Flood Estimation by Various Techniques for Small and Large Catchments

Rainfall runoff relation is very complex and depends on so many factors which require numerous assumptions. Misleading results may be obtained due to over simplification of the process. The various formulas developed for estimation of peak flood discharge are generally based on single geometric parameter, the catchment area which does not reflect true discharges on which hydraulic structures like protection gabion walls, weirs, protection embankments, small irrigation weirs built on torrential flood channels, culverts and bridges are designed. This results in loss of precious money of the state and repeated rehabilitations. This paper presents a procedure for estimating the peak flood discharge. A novel regional mathematical rainfall-runoff model was developed by full convolution of the synthetic unit hydrograph known as Snyder Method extended to include design return period of the selected storm and aerial reduction factor analysis. The model was tested against actual stream flow records by incorporating the flow records in the form of a regional flood frequency curve. The Synthetic Unit hydrograph and the design storm are related to find flood hydrograph corresponding to the design storm which may be routed through the hydraulic structure. Finally the developed mathematical model was analyzed for variation with respect to parameters of which it is composed of. The results were found within satisfactory limits of statistical tests.