Indicator-based Hydrological Resilience Framework for Urban Stormwater Management Systems

Abstract Urbanisation changes the nature of urban catchments by altering landcover, soil conditions and runoff storage capacity, resulting in increased runoff volume and peak flow due to disruption of the hydrological cycle. Contemporary stormwater management approaches such as Best Management Practice (BMP), Water Sensitive Design (WSD) and Sponge cities have introduced a new philosophy in stormwater management to reduce the impact of urbanization on surface runoff and improving the hydrological cycle in urban areas. These approaches mainly focus on hydrological mitigation by minimizing the impact of increasing runoff volume and peak flow. However, there are no robust approaches to evaluate the effect of changes in the hydrological characteristics of urban developed catchments on the resilience of stormwater management system to flooding. This paper introduces a novel framework to characterize the resilience of stormwater management systems in terms of the hydrological characteristics of an urban catchment. The framework is based on the differences in the peak flow and runoff volume of a catchment between the urbanized and greenfield conditions. A set of indices are defined to represent relationships between catchment performance capacities in stormwater management and design rainfall, culminating in the quantification of the hydrological resilience degree (\({R}_{hg}\)). The framework is tested in an urban catchment in Auckland, New Zealand to demonstrate the reduction in \({R}_{hg}\) as a function of rainfall depth and the influence of changes in hydrological characteristics. Different scenarios are analysed to demonstrate the effect of stormwater runoff control systems on resilience, with volume control devices providing the greatest increase in resilience. Mapping of the indices across sub-catchments provides a spatial representation of these changes and can be used as a tool in catchment management plans to optimize the hydrological mitigation and resilience of stormwater management systems.