Monitoring turbidity and sediment re-suspension induced by channel dredging and subaqueous disposal in a deficit lagoon

In order to test a procedure for sustainable management of sediment in Marano and Grado Lagoon, consisting of dredging the Coron channel and sediment disposal in a deeper part of the same channel, an impact assessment of turbidity and sediment re- suspension has been carried out, by means of Acoustic Doppler Current Profiler surveys, suspended particulate matter collection and placement of sediment traps. Dredging and disposal operations cause an alteration of water turbidity, generating plumes that are driven by tidal currents within the channel and persist in water column for hours. Tidal flats next to the channel are involved in an anomalous sedimentation rate, temporally and spatially restricted. Background concentration during dredging and disposal operations is consistent with those caused by the wind waves. Peak values of concentration in channel and maximum rates of sedimentation on tidal flat are consistent with those caused by clam fishing with mechanical dredges, permitted on the same areas. Results indicate the possibility to adopt this type of sediment management practice as a good low-impact provisional procedure in this part of the lagoon.