Testing a distributed approach for modelling sediment delivery

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Abstract
Both the theoretical basis of a distributed approach to sediment delivery and its agreement with basin sediment yield measurements are tested. At first, by using morphological data of five Apulian and four Calabrian basins, the applicability of a theoretically-based relationship for evaluating the sediment delivery ratio of each morphological unit SDR h, into which a basin is divided, is verified. Using the morphological data of the nine investigated basins, the sediment delivery relationship, i.e. the relationship of the basin sediment delivery ratio SDR Wand SDR h, is tested. The analysis showed that the relationships, proposed by Ferro (1997), establishing the dependence of the a coefficient of the sediment delivery relationship on the median travel time and on a drainage density index are yet applicable. The influence of the scale of the basin topographic map on the sediment delivery distributed approach is also studied. The analysis showed that the ratio between the a coefficient and the median travel time is scale-invariable while the link between the coefficient a and the drainage density index has to be re-calibrated because the drainage density index is dependent on the map scale used. Finally, the predictive capability of the sediment delivery distributed model is validated using the sediment yield measurements carried out in three small Calabrian basins and in the Apulian Triolo basin. The analysis showed that the model accuracy is dependent on the temporal scale used and the model reliability increases from the event to the annual scale.