Sediment deposition is an issue affecting many rivers. To oppose it, sediment withdrawals are often used. However, this practice can trigger further problems in river and coastal sections but, on the other hand, periodic removal of deposited sediments can reduce flooding risk. Also, these sediments can be used for beach nourishment. Therefore, before carrying out a sediment withdrawal, it is necessary to analyze the whole basin to evaluate the consequences for the sediment balance. This paper describes a methodology to evaluate the effects of river sediment withdrawals through a case study on the Amendolea River, a torrential river in southern Italy. In particular, the methodology is divided into three main phases. The first phase was developed with GIS software in order to perimeter and to morphometrically characterize the river basin and its hydraulically and sedimentologically homogeneous sub-basins. The second phase was developed using the HEC-HMS software in order to evaluate the hydrological balance of the basin and its sub-basins. The last phase was developed using the HEC-RAS software (through the SIAM model) in order to identify the areas in erosion, in deposition and in equilibrium. Moreover, through this model is possible to identify the sections where sediments can be withdrawn, and to estimate the possible morphological river changes due to withdrawals. In this case study, the sediments will be taken from the sections where the bottom has elevations near or above those of adjacent lands, such as to increase the flooding risk. Sediment withdrawals will be taken without eroding the bottom and at a distance from the river banks that does not unstabilize them. Finally, the methodology described in this paper is based on the joint use of various open source software and can be used in any other river with hydrological regime similar to the Amendolea River.

The paper describes a case study of the Tuccio River, which models and analyses its discharge, sediment transport and morphological evolution, and also identifies the possible causes of evolutionary and flooding phenomena. The Tuccio River is situated in the southern extremity of Calabria, on the Ionian coast, about 30 km from Reggio Calabria. Adjacent to the river there is a town (Melito Porto Salvo), an aqueduct, and varied economic activity, most of which is related to agriculture and breeding. This is an interesting case study because the riverbed has displayed several morphological changes, many of which were recent and related to the construction of hydraulic works. The entire riverbed study area was divided into two subsections. The downstream subsection is about 3.5 km long, it is heavily anthropised and has an elevation from the riverbed. Flooded areas were evaluated for this section. The second subsection is located about 10 km upstream from the river mouth, its length is over 3 km long and it is characterised by an erosive phenomena. The sediment transport in the section was modelled and the modelling became complex. In fact, the following software was used: MapWindow (to characterise the river basin), Google Earth Pro, QGIS and the GPS Visualizer application (for the reconstruction of the DEM), HEC-HMS (for hydrological modelling), HEC-RAS2D (for hydraulic and sediment transport modelling). From the results of the HEC-RAS2D modelling it was possible to observe that in the mountain section, 50,000 t/year were eroded on average. Moreover, a significant percentage of this material was deposited downstream. This situation, together with the presence of hydraulic structures, caused an elevation of the river bed, with an increase in flood risk. In conclusion, it is possible to state that large-scale modelling as described above is particularly useful for an effective understanding of river dynamics.