The numerical study of water exchange in the Xiangshan Harbour of Zhejiang Province, China

Based on a well-verified three-dimensional tidal flow mathematical model, the Xiangshan Harbour is divieled into seven areas, seven different dissolved conservative materials are used as tracers, an advection-diffusion water exchange numerical model is established, and an associated matrix method is applied to describing water exchange characteristics between districts, and between these districts and the sea. The concentration distribution of different tracers, is used to calculate water exchange matrixes of the 15th, 30th, 45th,60th and 80th day. According to the water exchange matrix in each moment, among the seven regions of the Xiangshan Harbour, exchanging with the outside water in Region I is the fastest, which has an exchange rate of 85% in 15 d, while the slowest Region Ⅶ only reaches about 10% after the same duration. In Region Ⅲ (the Xihu Inlet), Region Ⅵ (the Huangdun Inlet) and Region Ⅶ (the Tiegang Inlet)the water exchange speed is slow between these regions and the outside water,but is still significantly faster than other regions. The fastest is in Region Ⅵ, in which the original water accounts for 1.5% on the 15th day, and 0.3% on the 60th day. And the slowest is in Huangdun Inlet Ⅳ, in which the original water accounts for 22.7% on the 15th day, and 4.4% on the 60th day. Furthermore, the matrix suggests that water exchanges between the Xihu Inlet and the Huangdun Inlet and three inner inlets are very weak.