Abstract
It is easy to estimate the volume of the water in dams and plan its use. However, in the arid area, due to the low vegetation cover, the soil erosion in the catchment area is quite serious. The eroded soil enters the reservoirs, then, settled as sediment and reduces the water storage capacity of the dams. However, due to the financial reason, countermeasures such as dredging are not carried out in a lot of cases, especially in developing countries. One of the inexpensive ways to reduce the sediment amount is density current venting, discharging the flood turbid water downstream as density current. Whether the flood water forms the bottom density current depends on the temperature and the concentration of suspended solids of river water. Therefore, in order to optimize reduction in loss of water resource, the standard for decision making opening/closing of the dam gate is required. For this study, Joumine dam, located in the north of Tunisia was selected as study site. Two rainy seasons gave different amount of precipitation and different volume of run-off of the river. Then, the numerical experiment with the hydraulic computational simulation model was carried out. The water temperature and the concentration of the suspended solid of river inflow which changes depending on the scale of river inflow; these are the parameters that decide the density and varied as experimental condition for finding the threshold between bottom density current and diffusing in the middle. The result shows that the influence of the change of the water temperature on the form of flood water is not so strong. It is defined mainly by the scale of the flood and its maximum concentration of suspended solids. In cases that the maximum flow rate is above 40 m3/sec, the bottom density current is formed.
