Smart coastal management takes sandbar positions into account
Published: 14 June 2016
In the Netherlands, we already have many years of experience using sand replenishment to preserve our coastline. One way to do this is by depositing sand on the beach itself, but since the early 1990s, we are increasingly depositing sand off the coast, under water. This is cheaper than beach nourishment, meaning that we can deposit a larger volume of sand with the same budget. Another advantage of this approach is that the beach is no longer disrupted by the work.
Underwater sandbanks wander away from the coast
However, over time, submerged sandbanks start to ‘wander away’ from the coast. Existing sandbanks in the littoral zone have a net lifespan of 3 to 15 years. Incoming waves and longshore drift also have a number of effects on sandbanks’ behaviour. Strong, wave-driven longshore currents result in a net growth of the sandbanks, while in deeper waters, the absence of such littoral drifts causes sandbanks to erode. Walstra has analysed the behaviour of the submerged sandbanks with the aid of model calculations. Since underwater sand replenishment and sandbanks influence one another, this newly-obtained knowledge can be used to improve the design of the deposits.
The next step
Walstra: “For my dissertation, I studied the behaviour of the sandbanks. The next step for me will be to take a targeted look at the designs of the sand deposits. I intend to apply this model to a variety of deposit designs, in order to identify opportunities for increasing efficiency. In the Netherlands, most sand replenishment is handled by Rijkswaterstaat. Looking abroad, I believe this research could be put to good use in Florida, for example, since most of the coastal management there is based on offshore sand deposits too.”