Critical Examination of Shoreface Sediment Volume as an Indicator of Coastal Stability in Poland

Abstract

This paper presents analyses of a coastal stability indicator, recently introduced in Poland, that was based on a nearshore sediment volume found between +2 and −6 m ordinates. This purely empirical indicator was developed on the basis of long-term observations (made between 1957 and 22) of the morphologies of emerged beaches and detailed nearshore seabed monitoring consisting of 969 cross-shore profiles spaced every 5 m that were surveyed between 24 and 26 along the entire Polish coast. It was introduced to quantify the requirements for beach nourishment and adopted as the main erosion-control instrument dictated by the Coastal Protection Act of 23. Extensive seabed monitoring provided data for determining the shoreface sediment volume and led to the conclusion that a mean sediment volume (between 2 m above and 6 m below mean sea level) in excess of 1,5 m3 was a strong indicator of a stable coast. This assumption and the implications of it are discussed. Specifically, simple theoretical considerations pointed to a possible relationship of this indicator with the mean sediment diameter, D5, which was between .2 and .22 mm, and to a general relationship between D5 and shoreface sediment volumes.