Protecting eroded riverbanks along upper Trusan River through bio-engineering

A completed live-fencing using bamboo at Long Telingan. Photo © WWF-Malaysia/McKenzie Augustine Martin

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By WWF-Malaysia

LAWAS, Dec 13: Tucked deep in the Heart of Borneo, highland communities in Long Semadoh, Sarawak, are getting hands-on lessons on bio-engineering to address eroded riverbanks of the upper Trusan River.

Long Semadoh is located at 914m above sea level on the Maligan Highlands. The source of Trusan River, Maligan Highlands is an important water catchment area in Sarawak. It is also home to the Lun Bawang community.

The majority of the people here are farmers who grow the fragrant Adan rice. For years, the fertile valley, nourished and irrigated by Trusan River, have been transformed into productive paddy fields by the communities.

Over time, cultivated areas increased and encroached into the fragile riverbank buffers. The riverbanks were exposed to elements of nature such as increasing river flows and human factors such as land use changes in the upstream, leading to erosion of riverbanks.

The problem has turned from bad to worse after occasional floods that led to some paddy fields becoming damaged, and erosions causing farmers to lose their land. These resulted in income loss and negative impact on the overall river ecosystem and people’s livelihoods.

Community members working in ‘gotong-royong’ to carry planting materials across the river. Photo © WWF-Malaysia/McKenzie Augustine Martin

Through the grassroots platform of Forum Masyarakat Adat Dataran Tinggi Borneo (FORMADAT) and as requested by the communities, WWF-Malaysia (World Wide Fund for Nature-Malaysia) undertook this riverbank restoration pilot project. This project is supported by CIMB Islamic Bank from 2017 to 2019 through a RM600,000 fund.

In the initial stages, extensive dialogue sessions were held in 2017 and 2018 with the affected three villages: Puneng Trusan; Long Telingan; and Long Semadoh Rayeh. A hydrological study along a 5.2-km stretch of river was carried out in collaboration with the University of Nottingham Malaysia Campus (UNMC), led by Prof Christopher Gibbins, to assess the conditions of the eroded riverbanks.

A science-based and sustainable solutions were proposed, made in consultation with the villagers. It was agreed that bio-engineering or nature-based methods to restore the riverbanks will be utilised – possibly the first of its kind for Sarawak. The use of natural materials, especially those easily sourced from the villages is encouraged.

WWF-Malaysia started off with Puneng Trusan and Long Telingan to pilot this project. The villagers were provided with training and guidance on installing live-fencing, brush walls and geotextile mats using coconut coir instead of conventional concrete structures.

Previously, gabions were installed and locals planted bamboos, but they did not have a proper restoration plan. During heavy downpours, these structures failed to sustain. Other efforts included dredging the riverbeds and moving rocks to the banks, which did not work during high river flow in the monsoon period, causing further riverbank erosions along the stretches downstream. Factors of erosion at the catchment, river corridor and local site conditions must be included in any erosion management and strategy.

The installation of these bio-engineering methods were carried out through ‘gotong-royong’ under the guidance of Gibbins and Dr Teo Fang Yenn from UNMC. It was hard work but the villagers enjoyed learning something new.

“We installed brush wall, brush mattress, live-fencings and coconut coir geotextile mat at five degraded sites in Puneng Trusan and Long Telingan. We enjoyed the work as we get to learn something new and different,” said William Danor, a 60-year-old villager from Puneng Trusan.

William Danor, 60, from Puneng Trusan. Photo © WWF-Malaysia/Ezen Chan

In the past, he said the people depended on gabion installations to solve the problem of riverbank erosion, but this method did not last. They did not know about any bio-engineering approach.

“We never thought that natural materials from our surroundings can be used in such a manner to restore the eroded riverbanks,” said William.

Jelina Idung, 55, from Puneng Trusan, said it had been a hectic time for them as they had to juggle paddy planting and installing the bio-engineering solutions.

“But we managed to make time to help out. It’s good that both villages could take turns and work together to finish the tasks. I am a woman, and I didn’t excuse myself from helping others in carrying materials to the sites,” said Jelina.

Jelina Idung, 55, from Puneng Trusan. Photo © WWF-Malaysia/Ezen Chan

Long Telingan headman Alfred Balang Sibal, 60, said it is a blessing to have the opportunity to work with WWF-Malaysia and UNMC.

“We are also grateful for the funding from CIMB Islamic Bank. Without their help, the work couldn’t be done smoothly,” he said.

Alfred Balang Sibal, 60, Long Telingan headman. Photo © WWF-Malaysia/Ezen Chan

The villagers hoped that more eroded riverbanks will be restored. Through this project, they are not only protecting paddy fields along the riverbank from erosion, but also contributing in sustaining the environment.

WWF-Malaysia will be monitoring the effectiveness of the bio-engineering methods closely, especially during the monsoon season, to see how effective are the structures in withstanding the high energy water flow. WWF-Malaysia envisages the application of bio-engineering approaches and adopting this project as a model for mitigating riverbank erosion that can be applied to other sites.

Nature-based solutions, by applying green technologies or practices that are in tune with Mother Nature are encouraged. This project also demonstrated the importance of community partnership and willingness to work together in solving common problems affecting their livelihood. — DayakDaily