Urban Forestry and the Clean Water Act
description
Transcript of Urban Forestry and the Clean Water Act
Urban Forestry and the Clean Water Act
David J. Nowak
USDA Forest Service, Northern Research Station
Syracuse, NY
Outline
• I-Tree Hydro• Chesapeake analyses
i-Tree - Hydro• Management model designed to be
relatively easy to use• Object-oriented, physical based, semi-
distributed, topographic model• TOPMODEL theory is used to simulate
saturation excess overland flow (for forest area), base flow and ET process
• Warm weather, semi-distributed urban soil-vegetation-atmosphere transfer scheme (SVATS)
• C++ code with GIS inputs
i-Tree Hydro Strengths
• Specifically designed to incorporate urban tree and impervious surface effects on stream flow and water quality
• Built to simulate the dynamic forest interception, infiltration and ET processes as well as urban impervious effect on runoff generation.
• Calibrated against measure stream flow data
• Relatively easy to use
i-Tree Hydro Weaknesses
• Lacks capabilities of fully-distributed model
• Currently does not allow for specific locational designs of tree cover, impervious cover, or retention/detention ponds (operates on general cover types)
• Works on watershed basis (with gauging station)
Model Inputs• Hourly discharge data (USGS)• Digital elevation map (USGS)• Hourly weather and evaporation data
• Evaporation data calculated from weather data
• Structural information on watershed (NCLD and i-Tree Eco (UFORE) data) e.g.,• Tree cover• Impervious cover• Shrub and grass cover• LAI
Model Calculations• Topographic index with tree and impervious
cover• Interception routine• Canopy parameters (throughfall, storage
capacity, daily leaf and trunk area)• Depression storage (impervious)• Evaporation and transpiration from vegetation,
soil and water surfaces• Infiltration into soils• Subsurface, overland and impervious runoff
Model Outputs
• For each time step (1 hour for these simulations):• Canopy interception• Depression storage• Infiltration• Evapotranspiration• Surface and subsurface (base flow)
runoff• Channel discharge (total runoff)
Water Quality• Separate program with inputs from i-Tree
Hydro files• Multiple options that incorporate
universal soil loss equation; buildup wash off routines
• Currently only using EMC• Many other options need more input data
• Dissolved sediment / solid pollutant load• Septic load• Dissolved pollutant concentration
Preliminary Model Results• Watersheds
• Accotink (Washington, DC)• Baisman Run (Baltimore, MD)• Gwynns Falls (Baltimore, MD)• Mill Creek (Lancaster, PA)• Rock Creek (Washington, DC)
Baisman Run
Watershed Area (m2) 3,844,800
Percent Impervious cover 0.2
Percent Tree Cover 68.7
Percent of Tree Cover over Impervious Area 5
Percent Water Cover 0
Average Tree Leaf Area Index (LAI) 3.5
Percent Shrub Cover 7.8
Percent Grass Cover 20
Percent Evergreen Trees 4.2
Percent Evergreen Shrubs 21
Shrub LAI 3.9
Leaf on Day 80
Leaf off Day 294
Baisman Run
CRF1 = 0.56 CRF2 = 0.63CRF3 = 0.70
Red – Observed; Black - Modeled
020
4060
8095
0
100,000
200,000
300,000
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Runoff(m3/yr)
Tree Cover (%)
Impervious Cover (%)
Baisman Run
Baisman Run
0.0
10.0
20.0
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Percent Impervious Cover
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cent
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w
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Percent Tree Cover
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nnua
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Impervious held at 10%Canopy held at 70%
Watershed Area (m2) 61,910,100
Percent Impervious cover 21.3
Percent Tree Cover 31.9
Percent of Tree Cover over Impervious Area 10
Percent Water Cover 0.3
Average Tree Leaf Area Index (LAI) 3.5
Percent Shrub Cover 7.8
Percent Grass Cover 33.8
Percent Evergreen Trees 4.2
Percent Evergreen Shrubs 21
Shrub LAI 3.9
Leaf on Day 80
Leaf off Day 294
Accotink
Accotink
CRF1 = 0.67 CRF2 = 0.56CRF3 = 0.74
Red – Observed; Black - Modeled
100
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Runoff
(m3/yr)
Tree Cover (%)
Impervious Cover (%)
Accotink
Accotink – Storm Simulations2 year storm
10 year storm
50 year storm
Early In-Leaf Season
-50000
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m3/
hr
Trees
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Difference
Mid In-Leaf Season
-20000
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Hour
m3/
hr
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No Trees
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Late In-Leaf Season
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hr
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Early In-Leaf Season
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Mid In-Leaf Season
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Late In-Leaf Season
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hr
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Early In-Leaf Season
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200000300000
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Hour
m3/
hr
Trees
No Trees
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Mid In-Leaf Season
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m3/
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Trees
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Late In-Leaf Season
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Hourm
3/h
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Trees
No Trees
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Water Quality Results (median national pooled EMC)
Reduction (t/total hours)
WatershedTree
CanopyTotal %
reduction% per
% canopy TSS BOD COD TPSol P TKN
NO2NO3 Cu Pb Zn
Total hours
Accotink 31.9 3.7 0.1 40.3 8.5 33.0 0.19 0.08 1.1 0.39 8.2 37.5 95.4 8760
Baisman Run 68.7 12.1 0.2 4.5 1.0 3.7 0.02 0.01 0.1 0.04 0.9 4.2 10.7 6600
Gwynns Falls 27.0 3.3 0.1 44.9 9.5 36.8 0.21 0.08 1.2 0.44 9.1 41.7 106.2 8760
Mill Creek 7.1 1.6 0.2 12.3 2.6 10.1 0.06 0.02 0.3 0.12 2.5 11.4 29.1 4008
Rock Creek 27.0 5.2 0.2 136.8 28.9 112.2 0.65 0.26 3.7 1.34 27.9 127.3 323.9 8760
Water Policies – Total Maximum Daily Load (TMDL)• over 40% of our assessed waters still do not meet the
water quality standards of the Clean Water Act• TMDL specifies the maximum amount of a pollutant
that a waterbody can receive and still meet water quality standards
• urban vegetation may help keeping urban waterways below TMDL limits
On-Going Work
• Cross comparisons with Larry Band• 2005 and 2007 Pond Branch
• Other watersheds across US
Questions?