**7. Data Analysis and Representation**

Past research works (e.g., [14,21,22,24,26,47,76]) show a lack of tools able to synthesize numerical results for supporting decision-makers in different design and environmental conditions. Maps showing the predicted (e.g., maximum and mean) SSC at different water depths and DEP, as well as time series at different key sites, are recommended to support planning and environmental approval. However, uniform criteria for the analysis and representation of numerical results obtained within preliminary modeling phase and detailed modeling phase have to be defined consistently with the characteristics of the modeling objectives. Indeed, they have to be defined based on the main physical processes identified as of primary interest for the considered environmental context, operational phase and environmental critical issues (if any) in the neighboring of the intervention site. Then, they can be useful also to select modeling scenarios (see Section 3) suitable to assess the fate and transport of the handled sediments with sufficient accuracy for the purpose of impact assessment.

An integrated, flexible and replicable methodological approach for synthesizing parameters related to water quality variations that arise from sediment handling activities is proposed herein starting from the extension of the environmental assessment method for dredging activity (Dr-EAM) methodology proposed by Feola et al. [26] to different environmental context (i.e., off-shore, near-shore and enclosed basin this paper deals with). These evaluations are needed for the assessment of the environmental impacts related to sediment handling projects and, in particular, for the evaluation of the severity of impacts on sensitive environmental receptors.

Based on past research works (e.g., [22,26]), it is recognized the importance of defining reference levels representative of the baseline variability of parameters of interest (e.g., SSC, DEP) before the handling operations or, during the activities, in reference areas potentially not affected by the handling works. A series of multiple reference levels with growing environmental criticality should be used to quantify the significance of the effects related to turbidity plumes during the project execution (e.g., [77]). These (single or multiple) reference levels must be established based on literature, site-specific monitoring and expert judgment depending on the project features (e.g., extension, duration, volume of handled sediments) and the expected interactions with the environmental critical issues (if any).

The source–path–receptor model can be used to represent the link between the sediment re-suspension source (intervention site) and the receptor (e.g., [18]). Although beyond the scope of this paper, it is important to stress that for a proper correlation between the significance of physical effects to the severity of possible impacts on the biological compartment, reference levels definition should also consider site-specific receptor tolerance limits (when they are available and/or they can be inferred from specific stress-response curves) to the expected water quality variation during execution. The severity of impacts is related to the presence of the expected and/or detected environmental issues, their location (with respect to sediment source and local currents), their nature and their ecological status (Figure 7).

The evaluation of the significance of effects must necessarily consider different aspects of the induced perturbations to the environmental effects, such as intensity, duration and frequency of events of SSC and DEP increase (e.g., [10,26,78–81]). The relationship between intensity, duration of perturbation and the related environmental effects on the specific receptor can be derived on the basis of site-specific data, on literature data or by expert judgment. When literature information or field data representative of the study area are not available, the reference levels can be defined using modeling studies in order to perform an analysis of the variability intervals of the parameters of interest. It is important to produce maps that summarize the modeling results [14]. Following the indications proposed by Feola et al. [26], a flexible, consistent and integrated methodological approach is presented in terms of standard and easily replicable techniques. The approach is suitable to support the identification and an easy assessment of the magnitude of potential effects in relation to intensity, duration and frequency of deviations from identified reference levels. In particular, it is useful to define a discrete number of check-points for extracting time series of output parameters throughout the whole period of simulation. Check-points have to be regularly distributed in the domain with a spatial scale chosen as a function of the spatial variability of the numerical results. For each check-point, time series can be extracted at different depths in the water column and at the seabed then analyzed and combined to derive suitable statistical parameters and indexes related to intensity, duration, and magnitude of exceedance of reference levels. Maps representing these parameters allow direct comparison of effects due to sediment handling works activity at progressive distances from the re-suspension zone. If the selected parameter is of hydrodynamic type, it will be possible to identify, for each scenario on both a seasonal and annual basis, zones with a different agitation level, as it will be possible to represent the spatial variability of the dispersion and deposition of the turbidity plume as SSC in water column and DEP at the bottom. To account for the combined effect of different parameters (e.g., duration and intensity), that cannot describe the significance of the exceedance of the reference level if separately considered, different methodological approaches can be used.
