Flood forecasting in the watershed of Oued Dis Sebaou) using the FDFT method
Rainfall-runoff modelling in the case of flood forecasting may be studied by the first difference of the transfer function (FDTF) method, which is an extension of the unit hydrograph approach. In contrast to other methods, the FDFT method simultaneously provides both the transfer model by its first difference and an excess precipitation series. The principal advantage of the difference formulation is the diminution of the autocorrelation between successive flow data and the transfer function coefficients. The compilation algorithm proceeds iteratively by resolving alternately a multievent system which identifies the transfer function, and a deconvolution system which assesses the excess precipitation series event by event The initiatization is done with the total precipitation as a first approximation of the excess precipitations, since the results are only dependent on flood variations. The algorithm convergence is easily established if the various constraints are applied (positive values for the transfer function coefficients and the excess precipitations; normalization of the transfer function). Thus, the FDFT method only requires total precipitation and flood data in order to generate the transfer function and quantify the excess precipitation. It doesn't require that the production function be specified. once the Transfer fonction is calibrated and the excess precipitation estimated, the production function adjustment is carried out by resolving an input-output model type. The FDTF method has previously been applied successfully to simulated data. In the present study, the method has been applied to the Oued Dis watershed (Sebaou, Algeria) in order to test its performance using real data. The transfer function identification results proved satisfactory, but those related to the producton function adjustment were less satisfactory and degraded the overall quality ofthe validation results.