Case Study: Parking Lot Filter Strip

Filter Strip City of Proctor, MN

The City of Proctor, Minnesota needed a new town hall, but the land dedicated for the building was adjacent to Kingsbury Creek, a protected trout stream.

The City of Proctor and the building's designer, the architecture firm LHB, knew that they needed an innovative approach in order to protect the stream from the building's runoff. In order to minimize stormwater impacts, the building's parking lots were designed with 350 linear feet of sand/peat filter strips.

The filter strips consist of a two-foot-deep sand/peat mixture built on the existing clay soil. A grass buffer was placed on top at a sloping angle with riprap at the base of the slope, and all the strips were angled and fitted with drain pipes directed toward Kingsbury Creek. The object was to slow the rate at which the water flowed off the parking lot and entered the stream, allowing it to cool. The filter step also cools the runoff and provides a mechanism to filter out major pollutants.

Since installation in January 2001, the filter strip has worked well, and has not frozen over or clogged. Maintenance has been minimal, limited to having the building's maintenance team ensure that sand used during periods of snow is removed from the grass through raking and shoveling. The strips accept all the building's roof and parking lot runoff and ensure a cleaner, healthier Kingsbury Creek.

American Rivers 2004. Catching the Rain: A Great Lakes Resource Guide for Natural Stormwater Management. [Download the pdf file - 1.5 MB, new window]