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Abstract. An application of regression relationships depending on geomorphic parameters is proposed to predict the amount of the average annual suspended sediment yield at different sections of the drainage network. Simple and multiple regression relationships, utilising the drainage density and the hierarchical anomaly index as independent variables, based on data from 20 river basins of different size located in Italy, are here tested. An application is also shown for a small river basin located in central Italy where it is possible to compare the obtained suspended sediment yield estimates with reservoirs siltation data. The results confirm the potential applicability of regression equations for estimating the suspended sediment yield depending on the topological behaviours of the river network. A discussion of the reliability of the method for ungauged basins is also provided, which puts in light the necessity of additional tests to support the application of the approach to small size watersheds.

In the present work, a new simplified model approach for sediment delivery ratio (SDR) assessment is proposed. Modelling and assessing SDR is still an open question. Difficulties rise from the lack of sufficient data availability, on one side, and, on the other, from the inherent uncertainties including spatial variability and temporal discontinuity of the land cover, climatic, hydrological and geomorphological variables involved. The proposed SDR SIM model tries to skip over the limitations observed in other models generally adopted. A comparison with two different selected models amongst the most widespread simplified models, i.e. the area-model and the slope-model, is showed in application to a wide range of catchments extensions across different landscapes of Italy. The SDR SIM estimates were also evaluated against observed SDR over a validation dataset of 11 basins sparse over different regions of the world. The results showed the effectiveness of the proposed model approach based on easily available catchment parameters.

Sediment connectivity is a major topic in recent research because of its relevance in the characterization of the morphology of river systems and assessing of sediment transport and deposition. Currently, the connectivity indices found in the literature are generally dimensionless and need to be coupled with quantitative soil-loss data for land management and design purposes. In the present work, a simple methodology is proposed to assess two different indices, namely, the simplified connectivity index (SCI) and the specific sediment potential (SSP), based on geomorphometric tools that are commonly available in commercial and open-source geographic information system (GIS) platforms. The proposed metrics allows us to easily assess both the SCI and the SSP as functions of the estimated soil erosion per unit area of the catchment and of the inverse distance of each unit area from the river outlet, this distance being measured along the network path. The proposed indices have been devised to express, respectively, the potential sediment transfer ability and the sediment mass potentially available at a given section of the drainage network. In addition to other parameters used to describe the catchment characteristics potentially affecting the river sediment delivery capacity, the SCI and SSP indices can help to refine theoretical models in order to assess the sediment yield (SY) in ungauged river basins.