Island News

Seawalls damage coasts

Written By : ALUMECI NAKEKE. In many coastal villagers, seawalls are built to stop soil erosion. The community come together to raise thousands of dollars and built the cement structures
16 Aug 2008 12:00

image Written By : ALUMECI NAKEKE. In many coastal villagers, seawalls are built to stop soil erosion. The community come together to raise thousands of dollars and built the cement structures only to collapse with the raging tide.
But for seawalls withstanding the impact of nature, it has been found that it causes more damage then good by damaging the natural habitat of marine life.
Partners in Community Development Fiji scientific (PCDF) officer Iliapi Tuwai said it was impossible to build defence structures without severe impacts on natural habitats.
He said the current had to find another route which led to the erosion of nearby coasts to the walled area. And the waves also took whatever it could from the bottom of the structure when it went back.
“What it does is that it takes sand and everything out especially wherever there is a seawall and putting it in other places. In the long term the seashore will erode because of the wave motion and the seawall would also be damaged,” he said.
He said to one of the reasons this happened was the way the seawalls were constructed.
“People now realise that those seawalls are damaging their seashores because they were constructed in a vertical or upright position and when the waves come in they hit it and then they go back with the sand. Eventually as time goes on the foundation of those walls will soon fall,” he said.
“If you try to decrease the strength of the wave the seawall should be built in a vertical level and not upright because the waves will just smash it and wash the sand away from the bottom.
“The current has to find another route and it takes back the sand and whatever is at the foot of the seawall when it goes back. Eventually the walls would crack and finally come down.” He also said that the habitat of organisms that live there is affected and brings in destruction and changes to the marine life.
This was also confirmed by a team from the University of the South Pacific’s Institute of Applied Sciences at Votua Village on the Coral Coast posted on the Locally Marine Managed Area website.
They found that apart from other developments that was causing coastal erosion it was exacerbated by the building of seawalls and jetties, both of which prevented the natural flow of currents from depositing sand.
According to team they were told by one of the villagers that the seawall was not helping the erosion because when the waves hit the wall it took the sand away.
In Australia according to “Building Biodiversity” (July issue) it said that seawalls differ from natural shores.
Natural shores have a gradual slope, whereas seawalls were usually vertical. ‘This has an important but often ignored consequence because the extensive intertidal zone of natural shores is compressed into a very small area.
Animals living separated from each other in different parts of the intertidal zone on natural shores may come into contact on seawalls. Thus, competitive interactions, unlikely on natural shores can become important on seawalls.
Competitive interactions among individuals of the same species and among individuals of different species are important ecological processes, influencing ecosystem structure and functioning’.
PCDF have helped resorts to solve the problem of coastal erosion in Fiji some resorts protect their beaches by the construction of fish houses to decrease the strength of the waves before finally hitting the shores.
Tuwai said the fish houses were placed in front of the resorts and corals were also planted on the fish houses in which guests also took part.
“We are also trying to conserve corals because some of the areas have already been degraded and we can conserve it and put in place some strategies like growing corals, on the tables and in fish houses,” he said.
“This is just like any activity that was introduced in resorts and hotels in which the guests would come in and participate. It is also one area for people to come in and appreciate what is going on but at the same time those fish houses would decrease the strength of the waves.”
“That is the reason they are putting up those fish houses. Even though it is a small scale we have to put it in such a fashion that the waves will be absorbed or like a barrier to withstand all that. This has also been done in the Caribbeans in a very large scale but they have very large fish houses because of the devastation caused by these waves.”
He said the fish houses also had a purpose and that is to house the fish as well and that is why they plant corals around it. “The size of the fish house is up to you long as you can lift it. You have to arrange the stones and it is put together by cement and you could put in holes for the fish to go in,” he said.
“You can also plant the corals on the house by taking a ball of cement to stick a cookie which has the coral attached to it and it only tales a few minutes to stick it.
“Those are some of the activities carried out by the resorts and most of the tourists are attracted to this idea.
Another solution to coastal erosion carried out by resorts is to fill the shore with more sand which is expensive, said Tuwai.
He said one of the best methods of erecting seawalls is to arrange stones along the degraded area so that the sand that is brought in by the waves could settle in it.
Soon it would be covered with sand and would naturally get back

Note: Ms Nakeke is a Ocean Science Reporter with SeaWeb. SeaWeb is a non government organization that helps the media promote a healthy ocean.

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