Three geomorphological rainfall–runoff models based on the linear reservoir concept

Three geomorphological models, based on linear reservoirs cascade, are developed; two of the models are unit hydrograph (UH) models and one contains a non-linear routing approach. In the first UH model, each sub-basin is represented as a cascade of equal linear reservoirs (Nash's model) which directly discharges to the watershed outlet through a linear channel. In the second UH model each sub-basin is represented as a linear reservoir arranged in a sequence based on the drainage network. For both unit hydrograph models, parameters are explicitly derived, which make the models simple and applicable for real world problems. In the third model, output hydrographs of the sub-basins are calculated by the Nash model but with consideration of geomorphological properties of the sub-basins. Then, the obtained hydrographs are routed through the main channel using a non-linear kinematic wave model. Combination of the kinematic wave routing model (a non-linear routing model) and the Nash model (a linear lumped model) makes this third model more appropriate for runoff modeling.Two important properties of these three models are that they consider the effect of watershed geomorphology and include only one parameter which can be estimated using observed rainfall–runoff data. GIS tools are used for determining the watershed geomorphological parameters. The results of these models are compared with the Nash's black box and the geomorphological SCS models for the Amameh watershed, Iran. Although the results show that the proposed models yield good efficiency in rainfall–runoff modeling, the semi-distributed routing ability in the second and third models produces better results.