4.13 Floodplains

Goal 13 - Floodplains

Reduce the severity and frequency of flooding and high water by preserving and increasing the existing water storage capacity below 100-year flood elevations on all waterbodies within MCWD.

Discussion

An important strategy in the management of stormwater in the Langdon Lake subwatershed is the preservation of the upstream stormwater storage in Black and Saunders Lakes.  Key areas identified in this plan for conservation include wetlands that provide floodplain storage and areas that provide channel and stream floodplain and riparian zones.  Additional storage could be provided through the creation of depressional storage areas on new developments.

Desired Outcomes: No net loss of floodplain storage.

Metrics:   Acres net floodplain fill.

Goal 13.1 - Langdon Lake

Preserve the existing water storage capacity below the 100-year event elevation.

Actions

  1. Minimize development below the 100-year event elevation.
  2. No net loss of the wetland complexes that provide substantial upstream stormwater storage within this subwatershed.
  3. Encourage the development and maintenance of depressional storage within the subwatershed.
    1. Promote the acceptability of minor flooding and stormwater storage within the floodplain.

Goal 13.2 - Langdon Lake

Utilize District hydrologic and hydraulic data to identify potential public infrastructure high water impacts.

Actions

  1. The HHPLS noted that the 100-year water level at the Highway 110 crossing and the outlet berm from Saunders Lake exceeds the minimum 2 foot freeboard required by the District.  Local plans should identify these observed or potential locations and assess whether the risk of occasional flooding is acceptable or should be addressed.  Assist LGUS in determining specific impacts and potential improvements.
  2. Recommend that the City of Minnetrista consider raising the elevation of the outlet berm to provide the necessary freeboard.