TR-54 : Application of HEC-2 programme for water surface profile determination

Abstract

Depth of flow at various sections are needed for different discharges under different situations. Some of the situations encountered in practice are (i) bridges in the river environment (ii) channel improvement schemes (iii) food plain encroachment etc. Some times it would be necessary to predict up to what extent the back waters would reach by downstream daming or for fixing the FRL for a dam. Also flood plain marking would be needed. In such situations water surface profile computations are made. It is usual practice to use standard step method in such situations.

In USA and other countries a programme HEC-2 developed by Hydrologic Engineering Center, USA is extensively used for the above computations.

HEC-2 can compute water surface profiles for a gradually varied flow. The effect of obstructions such as bridges, weirs and other structures in flood plain can be studied. In a single run upto 14 profiles using the same cross sectional data can he computed. The program can take into account the reduction of the flow carrying capacity due to encroachment of flood plain.

The data requirement includes flow regime, starting elevation, discharge, loss coefficient, i.e. subcritical, super critical etc, cross sectional geometry and reach length. The computation of water surface profile in the tributary system, if necessary can be made after the computation of the main stream. The Manning's "n" values for flood plain and channel can be varies.

The programme is implemented on VAX-II Computer of N.I.H. and tested. The program is used to compute the water surface profile for several discharges in Omar river a tributary of the river Narmada.