By Mohamed Issa
UROA, Tanzania, March 21 (Thomson Reuters Foundation) - A visitor to the Nungwi Peninsula in Unguja, one of Zanzibar's twin islands, has their pick of luxury resorts, all promising access to golden beaches.
But resort owners trying to protect those beaches from coastal erosion, by erecting seawalls along the shore, are coming under fire from residents and marine experts, who say the trend destroys the environment and threatens the livelihoods of local communities.
Built perpendicular or parallel to the beach, vertical seawalls divert waves away from the beaches to slow the natural erosion process. In some cases, concrete piles are placed in front of the walls to help weaken the waves before they hit the walls.
The problem, say environmentalists, is that while the structures help keep resort beaches intact, the walls can speed up erosion on other parts of the island by diverting the waves to unprotected sections of the coast.
That can increase the intensity of other processes that disrupt the local ecosystem, such as wave scouring - when waves eat away at the base of structures such as cliffs - and over-topping, when waves pass over reefs.
There are about 500 metres of vertical seawalls along the beaches of Nungwi Peninsula, according to Peter Letitre, senior project manager at the Netherlands-based Deltares water research institute, with "more and more" being built all the time.
"The negative side is(they) accelerate the erosion by washing away the sand at the foot of the wall," Letitre said in an email interview.
DISAPPEARING DUNES, FLOODED GRAVES
Resort owners insist the seawalls are a matter of financial survival. According to official figures, in 2014 Zanzibar's islands had around 260 hotels - 20 of them boasting five stars.
Together they drew a large number of the 175,000 tourists who visited the country that year - and the tourism sector contributed between 25 and 27 percent to Zanzibar's gross domestic product.
But the country's beaches are under constant threat from erosion, a problem that is worsening as a result of sea level rise linked to climate change, scientists say.
In the village of Uroa, on the eastern coast of Unguja, villager Shaame Mcha Chambo told the Thomson Reuters Foundation that the present beach line represents a loss of more than 40 metres of landmass "eaten by the encroaching sea" over the past five decades.
Resorts on the islands are so concerned about the encroaching sea that they feel they have no choice but to put up seawalls, prioritizing protecting their property over the uninterrupted sea views that their guests expect.
But when resorts build walls to stop their sand disappearing, local communities can pay the price.
Chambo and two other Uroa villagers told Thomson Reuters Foundation that the construction of a seawall at one resort destroyed a major reef, while the erosion induced by the wall has almost cleared the trees that provided natural protection for the beach and has also indirectly contributed to the submerging of a key offshore sand dune.
"Our fathers and relatives who eke out their living from fishing used to stay at the dune as their transit point," they said, referring to the practice of fishermen stopping on the dunes for a few hours or even days to rest and plan future fishing trips.
"Look, the dune is no more and the fishing patterns of the people have been disrupted," he said.
Mariyama Ussi Khamis, a member of the Uroa executive committee that helps run the village, told the Thomson Reuters Foundation that in the five years since the lodge put up its seawalls, enough unprotected land has been lost to cause the village's coastal graveyard to succumb to seawater flooding.
"If the trend of erecting such seawalls is not reversed," she warned, the village of 3,050 people could see beach erosion threaten its burial sites, a market place and about 15 homes that sit along the shoreline.
Zanzibar's authorities seem to agree. In January, the government's Department of Environment stated that the lodge's 20-to-30-metre-long vertical seawall was built against regulations and has to be either removed or modified into slanted walls.
Also called gradient walls or revetments, slanted walls are better able to absorb the energy of the waves, which means less water is diverted to other parts of the coast.
Letitre of Deltares warns that if the government does not start considering large scale coastal management measures, in the long term the beaches in front of and adjacent to the seawalls will disappear.
Eventually, he said, there will be very little beach left for the walls to protect.
If developers insist on building walls on their beaches, he said, they should be slanted, and resorts should supplement them with beach nourishment. The process entails "artificial sand-re-circulation," where parts of the beach that have been depleted are filled in with sand brought in from elsewhere.
"In general these 'soft' solutions are preferred over 'hard' solutions (structures), since in general no erosive effects to other parts of the coasts occur if soft solutions are applied," he said. He noted that 'soft solutions' are generally better looking as well.
(Reporting by Mohamed Issa; editing by Jumana Farouky and Laurie Goering :; Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, climate change, women's rights, trafficking and property rights. Visit http://news.trust.org/climate)