A
structure that is built in order to extend the banks of a
stream or intracoastal river beyond the coastline. This is done to direct the direct the flow of a stream or tide and keep sediments moving so they are not deposited and fill in the
channnel. It also serves as protection from large waves that might prevent boats from travelling inland along the stream.
Jetties are built in
parallel pairs along both banks of the channel. Because they are
perpendicular to the coast they tend to interrupt
longshore drift and thus widen beaches.