Abstract: In this study, a hydrological method and habitat simulation method are adopted to estimate the ecological baseflow in the Zhangweixin River estuary. And based on MIKE21 FM, a salinity intrusion model is developed for this estuary to simulate saltwater intrusion to its original riverway and dredged riverway under the condition of different discharges by the Xinji sluice and to verify the estimation of its ecological baseflow. The result shows that the section from the Dakou River outlet to CS21 is a tidal flow dominant area that features the cross-sectional average of salinity and its streamwise variation both nearly independent of the sluice discharge. The section from CS21 to the sluice is dominated by the sluice discharge but controlled by the joint action of the sluice and the tidal flow. As the sluice discharge increases from 4 m3/s to 8 m3/s, the sluice dominant section extends 5 km further downstream, while a further increase in the sluice discharge up to 12 m3/s leads to nearly no more extension. Thus, we suggest that the ecological baseflow at the sluice should be 8 m3/s.

Key words: ecological baseflow, MIKE21 model, estuary, saltwater intrusion, tidal flow