This wetland system cleans storm water flowing to the Phalen Chain of Lakes.
The pipeline, sheet piles for the weirs and initial grading for the sedimentation basin were completed in 1996 and 1997. The final grading and permeable weir installation was completed during the winter of 1998-1999. The berm north of the old golf course was completed during the winters of 1999-2000 and 2000-2001. Those pipes have since been replaced by an open channel as part of the development of the golf course property, and a roadway was placed on the north side in the location of the berm.
In 2007 a water quality improvement project in Kohlman Basin involved the construction of permeable limestone barriers on the downstream side of the existing weirs to remove soluble phosphorus from runoff. The permeable limestone barrier is a engineered combination of large and small size limestone rock. As flows pass through the barrier, the soluble phosphorus binds with the calcium in the limestone and settles in the wetland. Over time the limestone will dissolve and need to be replaced.
The larger limestone rocks/boulders that add structural support to the barrier also provide substrate for periphyton (attached algae) growth and uptake of phosphorus. The limestone substrate can provide an eventual sink for the phosphorus taken up by the algae.