VARIATION IN SEDIMENT CONCENTRATION AND WATER DISCHARGE DURING STORM EVENTS IN TWO CATCHMENTS, NORTHEAST OF ALGERIA

The relation between concentration and discharge is not normally homogenous during the storm event, often producing hysteretic loops. In this study relations between sediment concentration and water discharge for hydrologic events are studied by analyzing temporal graphs (discharge and concentration versus time) in terms of spread and skewness. The hysteresis types of the discharge and concentration of 170 storm events have been analyzed to identify the relations between hysteretic loops and the associated controlling factors in the Saf Saf and Kebir West basins. Surveys of suspended sediment concentration and water discharge are being carried out at gauging stations. The selected storm events are based on samples having many sediment concentrations at water discharges. Comparing C/Q ratios at a given discharge on the rising and falling limbs of hydrographs is providing a consistent, reliable method for analyzing C-Q relations. Four common classes of such relations are determined such as single-valued line, clockwise loop, counterclockwise loop and figure eight. The plot of points has exhibited a hysteresis loop which is explained by the variability of sediment concentrations during storm events and seasonal effects. The most frequent floods at Saf Saf and Kebir West rivers are clockwise and single-valued line (62% and 59% of floods respectively) that have brought 73% and 81% of the total sediment flux. Intra-annual variability is very high. Over 31-years, the three biggest floods at each Saf Saf and Kebir West rivers have cumulated 97% and 68% of the total sediment flux and are of two classes