Influence of shoreline alignment on offshore sediment transport

The study of morphological processes along a coastal unit of 40 km in length in the nontidal Baltic Sea revealed a substantial variation of the shore-parallel component of wave energy flux, which is assumed to be proportional to the mass of alongshore sediment transport. A reduction of flux in transport direction e.g. due to changes in the shoreline alignment or in the shape of the coast implies a jam in the Ion-shore transport. It means that part of the sediment arriving must be deposited or diverted in offshore direction, i.e. in shore-normal transport. In order to resolve this contradiction sea surveys from different sources were used and analyzed as difference maps. It could be verified that instead of deposition at this erosive coast the reduction of longshore energy flux along a coastal stretch led to an offshore diversion of sediment out of the surf zone and accretion in 8 m to 12 m depth region, seaward of the active zone (5 m depth at the site), more than 2,000 m distant from the shore.