CS(AR)-16/96-97 : Application of HEC 2 programme for water surface profile determination of river Digaru at Sonapur, Assam

Abstract

Flow regime of any river for different discharge condition is essential to the water resources engineers, planners and managers. To know the depth of flow at different downstream reaches water surface profiles are computed using the information on the channel geometry and roughness coefficient for the river reach. Water surface profiles can be calculated by different methods. The most common and simple method is to calculate the water surface profile by standard step method in which profile is calculated reach by reach. The programme HEC-2 calculates water surface profiles for gradually varied flow by standard step method. It computes the water surface elevations and related hydraulic parameters at all locations of interests for given flow values. The data needed to perform these computations include flow regime, starting elevations, discharge, loss coefficients, cross section geometry, reach lengths etc. The effect of obstruction such as bridges, weirs and other structures in flood plain can be studied. In a single run, upto 14 profiles using the same cross section data can be computed. The programme can take into account the reduction of the flow carrying capacity due to encroachment of flood plain. The computation of water surface profiles in the tributary system, if necessary can, be made after the computation of the main stream. The Manning' "n" values for flood plain and channel can be varied.

In this report the programme HEC-2 has been implemented on river Digaru to compute water surface profile for several discharge conditions. In this reach, two bridges have been considered. The computed water surface elevations, critical water surface elevations, energy grade elevations and slope, velocity in the channel, flow area, top width and Froude Number in the reach are hereby reported in this report.