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: 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

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

11. Water Budget Annual Volume Reduction (%): Land Use (Impervious %) 0.5”
Runoff
1.0”
Rainfall
1.1”
2.8”
Residential (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%

12. Water Budget
Remaining Runoff After Implementing Volume Reduction Policies (acre-feet/acre):
Land Use (Impervious %)
No Controls
0.5”
Runoff
1.0”
Rainfall
1.1”
2.8”
Residential (50%)
0.59
0.26
0.19
0.13
0.02
Commercial (70%)
1.31
0.43
0.16
0.03
Fully Developed (100%)
1.82
0.56
0.33
0.21
0.04

13. 0.73 – 36.5 acre-feet/acre/year
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?
Land Use (Impervious %)
No Controls
0.5”
Runoff
1.0”
Rainfall
1.1”
2.8”
Residential (50%)
6.3
14.3
19.4
28.7
211.5
Commercial (70%)
2.8
8.6
14.6
23.5
141.9
Fully Developed (100%)
2.1
6.6
11.2
17.4
97.7
0.001 in/hr infiltration

15. Water Budget
To support 1 acre of wetland, how many acres of tributary area is required?
Land Use (Impervious %)
No Controls
0.5”
Runoff
1.0”
Rainfall
1.1”
2.8”
Residential (50%)
67.2
151.0
205.4
304.0
2239.2
Commercial (70%)
30.1
91.1
154.2
248.4
1503.0
Fully Developed (100%)
21.7
70.1
118.7
184.1
1034.6
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: 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: 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. Loss of hydrology to downstream lakes and wetlands
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?