Suitable Weir Heights to Improve the Provision of Environmental Flows in Urban Rivers

Abstract

Abstract Many studies have been conducted on environmental flow (e-flow) assessment and supply, but e-flow shortages remain common in many urban rivers. In addition to known reasons such as ever-increasing competition among water users and inadequate execution of designed e-flow supply plans, we propose that designing weir heights without explicitly considering e-flows is another major cause of this problem. In this paper, we suggest that the measures for satisfying e-flows be extended from the water supply stage to the river channel design stage. We establish a new weir height determination framework that would more effectively satisfy the required e-flows. The new framework differs from previous frameworks, in which flood control and water retention are the major concerns and the flow during floods is set as the inflow. In the new framework, e-flow provision and flow velocity maintenance are added concerns and the actual flows for e-flow supply are set as the inflow. As a case study of the new framework’s effectiveness, we applied it to the Shiwuli River, a typical channelized urban river in Hefei, China. The old framework specified too-high weir height to meet the e-flow requirements, whereas the new framework offered more reasonable heights that improved e-flow provision.