Permeabel groynes : experiments and practice in the Netherlands

Reports on model experiments and up to 20 years of practice in nature with a permeable groyne system, consisting of single or double permeable rows of wooden piles perpendicular to the beach, without bottom protection. This system costs only 10 to 25% of the impermeable stone groynes which have for centuries been used in the Netherlands. Model experiments conform that wave-induced currents in the protected areas are reduced to 65 percent and tidal currents even to 50 percent, depending on the pile screen figuration. Prototype measurements could not lead to straightforward conclusions with statistical significance: the effect of the pile screens on beach evolution is partly merged into natural fluctuations and trends. Wooden pile screens do not prevent the shoreward motion of tidal channels which can cause washing out of piles.