Estimation of design low flows for ungauged catchments
2001
Tafa Tulu (Ambo College of Agriculture, Ambo (Ethiopia))
The probabilities and return periods of recorded low flows of four catchment areas were analysed. Using an extreme value (Gumbel Type I) distribution, low flow frequency curves were plotted and extended to 100-year return period. For each catchment, low flow forecasting equations were derived from multiple regrssion analyses of rainfall (P), potential evapotranspiration (PET) and soil moisture (Sm) taking some of catchment elements into consideration. The frequency curves of PET, Sm and P were also plotted on extreme-value paper and the curves were extended to 100-year return period. These values were inserted in the derived equations, in which the computed values were very close to the reading obtained from the low flow frequency curves of the catchments. The derived equations can, therefore, be used to estimate low flows of the desired return periods of similar ungauged catchments using certain measurable catchment elements and meteorological data. The obtained equations can give satisfactory help in the planning and management of water development, storage and distribution systems.
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