SOFT ENGINEERING MEASURES
Beach nourishment
Beach nourishment slows down the erosion of beaches. It involves using sand from an external source to replenish the sand on a depleted beach. This sand may come from another beach or be dredged from the seafloor. This measure can successfully change a coast into a wide, sandy beach that offers protection to the immediate inland area.
// For example, beach nourishment restored the depleted beach at the coast of cape may point in New Jersey, United States of America. Another example is Sentosa, Singapore where beach material of fine sand was brought in to replenish Siloso, Palawan and Tanjong beaches. As a result, the beaches became aesthetically pleasing.
Disadvantage
However, beach nourishment also has its disadvantages. Firstly, trucking or piping in the sand can be expensive and time-consuming. Secondly, many beach nourishment projects around the world have developed problems.
// Coral reefs at Waikiki beach, for example, have been destroyed as sand used for beach nourishment was washed out to sea and suffocated the corals. Thirdly, re-nourished beaches can also be eroded again unless other management strategies are put in place.
Planting vegetation and stabilising dunes
Planting vegetation such as mangroves can help stabilise coastlines. As mangroves absorb wave energy through their dense root system, the value of maintaining and replanting mangroves is now widely recognized.
However, vegetation may take a number of years to be established before it can resist natural elements such as strips and human elements such as trampling or even vandalism.
Sand dunes can be stabilised by planting grasses. The roots of grasses anchor the sand and prevent erosion. Matting is often put over the dunes, and young grasses are planted into the sand through the matting. Over time, the grass becomes established and the dunes become more stable. The matting then rots away, adding nutrients to the sand
To prevent the vegetated dunes from being disturbed by human traffic, fences and access paths need to be built. One disadvantage of this is the costs incurred from maintaining the fences and pats, with fences needing to be replaced with taller ones over time as sand accumulates
// For Example, the coast along Triton Place, Western Australia has vegetated sand dunes and an access fence.
Encouraging coral reef growth
Measures can be taken to advance coral reef growth. Coral reefs help weaken wave energy and serve as a breeding ground and nursery for fish. Artificial reefs can be created by placing lasting materials such as steel or concrete onto the seafloor. Corals, together with other marine creatures and vegetation, colonise these materials and start to function as a natural reef.
Since 1996, the Maldives, which is a Low-lying archipelago in the Indian Ocean, has been operating a coral-growing Programme to help curb severe beach erosion on its many islands. A structure of welded construction steel rods has been placed off the coast of one of its resort islands of Ihuru. The structure is charged with Low-voltage solar-generated electricity to speed up coral growth. Corals are reportedly growing three to five times faster than normal, and the island now sustains a large variety of corals, marine animals and organisms. The project has received international recognition.
However, it is not easy to encourage coral reef growth as sites need to be surveyed to ensure maximum opportunity for growth. The dangers of siltation also need to be overcome or avoided. Coral growth may be slow, taking perhaps over 20-30 years before results appear. Even then, coral growth may not be significant
HARD ENGINEERING MEASURES
Sea walls
Sea walls are constructed to protect coastlines against wave attack by absorbing wave energy. Most seawalls are made of concrete or stone and are built parallel to the coast.
However, seawalls are costly to build and maintain as constant repairs have to be made to prevent their collapse. Seawalls absorb only some wave energy and reflect incoming waves. Most seawalls achieve only initial success. The powerful backwash of reflected waves washes away the beach materials at the foot of and beneath the seawall. This erosion by waves eventually undermines the base of the seawalls, leading to their collapse.
// For example, a seawall along the coast of Drakes Island in England collapsed due to erosion occurring at its base.
Gabions
Gabions are wire caged usually filled with crushed rocks. These cages are built along a shore or behind a beach to prevent or reduce coastal erosion by weakening wave energy.
Gabions absorb wave energy better than seawalls. This is because the gaps between the rocks allow water to filter through. This way, gabions prove to be successful defences against high energy waves.
// For example, gabions along the Andaman coast in Thailand successfully protect the coast from erosion.
However, wire cages are unsightly. They are also costly as they need to be maintained regularly. Gabions are easily corroded by seawater and damaged by excessive trampling or vandalism.
// For example, gabions were installed when the East Coast park in Singapore was first reclaimed. The gabions were subsequently removed as they were vandalised.
Breakwaters
Breakwaters help break the force of oncoming waves. They can be built either parallel to the coast or with one end attached to the coast. When constructed offshore, breakwaters can create a zone of calm water to form beaches. The calm water zone is often used as a sheltered Harbour for boats.
// For instance, a breakwater in Almeria, Spain, successfully protects the coast from erosion.
Breakwaters have their disadvantages. They are aesthetically unappealing and are costly to build. Breakwaters also protect the coast unevenly. Materials deposited in the zone behind the breakwater are protected while those in the zones located away from the breakwater are subjected to wave action and possible erosion.
// For example, breakwaters built in Portland Harbour, England resulted in erosion and flooding problems, which affected properties, beaches and communication infrastructure.
Groynes
Grounds are low walls constructed at right angles to the shore to retain sediments that might otherwise be removed due to longshore drift. These structures absorb or reduce the energy of the waves and cause materials to be deposited on the updraft side of the ground facing the longshore drift.
// A series of groynes along the coast of Eastbourne, United Kingdom, successfully maintains beaches along the coast.
However, groynes are unsightly and expensive to build and maintain. Moreover, no new materials are carried and deposited on the downdrift side which is not protected by the groyne. As a result, longshore drift will gradually erode away the unprotected part of the beach.
// For example, large amounts of sediments were eroded on the downdrift side of a ground built along Sandy Hook in New Jersey, United States of America. The ground was eventually demolished.
To prevent or reduce the erosion of beach materials on the downdrift side of the groyne, the tips of groynes are sometimes angled about 10 degrees, depending on the direction of the prevailing waves. If successful, groynes can help sustain and even extend beach areas
Tetrapods
Tetrapods are four-pronged concrete structures that help dissipate wave energy. They are stacked offshore in an interlocking position.
- In contrast to breakwaters or seawalls, tetrapods allow water to pass around them rather than hit against them. Hence, no powerful backwash is generated, which reduces the possibility of tetrapods being damaged by waves.
- Tetrapods are pre-casted, which means they are cast into their final shape before being positioned.
- They can be placed quickly compared to other structures which may take time to build while coasts are still under attack from waves.
// An example would be Crescent City, a town on the coast of Northern California. Tetrapods have been used for many years in the town, to defend against coastal erosion and to reduce the impact of tsunamis, which occurred 31 times between 1933 and 2008. On the other hand, tetrapods are aesthetically unappealing and expensive to build. They are also dangerous to swimmers, surfers and boaters.
