Author: Kate Hopkins

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Figure 4.2
Rappahannock River Basin
Watershed Model Segments with
State and County Boundaries
Rappahannock River Basin
in the
Chesapeake Bay Watershed
/V State Boundary
/^y WSM Segments and Contiguous County Lines
/V County Lines
9 0 9 18 Miles
Chesapeake Bay Program
N
+

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The Rappahannock River has a mean depth of 4.8 m (Table 4.2) with a deep channel flanked
by shallow shoals of the estuary. There is a salinity gradient that causes tidal mixing along this
stretch of the tidal river. The lower estuary experiences strong stratification during the summer
months that restricts mixing between the low dissolved oxygen bottom waters and more
oxygenated overlying surface waters. At the mouth, a shallow sill restricts the flow of bottom
water from the river out into the Chesapeake Bay. Dissolved oxygen concentrations below 5
mg/L typically appear in deep waters in May or June when water temperatures exceed 20 °C.
The anoxia/hypoxia is most pronounced in August. Among Virginia's tributaries, this water
body has the longest water residence time of 53 days (Table 4.2).
Table 4.2 Virginia Tidal River Characteristics
Tidal River
Surface Area
(106m2)
Volume - mlw
(106m3)
Mean Depth
(m)
Mean Residence
Time (days)
James
658
2,399
3.3
31
York
256
909
4.3
35
Rappahannock
401
1,782
4.8
53
Sources: Cronin (1971); Hagy and Boynton (1999)
York River Basin
The York River Basin constitutes about 6.5% (-3,000 square miles) of the Commonwealth
(Table 4.1). The basin is composed of the Pumunkey and Mattaponi Rivers and is located within
the Piedmont and Coastal Plain physiographic province (Figure 4.3). Although the Pumunkey
and Mattaponi rivers are often presented collectively as the York River Basin, each river has
unique basin, discharge, and water-quality characteristics. The Pumunkey Basin is of low relief
and relatively wide, and tends to produce storm flows that are slow to peak and recede. Lake
Anna in the Pumunkey Basin also attenuates storm flow and loads. The Mattaponi Basin has
relatively low relief and extensive wetland areas. It is the more northerly and smaller of the two
rivers. Storm flows are even slower to peak and recede than the Pumunkey River. Nearly 70%
of the York Basin is covered by forest and about 20% are classified as agricultural land. The
basin as a whole contains significant percentages of barren land, open water, and wetlands.
The average depth of the York River is 4.3 m (Table 4.2) with hypoxia observed frequently
in the deep waters. The York River is long and straight from West Point down to Gloucester
Point. The tidal river has a deep channel running along its axis flanked by shallow shoals. There
is a strong salinity gradient that causes a significant amount of tidal mixing along this stretch of
the river. At the river mouth, a deep channel cuts across the shallow shoals of Mobjack Bay and
the southern shore. This lower York area experiences strong stratification restricting mixing
between the low dissolved oxygen bottom waters and more oxygenated overlying surface waters.
During summer low river flows and with a water residence time of 35 days, conditions are
favorable for depressed dissolved oxygen conditions in deeper waters.
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Figure 4.3
York River Basin
Watershed Model Segments with
State and County Boundaries
/V State Boundary
/^y WSM Segments and Contiguous County Lines
/V County Lines
9 0 9 18 Miles
Chesapeake Bay Program
N
+

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James River Basin
The James River Basin includes about 25% of the Commonwealth of Virginia and
encompasses nearly 10,200 square miles (Table 4.1). This basin extends from the eastern part of
West Virginia through four physiographic provinces: Valley and Ridge, Blue Ridge, Piedmont,
and Coastal Plain (Figure 4.4). As a result, this is the most varied basin in terms of geology and
physiology. The James has a much greater portion in the Piedmont versus the Valley and Ridge
compared to the Potomac and particularly the Susquehanna. Therefore, stream flows and
sediment delivery within this basin are unique. Streamflow varies widely with time, depending
on precipitation patterns that can result in either very localized or widespread storm flow events.
The overall geography of the James basin makes for a very effective sediment delivery
system. The primary river channel of the James is much lower in elevation then the surrounding
plateaus. Smaller creeks flow directly into the mainstem James River from steep-sloped gullies
draining the surrounding lands. The underlying soils/substrate in the Piedmont have a much
higher tendency to erode, leading to significant sediment runoff and re-distribution to the
downstream river valleys. Most of this land erosion occurred in the eighteenth and nineteenth
centuries. On a geological time scale, the headwaters region of the James basin is eroding about
four times faster then the rest of the basin, thereby delivering more sediments across the fall line
to the tidal river. In the Piedmont region of the James basin, the erosion rates are also elevated.
Of Virginia's three major tributaries, the James River has the largest surface area and volume
(Table 4.2). Despite having the shallowest average depth (3.3 m) and the shortest mean
residence time (31 days) among Virginia's estuaries, the James River has a second hole about 15
km from the hole at the mouth. The holes are connected by a dredged navigational channel
about 14 m deep. The James has strong non-tidal circulation (Kuo and Neilson, 1987). Hypoxia
(dissolved oxygen concentrations < 5 mg/L) is rarely reported from bottom waters of the James,
but occurs more frequently in the Elizabeth River, a sub-tributary near its mouth.
Eastern Shore Basin
The Eastern Shore Basin is the smallest of the lower tributaries and is located within the
Coastal Plain physiographic province. The area is characterized by a gently sloping land surface
and dissected lowland with a series of ocean-cut inlets (Figure 4.5).
Hydrology
The primary freshwater flow to Chesapeake Bay is the Susquehanna River (~ 62% of total
gauged freshwater flow) which empties into the northern portion of the Bay. Other major
freshwater sources are the Potomac (—18%) and James (~11%) (Cerco, 1993). The Potomac
empties midway down the Bay while James is the southern-most tributary. Between the
Potomac and James, the York and Rappahannock each contribute about 3% of freshwater flow to
the Bay. An annual runoff cycle exists in the major tributaries. Peak flows typically occur in
March or April while minimum flows occur in August and September.
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Figure 4.4
James River Basin
Watershed Model Segments with
State and County Boundaries
James River Basin
in the
Chesapeake Bay Watershed
CHESAPEAKE
42
/V State Boundary
/^y WSM Segments and Contiguous County Lines
/V County Lines
20 0 20 40 Miles
Chesapeake Bay Program
N
+

-------
Figure 4.5
Eastern Shore Virginia
Watershed Model Segments with
State and County Boundaries
Eastern Shore Virginia
in the
Chesapeake Bay Watershed
42
Che&apeake Bay Program
6	0	6	12 Miles
N
+
/V State Boundary
/V WSM Segments and Contiguous County Lines
/V County Lines

-------
Based on mean annual discharge in cubic feet per second (cfs), Virginia's lower tributaries
have modest flows compared to the Susquehanna, the Bay's largest tributary (Table 4.3). The
James discharged just over 8,000 cfs (mean annual discharge James + Appomattox) while both
the York (Mattaponi + Pumunkey) and Rappahannock were under 2,000 cfs (Figure 4.6). The
basins also showed differing spatial and temporal discharges. While the York and
Rappahannock basins had mean maximum annual mean discharges in 1993 and 1994 (as did the
Susquehanna), the James and Potomac had maximum discharges in 1985. As shown below,
annual average discharges for Virginia's three major tributaries varied greatly over the 1985-
1995 period.
Table 4.3 Annual Mean Discharge (cfs) from Seven Major Basins in the Chesapeake Bay
Year
Susquehanna
Potomac
Rappahannock
Mattaponi
Pumunkey
Appomattox
James
1985
30,470
11,570
1,533
523
1,111
1,271
7,526
1986
41,240
8,133
879
335
621
760
4,195
1987
32,260
11,470
1,579
Nd
1,171
1,441
8,829
1988
27,160
8,712
974
Nd
648
732
3,757
1989
39,860
11,960
1,806
Nd
1,175
1,437
9,341
1990
48,310
10,450
1,823
600
1,128
1,125
8,379
1991
29,670
9,273
1,180
265
568
811
6,956
1992
35,500
9,771
1,906
342
633
820
7,173
1993
52,480
16,990
2,390
744
1,485
1,838
8,836
1994
51,700
16,680
2,117
769
1,553
1,445
8,275
1995
27,970
9,266
1,818
376
869
1,097
7,062
Average
37,870
11,298
1,637
494
997
1,162
7,303
Max.
467,000
293,000
51,500
7,780
20,400
14,100
199,000
MaxYear
1993
1985
1993
1994
1994
1985
1985
Min.
821
514
69
7
47
32
763
MinYear
1985
1991
1987
1991
1991
1993
1986
The mean minimum annual discharges were similar for the three largest Bay tributaries.
Susquehanna, Potomac, and James had minimum annual discharges less than 1,000 cfs.
Minimal annual averages for the York and Rappahannock were less than 100 cfs.
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Figure 4.6 Lower Chesapeake Bay Basin Discharges
Loadings
Nutrient and sediment loads from above and below the fall lines within each tributary to the
Bay were evaluated. The external loads were comprised of: (1) fall line loads, (2) below-fall line
loads, (3) point source loads, and (4) atmospheric loads directly to the water surfaces of the Bay
and tributaries. Fall line and below-fall line loadings were calculated from the Watershed
Model. Point source loads were obtained from inventories provided by the Virginia Department
of Environmental Quality and their Discharge Monitoring Reports. Atmospheric loadings were
provided by RADM or by a regression of NADP data as described in Section 1.
Four reference loadings were used to establish the extent of reductions as comparisons: 1)
1985 Baseline Conditions, 2) 1996 Progress, 3) Full Voluntary Program Implementation, and 4)
Current Limit of Technology. Refer to Section 2 for the complete scenario descriptions.
As noted previously in Section 2, these scenarios provided key simulations for comparisons
to other, more specific, scenarios used to determine water quality and living resource responses
over a wide range of possible management actions. The 1985 Baseline Conditions and the Limit
of Technology scenarios were, respectively, the highest and lowest nutrient and sediment loads
simulated of all the management scenarios. The 1996 Progress scenario provided a best estimate
of current conditions and the Full Voluntary Program Implementation scenario estimated loads
under application of a voluntary non-point source program to the fullest extent.
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A matrix was developed for each tributary that contained information in three columns
regarding scenarios, estimated loads, and estimated water and habitat quality measurements of
living resource responses. Loads were determined for nitrogen for point sources, non-point
sources, and total loads (in pounds); phosphorus for point sources, non-point sources, and total
loads (in pounds), and total sediment loads (in tons).
Using the 1996 Progress scenario as an estimate of the current load conditions, the lower
tributary load of nitrogen was 22% of the total Signatory State nitrogen load. The lower
tributary phosphorus load was 37% of the total Signatory State load for this nutrient. The
Signatory States are those that signed the 1983 Chesapeake Bay Agreement and include PA,
MD, VA, and DC.
Sediment loads comprised eroded material from the watershed as well as from shoreline
erosion along the tidal Bay and tributaries. The lower tributary sediment load was 40% of the
total Signatory State sediment load for the 1996 Progress scenario. Shoreline erosion was
largely uncontrollable and accounted for an estimated 7% of the total sediment loads to the lower
tributaries.
Among the VA portions of the lower Bay tributaries, the James had the highest estimated
loads of nutrients and sediment, comprising over 65% of the nitrogen, nearly 75% of the
phosphorus, and 80% of the sediment loads from the major VA watersheds (Table 4.4). These
results are for the 1996 Progress scenario. After the James, the highest loads of nitrogen,
phosphorus and sediment came, in order, from the Rappahannock, York, and Eastern Shore
basins.
Table 4.4 Percentage of Total Virginia Loadings by Basin
Basin
Nitrogen
Phosphorus
Sediment
Rappahannock
15 %
13 %
12%
York
14%
10%
7%
James
67%
74%
80%
Eastern Shore
4%
3 %
1 %
Source: Chesapeake Bay Program Phase IV Watershed Model 1996 Progress Scenario
For the 1996 Progress scenario and among all major Chesapeake Bay basins and regions, the
James River basin accounted for the largest total phosphorus load delivered to the Bay on an
average annual basis over the Watershed Model simulation period of 1985-1994 (Table 4.5).
This load of 4.1 million lbs./year was greater than simulated results for the Potomac (3.9 million
lbs./year) and the Susquehanna (3.5 million lbs./year).
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Table 4.5 Mean Annual Nutrient and Sediment Loads and Yields for the Major Basins and Regions
of the Chesapeake Bay Watershed (1985-1994)
Basin
Total Nitrogen
Total Phosphorus
Sediment
(106 lb/yr)
(lb/acre/yr)
(106 lb/yr)
(lb/ac/yr)
(106ton/yr)
(ton/ac/yr)
Susquehanna
116.8
6.7
3.5
0.2
0.97
0.06
Patuxent
5.6
9.6
0.4
0.7
0.18
0.30
Western Shore MD
18.9
22.6
0.8
1.0
0.12
0.15
Eastern Shore MD
32.9
11.4
2.6
0.9
0.55
0.19
Potomac
64.6
7.1
3.9
0.4
2.52
0.28
Rappahannock
9.0
5.2
0.7
0.4
0.30
0.17
York
8.0
4.2
0.5
0.3
0.16
0.08
James
39.0
6.0
4.1
0.6
2.00
0.31
Eastern Shore VA
2.4
11.5
0.2
0.9
0.04
0.18
Source: Chesapeake Bay Program P
lase IV Watershed Model 1996 Progress Scenario
The James River basin load of nitrogen (39.0 million lbs./year) ranked third among major
Chesapeake Bay watersheds and regions, behind the Susquehanna (116.8 million lbs./year) and
Potomac (64.6 million lbs./year) loads (Table 4.5). The James annual mean sediment load for
the 1996 Progress scenario (2.00 million tons/year) was second among the Bay's major basins.
Only the Potomac River watershed had higher yearly sediment loads at 2.52 million tons/year.
The James had the highest sediment yield expressed as a unit weight per unit area (lb/acre)
among all major Chesapeake Bay catchments (Table 4.5). Again for the 1996 Progress scenario,
this average annual yield was 0.31 tons/acre for the James while the Patuxent ranked second with
0.30 tons/acre export of sediment. For both total nitrogen and total phosphorus, Eastern Shore
VA ranked second among the Bay regions for export per unit area. The Western Shore MD area
had the highest yields for these nutrients.
Limiting Nutrients
Management of an estuary or the rivers that flow into an estuary such as Chesapeake Bay are
best accomplished over large time periods due to the wide variation in flows and loads. For this
analysis, we looked at the nutrient(s) most limiting phytoplankton during the critical growing
season (spring and summer). Each tributary was separated by salinity into upper (low
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salinity/tidal fresh), middle (moderate salinity/mesohaline) and lower (high salinity/polyhaline)
regions.
Many processes control the growth and accumulation of algae in aquatic systems (Fisher and
Butt, 1994). Light is essential for photosynthesis and plant nutrients, like inorganic forms of
nitrogen, phosphorus, and silicon, are required to sustain phytoplankton (algae) growth rates.
Only dissolved inorganic forms of nitrogen and phosphorus are available to algae for primary
production. Inorganic forms of nitrogen are either ammonia (NH4) or nitrate (NO3) with algae
preferring the former. There is a single form of dissolved inorganic phosphorus (PO4). The
accumulation of algal biomass requires consideration of growth rates in conjunction with
transport losses, grazing, sinking, and cell death. Both the Watershed Model and CBEMP
simulate and characterize algal biomass accumulation.
Like most fresh water systems, non-tidal rivers (above the fall line) were phosphorus limited.
The entire James River below Richmond was nitrogen limited during the spring and summer
seasons. The tidal fresh regions of the Mattaponi and Pumunkey Rivers of the York basin were
phosphorus limited during the spring. During the summer, the upper tidal reaches of these two
rivers were phosphorus limited while the rest of the tidal York River was nitrogen limited. The
Rappahannock River was phosphorus limited during the spring, but switched to nitrogen
limitation during the summer. Also, the tidal fresh regions of the James, York, and
Rappahannock were light limited, particularly after storm delivery of high sediment loads (Haas
and Webb, 1998).
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4.2 Rappahannock Basin Loads
Nitrogen loads in the Rappahannock were primarily from agricultural sources with the
estimated 1996 loads, from highest to lowest, being cropland, urban (including septic systems),
pasture, forest, and point sources (Figure 4.7). The loading rate was a measure of nutrient and
sediment loads coming off a unit area of land (such as an acre) over a unit of time (such as a
year). Cropland often has a higher loading rate for nutrients and sediment than other sources, but
other sources may cover more area in a basin and therefore, comprise a larger load.
Figure 4.7 Rappahannock Nitrogen Loads By Source
Point Sources
5%
Atmos. Dep. to
Water
3%
Urban Loads
14%
Forest
12%
Animal Wastes
1%
Cropland
52%
Pasture
13%
Estimated Rappahannock phosphorus loads were highest for agriculture, then pasture, point
sources, and urban, followed by forest, animal wastes, and atmospheric deposition (Figure 4.8).
Figure 4.8 Rappahannock Phosphorus Loads By Source
Point Sources
1
Atmos. Dep.
Water
2%
Urban Loads
10%
Forest
^	| Cropland
Animal Wastes '	' 55%
2%
Pasture
18%
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Nitrogen loadings were simulated as delivered to the tidal portions of the Rappahannock
River in two forms: organic (58%) and inorganic nitrogen (42%) with inorganics in the species
nitrate (37%) and ammonia (5%) (Figure 4.9). Estimated nitrogen loads were based on the
Chesapeake Bay Watershed Model 1996 Progress scenario.
Figure 4.9 Nitrogen Species Delivered to the Rappahannock
River Fall Line
OrgN
58%
Estimated total nitrogen (TN) delivered below the fall line was from both non-point sources
(94%) and point sources (6%) (Figure 4.10). These loads were in the same organic/inorganic
forms. Most of the ammonia came from non-point sources (60%) while the nitrates and organic
nitrogen came from agricultural sources (99% and 97%, respectively). In the nitrogen limited
tidal waters, algae (phytoplankton) prefer dissolved forms of ammonia and uptake of nitrate
occurs when the available ammonia has been depleted.
Figure 4.10 Rappahannock Nitrogen Species Below Fall Line
NH4
60%
~ NPS BPS
40%
N03
99%
1%
97%
94%
OrgN
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Estimated sediment loads have no point source component, but include shoreline erosion
which amounted to 0.042 million tons/year. Cropland accounted for the largest source of
sediment (48%) followed by forest (25%), pasture (20%), and urban lands (7%) (Figure 4.11).
Figure 4.11 Rappahannock Sediment Loads By Source
Urban Loads
7%
Forest
25%
Cropland
48%
Pasture
20%
Along with the 1996 Progress loads, estimated loads for the Rappahannock scenario runs are
shown in Table 4.6. Load estimates are a function of the loading rate from each source and the
amount of land area in the basin covered by each source.
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Table 4.6 Tidal and Western Shore Rappahannock Loads by Scenario
Scenario
Loads*
(Nutrients in million lbs., Sediment in million tons)

Nitrogen
Phosphorus
Sediment

PS
NPS
Total
PS
NPS
Total
Total
1985 Baseline Conditions
0.4
9.8
10.3
0.18
0.76
0.94
0.36
1996 Progress
0.5
8.5
9.0
0.08
0.62
0.69
0.30
1996 Progress/TS Above
0.5
8.5
9.0
0.08
0.62
0.69
0.30
BNR-BNR Equivalent/TS Above
0.3
6.7
6.9
0.07
0.60
0.66
0.29
Interim Bay Agreement Goal/TS Above


6.5


0.62
0.32
Midpoint 1996-Full Volun. Imp.
0.4
7.1
7.5
0.05
0.56
0.61
0.28
West Shore VA Full Volun. Imp./TS Above
0.5
8.3
8.8
0.08
0.61
0.68
0.30
Full Voluntary Imp./TS Above
0.2
5.8
6.0
0.02
0.51
0.53
0.27
Full Voluntary Implementation
0.2
5.8
6.0
0.02
0.51
0.53
0.27
Current Limit of Technology
0.1
5.0
5.1
0.00
0.43
0.43
0.24
*Includes loads for Western Shore Rappahannock which are 5.8% (TO), 4.3% (TP), and 3.6% (sediment)
of the total Rappahannock load for 19i!5 Baseline Conditions. Sediment loads do not include 0.042
million tons of shoreline erosion load.
4.3 York Basin Loads
The York has more urban and forest land than the Rappahannock basin. Based on estimated
1996 conditions, agriculture dominated nitrogen loads with cropland, pasture, and animal wastes
responsible for 37%, 5%, and 1% of the total delivered nitrogen load, respectively. Point sources
were responsible for 20%, while urban (including septic) and forest were 17% and 16%,
respectively (Figure 4.12).
IV- 17

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Figure 4.12 York Nitrogen Loads By Source
Point Sources
20%
Atmos. Dep. to
Water
4%
Urban Loads
17%
Cropland
37%
Forest
16%
Pasture
5%
Animal Wastes
1%
York phosphorus loads were highest for agriculture, point sources, and urban, followed by
pasture, forest, atmospheric deposition, and animal waste (Figure 4.13).
Figure 4.13 York Phorphorus Loads By Source
Point Sources
33%
Atmos. Dep. to
Water
4%
Urban Loads
10%
Cropland
44%
asture
3%
Animal Wastes
1%
Nitrogen loads were delivered to the tidal portions of York in two forms: organic (53%) and
inorganic nitrogen (47%) with inorganics in the species nitrate (42%) and ammonia (5%)
(Figure 4.14). These estimates were based on the Watershed Model 1996 Progress run. Organic
nitrogen from agricultural runoff is not available to algae as part of primary production, but
accumulates in the sediments where it undergoes decay by bacteria.
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Figure 4.14 Nitrogen Species Delivered to the York River Fall Line
OrgN
53%
The total nitrogen (TN) delivered below the fall line was from both non-point sources (76%)
and point sources (24%). These loads were in the same organic/inorganic forms, but their
sources differed (Figure 4.15). Most of the ammonia came from point sources (81%) while the
nitrates and organic nitrogen came from agricultural sources (98% & 93%, respectively). In the
nitrogen limited tidal waters, algae (phytoplankton) prefer dissolved forms of ammonia and then
nitrate when the available ammonia has been depleted.
Figure 4.15 York Nitrogen Species Below Fall Line
OrgN
93%
7%
TN
76%
24%
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Estimated 1996 Progress scenario sediment loads in the York basin were slightly more than
half that of those for the Rappahannock although shoreline erosion loads for the York were
greater. Estimated sediment loads from shoreline erosion were 0.072 million tons/year which is
the greatest among the Virginia tributaries. Cropland accounted for the largest source of
sediment (57%) followed by forest (31%), pasture (8%), and urban lands (4%) (Figure 4.16).
Figure 4.16 York Sediment Loads By Source
Estimated loads for all scenario runs for the York tidal river are shown in Table 4.7. Load
estimates are a function of the loading rate from each source and the amount of land area in the
basin covered by each source.
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Table 4.7 Tidal and Western Shore York Loads by Scenario
Scenario
Loads*
(Nutrients in million lbs., Sediment in million tons)

Nitrogen
Phosphorus
Sediment

PS
NPS
Total
PS
NPS
Total
Total
1985 Baseline Conditions
1.3
6.9
8.2
0.42
0.44
0.85
0.19
1996 Progress
1.6
6.4
8.0
0.18
0.36
0.54
0.16
1996 Progress/TS Above
1.6
6.4
8.0
0.18
0.36
0.54
0.16
BNR-BNR Equivalent/TS Above
0.8
5.1
5.9
0.15
0.36
0.5
0.16
Interim Bay Agreement Goal/TS Above


4.5


0.60
0.17
Midpoint 1996-Full Volun. Imp.
1.0
5.5
6.6
0.11
0.34
0.45
0.16
West Shore VA Full Volun. Imp./TS Above
1.6
6.2
7.8
0.18
0.36
0.54
0.16
Full Voluntary Imp./TS Above
0.5
4.6
5.1
0.05
0.32
0.37
0.15
Full Voluntary Implementation
0.5
4.6
5.1
0.05
0.32
0.37
0.15
Current Limit of Technology
0.3
4.0
4.3
0.01
0.26
0.27
0.13
*Includes loads for Western Shore York which are 18 3% (TN). 9.8% (TP), and 13.8% (sediment) of the
total York load for the 1985 Baseline Conditions. Sec iment loads do not include 0.072 million tons of
shoreline erosion load.
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4.4 James Basin Loads
James basin loads, estimated by the 1996 Progress scenario, were dominated by point
sources, followed by sources from urban land, cropland, forest, pasture, atmospheric deposition,
and animal waste (Figure 4.17).
Figure 4.17 James Nitrogen Loads By Source
Cropland
14%
Point Source
49%
Atmos. Dep. to
Water
2%
Pasture
4%
Animal Wastes
1%
Forest
9%
Urban Loads
21%
Phosphorus loads to the James were greatest from point sources, followed by cropland,
forest, urban, and pasture. Animal waste and atmospheric deposition contributed the least to the
total phosphorus load (Figure 4.18).
Figure 4.18 James Phosphorus Loads By Source
Point Source
40%
Atmos. Dep.
Water
1%
Cropland
20%
Pasture
11%
Animal Wastes
1%
Forest
14%
Urban Loads
13%
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Nitrogen loads were delivered to the tidal portions of James River in two forms. Organic
nitrogen accounted for two-thirds of the total nitrogen loads while inorganic nitrogen (in the
species of nitrate and ammonia) represented the remaining 33% (Figure 4.19). Most of the
organic nitrogen was from agricultural runoff.
Estimated total nitrogen delivered below the fall line came equally from point and non-point
sources (Figure 4.20). These loads were in organic and inorganic forms in varying source
proportions. Most of the ammonia (93%) came from point sources while the nitrates and organic
nitrogen came from agricultural sources (81% and 75%, respectively). In the nitrogen-limited
tidal waters, algae (phytoplankton) prefer dissolved forms of ammonia and uptake of nitrate
occurs when the available ammonia has been depleted.
Figure 4.19 Nitrogen Species Delivered to the James River Fall Line
NH4
4%
Oi
6'
N03
.29%
Figure 4.20 James Nitrogen Species Below Fall Line
NH4
~ NPS BPS
N03
7%
0
93%
81%
0
19%
OrgN
TN
75%
0
25%
50%
50%
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Estimated sediment loads were dominated by forest sources, followed by cropland, pasture,
and urban source loads (Figure 4.21). Shoreline erosion for the James amounted to 0.051 million
tons/year or about 3% of the total sediment load for the 1996 Progress scenario.
Figure 4.21 James Sediment Loads By Source
Urban Loads
7%	Cropland
Along with the estimated 1996 Progress loads, results for the James tidal river are shown for
all modeling scenarios in Table 4.8. Load estimates are a function of the loading rate from each
source and the amount of land area in the basin covered by each source.
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Table 4.8 Tidal James River Loads by Scenario
Scenario




Loads





(Nutrients in million lbs., Sediment in million tons)

Nitrogen
Phosphorus
Sediment

PS
NPS
Total
PS
NPS
Total
Total
1985 Baseline Conditions
22.1
19.1
41.2
3.58
2.54
6.12
2.0
1996 Progress
17.9
18.6
36.5
1.52
2.38
3.90
2.0
1996 Progress/TS Above
17.9
18.6
36.5
1.52
2.38
3.90
2.0
James AFL BNR Equiv./TS Above
17.4
17.5
34.9
1.46
2.36
3.82
1.9
James AFL, BFL TF & Appomattox
BNR Equiv./TS Above
11.5
16.6
28.1
1.36
2.35
3.71
1.9
James TF BNR Equiv. For N/TS Above
11.5
16.6
28.1
1.52
2.38
3.90
2.0
BNR-BNR Equivalent/TS Above
8.3
15.4
23.7
1.34
2.34
3.68
1.9
Current LOT Sediment/TS Above
17.9
18.6
36.5
1.52
2.38
3.90
1.7
Extreme Sediment Reduction/TS Above
17.9
18.6
36.5
1.52
2.38
3.90
1.2
Interim Bay Agreement Goal/TS Above


29.4


3.95
1.9
Midpoint 1996-Full Volun. Imp.
12.1
16.6
28.7
1.01
2.25
3.25
1.9
Full Voluntary Imp./TS Above
6.2
14.6
20.8
0.49
2.11
2.60
1.8
Full Voluntary Implementation
6.2
14.6
20.8
0.49
2.11
2.60
1.8
Current Limit of Technology
3.7
12.3
16.0
0.10
1.77
1.87
1.7
Does not include loads for Western Shore J;tmes. Sediment bads do not include 0.051 riillion tons of
shoreline erosion load.
4.5 Eastern Shore Basin Loads
Eastern Shore basin loads were primarily from agricultural sources (Figure 4.22). Estimated
nutrient loads for the 1996 Progress scenario have the unusual feature of increased point source
loads for both nitrogen and phosphorus compared to the 1985 Baseline.
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Figure 4.22 Eastern Shore Nitrogen Loads By Source
Point Source
17%
Atmos. Dep. to
Water
3%
Urban Loads
9%
Forest
6%
Pasture
1%
Cropland
64%
Sources of phosphorus loads from the Eastern Shore (in order from greatest to least) were
cropland, point sources, and an "other" category comprising forest, urban, pasture, animal waste,
and atmospheric deposition (Figure 4.23).
Figure 4.23 Eastern Shore Phosphorus Loads By Source
Other
9%
Point Source
30%
Cropland
61%
As seen in Figure 4.24 for the Watershed Model 1996 Progress run, point sources were 17%
of the total delivered nitrogen loads from the Eastern Shore. While non-point sources
represented almost 100% of the organic and nitrate fractions, the majority (77%) of ammonia
originated from point sources.
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Figure 4.24 Eastern Shore Nitrogen Species Below Fall Line
OrgN
TN
Eastern Shore sediment sources are depicted in Figure 4.25 and included, from greatest to
least load, cropland, forest, urban, and pasture. Estimated sediment loads from shoreline erosion
were 0.019 million tons, the lowest among major regions in Virginia.
Figure 4.25 Eastern Shore Sediment Loads By Source
Urban Loads
3%
Forest
9%
Pasture
1%
Cropland
87%
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Estimated loads for all scenario runs for the Eastern Shore are shown in Table 4.9. Load
estimates are a function of the loading rate from each source and the amount of land area in the
basin covered by each source.
Table 4.9 Eastern Shore Virginia Loads by Scenario
Scenario
Loads
(Nutrients in million lbs., Sediment in million tons)

Nitrogen
Phosphorus
Sediment

PS
NPS
Total
PS
NPS
Total
Total
1985 Baseline Conditions
0.287
2.398
2.685
0.006
0.193
0.199
0.049
1996 Progress
0.407
2.271
2.677
0.056
0.147
0.203
0.040
1996 Progress/TS Above*
0.407
2.271
2.677
0.056
0.147
0.203
0.040
Updated 1996 Progress/TS Above*
0.407
2.187
2.594
0.056
0.156
0.212
0.038
BNR-BNR Equivalent/TS Above
0.026
1.442
1.467
0.049
0.145
0.194
0.039
Interim Bay Agreement Goal/TS Above


1.776


0.093
0.036
Midpoint 1996-Full Volun. Imp.
0.212
1.840
2.052
0.029
0.139
0.167
0.036
East Shore VA Full Volun. Imp./TS Above
0.018
1.410
1.427
0.002
0.130
0.131
0.032
Full Voluntary Imp./TS Above
0.018
1.410
1.427
0.002
0.130
0.131
0.032
Full Voluntary Implementation
0.018
1.410
1.427
0.002
0.130
0.131
0.032
Current Limit of Technology
0.010
1.288
1.297
0.000
0.096
0.097
0.024
*These 1996 Progress simulated loads were used for tie combined w atershed and Chesapeake Bay model
scenarios. Subsequent to this run, the Eastern Shore tributary team corrected the acres of conventionally
tilled and conservation tilled cropland. The values for the adapted cropland 1996 scenario are reported
under "Updated 1996 Progress/TS Above". The magnitude of the differences between the two 1996
Progress scenarios is slight and will hs.ve little effect on the water quality response s.
IV- 28

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Section 5: Water Quality and Bay Grass Responses
5.1 Overview
Habitat Requirements for Chesapeake Bay Living Resources (CEC, 1988) published in
response to the 1987 Chesapeake Bay Agreement provides "for the restoration and protection of
the living resources, their habitats and ecological relationships". These water quality goals and
requirements are considered from the point of view of maintenance, protection, and improvement
of an aquatic ecosystem. The focus is on Bay fisheries and supporting aquatic life, including the
benthic communities and submerged aquatic vegetation (SAV). Details on the development of
water quality requirements are provided in Chesapeake Bay Program (1993), Dennison et al.
(1993), Batiuk et al. (1992), Jordan et al. (1992), and Funderburk et al. (1991).
The principle water quality parameters included 1) dissolved oxygen (DO), 2) light
attenuation affecting underwater Bay grasses, 3) chlorophyll a, 4) total suspended solids (TSS),
and 5) dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP). Water
quality and living resource goals unique to the conditions in each tributary were used as guidelines
in the assessment of tributary nutrient and sediment reduction strategies.
Dissolved Oxygen
Dissolved oxygen is a major factor affecting the survival, distribution, and productivity of
aquatic living resources. Because of natural fluctuations in dissolved oxygen and the sensitivity of
the many key Bay species to low concentrations, dissolved oxygen habitat requirements are
determined in three regions: 1) above the pycnocline, 2) below the pycnocline, and 3) in spawning
areas. Living resource sensitivity to low oxygen concentrations depends upon life cycles,
temperatures, salinity, duration of exposure, and other stress factors such as contaminants. By
selecting conditions acceptable for the reproduction, growth, and survival of a variety of sensitive
species, habitat requirements can be established that will also protect the Bay's other living
resources.
Dissolved oxygen tolerance information was compiled and interpreted for fourteen target
species of fish, mollusks, and crustaceans (Funderburk et al., 1991), including both commercial
and recreational fish and shellfish. Exposure to low dissolved oxygen (less than 0.5-1.5 mg/L)
was found to be lethal, during some life stages, to all of the target species for which exposure
information was available. While many species can live in waters with severely depressed or
hypoxic dissolved oxygen conditions (between 1.5 and 3.0 mg/L), deleterious effects on growth
and reproduction occurred. The dissolved oxygen goals are summarized below in Table 5.1.
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Table 5.1 Summary of Dissolved Oxygen Goals
Dissolved Oxygen Goal
Location & Other Specifications
At least 1.0 mg/L at all times
Throughout the Bay and tidal tributaries, including
sub-pycnocline waters
Less than 3.0 mg/L for less than 12 hours and
intervals between excursions between 1.0 to 3.0
mg/L at least 48 hours
Throughout the Bay and tidal tributaries, including
sub-pycnocline waters
Monthly mean of 5.0 mg/L or better at all times
All times throughout waters above the pycnocline
At least 5.0 mg/L at all times
Throughout the water above the pycnocline in
spawning reaches, spawning rivers, and nursery
areas.
Sources: Chesapeake Bay Program (1993); Jordan et a
1. (1992).
The model-calculated response of dissolved oxygen to nutrient load reductions was
determined as seasonal (specifically summer) average concentrations as well as the extent and
duration of dissolved oxygen concentrations under the thresholds of anoxia (<1.0 mg/L) and
hypoxia (<3.0 mg/L). The two thresholds were assigned a quantity determined by calculating the
volumetric and temporal extent of dissolved oxygen below their respective DO levels. These
"anoxic volume-days" (AVD) and "hypoxic volume-days" (HVD) have units of m3-days.
The model AVD and HVD output was tracked on a cell-by-cell basis over time and a sum of
the volume less than the threshold concentration was accumulated over estuary model segments
for each scenario. A ten-year total of volume-days was then computed. A summery of the anoxic
volume-days for Virginia's lower tributaries for three key scenarios is provided in Figure 5.1. A
matrix for each tributary describing the percent improvements from 1985 conditions for key water
and habitat quality parameters associated with each scenario is also provided (Tables 5.3 - 5.6).
Based on 1996 Progress scenario conditions, the Rappahannock accounted for 96% of anoxia in
Virginia tributary waters.
V- 2

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180
160
140
120
100
80
60
40
20
Figure 5.1 Virginia Total Amount Of Anoxic Water
I 1985 Baseline Conditions
CH 1996 Progress
CH Full Voluntary Implementation
Rappahannock
York
James
Eastern Shore VA
Submerged Aquatic Vegetation
Submerged aquatic vegetation (SAV) refers to underwater vascular plants. These aquatic
plants perform a number of valuable ecological roles. The plants are a major food source for
waterfowl, provide habitat and shelter for a variety of fish and shellfish, and are habitat to many
smaller organisms that serve as food to larger organisms, including valued commercial and
recreational fishes. Historically, SAV has been abundant throughout Chesapeake Bay. However,
today's populations are only a remnant of the once thick beds that provided shelter to the Bay's
thriving seafood industry. The drastic decline of SAV, first noted in the 1970's, sparked the
concern of Bay scientists and managers and prompted investigations into the cause for SAV loss
and methods to restore this key resource.
The general consensus of Bay scientists is that the loss of SAV in Chesapeake Bay is due to
decreased light penetration throughout the water column and bio-fouling of the plant leaf
surfaces, caused by excessive loadings of nutrients and sediments from the watershed. Excessive
nutrients and sediments decrease water clarity and therefore, reduce available light necessary for
the plants to grow and reproduce. Habitat requirements most applicable to SAV are those water
quality parameters that contribute to light attenuation, or extinction, and include 1) total
suspended solids (TSS), 2) chlorophyll a, and 3) light attenuation by dissolved organic material.
While light is the major parameter controlling SAV distribution, nutrients such as dissolved
inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) indirectly contribute to light
attenuation by stimulating growth of algae within the water column and on the leaves and stems
V- 3

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of SAV. SAV habitat requirements are defined as the minimal water quality levels necessary for
SAV survival.
The diversity of SAV communities, coupled with their wide salinity ranges, led to the
establishment of separate requirements based on salinity for one-meter and two-meter depths. A
summary of SAV habitat requirements is provided elsewhere (CBP, 1993; Dennison et al., 1993,
Batiuk, 1992, Funderburk et al., 1991). To measure progress in SAV restoration, a tiered set of
SAV distribution targets was established for the Chesapeake. Each tier represents an expansion in
SAV distribution based on prior measurements of cover or on depth increments. As seen in Table
5.2, "Tier I" describes SAV restoration to areas currently or previously inhabited by SAV as
mapped through regional and Bay-wide aerial surveys from 1971 through 1990. "Tier II" is
restoration of SAV to all shallow water areas delineated as existing or potential SAV habitat to
the one-meter depth contour. "Tier III" is restoration of SAV to all shallow water areas
delineated as existing or potential SAV habitat down to the two-meter depth contour.
Table 5.2 SAV Habitat Requirements
TF=Tidal Fresh (<0.5 ppt salinity)
OL=01igohaline (0.5 to 5.0 ppt salinity)
ME=Mesohaline (5.0 to 18.0 ppt salinity)
PO=Polyhaline (>18 ppt salinity)
One Meter Restoration
Water Quality Parameter
Value
Other Specifications
Light Attenuation (Kd) (m1)
<2.0
<1.5
i i
For TF and OL regions
For ME and PO
Total Suspended Solids (mg/1)
<15
For TF , OL , and ME regions and PO
Chlorophyll a (ug/1)
<15
For TF , OL , and ME1 regions and PO2
Dissolved Inorganic Nitrogen (mg/1)
<0.15
1 2
For ME regions and PO
Dissolved Inorganic Phosphorus (mg/1)
<0.02
<0.01
For TF1, OL1, and PO2
For ME and PO
Two Meter Restoration
Light Attenuation (Kd)
<0.8
For TF , OL , and ME regions and PO
1 Critical Life Period for SAV is April through October
2Critical Life Period for SAV is March through November
V- 4

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The Chesapeake Bay Estuary Model Package simulates three generalized species of SAV that
are restricted to the littoral zone within the two-meter contour. In the model, the littoral zone is
represented as having a constant mean depth of one meter. As described in Section 1, three
additional state variables of shoots (above-ground biomass), roots (below-ground biomass), and
epiphytes (attached growth to leaves) are modeled within this zone.
The model is parameterized to simulate a single species for each salinity regime: 1) wild celery
(Vallisneria americcma) for tidal fresh regions, 2) widgeon grass (Ruppia maritima) in regions of
moderate salinity (mesohaline), and 3) eelgrass (Zostera marina) for high salinity (polyhaline)
regions. The output is displayed as either area (hectares) of Bay grasses or Bay grass density in
grams carbon per square meter (g C/m2).
The summer Bay grass density for the lower tributaries is shown for three key scenarios in
Figure 5.2. An important goal in SAV restoration is to achieve densities in and above a 25-50 g
C/m2 range. Densities in this range are capable of modifying local habitat and persist under pulses
of poor water quality conditions (Moore, 1997).
125
100
Figure 5.2 Virginia Summer Bay Grasses Density
Ļ 1985 Baseline Conditions
n 1996 Progress
~ Full Voluntary Im
-
03
3
cr
75
e
-p 50
6b 25
d
13
d
d
-
o
7T
W
3
n	ffc
>
All regions of Virginia's tributaries show improved densities with reductions in nutrient and
sediment loads. For the lower regions and western shores of the Rappahannock and York,
important regions of SAV in the lower Chesapeake, nutrient and sediment reductions beyond
1996 levels are estimated to be particularly beneficial to the grasses' ability to withstand pulses of
V- 5

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poor water quality.
The area of SAV coverage is another indicator of SAV health. Figure 5.3 graphs the extent
of SAV coverage in the lower tributaries. With the exception of the Lower Rappahannock, tidal
fresh James, and the Eastern Shore, reductions in nutrient and sediment loads are estimated to
have a greater influence on improved SAV density than expansion of SAV coverage.
Figure 5.3 Virginia Summer Bay Grasses Area
I 1985 Baseline Conditions
n 1996 Progress
EH Full Voluntary Implementation
d
Ļa
Ļa
d
Ļa
Ļa
d
Ļa
Ļa
to
-
Ļa
o
*Ļ
S3
-3
>
Chlorophyll
Another water quality parameter used as an indicator of the Bay=s health is chlorophyll.
Chlorophyll concentrations, along with algae (or phytoplankton) growth rates, are employed to
compare the relative health of an ecosystem, as measured by primary production or how much
algae is being produced. While chlorophyll concentrations were not excessive in the
Rappahannock and York Rivers, elevated concentrations were observed in the tidal fresh James
(Figure 5.4). Chlorophyll concentrations greater than 10 ug/L in the tidal fresh regions are
considered to be indicative of unhealthy algal levels. In more saline waters of the lower estuaries,
concentrations greater than 5 ug/L designate unhealthy levels of algal growth.
V- 6

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Figure 5.4 Virginia Summer Surface Chlorophyll Concentration
1 1985 Baseline Conditions
D 1996 Progress
n Full Voluntary Implementation 1






111
iy
i
i-d
ii
Upper Rap.	Lower Rap.	Middle York	Upper James	Lower James
Middle Rap.	Upper York	Lower York	Middle James
5.2 Rappahannock Basin Water and Habitat Quality
Dissolved Oxygen
Of Virginia's three largest tributaries, the Rappahannock had the most extensive areas of
anoxia (Figure 5.1). Within the Rappahannock basin itself, the lower portion of the tidal tributary
had the largest volume of anoxic water, followed by the Western Shore, and then the Middle
Rappahannock. It should be noted that the Western Shore Rappahannock includes a portion of
the Virginia mainstem Bay.
The estimated ten-year average AVD in the lower tidal Rappahannock was around 11 billion
cubic meter-days under 1996 Progress conditions. However, when viewed on an annual basis
with varying flows, most of the anoxic volume occurred in a single year (Figure 5.5). For the
1996 Progress scenario, the 1991 hydrology year had a total AVD of about 40 billion cubic
meter-days while the 1986 hydrologic year estimate was as low as 4 billion cubic meter-days.
V- 7

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50
40
Figure 5.5 Tidal Rappahannock Total Amount of Anoxic Water
(1985-19945)
cs
-a
30
20
10
-Q
3
I 1985 Baseline Conditions
CH 1996 Progress
n Full Voluntary Implementation
I I
hll
i
i
1985 1986 1987 1988 1989 1990 1991 1992 1993 1994
According to the modeled responses for the 1996 Progress run, there was a 16%
improvement in AVD in the Rappahannock resulting from nutrient management changes
implemented since 1985 (Table 5.3). An additional 23% improvement in AVD was achieved with
implementation of tributary strategies in the Potomac and basins further north of the Potomac.
Full Voluntary Program Implementation in Virginia's lower tributaries provided an additional
10% improvement to dissolved oxygen conditions in this river. Full Voluntary Program
Implementation throughout the entire Bay achieved nearly an 80% overall improvement and
almost eliminated anoxia in the Rappahannock. This level of reduction nearly equated to the same
level of response as the Limit of Technology controls applied throughout the entire Bay
watershed.
Equivalent changes in the volume of hypoxic waters (<3.0 mg/L) were also seen. While
significant benefits were calculated when greater load reductions were taken from the entire
watershed, reductions of nutrients (and nitrogen, particular) within the Rappahannock were
estimated to be more cost effective in improving Rappahannock low dissolved oxygen conditions
than equivalent reductions outside the basin.
Submerged Aquatic Vegetation
The Western Shore Rappahannock maintained a relatively dense population of SAV under
the estimated 1996 Progress scenario conditions (Figure 5.2). The densities were more than
twice the estimates in the Lower Rappahannock. Both the Lower and Western Shore
V- 8

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Rappahannock had significant improvements in SAV density with nutrient and sediment
reductions beyond 1996 conditions. In fact, SAV densities were sufficient to withstand periods of
poor water quality conditions, like those during storm events.
Modeled results for the Rappahannock indicated that SAV responded to nutrient and sediment
reductions by increasing the density and health within existing SAV areas with only a slight
expansion of SAV area (Figure 5.3, Table 5.3).
Table 5.3 Tidal and Western Shore Rappahannock Percent Improvements from 1985 Conditions for
Key Water and Habitat Quality Measurements
Scenario
Loading
Reductions
Water And Habitat
Quality Improvements

Nitrogen
Reduction
Phosphorus
Reduction
Sediment
Reduction
Anoxic
Water
Habitat Bay Bay
<3 ma/L Grasses Grasses

PS
NPS
TOT
PS
NPS
TOT
TOT
(<1 mg/L
DO)
DO
Area
Density
1996 Progress
-25!
13
13
56
18
27
17
16
11
9
28
1996 Progress/TS Above
-25!
13
13
56
18
27
17
39
27
9
47
BNR-BNR
Equivalent/TS Above
26
32
33
62
22
29
20
45
31
9
52
Interim Bay Agreement
Goal/TS Above


37


34
11
47
32
9
49
Midpoint 1996-Full
Voluntary Implement.
0
28
27
72
26
35
22
50
35
9
57
West Shore VA Full
Volunt. Imp./TS Above
-25!
15
15
56
20
28
17
39
27
9
52
Full Voluntary Imp./
TS Above
50
41
42
89
33
44
25
49
34
9
61
Full Voluntary
Implementation
50
41
42
89
33
44
25
79
57
17
77
Current Limit of
Technology
75
49
50
100
43
54
33
86
66
19
84
* Negative values indicate percent increase in nutrient loads over 1985 Baseline Condition loads.
There was almost a 30% improvement in Bay grass density between the 1985 Baseline and
1996 Progress runs and an additional 20% was achieved with implementation of tributary
strategies in the Potomac and basins further north. An additional 5% to 15 % density increase
was expected from nutrient and sediment controls within Virginia's tributaries up to Full
V- 9

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Voluntary Program Implementation controls in Virginia's lower tributaries. Full Voluntary
Program Implementation throughout the entire Bay achieved nearly an 80% overall improvement
in SAV density from the 1985 Baseline. This level of improvement nearly equated to the SAV
response if Limit of Technology controls were applied throughout the entire Bay, reaching 84%
increase in density over 1985 conditions. Changes in Rappahannock SAV density were estimated
to be particularly responsive to nutrient and sediment reductions within the Rappahannock as
compared to equivalent reductions outside the basin.
5.3 York Basin Water and Habitat Quality
Dissolved Oxygen
Under estimated 1996 conditions, the York had only 2% of the anoxic waters relative to the
levels of anoxia in the Rappahannock (Figure 5.1), but reduced anoxia and hypoxia were modeled
with reductions in nutrients, particularly nitrogen. According to the simulated responses, the
1996 Progress scenario indicated there was more than a 10% improvement in anoxic volume-days
with nutrient management changes implemented since 1985 (Table 5.4). An additional 20%
improvement was anticipated with implementation of tributary strategies in the Potomac and
basins further north.
Full Voluntary Program Implementation in Virginia's lower tributaries provided an additional
15% improvement of dissolved oxygen conditions in the York. Full Voluntary Program
Implementation throughout the entire Bay achieved more than a 20% further improvement. This
70% overall improvement from 1985 Baseline conditions would almost entirely eliminate York
anoxia. The Full Voluntary Implementation level of anoxia reduction was just short of the
estimated Limit of Technology improvement for the entire Bay, determined to be 80% overall
when compared to the 1985 Baseline. Nutrient controls within Virginia's tributaries under both
the BNR-BNR Equivalent and Interim Goal scenarios resulted in only a moderate improvement of
44%.
Submerged Aquatic Vegetation
The Lower York, Mobjack Bay, and Western Shore York maintained dense populations of
SAV for the 1996 Progress run (Figure 5.2). Generally, SAV densities were comparable between
the York and Rappahannock, but the area coverage of SAV in the York was more than twice that
of the Rappahannock (Tables 5.3 and 5.4).
v-io

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Table 5.4 Tidal and Western Shore York Percent Improvements from 1985 Conditions for Key
Water and Habitat Quality Measurements
Scenario
Loading
Reductions
Water And Habitat
Quality Improvements

Nitrogen
Reduction
Phosphorus
Reduction
Sediment
Reduction
Anoxic
Water
Habitat Bay Bay
<3 ma/L Grasses Grasses

PS
NPS
TOT
PS
NPS
TOT
TOT
(<1 mg/L
DO)
DO
Area
Density
1996 Progress
-23!
7
2
57
18
36
16
13
10
1
22
1996 Progress/TS Above
-23!
7
2
57
18
36
16
34
27
3
31
BNR-BNR
Equivalent/TS Above
38
26
28
65
19
41
15
44
34
4
36
Interim Bay Agreement
Goal/TS Above


45


29
11
44
34
4
35
Midpoint 1996-Full
Voluntary Implement.
23
20
20
74
23
47
16
46
37
4
38
West Shore VA Full
Volunt. Imp./TS Above
-23!
10
5
57
18
36
16
38
28
3
33
Full Voluntary Imp./
TS Above
62
33
38
88
27
56
21
49
37
7
41
Full Voluntary
Implementation
62
33
38
88
27
56
21
72
59
7
49
Current Limit of
Technology
77
42
48
98
41
68
32
80
68
9
54
* Negative values indicate percent increase in nutrient loads over 1985 Baseline Condition loads.
According to optical model estimates (Gallegos, 1994; CBP, 1999), variations in chlorophyll
concentrations were primarily responsible for the variability in light attenuation in some tidal
tributaries while in other tributaries, total suspended solids dominated. For the Lower York and
Mobjack Bay, estimates of the optical model found that habitat requirements for SAV were met
for 0.5 meter and 1.0 meter at three monitoring stations in these regions. At another monitoring
station in the Lower York (LE4.2 in Table 5.5), only the 0.5 meter requirements were met.
Modest reductions in both chlorophyll and sediments (about 20%) were needed near this station
to meet the 1.0 meter SAV habitat requirements (Table 5.5).
In order to reach the 2.0 meter requirements in Mobjack Bay, significant reductions in both
total suspended solids and chlorophyll levels were essential (monitoring stations WE4.1 and
WE4.3 in Table 5.5). Specifically, over 50% reductions were required for both parameters. In
v-n

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Mobjack Bay, sediment reductions were the most feasible alternative to improving light
attenuation for 1.0 meter; however, extreme reductions in both sediments and chlorophyll were
needed to meet the 2.0 meter requirements.
Table 5.5 SAV Habitat Requirements for Water Quality Attenuation in the York River: Percent
reductions needed to meet SAV habitat requirements for 1.0 and 2.0 meters
Station
LE4.2 1.0 m
WE4.1 2.0 m
WE4.3 2.0 m
Parameter causing
non-attainment of
habitat
CHLA
TSS
CHLA
TSS
CHLA
TSS
Reductions needed to
meet habitat
requirements
20%
21%
63%
63%
62%
62%
TSS only reductions
needed to meet habitat
requirements
N/A
76%
N/A
70%
N/A
68%
There were positive responses of grass densities to nutrient reductions with over a 20%
improvement in SAV density between the 1985 Baseline and 1996 Progress conditions (Table
5.4). An additional 10% was achieved with implementation of tributary strategies in the Potomac
and basins further north of the Potomac. Up to an additional 10% improvement was estimated
from nutrient and sediment controls within Virginia's tributaries. Full Voluntary Program
Implementation throughout the entire Chesapeake basin achieved nearly a 50% improvement in
SAV density over 1985 conditions. This increase was close to the estimated Limit of Technology
SAV density improvement of 54%. Only a modest expansion of Bay grass areas was associated
with progressive nutrient and sediment controls (Table 5.4).
Within the lower tributaries, the importance of controlling nutrient loads in order to improve
SAV habitat was seen when comparing scenario results from 1996 Progress/Tributary Strategy
Above, Full Voluntary Program Implementation/Tributary Strategy Above, and Full Voluntary
Program Implementation scenarios (Table 5.6). The comparison was made between Chesapeake
Bay basin-wide total nitrogen loads and the percent improvement in York SAV density to assess
the impact of local versus Bay-wide controls. Using the 1996 Progress/Tributary Strategy Above
scenario as the basis, reductions in nitrogen loads in the lower tributaries were about twice as
effective in improving SAV density in the York than nitrogen load reductions in the entire
Chesapeake basin. Specifically, there was a 4.7% improvement in York SAV density per 10
million pounds nitrogen removed in the lower tributaries compared to a 2.4% improvement in
York SAV density per 10 million pounds nitrogen removed in the Chesapeake watershed.
V-12

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Table 5.6 Relative Improvements in York SAV Density to Nitrogen Load Reductions in the Lower
Tributaries and in the Chesapeake Basin
Scenario
TN
Loads
TN Reduction
Relative to
1996 Progress/
Tributary
Strategy Above
Scenario
SAV Improvement
Relative to
1996 Progress/
Tributary
Strategy Above
Scenario
Percent
Improvement of
SAV for 10
Million Pounds of
Nitrogen
Reduced
1996 Progress/
Tributary Strategy Above
299.2
0
0
0
Full Voluntary Program
Implementation/
Tributary Strategy Above
277.9
21.3
10%
4.7
Full Voluntary Program
Implementation
225.6
73.6
18%
2.4
5.4 James Basin Water and Habitat Quality
Dissolved Oxygen
The James is an unusual Chesapeake basin in that the lower tidal James, generally, has
sufficient oxygen levels for living resources. This may be due, in part, to this region's proximity
to the Bay mouth which maintains relatively high oxygen concentrations in the bottom waters of
the James. In addition, a high salinity gradient between the tidal fresh James and the mouth
creates a relatively strong, gravity-driven circulation in the James, reducing bottom water
residence time and exposure to sediment oxygen demand (Kuo and Neilson, 1987). There were
few observations of dissolved oxygen concentrations less than 1 mg/L in the James. The
exception was the Elizabeth River, a tributary located at the mouth of James. Model estimates of
James anoxia are about 1% of the total anoxia in the lower tributaries (Figure 5.1).
Nevertheless, improvements in the slight amount of anoxia were calculated with reduced
loadings. According to the modeled responses, the 1996 Progress run indicated there was a 20%
improvement in hypoxic volume days (HVD, DCK3.0 mg/L) due to nutrient management changes
implemented since 1985 (Table 5.7). A further 10% improvement in HVD would be anticipated
with implementation of tributary strategies in the Potomac and basins further north. Nutrient
reductions within the lower tributaries provided up to an additional 20% improvement to
dissolved oxygen conditions in the James. Full Voluntary Program Implementation throughout
the entire Bay would achieve an overall 67% improvement in hypoxia compared to 1985 Base
conditions. This level of reduction was short of the estimated 75% improvement over 1985
Baseline conditions for the Limit of Technology scenario applied throughout the entire Bay.
V-13

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Table 5.7 Tidal James Percent Improvements from 1985 Conditions for Key Water and Habitat
Quality Measurements
Scenario
Loading
Reductions
Water And Habitat
Quality Improvements

Nitrogen
Reduction
Phosphorus
Reduction
Sediment
Reduction
Anoxic
Water
Habitat Bay
<3 ma/L Grasses
Bay
Grasses

PS
NPS
TOT
PS
NPS
TOT
TOT
(<1 mg/L
DO)
DO
Area
Density
1996 Progress
19
3
11
58
6
36
2
16
20
210
95
1996 Progress/TS Above
19
3
11
58
6
36
2
27
30
210
95
James AFL BNR
Equivalent/TS Above
21
8
15
59
7
38
6

40
210
108
James AFL/BFL TF/App.
BNR Equiv./TS Above
48
13
32
62
7
39
7

32
354
221
James TF BNR Equiv.
For N/TS Above
48
13
32
58
6
36
2

40
354
200
BNR-BNR
Equivalent/TS Above
62
19
42
63
8
40
7
47
51
354
217
Current LOT
Sediment/TS Above
19
3
11
58
6
36
17
22
26
277
189
Extreme Sediment
Reduction/TS Above
19
3
11
58
6
36
40
20
26
489
789
Interim Bay Agreement
Goal/TS Above


29


35
3
41
44
242
90
Midpoint 1996-Full
Voluntary Implement.
45
13
30
72
12
47
6
46
51
334
227
Full Voluntary Imp./
TS Above
72
24
50
86
17
58
9
52
57
486
410
Full Voluntary
Implementation
72
24
50
86
17
58
9
62
67
486
411
Current Limit of
Technology
83
36
61
97
30
69
17
72
75
741
1861
Submerged Aquatic Vegetation
Of the four lower Virginia tributaries excluding their western shores, the James had the lowest
SAV densities and coverage under all scenario conditions (Figures 5.2 and 5.3). Western Shore
James, an area along the Chesapeake shoreline just south of the York Basin, was the only region
V-14

-------
of the James with significant SAV density under the estimated 1996 Progress conditions (Figure
5.2). There is little modeled SAV response in the lower James, even at maximum nutrient and
sediment reductions, but in the tidal fresh or upper James, there were beneficial responses in SAV
and chlorophyll to these reductions. According to an optical model (Gallegos, 1994; CBP, 1999),
habitat requirements for SAV were met for 0.5 meter under current conditions for all the tidal
fresh (TF) stations. However, reductions in both total suspended solids and chlorophyll were
needed to meet the 1.0 meter (Table 5.8) and 2.0 meter requirements.
Table 5.8 SAV Habitat Requirements for Water Quality Attenuation in the Tidal Fresh James River:
Percent reductions needed to meet SAV habitat requirements for 1.0 meter
Station
TF 5.5
TF 5.5A
TF 5.6
Parameter causing
non-attainment of habitat
CHLA
TSS
CHLA
TSS
CHLA
TSS
Reductions needed to
meet habitat requirements
37%
38%
42%
44%
10%
13%
Alternative reductions to
meet habitat requirements
61%
33%
61%
40%
22%
11%
TSS only reductions
needed to meet habitat
requirements
N/A
46%
N/A
54%
N/A
15%
CHLA only reductions
needed to meet habitat
requirements
100%
N/A
100%
N/A
44%
N/A
According to CBEMP results, surface chlorophyll levels in the tidal fresh region would be
reduced over 50% from the 1985 Baseline under various BNR runs (Table 5.9). These reductions
would meet the 1.0 meter SAV requirements. Only modest sediment reductions (<10%) were
achieved for most of the scenarios (Table 5.9). In fact, only the Limit of Technology and Extreme
Sediment Reduction/Tributary Strategy Above scenarios produced significant sediment reductions
of 16% and 40%, respectively. Therefore, chlorophyll reductions may offer the best management
option to improve light penetration in this section of the river. Only TF 5.6 would approach the
1.0 meter requirements at Limit of Technology sediment reductions while TF 5.5 and 5.5A would
need "extreme" sediment reductions to meet the 1.0 meter requirements.
V-15

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Table 5.9 Tidal Fresh James Percent Improvements from 1985 Conditions for Key Water and
Habitat Quality Measurements
Scenario
Loading
Reductions
Water And Habitat
Quality Improvements

Nitrogen
Reduction
Phosphorus
Reduction
Sediment
Reduction
Surface
Chlorophyll
Surface
Light
Bay Bay
Grasses Grasses

PS
NPS
TOT
PS
NPS
TOT
TOT
Cone.
Atten.
Area
Density
1996 Progress
27
3
17
50
6
27
2
23
10
210
109
1996 Progress/TS Above
27
3
17
50
6
27
2
23
10
210
109
James AFL BNR
Equivalent/TS Above
30
12
22
54
8
30
6
25
12
210
123
James AFL/BFL TF/App.
BNR Equiv./TS Above
63
19
44
54
8
30
6
52
16
354
262
James TF BNR Equiv.
For N/TS Above
63
19
44
50
6
27
2
52
15
354
237
BNR-BNR
Equivalent/TS Above
63
19
44
54
8
30
6
52
16
354
253
Current LOT
Sediment/TS Above
27
3
17
50
6
27
16
23
15
277
222
Extreme Sediment
Reduction/TS Above
27
3
17
50
6
27
40
22
22
489
982
Interim Bay Agreement
Goal/TS Above


32


47
3
28
9
242
101
Midpoint 1996-Full
Voluntary Implement.
49
13
34
67
11
38
5
42
15
334
263
Full Voluntary Imp./
TS Above
71
23
50
83
16
49
8
61
20
486
485
Full Voluntary
Implementation
71
23
50
83
16
49
8
61
20
486
485
Current Limit of
Technology
82
34
61
96
29
62
16
72
25
641
2352
Chlorophyll
According to model simulations, chlorophyll a concentrations responded positively to nutrient
reductions in the tidal fresh James. There was over a 20% improvement in chlorophyll levels
between the estimated 1996 Progress and 1985 Base conditions. An additional 30% may be
V-16

-------
achieved with implementation of nitrogen controls at BNR levels. Model results showed that
nutrient reductions within the watershed areas contributing to the tidal fresh region were most
responsible for chlorophyll a reductions in the tidal fresh James. Further improvements in this
parameter could be achieved with reductions associated with Full Voluntary Implementation
(61% improvement over 1985 conditions).
5.5 Eastern Shore Basin Water and Habitat Quality
Dissolved Oxygen
Dissolved oxygen responses reported here refer to conditions in the eastern half of Virginia's
mainstem, and not the shallow waters or small coastal basins isolated in the Eastern Shore of the
Bay. As estimated by the 1996 Progress scenario, there was more than a 15% improvement in
anoxic volume-days given the nutrient management changes implemented since 1985 (Table
5.10). A further 30% improvement could be anticipated with implementation of tributary
strategies in the Potomac and basins further north. Full Voluntary Program Implementation in
Virginia's lower tributaries would provide an additional 5% improvement to dissolved oxygen
conditions in this region. Full Voluntary Program Implementation throughout the entire Bay
would achieve nearly an overall 75% improvement from the estimated 1985 Base conditions and
almost eliminate anoxia in this region. This level of reduction was just short of Limit of
Technology scenario results with these conditions applied throughout the entire Bay. Nutrient
controls within Virginia's tributaries at BNR-BNR equivalent levels and at VA interim goals
resulted in only modest improvements in anoxia when compared to 1996 Progress conditions in
Virginia.
Submerged Aquatic Vegetation
The Eastern Shore maintains a relatively dense and extensive coverage of SAV under
estimated 1996 Progress scenario conditions (Figures 5.2 and 5.3). Of the four lower tributary
basins, the Eastern Shore has the greatest area coverage. According to the modeled responses,
the area of Bay grasses showed only modest improvements (< 10%) with nutrient controls up to
Full Voluntary Implementation reductions throughout the entire Bay (Table 5.10). For this and
the Limit of Technology scenarios, SAV area increases of 17% from the 1985 Baseline were
estimated.
Improvements to grass densities showed more positive responses to nutrient reductions.
There was more than a 20% improvement in Bay grass density between the estimated 1985 Base
and 1996 Progress scenario conditions, and almost an additional 15% anticipated increase with
implementation of tributary strategies in the Potomac and basins further north. Up to an
additional 10 % improvement in SAV density would be expected from nutrient controls within
Virginia's tributaries. Full Voluntary Program Implementation in the entire Bay watershed would
provide for almost a 60% overall improvement to Bay grass densities as compared to the
estimated 1985 Baseline. This level of density almost equates to the same response if Limit of
V-17

-------
Technology reductions were applied throughout the entire Bay.
Table 5.10 Tidal Eastern Shore Virginia Percent Improvements from 1985 Conditions for Key Water
and Habitat Quality Measurements
Scenario
Loading
Reductions
Water And Habitat
Quality Improvements

Nitrogen
Reduction
Phosphorus
Reduction
Sediment
Reduction
Anoxic
Water
Habitat
<3 mg/L
DO
Bay Bay
Grasses Grasses

PS
NPS
TOT
PS
NPS
TOT
TOT
(<1 mg/L
DO)
Area
Density
1996 Progress
-41
5
0
-815
24
-2
19
17
15
3
22
1996 Progress/TS Above
-41
5
0
-815
24
-2
19
44
36
8
36
Updated 1996
Progress/TS Above
-41
9
3
-815
19
-6
21




BNR-BNR
Equivalent/TS Above
91
40
45
-698
25
3
20
47
38
8
42
Interim Bay Agreement
Goal/TS Above


34


53
27
47
38
8
41
Midpoint 1996-Full
Voluntary Implement.
26
23
24
-370
28
16
27
55
43
8
46
East Shore VA Full
Volun. Imp./TS Above
94
41
47
74
33
34
35
45
36
8
41
Full Voluntary Imp./
TS Above
94
41
47
74
33
34
35
49
40
8
45
Full Voluntary
Implementation
94
41
47
74
33
34
35
74
65
17
59
Current Limit of
Technology
97
46
52
97
50
52
50
81
72
17
64
* Negative values indicate percent increase in nutrient loads over 1985 Baseline Condition loads.
The effect of nutrient reductions in different regions of the Bay on Eastern Shore SAV
densities can be seen in Figure 5.6. For five scenarios, nitrogen load reductions relative to the
1985 Base are plotted against estimated increases in SAV densities, again relative to 1985
conditions. Each of the scenarios represents, incrementally, greater nitrogen reductions from
different regions of the Bay, first for estimated 1996 conditions throughout the Bay, then for
estimated 1996 conditions in the lower tributaries and Tributary Strategy loads in the basins of the
V-18

-------
Potomac and above. The third scenario is the estimated Full Voluntary Program conditions in the
Eastern Shore only, with 1996 conditions in the Rappahannock, York, and James and Tributary
Strategy conditions in the basins of the Potomac and above. The final two scenarios are the
estimated Full Voluntary Program Implementation conditions in all of the lower tributaries with
Tributary Strategy levels in the Potomac and above, and finally, Full Voluntary Program
Implementation conditions throughout the Chesapeake watershed. Note that the value of the
slope, or the rise of the graph line divided by the run of the line, changes in Figure 5.6.
The slope represents, in large part, the relative improvement in Eastern Shore SAV density to
reductions in nitrogen from different regions. An examination of slope 2 in Figure 5.6 shows that
even a slight decrease in nitrogen loads in the Eastern Shore is estimated to result in large relative
improvements in Eastern Shore SAV density. Eastern Shore nitrogen controls associated with
Full Voluntary Implementation are estimated to be up to 25 times more effective in increasing
SAV density than the same amount of nitrogen reductions taken in other regions of the Bay.
.1?
' 75
o
75
75 ^
&
S-H P
o
m
a 1
ĻI s,
2	O
75 W2
g
H g
o
75
03
a
o
Figure 5.6 Relative Load Reduction Effectiveness for
Eastern Shore VA SAV Density Improvements
35
30
25
20
15
This plot shows that reductions in Eastern
Shore total nitrogen load are most
—cost-effective and provide the greatest
increases in East Shore Bay grass density.
10
Full Voluntary Implementation!
slope 4=0.16
slope 3 0. IQ^+TFull Vol. Imp./Trib. Strat. Above
E. Shore Full Vol./Lower Tribs.
1996/Trib. Strat. Above
slope 2=2.47
"1996 Progress/Trib. Strat. Above
slope 1=0.25
F1996 Progress
20
40
60
80
100
120
140
Basin-Wide Reduction in Total Nitrogen Load
(million lbs. per year)
5.6 Conclusions and Findings
Dissolved Oxygen
Of Virginia's tributaries, the Rappahannock had the most anoxic and hypoxic waters. The
Rappahannock has a deep channel running the length of the tributary with a shallow sill just off
V-19

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the mouth, which prevents the deeper, low-oxygen water of the Rappahannock from exchanging
with open Bay waters. Most of the Rappahannock anoxic events began in the spring and
extended throughout the summer months. Low dissolved oxygen conditions in the Rappahannock
responded favorably to nutrient reductions, particularly for nitrogen, in the Potomac and basins in
the upper Bay region as well as controls within the basin. Nutrient reductions within the
Rappahannock are estimated to be more cost effective in the reduction of anoxia and hypoxia than
equivalent reductions outside the basin.
Anoxia in the York River was limited to just the high-salinity regions near the mouth.
Compared to the Rappahannock, low oxygen conditions were less severe in spatial extend and
duration. According to monitoring studies, the onset of anoxia in the York was caused by
stratification of the water column most prevalent during Spring-Neap tides. Improvements in
low dissolved oxygen are seen with nutrient reductions in the Potomac and basins in the upper
Bay region, as well as controls within the York.
There were few observations of dissolved oxygen concentrations less than 1 mg/L in the
James River except for the Elizabeth River, a tributary located at the mouth of James River.
Unlike other basins, low dissolved oxygen responded almost solely to controls within James
River. For dissolved oxygen levels, Virginia's mainstem Eastern Shore region responded
favorably to nutrient reductions in the Potomac and basins in the upper Bay region while local
controls caused little effect.
Submerged Aquatic Vegetation
Since SAV habitat requirements are defined as the minimal water quality levels necessary for
SAV survival, SAV requirements for healthy grass beds were expected to be less than required to
establish new beds. Therefore, higher or cleaner water quality conditions would be necessary for
re-establishment of new beds. For example, eelgrass (Zostera marina) would only re-colonize
after more hardy forms were established and SAV responses to nutrient and sediment reductions
in the model should be considered conservative.
Model results showed that SAV responded favorably to both sediment and nutrient controls in
Virginia's tributaries. While most of the improvements were located in the lower estuaries of the
York, Rappahannock, and Eastern Shore, some improvements were modeled in the tidal fresh
James, but these were very modest (<5 gm C/m2). Historical photographs of the James River
showed SAV along shallow flats (<1 meter) in the tidal fresh area and extending out to 1 meter in
the lower estuary/western shore region.
The Western Shore Rappahannock, Western Shore York, Lower York, Mobjack Bay, and the
Eastern Shore maintain some of the healthiest grass beds in Virginia's waters. While the area of
Bay grasses showed modest improvements with nutrient controls, there were positive responses
for grass densities. Grass densities improved with implementation of tributary strategies in the
Potomac and basins further north as the regions of SAV coverage in the lower tributaries were
V-20

-------
influenced by water quality conditions of the lower mainstem Bay, but local reductions of
nutrients and sediment were more effective in improving SAV densities than equivalent reductions
from outside the basin.
The area of Bay grasses on the Eastern Shore showed only modest improvements with
nutrient controls until Full Voluntary Implementation was simulated throughout the entire Bay.
Improvements in SAV density; however, were more positive. There was a predicted 14%
improvement through implementation of tributary strategies in the Potomac and basins further
north. An additional 6% to 10% would be expected from nutrient controls within Virginia's
tributaries. Full Voluntary Program Implementation in the entire Bay watershed would provide
almost a 60% improvement in Eastern Shore Bay grass density.
Chlorophyll
Elevated chlorophyll concentrations have been reported in the tidal fresh portions of James
River. Observations often exceeded 30 ug/L at and below Hopewell, VA. Concentrations greater
than 10 ug/L in tidal fresh estuaries are considered ecologically unhealthy. Of 40 tidal systems
analyzed worldwide, the James River had one of the highest reported levels of chlorophyll
(Monbet, 1992). The other two estuaries with similar high levels were the Potomac and Patuxent
rivers that are both point-source dominated. All of the Chesapeake Bay and its tributaries were
classified as low-energy or microtidal systems making them more sensitive to dissolved nitrogen
concentrations (Monbet, 1992).
While Virginia's three major tributaries showed surface dissolved inorganic nitrogen above 0.4
mg/L during winter and spring, only the James River had elevated concentrations year-round
(above 0.5 mg/L in the tidal fresh region). In fact, of all the microtidal estuaries investigated by
Monbet, dissolved inorganic nitrogen levels were highest in the James and Potomac rivers.
Among Virginia's tributaries, algal turnover or growth rates, were highest in the James (Dauer
et al., 1998). While these rates may be controlled by either available nutrients or the amount of
available light, it was determined that the tidal fresh James was light-limited (Haas and Webb,
1998; Lung, 1986) and therefore, sediment inputs could be limiting algal growth here. However,
if light limitation was removed or reduced through sediment reductions, there would be sufficient
nutrients in the form of dissolved inorganic nitrogen (DIN) to support higher algal populations.
This suggests that any improvements in water clarity through sediment controls would have to
include further reductions in dissolved inorganic nitrogen; otherwise, removing light limitation
alone could cause further increases in chlorophyll concentrations.
V-21

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Section 6: Small Coastal Basin Monitoring and Modeling
6.1 Background:
Virginia's small coastal basins are located in the high salinity waters of the lower Chesapeake
Bay. While fresh water and associated nutrient and sediment loads pour into the Bay from the
major river systems, the lower Bay is mostly influenced by coastal ocean waters. The highest
salinity waters are along the Virginia Eastern Shore. This portion of the Bay is influenced by
coastal waters that enter through the Bay mouth and flow northward along the Eastern Shore.
Water along the Western Shore is more of a mix of riverine freshwater and oceanic salt water.
Much of the lower Bay, its tributaries, and small basins are shallow except for a few deep
channels. Salinity and water temperatures fluctuate depending on depth and season. This
environment provides a unique and challenging habitat for a number of important living resources.
Microscopic phytoplankton and zooplankton inhabit the water column, utilize the abundant
nutrients, and also provide food for numerous fish species.
Submerged aquatic vegetation (SAV) areas are a unique habitat and a valuable indicator of
water quality. SAV covers the shallows of many small basins, including Mobjack Bay, Eastern
Shore, and Tangier Island, with relatively high densities. Environmental status and trends
information for these portions of the Bay are found in "Basin-Specific Characterizations of
Chesapeake Bay Living Resources Status" (September, 1994) and "First Annual Report on the
Development and Implementation of Nutrient Reduction Strategies for Virginia's Tributaries to
the Chesapeake Bay" (1996 Report of the Secretary of Natural Resources - November, 1996).
Unfortunately, there are few monitoring stations in the small coastal basins aside from the
Virginia shellfish bacteriological monitoring program and a few citizen monitors. It was
determined that the Chesapeake Bay Estuary Program Model (CBEMP) would have limited use in
targeting nutrient reductions in the coastal basins of the Eastern and Western Shores because this
large Bay model does not have the spatial or temporal resolution needed for small areas.
The Watershed Model Phase 4.1 (Section 1.3) provided estimates of nitrogen and phosphorus
loads from simulated land uses to the small coastal basins from six below-fall line model segments
(Figure 6.1, Table 6.1). Landuses used to estimate loads were determined by the Environmental
Monitoring and Assessment Program (EMAP) using remote sensing data on a scale of 660 square
meters or 0.165 acres (See: Chesapeake Bay Watershed Model Land Use and Model Linkages to
the Airshed andEstuarine Models at http://www.chesapeakebay.net/ model.htm).
VI- l

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II
State and County Boundaries in
Chesapeake Bay Watershed
Phase IV Model Segments:
Western Shore Virginia
Model-Segment Boundaiy
fhf County Baundify
S LbI . v.* i. \40, v5>ami you
OS M# f- xwi ;ĢC	J,	.:Ļ ĻĻ iCIS aitfChcii
Ļ ĻĻĻ :. ĻĻĻ:..
17
VI- 2

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State and County Boundaries in
Chesapeake Bay Watershed
Phase IV Model Segments:
Eastern Shore Virginia
t;Jk5frattSftfc.
/y Mi 'del Viinait Boundary
pj G iLiiily Boundary
/y State Boundary
BH. Model SegiTEiils: 440
+
E3Ŗ f.W .	. ~ Ifc i*i* t,-*1 fce\Wģ i.Ģ- I, 'Ļ
; ģ•; TTtiuii
II
VI- 3

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Table 6.1 Watershed Model Segments and Counties
Phase IV Model
Segments
County
Western Shore
580 & 930
940
950
960
Northumberland (580 & 930) Lanchaster (930)
Gloucester, Mathews & Middlesex
York, Hampton & Newport News
Norfolk, Chesapeake and VA Beach
Eastern Shore
440
Accomack & Northhampton
While the relatively small scale of the Watershed Model segments used for small coastal basin
loads allowed for a comparison of loads under different management alternatives, it was
determined that this model was also not appropriate for small coastal basin management and
additional monitoring and modeling were needed.
6.2 Small Coastal Basin Monitoring and Modeling
Realizing the limitations of the Chesapeake Bay Program's watershed and water quality
models, small coastal basin monitoring and modeling was conducted to further guide nutrient
reduction efforts in support of the Tributary Strategies. It was determined that it was neither
practical nor feasible to monitor and model all the small coastal basins of Virginia. In order to
support Virginia's tributary strategy development, an effort was directed towards targeted
monitoring and modeling.
The first stage included water quality monitoring needed to calibrate a small coastal basin. It
was decided to test a model developed for Lynnhaven Inlet. The Tidal Prism Model (TPM) of
the Lynnhaven Inlet was developed by scientists from the Virginia Institute of Marine Science
under a Virginia Coastal Resources Management Program Grant in 1993-1994.
In order to determine the extent of application of TPM to other small coastal basins in
Virginia, four target basins were selected: 1) Piankatank and 2) Poquoson Creeks on the Western
Shore, 3) Cherrystone and 4) Hungars Creeks on the Eastern Shore (Figure 6.2).
Monitoring data was used to test modeling applications in these four basins to determine the
extent of TMP application to other small basins. A year-long water quality monitoring program in
the target tributaries began in January of 1997. Results from the study provided data to calibrate
and assess the full capabilities of TPM (Table 6.2)
The modeling effort consisted of three tasks: 1) pre-calibration simulations to reference
basins; 2) calibration/confirmation to monitoring data and assess TPM applications to other
basins; and 3) conduct nutrient reduction scenarios for each of the four basins. While the TPM
did not contain the full ecosystem or biological components as the larger CBEMP (Section 1.4), it
simulated most of the important chemical and physical parameters for the Bay and tributaries
VI- 4

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Figure 6.2 Virginia Target Coastal Basins
6.3 Summary and Conclusions
Most of the nutrient inputs to these small coastal basins were associated with non-point
sources. Therefore, water quality along the shorelines and upper portions of the basins
characterized as tidal fresh were influenced by runoff while the higher salinity regions were
influenced more by bay/ocean water quality (Kuo et al., 1998).
Observed concentrations of dissolved inorganic nitrogen and phosphorus were all very low
while high chlorophyll a concentrations were observed in all basins in late winter and early spring.
Spatial distributions suggested that the winter-spring algal blooms originated from the Bay.
Summer algal growth was mostly in the shallow landward end of the basins except for Hungars
Creek. There, chlorophyll a concentrations were low and did not exhibit a distinct spatial pattern.
Dissolved oxygen concentrations were generally above 5.0 mg/L except for several
observation from Piankatank River where it was low (>3 mg/L) and restricted to the bottom
waters during the summer months. Total suspended sediment (TSS) concentrations exceeded
SAY requirements in all four basins and in all seasons. Except for Hungars Creek, spatial
distributions indicated that local sources, either from watershed runoff or shoreline erosion, had
significant contributions to the excessive TSS levels.
Salinity distributions were simulated well by the TPM in all four basins (Kuo et al, 1998).
However, it was determined that better characterization of non-point source loadings was
required prior to usage of the TPM for scenario runs. Model simulations and field data provided
VI- 5

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an overall characterization of the small coastal basins and uncovered unique features of the basins
investigated.
Water quality in the lower portions of the small basins was dominated by the conditions at the
mouth of each basin. Water quality data at the mouth would be required for any further model
applications. These data could be obtained through monitoring or the three-dimensional water
quality model of the Bay and major tributaries. Non-point source loadings during and
immediately following runoff events dominated the tidal fresh portions of the basins. The use of a
more sophisticated watershed model to generate loading inputs will be required for any further
simulations.
VI-
6

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Table 6.2 Number of Data Points Failing to Meet SAV Requirements (Kuo et al., 1998)
() indicates observed values
Month
Feb.
April
June
Aug.
Oct.
Dec.
Poquoson
River
(5 stations,
6 data points)
Chlorophyll
6
1
0
2
0
0
DIN
0
0
0
0
0
0
P04
0
0
0
0
0
0
TSS
2
2
4
5
1
0
DO<5
0
0
0
0
0
0

Piankatank
River
(4 stations,
5 data points)
Chlorophyll
1
4
1
2
0
0
DIN
4*
0
0
0
0
0
P04
0
0
0
0
0
0
TSS
3
3
2
1
2
0
DO<5**
0
0
3 (>3.9)
3 (>2.8)
1 (>4.7)
0

Cherrystone
Inlet
(4 stations,
5 data points)
Chlorophyll
3
3
0
1
0
0
DIN
0
0
0
0
0
0
P04
0
0
0
0
0
0
TSS
3
5
3
2
5
2
DO<5**
0
0
1(4.9)
0
0
0

Hungars
Creek
(3 stations,
4 data points)
Chlorophyll
3/3
4
1
0
0
0
DIN
0
0
0
0
0
0
P04
0
0
0
0
0
0
TSS
3/3
0
1
0
4
2
DO<5
0
0
0
0
0
0
* Mostly nitrite-nitrate nitrogen, -0.15 mg/1 ** Occurred only from bottom waters
Chlorophyll <15 mg/m3; DIN <0.15 mg/L; DIP <0.01 mg/L (mesohaline), <0.02 (polyhaline);
TSS <15 mg/L
VI- 7

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Chesapeake Bay Program, 1994. Basin-specific characterizations of Chesapeake Bay living
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Appendix A: Phase IV Chesapeake Bay Watershed Model Documentation
Phase IV Chesapeake Bay Watershed Model Application & Calculation of Nutrient &
Sediment Loadings
Complete copies of the Chesapeake Bay Watershed Model Appendices can be obtained at:
http://www.chesapeakebay.net/search/pub_action.cfm?SubjectCriteria=MODSC&STARTROW=
1 &MAXROW S=10& SEARCH_TYPE=SUBCOMMITTEE&GROUP_AFFIL=Modeling&GRO
UP INIT=MODSC&BOOLEANOP=AND
Appendix A: Hydrology Calibration Results. Technical Report CBP/TRS 196/98 and EPA
903-R-98-004, U.S. EPA Chesapeake Bay Program, Annapolis, MD.
Appendix A documents in detail the Phase IV Watershed Model hydrology calibration. The
results are presented as plots and statistical tables that compare the simulated and observed flows
for the 8 years of calibration (1984-1991) for 17 flow calibration stations of the Chesapeake Bay.
Specifically, this appendix includes the following plots: (1) observed and simulated flows; (2)
actual error of the low; (3) observed and simulated cumulative flows; (4) actual error versus
percentile sample population; (5) paired frequency distribution of simulated and observed data
versus percentile of population; and (6) scatter plot and regression of simulated versus observed
with ideal line. The appendix also contains the following statistical tables: (1) comparison of
annual total observed and simulated flows; (2) comparison of daily and average monthly total flow
observed and simulated regressions; and (3) average seasonal regressions. Regression statistics
include r-squared, intercept, and slope statistics for the entire data set, on an annual basis and on a
seasonal basis.
The daily observed and simulated flow plots generally show good to excellent agreement
between the model and data. The differences are mainly attributable to storm events and high-
flow, snowmelt events of the spring freshet. The observed and simulated cumulative flows versus
time show both under- and over-estimation relative to the observed flow, but no particular bias
for any of these stations. The actual error plots generally display a flat curve around 0 cubic feet
per second (cfs) and a sigmoidal shape indicating the errors are normally distributed. A sigmoidal
plot centered on 50% of the population indicates a lack of bias in the simulation.
The frequency distribution of paired simulated and observed flow plotted against percentile of
sample population show good agreement, with the greatest differences between simulated and
observed occurring during very high flows (95th percentile or higher) or very low flows (5th
percentile or lower). In the scatter plots, the ideal line (slope = 1, intercept = 0) is drawn as a
point of reference for the flow data and the flow regression statistics are displayed. As a point of
comparison, the tabular regression statistics are for the log flow regression and the regression
statistics displayed on the scatter plot are for untransformed flow data.
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Appendix B: Water Quality Calibration Results. Technical Report CBP/TRS 196/98 and EPA
903-R-98-003, U.S. EPA Chesapeake Bay Program, Annapolis, MD.
Appendix B documents the water quality calibration of the Phase IV Watershed Model.
Simulated and observed concentrations are compared for 8 years of calibration (1984-1991) at 15
water quality stations. Calibration data is shown for temperature, dissolved oxygen, total
suspended sediment, total phosphorus, organic and particulate phosphorus, phosphate, total
nitrogen, nitrate, total ammonia, and organic nitrogen.
The following plots are completed for each constituent: (1) observed and simulated
concentrations; (2) observed and simulated loads (temperature loads are not calculated); (3)
scatter plot and regression of simulated versus observed concentrations; (4) observed and
simulated actual error of paired data (simulated concentration - observed concentration); (5)
frequency distribution of paired simulated and observed data, i.e. coincident observed and
simulated concentrations, and (6) frequency distribution of all simulated and observed data.
The daily observed and simulated concentration plots generally show good to excellent
agreement between the model and data for temperature, dissolved oxygen, and total suspended
sediment and fair to good agreement on other water quality constituents. Generally, as the
number of water quality observations at a station increases, the calibration improves.
The simulated and observed load plots are developed from the observed mean daily flow and
concentration compared to model estimated loads. Overall, the load comparisons range from fair
to excellent depending, in different cases, on the simulation of flow or the simulation of
concentration.
Scatter plots of observed and simulated concentrations are shown with the ideal line (slope =
1, intercept = 0) drawn to assist interpretation of the plots with changing x and y axis scales. The
actual regression line slope, intercept, correlation coefficient, standard error of the slope, standard
error of the intercept, and the number of observation are shown in the plot legend.
The actual error plot is calculated as the difference of the simulated and observed
concentrations plotted against time and is useful for indicating calibration bias and the actual
magnitude of errors. The two frequency distribution plots are useful for examining the differences
between the observed and simulated concentrations with respect to concentration magnitude and
frequency of occurrence. Generally, calibration is best in the central area of the data and
calibration performance is least in the tails, particularly the 10th and 90th percentiles.
Appendix D: Precipitation & Meteorological Data Development & Atmospheric Nutrient
Deposition. Technical Report CBP/TRS 181/97 and EPA 903-R-97-022, U.S. EPA Chesapeake
Bay Program, Annapolis, MD.
Precipitation and meteorological input data are the primary forcing functions of the Watershed
Model. Flow, non-point source loads, and reaction rates all primarily depend on the continuous
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time series of input precipitation, temperature, evaporation, and solar radiation. Appendix D
documents the development of precipitation, meteorological, and atmospheric deposition data.
Chesapeake Bay Watershed Model Land Use and Model Linkages to the Airshed and
Estuarine Models. U.S. EPA Chesapeake Bay Program, Annapolis, MD.
This document replaces the older Appendix E and contains the methods for determining both
the Chesapeake Bay Program Land Use and the Phase IV Watershed Model Landuse. Land use
is developed from several sources including the GIS coverages of EMAP, GIRAS, and CCAP,
augmented by information from the Agricultural Census, the National Tillage Information Center
(NTIC), and other Federal and State sources. This publication documents the steps used to
construct the land use data used in the Watershed Model including the methodology for hind-
casting and forecasting of model land uses and the development of model segmentation and model
linkages.
Appendix F: Point Source Loadings. Technical Report CBP/TRS 207/98 and EPA 903-R-98-
014, U.S. EPA Chesapeake Bay Program, Annapolis, MD.
Appendix F documents, in detail, the Phase IV Chesapeake Bay Watershed Model point
source nutrient data assimilation process for the facilities located in signatory and non-signatory
jurisdictions of the Chesapeake Bay Watershed. This document includes a description of the data
sources, the methods of assimilation, types of analysis performed to determine nutrient reduction
estimates, and trends in nutrient loadings discharged to the Chesapeake Bay Watershed. The
Phase IV Watershed Model Point Source Database includes information for approximately 612
(the exact number varying depending on the year) active industrial, municipal, and federal facilities
discharging directly to surface waters within the Chesapeake Bay watershed from all signatory
and non-jurisdictions including: New York, Pennsylvania, Maryland, Delaware, District of
Columbia, Virginia and West Virginia. Facility information, and flow and loading data are
included for each of the 612 facilities for the years 1985 through 1996, 2000, Tributary Strategy
Implementation (which is expected to occur after the year 2000) and additional nutrient reduction
scenarios. The following flow and loading parameters are included: flow, total nitrogen, nitrate,
organic nitrogen, total phosphorous, phosphate, organic phosphorous, biochemical oxygen
demand, and dissolved oxygen.
The nutrient point source loading data are presented in both loads discharged at end of pipe
and loads delivered to the Chesapeake Bay. To determine delivered loads, delivery factors were
applied to the discharged loads to estimate attenuation as loads travel down the tributaries to the
mainstem of the Chesapeake Bay. The total nitrogen load delivered to the Chesapeake Bay has
decreased by 14 percent from 1985 to 1996, and is expected to decrease 27 percent from 1985 to
2000, and 33 percent from 1985 and Tributary Strategy Implementation (after 2000). These
reductions are primarily due to facilities implementing biological nitrogen removal. The total
phosphorous load delivered to the Chesapeake Bay has decreased 50 percent from 1985 to 1996,
and is expected to decrease 55 percent from 1985 to 2000.
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Appendix H: Tracking Best Management Practice Nutrient Reductions in the Chesapeake
Bay Program. Technical Report CBP/TRS 201/98 and EPA 903-R-98-009, U.S. EPA
Chesapeake Bay Program, Annapolis, MD.
Appendix H documents the work of the Chesapeake Bay Program Nutrient Subcommittee and
the Tributary Strategy Workgroup. The Tributary Strategy Workgroup is made up of
Chesapeake Bay Program scientists, engineers, and managers who work closely with the
Chesapeake Bay Watershed Model in estimating the progress toward Chesapeake Bay nutrient
reduction goals. Appendix H provides a summary of the methodologies used in tracking nutrient
reduction goals with the Phase IV Watershed Model and outlines the data management
procedures used for BMP tracking within each state. Information on nutrient application rates,
land use conversions, and the application of land use-based BMP efficiency rates within the Phase
IV Watershed Model is presented.
Appendix I: Operations Manual. Technical Report CBP/TRS 209/98 and EPA 903-R-98-016,
U.S. EPA Chesapeake Bay Program, Annapolis, MD.
Appendix I discusses the Chesapeake Bay Phase IV Watershed Model operating procedures.
The Phase IV Watershed Model is a comprehensive package for simulation of watershed
hydrology and water quality based on the Hydrological Simulation Program - FORTRAN (HSPF)
code. The Phase IV Watershed Model allows the integrated simulation of land and soil
contaminant runoff processes with in-stream hydraulic and sediment-chemical interaction. The
Phase IV Watershed Model partitions the Chesapeake Bay into 86 segments. Each segment is
further divided into nine land uses which are: conventionally tilled cropland, conservation tilled
cropland, hayland, pasture, forest, pervious urban, impervious urban, animal waste, atmospheric
deposition to water surfaces. The model generates daily non-point source edge-of-stream (EOS)
nutrient loads for each land use on a unit area basis and daily nutrient loads delivered to the Bay.
The simulation of the entire Chesapeake Bay Basin necessitates the running of 29 separate input
decks. Each input deck, as it is currently designed, can simulate up to 3 segments of the basin.
The simulation period is 12 years and spans from January, 1984 to December, 1995.
Each model run produces a history of the runoff flow rate, nutrient and sediment loads and
concentrations, along with a history of water quantity and quality at any designated point in the
watershed. The Chesapeake Bay Watershed Model generates edge-of-stream loads for the land
uses simulated, as well as nutrient concentrations and loads in each segment.
A - 4

-------
Appendix B: Scenario Descriptions
Key Scenarios
SCENARIO
DESCRIPTION
1985 Baseline
Conditions
Represents the conditions of the entire Chesapeake Bay watershed in 1985 with
respect to non-point source, point source, and atmospheric loads. Rationale.
Establishes a reference to which other scenarios will be compared. Also needed to
compare status and trends monitoring data to model results for the Technical
Synthesis.
>	1985 land uses are generally back-projected from 1990 Environmental
Monitoring and Assessment Program (EMAP) land use data with the
incorporation of 1982 and 1987 Agricultural Census estimates.
>	Septic system loads and animal waste loads are estimated using 1985 watershed
human population and animal population estimates, respectively.
>	Best Management Practice (BMP) implementation is also at 1985 levels.
>	Atmospheric wet deposition of nitrate and ammonia are based on a regression of
National Atmospheric Deposition Program (NADP) data. Dry deposition of
nitrate is determined from average proportions of wet and dry deposition
calculated by the Regional Acid Deposition Model (RADM). Atmospheric
deposition of nitrate and ammonia are input to both land and water surfaces.
Atmospherically deposited phosphorus and organic nitrogen are input only to
water surfaces.
1996 Progress
Represents the conditions of the entire Chesapeake Bay watershed in 1996 with
respect to non-point source and point source loads. Rationale. This scenario
examines progress in reducing point source and non-point source nutrient and
sediment loads from 1985 to 1996 and represents an estimate of the current water
quality and living resource conditions in the lower tributaries.
>	1996 land uses are generally forward-projected from 1990 Environmental
Monitoring and Assessment Program (EMAP) land use data with the
incorporation of 1992 and 1997 Agricultural Census estimates..
>	Septic system loads and animal waste loads are estimated using 1996 watershed
human population and animal population estimates, respectively.
>	Best Management Practice (BMP) implementation is at levels of 1985 Baseline
Conditions.
>	Atmospheric deposition is at levels of 1985 Baseline Conditions.
Midpoint
1996 Progress -
Full Voluntary
Program
Implementation
This is a derived scenario using point and non-point sources loads for all
Chesapeake Bay basins midway between the 1996 Progress scenario and Full
Voluntary Program Implementation. Reductions vary by major basin.
Atmospheric deposition for this scenario would assimilate these loads from both the
1996 Progress and FVPI scenarios. Rationale. This scenario examines tributary
water quality and living resource response midway between a "no further action"
management strategy (1996 Progress) and nutrient and sediment reductions
estimated under a management strategy that achieves maximum reductions under a
voluntary program (FVPI).
B- 1

-------
Full Voluntary
Rationale. Projects loads under maximum feasible management implementation
Program
using a voluntary program throughout the Chesapeake Bay watershed. It is based on
Implementation
current technology, expanded program financing, and a maximum of 75% cost share
- FVPI
by states. Time and availability of technical staff are not considered.

The following agriculture, urban, and atmospheric deposition methodologies apply to

the Full Voluntary Program Implementation scenario basin-wide unless otherwise

specified. Nutrient reductions are given for nitrogen and phosphorus as percent

reduced or pounds per acre. Phosphorus reductions are based on TSS reduction

percentages. The base year for land use is the year 2000.

AGRICULTURE:

> NON-POINT SOURCE:

Land use changes:

• 75% conservation tilled acres.

• 25% conventionally tilled acres.

• Retirement of highly erodible cropland: 1% of the total conventional till,

conservation till, and hayland in all geographic areas. Defined as all

future state/federal programs designed to take cropland out of

production for extended periods of time which is not counted as part of

another nutrient reduction program, such as forest buffers. It is

assumed that retired acreage is maintained in an unfertilized unharvested

permanent grass. Note: Federal/state programs prior to 1998 are

included within Phase IV of the Watershed Model for all years and

scenarios.

BMP 18 - Forest Buffers

• Implemented on both sides of the stream.

• 35 feet in width.

• 10% of the unbuffered stream miles in conventional till, conservation

till, and hayland converted to forest buffers.

• 10% of existing grass buffers in conventional till, conservation till, and

hayland converted to forest buffers.

• Pasture is not buffered (addressed under BMP 7 - Streambank

Protection).

• Two up-gradient acres receive a nutrient reduction benefit. The nutrient

reduction varies with model segment and land use.

BMP 17 - Grass Buffers

• 10% of the unbuffered stream miles in cropland are converted to grass

buffers.

• Two up-gradient acres receive a nutrient reduction benefit. The nutrient

reduction varies by model segment.
B- 2

-------
Full Voluntary
BMP 1 - Soil and Water Quality Conservation Plan (SWQCP)
Program
Cropland/Hayland
Implementation
• 80% of the conventional till, conservation till, and hayland acres.
- FVPI
• Nutrient reductions vary with land use:
(continued)
N P

Conventional Till 10% 40%

Conservation Till 4% 8%

Hayland 4% 8%

BMP 2 - Soil and Water Quality Conservation Plan (SWQCP) Pasture

• 80% of pasture acres.

• Reduction rate: N = 20% and P = 14%.

BMP 3 - Cover Crop

• 80% of the conservation till, conventional till, and hayland acreage in

the Coastal Plain, Potomac River basin and south.

• 80% of the silage corn acreage above the Potomac. Silage acreage is

defined a 20% of the total conservation till and conventional till acres

(80% of the 20%).

• Nutrient reductions vary with model segment. The range is N = 34-51%

and P = 10-20%.

BMP 4 - Animal Waste Management and Runoff Control

• Applied to 80% of total manure acres. Converted acres go into pasture.

BMP 7 - Streambank Protection w/ Fencing

• Implementation assumes fencing on both sides of stream.

• 15% of the unprotected stream miles in pasture.

• The area affected is determined by adding the stream miles w/o fencing

on one side of the stream + (2 times) stream miles w/o fencing on both

sides of the stream.

• Nutrient reduction of N = 75% and P = 75% is applied to 51

acres/stream mile.

BMP 19 - Streambank Protection w/o Fencing

• Implementation assumes fencing on both sides of stream.

• 15% of the unprotected stream miles in pasture.

• The area affected is determined by adding the stream miles w/o fencing

on one side of the stream + (2 times) stream miles w/o fencing on both

sides of the stream.

• Nutrient reduction of N = 40% and P = 40% is applied to 51

acres/stream mile.
B- 3

-------
Full Voluntary

BMP 8 - Nutrient Management Planning
Program

• Applied to conventional till, conservation till, and hayland acres at the
Implementation

following rates: 95% in MD, 75% in VA, PA, and non-signatory states.
- FVPI

• Reduction varies with model segment with an N and P range of 5-39%
(continued)

and 5-35% respectively.


BMP 9 - Grazing Land Protection


• 30% of the pasture land.


• Reduction rates: N = 50% and P = 25%.

URBAN:

>
POINT SOURCE:


Sewaee Treatment Plants (STPs):


• BNR or equivalent technology at all major municipal and industrial


treatment plants basin-wide. Apply concentrations of N = 5.5 mg/L


and P = 0.18 mg/L. STPs reporting concentrations below these levels


will use reported figures.


Combined Sewer Overflows (CSOs):


• 30% of flow routed through a collection facility.


• 10% connected to BNR-based STPs and 60% uncontrolled.


• Applies to DC only.

>
NON-POINT SOURCE:


SeDtic Systems:


BMP 15 - Septic Connections


• 1% of the existing septic systems. Connections assumed going to a


treatment plant using BNR or equivalent technology. Base year is


1997. This BMP does not apply to non-signatory states.


• Reduction rate: N = 80% and P = 0%


BMP 14 - Septic Denitrification


• 100% of new systems and 50% of replacement systems not connected to


a STP. Replacements are estimated to be 5% of total systems. Base


year is 1997. This BMP does not apply to non-signatory states.


• Reduction rate: N = 50% and P = 0%


BMP 13 - Septic System Pumping


• Applied to 50% of the septic systems not connected to a STP. Based on


a 5-year cycle, assumed that proper maintenance provides benefits


throughout the 5-year cycle and that all systems have been pumped at


least once. This BMP does not apply to non-signatory states.


• Reduction rate: N = 5% and P = 0%
B- 4

-------
Full Voluntary

Urban Pervious:
Program


Implementation

BMP 16 - Urban Nutrient Management
- FVPI

• N and P will be applied to the same percentage of urban pervious acres
(continued)

as in LOT but at a reduced rate (50%).


• 30% of the acreage receives fertilizer at a reduced rate.


• N and P reduction rates are N = 8.5% and P = 11%.


• Remaining acreage (70%) receives no fertilizer.


BMP 11 - Erosion and Sediment Control


• Applied to 85% of the disturbed area. The number of disturbed acres is


defined as all new urban pervious and impervious acres after 1997.


Non-signatory states are not included in this BMP.


• Reduction rates: N = 33% and P = 50%.


BMP - Forest and Grass Buffers


• Implement a 35-foot forest buffer and 35-foot grass buffer on 10%


(each) of the urban pervious stream miles not currently in forest buffers.


• Grass buffers do not receive fertilizer.


• Both buffer types receive nutrient reduction benefits on two up-gradient


acres. The nutrient reduction varies by segment.


Urban Impervious:


BMP 12 - SWM Ponds


• Up through 1990, 5% urban impervious acreage is considered serviced


by SWM retrofits. Apply wet pond efficiencies of N = 32% and P =


46%.


• All new (after 1990) urban impervious acreage is considered serviced


due to SWM regulations. Apply dry pond efficiencies of N = 27% and


P = 47%.

OTHER:

Reductions Activities Outside the WSM:

>
Marine Pump-outs

>
Shoreline Protection (tidal):


• Structural


• Nonstructural
B- 5

-------
Full Voluntary
ATMOSPERIC DEPOSITION:
Program


Implementation
Atmospheric deposition assumes air emission controls associated with the Annual
- FVPI
2010 812 Prospective Projection air scenario.
(continued)



>
Stationary Sources (annual controls)


• Emissions of no more than 0.15 lb./mm BTU from utility and large


industrial sources in 37 states or most of the RADM/RPM domain.

>
Mobile Sources (annual controls)


• Tier 1 Light Duty Vehicle emission standards


• Heavy Duty Vehicle 2 gm standard


• Phase II Federal Reformulated Gasoline


• National Low Emission Vehicle (NLEV) program


• High and Low Enhanced Inspection and Maintenance (I/M) and Basic I/M


as specified by individual states.
B-
6

-------
Current Limit
Estimates the maximum level of nutrient and sediment reductions given unlimited
of Technology
resources, unlimited cost share, and 100% landowner participation. A "do
-LOT
everything, everywhere" policy is applied using current available technologies. Time

and availability of technical staff is not considered. Rationale. This scenario

examines the maximum load reductions of nitrogen, phosphorus, and sediment, and

represents an estimate of the maximum improvement in water quality and living

resource conditions in the lower tributaries.

The following agriculture, urban, and atmospheric deposition methodologies apply to

the Current Limit of Technology scenario basin-wide unless otherwise specified.

Nutrient reductions are given for nitrogen and phosphorus as percent reduced or

pounds per acre. Phosphorus reductions are based on TSS reduction percentages.

The base year for land use is the year 2005.

AGRICULTURE:

> NON-POINT SOURCE:

Land use changes:

• 75% conservation tilled acres.

• 25% conventionally tilled acres.

• It is assumed that crops are grown within the Chesapeake Bay Basin

that cannot be planted using conservation tillage methods and that the

distribution of those crops is uniform throughout the basin.

Retirement of highly erodible cropland through CRP

• CRP acreage cannot exceed 25% of the total cropland acres within a

county.

• Total cropland acres is the sum of all conventional till, conservation till,

and hayland acreage within a specified geographic area.

• CRP acreage is calculated by taking (25% * total cropland acres) - (the

combined acreage from all state and federal programs designed to take

cropland out of production for extended periods of time, such as forest

buffers).

• Assumed that at least 25% of the total cropland within a county meets

CRP requirements.

• It is assumed that retired acreage is maintained in an unfertilized

unharvested permanent grass.

BMP 18 - Forest Buffers

• Implemented on both sides of the stream.

• 100 feet in width on both sides of stream.

• 100% of the unbuffered stream miles in conventional till, conservation

till, and hayland converted to forest buffers.

• Pasture is not buffered (addressed under BMP 7 - Streambank

Protection).

• Two up-gradient acres receive a nutrient reduction benefit.
B- 7

-------
Current Limit
BMP 17 - Grass Buffers
of Technology
• None
-LOT

(continued)
BMP 1 - Soil and Water Quality Conservation Plan (SWQCP)

Cropland/Hayland

• 100% of the conventional till and conservation till.

• Nutrient reductions vary with land use:

N P

Conventional Till 10% 40%

Conservation Till 4% 8%

Hayland 4% 8%

BMP 2 - Soil and Water Quality Conservation Plan (SWQCP) Pasture

• 100% of pasture acres.

• Reduction rate: N = 20% and P = 14%.

BMP 3 - Cover Crop

• 100% of the conservation till, conventional till, and hayland acreage in

the Coastal Plain, Potomac River basin and south.

• 100% of the silage corn acreage above the Potomac. Silage acreage is

defined a 20% of the total conservation till and conventional till acres

(100% of the 20%).

• Nutrient reductions vary with model segment. The range is N = 34-51%

and P = 10-20%.

BMP 4 - Animal Waste Management and Runoff Control

Applied to 100% of total manure acres. Converted acres go into pasture.

BMP 7 - Streambank Protection w/ Fencing

• Implementation assumes fencing on both sides of stream.

• 100% of the unprotected stream miles in pasture.

• The area affected is determined by adding the stream miles w/o fencing

on one side of the stream + (2 times) stream miles w/o fencing on both

sides of the stream.

• Nutrient reduction of N = 75% and P = 75% is applied to 51

acres/stream mile.

BMP 19 - Streambank Protection w/o Fencing

• None

BMP 8 - Nutrient Management Planning

• Applied to 100% of the conventional till, conservation till, and hayland

acres.

• Reduction varies with model segment with an N and P range of 5-39%

and 5-35% respectively.
B- 8

-------
Current Limit

BMP 9 - Grazing Land Protection
of Technology

• 100% of the pasture land.
-LOT

• Reduction rates: N = 50% and P = 25%.
(continued)



URBAN:

>
POINT SOURCE:


Sewaee Treatment Plants (STPs):


• BNR or equivalent technology at all major municipal and industrial


treatment plants basin-wide. Apply concentrations of N = 3.0 mg/L and


P = 0.075 mg/L.


Combined Sewer Overflows (CSOs):


• 50% of flow routed through a collection facility.


• 30% connected to BNR-based STPs and 20% uncontrolled.


• Applies to DC only.

>
NON-POINT SOURCE:


SeDtic Svstems:


BMP 15 - Septic Connections


• 2% of the existing septic systems. Connections assumed going to a


treatment plant using BNR or equivalent technology. Base year is 2000.


This BMP does not apply to non-signatory states.


• Reduction rate: N = 80% and P = 0%


BMP 14 - Septic Denitrification


• 100% of new systems and 50% of replacement systems not connected to


a STP. Replacements are estimated to be 5% of total systems. Base


year is 1997. This BMP does not apply to non-signatory states.


• Reduction rate: N = 50% and P = 0%


BMP 13 - Septic System Pumping


• Applied to 100% of the septic systems not connected to a STP. Based


on a 5-year cycle, assumed that proper maintenance provides benefits


throughout the 5-year cycle and that all systems have been pumped at


least once. This BMP does not apply to non-signatory states.


• Reduction rate: N = 5% and P = 0%
B- 9

-------
Current Limit
Urban Pervious:
of Technology

-LOT
BMP 16 - Urban Nutrient Management
(continued)
• 30% of the acreage receives fertilizer at a reduced rate.

• N and P reduction rates are N = 17% and P = 22%.

• Remaining acreage (70%) receives no fertilizer.

BMP 11 - Erosion and Sediment Control

• Applied to 100% of the disturbed area. The number of disturbed acres

is defined as all new urban pervious and impervious acres after 2000.

Non-signatory states are not included in this BMP.

• Reduction rates: N = 33% and P = 50%.

BMP - Forest and Grass Buffers

• Install a 35-foot forest buffer on both sides of stream on 50% of the

urban pervious stream miles not currently in forest buffers.

• The remaining 50% is considered in grass buffers.

• Both buffer types receive nutrient reduction benefits on two up-gradient

acres.

Urban Impervious:

BMP 12 - SWM Ponds

• Up through 1990, 50% urban impervious acreage is considered serviced

by SWM retrofits. Apply wet pond efficiencies of N = 32% and P =

46%.

• All new (after 1990) urban impervious acreage is considered serviced

due to SWM regulations. Apply dry pond efficiencies of N = 27% and

P = 47%.

Mixed-Open:

BMP 16 - Urban Nutrient Management

• Acreage receives no fertilizer.

BMP 11 - Erosion and Sediment Control

• No BMPs installed, no reductions taken (edge-of-field load should be

minimal due to assumed cover and no additional nutrient source loads).

BMP 12 - SWM Ponds

• None installed.

BMP - Forest Buffers

• Forest buffer (100-feet per stream side) installed along all streams not

currently in forest.

BMP - Grass Buffers

• None installed.
B- 10

-------
Current Limit
OTHER:
of Technology


-LOT
Potential Reductions Outside the WSM:
(continued)
>
Marine Pump-outs

>
Shoreline Protection (tidal):

>
Forest Conservation

>
Tree Planting

ATMOSPERIC DEPOSITION:

Atmospheric deposition assumes the maximum practical level of air emission

controls are applied year-round in 37 states east of the Rocky Mountains through the

simulation period.

>
Stationary Sources (seasonal controls)


• Emissions of no more than 0.15 lb./mm BTU from utility and large


industrial sources in 37 states or most of the RADM/RPM domain.

>
Mobile Sources (annual controls)


• High Mobile Sources (annual controls)


• Tier 1 Light Duty Vehicle and Heavy Duty Vehicle emission standards


• Phase II Federal Reformulated Gasoline


• National Low Emission Vehicle (NLEV) program


• High Enhanced Inspection and Maintenance and maximum Low Emission


Vehicle benefits for all counties in the 37-state domain, regardless of ozone


attainment.
B- 11

-------
Ranging Scenarios
SCENARIO
DESCRIPTION
VA 1996 Progress /
Tributary Strategy
Above
Represents non-point source and point source loads with respect to 1996
Progress conditions for Virginia's lower tributaries while the northern
Chesapeake Bay tributaries (Potomac and above) implement Tributary
Strategy load reductions. Rationale. This scenario determines an aspect of
load reductions occurring at different levels in different basins. In this case,
load reduction in the lower Virginia tributaries are relatively less than the load
reductions in the tributaries of the Potomac and above. This scenario develops
estimates of the affect Tributary Strategy load reductions from outside the
lower Virginia tributaries have on water quality and living resources in
Virginia waters.
VA BNR-BNR
Equivalent /
Tributary Strategy
Above
This is a derived scenario where biological nutrient removal (BNR) is
simulated at above- and below- fall line point sources in Virginia's lower
tributaries. All of Virginia's lower tributaries are at BNR conditions for point
sources except the Rappahannock with BNR only applied to >1 million gallon
per day (mgd) facilities. Point source effluent concentrations of 8.0 mg/L TN
and 2.0 mg/L TP are applied to flows projected to 2000 levels. For facilities
with 1996 discharge TN concentrations less than 8.0 mg/1, the 1996
concentrations are used.
Non-point source loads in the lower tributaries are reduced by basin to the
same (Equivalent) PS:NPS load ratio prior to BNR removal. These non-point
source loads are calculated using the following ratio and solving for BNR non-
point source loads:
1996 Progress PS loads - BNR PS loads = 1996 Progress NPS loads - BNR NPS loads
1996 Progress PS loads - FVPI PS loads 1996 Progress NPS loads - FVPI PS loads
Solids are reduced to a non-point source phosphorus ratio. Northern
Chesapeake Bay tributaries (Potomac and above) are at Tributary Strategy
load levels.
The Watershed Model was not run for this scenario. Instead, point source
delivered loads were calculated by using 1996 transport factors and the edge-
of-stream BNR point sources described above. Rationale. This scenario
examines a moderate point source load reduction and a measure of an
equivalent nutrient reduction from non-point sources.
VA Interim Bay
Agreement /
Tributary Strategy
Above
Nutrient reductions in the lower Virginia tributaries at a 40% interim nutrient
reduction goal while loads in the northern Chesapeake Bay tributaries
(Potomac and above) are at Tributary Strategy levels. Rationale. This
scenario estimates water quality and ecosystem response to controllable loads
in the lower Virginia tributaries set at 40% of 1985 Baseline Conditions.
B- 12

-------
VA Full Voluntary
Program
Implementation /
Tributary Strategy
Above
Virginia's lower tributaries are at Full Voluntary Program Implementation
load levels and the Northern Chesapeake Bay tributaries (Potomac and above)
are at Tributary Strategy amounts. Atmospheric deposition is at levels of Full
Voluntary Program Implementation in the basins and tidal waters of the lower
Virginia tributaries and at 1985 Baseline Conditions for the Potomac River
basin and watersheds above. Rationale. This scenario determines an aspect of
load reductions occurring at different levels in different basins. In this case,
load reductions in the lower Virginia tributaries are relatively greater than the
load reductions in the tributaries of the Potomac and above.
B- 13

-------
Geographic Management Scenarios
SCENARIO
DESCRIPTION
VA Eastern Shore
FVPI /
Tributary Strategy
Above
Eastern Shore VA loads for point sources, non-point sources, and atmospheric
deposition at Full Voluntary Program Implementation levels. All other lower
VA basin loads (Rappahannock, York, lames, and Western Shore VA) at 1996
Progress amounts. Northern Chesapeake Bay tributaries (Potomac and above)
at Tributary Strategy loads. Rationale. This scenario determines an aspect of
load reductions occurring at different levels in different basins. In this case,
nutrient and sediment reductions in the Virginia Eastern Shore are relatively
greater than load reductions in all other tributaries.
VA Western Shore
FVPI/
Tributary Strategy
Above
Western Shore VA loads for point sources, non-point sources, and atmospheric
deposition at Full Voluntary Program Implementation levels. All other lower
VA basin loads (Rappahannock, York, lames, and Eastern Shore VA) at 1996
Progress amounts. Northern Chesapeake Bay tributaries (Potomac and above)
at Tributary Strategy loads. Rationale. This scenario determines an aspect of
load reductions occurring at different levels in different basins. In this case,
nutrient and sediment reductions in the Virginia Western Shore are relatively
greater than load reductions in all other tributaries.
VA Current LOT
Sediment /
Tributary Strategy
Above
Virginia's lower tributaries at Current Limit of Technology for total suspended
solids (about 33% reduction from 1985 Baseline Conditions). Loads from
point sources, non-point source nutrients, and the atmosphere in the lower
Virginia tributaries are at 1996 Progress levels. Northern Chesapeake Bay
tributaries (Potomac and above) are at Tributary Strategy load levels.
Rationale. This sensitivity scenario examines the relative effect of the most
stringent reductions of suspended sediment loads within the feasible region, with
an estimate of the 1996 level of nitrogen and phosphorus controls.
VA Extreme Sediment
Reduction /
Tributary Strategy
Above
Virginia's lower tributaries are at 40% load reduction of total suspended solids
from 1985 Baseline Conditions. (Pristine sediment load reduction is about
43% from the baseline). Loads from point sources, non-point source nutrients,
and the atmosphere in the lower Virginia tributaries are at 1996 Progress levels.
Northern Chesapeake Bay tributaries (Potomac and above) at Tributary
Strategy load levels. Rationale. This sensitivity scenario examines the relative
effect of sediment reductions outside the feasible region with an estimate of the
current level of control for nitrogen and phosphorus to determine the impact
suspended sediment loads have on lower tributary water quality and living
resources.
B- 14

-------
York River
This is a Watershed Model scenario developed solely for the York basin. York
2010 Scenario
point source effluent concentrations at BNR levels of 8.0 mg/1 TN are applied

to year 2000 flows. For facilities with 1996 TN discharge concentrations less

than 8.0 mg/1 and facilities less than 1 mgd, the 1996 concentrations are used.

Point source TP loads in the York apply 1996 concentrations to projected 2000

flows. Year 2000 land uses, septic system loads and animal numbers are

employed while atmospheric deposition is at 1985 Baseline Conditions. The

CBEMP was not run for this scenario.
Rationale. This scenario examines non-

point source load reduction potential in
2010 with the implementation of BMPs

assuming land uses, animal numbers, and septic system loads remain at 2000

levels and point source loads are capped at BNR levels. Non-point source loads

in the York are simulated with the following 2010 projection of BMPs:

Farm Plans
304,605 acres

Nutrient Management
185,749 acres

Agricultural Land Retirement
37,763 acres

Grazing Land Protection
7,907 acres

Stream Protection
384 acres

Cover Crops
39,641 acres

Grass Filter Strips
990 acres

Woodland Buffer Filter Area
101 acres

Forest Harvesting
11,965 acres

Animal Waste Control Facilities
14 systems

Poultry Waste Control Facilities
9 systems

Loafing Lot Management
0 systems

Erosion and Sediment Control
2,556 acres

Urban SWM/BMP Retrofits
17,497 acres

Urban Nutrient Management
500 acres

Septic Pumping
0 systems

Shoreline Erosion Protection:


nitrogen reduction
35,266 pounds

phosphorus reduction
23,128 pounds

sediment reduction
735 tons
B- 15

-------
James Above-Fall
Line at BNR-BNR
Equivalent /
Tributary Strategy
Above
Above-fall line James loads at BNR-BNR Equivalent or above-fall line James
point sources at BNR concentrations for TN and TP and 2000 flows. For
facilities in the above-fall line James with 1996 TN concentrations less than
BNR concentrations, the 1996 concentrations are used. Non-point source loads
for the above-fall line James are at a BNR equivalent levels of control. The
Appomattox, below-fall line James, and other VA tributary loads at 1996
Progress. Northern Chesapeake Bay tributaries (Potomac and above) are at
Tributary Strategy load levels. Rationale. This scenario examines the water
quality and living resource response to BNR-BNR Equivalent load reductions in
the above-fall line James.
James Above-Fall
Line, Appomattox, &
Below-Fall Line
Tidal Fresh James at
BNR-BNR Equivalent
/ Tributary Strategy
Above
Loads discharging into the tidal fresh James at levels of BNR-BNR Equivalent.
For facilities discharging into the tidal fresh James with 1996 TN
concentrations less than BNR concentrations, the 1996 concentrations are used.
The James regions discharging below the tidal fresh portion of the James and
other Virginia lower tributaries are set to 1996 Progress loads. Northern
Chesapeake Bay tributaries (Potomac and above) at Tributary Strategy load
levels. Rationale. This scenario examines the water quality and living resource
response to BNR-BNR Equivalent load reductions in regions discharging to the
tidal fresh James.
James Tidal Fresh at
BNR-BNR Equivalent
For Nitrogen /
Tributary Strategy
Above
Loads discharging into the tidal fresh James at levels of BNR-BNR Equivalent
for nitrogen only. James discharging to the tidal fresh region at 1996 Progress
for phosphorus and sediment. For facilities discharging into the tidal fresh
James with 1996 TN concentrations less than BNR concentrations, the 1996
concentrations are used. The James regions discharging below the tidal fresh
portion of the James and other Virginia lower tributaries are set to 1996
Progress loads. Northern Chesapeake Bay tributaries (Potomac and above) are
at Tributary Strategy load levels. Rationale. This scenario examines the water
quality and living resource response to BNR-BNR Equivalent load reductions
for nitrogen only in regions discharging to the tidal fresh James. It quantifies
the importance of nitrogen versus phosphorus controls.
B- 16

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