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City of Madison Engineering | Photo Credit: Archie Nicolette
LAKE EDGE PARK DEBRIS & SEDIMENT CATCHMENT
Prior to the installation of the sediment basin, this area was an under utilized public park with a 7 ft by 4.5 ft corrugated steel arch pipe running below it, discharging directly into Lake Monona. The pipe drained a 330-acre watershed in the cities of Madison and Monona. The are is primarily residential with some commercial and institutional land use. Since the watershed was developed primarily in the 1960’s, little thought was given to stormwater management other than draining the land in an efficient manner.

The runoff from this watershed, as with all urban stormwater runoff, contains suspended sediment, street debris and nutrients such as phosphorus. The existing pipe drains to the west side of Lake Monona which historically has very limited water depths due in large part to prevailing winds (west to east) in the region pushing debris to that side of the lake.

Watershed map

Watershed map

The project to construct the sediment basin involved justifying the use of the parkland for storm sewer. Justification was done by modeling the existing sediment load to the pipe and designing a pond to remove 40% of the Total Suspended Solids (TSS), on an average annual basis, from the stormwater runoff.

The outfall pipe was removed and the area was excavated 5 to 6 feet below existing grade and a gabion outlet structure was constructed at the lake. This excavation had the affect of creating a pond during the summer months. The bottom of the pond is paved with a porous concrete base so that when lake levels are dropped in the winter, the captured sediment may be removed with heavy equipment and disposed of at the landfill.


During construction

During construction

After construction

 

 

For more information on this project, please contact Greg Fries, City Engineering, at 267-1199.