Comparing green infrastructure to grey infrastructure to reduce stormwater network overflow and cost

Abstract:

Green Stormwater Infrastructure (GSI) has become a viable and popular solution in both managing stormwater-related challenges, and in preserving green spaces in highly urbanized areas. In the city of Dallas, GSI is one of the solutions considered in stormwater management. This study aims at comparing the efficiency of green vs grey infrastructure in the areas in city of Dallas where flooding is a major issue. In this project, high priority areas to invest in stormwater projects were identified (Study detailed in another presentation) using the SWMM 5.0 model. The subwatersheds of the overflown junctions identified in SWMM were considered opportunity watersheds for GSI investment projects. Such subwatersheds were then further investigated to compare the efficiencies of green, i.e. bioretention cells, rain gardens, and rainwater harvesting, vs grey infrastructure, i.e. increasing the capacity of existing pipe systems, in reducing the overflow volumes. The results show that while neither option was able to eliminate the overflow in three of the seven priority watersheds, green infrastructure reduces overflow at a much lower cost, by 48% to 60% in all watersheds. Also, the results show that in the remaining four watersheds, GSI could eliminate the overflow from the 100-year storm, while grey infrastructure improvement eliminated overflows in one. The results suggest that green infrastructure is a promising cost-effective solution for stormwater management problems in the city of Dallas, and GSI should be considered first for capital investment while grey infrastructure should complement GSI to meet flow reduction targets when GSI alone is not enough.