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How do Wetlands Factor into New Infiltration Policies?

How do Wetlands Factor into New Infiltration Policies?. Todd Hubmer, PE. Wetland Conservation in the News. Wetland Benefits. Habitat – Plants & Animals Water Quality – Filter & Clean Runoff Groundwater Recharge – Hold & Infiltrate Runoff

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How do Wetlands Factor into New Infiltration Policies?

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  1. How do Wetlands Factor into New Infiltration Policies? Todd Hubmer, PE

  2. Wetland Conservation in the News

  3. Wetland Benefits • Habitat – Plants & Animals • Water Quality – Filter & Clean Runoff • Groundwater Recharge – Hold & Infiltrate Runoff • Flood Protection – Store Water during Snow/Rain Events

  4. Wetland Types Groundwater Dependant • FENS • Streams • Marshes • Bogs

  5. Wetland Types Surface Water Dependant • Vernal Pools • Marshes • Flood Plain Fringe

  6. Do Current Trends in Watershed Management Anticipate Impacts to Wetlands?

  7. Current Policies • Require stormwater runoff to be treated before discharge • Trends for water quality treatment are focused on runoff volume reduction • Volume reduction through infiltration, water reuse, rainwater harvesting, etc.

  8. Current Policies • Require onsite retention of stormwater runoff in the amount of: • 0.5” Runoff over impervious • 1.0” Rainfall from impervious • 1.1” Runoff over impervious • 2.8” Rainfall (two-year storm) from contributing drainage area • No provisions for looking at downstream water budget impacts

  9. Water Budget Watershed Runoff Contributions:

  10. How do the policies affect the water budget in a watershed? 2.8” Rainfall 1.1” Runoff 0.5” Runoff 1.0” Rainfall

  11. Water Budget Annual Volume Reduction (%):

  12. Water Budget Remaining Runoff After Implementing Volume Reduction Policies (acre-feet/acre):

  13. Water Budget Wetland Water Losses: Evaporation: (3 feet/year) 3.0 acre-feet/acre/year Total: 3.73 – 39.5 acre-feet/acre/year Infiltration: (0.001 – 0.05 in/hr) 0.73 – 36.5 acre-feet/acre/year

  14. Water Budget To support 1 acre of wetland, how many acres of tributary area is required? 0.001 in/hr infiltration

  15. Water Budget To support 1 acre of wetland, how many acres of tributary area is required? 0.05 in/hr infiltration

  16. Case Study • Drainage Area: 42 acres • Pre-development runoff (Ag.) • 13.4 af • Post-development runoff (50% Imp.) • 0.5” Runoff: 11.0 af • 1.0” Rainfall: 8.0 af • 1.1” Runoff: 5.5 af • 2.8” Rainfall: 0.8 af

  17. Case Study • Drainage Area: 42 acres • Pre-development runoff (Ag.) • 13.4 af • Post-development runoff (100% Imp.) • 0.5” Runoff: 23.5 af • 1.0” Rainfall: 13.8 af • 1.1” Runoff: 8.8 af • 2.8” Rainfall: 1.7 af

  18. Benefits of Volume Reduction Using Infiltration • Mimics natural water cycle • Recharges groundwater • Contributes clean base flow to nearby streams • Provides pollutant removal • Can be a cost effective way to treat stormwater • May be constructed underground to maximize useable space onsite • Can incorporate native vegetation and trees • Mitigates temperature impacts

  19. Concerns about Volume Reduction Using Infiltration • May contaminate groundwater or soil • Potential for failure due to siltation and clogging over time • Cannot be used in soils with low permeability • Cost increases in areas with soils having low infiltration rates • May increase local subsurface water elevations (basement flooding) • Loss of hydrology to downstream lakes and wetlands

  20. Wetland Benefits ?? ?? • Habitat – Plants & Animals • Water Quality – Filter & Clean Runoff • Groundwater Recharge – Hold & Infiltrate Runoff • Flood Protection – Store Water during Snow/Rain Events ?? ????

  21. Do current volume reduction policies have the potential to undermine our efforts to protect Minnesota’s wetlands?

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