Notched Groins Impact on Beach Nourishment

The elevation change maps established that in general, the groin notching was partially successful in reducing shoreline asymmetry in consequence of sediment transport bypassing through the notches. Differences in behavior and patterns of elevation change adjacent to each individual notched groin was observed even though they were all notched according to the same specifications. While all three notched groins were effective in stabilizing the adjacent shoreline, they varied in their effectiveness at promoting longshore sediment transport through the notch. This is likely attributable to the relative location of the notched groins within the groin field and the characteristics of the post-nourishment morphological evolution; the direction of net annual longshore sediment transport at Deal beach is northward, which caused the southern areas of the study site to narrow and the northern areas of the study site to widen. Consequently, the notched groins in the wider sections of beach did not function as intended, as the notches filled in with sediment causing them to mimic the behavior of a traditional groin, including restricted longshore sediment transport and significant erosion/accretion offsets. In the narrower section of beach, the notched groin functioned as designed, such that the notch was located in the swash zone and therefore allowed bi-directional sediment transport and maintained a stable and relatively symmetrical shoreline. Thus, the notched groins performed most effectively when the notch was consistently located toward the seaward end of the swash zone.