Abstract: An empirical relationship, taking discharge of ebb tide as a variable, is developed by using the field hydrograph data of ten estuaries, while the discharge of ebb tide is not an independent variable which varies with the width and area of the estuary. Based on the equilibrium concept of sediment transport of flood and ebb tide, the discharge of ebb tide can be written as a function of annual runoff and ebb tide duration, so it becomes an independent variable, favourable to the analysis and forecast of impacts of human activities. According to it, the data verification of several existing estuaries in Zhejiang Province and impacts of human activities (water diversion, and construction of reservoir and tidal barrag) is carried out and the average error is 15%.