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Doubts remain about plan to build tsunami wall in Palu
Most of Central Sulawesi’s Palu residents were getting ready for maghrib (sunset) prayer or dinner when a 7
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span>Most of Central Sulawesi’s Palu residents were getting ready for maghrib (sunset) prayer or dinner when a 7.4-magnitude earthquake from the nearby Palu-Koro fault jolted the city and its surrounding areas on Sept. 28, 2018.
The quake later caused a submarine landslide in Palu Bay, triggering tsunami waves measuring up to 7 meters in height. The wave led to severe casualties and damage, killing more than 4,000 people and destroying thousands of buildings.
As Palu and its surrounding areas are rebuilding themselves brick by brick, the government has hatched a plan to build a seawall along the beaches facing the bay, intended as protection against incoming tsunami waves.
When the plan was announced, it immediately drew ire from scientists and activists, who say the seawall would not do well against future tsunamis.
The plan was first conveyed in a reconstruction plan for regions in Central Sulawesi affected by the earthquake and tsunami made by the National Development Planning Agency (Bappenas) in early 2019. According to the plan, the 6-m vertical seawall was proposed by the Japan International Cooperation Agency (JICA).
Widjo Kongko, a tsunami expert from the Agency for the Assessment and Application of Technology (BPPT), was among the scientists opposing the seawall plan.
“Seawalls have yet to be proven effective in preventing an area from being swept by tsunami waves, including in Japan,” Widjo told The Jakarta Post recently.
He added that any projects to rebuild the destroyed Palu and its surrounding areas should prioritize the value of disaster mitigation, as the area was unstable and disaster-prone.
Palu is prone to earthquakes because it is located near the Palu-Koro fault. The fault is a fracture in the Earth’s crust that runs underneath Sulawesi island from the Makassar Strait to the northern part of the Boni Gulf in southern Sulawesi. Palu-Koro is considered an active fault with a motion that ranges between 30 and 44 millimeters per year.
An activist with the Central Sulawesi chapter of the Indonesian Forum for the Environment (Walhi), Aries Bira, echoed Widjo, saying there had yet to be any scientific studies regarding such seawall.
“There are also documents required for the project, such as environmental impact analysis documents. We also don’t know whether the project is compatible with the new version of Palu’s spatial plan,” Aries said.
He also questioned whether local residents, especially those affected by the earthquake and tsunami disaster in 2018, had been involved in the deliberation process for the reconstruction.
Both Widjo and Aries agreed that replanting mangrove trees along the coast of Palu Bay would be more effective in protecting the land against tsunami waves.
“There is evidence on the western coast of Palu Bay, where tsunami waves couldn’t reach the land in 2018 because it was blocked by intact mangrove forests. It has been local wisdom to protect the area against tsunamis for generations,” Widjo said.
However, he admitted it would be a challenge to plant mangroves in the eastern part of the bay due to the geographical structure of the beach there. Widjo suggested authorities build a dike with an access road on top of the structure rather than a vertical seawall as coastal protection against tsunamis.
President Joko “Jokowi” Widodo was among officials dismissing the concerns surrounding the seawall, saying it should be erected immediately to protect the area from future disasters.
“Stop all debate regarding this structure, and start the construction immediately!” the President said.
It took no time for the government to answer Jokowi’s call, as local officials said the seawall would be included in the Palu rehabilitation plan, although there were some alterations.
The Public Works and Housing Ministry’s head of disaster management in Central Sulawesi, Arie Setiadi Moerwanto, told journalists recently that the ministry would start the construction project for a 7.2-kilometer coastal dike at Silabeta Beach.
Arie said the dike would be constructed using stones as the main material and be 3 m tall — the same height as the highest tide. The structure would also be covered in water-resistant bio-synthetic materials.
“We have heard the people’s concerns. However, some places at Talise Beach are not suitable for mangroves. We will still plant the trees along with the construction of the dike,” Arie told journalists recently.
Commonly known as intertidal plants, mangroves mostly grow in coastal areas where freshwater mixes with seawater. The plant also needs sediment composed of accumulated deposits of mud. However, most parts of Talise Beach are sandy.
He added the dike would also prevent seawater from intruding further inland due to land subsidence along the coastal area. Mangroves or other coastal plants would also be planted in front of the coastal dikes.
Both central government and local authorities are planning to build more structures on beaches along Palu Bay, as Arie’s office is currently planning on the construction of other structures along the coast.
