Coastal defence of beaches, cities and communities located close to oceans and seas is a primary activity of the dredging industry.
According to the United Nations Environmental Programme (UNEP), half the world’s population lives within 60 kilometres of the sea, and three-quarters of all large cities are located on the coast. With the risks of climate change and the pressure of pollution from urban areas, these communities are more and more vulnerable.
These densely populated coastal cities are economic hubs, often representing major ports with their related industrial businesses, such as shipping and commercial fishing. Coastal areas also support tourism with a focus on beaches, hotels and cruise harbours.
To complicate matters, these coastal areas are also home to rich and fragile natural habitats.
Causes of coastal erosion
Coastal protection provides defence against flooding and erosion, which can be caused by:
- waves and tides,
- currents and
- littoral drift, i.e., the transport of sediments along a coast at an angle to the shoreline in the littoral zone (the surf line).
Climate change, resulting in melting ice caps and more frequent and more severe storms, have aggravated these conditions.
Coastlines and their ecosystems vary considerably but all require some degree of maintenance and protection, for instance:
- Sandy beaches with dunes are subject to the waves, tides, winds, and currents which can drag sand out to sea and bring it back in places where it may not be needed. Maintenance dredging seeks to replenishment these beaches and restore their natural beauty as well as their function as a barrier against flooding.
- Wetlands provide essential ecosystem services including erosion and flood protection, protection of natural habitats with unique species of flora and fauna. Commercial fisheries as well as recreational facilities are often near wetlands.
- Coral reefs whether in warm or cold waters are unique natural barriers, protecting coastal cities, communities, and beaches from ocean waves and limiting the vulnerability of coasts to wave action and storm damage.
- Mangroves provide natural protection and can be part of coastal protection strategy against wave damage, storms, and erosion. Their dense roots bind and build soils and slow down the effects of wind and waves. Restoring and protecting them by careful dredging should be a part of an overall coastal defence scheme.
Dredging must always consider these assets and can play a key role in protecting and restoring them.
Dredging & coastal protection
A variety of dredging solutions may include:
soft engineering solutions including sand dune stabilisation and beach nourishment.
- construction of hard structures such as seawalls;
- breakwaters to protect exposed harbours;
- underwater bunds;
- fixed piers or open-piled jetties;
- sand traps such as groynes;
- coastal armouring with revetments, gabions, riprap and acropodes.