Thermal Mitigation of Urban Storm Water by Level Spreader-Vegetative Filter Strips

A study was conducted in Louisburg, North Carolina, to determine the effect of level spreader-vegetative filter strip (LS-VFS) storm-water control measures (SCMs) on runoff temperature and thermal loading. Two LS-VFS systems draining an urban catchment were monitored during the summers of 2008 and 2009. The first VFS was 7.6 m wide and entirely grassed. The second was 15.2 m wide, with the first-half grassed and the second-half wooded. Runoff temperatures and thermal loads from the urban catchment tended to peak toward the beginning of a storm event. Median and maximum storm temperatures were significantly reduced across both the 7.6-m and 15.2-m LS-VFSs. However, median and maximum effluent temperatures for both filter strip lengths were significantly greater than the 21 C trout threshold. Mean and median effluent temperatures from the 15.2-m LS-VFS were slightly lower (< 1 degrees C) than those from the 7.6-m LS-VFS, which may show the impact of increased filter strip width and/or the shading from wooded vegetation on effluent temperatures. Expected differences between influent and effluent temperatures (both median and maximum) were greater as the influent temperature increased. Substantial and statistically significant (alpha = 0.05) thermal load reductions were observed in both LS-VFSs because of measured reductions in both temperature and flow volume. Thermal load was eliminated in seven of 38 storm events because of infiltration of the entire runoff volume in the filter strips. The ability of LS-VFS systems to reduce storm-water temperatures and thermal loads supports their use in thermally sensitive watersheds. DOI: 10.1061/(ASCE)EE.1943-7870.0000367. (C) 2011 American Society of Civil Engineers.