LAKE NASSER FLOOD ANALYSIS

Abstract

The Nile River has undergone a wide variety of floods over history. This has had some major effects on the river water levels and discharges. The purpose of this research was to simulate flood behavior and analyze the effects of the resulted water levels which should not exceed 182 m for dam safety considerations. It also includes the simulated water discharges due to different scenarios and their effects on Lake Nasser storage capacity, hydraulic structure safety and bank overtopping. A numerical model (one dimensional model), developed by the author, was used for this analysis. Different parameters were used to form the model input, such as developed relationships for Lake Nasser water surface area at different water levels and volumes by using satellite remote sensing images and hydrographic survey maps of Lake Nasser. Toshka spillway discharges are related to different water levels upstream HAD using regression equations. The model uses the possible inflow discharges, different outflow conditions and water level values for the simulation analysis. It takes into account the Sudanese water abstraction and different water losses such as seepage and evaporation. The numerical model deals with both the current condition of not operating ELSheikh Zayed Canal and the future condition of the water outflow into El-Sheikh Zayed Canal to simulate the most critical cases. El-Sheikh Zayed Canal operation can have some effects for both on the water levels upstream HAD and lake storage, especially during low floods. Different routing scenarios were considered during this analysis, such as the annual simulation of different floods and the multiple- year simulation for different consecutive floods for a period of one to ten years of successive low and high inflows. The process of raising and lowering the initial water level upstream HAD at the beginning of the water year were analyzed and some proposed operation rules were proposed. Raising water levels at the beginning of the water year will have a positive effect on the lake storage and water availability in case ofthe multiple years of low floods. Lowering upstream water levels at the beginning of the water year, to avoid higher risks for the future high floods did not major effects on the maximum simulated outflow values downstream HAD or their durations for inflows 130 and, 150 bcrnly. Using movable gates for Toshka Spillway ts recommended to enable more control on flood water level to be able to discharge more water during high floods to ensure safety and to save more water in low floods. Different probabilities of possible Nile floods were evaluated. Different exceeding and less than probabilities for different possible floods were estimated. The historical data were used to perform flood forecasting for the future floods by using different statistical forecasting methods. The effect of the resulted outflow from different scenarios on a case study such as reach 4 was studied. This reach was selected for many reasons such as the frequent water overtopping of the two banks during the past high flood years and it is the longest reach along the Nile River. In addition to these factors, Reach 4 is exposed to human interventions, bank erosion and navigation bottleneck. The mathematical model HEC-2 was used to compute the water surface profile along the reach using the surveyed cross sections. The calibration results show close relationship between the observed and the predicted values. The effect of different flood conditions on the water surface profile was evaluated and some areas subjected to inundation were determined