Quantification of longshore sediment transport and compartments in urban areas: A case study of shores of Tallinn, the Baltic Sea

Abstract

We analyse sediment transport patterns along shores of urbanised bays of complicated shape. The focus is on shores of Tallinn on the southern coast of the Gulf of Finland, the Baltic Sea. A detailed reconstruction of the wave climate in the study area with a spatial resolution of 260 and 470 m is generated using triple-nested high-resolution versions of the WAM and SWAN models. The models are forced with three wind data sets: 32 years of high-quality one-point marine winds, ERA5 winds for 1990–2021, and BaltAn65+ winds for 1986–2005. The main properties of potential wave-driven alongshore transport and its convergence and divergence points along sedimentary shores of five bays of greatly different size and orientation are established from the time series of wave properties using the CERC approach. Four smaller bays serve as separate sediment compartments. Harbours and jetties divide the sedimentary shore of the interior of the largest bay, Tallinn Bay, into one almost isolated and four weakly connected compartments. The southern shore of this bay hosts a persistent divergence area of littoral drift that subdivides the almost isolated compartment into two distinct sedimentary cells. Changes to the dry beach in a major accumulation area in one of these cells are evaluated using a combination of airborne and terrestrial laser scanning.