Field experiments with different fractions of painted sediments to study material transport in three coastal sites in Estonia

Our current understanding of the morphodynamics in swash and surf zones is limited due to their turbulent and irregular nature. The importance of this zone to sediment transport led us to perform a sophisticated field experiment using painted sediments. Sediments collected locally from beach ridges were sorted into the following diameters: 1–2 5 cm, 2.5–5 cm and 5–10 cm. The sediments were painted, amassed in piles and placed at 0.5–10 m depths in three sites near the Estonian coast. The locations were recorded with GPS devices and photographed. The sediment piles placed in the sea were monitored at least once after an intense storm or once before and after the storm season. Some sediments were placed on the shoreline and monitored daily for a shorter period. Hydrodynamic parameters were also measured or hindcasted during the experiment. We found that wave breaking during storms can take place even at 6 m depth, but mostly between 2–4 m depth. Sediment fractions between 1–10 cm diameters can be transported over 20 m towards the shore. Even sediment piles at 10 m depth were moved 2–4 m, but towards the open sea. Sediments accumulated on the shoreline moved up to 3 m/hour along the shore and approximately 350 m during three months. We also found that calm periods can be more influential in places where regular vessel-generated waves wash the shores. As vessel-generated waves often approach from a different angle than natural waves, they can cause notable erosion during the periods when natural waves are weak or absent.