The construction of Ethiopian Dams, GERD (Grand Ethiopian Renaissance Dam) and Karadobi, will definitely cause many impacts on Sudanese dams on the Blue Nile during initial filling and full operation of the two Ethiopian dams, respectively. The flow of the Blue Nile , entering Sudan (upstream Roseires Dam), will be regulated so that the flood hazard will not be there, as the Blue Nile flow will be in the range (100-200 million cubic meter per day) compared to the high flood discharges (800-1000 million cubic meter per day) during the last period of August. A mathematical model has been developed using GIS software tools (HEC-GeoHMS and HEC-HMS 4.0) and Rainfall characteristics data for 12 sub-catchments for Blue Nile system within Ethiopia. This model has been used to forecast water inflows coming at GERD before and after the construction of Karadobi dam. Therefore, releases downstream GERD that entering Sudan will be known. It is worth mentioning that the GERD full capacity is 74 Billion cubic meters and the generated power is 6000 MW, as Karadobi dam which has not been constructed yet with full capacity of 40.22 Billion cubic meters and the generated power is 1600 MW.

Dr.Adil Mohamed Elkhidir*, Ahmed Hassan Aboalbasher Ali**, Ahmed Adil Eltayeb Abd-Elnour**, Osama Gism Elseed Bahkeet** *Associate Professor, Civil Department –Faculty of Engineering- University of Khartoum ** Graduated in 2017 - Civil Department –Faculty of Engineering- University of Khartoum