The relationship between suspended sediment settling velocity and water table sinking rates in intermittent lakes in karstic depressions

The conditions for sediment accumulation in the intermittent lakes of subsidence dolines were modelled in laboratory. For a given water table sinking rate we investigated the grain size and settling velocity of the sediment that is deposited in the basin. Two types of suspension were made that had natural-like characteristic features. In both types, the size of the single-grained, solid material was smaller than 0.063 mm and their concentration was 0.2 m/m %. One of the suspension types was also loaded with shredded vegetable residues in a concentration of 0.05 m/m % because vegetable residues occur in the intermittent lakes of dolines and in the sediment of karstic depressions too. The sedimentation rate was determined in a measuring tube for both concentrates in a water depth of 5.0, 7.5 and 10.0 cm. The sedimentation speed was greater in all water-layer thicknesses in the suspension that contained vegetable waste than in the system that only contained clay. The presence of vegetable residues increased the sedimentation rate thus, the quantity of the deposited material too. It can be concluded that sedimentation occurs in the sediment basin if the sedimentation speed of the grains of the suspension is greater than (or equal to) the velocity of water table decline in the basin. This nature of sedimentation can be regarded as a characteristic of the lakes of the bearing karstic depressions. Thus the sedimentation of the suspended material of the lake and its quantity is determined by the velocity of water table decline of the lake.