CS(AR)-3/98-99 : Development of geomorphological instantaneous unit hydrograph for Myntdu-Leska basin

Abstract

Instantaneous unit hydrograph (IUH) serves as a versatile tool for the estimation of flood hydrograph of a basin due to complex storms. Since the conventional methods of development of IUH such as Nash and Clarke method require adequate rainfall and runoff data, which are not very common for the watersheds in India, an approach capable of deriving IUH from geomorphological features has been used.

According to the theory of GIUH (Gupta et al., 1980) rainfall that occurs over a basin is assumed to be composed of infinite number of non-interacting drops of uniform size. After spending some time in one state (channel or overland region) the drops make transitions from one state to the other to reach the basin outlet. Therefore the time distribution of one drop chosen at random from the basin defines the IUH of the basin.

In this study a GIUH model is developed using the generalised theory. Assuming one parameter exponential time distribution for the movement of drops in every state the functional relationship is developed. A general-purpose software is developed for the model. The model is capable of directly estimating the DRH from the net effective hyetograph using, the geomorphologic parameters of a basin of order less than or equal to I 7.

The rainfall-runoff data of Myntdu-Leska basin of Meghalaya are used in this study for calibration and validation of the model. The average hyetographs of two storm events of this basin are used to estimate the DRH. The comparison of estimated to actual hydrograph indicates that the response of the GIUH model gives a higher and delayed peak discharge. However, the total runoff from the basin matches with the actual values.