The influence of spatial wind inhomogeneity on flow patterns in a small lake

A two-dimensional vertically averaged flow model was applied to study the c irculation patterns in Lake Belau (Northern Germany). The lake is north-sou th oriented, with a maximum extension of 2.2 km and is situated in a dead i ce hole with steep slopes on the east and west coasts. A parr of the coasta l area is covered with forest, creating a strong shelter from prevailing so uth-westerly winds. The system of shallow water equations is discretized wi th the modified Utnes (1990) scheme which is characterized by a semi-decoup ling algorithm. The continuity equation is rearranged to Helmholtz equation form. The upwinding Tabata (1977) method is used to approximate convective terms. Extensive wind (more than 60 observations) and current measurements (5 points) conducted all over the lake enabled us to verify the simulation results with observations. Under spatially homogeneous wind conditions the model predicts a two cell circulation system, that covers most part of the lake. Taking the spatial variation of wind speed due to shelter into accou nt, the flow field changes drastically. The two cell system is replaced by one large cell, with a strong reverse jet along the western shore. The shel tering effect of the surrounding hills and vegetation have a pronounced eff ect on the circulation pattern. It appears that in general this fact cannot be neglected in numerical lake flow simulations. (C) 1999 Elsevier Science Ltd. All rights reserved.