Development and evaluation of extreme value type-I unit hydrograph model

Hydrologic data of Gagas sub-catchment of Ramganga reservoir catchment, in Uttarakhand with an area of 506 sq. km. was analyzed to develop unit hydrographs. The extreme value type I distribution function was used to develop unit hydrograph model of the sub-catchment. Model parameters were determined by method of moments. Direct run off hydrographs were developed by convolving effective rainfall values with one hour unit hydrograph (I-h UH) derived by extreme value type I distribution function for evaluating the prediction performance of the model. Quantitative performance based on statistical measures like coefficient of efficiency and absolute relative error in computed peak flow rates were evaluated in order to test the validity and assess the applicability of the model. The average values of coefficient of efficiency and absolute relative error in computed peak flow rates were observed to be 0.92 and 6.76 per cent, respectively. Thus, extreme value type-I unit hydrograph model can be suitably used to simulate the direct run off hydrographs of Gagas sub-catchment.