Ephemeral flow modelling in arid regions

Flow hydrographs in arid upland basins, where the runoff is directly related to the rainfall, are simulated by a combination of regression and differential equation techniques. The rising limb of the hydrograph is modelled through a regression analysis and the recession portion through a conceptual analog of discharge from a single leaky reservoir, which is described by a continuity equation and by discharge–stage and storage–stage relations at the basin outlet. A good agreement between observed and model-predicted recession curves was obtained by optimizing the reservoir leakage rate and the initial storage in the reservoir. Best parameter values are physically realistic and best reservoir configuration has leakage that varies as the cube of stage for the initial event of the season in the organised stream network and as the square of the stage for rest of the events. The technique can be applied to the ungauged flow events through parameterization.