Analysis of a unit hydrograph model based on watershed geomorphology represented as a cascade of reservoirs

In this paper, a new unit hydrograph (UH) method is proposed and analysed. The method represents the watershed as a cascade of reservoirs, which in turn are determined from watershed morphology. This cascade can be obtained in two different ways: (i) from the sub-watershed network structured along the drainage network and (ii) by areas limited by iso-distance curves to the outlet point. The two most important characteristics of the UH model are: (a) it explicitly includes the watershed morphology in its formulation and and (b) it depends on only one uncertain parameter. The model has been applied to a small 169 ha agricultural watershed located in Central Navarre (Spain), where rainfall and runoff data were available. Model analysis focused mainly on two aspects: a sensitivity analysis of the uncertain parameter, and the influence of the watershed division procedure and detail level in watershed division. Results showed that the model response was similar when using the two above-mentioned approaches. Also, when considering different detail levels in watershed division, there were no differences in model response once a threshold value was exceeded. The model was sensitive to variations in the value of the uncertain parameter.