*4.1. Simulation Conditions*

Similar to former studies on the spillover of saltwater, the spillover of sediment in the Yangtze Estuary is studied using the condition of a spring and a neap tide in dry seasons, when the sediment spillover in the Yangtze Estuary is considered to be most significant.

At the upstream boundary, the river discharge and sediment concentration are set to 19,000 m<sup>3</sup>/s and 0.112 kg/m3, respectively. The flow and sediment fluxes at Datong are then respectively calculated to be 16.41 × 10<sup>8</sup> m<sup>3</sup> and 18.39 × 10<sup>4</sup> tons per day. The seaward boundaries are forced by the tide-level histories of a spring tide and a neap tide, respectively, which leads to two tests of 1-day simulation. Nine cross-sections are arranged to record the histories of the flow rates and the sediment transport rates (see Figure 3). For the sake of convenience, the divisions of North Branch are defined as follows: the upper reach (from the bifurcation of North and South Branches to Station QLG); the middle reach (from Station QLG to SHG); the lower reach (from Station SHG to STG); the tail reach (from Station STG to LXG).
