Abstract: Conventional methods for calculating ecological instream flow demand could not be applied directly to data-scarce rivers as they require observational hydrological or biological data in long sequence. Tongshun River in Wuhan reach is a plain river with data scarcity as it has obvious swales without data of long sequence. We arranged ten representative sections in Tongshun River in Wuhan reach, and replaced long-sequence measured flow with artificial trial flow to obtain the relationship between artificial trial flow and hydraulic parameters such as river width, water depth, average velocity and wetted perimeter using MIKE11. On this basis, we calculated the ecological instream flow demand in the study area using the wetted perimeter method and the eco-hydraulics method which are based on the correlation between hydraulic parameters and discharge. Results demonstrated that the ecological instream flow demand on the prerequisite of maintaining the basic morphology and habitat of Tongshun River should be at 26 m³/s. The calculation scheme proposed in this paper provides a feasible means to calculating the ecological instream flow demand in data-scarce plain rivers.

Key words: ecological instream flow demand, data-scarce, wetted perimeter method, eco-hydraulics method, Tongshun River in Wuhan reach