todd hubmer, pe. wetland conservation in the news
TRANSCRIPT
How do Wetlands Factor into New Infiltration Policies?
Todd Hubmer, PE
Wetland Conservation in the News
Wetland Benefits
Habitat – Plants & AnimalsWater Quality – Filter & Clean RunoffGroundwater Recharge – Hold & Infiltrate RunoffFlood Protection – Store Water during Snow/Rain Events
Wetland TypesGroundwater Dependant
FENSStreamsMarshesBogs
Wetland TypesSurface Water Dependant
Vernal PoolsMarshesFlood Plain Fringe
Do Current Trends in Watershed Management Anticipate Impacts to
Wetlands?
Current PoliciesRequire stormwater runoff to be treated before dischargeTrends for water quality treatment are focused on runoff
volume reductionVolume reduction through infiltration, water reuse,
rainwater harvesting, etc.
Current Policies
Require onsite retention of stormwater runoff in the amount of:
1. 0.5” Runoff over impervious2. 1.0” Rainfall from impervious3. 1.1” Runoff over impervious4. 2.8” Rainfall (two-year storm) from contributing drainage area
No provisions for looking at downstream water budget impacts
Water Budget
Land Use (Impervious %)Annual Runoff Volume
(acre-feet/acre)
Agricultural (0%) 0.32
Residential (50%) 0.59
Commercial (70%) 1.31
Fully Developed (100%) 1.82
Watershed Runoff Contributions:
How do the policies affect the water budget in a watershed?
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0%
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90%
100%
Fully Developed -100% Impervious (P8)
Commercial - 70% Impervious (P8)
Residential - 50% Impervious (P8)
Volume Reduction Requirement (Rainfall in Inches)
% A
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ua
l V
olu
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Re
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0.5” Runoff
1.0” Rainfall
1.1” Runoff
2.8” Rainfall
Water Budget
Land Use (Impervious %)0.5”
Runoff1.0”
Rainfall1.1”
Runoff2.8”
RainfallResidential (50%) 55.5% 67.3% 77.9% 97.0%Commercial (70%) 67.0% 80.5% 87.9% 98.0%Fully Developed (100%) 69.0% 81.7% 88.2% 97.9%
Annual Volume Reduction (%):
Water Budget
Land Use (Impervious %)No
Controls0.5”
Runoff1.0”
Rainfall1.1”
Runoff2.8”
Rainfall
Residential (50%) 0.59 0.26 0.19 0.13 0.02Commercial (70%) 1.31 0.43 0.26 0.16 0.03Fully Developed (100%) 1.82 0.56 0.33 0.21 0.04
Remaining Runoff After Implementing Volume Reduction Policies (acre-feet/acre):
Water BudgetWetland Water Losses:
Infiltration: (0.001 – 0.05 in/hr)
0.73 – 36.5 acre-feet/acre/year
Evaporation: (3 feet/year)
3.0 acre-feet/acre/year
Total: 3.73 – 39.5
acre-feet/acre/year
Water Budget
Land Use (Impervious %)No
Controls0.5”
Runoff1.0”
Rainfall1.1”
Runoff2.8”
Rainfall
Residential (50%) 6.3 14.3 19.4 28.7 211.5Commercial (70%) 2.8 8.6 14.6 23.5 141.9Fully Developed (100%) 2.1 6.6 11.2 17.4 97.7
To support 1 acre of wetland, how many acres of tributary area is required?
0.001 in/hr infiltration
Water Budget
Land Use (Impervious %)No
Controls0.5”
Runoff1.0”
Rainfall1.1”
Runoff2.8”
Rainfall
Residential (50%) 67.2 151.0 205.4 304.0 2239.2Commercial (70%) 30.1 91.1 154.2 248.4 1503.0Fully Developed (100%) 21.7 70.1 118.7 184.1 1034.6
To support 1 acre of wetland, how many acres of tributary area is required?
0.05 in/hr infiltration
Case Study
Drainage Area: 42 acresPre-development runoff (Ag.)
13.4 afPost-development runoff (50% Imp.)
0.5” Runoff: 11.0 af1.0” Rainfall: 8.0 af1.1” Runoff: 5.5 af2.8” Rainfall: 0.8 af
Case Study
Drainage Area: 42 acresPre-development runoff (Ag.)
13.4 afPost-development runoff (100% Imp.)
0.5” Runoff: 23.5 af1.0” Rainfall: 13.8 af1.1” Runoff: 8.8 af2.8” Rainfall: 1.7 af
Benefits of Volume Reduction Using Infiltration
Mimics natural water cycleRecharges groundwaterContributes clean base flow to nearby streamsProvides pollutant removalCan be a cost effective way to treat stormwaterMay be constructed underground to maximize
useable space onsiteCan incorporate native vegetation and treesMitigates temperature impacts
May contaminate groundwater or soilPotential for failure due to siltation and clogging over
timeCannot be used in soils with low permeabilityCost increases in areas with soils having low
infiltration ratesMay increase local subsurface water elevations
(basement flooding)Loss of hydrology to downstream lakes and
wetlands
Concerns about Volume Reduction Using Infiltration
Wetland Benefits
Habitat – Plants & AnimalsWater Quality – Filter & Clean RunoffGroundwater Recharge – Hold & Infiltrate RunoffFlood Protection – Store Water during Snow/Rain Events
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Do current volume reduction policies have the potential to undermine our efforts to protect
Minnesota’s wetlands?