The present work deals with flash floods, hydrogeological and hydrogeochemical conditions of Wadi Al-Qarn. This basin is subdivided into seven hydrographic sub-basins. The studying of the hydromorphometric parameters of these sub-basins shows low bifurcation ratios and high values of drainage densities and frequencies, consequently more possibilities for flash floods. W. Atallah and W.Zydun sub-basins are nearly circular in shape and they have high values of relief and ruggedness number and acquire the highest values of maximum runoff. Therefore, they are classified as very dangerous sub-basins. Under such conditions the construction of alternative barriers or boulder dams at the upstream parts of these basins will minimize flooding hazards and give more chance for groundwater recharge and improve groundwater quality.
The main water bearing formations within W. Al-Qarn basin are the basement rocks, the Nubian sandstone and the Quaternary aquifers. The basement rocks represent the main catchement area and watersheds. The Nubian sandstone aquifer exists under confining conditions and the present wells are characterized by natural flowing. The upward elevations of water levels in wells, decrease in electric conductivity, water salinity and concentrations of ions in water samples after the intensive precipitation indicate that the aquifers are mainly recharged during times of torrent floods. The hydrochemical compositions of the water samples indicate that the basement rocks and the Quaternary aquifers belong to Na2 SO4 water type of meteoric origin, while the Nubian sandstone aquifer reflects Mg Cl2 water type of marine origin diluted with meteoric water percolation.
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