Hard Engineering Techniques Flashcards
Sea Walls
Giant walls that span entire coastlines and attempt to reduce erosion and prevent flooding in the process. They’re big, ugly and very expensive requiring constant maintenance so that they don’t fail. They also produce a strong backwash in waves which undercuts the sea wall making their long term sustainability questionable.
Traditionally, sea walls are large flat walls however more modern sea walls have a curved structure that reflects waves back into incoming waves, breaking them up and further reducing erosion.
Groynes
They’re low lying wooden walls that extend out to sea. The idea of groynes is to capture sand that moves down the beach via longshore drift and help build up a larger section of beach in front of an area that’s experiencing coastal erosion. The new beach will increase the distance that waves have to travel to reach the coast and, in the process, they’ll lose most of their energy, reducing their impact. Groynes are pretty effective but they have one major drawback. Groynes will remove a lot of the sand that’s present down-drift of the beach which will result in a thinner beach at this area. This, in turn, means that sections of the coast will be more exposed to erosion down drift of the groynes which can create new problems relating to coastal management.
Gabions
Gabions are quite simply bundles of rocks in a metal mesh. They’re placed at the base of a cliff in an attempt to reduce the impact of waves on the cliff and prevent the cliff from being undercut. They’re not particularly effective and they’re quite unsightly but they’re sure as hell cheap.
Revetments
Revetments are concrete (or in some cases wooden) structures that are built along the base of a cliff. They’re slanted and act as a barrier against waves not too dissimilar to a sea wall. The revetments absorb the energy of the waves, preventing the cliffs from being eroded. Revetments can be modified so that they have rippled surfaces, which further help to dissipate the wave energy. Revetments are normally successful at reducing coastal erosion but they are expensive to build. Once built however, they don’t require as much maintenance as a sea wall.
Rip Rap
Riprap are just rocks and stones that have been put against the base of a cliff. They’re similar to gabions in their purpose but they aren’t bound together in a mesh. This makes them look slightly more appealing as they blend into the environment better however the rocks are susceptible to being moved by the sea.
Breakwaters
Breakwaters are offshore concrete walls that break incoming waves out at sea so that their erosive power is reduced to next to none when they reach the coast. Breakwaters are effective but they can be easily destroyed during a storm and they don’t look particularly nice.
Tidal barriers
Big, retractible walls built across estuaries that can be used as a floodgate to prevent storm surges. They’re hugely effective but they’re also hugely expensive.
