River discharge contribution to sea-level rise in the Yangtze River Estuary, China

Sea level changes in the Yangtze River Estuary (YRE) as a result of river discharge are investigated based on the monthly averaged river discharge from 1950 to 2011 at the Datong station. Quantification of the sea level contribution is made by model computed results and the sea level rates reported by the China Sea Level Bulletin (CSLB). The coastal modeling tool, MIKE21, is used to establish a depth-averaged hydrodynamic model covering the YRE and Hangzhou Bay. The model is validated with the measured data. Multi-year monthly river discharges are statistically calculated based on the monthly river discharges at Datong station from 1950 to 2011. The four characteristic discharges (frequency of 75%, 50% and 25%, and multi-year monthly) and month-averaged river discharge from 1950 to 2011 are used to study the seasonal and long-term changes of sea level. The computed sea level at the Dajishan and Lvsi stations are used to study the multi-time scale structure of periodic variation in different time scale of river discharge series. The results reveal that (1) the sea level rises as the river discharge increases, and its amplification decreases from upstream to the offshore. (2) The sea level amplification on the south coast is greater than that on the north coast. When river discharge increases by 20,000 m3/s, the sea level will increase by 0.005-0.010 m in most of Hangzhou Bay. (3) The sea level at the Dajishan station, influenced by river discharge, increased 0.178 mm/y from 1980 to 2011. Correspondingly, the sea level rose at a rate of 2.6-3.0 mm/y during the same period. These values were provided by the CSLB. The increase in sea level (1980-2011) at the Dajishan station caused by river discharge is 6.8-8.9% of the total increase in sea level. (4) The 19-20 year dominant nodal cycle of sea level at the Dajishan and Lvsi stations is in accord with 18.6 year nodal cycle of main tidal constituents on Chinese coasts. It implies that the sea-level change period on the coast of the Yangtze River is mainly controlled by tides.