Jetties

Jetties are long, narrow structures that extend from the shore into a body of water with the purpose of influencing coastal processes and protecting navigation channels. They are commonly built at harbor entrances or river mouths and can occur as a pair facing each other or as single structures on one side of an inlet. The primary function is to stabilize and widen a navigable channel by interrupting longshore sediment transport and reducing inlet migration, while also shielding the entrance from waves to improve safe vessel access.

Construction materials and techniques vary, but typical jetties use rock, concrete, or rubble to form revetments and are built as rubble-mound, caisson, or pile-supported structures. They are designed to resist wave loading and scour, and maintenance often includes dredging the channel to maintain depth and repairing damage from storms.

Impact on coastal systems: Jetties alter natural sediment transport and wave regimes, which can lead to sediment buildup on the updrift side and erosion on the downdrift side of the inlet. This can change nearby beaches, coastal habitats, and tidal circulation patterns. While beneficial for navigation, jetties may necessitate ongoing coastal management and environmental monitoring to mitigate unintended effects.

Applications and history: Jetties have been used since ancient times to protect harbors and improve access for ships. Today they remain a common coastal engineering solution for stabilizing channels at a range of scales, from small ports to large commercial harbors, with design adapted to local hydrodynamics, sediment supply, and ecological considerations.