PRELIMINARY ANALYSIS OF TIDAL LEVEL CHANGE DUE TO RIVER DISCHARGE IN THE YANGTZE RIVER ESTUARY, CHINA

摘要

Long-term tidal levels at tidal gauges are frequently used to analyze the sea level change. The sea level records involve glaciers melting, land subsidence, earth surface temperature rise and river discharge change and so on. However, the contribution of these factors on sea level rise (SLR) is not clear. In this paper, the Yangtze River Estuary (YRE) is chosen as a prototype to preliminary study the responses of the mean tidal level change to the river discharge. Firstly, MIKE21 is selected to establish a depth-averaged hydrodynamic model covering the YRE and the Hangzhou Bay. Then, this model is well validated with the measured data. After that the validated model is run with different monthly river discharges at Datong station (i.e., tidal limit, about 640 km upstream from the river mouth) from 1950 to 2011. Analysis of monthly river discharges from 1950 to 2011 at Datong station reveals that the monthly river discharge from 1950 to 2003 presents an increasing trend, while decreasing from 2004 to 2011 after the impoundment of Three Gorge Dam (TGD) in 2003. The simulations point out that the mean tidal level at Dajishan station (represented station in the coastal water of the YRE) is influenced by river discharge with an increasing rate of 0.055 mm/y from 1950 to 2011 and a decreasing rate of 0.056 mm/y from 2004 to 2011. Meanwhile, the increasing rate of mean tidal level (1980-2011) at Dajishan station caused by river discharge only accounts for 5.6%-8.9% of that provided by the China Sea Level Bulletin (i.e., the value of 2-3 mm/y including the impact of all factors) in the same period.