Holistic Watershed Management for Existing and Future Land Use Development Activities:
Opportunities for Action for Local Decision Makers:
Phase 2 -FDC Application Modeling (FDC 2A Project)
SUPPORT FOR SOUTHEAST NEW ENGLAND PROGRAM (SNEP) COMMUNICATIONS STRATEGY AND
TECHNICAL ASSISTANCE
Factsheets
September 30, 2022
Prepared for:
U.S. EPA Region 1
Prepared by:
Aa
PARADIGM
ENVIRONMENTAL
GleC
Blanket Purchase Agreement: BPA-68HE0118A0001-0003
Requisition Number: PR-R1-20-00322
Order: 68HE0121F0052
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Future Landscape in the Taunton River Watershed
Future land use based on Business-as-Usual trends project continued conversion of forests into
developed land use types1.
The Taunton River watershed is projected to lose 57% of it's unprotected forests, primarily to residential
development.
Recent Trends 2010 Recent Trends 2060
Agriculture
7%
Unprotected
Forest
38%
Conserved
Forest
13%
High Density
Development
4%
Other
10%
Low Density
Development
23%
Water
Low Density
Development
33%
High Density
Development
6%
Unprotected
Forest
16%
Other
10%
Agriculture
7%
Conserved
Forest
23%
Thompson, J.R., Plisinski, J.S., Olofsson, P., Holden, C.E., Duveneck, M.J., 2017. Forest loss in New England:
A projection of recent trends. PLoS One 12. https://doi.org/10.1371/JOURNAL.PONE.0189636
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Recent Trends 2010
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Future Climate Impact
Future climate projections can vary
widely based on the Global Circulation
Model (GCM) and Relative
Concentration Pathway (RCP) used. This
project used models based on RCP8.5
(increasing carbon emissions based on
historic rates) that increased
precipitation from 4%and
temperature by 8%-16%.
These climate projections align with
those from the Massachusetts Climate
Change Report2, which estimates
annual precipitation increases of 5-8%
by 2064. While annual average
precipitation is projected to increase,
summer months are expected to
become drier leading to ecodeficits
(flows lower than current conditions);
winters are expected to have increased
precipitation rates3.
2MA EOEE, 2011. Climate Change Adaptation Report.
3Hayhoe, C.P., Wake, T.G., Huntington, L., Luo, M.D., Schrawtz, J.,
Sheffield, E., Wood, E., Anderson, B., Bradbury, A., Degaetano,
T.J., Wolfe, D., 2006. Past and Future Changes in Climate and
Hydrological Indicators in the U.S. Northeast. Clim Dyn 28, 381-
707. https://doi.org/10.1007
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Changes to Hydrology and Water
Quality Under Future Conditions
Across the Taunton River
watershed, increased future
impervious cover, regardless of
future climate conditions,
increases runoff volume and
nutrient loads while decreasing
groundwater recharge (GW) and
evapotranspiration (ET).
The amount of precipitation in a
particular climate change model
(wet, median, or dry) can amplify
or dampen the change in
hydrology and water quality
compared to future land use alone
(e.g., a wet future climate has
more runoff than a dry one).
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Future Land Use Impacts on a Small
Urbanized Catchment
726
(39.9%)
Future land use impacts on hydrology
and water quality for the Upper
Hodges Brook, a small urbanized
subwatershed, largely match those of
the Taunton River Watershed.
1000
When only future land use is
considered, greater amounts of
impervious cover increases flows
across the FDC. Decreased
evapotranspiration is one of the main
drivers leading to increased runoff.
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Historic Climate
638
(35.1%)
457
(25.1%)
\ 323
\ (17.7%)
402
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(22.1%)
Ecodeficit: 0.0 cfs/day (0.0 MG/year)
¦Baseline/Existing Conditions
Overland Flow (MG/yr)
Interflow (MG/yr)
Groundwater (MG/yr)
Evapotranspiration (MG/yr)
Ecosurplus: 0.4 cfs/day (90.0 MG/year)
2060 Land Use, Historic Climate
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Percent of time discharge was equaled or exceeded
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Future Land Use and Climate Impacts
on a Small Urbanized Catchment
When simulated with the Ecodeficit
dry future climate scenario, the
Upper Hodges Brook experiences
ecodeficits across all but the highest
10% of flows. Reduced moderate to
low flows can negatively impact
aquatic habitats while greater high
flows can increase erosion and
sediment loads.
Baseline
2060 FLULC,
Ecodeficit 8.5 Dry
Overland Flow (MG/yr)
Interflow (MG/yr)
Groundwater (MG/yr)
Evapotranspiration (MG/yr)
Ecodeficit: 0.4cfs/day (90.5 MG/year)
Ecosurplus: 0.3 cfs/day (66.9 MG/year)
¦Baseline/Existing Conditions
— — miroc-esm-1 - RCP 8.5 Dry
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Future Land Use and Climate Impacts
on a Small Urbanized Catchment
When simulated with the Ecodeficit
median future climate scenario, the
Upper Hodges Brook experiences
ecodeficits across most moderate
and low flows. Ecosurpluses are
experienced across the highest 15%
of flows.
Baseline
2060 FLULC,
Ecodeficit 8.5 Median
450
(24.7%)
\ 276
\ (15.2%)
Overland Flow (MG/yr)
Interflow (MG/yr)
Groundwater (MG/yr)
Evapotranspiration (MG/yr)
Ecodeficit: 0.3 cfs/day (68.2 MG/year)
Baseline/Existing Conditions
Ecosurplus: 0.3 cfs/day (79.9 MG/year)
cesml-cam5-l - RCP 8.5 - Median
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Future Land Use and Climate Impacts
on a Small Urbanized Catchment
Despite increased impervious cover,
the Wet future climate scenario has
similar interflow and groundwater as
the baseline historical conditions.
The highest 40% of flows have
ecosurpluses while the lowest 60% of
flows have ecodeficits.
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Ecodeficit 8.5 Wet
372
(20.
683
(35.5%)
308
(16.
414
(22.
480
(24.9%)
\ 326
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437
(22.7%)
Overland Flow (MG/yr)
Interflow (MG/yr)
Groundwater (MG/yr)
Evapotranspiration (MG/yr)
Ecodeficit: 0.2 cfs/day (55.9 MG/year) Ecosurplus: 0.8 cfs/day (182.4 MG/year)
Baseline/Existing Conditions — — mri-cgcm3-l - RCP8.5 - Wet
Percent of time discharge was equaled or exceeded
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Next-Generation SCM Design and
Treatment Efficiency
Current MassDEP and MS4 control
standards require specific capture
depths that aim to reduce TP by
60% and TSS by 90%. SCMs were
sized to meet these targets using a
Design Storage Volume (DSV).
These current standards may not
provide enough treatment to
protect water quality with
continued development and
climate change.
The next-generation of SCMs were
sized to meet predeveloped
recharge conditions with no net
increase in nutrient export. These
SCMs achieve high control
performance, even under future
climate conditions.
MassDEP/MS4 Control ¦ High Control
HSG-A HSG-B HSG-C HSG-D HSG-A HSG-B HSG-C HSG-D
Surface Infiltration Practices
Subsurface Infiltration Practices
MassDEP/MS4 Control ¦ High Control
HSG-A HSG-B HSG-C HSG-D HSG-A HSG-B HSG-C HSG-D
Surface Infiltration Practices Subsurface Infiltration Practices
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Site-Scale Stormwater Management with Green
Infrastructure and Conservation Development Practices
When conservation development practices are
configured as a system at the site-scale, near
predevelopment hydrology can be achieved, peak flows
attenuated, and pollutants controlled.
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Watershed-Scale SCM Treatment Efficiency
The Upper Hodges Brook subwatershed as a simulation test-bed for next-generation SCM evaluation.
These High control level SCMs provide benefits across the entire flow regime; the FDCs below show
that High control SCMs reduce ecodeficits caused by future land use and climate and are closer to
predevelopment hydrology, especially at high flow rates.
^—Developed, no BMPs Developed, with BMPs Pre-Development
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Flow-Exceedance Percentiles
Flow duration curve with MS4 control SCMs treating 80% of the Upper
Hodges Brook subwatershed's impervious cover under historic LULC
and climate conditions
Flow duration curve with High control SCMs treating 80% of the Upper
Hodges Brook subwatershed's impervious cover under future LULC and
climate conditions
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Watershed-Scale SCM Treatment
Efficiency
As well as providing flow regime
benefits for a small urbanized
watershed, Conservation
Development practices (High
control SCMs and regulations that
require treating flow from 80% of
impervious cover) the watershed's
TP load is reduced by 48%
compared to 14% for the
Business-as-Usual scenario (MS4
control SCMs and 30% of IC area
treated) while accounting for
future land use and climate.
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Business-as-Usual
Land Use: Future based on
recent trends
Climate: Future (increased
precipitation and
temperature)
SCMs: Conventional
IC Treated: 30%
Conservation Development
Land Use: Future based on
recent trends
Climate: Future (increased
precipitation and
temperature)
SCMs: Conservation
IC Treated: 80%
Hypothetical Maximum
Land Use: Future based on
recent trends
Climate: Future (increased
precipitation and
temperature)
SCMs: Conservation
IC Treated: 100%
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