Suitable Conservation Techniques for the Nyando River Catchment Area. Lake Victoria Basin. Unpublished Study Report

KIPNGETICH PROFBIAMAHELIJAH. "Suitable Conservation Techniques for the Nyando River Catchment Area. Lake Victoria Basin. Unpublished Study Report.". In: Bloemfontein, South Africa. Kisipan, M.L.; 1999.


In semi arid Kenya, the occurrence of flush floods and soil erosion on agricultural watersheds is attributed to intense rainstorm events of short duration. Thus when agricultural watersheds have no erosion control structures in place, the generation of direct runoff would increase with cultivation. Of the two components of runoff namely, runoff volume and peak runoff discharge, the consideration of peak runoff discharge rate is critical to the design of effective hydraulic structures for controlling floods and soil erosion. In order to accurately predict a watershed's peak runoff discharge, it is important to select a model that is deterministic and yet simple to use. The model should be able to consider the time distribution of runoff response as influenced by Watershed characteristics. The time to peak runoff discharge is largely influenced by the time of concentration. The time of concentration depends on the shape, size and relief of the watershed. In Iiuni Watershed, the Nash model, a parsimonious deterministic model, was selected to predict peak runoff discharges. This model uses the instantaneous unit hydrograph principle to simulate the direct runoff hydrographs and estimate peak runoff discharge. The Nash model was applied using input parameters derived from the watershed's rainfall-runoff characteristics. The results obtained showed that the Nash model was good in predicting peak runoff discharges. This statistic of comparison, R2 (coefficient of efficiency) for the model was above 70% for the model which is indicative of good model prediction of peak runoff discharge (Nash and Sutcliffe, 1970). From this analysis, the Nash model is recommended for the estimation of peak runoff discharge from un-gauged agricultural watersheds in Kenya.




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