Evaluation and Update of Two Regional Methods (ORSTOM and CIEH)

The ORSTOM and CIEH methods are the most popular method used in West Africa to estimate the design flow, that is needed in the design of hydraulic structures. However, these methods, based on hydrological data collected before 1965 and 1983 for ORSTOM and CIEH respectively, showed some shortcomings and deviations in the estimation of these forecasts. This study, therefore, assesses the design ow on data collected from some watersheds in Benin and Niger using a frequency analysis. These estimations are therefore compared with estimations obtained using the ORSTOM and CIEH methods on the same watersheds. As result, we observe an important under-estimation of the flows with the ORSTOM method, whereas the CIEH method gives higher values. The use of the log linear regionalization method, considering the area of the watershed basin and the global slope index, gives very interesting results and good perspectives of estimation on few or no data watersheds basins. . . .