Testing Sediment Connectivity at the Experimental SPA2 Basin, Sicily (Italy)

The concept of sediment delivery can be used as a measure of sediment connectivity, and it can be linked to the structural connectivity (morphological unit, slope length, slope steepness, travel time) of a basin and to the hydrological connectivity (rainfall-runoff processes at morphological unit scale). In this paper, the sediment connectivity concept was tested at basin scale applying SEdiment Delivery Distributed model, which takes into account the hillslope sediment transport, and using sediment yield measurements carried out at SPA2 experimental basin (Sicily, Italy). For the SPA2 basin discretized into morphological units, the SEdiment Delivery Distributed model was first calibrated at event scale using the sediment yield measurements carried out at the outlet of the experimental basin in the period April 2000-March 2015. The model calibration was used to determine the relationships useful for estimating the unique coefficient βe of the model appearing in the expression used to calculate the sediment delivery ratio of each morphological unit. The developed analysis allowed establishing that the functional connectivity is dependent on the magnitude of erosion events, and for low events the sediment connectivity is only governed by its structural component. Then, at annual scale, the model was calibrated for the period 2000-2015, and relationships for the estimate of the coefficient βa taking into account the intensity of erosion events occurring in each year were determined. Finally, a physical interpretation of β coefficient at the two temporal scales (βe, βa) and its link to sediment connectivity was proposed.