Chesapeake Bay Program Modeling Subcommittee Quarterly Review and Joint Meeting with the Sediment Workgroup July 2, 2008


Chesapeake Bay Program
Modeling Subcommittee Quarterly Review and
Joint Meeting with the Sediment Workgroup

Chesapeake Bay Program Office; Annapolis, MD
July 2, 2008

MEETING SUMMARY

Meeting Materials

Meeting Website: http://archive.chesapeakebav.net/calendar.cfm?eventdetails=9048

•	Agenda 7-2-08

•	Chesapeake Modeling Symposium - Presentation by Kevin Sellner

•	Overview of WQSTM Objectives for the Clarity Simulation - Presentation by Carl
Cerco

•	Foundations of the Suspended Solids Model - Presentation by Carl Cerco

•	Characteristics of Sediment Transport Module for CBP WOM - Presentation by
Sung-Chan Kim

•	Refining the Calibration of WQSTM for Simulation of the Claritv/SAY Water
Quality Standard- Presentation by Carl Cerco

•	Shallow Water Monitoring - Presentation by Carl Cerco

•	Attachment A: Initial Scoping Scenarios for the Water Quality and Sediment
Transport Model's Assessment of the Claritv/SAY Water Quality Standard

•	SAY Application - Presentation by Carl Cerco

•	Phase 5.1 Progress

•	DRAFT Response of the Modeling Subcommittee to the Second STAC Review of the
Phase 5 Community Watershed Model (July 1, 2008)

•	Comments on CBPO Draft Response to STAC Phase 5 Review

I.	Announcements and Amendments to the Agenda	Linker

•	Lewis Linker, Modeling Subcommittee Chair and Sediment Workgroup Coordinator,
began the meeting at 9:00 am. Introductions were made and the meeting's agenda was
reviewed.

II.	Chesapeake Modeling Symposium 2008	Sellner

Presentation: http://archive.chesapeakebav.net/pubs/calendar/MODSC 07-02-08 Presentation 1 9048.pdf

•	Kevin Sellner, CRC, described the outcomes of the Chesapeake Community
Modeling Program's (CCMP) May 12-14 Chesapeake Modeling Symposium. This
symposium showcased existing Chesapeake modeling efforts and promoted
information exchange and open modeling in the region.

•	This symposium was a venue to:

o Promote information exchange and open modeling in an attempt to stimulate

cross-pollination across modeling teams and paradigms
o Identify and showcase existing modeling efforts
o Encourage future community modeling and data sharing

1

-------
o Present the latest CCMP progress

o Encourage more bottom-up interaction between CCMP and the community
o Facilitate the development of an inventory of models and data sets, and
stimulate collaborative research on data processing and modeling

• The 3-day symposium included 9 workshops, 7 plenary talks, 27 break out discussion
sessions, and over 70 presentations and papers (which are available for download at
the following website: http://www.chesapeakemeetings.com/CheMS20Q8/web-
sessions.php).

• A product of the symposium was the Chesapeake Bay Basin Assets diagram (see
slide 13). This diagram identifies data sets, models, and products. Let CCMP know if
there is something that you think needs to be added to this diagram.

• CCMP will hold modeling symposiums every two years.

• CRC is holding a regional conference in March 2009 on ecosystem-based
management. Modeling sessions can be included in this conference.

III. Overview of WQSTM Objectives for the Clarity Simulation Cerco

Presentation: http://archive.chesapeakebav.net/pubs/calendar/MODSC 07-02-08 Presentation 2 9048.pdf

• Carl Cerco provided an overview of the WQSTM objectives for the sediment
simulation for assessment of the shallow water clarity water quality standard.

• A lot of issues were raised after the completion of the last version of the model
(13,000 cell). These issues included:

o Absence of sediment resuspension

o Bank loads (magnitude, below sea level, periodicity)

o Light attenuation (partial absorption model, parameter evaluation)

• Following are a list of actions that have been taken to help remedy these issues in the
new version of the model:

Sediment Resuspension
o Net settling of fixed solids was replaced with dynamic settling and

resuspension.
o Solids classes were increased from one to four,
o Resuspension is now driven by shear stress from waves and currents.

Bank Loads

o A state-of-the-art detailed spatial estimate was completed by Halka and
Hopkins.

o Below-sea-level erosion as a fraction of above sea level,
o The timing is related to local daily wave energy and storm surge.

Light Attenuation

o The partial absorption model has been replaced with an advanced optical
model.

o It accounts for scattering and absorption by solids and color,
o It is parameterized spatially and temporally, as far as possible, by
observations.

IV. Foundations of the Sediment Transport Model Cerco/Kim

• Carl Cerco and Sung-Chan Kim reviewed the model structure, state variables, bed
model, and forcing functions.

-------
Carl Cerco

Presentation: http://archive.chesapeakebav.net/pubs/calendar/MODSC 07-02-08 Presentation 3 9048.pdf

•	Suspended Solids Model

o The suspended solids model operates on a 57,000 cell grid,
o Shear stress from currents is generated by the CH3D hydro model,
o Shear stress from waves is from the independent wave model,
o Solids calculations are conducted in the water quality model,
o There are four non-cohesive sediment classes: fine clay, clay, silt, and sand,
o Assumptions include: no coagulation; no bedload; distributed load splits from
the Watershed Model; and bankload splits recommended by originators

•	ROMS Bed Model

o The ROMS Bed Model includes seven layers that are initially 1 cm thick. The

number of layers and layer thickness do not change,
o No erosion or deposition through the bottom of the bed.
o No provision to change critical shear stress as a function of depth into

sediments or material age.
o The bed will armor. Erosion of clays and silt leaves sand behind.

•	SAV Feedback Effects

o Computed SAV reduces computed bottom shear stress,
o Reduction is proportional to fraction of cell depth occupied by SAV.

Sung-Chan Kim

Presentation: http://archive.chesapeakebav.net/pubs/calendar/MODSC 07-02-08 Presentation 4 9048.pdf

•	Sung-Chan showed the group graphs depicting wave height and period at three
different Bay stations (Calvert Cliffs, Mid Bay, Poplar Island), he explained how the
BBL model estimates bottom shear stress, and he shared animations for a large
flooding event in January 1996 and for a whole year in the mid-Bay and lower-Bay.

•	Summary:

o Young and Verhagen's (1996) depth-limited fetch-limited parametric wave
model gives reasonable wave heights and periods especially in the Upper and
Mid Bay.

o The bottom boundary layer model (Harris) estimates bottom stresses resolving

spatial and temporal (tidal and subtidal) variations,
o Upper Bay ETM varies with tidal and event scales.

o Cross-Bay sediment concentrations vary with corresponding bottom stresses
(as well as advection).

V. Sediment Simulation Progress Since the April 2008 Quarterly	Cerco

Presentation: http://archive.chesapeakebav.net/pubs/calendar/MODSC 07-02-08 Presentation 5 9048.pdf

•	Carl Cerco presented the progress that has been made on refining the calibration of
the Water Quality and Sediment Transport Model (WQSTM) for the simulation of the
clarity/SAV water quality standard.

•	Carl's summary points and recommendations:

o The model represents the general behavior and distribution of suspended
solids and light attenuation in the bay and most major tributaries.

3

-------
o Improved representation of suspended solids and light attenuation, especially

along the bay axis, is desirable,
o We have been applying a universal set of model parameters (settling velocity,
etc.). Improvements by following this path are unlikely. The best hope, right
now, is in spatially varying settling velocities,
o We can continue this process indefinitely.

o Our strongest recommendation is to apply the model as it exists in sensitivity
analyses and screening scenarios. Implement improvements as model
behaviors become apparent.

• Comments:

o We should look into whether or not we have the salinity right in the Patuxent.

This may help us determine how to tune the settling velocity,
o Getting the light attenuation correct is important for the SAV standard. Carl
said that they will attempt to improve the solids in the limited amount of time
that they have. However, we may just need to recognize and take into account
that the light attenuation model has some gaps in it.
o The turbidity max was missing in the lower Bay.
o For KE, we again had a step function.

o All adjustments that are made should be locked so that they don't have to be

made again when scenario runs are performed,
o It is important to get the boundary conditions right in the shallow water area,
o It is probably not a good idea to adjust the mechanics spatially, which is what
you would be doing if you vary the parameter spatially. This hides hints that
the model is doing something wrong,
o Rather than varying the parameter spatially, one option may be to add another
size class. This would allow the settling velocity to be altered in a way that
corresponds to a change in size class. However, this may be difficult since we
are data limited.

o Since we only have six weeks left until we need to provide this model, a
compromise may be to improve the boundary conditions while at the same
time recognizing that there is a failure in the model's current structure of
inputs in certain areas (such as the lower turbidity max),
o Rather than adjusting the fundamentals of the model to correct KD, one option
may be to take the difference between what is observed and what is predicted
and apply that as something like a correction factor.

• ACTION: In the six weeks that are remaining, Carl agreed to take another look at the
solids and potentially adjust the light attenuation model.

VI. Simulation of Shallow Water SAV/Clarity Water Quality Standard Cerco

Presentation: http://archive.chesapeakebav.net/pubs/calendar/MODSC 07-02-08 Presentation 6 9048.pdf

• The Modeling Subcommittee reviewed information regarding the shallow water
simulation, including sediment resuspension, refined shore erosion estimates, and the
SAV simulation. An emphasis was placed on the calibration of the SAV acres,
observed and simulated, in the different Chesapeake Bay segments.

• Carl's summary points and recommendations:

o With few exceptions, the differences (computed and observed) between deep
and shallow-water attenuation are small, just a few tenths of a unit.

-------
o The computed components of attenuation are site-specific,
o There is, perhaps, a tendency for clays to be more significant at deep stations

and less significant at shallow stations,
o It will likely take an extensive series of sensitivity runs to sort this out:

¦	Eliminate distributed loads

¦	Eliminate bank loads

¦	Eliminate open boundary conditions

¦	Eliminate SAV feedback effects

•	Comments:

o Eliminating resuspension should potentially be added to this list,
o We need to understand why we are getting the results that we are getting,
o There is no sediment size information in the standard shallow water
monitoring program.

VII. Initial Scoping Scenarios	Linker

Handout: http://archive.chesapeakebav.net/pubs/calendar/MODSC 07-02-08 Handout 1 9048.pdf

•	The Modeling Subcommittee reviewed and discussed the proposed initial scoping
scenarios for the WQSTM's assessment of the clarity/SAV water quality standard
(see handout).

•	Comments on the handout:

o A scenario that eliminates resuspension loads should be added,
o A scenario that sets the ocean boundary to zero should be added,
o For the sediment response scenarios, if you turn off the watershed inputs, how
much of a spin-up do you need? Is a ten year spin-up adequate?

¦	The model may need to be run until equilibrium is reached. If this is
more than ten years, how many more years are needed?

¦	Since there are so many possible scoping scenarios, one option may be
to run each of them for a relatively short period of time in order to
narrow down the choices as to which ones should be run longer.

o A scoping scenario that looks at the influence of direct drainage above or
below the fall line could be useful for the TMDL.

•	Timeline

o July 17th: Review and approval of the initial scoping scenario plans by the

Reevaluation Technical Workgroup
o July 21st: Review and approval of the initial scoping scenario plans by the

Water Quality Steering Committee
o August 18th: Initiate first scoping scenarios

o October 7th-8th: Completion of key initial scoping scenarios prior to the Oct.

7th-8th MDSC/SedWG Meeting
o October: Presentation of the key initial scoping scenarios to the Water Quality
Steering Committee at their October meeting date

•	The Sediment Workgroup will also be helping to develop a maximum feasible
sediment reduction scenario. This scenario should be completed in January 2009.

•	The Modeling Subcommittee will have time to review the scoping scenarios before
they go to the Water Quality Steering Committee.

5

-------
• ACTION: Lewis will revise the handout based on today's comments and will send it
out to Modeling Subcommittee members for review.

• DECISION: The Modeling Subcommittee had no objections to moving forward with
the initial scoping scenario plan as revised at today's meeting.

VIII. Simulation of Shallow Water SAV/Clarity WQ Standard (Cont.) Cerco

Presentation: http://archive.chesapeakebav.net/pubs/calendar/MODSC 07-02-08 Presentation 7 9048.pdf

• Initial conditions: How do we initialize the model? Every cell and depth increment?
Without population processes, do initial conditions matter?

• SAV areas: What is the appropriate area in which to allow SAV to grow? If we allow
all area within the 2 m contour we get way too much SAV. Is the process
deterministic?

• Other processes: Should we consider local mortality (e.g., from wave action)? Vary
the ratio of detrital epiphytic material to viable epiphytes?

• Carl's summary points, conclusions, and recommendations:

o The SAV unit model is reasonably well calibrated. SAV responds as expected

to changes in light attenuation,
o Can anyone with GIS skills help to establish initial conditions for SAV?
o We suspect the changes in light attenuation over 7 years are too small to
promote significant trends in SAV. We need to do two things:

¦ Shock the model with major changes in light attenuation. Examine
SAV response.

¦ Validate the model to long term data when the 20-year model runs are
executed.

• Carl will start to gather biomass information.

• A full 20-year run should be initiated as soon as the code is completed in mid-August.

• How much is the biomass feedback effect contributing to this overestimation? This
would be interesting to look at.

IX. Comments from the Sediment Transport Model Review Team

• The Sediment Transport Model Review Team provided their initial response to the
questions listed in today's agenda. They will provide written responses at a later date.

Chris Sherwood

• The model is vastly improved. It has more physics and more processes incorporated
into it, which will make it a better model for its intent.

• Some of the simulations that Sung-Chan presented today, such as how the model
reacts to an event, were simulations that Chris had been looking forward to seeing for
some time.

• He didn't get much of a sense of how the model responds to changing parameters
(e.g., settling velocity). It is beneficial to document how the model changes when
adjustments are made.

• The component of the model that he has the biggest reservations about is the light
model. It would be nice if this component incorporated size and if it didn't have
spatial variation.

-------
• Rather than introducing spatial variation, it may be possible to instead introduce
another state variable to help address these issues.

• The model has a lot of the important structures that it needs to effectively simulate
shallow water light attenuation in the shallow water areas of the Chesapeake. The
model's improved shore erosion, resuspension, watershed inputs and estuarine
boundary conditions should help result in more accurate model responses.

• The sediment transport model seems to be doing the right thing. It would be
interesting to see how sediment inertia affects this.

• From his point of view, it seems that the SAV model is running well. However, this is
not his area of expertise.

• For the next generation of the model, the same types of improvements should
continue to be made (such as adding physical processes and trying to more accurately
capture what is actually going on in the real world).

• The sensitivity analysis and the scenario testing should reveal a lot about how the
model responds.

Allen Teeter

• In general, the sediment transport model seems to be reproducing the general
characteristics of sediment transport in the Bay.

• With respect to shoreline erosion, is the model forming a sand layer where the
sediment is being deposited? Sung-Chan said that he would check to see if this is
happening.

• He liked Sung-Chan's vertical comparison of shallow water sites.

• Further sensitivity tests on the erosion parameters and the settling parameters would
be helpful.

• Perhaps adjusting the erodibility parameter would be more justifiable in a spatial
sense than adjusting the settling parameter.

• For the next generation of the model, it would be useful to:

o Add more processes
o Potentially adjust the settling rates

o Incorporate some linear varying bed properties in the bed model so that there

aren't jumps when the layers change
o Vary erodibility with depth through some consolidation or hardening of the
bed

o Possibly add several more grain classes

Larry Sanford

• The model has come a long way and overall is looking pretty good.

• The fact that the processes are behaving as they should is a big leap forward.

• If you are going to tinker with it to make it agree better, tinker with something at the
end rather than something in the middle such as a basic mechanism.

• It may be helpful to readjust the settling speeds so that they are more evenly
distributed. There is a huge gap between the current settling parameters (specifically
between clay and silt).

-------
• If he were going to adjust the settling speeds, the metric that he would look for would
be more of a clearing in slack water.

• For the future, another feedback for SAV may be to adjust it by the bottom sediment
type, if that information is available.

• Could we make the organic carbon behave like a sediment particle in the model?

• He agreed with Allen that moving towards implementing flocculation in some format
may help to address some of the spatial issues such as the sharpness of the turbidity
maximum.

• The Modeling Subcommittee thanked the review team for their comments and invited
them to continue to participate in future Modeling Subcommittee meetings.

X. Status of the Phase 5.1 Model Shenk

Handout: http://archive.chesapeakebav.net/pubs/calendar/MODSC 07-02-08 Handout 2 9048.pdf

• See the handout for an update on the status of the Phase 5.1 model, which includes
information on the data and processes that have been revised.

• Phase 5.1 will be completed and linked to the Water Quality and Sediment Transport
Model in mid-August.

XI. Response to the 2nd Phase 5 Review Linker

• Modeling Subcommittee members reviewed the July 1st draft of the Modeling
Subcommittee's response to the second STAC review of the Phase 5 Community
Watershed Model, as well as the comments that were received.

• Lewis received comments from many of the Modeling Subcommittee members
during the early-June comment period. These comments will be incorporated into the
Modeling Subcommittee's final response.

XII. Adjourn

• The meeting was adjourned at 2:00 pm.

Participants

Steve Bieber

COG

sbieber(fl),mwcos.ors

Sally Bradley

CRC/CBP

sbradlev®,chesapeakebav.net

Carl Cerco

US Army ERDC

carl. f. cerco(o>,usace. armv .mil

Monir Chowdhury

DC DOE

monir. chowdhurv(«),dc. sov

Lee Currey

MDE

lcurrev(«),mde. state, md. us

Bill Keeling

VADCR

william.keelinsfaidcr. virsinia.sov

Sung-Chan Kim

US Army ERDC

suns-chan.kimffl),usace.armv.mil

Lewis Linker

EPA/CBP

1 inker, lewis® epa.yov

Ross Mandel

ICPRB

rmandel(o>,icDrb.ors

Kevin Sellner

CRC/STAC

sellnerk® si.edu

Gary Shenk

EPA/CBP

sshenkfo),chesaoeakebav.net

Chris Sherwood

USGS

csherwood(o>,usss. sov

Rou Shi

MDE

rshi(o),mde. state.md.us

Allen Teeter

CHT

cht alien®,canuflv.net

-------
Harry Wang
Ping Wang

VZMS

UMCES/CBP

hvwang@vims.edu
pwang@chesapeakebav.net

On the phone:
Kenn Pattison
Larry Sanford

PA DEP

UMCES

kpattison@state.pa.us
1 sanford@hpl. umce s. edu

9

-------