10.7.4: Dune Reinforcement

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Page ID: 16448

Judith Bosboom & Marcel J.F. Stive
Delft University of Technology via TU Delft Open

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Nourishment of the dune area is usually done if the volume of material in the dune ridge is insufficient to cope with dune erosion during the design storm. In such cases, the hinterland may be exposed to flooding, not because of ongoing erosion, but simply because the existing dunes are not strong enough to withstand extreme conditions. The protection level of the land behind the dunes is increased more effectively by making a row of dunes wider than by making them higher.

Figure 10.35d repeats the two options to reinforce a row of dunes with sand. Reinforcement at the back side of the dunes increases the safety level but has no morphological impact. Often it may not be feasible to place sand at the landward side of the dune due to existing infrastructure and properties.

In the case of sea-side reinforcement, it seems that only a relatively small volume of sand is required. However, the widening of the dunes in the seaward direction disturbs the dynamic equilibrium of the cross-shore profile (the dune foot being suddenly too close to the MSL). The same holds if the dry beach is nourished to compensate for storm losses. As a result, sand from the new dune or beach area is transported in the seaward direction and the additional volume of sand will be redistributed over a large part of the cross-shore profile (say up to the active part of the cross-shore profile). Therefore, relatively large volumes of sand are required since not only the face of the dune has to be shifted in the seaward direction, but also the active part of the cross-shore profile.

截屏2021-12-15 下午8.12.38.png — Figure 10.37: Dune reinforcement over a limited alongshore distance of 2 km and with a 40 m cross-shore extent (this is after the cross-shore redistribution). The expected alongshore redistribution is drawn.

A similar redistribution of sand needs to be taken into account in the alongshore direction, as shown in Fig. 10.37. A purely local dune reinforcement will therefore have a short life-time.

Widening and heightening of the dunes may not always be the preferred option of property owners close to the dune, because houses may end up further from the sea and sea views may be lost.