DP-5 : Flood routing (Muskingum cunge procedure)

Abstract

Flood routing in a natural river is complicated by the presence of irregularities of cross-section and by the presence of lateral flow. It is now possible to quantify the effect of irregularities in the width and the corresponding effect of storage caused by them. These irregular sub reaches act as a series of reservoirs and provide attenuation.

Cunge brought out certain salient features of Muskingum method and stated that the attenuation seen in the routed flow using Muskingum model is just because of the numerical error and not due to the ability of the model. He showed that the finite difference approximation used in Muskingum method is also an approximation of a diffusion equation using Taylor series expansion. Cunge has developed a method of estimating the attenuation parameter using average width and slope of a river. R.K.Price worked further and improved it to include the variations in the width and slope. The routing parameter x is related to the attenuation parameter.

Based on the value of attenuation parameter and wave speed 'C' using the recurrence relation available in Flood Studies Report, Vol.III of National Environmental Research Council, London, a FORTRAN programme capable of routing the flow was developed in National Institute of Hydrology, Roorkee with following features in addition to routing: (a) finds the attenuation parameter given physical features viz. the widths, slopes, and reach lengths for a given discharge, (b) the lateral flow is obtained as the difference in observed inflow and outflow quantities and distributed as per the ordinates of either inflow or outflow as opted, and (c) the results are plotted in addition to Printing of the discrete value.

The programme has been explained fully in the documentation with flow Chart. The input specifications and the output descriptions are also given. An example using the data of a flood in the reach between Mortakka and Garudeshwar on the river Narmada is also given in Appendix 1.