Morphological development of coasts at very oblique wave incidence

This study focuses on one distinct feature to be found on coasts exposed to a very oblique wave incidence, namely an accumulating spit. That is a spit where no retreat of the shoreline is going on along the spit. This requires a monotonically decreasing sediment transport capacity from the updrift stretch of coast, along the spit as the coast curves away from the approaching waves towards the tip of the spit. A one-line model for the coastline development predicts that accumulating spits can exist on coasts exposed to waves approaching at angles larger than 45 degree only. It is suggested that such a spit grows without changing its shape i.e. an equilibrium form emerge if the coast is exposed to a constant wave climate. During experiments conducted in a wave tank where a uniform stretch of coast was exposed to waves approaching at a very oblique angle an accumulating spit was formed at the down-drift end of the coast. The spits approached equilibrium forms when constant wave climates were applied. The sediment transport around the spit has been investigated by two-dimensional models. The characteristic length scale for the equilibrium form depends linearly on the width of the surf zone for constant wave incidence at the updrift stretch of coast. The factor of proportionality is in reasonable agreement with the experimentally found.