*Article* **Study on the Spillover of Sediment during Typical Tidal Processes in the Yangtze Estuary Using a High-Resolution Numerical Model**

### **Dechao Hu 1, Min Wang 2, Shiming Yao 2 and Zhongwu Jin 2,\***


Received: 16 August 2019; Accepted: 24 October 2019; Published: 1 November 2019

**Abstract:** Because of special morphologies and complex runoff–tide interactions, the landward floodtide flows in Yangtze Estuary are observed to spill over from the North to the South Branches, carrying a lot of sediment. To quantitatively clarify the spillover problem, a two-dimensional numerical model using a high-resolution channel-refined unstructured grid is developed for the entire Yangtze Estuary from Datong to river mouths (620 km) and part of the East Sea. The developed model ensures a good description of the river-coast-ocean coupling, the irregular boundaries, and local river regimes in the Yangtze Estuary. In tests, the simulated histories of the tidal level, depth-averaged velocity, and sediment concentration agree well with field data. The spillover of sediment in the Yangtze Estuary is studied using the condition of a spring and a neap tide in dry seasons. For a representative cross-section in the upper reach of the North Branch (QLG), the difference of the cross-sectional sediment flux (*CSSF*) between floodtide and ebbtide durations is 43.85–11.26 × 10<sup>4</sup> t/day, accounting for 37.5–34.9% of the landward floodtide *CSSF*. The mechanics of sediment spillover in Yangtze Estuary are clarified in terms of a successive process comprising the source, transport, and drainage of the spillover sediment.

**Keywords:** Yangtze estuary; tidal flows; sediment transport; sediment spillover; morphological dynamics; high-resolution; numerical model
