Urbanization and stream ecosystems: the role of flow hydraulics towards an improved understanding in addressing urban stream degradation

Abstract

Catchment urbanization is widely recognised as a primary driver of stream degradation by increasing stormwater runoff, which causes major changes to key ecosystem processes. Reinstating the “natural” hydrogeomorphic conditions is central in designing successful, self-sustaining restoration actions; however, addressing urban stream degradation by re-establishing the hydrogeomorphic conditions remains a challenge, and comparatively limited measurable progress has been observed, particularly in achieving ecological objectives. This review articulates that stream restoration goals might be better achieved when management measures take a broader approach that considers anticipated hydraulic condition effects that liaise relationships between flow and ecology. The study argues that fluvial systems are characterised by complex and dynamic ecosystem processes primarily governed by the hydraulic conditions (e.g., velocity, depth, shear stress); thus, as the practice of addressing urban stream restoration becomes increasingly common, it is critical to explore and understand the anticipated response of the hydraulic conditions. It describes how hydraulic regime consideration provides further opportunity for a holistic approach to urban stream management given their capacity to account for multiple ecological and geomorphic objectives. This review suggests that developing suitable flow–biota–ecosystem processes nexus is critical to addressing urban stream degradation, and hydraulic consideration in restoration actions provides an important step towards that. It discusses opportunities to evolve management actions to achieve restoration goals by highlighting how the management of the two key levers (addressing altered flow regime and morphology) to improve the hydraulic conditions can help to address the urban stream disturbance.