Soft Engineering and Hard Engineering

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Hard engineering refers to the construction of physical structures to defend against erosive power of waves To protect a coast from erosion, people have built seawalls in front of a cliff or along the coast. A seawall is usually made of concrete. It acts as a buffer and absorbs energy of breaking waves especially during storms where the waves are strong, thus protecting the coast. A seawall shields and protects the coast from the direct impact of the incoming waves, thus reducing erosion. However, a seawall may not protect a coast from erosion in the long run. As waves break against the seawall, the energy from the waves is redirected downwards, to the base of the seawall, resulting in a strong backwash. The backwash erodes the beach beneath and wears away the base of the seawall, causing it to weaken and eventually collapse. Hence seawalls have to be carefully maintained. It is also expensive to build seawalls. One example is the seawall at Galveston, Texas, USA. It was built for protection of the city after the 1900 hurricane. Another example is the seawall in Vancouver, Canada. It is a stonewall that was constructed around the perimeter of Stanley Park to prevent the erosion of the park’s foreshore. It was built because the waves created by ships passing through the area were eroding the coast.

In some coastal areas, people have built breakwaters off the coast but parallel to it in order to protect the coast from high-energy waves. A breakwater is usually made of granite. It creates a zone of sheltered water between itself and the coast, so that waves will break against it before reaching the coast. The calm waters will deposit materials, forming beaches. Calm waters generate further material deposition for beach accretion or beach build-up. However breakwaters are unable to provide full protection as they still leaves areas of the coast unprotected. The unprotected areas will be prone to erosion. Besides, protection on one part of the coast causes problems further down the coast. One example is the breakwaters in Singapore. They are built along the beaches at East Coast Park, as well as Siloso Beach on Sentosa Island.

In some places, to protect a beach from erosion by high-energy waves, people have built groynes along the beach. A groyne is a low wall built at right angles to prevent materials from being transported away by the longshore drift encouraging build-up of beach. This enables the transported materials to accumulate on the side of the groyne facing the longshore drift. However, on the other side of the groyne, the materials carried by the longshore drift will not replenish the beach. Hence the beach further down the coast may be eroded away. While a series of groynes can help to reduce this effect, they spoil the natural beauty of the coastal environment. Also groynes fail to keep the beach fully intact and aligned but instead cause it to be like the teeth of a saw. For example the groynes of Sussex, United Kingdom and those at the East Coast Park, Singapore have been built to build up the beach on the up drift side.

Gabions are wired cages filled with crushed rocks, piled up along the shore to form a wall to protect the coast from erosion and weaken wave energy. They are also used to protect other coastal protection structures such as seawalls. However, they only offer short-term protection of 10 years. The wires cages are easily destroyed by powerful waves, easily corroded by seawater and easily trampled on and vandalized by humans. They are cheap and affordable but ugly and ruin the natural beauty of coasts. They require regular maintenance and if not properly maintained, wire cages are unsightly and dangerous along the beach. One example is in Hornsea Beach in England. Timber groynes afford protection and an on going refurbishment program ensure this has continued. The groynes on Hornsea beach ensure wide and relatively steep beaches.

Soft engineering involves applying knowledge of natural...
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