Low Flow and Stormwater Quality in Urban Channels

A water quality monitoring effort in a concrete-lined, urban channel yielded a comprehensive data base to evaluate low flow and stormwater quality. The low flow effluent-dominated regime was affected largely by benthic algal production and respiration resulting in large diurnal DO fluctuations. QUAL II was used to simulate the system as an aid in defining cause-effect relationships and to calculate production and respiration rates which were much higher than those reported for natural stream systems. Stormwater effects on DO were found to be minimal with BOD₅ levels low and DO levels near saturation. Stormwater loads of total suspended solids and nutrients were found to be a major contributor to total pollutant loads.