In this study, HEC 2 programme has been implemented on river Digaru to compute flow regime or the water surface profile for various discharge conditions. In this reach, two bridges have been considered to compute water surface elevations, critical water surface elevations, energy grade elevations & slope, velocity in the channel, flow area, top width and Froude Number.

The depth of flow at different downstream reaches for various water surface profiles is computed based 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 being the 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 and reach lengths.

The effect of obstruction such as bridges, weirs and other structures in flood plain can be studied. In a single run, up to fourteen 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. Also, the manning ‘n’ values for flood plain and channel can be varied under this programme.

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