Effect of typical low-impact development measures on control of thermal loads from urban stormwater runoff.

Ground hardening in urban areas increases the risk of thermal enrichment in surface rainwater runoff. Moreover, the thermal pollution from rainwater runoff has become an important problem that damages the urban aquatic environment. Current studies have focused mainly on the potential hazard caused by runoff thermal pollution to aquatic microorganisms. However, there are few studies on the efficacy of controlling runoff thermal load through low-impact development (LID) and renovation in urban areas. The effects of LID modification were evaluated by monitoring the characteristics of the runoff thermal load on each underlying surface in the study area and conducting laboratory-scale bioretention experiments. The results showed that the initial thermal effect of each underlying surface was significant after the start of rainfall, based on the thermal load. Ceramic granules are remarkable bioretention fillers. Their average heat load and volume reduction rates are 55.6 % and 32.7 %, respectively. After LID modification, the thermal load of surface runoff in the study area decreased to 73.42 % under similar rainfall conditions. After the secondary treatment of the bioretention facility, the total thermal load of the outflow facility was 31.40 % of that before renovation. The peak thermal load reduced by 69.15 % and was delayed for 10 min. The control effect differed statistically.