Modeling the response of shoreface-connected sand ridges to sand extraction on an inner shelf

Abstract

Shoreface-connected sand ridges are rhythmic bedforms that occur on many storm-dominated inner shelves. The ridges span several kilometers, are a few meters high, and they evolve on a timescale of centuries. A processbased model is used to gain a fundamental insight into the response of these ridges to extraction of sand. Different scenarios of sand extraction (depth, location, and geometry of the extraction area; multiple sand extractions) are imposed. For each scenario, the response timescale as well as the characteristics of the new equilibrium state are determined. Results show that ridges partially restore after extraction, i.e., the disturbed bathymetry recovers on decadal timescales. However, in the end, the ridge original sand volume is not recovered. Initially, most sand that accomplishes the infill of the pit originates from the area upstream of the extraction, as well as from the areas surrounding the pit. The contribution of the latter strongly decreases in the subsequent time period. Depending on the location of the pit, additional sand sources contribute: First, if the pit is located close to the downstream trough, the pit gains sand by reduction of sand transport from the ridge to this trough. Second, if the pit is located close to the adjacent outer shelf, the ridge recovery is stronger due to an import of sand from that area. Furthermore, pits that are located close to the nearshore zone have a weak recovery, deeper pits have longer recovery timescales, wide and shallow pits recover most sand, while multiple sand pits slow down the recovery process.