SEDIMENT ENTRAINMENT IN KARST BASINS

In this paper, the suspension of sediments induced by groundwater jets in two basins of a karst lake (basin I and II of lake Banyoles, Catal onia) is studied. Field experiments were carried out during the period 1989-1994 to investigate the sediment dynamics within the basins. Dur ing this period, the sediment in basin I (B1) was found to be permanen tly in suspension while the sediment in basin II (B2) remained at the bottom of the basin, except on two occasions when the ground water dis charge increased and caused resuspension. A two-dimensional k-epsilon turbulence model was used to simulate the suspension of the sediment a nd the formation of the lutocline (the interface of the suspended sedi ment). The model predicts a reduction of the turbulent kinetic energy at the lutocline due to the buoyancy flux. This is used to estimate th e inflow into the basins and the maximum height that the lutocline can rise, which is found to depend on the settling velocity, the mean inf low rate and the geometry of the basin. Also, the model is used to pre dict the water circulation below the sediment interface.