Lojing Sabo Dam: Technology Tracks Risk, Engineering Responds

The second and final article in this two-part report explores the expertise and technology behind the construction of the Lojing Sabo Dam, including how its location and design were determined, the use of technology, as well as monitoring and maintenance measures to ensure the structure’s long-term effectiveness.

 

The damage visible on a road may merely be the final manifestation of a threat that began much further upstream.

In Lojing, heavy rainfall can trigger the movement of water together with soil, rocks, timber and debris from slopes before the flow converges towards Federal Route FT185, as occurred on Jan 3, 2021, causing extensive damage at Section 61 of the Lojing-Gua Musang Road.

The incident prompted the Public Works Department (JKR) to review its mitigation approach, as merely repairing damage downstream would not be a comprehensive solution if the threat upstream remained unaddressed.

Based on technical assessments and the success of three previous projects, JKR identified the Sabo Dam approach as the best solution and decided to construct one at Section 61 of the route.

JKR director-general Datuk Ibrahim Esa said construction of the project was fully completed on July 14, 2026, after being carried out for 13 months from June 18, 2025.

“The main rationale for its implementation is to provide a long-term solution or mitigation against debris flow risks that could affect the safety of road users, infrastructure and the accessibility of Federal Route FT185,” he told Bernama.

The nearly RM11 million project involves more than just the construction of a single structure. It is a comprehensive mitigation and rehabilitation package comprising a Sabo Dam, debris flow barrier, slope repair and strengthening, drainage systems, pavement works, road rehabilitation and utility relocation.

The project also involved the acquisition of about 1.7 acres of land to provide sufficient space for the entire mitigation system to be developed more effectively.

 

BREAKING THE CHAIN OF RISK

Sabo Dam is a Japanese technology, with ‘sabo’ referring to sand control. In Malaysia, the Lojing Sabo Dam is the fourth such structure in Peninsular Malaysia, after those in Raub, Pahang; Seremban, Negeri Sembilan; and Baling, Kedah.

However, the project adopts a distinct approach by integrating several components into a layered protection system.

Ibrahim said the decision to construct the Sabo Dam was made following a technical assessment that took into account the history and causes of previous incidents, the valley-like terrain between two slopes, the presence of debris materials upstream and the road’s exposure to flows during heavy rainfall.

“The Lojing Sabo Dam adopts an integrated approach, combining the Sabo Dam, debris flow barrier, slope repairs and drainage system as a layered protection system,” he said.

The main function of the Sabo Dam is to control the movement of sediment and debris from upstream areas, slow the flow and reduce its impact energy before it reaches downstream areas.

During heavy rainfall, water flowing from higher ground can carry soil, sand, rocks, large boulders, timber and other debris.

The Sabo Dam helps trap or retain some of these materials, while the debris flow barrier provides an additional layer of protection to trap rocks, timber and debris.

The combination is intended to reduce the amount and size of debris reaching the road, minimise the impact on roads, bridges and drainage systems, and reduce the likelihood of roads being buried or cut off.

However, the structure is not designed to stop landslides at their source.

Slope instability risks are addressed through slope rehabilitation and drainage management, while the Sabo Dam and debris flow barrier control materials that have already moved downstream.

 

NO ONE-SIZE-FITS-ALL DESIGN

Behind what appears to be a physical solution, the actual engineering work begins much earlier, determining where the structure should be built and how it should function under real-world conditions.

Director of JKR’s Slope Engineering Branch Mohd Shaifuddin Abdul Razak said the location of the Sabo Dam was selected based on topographical, geological and hydrological studies, as well as analysis of debris flow paths.

“For the FT185 Section 61 area, the technical assessment found that the terrain resembles a valley between two slopes, with limited vegetation cover.

“This combination increases the likelihood of rainwater and loose materials from upstream areas converging along the route and moving towards the road during heavy rainfall,” he said.

He said the location also had a history of serious landslides and debris flows in 2021, which affected the FT185 route.

In determining the location, JKR had to identify where potential debris originated, where it would move, the shape and gradient of the valley, geological conditions and the structural foundation, the available space for trapping materials, the distance from the road, as well as access for construction and maintenance.

“This means we are not merely looking for a suitable place to build a structure, but the most effective location to break or reduce the chain of risk from upstream areas to downstream infrastructure,” he said.

The same approach was applied to the design, as a Sabo Dam is more than just a concrete structure.

The structure must interact with water, soil, rocks and sediment during a debris flow.

Parameters assessed include the topography and geometry of the valley, the size and characteristics of the catchment area, rainfall data, the rate and path of water flow, estimated debris volume, the size of boulders and timber, as well as the velocity and impact force of the flow.

Geological conditions, foundation strength, structural stability, potential erosion and scouring, sediment storage or control capacity, as well as maintenance access requirements, are also taken into account.

For this reason, the design of a Sabo Dam must be site-specific and cannot simply be transferred from one location to another without proper study.

 

TECHNOLOGY BECOMES THE EYES AND EARS

JKR’s approach to disaster risk management has also evolved alongside the use of monitoring technology.

Mohd Shaifuddin said JKR is using and expanding the use of technology in slope management and monitoring according to the level of risk and requirements of each location.

These include the Landslide Early Warning System, rainfall monitoring, slope movement monitoring, as well as geotechnical and surveying instruments.

Along the FT185 corridor, JKR has installed three Robotic Total Stations and one Global Navigation Satellite System (GNSS) at Sections 44 and 46 to monitor slope surface movement.

Rainfall and slope movement data can help JKR issue warnings and take operational action when necessary.

Drones also assist with aerial inspections, particularly at high slopes or locations that are difficult and dangerous to access physically.

However, not all Sabo Dams require the same type of sensors.

Monitoring methods must be selected according to the risks and requirements of each site. Some locations may be adequately monitored through physical inspections and drones, while higher-risk areas may require additional instrumentation.

 

THE REAL TEST IS STILL AHEAD

Although the project has been completed, JKR cannot yet claim a specific level of risk reduction, as the Sabo Dam only began operating on July 14, 2026. The monitoring period is therefore still too short to draw statistical conclusions based on actual performance.

Mohd Shaifuddin said its effectiveness would need to be assessed using field data over a longer period, particularly after several episodes of heavy rainfall and during the monsoon season.

Among the factors to be assessed are the amount of sediment and debris successfully trapped, the condition of the structure following incidents, the possibility of overtopping or damage, the condition of the debris flow barrier, the level of erosion or scouring, the amount of material reaching the road, as well as the need for road closures and repairs.

This approach means the structure’s performance will be assessed based on evidence, rather than assuming that construction alone has eliminated the risk.

The reality is that no engineering structure can guarantee zero risk.

 

COMPLETION DOES NOT MEAN THE JOB IS DONE

Another less visible challenge is ensuring that the Sabo Dam continues to function after construction machinery has left the site.

The structure is designed to trap sediment, rocks, timber and debris. Therefore, accumulated materials must be inspected and removed once they reach a level that could reduce the structure’s effective capacity.

Maintenance includes regular inspections as well as special inspections following heavy rainfall or extraordinary events.

The quantity of accumulated sediment, rocks and timber, structural cracks or damage, the condition of the debris flow barrier, erosion around the foundation and downstream areas, bank stability, the condition of water channels and access for cleaning must all be monitored.

“Completion of construction does not mean the responsibility is over. The long-term performance of a structure depends greatly on inspection, monitoring and maintenance throughout the asset’s lifespan,” said Mohd Shaifuddin.

 

CALCULATING THE TRUE VALUE OF MITIGATION

From an economic perspective, the Sabo Dam cannot be assessed solely based on its construction cost.

According to JKR, preventive and mitigation measures can be more economical in the long term compared with repeated repair works, but the assessment must be based on life-cycle costs.

Costs that can be avoided include repairs to roads and bridges, debris removal, emergency mobilisation, losses resulting from road closures, as well as additional travel time and costs.

Disruption to the delivery of agricultural produce and goods, loss of economic and tourism activities, as well as risks to road users’ lives are also part of the considerations.

However, the Sabo Dam also incurs inspection, sediment removal and maintenance costs.

Therefore, mitigation investments need to be assessed based on the balance between risks, life-cycle costs and expected benefits.

 

FROM JAPAN, ADAPTED FOR MALAYSIA

The Sabo concept has a long and well-established history in Japan, which is among the leaders in sediment disaster management.

However, the basic principles of the technology do not mean that designs from Japan can simply be applied wholesale in Malaysia.

JKR has adapted the technology to local geology and soil types, terrain, catchment characteristics, tropical rainfall intensity, the expected volume and size of debris, the location of roads and bridges, available construction materials, as well as operational and maintenance requirements.

The Lojing project was implemented through the technical expertise of JKR together with local contractors and consultants, combining international knowledge and best practices with local experience in slopes, drainage, roads and disaster management.

It demonstrates Malaysia’s ability to adapt proven overseas technology to its own tropical climate and infrastructure needs.

 

A MODEL FOR THE FUTURE, NOT AN ABSOLUTE SOLUTION

Ibrahim said the Lojing project has the potential to become a reference model as it demonstrates a shift in approach — from merely repairing roads after disasters to managing risks upstream before debris reaches infrastructure.

However, the approach cannot be directly applied to all highland areas.

Each location has different geological conditions, rainfall levels, catchment sizes, types of debris, terrain and assets that need to be protected.

Therefore, JKR assesses each location based on its history of debris flows, landslides or mudflows, geological conditions and steepness, catchment area, loose materials upstream, rainfall patterns, the distance between debris flow paths and roads or settlements, as well as the number of residents and road users exposed to risk.

The strategic importance of the route, land and space suitability, environmental impact, implementation costs, benefits and long-term maintenance capabilities are also taken into consideration.

In some areas, a more suitable solution may not be a Sabo Dam, but rather drainage improvements, slope stabilisation, debris barriers, retention ponds, early warning systems or a combination of several measures.

Against the backdrop of climate change and increasingly unpredictable rainfall patterns, approaches such as Lojing offer an important signal for the future management of the country’s infrastructure.

The challenge is no longer simply to build stronger roads, but to understand what is happening upstream, identify how water and debris move, determine the most critical points for intervention and ensure that the protection system continues to function throughout its lifespan.

In Lojing, the shift began with a simple idea: disasters do not necessarily have to be waited for on the road before action is taken.

Risks can be managed earlier upstream through engineering, technology and continuous maintenance.

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