Interference in the coastal region results in changes in the coastal processes. There may be many reasons for this interference: stabilization of a shoreline, protection of the land from waves and surges, protection of a harbour and fixing the position of a river mouth or tidal inlet, for example. Additional human activities which interfere with coastal processes may include the extraction of oil and gas or the blockage of river sediment by a barrier. The changes in coastal processes due to human interference often lead to new coastal engineering problems.

Harbour protection
Ships manoeuvring slowly while entering a harbour must be provided with clear sailing. This requires that the entrance must be protected from the effects of local currents and waves. It is usually achieved by building breakwaters or jetties into the sea.

A second purpose of these breakwaters is to prevent rapid siltation of the harbour approach channel (see Fig. 54). The long shore transport in the surf zone is blocked by the breakwaters; hence the siltation rate is reduced. However, in situations with a net long shore transport of sediment, a new problem has been created. The interrupted sediment transport leads to accretion on the updrift side of the harbour entrance and to erosion on the other side (see Fig. 55 and Fig. 56). Since the long shore current is not fed with sediment on the downdrift side, the current erodes the coast in order to attain its previous sediment load.

The entrance channel to many harbours is artificially deepened in order to give access to modem large ships. Such a deepened channel requires regular maintenance, since siltation will tend to reduce the water depth to its previous value (see Fig. 57).