Development of a distributed catchment model for Kolar basin - A research report by National Institute of Hydrology

In this study, a spatially distributed unit hydrograph was developed for the Kolar basin in Madhya Pradesh using Arc Info GIS package. The one-hour distributed hydrograph was determined for the basin using S hydrograph technique from the time-area diagram of the basin.

The time-area diagram was developed by compiling the time of concentration of unit incremental intervals against the drainage area. The time of concentration was determined by dividing the flow length with flow velocity of the basin.

The error free Digital Elevation Model (DEM) created by Arc Info GIS was used to generate the drainage flow network. It was assumed that every cell in the DEM contains a channel. The flow velocity in the basin was computed by the derived equation by combining the continuity and Manning’s equations.

Curve Numbers were assigned according to the land use and soil type. The largest rainfall intensity block was applied uniformly over the basin to generate different rainfall intensity in each cell according to the Curve Numbers assigned thus resulting in a spatially distributed rainfall excess.

Six rainfall storm events were considered for the simulation of direct runoff hydrographs. The percentages of error of the observed peak flow with the simulated peak flow and the observed time with the simulated time to peak for all storms were computed.

This type of distributed unit hydrograph can be developed for any ungauged catchment without rainfall and runoff data since the development involves watershed hydraulics. The derived unit hydrograph can be used to get the direct runoff hydrograph by convoluting the rainfall excess hyetograph.

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