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Hybrid structure offers hope for sinking villages
Under threat: Tidal flooding, locally known as the rob, inundates Sriwulan village in Demak regency, Central Java, as a result of coastal erosion
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nder threat: Tidal flooding, locally known as the rob, inundates Sriwulan village in Demak regency, Central Java, as a result of coastal erosion. Many villages on the coastline of Demak are threatened by coastal erosion and land subsidence.(JP/Donny Fernando)
Forty-six-year-old Mat Sairi from Timbulsloko village in Demak regency, Central Java, has been worried for several years that one day he will lose his fish pond as a result of massive coastal erosion that has been consuming the village inch by inch for the last 20 years.
While erosion is a natural phenomenon that occurs in coastal areas, the phenomenon has been getting worse in Demak as a result of, among other things, unsustainable land use as residents cut mangrove trees that serve as the beach’s natural protection against sea waves and land reclamation in the neighboring city of Semarang.
Timbulsloko is among the villages on Demak’s northern coast hit by the massive erosion over the last decade. Data from the Maritime Affairs and Fisheries Ministry recorded the regency had lost around 550 hectares of coastal land in the past 15 years. Meanwhile, it only regained 179 ha through natural sedimentation.
At this rate, Mat would completely lose the land where he has lived for years as well as his main source of livelihood in the next few years.
Since 2015, the Maritime Affairs and Fisheries Ministry has been coming to Timbulsloko and its neighboring villages affected by the erosion bringing bamboo fences, an approach intended to restore the lost land and mangrove forests. The ministry calls such fences “hybrid engineering” structures.
For years, the government has been installing concrete structures such as seawalls and wave barriers to protect coastal areas from erosion. These structures, however, only protect the land from being further eroded, but do not reclaim the lost land, as natural sedimentation is blocked by such structures.
The concrete structures could also trigger worse erosion in other coastal areas. This is happening in the neighboring city of Semarang, where its concrete tidal flood control structures are believed to have worsened erosion in Demak.
The permeable structure — two parallel bamboo fences with the space between them filled by twigs — will trap mud sediment brought by the tide and sea waves, allowing it to consolidate into a mass of land.
A similar approach has been used in the Netherlands for centuries, when Dutch people tried to reclaim land on the Wadden Sea.
“This is in line with the principle of building with nature, as we only use this structure to accelerate a natural process occurring on the coast,” said Abdul Muhari, the ministry’s coastal disaster mitigation section head.
When the aquaculture trend was popular in Demak almost a decade ago, the regency’s coastal residents converted their land into fish ponds while cutting a significant number of mangrove trees in the process, thus preventing the accretion of sediment and worsening erosion in the area.
The new mass of land would later catch mangrove seeds brought by the tides, which will eventually grow as trees and form new mangrove forests along the coastline.
Sairi said the effort to reclaim lost land in the village had started to bear fruit. “In several places across the village, it had formed sediment [that help to grow] mangrove naturally. It will eventually protect the village from the sea waves,” he said.
The Jakarta Post had a chance to observe the bamboo fences by taking a boat trip along the coastline of several villages in Demak — Timbulsloko, Bedono and Purworejo — and saw that sedimentation had formed behind several hybrid structures in those villages. Those in Purworejo showed more significant progress, as a small group of mangrove trees was seen growing in the sedimentation.
The Post’s reporting on the impact of climate change was funded with a grant from the Society of Indonesian Environment Journalists and the United Nations.
However, not every local resident along the northern coast of Demak embraces the structure. Only a handful of residents of Purworejo village in the regency understand the structure’s function and declare their commitment to protect it, a community leader has claimed.
Local school headmaster Maftuhin, 51, said he had found several residents using bamboo from the structure for fences at their houses. He could identify that the bamboo had come from the structure as it was painted white.
Prior to building the structure, the ministry and its contractor painted the bamboo with wood paint as protection against barnacles.
When Maftuhin asked the residents where they had gotten the bamboo, the residents answered that they found it lying on the beach.
“I don’t want to presume that they deliberately took the bamboo directly from the structure. However, they should at least return it to the beach rather than using it as their house fence. This might show that they don't care much about the hybrid structure,” Maftuhin told the Post.
The village — located about one hour by car from Timbulsloko — has lost some of its coastal land to rampant erosion. However, the phenomenon has yet to affect residents’ houses like in its neighboring village; it is rare to see a house permanently inundated by seawater in Purworejo.
However, the village’s coastal land has been decreasing fast, prompting the Maritime Affairs and Fisheries Ministry to install the hybrid structure ahead of the village’s beach.
“Maybe this is why people in Purworejo are as yet unaware of the importance of the hybrid structure, while we actually need it so our village won’t become inundated like our neighbors’,” Maftuhin said.
Maftuhin added he had continued to spread the word about the importance of coastal area reclamation measures through, for example, religious gatherings among female villagers.
“Tell your husbands that we should keep those structures in our villages, as it would help us to protect the village. Of course, you don’t want to have the same fate as our neighbors in Bedono, right?” Maftuhin told villagers during a religious gathering recently.
The structure needs to be maintained regularly, as it would be damaged by seawater or marine animals. This, however, is often overlooked by the local administration and communities who are responsible for taking care of the structure a year after its construction.
A consortium of environmental groups, including Wetlands International Indonesia, has been working with local residents in an attempt to reclaim the villages’ coastal area.
The environmental groups assist groups of local residents by educating them on farming fish and clams, among other things, in mangrove forests — an approach called Mixed Mangrove Aquaculture. In exchange, the residents are required to support the efforts to protect the coastal area, including the maintenance of the hybrid structures.
“If these villagers say they need materials to maintain the structure, we will tell them to make a proper plan for its maintenance. Later, we will provide them with the materials they asked for,” said Apri Susanto Astra of Wetlands International Indonesia.
