Comparison of marine sediment extraction sites by means of shoreface zonation

Marine sand and gravel resources receive an increasing interest, leading to greater quantities of dredged material. Nevertheless, knowledge concerning negative impacts on adjacent coastal sediment transport systems and the duration necessary for the physical regeneration of extraction sites is scarce. Here we assess time scales of regeneration of three extraction sites situated in the Baltic Sea by investigating sonographic data sets covering several years. We incorporate data from other extraction sites and compare the results by applying a shore-normal zonation of the shoreface. Hence, limiting depths of the upper and lower shorefaces are calculated from wave statistics. From our comparisons we conclude that the time scales of regeneration are most profoundly determined by the position of the extraction site relative to the seaward limit of the shoreface. Locating extraction sites well beyond this limit therefore implies a slow regeneration. In contrast, material extractions on the upper shoreface may exhibit a fast regeneration, but negative impacts on the coastal sediment budget cannot be excluded. Additional factors controlling the velocity of regeneration are the depth of the extraction as well as the character and availability of the potential material for regeneration. As a consequence, there is no ideal location for marine sediment extraction. The appropriate place should be a well-balanced compromise allowing fast regeneration together with a minimised impact on the coastal sediment budget.