Hydrological Evaluation of Influence of Green Stormwater Infrastructure on Neighborhood-Scale Semi-Arid Nested Watersheds in Tucson, Arizona

Abstract

In drylands, water availability is the limiting factor in the stability and growth of environmental and human systems, yet drought and flooding present a water management paradox in urban centers. The objective of this study was to understand the cumulative impact of green stormwater infrastructure (GSI) on hydrological responses in semi-arid urban neighborhoods, as a function of storm magnitude and GSI implementation levels via monitoring of two separate (paired) nested watersheds. Correlation and regression analyses show that the nested watersheds displayed variable coherence between upstream and downstream subwatersheds in terms of runoff response (peak discharge, runoff volume, runoff ratio). Data had high variability with bias towards small precipitation and runoff events. Significant differences observed between the two paired watersheds in peak flow and volume point to larger scale influences by the drainage system such as natural channel design (aka unlined channel) compared to impervious, concrete channels. This study highlights the difficulties in empirically assessing the impact of small-scale decentralized GSI features on runoff responses in semi-arid urban watersheds with many complex and interacting landscape factors. Recommendations for increasing the watershed-scale runoff influence of GSI include 1) increasing GSI implementation within watersheds (beyond maximum in observed watersheds), 2) consideration of pervious channels as GSI that can promote infiltration and channel transmission losses in arid and semi-arid systems and 3) conduction of with high-resolution modeling studies that can evaluate the influence of multiple small-scale GSI features that can be used to compare to results of empirical analyses.

Keywords: green stormwater infrastructure, urban hydrology, watershed analysis, stormwater management, empirical analysis