An analytical model for preliminary assessment of dredging-induced sediment plume of far-field evolution for spatial non homogeneous and time varying resuspension sources

In recent years, increasing attention has been paid to assess the dispersal of resuspended sediments and related water quality problems due to dredging operations. This paper presents an analytical model aimed to predict the temporal evolution and spatial distribution in the far field of the suspended sediments concentration increase related to dredging activities or open water sediments disposal. In particular, whatever the dredging source strength and geometry can be considered to define the suspended sediments concentration leaving the immediate vicinity of the resuspension source. Indeed, a feature of the model is the removing of the hypotheses of continuous source and steady state, peculiar to the majority of available theoretical models. Hence, the proposed model is able to describe different dredging resuspension sources and to provide the temporal and spatial picture of the resulting plume. Of course, some hypotheses have to be assumed in order to make possible to achieve the analytical solution of the governing equation: the model is two dimensional in the horizontal plane; the ambient currents are assumed to be homogeneous in space and slowly time varying; the turbulent diffusion coefficients and flocculent settling velocity are homogeneous in space; the water depth is constant; the domain is infinite. Even with its limitations, the model is still able to provide a worst case preliminary assessment of sediments plume migration very useful to guide more detailed numerical analysis and to select the more appropriate simulation scenarios. The analytical model is detailed in order to be used for numerical model testing purposes. A series of practical applications is described through the paper (i) to catch the general features of the involved far field phenomena, (ii) to compare the model results to those of previous researches and (iii) to provide a series of benchmark cases useful for the testing of numerical models. The proposed model may be also used as a first rough prediction of the area affected by plume dispersion by considering different dredging scenarios (i.e. different equipment and operational techniques and forced by site-specific environmental conditions), and thus to provide a basis for more sophisticated modeling aimed to support dredging projects planning and management