Study of the evolution of the water quality of the Babar dam (South-East of Algeria) and the impact of the dam failure on the environment

Résumé

This thesis is designed to assess the impact of wastewater, industry and agriculture on the quality of the Babar dam surface water and their environmental impacts. The rupture of this work is also discussed. Environmetric techniques such as cluster analysis, principal component analysis, and factor analysis and time series analysis were used to evaluate variations in surface water in the Baber watershed. A total of 21 samples were collected. Eleven parameters were determined on every sample representing three different sampling stations. The salinity in the Eastern part (S1) with high TDS, Western part (S2) with low TDS and in the dam (S3) with intermediate TDS. The water type is SO4- Na for S1, for S2 it is HCO3-Ca-Mg and SO4-Ca-Mg, mixed water in the dam. In the cluster analysis, seven variables were classified into two clusters controlled by SO4 and 21 samples are grouped into 3 statistical groups coinciding with the station S1, S2 and S3. Factor analysis indicates two factors, which explained 87% of the total variance in water quality data set. Two factors which are salinization and sulfates explain 73% and 14% of the total variance respectively. Time series analysis showed that Ca, Mg, Na, Cl and SO4 have very similar trend with TDS and K have similar pattern to NO3. It suggests that five components control TDS. K and NO3 resulted from fertilizers and domestic sewages inputs from the tributaries of river. The temporal evolution of the physico-chemical parameters was followed for nearly 39 months, which showed that most of the trends were negative except for K (41.56%), NO2 (5%) and NO3 (35.62%). The use of potash fertilizers and the dumping of discharges from villages directly into the dam basin is likely to result in an increase in K +. The increase in NO3 is mainly due to fertilizer input and nitrification of ammonium (-61%) which was accompanied by low dissolved oxygen contents (-7.5%). A failure analysis of Babar dam on WADI EL ARAB was performed to demonstrate the impact of the flood wave and velocities on the four villages downstream of the dam as Hella, Kherenne, Chebla and El Oueldj. This model is dedicated to the description of the floods at the dam following a breach in the dike. The main factors taken into account in this simulation are: the flood water level and the flood hydrograph. This flood risk analysis succed results indicating that the maximum flood wave flow recorded at the breach is 9253.02 m³ / s), and is beginning to minimize downstream of the dam along the Oued El Arab where it arrived at the last village with low flow (Qmax = 1110.64m3/s). This simulation allowed drawing the risk map which shows the areas threatened by flood wave that would result from a total rupture of the work, and consequently can be developed a plan of security measures to moderate as much as possible the consequences of the floods. A sensitivity analysis was conducted to see the parameters of impact of the breach on the dam failure scenario, it confirmed that these parameters as formulation time, breach width and side slope have a great influence on the dam failure scenario.

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