SPECIAL ASPECTS OF DEFORMATION OF COASTAL PROFILE DURING A FULL STORM CYCLE

Abstract

Deformations of the coastal accumulative profile during a full storm cycle can be related both to the special aspects of individual storms and to seasonal cycles of wave activity. There is a concept of a “winter” and a “summer” type of coastal profile. The difference between these types of profiles is the isolation of the outer underwater berm in winter due to the transfer of sand material to depth and an increase of slopes in the surf zone in summer due to the transfer of sand material to the shore. In this case, the post-storm relief is determined by the character of the wave intensity reduction phase, i.e., the storm attenuation phase. The attenuation of the storm can be prolonged and accompanied by local peaks in wave heights, which will decrease gradually. In this case, the storm has a high potential for beach recovery and the underwater berm may shift toward the shore. In another case, storm attenuation can occur relatively quickly – the original profile is not recovered and at the end of the storm, the profile shape reflects the erosion in the peak phase. Relevant is the determination of the special features of the resulting deformations at the end of the storm cycle, in particular at the end of the storm attenuation phase. In this paper, the special features of storm deformations of the coastal sand profile, which were observed during field experiment on the Bulgarian coast and during monitoring observations on the Baltic Spit, are considered. In one case (the Bulgarian coast) it is a transition from the typical “summer” profile to the “winter” profile. In another case (Baltic Spit), a shift of the outer underwater berm toward the shore was revealed, which can be considered as a transition to the “summer” profile. It is revealed that the features of the storm attenuation stage in the two cases under consideration have specific differences. It is shown that transformations of the coastal profile, characterized as seasonal, can occur during the full cycle of a single storm event.