Assessing the impacts of green stormwater infrastructure on urban stormwater quantity and quality using PCSWMM: A case study of Northern Oklahoma College, Enid campus stormwater pond

Urban stormwater management has become a pressing environmental issue due to rapid urbanization and changing climate. Excessive stormwater runoff contributes to erosion, sedimentation, and flooding, leading to water quality degradation in the receiving water bodies. In response to this, sustainable solutions such as Green Stormwater Infrastructure (GSI) for urban stormwater management have become increasingly important. This study examined the effectiveness of GSI practices in managing the stormwater quantity and quality in an urban watershed. The Northern Oklahoma College (NOC) Enid campus pond and the surrounding area were selected as the case study area. This campus pond receives runoff from 917 acres of urban catchment which has led to excessive sedimentation in the pond. To study the impacts of stormwater runoff and understand the status of the pond, water samples were collected during the baseflow and stormflow events and analyzed for pH, Escherichia coli, dissolved oxygen, temperature, turbidity, total suspended solids (TSS), nitrate, total nitrogen, and total phosphorous (TP). The Personal Computer Storm Water Management Model (PCSWMM) was employed to simulate stormflow in the study area under five design storms with recurrence intervals ranging from 1-year to 25-year. The model was calibrated using the field-collected flow depth, and TSS data. Different scenarios were developed within the model to compare the effectiveness of four GSI practices: bioretention cell (BRC), infiltration trench (IT), rain garden (RG) and vegetative swale (VS) in runoff and TSS reduction. The water quality assessment found turbidity, TSS, TP and E. coli as the parameters of major concern. Model simulation results confirmed the effectiveness of the GSI practices, with BRC being the most effective in the reduction of peak inflow, total inflow volume and peak TSS influx into the pond with up to 86.8%, 74.9% and 61% reduction, respectively. Additionally, a combination of GSI practices for the campus pond area were identified with the aim of helping NOC for potential implementation. The findings presented in this study are expected to provide a better understanding of the impacts of urban stormwater runoff on receiving water bodies as well as aid in identifying the best GSI practices for stormwater impact mitigation.