Green infrastructure design for stormwater runoff and water quality: Empirical evidence from large watershed-scale community developments

Green infrastructure (GI) design is advocated as a new paradigm for stormwater management, whereas current knowledge of GI design is mostly based on isolated design strategies used at small-scale sites. This study presents empirical findings from two watershed-scale community projects (89.4 km² and 55.7 km²) in suburban Houston, Texas. The GI development integrates a suite of on-site, infiltration-based stormwater management designs, and an adjacent community development follows conventional drainage design. Parcel data were used to estimate the site impervious cover area. Observed streamflow and water quality data (i.e., NO3-N, NH3-N, and TP) were correlated with the site imperviousness. Results show that, as of 2009, the impervious cover percentage in the GI site (32.3%) is more than twice that of the conventional site (13.7%). However, the GI site's precipitation-streamflow ratio maintains a steady, low range, whereas this ratio fluctuates substantially in the conventional site, suggesting a "flashy" stream condition. Furthermore, in the conventional site, annual nutrient loadings are significantly correlated with its impervious cover percentage (p < 0.01), whereas in the GI site there is little correlation. The study concludes that integrated GI design can be effective in stormwater runoff reduction and water quality enhancement at watershed-scale community development.