Evaluation of physical properties of dredged sediments for beach nourishment.

Many beaches along the coast of Emilia-Romagna Region are eroding, which threatens habitat, property, public infrastructure, and the tourist industry. Loss of sand can be attributed to natural factors such as storms, waves, currents, tides, wind, sand supply and quality, etc. Shortages of sediment can also arise from man-made activities including extensive sand mining of river beds, plus the large-scale destruction of natural shoreline defences for urban and tourist development. Legislative and regulative constraints at national and regional level address these issues toward exploitation of offshore sand deposits to replenish beach erosion occurring at regional scale, but only few deposits are elected as potentially compatible with beach nourishment projects. On the other hand, some hundred thousands cubic meters of sediments regularly dredged from ports located along the regional shoreline, have been and are being disposed in rehandling facilities, namely, Confined Disposal Facilities (CDFs), and could represent an alternative source for beach nourishment material. One of the property of interest in the performance of replenishment/nourishment projects is the physical compatibility between the fill material and the ‘native’ material of the beach. Typically, grain size is the most commonly evaluated in trying to match a fill material with a native material mainly because of its potential mechanical performance within the hydrodynamics of the beach environment. In this paper, a comparison of the grain size parameters of dredged sediments vs. nourishing beach sediments along Emilia-Romagna shoreline is presented. Surface sediment samples were taken from the beach at different depths along Lido di Dante shoreline (Ravenna, Italy) to characterize pre-nourishment conditions. Several representative composite samples were also taken from a confined disposal facility (CDF) located within the harbour area of Ravenna town. Standard grain-size analysis tests were conducted for all samples to obtain their grain-size distribution curves, which were then used to assess the compatibility of dredged sediments for beach nourishment. The results indicate that native beach sediments show variations in grain-size distribution from the profile of the beach face to the lower foreshore, but were dominated by medium and fine sands. Grain-size distributions of dredged material were quite similar, with some exceptions. Previous experiences suggest that similar composition of the native beach and filling material could help controlling the post-nourishment profile stability, and prediction of the required fill volume to provide the desired beach width can then be performed with a reasonable degree of accuracy.