الفهرس 
CHAPTER (1): INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Rivers are a major source of water and consequently major civilizations have developed along river banks and on flood plains. The diversion of water from rivers is one of the ancient human activities in the field of hydraulic engineering. Water from river could be diverted either by gravity or by pumping. Intake structures are built to divert water from rivers for irrigation, industrial use, cooling of power plants, domestic water supply and even navigation. As the flow approaches the intake, it is accelerated laterally by the suction pressure at the end of the branch channel. This causes the flow to divide so that a portion enters the branch channel. The portion of flow withdrawn by the branch canal is delineated by a curved shear-layer surface, denoted as the dividing stream–surface. Due to the streamwise curvature of the dividing stream–surface, a separation zone is formed along the inner wall of the branch channel. This leads to the occurrence of a three–dimensional complex flow. It is worth to mention that, water in rivers carries a considerable amount of sediment. Once sediment enters the branch channel, it settles in the separation zone. On the other hand, scour occurs in the high velocity region at the downstream corner. The accumulation of sediment at the entrance of the branch channel might block it and ultimately might lead to the shutting down of the plant to remove the sediment from the power plant intake structure. This will result in the reduction of the flow capacity and requires costly maintenance operations. Furthermore, it could cause disorders to the screens and could obstruct the branch channel bays at lower water stages completely. In addition, due to the streamwise curvature of the portion of flow that is withdrawn to the branch channel, strong vortices occur at the entrance of the branch channel. These vortices induce high levels of unsteady swirl inside the pump column thus affecting the cooling system. Moreover, flow asymmetry might cause structural problems to the pump mountings due to pump and pipe vibration. All these phenomena result in impeller cavitation, uneven impeller loadings, noise, and vibrations thus reducing the efficiency of the pumps. The main variables that influence the flow at diversion are: discharge, bed width, the cross–section shape, the longitudinal slope, and boundary roughness of main and branch channels, intake location, the angle of off–take branch channel, upstream and downstream conditions at the main and downstream conditions at the branch channels, and intake inlet shape and level. Due to the various involved parameters, the design of intakes is really difficult. In the literature, many structures faced several problems as a result of flow diversion such as Kewaunee Nuclear Power Station, USA, [30], El-Sheikh Zayed Expanding station, [13], New Assuit Power Station, [18], El-Nasr channel intake, [1], Baricho Intake, Kenya, [65], El-Walydia Power Plant, [2], Iowa power’s Council Bluffs Power Station, USA, [46], Albuquerque’s main water source, USA, [5], branch channels from the Yellow River in China, [8], water treatment plants in the mountainous areas of western Venezuela, [25], and The Council Bluffs Unit 3 thermal power-generating station, Omaha Public Power District, and Union Electric’s Labadie Station, USA, [47]. It is thus important to maintain suitable flow characteristics at open channel diversion in order to reduce the accumulation of sediment in the diverted (branch) channel, redistribute velocities at the branch channel, and minimize the length and width of the separation zone inside the diverted channel inlet. Designers suggested different techniques to mitigate the problem even though there is no standard design for water intake structures. This is attributed to the fact that each diversion junction has its own flow characteristics and consequently the design must be tailored to the junction conditions. This chapter includes an introduction to the study of the flow characteristics at open channel dividing junctions and the objectives of the study. In addition, it contains lay out of the report. 1.1 STUDY OBJECTIVES The present study was carried out with the objectives of improving the velocity distribution in the tributary (branch) channel, minimizing the area over which separation zone occurs, and reducing the amount of sediment that accumulates in the branch channel. This was achieved by:
* investigating the effect of intake entrance modifications on the flow characteristics at open channel diversions experimentally.
* evaluating the performance of a 2D numerical model [Surface Water Modeling System (SMS)] in simulating the flow at open channel divisions and studying numerically the influence of bed width ratio on the flow features at the dividing junction with sharp or curved upstream corner shapes. The study also aimed to investigate the effect of shape of the upstream and downstream edges of the diverted channel inlet and the bed configuration of Furthermore, it could cause disorders to the screens and could obstruct the branch channel bays at lower water stages completely. In addition, due to the streamwise curvature of the portion of flow that is withdrawn to the branch channel, strong vortices occur at the entrance of the branch channel. These vortices induce high levels of unsteady swirl inside the pump column thus affecting the cooling system. Moreover, flow asymmetry might cause structural problems to the pump mountings due to pump and pipe vibration. All these phenomena result in impeller cavitation, uneven impeller loadings, noise, and vibrations thus reducing the efficiency of the pumps. The main variables that influence the flow at diversion are: discharge, bed width, the cross–section shape, the longitudinal slope, and boundary roughness of main and branch channels, intake location, the angle of off–take branch channel, upstream and downstream conditions at the main and downstream conditions at the branch channels, and intake inlet shape and level. Due to the various involved parameters, the design of intakes is really difficult. In the literature, many structures faced several problems as a result of flow diversion such as Kewaunee Nuclear Power Station, USA, [30], El-Sheikh Zayed Expanding station, [13], New Assuit Power Station, [18], El-Nasr channel intake, [1], Baricho Intake, Kenya, [65], El-Walydia Power Plant, [2], Iowa power’s Council Bluffs Power Station, USA, [46], Albuquerque’s main water source, USA, [5], branch channels from the Yellow River in China, [8], water treatment plants in the mountainous areas of western Venezuela, [25], and The Council Bluffs Unit 3 thermal power-generating station, Omaha Public Power District, and Union Electric’s Labadie Station, USA, [47].