Abstract
In the present study we describe a straightforward and highly replicable methodology to assess the anthropogenic sediment budget within a coastal system (the Northern Tuscany littoral cell, Italy), specifically selected in a partially natural and partially highly urbanized coastal area, characterized by erosion and accretion processes. The anthropogenic sediment budget has been here calculated as an algebraic sum of sediment inputs, outputs and transfer (m3) within a 40 year time interval (1980–2020). Sediment management strongly influences the sediment budget and, even if its evaluation is crucial to assess the efficiency of a coastal management policy, it is often difficult to quantify the anthropogenic contribution to sedimentary processes. Different types of intervention are carried out by a variety of competent authorities over time (Municipalities, Marinas, Port Authorities), and the correct accountability of sediment budget is no longer known, or possible, for the scientific community. In the Northern Tuscany littoral cell, sedimentation is concentrated in a convergent zone and updrift of port structures, which have determined a series of actions, from offshore dumping and disposal into confined facilities (sediment output), to bypassing and redistribution interventions (sediment transfer); conversely, river mouths and coastal areas protected by groins and barriers are subjected to severe erosion and coastline retreat, resulting in many beach nourishments (sediment input). The majority of coastal protection interventions were carried out to redistribute sand from one site to another within the study area (2,949,800 m3), while the sediment input (1,011,000 m3) almost matched the sediment output (1,254,900 m3) in the considered time interval. A negative anthropogenic sediment budget (−243,900 m3) is here documented.
Highlights
The anthropogenic pressure in coastal zones is constantly increasing [1,2]
The whole cell has been subdivided into five smaller sub-cells in a further processing of the dataset (Figure 1b): in this case sediment transfers from one sub-cell to another factored in the calculation of the sediment budget as sediment inputs and outputs
As the contamination thresholds corresponding to suitable sediment management options have been updated through the years in accordance with the evolving legislation framework, in the present paper we considered only the possibility that sediment volume collected during a dredging operation can be partially used for nourishment, or disposed into confined facilities or dumped out of the coastal system [71]
Summary
The anthropogenic pressure in coastal zones is constantly increasing [1,2]. The socioeconomic values and the benefits characterizing such areas are attracting people that increasingly choose to live there. Coastline modifications have become a chronic problem for coastal communities, and the anthropogenic impact due to human activities (e.g., harbor maintenance, beach facilities, coastal protection schemes) is increasingly becoming a driver of shoreline changes [15,16,17,18]. The mismatch between natural and anthropogenic influence on coastal and human activities and interests is evidenced by many protection schemes characterizing the most inhabited coastal regions. Despite such effort, a large number of European coastal zones still show a high degree of exposure to erosion processes [19]
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