COASTAL ZONE DYNAMICS DURING ARTIFICIAL NOURISHMENT

Abstract

The nearshore zone of the Hel Peninsula has a hydro-geomorphological system which, together with the influence of the port at Wladyslawowo, causes permanent erosion of the basal and central part of the peninsula's sea coast. After a period during which traditional methods of coastal defence (seawalls, groynes) were used, a massive artificial nourishment of the dune and beach was realised in the years 1989- 1995. The borrow material used was of lagoon and marine origin. The progress of morpho- and lithodynamic processes was evaluated basing on quantitative analyses of changes in topography and granulometry. In the land part of the coastal zone, accretion of deposits resulted in rebuilding of the dunes and beaches. In the nearshore zone, accretion occured on the beach slope, and resulted in the development of shore terraces and breaker bars (especially the outer breaker bars). This was accompanied, by related with the accretion, processes of erosion in the form of U-shaped troughs. These processes proceeded at small changes in the erosion/accretion (e/a) system of the nearshore zone in the whole region. Smaller input of sandy material into the nearshore zone resulted in gradual return of the e/a system to initial state. If the safety of the peninsula is to be maintained, artificial nourishment must be executed every year. Frequency and volumes of renourishment will depend on the quality of used material. Therefore new sources of borrow material must be seeked.