Evaluating the PEM passive beach drainage system in a 4-year field experiment at Egmond (The Netherlands)

• We evaluated a passive vertical beach drainage system using annual profile surveys.
• The system was installed from 2006 to 2010 on the beach at Egmond (NL).
• The first 2 years the test area was dominated by nourishments placed in 2004/2005.
• From then onward the test area behaved similarly as the adjacent (reference) area.
• The drainage system had no measurable effect on the beach and dune volumes.

The PEMs' (Pressure Equalizing Modules) passive vertical drainage system was tested at the coast just south of Egmond (The Netherlands) from November 2006 to December 2010. The present study aims at providing qualitative and quantitative insight into the impact of the PEMs on the nearshore morphological development at Egmond. The evaluation is based on a comparison of the annually observed temporal evolution of the nearshore morphology prior, during and after the PEM installation period. To this end a number of aggregated volumetric profile parameters derived from the surveys were compared for the test area and for an adjacent area which acted as a reference. Besides the PEMs, the study area is also influenced by beach and shoreface nourishments. Therefore, the nourishments carried out just north and south of the Test and Reference areas in 2004 and 2005 prior to the installation of the PEMs were specifically considered in the analysis. From 2008 onward the morphological behavior of the nearshore zone was dominated by the alongshore coherent net offshore migration of the multiple bar system and no obvious feeding of sand from the nourishments toward the Test and Reference areas could be identified. The influence of the nourishments, the PEMs, and the natural variability were difficult to distinguish at the Test and Reference areas. Therefore, the morphological development of the Test area relative to that of the Reference area was adopted as the primary evaluation criteria. Interestingly, the installation period (2007–2010) exhibited statistically significant different CSIs (coastal state indicators) compared with the 4 years prior to installation (2003–2006) for both the Test and the Reference areas. Because both the Test and the Reference areas exhibited very similar behavior prior, during and after the PEM installation period, the analysis was unable to identify the impact of the PEMs. No influence of the PEMs on the local beach and dune morphology could be established. Considering the above and given the fact that the PEM system was also not able to induce a measurable accretion at a similar experiment in Denmark we consider it unlikely any efficacy of the PEM system will be identified in future experiments.