Runoff Volume Reduction by a Level Spreader–Vegetated Filter Strip System in Suburban Charlotte, N.C.

The premise of low impact development (LID) is to reduce runoff volumes while simultaneously matching target (often predevelopment) infiltration and evapotranspiration volumes. Many structural practices used in LID, such as bioretention, infiltration trenches, and permeable pavement, require a seasonally high water table (SHWT) to be 1–2 m from the surface. Conversely, level spreader–vegetated filter strip systems can be implemented in locations where a SHWT would restrict the use of other practices. A 19.4 m long reinforced concrete level spreader upslope of a 900 m2 mixed grass/weed vegetated filter strip was monitored for runoff reduction for 23 precipitation events from November 2005 to January 2007 in Charlotte, N.C. The practice treated runoff from a 0.87 ha (2.15 acre) residential watershed. Of the 23 monitored events, only 3 produced outflow. All events which produced outflow exceeded 40 mm (1.6 in.) of precipitation. Cumulative volume reduction associated with the events was 85%, which compares favorably to other LID structural practices tested in the region. Because of its simple design, construction, and maintenance, and its ability to be sited in locations with otherwise restrictive SHWTs, level spreader–vegetated filter strips may be a valuable LID practice.