| Based on the water level data of East Taihu Lake on August 1984, and the lake current data of Taihu Lake on September 1993, this paper discusses application of the method of numerical inlay to set up an inlay-mesh model of the characteristics of East Taihu Lake's wind-driven currents in various wind regimes.
Taihu Lake (30°55'40" - 31°32′ 58"N and 119°52'32" - 120°36′ 10"E) is one of the famous five fresh water lakes in China, and the largest lake in Jiangsu Province. East Taihu Lake is a shallow Water bay on the east part of Taihu Lake, and has area of 130.0 km2, maximum depth of 1.3 m, mean depth of 0.9 m and volume of 1.81 ×108 m3.
Based on the shallow water characteristics of Taihu Lake, the continuity equation and the momentum equations in Cartesian coordinates can be written as
(See PDF)
where Δ is Laplace operator. Here (x, y, z) form the right-hand coordinate system (x is eastwards, y is northwards, z is positive upward with the origin at the lake surface), u, v the horizontal velocity component, f the Coriolis’ parameter which can be assumed to be constant, g the acceleration of gravity, vn the vertical eddy viscosity, h = h(x, y) is the water depth, E the amplitude of lake surface waves.
The boundary conditions are given as (Equations here, see the PDF)
where LI is the coast of Taihu Lake, n the vector normal to the surface of the coast of Taihu Lake, V= (u, v) the lake current. (Equations here, see the PDF)
where L2 is the coast of East Taihu Lake, n has the same meaning with that in formula (2), VR(t) the lake current on the water boundary.
The results showed that the wind on the lake area determines the water current types and distribution; that opposite direction winds cause the opposite rotation gyres. The direction of wind-driven current is almost the same as the wind direction during the early period of wind forcing (Fig.1). The stable wind-driven current is the resultant combination of some gyres and coastal currents in the lake (Fig.2). In the case of NW wind, the water of West Taihu Lake flows into East Taihu Lake, and generate some gyres there, so that the polluted water from West Taihu Lake may remain in East Taihu Lake. In the case of SE wind, the water of East Taihu Lake flows into West Taihu Lake. In this case, East Taihu Lake is not influenced by the polluted water of West Taihu Lake. Wind-driven current is the important factor in summer which causes the water quality of East Taihu Lake to be of higher quality than that of West Taihu Lake, and the cyanobacteria bloom in West Taihu Lake to be heavier than that in East Taihu Lake. |
