Field Evaluation of Level Spreaders for Runoff Reduction and Water Quality Impacts

Traditional construction practices lead to degradation of watershed hydrology through increased flow in pipe networks, increased flow volumes, decreased groundwater recharge, and increased peak flows. Recent regulations in North Carolina have led to the use of level spreaders in combination with a vegetated buffer as an end-of-pipe method to reduce erosion and decrease stresses on riparian buffers. However, little research has been done to evaluate their effectiveness. A total of four level spreaders were studied at two sites, Apex and Louisburg, NC. At each site, stormwater from small, impervious watersheds (0.4 ha or less) was conveyed proportionally to two level spreaders. Flow was released along the length of the level spreaders and into two vegetated buffers. This study evaluated the hydrologic and water quality impacts of level spreaders (combined with vegetated buffers) as an LID practice. The idea is to disperse flow across the length of the buffer, in order to improve infiltration capacity of the buffer. Varying buffer widths and buffer vegetation were studied. Preliminary findings show that substantial reduction in peak flow rate and flow volume can be expected when this LID practice is implemented. This system was also studied for its impacts on nitrogen, phosphorous, suspended solids, and runoff temperature. Further data collection and analysis should provide design engineers guidance on the functionality of this system.