5 Conclusion

In conclusion, remote sensing, geological studies, DEM and fieldwork data were used in a GIS to determine a flash flood hydrograph for the Wadi El Abiad sub-catchment. The main channels on the braided alluvial fan of the sub-catchment are blocked by three dykes; one in the upstream of Wadi Naout and the other two are consecutive on the main channel to the east (at Wadi Umm Rasses). Flash flood flow loaded with fine sediments occur on average once every two years. Most of the flow is delivered to the channel are very little. The dyke upstream of Wadi Naout has a sufficient storage capacity, and it will not be fully clogged with sediments during the coming 50 years. On the other hand, the upstream dyke erected on the broader stream (at Wadi Umm Rasses) receives appreciable amounts of runoff and sediment loads. Field observations suggest that the complete silting up of the dyke pool area is imminent before the end of the coming 50 years , therefore the efficiency of these dykes are also being decreased due to deposition of sediment loads associated with the flash floods.