Overlaying and Linking Low Flow and Floodplain River Reaches for Rapid Assessment of Mitigation Measures

Low flow channels and floodplains are linked elements in a river corridor. At low flows river channels often meander and at high flows meanders are frequently overtopped with floodwaters flowing out of bank through the floodplain. During high flows the flood water takes a short cut with the floodplain conveying a significant amount of flow and taking a much shorter route than the flow in the low flow channel.

Level of service requirements for rivers often only allow out of bank flow for events of ARI in excess of 5 years. In sections of the river where the level of service is not met mitigation can be achieved by identifying and protecting a formal overland flow path which follows a straight alignment within the river corridor.

This paper examines how a 1-D hydraulic model simulating the linkage and hydraulic behaviour between a low flow channel and floodplain was discretised (for a river corridor with a significant difference in flow length between channel and floodplain). It also describes how this setup enables the modeller to simulate mitigation options such as formalising a straight overland flow path and discusses the advantages, effects and constraints of mitigation options and the model setup.