Estimation of River Discharge Outside the Regime of Uniform Flow

The flow discharge computation is based on assumptions about the energy grade line slope and the water level to estimate the stream flow with the hydraulic model of Manning's equation. The purpose of this paper is to improve the river discharge prediction using a modified practical Manning's equation for non-uniform but also for uniform flow conditions by using free surface slope, bed slope, friction coefficient and the flow depth. This paper presents an improvement in the integration of the average velocity in gradually varied flows. To validate the modified equation, experimentations have been carried out in the hydraulic laboratory of Ain Temouchent University (Algeria) for 23 flow discharges through two measurement sections; we have got 46 values of the average velocity, the bed slope and free surface slope. The results compare very well with the experimentations. A very good agreement has been found between measured and computed velocities with a coefficient of determination R-2 (97.91% for section A and 99.45% for Section B) with the normalized RMSE low than 2.4%. This could be a very useful contribution for the literature. No closer-form of this modified Manning equation is available in the literature.