By Badri Paudyal, IANS
Kathmandu : Five years ago, landslides on highways made frequent headlines in Nepal. Today the worry in people’s minds as they travel by road has changed to relief, reports science site Scidev.net.
This is a result of bioengineering technology, which, along with conventional civil engineering, has helped combat landslides in Nepal.
When landslides occurred in Krishnabhir, some 80 km from here, they were a nightmare for those travelling on the Prithvi highway, the main transport artery of the nation.
Landslides, which together with floods are the second-biggest disaster-related killer in Nepal, frequently blocked the road between 1999 and 2003, disrupting essential supplies to the capital.
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.
Bioengineering combines vegetation – grass, shrubs and trees – with minor structures such as small dams, walls and drains to manage water and debris and 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 to minimise costs and maximise benefits.
The main causes of landslides in Nepal are steep slopes and excessive rainfall during the monsoon. Building activity, which disturbs the 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 – 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 percent of those in Nepal – are treated largely with vegetation.
The Krishnabhir landslides required a tailored approach. Usually slopes are protected first, but here work on water and debris management was given priority as they were the main triggers for landslides in the area.
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 – and bioengineering.
“[Krishnabhir] has seen unique bioengineering work in the country, which has given a permanent solution to the notorious landslide,” says Naresh Man Shakya of Nepal’s Department of Roads (DoR).
Planted vegetation helps stabilise areas in the long term, with plants gradually taking on the functional work of the engineering structures.
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 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.
Says Maya Kandel, who runs a small tea and food shop in Krishnabhir: “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 concept of bioengineering in road construction was introduced 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.
Now the DoR is paving the way for the bioengineering of roadside slopes.
Prakash Bhakta Upadhyaya, an engineer at the Bharatpur Division Office of the DoR, says in his experience bioengineering leads to comparatively less slope degradation.
“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.
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.
Strict legal provisions are necessary regarding land use in disaster-prone areas, Joshi adds.
Bioengineering techniques can be used in other mountainous countries with a topography similar to Nepal’s, 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.