Initial adjustment of underwater profiles after nourishment in a mild wave climate: a case study near Klaipėda, the Baltic Sea

Abstract

We analyze the spatio-temporal dynamics of sand relocation for beach nourishment in the low-energy coastal segment north of the Port of Klaip & edot;da, eastern Baltic Sea, under mild wave conditions, with significant wave heights below 0.9 m and water level variations from -30 to 44 cm with respect to the long-term average. In summer 2022, about 180 000 m3 of sand was added approximately 120 m from the shore at water depths of 2-3.5 m to form a 750 m long underwater bar. Sand relocation is evaluated based on repeated water depth measurements along 114 cross-shore coastal profiles. Some sand was rapidly transported to greater depths, down to about 6 m, even though wave conditions were particularly mild. The predominant sand motion was directed offshore, and characteristically for the area, wave-driven sediment transport was directed to the north. The analysis confirms that even very mild wave conditions can substantially relocate large volumes of deposited sand in shallow water, both offshore and onshore, from its original location during the initial adjustment phase following nourishment.