302 - Impervious Cover Characterization in Urban Watersheds: Effects of Spatial Data Resolution and Availability

Estimating the contribution of impervious areas (IAs) to stormwater runoff generation in urban watersheds is complex due to the multitude of contributing factors including the spatial distribution of IAs. Three metrics to estimate this contribution are Total IA (TIA), Directly Connected IA (DCIA), and Effective IA (EIA). However, the availability and resolution of spatial data pose significant challenges. In this study, the distribution of TIA and DCIA were determined and compared with EIA in nine urban catchments with diverse sizes (16 to 2035 ha) and land uses in St. Paul, Minnesota. Using spatial programming, surface runoff was tracked from source to discharge point, through eleven scenarios incorporating land cover (LC) data with various sources and resolution (60 cm to 30 m), different runoff collection types (city drainage system versus roads), and various options for rooftop connectivity to sewer systems.
The results indicate that the TIA fractions derived from two different data sources, nationally available imperviousness data (30-m resolution) and the locally prepared high resolution LC data (60-cm resolution) exhibit no statistically significant differences. Additionally, substituting road networks (readily available data) with drainage inlets (less readily available data) as the runoff collection system yields similar DCIA values, with a 95% confidence interval. The scenario analysis of rooftop connectivity highlights that zero connectivity aligns DCIA and EIA values more closely compared to 100% connectivity. These findings provide valuable insights into the spatial characterization of urban IAs, enhancing runoff volume determination in ungauged urban watersheds.