Evaluating the performance of a bioswale in decreasing stormflow and pollutant loads

Much of the world's urban stormwater is not treated or filtered before it enters a local body of water. This is a potential issue as stormwater that runs off impermeable surfaces such as driveways, parking lots and roads, often carries pollutants. Additionally, these impermeable surfaces can increase stormwater runoff flow volumes by decreasing infiltration into the soil. This increased volume of stormflow can lead to erosion and reduced local groundwater recharge time. Bioswales are one effective method to remediate these issues, as they have been shown to reduce both pollutant loads and flow volume. This study evaluates the performance of a bioswale, located at Butte College in Oroville (northern California) for its pollutant loads and flow reduction during storm events. Flows will be measured with a system of weirs and flumes in combination with pressure transducers, while nutrient (NO₃, NH₄, PO₄-P, DOC, TDN) and heavy metal concentrations will be measured in grab samples at California State University, Chico. Preliminary results have shown the bioswale capable of reducing flow volumes by 89%, nutrient loads from 56% (PO₄-P) to 98% (NH₄) and DOC loads by 66%. Heavy metal loads have seen reductions ranging from 56% for Cu to 97% for Zn. This study will further our understanding of bioswale performance in stormwater management.