When longshore sediment transport is interrupted by a construction along a coast, e.g harbour moles or a dredged approach channel, the equilibrium of the coastline may be disturbed. When the disruption is caused by breakwaters, the longshore transport that is held back will cause accretion updrift of the breakwaters and erosion downdrift of them. The updrift accretion may eventually result in the harbour entrance shoaling. The downdrift erosion might cause difficulties when valuable areas are situated close to the coastline or when the coastline forms a coastal protection for land behind it. When the disruption is (caused by a dredged channel, no accretion updrift of the channel will occur since the material is trapped in the channel. This means, however, that here too there is a lack of material downdrift and erosion will again occur there.