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 processes to stabilize the coast and reduce erosion and focuses on planning and management to encourage minimal human interference and allowing nature to take its course. A coastal dune is a ridge of sand piled up by wind on the coast. Coastal dunes are common in countries where the coasts have vegetation like spinifex and marram grass and are exposed to strong winds from the oceans. The dunes form as a result of the vegetation trapping and stabilizing the sand. On some coasts, the dunes extend several kilometers inland and to heights of more than 100 meters.
Coastal dunes, which act as barriers along the coast, protect human property like houses and roads against coastal erosion and flooding from waves. The dunes also provide a habitat for many animals including migratory birds. On some coasts, human activities have disturbed the coastal dunes. Moving vehicles and people walking across the dunes have damaged the vegetation on the coast. The loss of vegetation causes the sand to be easily blown inland, which can cover nearby roads, farms and buildings. In the southwestern coast of France, dunes that have moved inland have caused entire towns to be abandoned.
Dunes can be stabilized by growing trees, shrubs and grass whose roots trap and anchor soil which prevents the sand from being blown inland. However, it is only an effective short-term measure. Vegetation growth cannot totally prevent erosion if human activities like property and resort development continue to take place along coastal areas. Difficulty is faced in seeking cooperation from those with investments in coastal areas. An example is the coastal dunes in Omaha Beach, New Zealand, which are stabilized by marram grass.
In some countries, people have planted mangroves to help protect the coast against erosion by strong waves and winds. Many of the mangrove trees have prop roots or kneed roots that grow and spread trapping sediments to form small islands and thus extend coastal land seawards. Mangrove adds greenery to the environment and enhances the beauty of the landscape. Also the spawning grounds of fishes, crabs and prawns. Not all coastal areas can support growth mangroves especially those affected by destructive waves. With the growth of mangroves, coast becomes shallower disrupting coastal transport and port activities.
Effectiveness of this measure is seen in lesser damage suffered from 2004 Indian Ocean Tsunami in mangrove-rich coastal areas of Bangladesh when compared with areas like Sri Lanka without mangroves. Malaysian government is now planting mangroves along its coastline and villagers of Sulawesi, Indonesia are planting mangroves along coastal villages. In some countries, people carry out beach nourishment to protect the coast. This involves transporting sand from other areas to replace sand lost to longshore drift and erosion. The beach can be extended seawards improving beach quality. It also maintains the natural beauty of the area.
An example is the beach nourishment on Gold Coast, Australia, has widened the beach, thus improving its quality. However, beach intactness through beach nourishment is only for 10 years as beach erosion is a continual process. Regular replenishment is necessary to ensure beach intactness but costly to transport large quantities of bulky heavy sand to fill up the beach as abundant sand is needed. An example is the beach nourishment on 24km Miami Beach in 2005 cost S$105 million. Imported sand gets washed out to sea, covers and kills the coral. Coral reefs are masses of rock-like substances called corals growing in shallow seas.
They protect beaches against coastal erosion by reducing the speed of the waves approaching the coast. Hence, by the time the waves reach the shore, most of their energy would have been lost. They enhance natural environment and fishing opportunities. However, over the years, human activities, such as dynamite, fishing, sand mining and land reclamation, have destroyed a number of coral reefs. The negative impact of human activities, such as water pollution, has aggravated the problem because corals can only grow well in clear waters. In some countries like Malaysia, the government has taken measures to encourage the growth of coral reefs.
For example, they have banned fishing within certain protected areas, as well as built wastewater treatment facilities in coastal settlements. In other countries, people have planned artificial reefs to allow corals to grow. However the success of these measures in the long run depends on the cooperation of various groups of people, including industries, fisherman and governing authorities, it also requires constant effort to reduce water pollution. Another e. g. is in the Maldives. The coral growing has been carried out to combat beach erosion on many islands, called Ihuru Necklace.
In conclusion, soft engineering is very environmentally friendly. They protect the coastlines from erosion and do not have adverse effects on the environment. They also improve aesthetics and are cheap because they use living structures, which tend to mature and stabilize with time reducing maintenance costs. However, they require long periods of time before they can fully reduce coastal erosion. Also encouraging more and more people to support soft engineering measures are difficult because business ventures may lose out to these measures. Thus, it should combine with the hard-engineering measures to work together to protect the coast.