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Nepal is using plants and modern engineering to combat the landslides that regularly plague the nation. Badri Paudyal reports.

Five years ago, landslides and road blocks on the highways were a common subject in Nepal's news. But now, the worry in people's minds as they travel by road during monsoons has been replaced by a sense of relief.

Combined with floods, landslides are the second biggest disaster-related killer in Nepal. And when landslides occurred in Krishnabhir, situated 82.5 kilometres west of the capital Kathmandu, they were a nightmare for the hundreds of thousands of people travelling on the Prithvi highway, the main transport artery of the nation. Landslides frequently blocked the road between 1999 and 2003, disrupting essential supplies to Kathmandu and adjoining hill areas.

But things are different now. Krishnabhir has received a total facelift. It is one of more than 100 major landslide sites that have been stable since 2003–2004.

These facelifts — mainly along the 110 kilometre Naubise Mungling section of Prithvi highway and the 36 kilometre Mungling Narayanghat highway of central Nepal — are a result of bioengineering technology, which along with conventional civil engineering, has helped combat landslides in Nepal.

The facelift

Bioengineering combines vegetation — grass, shrubs and trees — with minor structures such as small dams, walls and drains to manage water and debris, to protect and stabilise slopes.

Its legacy lies in Nepali farmers' centuries-old use of trees on the terraced slopes of their farmland and forests. Scientists have combined this indigenous method with modern engineering structures to minimise the cost and maximise the benefits.

The main causes of landslides in Nepal are steep slopes, combined with loose material and excessive rainfall during monsoons. Human building activities such as excessive cutting into hillsides, disturbing natural drainage systems and inappropriate land use also contribute to landslide risk.

Usually, deep-seated landslides — those where earth becomes detached from deeper in the ground and the volume of the landslide is bigger — are treated with complex civil engineering structures, including large supporting walls, extensive drainage measures and technologies for anchoring unstable slopes to more solid ground.

Shallow-seated landslide sites — which make up 80 per cent of those in Nepal — are treated largely with vegetation.

The notorious Krishnabhir landslides required a tailored approach. Usually slopes are protected first, but in Krishnabhir work on water and debris management was given priority, as they were the main triggers for landslides in the area and had already disturbed previous rehabilitation efforts.

Once the water and debris were dealt with — by constructing dams and drains to direct water in the least harmful way — slope protection activities were introduced. These included structures such as wire nets, low-height retaining walls, bolster tubes — a tube or wire containing stones used for drainage — and bioengineering.

"[Krishnabhir] has become unique bioengineering work in the country, which has given a permanent solution to such a notorious landslide", says Nepal's Department of Roads (DoR) geotechnical engineer Naresh Man Shakya, chief architect of landslide treatment activities in Krishnabhir.

Krishnabhir in 2003 and today
Credit: Naresh Man Shakya, Badri Paudyal

Planted vegetation helps stabilise areas in the long term, with plants gradually taking on the functional work of the engineering structures. It's a perfect handover. As Shakya says, "Plants need around three years to gain their engineering function and become stronger as they grow older, while civil structures become weaker as they get older."

Among the plants mainly used in Krishnabhir were primary grass plants like kans, babiyo, amliso, and napiere. Large trees like khayer, bakaino, bhujetro, epil and bamboos were also used.

The grasses perform the function of retaining small loose debris, while shrubs form 'walls' to catch debris. Bamboos strengthen slopes and remove large quantities of water from the soil.

Some of the broad-leaf plants like bhujetro can grow in harsh conditions, even on the rock surface. Apart from strengthening the slope, their broad leaves also intercept rainfall, minimising its impact on the soil surface.

And the plants have another function — to fulfil household and agricultural needs. Local people can use firewood, grass and fodder and can use some plants as a source of income.

People living at the roadside have benefited greatly. Maya Kandel runs a small tea and food shop nearby Krishnabhir. She is happy to find the market prospering as the road is improved. She says, "It was so difficult during the landslides as we were caught in the middle. The area is settled now and we are really glad."

The road to bioengineering

The concept of bioengineering in road construction was introduced in Nepal 40 years ago with roadside plantations in a US-assisted project on the Dhangadhi Dadeldhura highway in western Nepal. It was later applied in the Lamosangu Jiri highway in the country's central hills region, built with Swiss assistance.

Bioengineering in the modern sense was first introduced on a massive scale with the involvement of the UK-based Transport Research Laboratory on the eastern Dharan Dhankuta highway, supported by the British government. They then facilitated the transfer of the technology to Nepali institutions and professionals.

Now the DoR is paving the way for the bioengineering of roadside slopes. DoR's division offices throughout Nepal now use bioengineering in the construction, maintenance and upgrading of all roads, especially in hilly and mountainous areas.

The Krishnabhir and Mungling-Narayanghat highway in central Nepal, the Dang-Surahi section of the East-West highway, and the Masot Khola section of Lamahi-Tulsipur road in the country's mid-west are some examples of successful landslide rehabilitation works carried out by the DoR.

Prakash Bhakta Upadhyaya, an engineer at Bharatpur Division Office of the DoR, says in his experience bioengineering leads to comparatively less slope degradation.

Debris flow drainage constructed
at Krishnabhir
Credit: Badri Paudyal
"Early incorporation of bioengineering into planning, designing and construction processes will reduce the life-cycle cost of roads to a considerable extent," he added.

The Department of Soil Conservation and Watershed Management (DOSCWM) and Department of Water-Induced Disaster Prevention are also using bioengineering in landslide treatment.

The DOSCWM alone has completed about 600 landslide treatment works across the country through its nationwide network of 55 district offices. The department has also developed a model demonstration site in Godamchaur village in the Lalitpur district, south of Kathmandu valley, to display how bioengineering minimises the occurrence of landslides.


Future bioengineering

Despite these efforts there are still landslides in some parts of the country. But Jagannath Joshi, assistant technology development officer at the DOSCWM says, "We cannot provide full solutions to landslides, but by studying their natural process and ground conditions, and applying corrective measures we can prevent them or minimise their harmful impact."

Joshi says the country also needs to map locations vulnerable to landslides to identify disaster prone areas and develop a system of forecasting.

He says that if hazard mapping and preventative measures were made mandatory in development activities that could cause landslides — like building roads, reservoirs, dams, irrigation canals and mining works — they could minimise harm.

Similarly, strict legal provisions are necessary regarding land use in disaster prone areas, Joshi adds.

Preventing landslides with bioengineering is a long process and a combination of various activities, rather than a one-off activity. Input and insight from a multidisciplinary team of experts, including geologists, geomorphologists, geotechnical engineers, hydrologists, botanists, civil engineers and social scientists is necessary.

But that cooperation is itself an advantage. As Naresh Man Shakya says, "The combination of different sciences and people makes bioengineering a holistic approach in addressing a challenging problem. That, and its use of local materials and potential for local use and involvement of local people makes it harmonious, sustainable, environmentally friendly and participatory."

Bioengineering techniques can be used in other mountainous countries with a similar topography to Nepal, providing a low cost solution to the problem of landslides in geologically weak and fragile areas. Maximising the use of locally available materials and resources — making the entire process less expensive — is another advantage.

Keeping landslides out of the news is a bonus.

This article is part of a Spotlight on Science in the Himalayas.