Watershed Management Planners Recommend an Achievable Goal of 10% Increased Infiltration
Will Retain Long-term Goal of 25% Recovery of Lost Infiltration as Discussion Guide Only
From the time of European settlement of the Lake Wingra watershed around the 1830’s to the present time, the amount of rainfall and snow melt that soaks into (infiltrates) the soil, enters the groundwater, and then flows into Lake Wingra has been reduced by an estimated 99,234, 028 cubic feet (cf) according to figures provided by the Wisconsin Geological and Natural History Survey. (This amount is down from an estimate of pre-settlement percolation/infiltration of 278,842,408 cubic feet of water.) Watershed planners developing a Wingra Watershed Management Plan now hope to recapture about 10% of this “lost infiltration” through various engineered approaches to handling storm water.
The Wingra Watershed Planning Steering Team late in 2013 recommended adopting the short-term goal to capture about 10% of that “lost infiltration”, according to notes of the October 17, 2013 meeting at which the recommendation was made. A long-term target of recapturing 25% of “lost infiltration” will be retained as an aspirational goal for long-range planning discussions.
The Wingra Watershed Plan is a joint effort of the Friends of Lake Wingra (FoLW) and the City of Madison Engineering Division to write an overall storm water management plan (but not an ecological or restoration management) to achieve four general goals for the Lake Wingra Watershed:
- Clean, clear water
- Restored spring flow
- Abundant native plants and animals
- Stewardship and enjoyment
These restoration goals come from the FoLW 2009 document, “Lake Wingra: a vision for the future” and they clearly depend upon achieving the outcome of replenished groundwater. Although the focus of the FoLW 2009 strategic plan is on the lake itself, achieving them will have great benefit for, and enhance the restoration potential of, the wetlands and uplands that surround Lake Wingra.
While the recommenced infiltration amount has not been changed much, the new infiltration target is based upon a different reference condition and represents a scaling back of aspirations to what the planners view as a realistic and achievable. Instead of establishing an infiltration target as a percentage of groundwater flow to Lake Wingra, the new recommendation infiltration target will be a percentage of water infiltration lost since settlement and “development” of the area. It is not clear from the discussions if, or over what time period, the increased infiltration meet the goal of “restored spring flow.”
At the meeting, Strand Associates, the engineering firm retained by the City to facilitate the planning, presented more than a dozen strategies/projects–including bio-retention basins/rain gardens for commercial properties. All of these projects would have to be completed to meet the infiltration goal. The list of proposed infiltration strategies has been requested from Engineering Division officials.