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Balancing Wetlands Conservation With Volume Reduction Policies in Minnesota

Explore the implications of volume reduction policies on Minnesota's wetlands, detailing benefits, concerns, and case studies. Learn how these policies impact water budgets and the need for balancing conservation and stormwater management efforts.

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Balancing Wetlands Conservation With Volume Reduction Policies in Minnesota

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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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