Influences of sand excavation on low water level in the lower reaches and delta of Dongjiang River

The low water levels at some hydrologic stations in the lower reaches and delta of the Dongjiang River with different assuring probabilities from 1964 to 2003 are calculated.Considering the sand excavation,analyses show that the low water levels at Huiyang and Boluo,dominated by runoff,have been decreasing since 1980′s,while the water levels at Fanwu,Shilong and Dasheng in the tidal reach have been increasing since 1990′s.The huge sand excavation is the main reason for degradation of the low water level.The channel-fill volume is increased and river bed's level is decreased apparently after huge sand excavation.The strengthening of the tidal power caused by the significant topographic change is responsible for the rise of the low water levels in the tidal reach.