This thesis project monitors the quantity and quality of stormwater entering and leaving a bioretention system in Coralville, Iowa. Bioretention is among many engineered solutions designed to provide treatment for runoff that might otherwise be drained directly to a body of water. Increased quantities of stormwater can impact stream morphology, degrade aesthetics, increase flood frequency, peak flow, and peak duration; as well as increased sedimentation and sediment transport. Decreases in water quality can impair fish or other aquatic populations, and increase the treatment requirements for downstream intakes. The number of communities, presently 47, affected by stormwater control ordinances increases as the Environmental Protection Agency continues to require smaller Municipal Storm Sewer Systems to adhere to National Pollutant Discharge Elimination System permits.
The City of Coralville is setting an example by using infiltration practices to treat runoff from a 4-lane divided thoroughfare. Preliminary monitoring shows that the system in Coralville provides an average reduction in effluent temperature g of 3.7°C, an average reduction in peak flow of 2 cfs, and an average peak delay of 45 minutes. The project provides infiltrative treatment for the water quality volume and the empirical curve number for the project is 77.4. The urban runoff to the project is within literature values and the pollutant concentrations in the project effluent are below legal limits.