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This research study the rate of energy dissipation losses taking place in various types of stepped spillway geometries (end sill at all steps, inclined at all steps, inclined between two steps, end sill between two steps, combination of inclined and end sill on the stepped spillway starting with end sill and combination of inclined and end sill on the stepped spillway starting with inclined ). The models were made from wooden materials each having a chute angle of 45 , model height of 24cm, step height 4cm and number of steps 6. Variable flow discharges were applied on each model geometry and the hydraulic parameters were measure and energy dissipation rates were calculated and compared. The result shows that the effect of steps geometry on energy dissipation on stepped chute is significant as the ratio of energy losses to the upstream energy varies from 49% to 70%. The result also indicated that the energy dissipation rate on model C (inclined between two steps) is highest among all the test models. Equations were developed for predicting energy dissipated over the spillway and for calculating the flow rate in stepped chute. Results of the modelled equation were compared with that of experimental studied. The percentage difference between between the values predicted by the modelled equation and that of actual experimental values range 1.10% to 5.12%. this shows that there is a good agreement between the predicted values and experimental values.



1.1                                                  BACKGROUND OF THE STUDY

Recent advances in technology have led to the construction of large dams, reservoirs and channels. This progress has necessitated the provision of adequate flood disposal facilities and safe dissipation of the energy of the flow, which may be achieved by providing steps on the spillway face. Stepped Spillways are been used more than 3000 years ago. Stepped spillway is generally a modification on the downstream face of a standard profile for an uncontrolled ogee spillway. At some distance in the downstream of the spillway crest, steps are fitted into the spillway profile such that the envelope of their tips follows the standard profile down to the toe of the spillway. A stepped chute design increases higher energy dissipation and thus reduces greatly the need for a large energy dissipator at the toe of the spillway or chute (Thandaveswara, 2005).

A spillway is usually the most important appurtenant facility to a dam. The function of dam spillway is to provide an efficient and safe means of conveying flood discharges to the downstream channel. The spillway design primarily depends on the dam type and location, reservoir size and operation. Spillways can be classified based on (i)their function (main, emergency, and auxiliary), (ii) their hydraulic type {free over fall,overflow,chute,siphon etc.}, and (iii) their mode of control (ungated and gated). While the number of new dams under construction in the world is declining, the Number of existing dams that have had to be upgraded to meet current hydraulic and seismic criteria are increasing. This is especially true for smaller embankment dams that have been judged to have inadequate spillway capacity and are unable to....

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