Designers of the Batang Toru Hydropower Plant in North Sumatra have considered the risk of earthquakes and followed the standards and regulations set by the International Commission on Large Dams (Icold), in consultation with experts from China, France, Taiwan and Indonesia. (Photo courtesy of North Sumatra Hydro Energy)

Batang Toru Hydropower Plant Designed to Withstand Quakes, Expert Says

MAY 31, 2019

Jakarta. The Batang Toru Hydropower Plant will neither uses a reservoir nor depend on a giant dam to power it, thus its volume will be so small that earthquakes pose little to no risk, an expert said.

The designers have considered the risks of earthquakes and followed the standards and regulations set by the International Commission on Large Dams (Icold), in consultation with experts from China, France, Taiwan and Indonesia.

The construction of the plant can only start once the Indonesian Dam Safety Commission, which resorts under the Ministry of Public Works and Housing, gives the green light.

Didiek Djarwadi, head technical commissioner for seismic aspects of dam design at the National Committee on Large Dams (KNIBB), explained that the plant is located 5 kilometers from a techtonic fault, but that the dam site has been prepared to withstand earthquakes. Didiek said he and his team have collected data on the epicenters of all earthquake that occurred in North Sumatra between 1900 and 2016 and that that the closest tectonic fault is inactive.

He said all seismic surveys, including a hazard assessment and hazard analysis for the Batang Toru hydropower plant, were completed in March 2017. Additionally, seismic parameters for the plant comply with the regulations set out in Icold Bulletin No. 148, which deals with the selection parameters for large dams, where the "total hazard" is calculated, including the subduction zone, shallow crustal and background, or Benioff zone.

The study found a slip rate of 5 millimeters per year between Sarulla and Sipirok, located in North Tapanuli and South Tapanuli districts, respectively. Meanwhile, the dam that is being constructed for the hydropower plant is located 4.5 kilometers from the fault and designed to withstand seismic activity.

"This is the geophysical study we conducted for the Batang Toru hydropower plant. So the plant can be built safely, as long as we follow the rules and standards," Didiek said.

He added that the study also calculated several possibilities after considering the seismic data for North Sumatra he and his team have collected over the years.

"These results from our studies are what we set as parameters for the construction of this hydropower plant, in accordance with the rules and specifications from Icold, including measures against seismic activity. From our calculations, earthquakes happen quite frequently in the area, but they're usually no more than magnitude 2 and can barely be felt by humans," Didiek explained.

He said there are two "windows" from which to calculate the intensity of earthquakes: distance and magnitude. These windows ultimately determine what effect an earthquake could have on a dam's structure. In this case, the nearest epicenter 4.5 km away, and the largest magnitude recorded was 6.7.

"Because of this, we recommend a threefold safety factor for the dam structure. The concrete for this dam must withstand three pull forces created by an earthquake," Didiek said.

For example, when the Singkarak hydropower plant was rocked by a 6.8-magnitude earthquake in 2007, the structural integrity of the dam remained sound, even though the earthquake epicenter was only 2 kilometers away, he said.

"We've done some in-depth and detailed research since 2016, but the results were never made public because it's company owned. We've followed recommendations and warnings from professor Tengku Abdullah Sani [of the Bandung Institute of Technology], and we've confirmed that the Batang Toru hydropower plant is located within a red zone," he said.

Regarding the plant's powerhouse, Didiek said the same regulations were followed as with the construction of the dam, as specified by the Icold bulletin, which states that it should not to be built on top of a fault and that the concrete used in the construction should have adequate strength to withstand powerful earthquakes.

Looking back at the research conducted over 116 years, almost all areas in Indonesia are prone to earthquakes. The earthquake epicenters in Indonesia are spread out almost evenly, Didiek said.

"If we can't build in areas close to epicenters, we'll never build anything," he added.