Kystdrift

Kystdrift is the alongshore movement of beach and nearshore sediments driven by the action of waves arriving at a coastline at an oblique angle. When waves strike the shore obliquely, the water washes up the beach at an angle (swash) and drains back perpendicular to the shore (backwash). The resulting net transport is parallel to the coastline, creating a longshore current that carries sediment along the shore.

Over time, kystdrift redistributes sand along the coast, shaping beaches and forming landforms such as spits, bars, and barrier systems. The rate of transport depends on wave height, period, angle of approach, sediment size, beach slope, and nearshore bathymetry. Transport is often episodic and seasonal, with higher rates during storms or periods of persistent winds.

Coastal features and shoreline change are sensitive to human activity as well. Structures such as groins and jetties interrupt natural alongshore transport, causing erosion downdrift or sediment buildup updrift. Management practices, including beach nourishment, dune restoration, and barrier maintenance, aim to balance sediment budgets and mitigate erosion or excessive deposition.

Kystdrift is a central concept in coastal geomorphology and erosion control, helping explain how coastlines respond to natural wave climate and to human interventions. Understanding this process supports planning for sustainable beaches, hazard mitigation, and coastal resilience in the face of climate-driven changes in wave regimes and sea level.