If the rate of erosion due to a severe storm surge is unacceptably large during design conditions, the use of structures may be helpful in reducing the rate of erosion.
Series of groynes do not help to reduce the associated offshore directed sediment transport. In principle, series of emerged breakwaters or submerged breakwaters reduce the wave heights landward of these structures and consequently may have the effect of reducing the rate of dune erosion. However, due to the increase of the still water level associated with a storm (the surge), the effectiveness of these types of structures in reducing the wave heights under storm conditions is limited (see also Sect. 10.5.4). Also, wave overtopping of the breakwater segments may lead to concentrated rip currents in between the breakwater segments and therefore quite adverse effects (as for permanently submerged breakwaters). Further, the use of detached breakwaters for reduction of storm erosion may have undesirable consequences because of the inevitable impact on longshore transport gradients.
By contrast, the structures that can be effective in protection of the mainland against storm-induced erosion and flooding are: