Summary of wetland design criteria
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Design Criteria Shallow Wetland Pond/Wetland ED Shallow Wetland*
Wetland/Watershed Ratio (Ac/Ac) 0.2 0.1 0.1
Minimum Drainage Area (Ac) 25 10 25
Length to Width Ratio (minimum)(ft/ft) 2:1 2:1 2:1
Extended Detention (ED) No Optional Yes
Allocation of Vwq (pool/marsh/ED) in % 25/75/0 70/30/0(includes pond volume) 25/25/50
Allocation of Surface Area (deepwater/low marsh/high marsh/semi-wet) in % 20/35/40/5 45/25/25/5 (includes pond surface area) 10/35/45/10
Forebay Required Required Required
Micropool Required Required Required
Outlet Configuration Reverse-slope pipe or hooded broad-crested weir Reverse-slope pipe or hooded broad-crested weir Reverse-slope pipe or hooded broad-crested weir

*Note: The ED Shallow Wetland design guidance does not meet the MPCA requirements for permanent volume. The guidance may be applied in a stormwater retrofit situation where area requirements preclude the use of a Shallow Wetland

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