Performance and Cost-Based Comparison of Green and Gray Infrastructure to Control Combined Sewer Overflows

Abstract

Rainwater harvesting (RWH) is being used more often today as a water supply and stormwater management green infrastructure (GI). In recent years, GIs in urban water engineering have gained attention due to their lower lifecycle costs—in both implementation and operation phases—rather than traditional gray approaches. The research described in the present paper compared implementation of RWH systems to gray approaches previously designed as a part of the long-term control plan (LTCP) for combined sewer overflow (CSO) control in Toledo, Ohio. RWH scenarios in this study were defined based on different system capacities and release policies, and then combined gray and green scenarios were analyzed according to their hydrologic performance and cost. This study employed long-term continuous hydrologic and hydraulic (H&H) simulations as well as lifecycle cost (LCC) analysis techniques. The results showed that greening the LTCP via RWH could improve the lifecycle cost-effectiveness by 48%. The captured rainwater was considered to supply toilet flushing water demand in buildings.