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<p><strong>Abstract: </strong></p> <p>Experimental investigation on flat stepped spillway were conducted with two different width 0.52m and 0.28m on 26.67<sup>0</sup> slope under nappe flow regimes. The study assessed the rate of energy dissipation at the toe of the spillway for unit discharge, q, ranging from 0.00954m<sup>2</sup>/s to 0.078854 m<sup>2</sup>/s for Froude number (F<sub>r</sub>) between 0.5 to 0.85. The stepped chute comprised 10 identical steps having 0.10-m step heights and 0.2-m length. It is observed that the rate of energy dissipation at the step edge was relatively observed to be higher in the wider channel. The energy dissipation rate decreased from 3.81% to 26.135% by decreasing the channel width by 46.15% under same unit discharges. It signifies that the width of channel has certain influence on energy dissipation efficiency of spillway under same slope. Therefore, wider channel should be taken for design of stepped spillway under nappe flow regime. The variation in energy dissipation is due to the variation in mean air concentration between two widths. For further validation of these experimental observations, computational fluid dynamics (CFD) models were also used with k-ɛ turbulence model and0.010 m mesh size. </p> <p><strong>Keywords:</strong> stepped spillway, energy dissipation, channel width, CFD</p>

our society gets huge benefits from the water storage dams, but the consequences are devastating if a dam fails. It causes extensive damage to the life and properties mostly due to short warning time. Important factors governing failure studies are the breach parameters that help to quantify the risk associated with dam break floods. Many empirical equations have been developed for predicting the breaching parameters associated with peak outflow and these equations are generally developed by regression analysis from the record of dam failure data. In the present work, a hypothetical failure of dam is modelled using MIKE 11. The required inputs in terms of PMF, river cross sections, area-elevation-capacity curves, Stage-Discharge data and dam specifications are provided for modelling. Towards this, data from Sarabgarh dam project in Orissa is used to model the breach parameters and propagation of flood waves in the downstream reaches using Mike 11 and other software. The flood hydrograph at different stations are analyzed to estimate the risk of overtopping of river bank and flooding. Besides a sensitivity analysis for various parameters that affects the maximum discharge and maximum water level has been carried out successfully.