Tuesday, 6 December, 2022

Building Safer Hill Roads Through Bio-engineering

Navaraj Pokharel

In the recent past, almost all of the travellers travelling via Prithvi Highway were well aware about the frequent landslide at Krishnabhir in Dhading. Later, this landslide was controlled. Nowadays no landslide there is disrupting the highway movement of vehicles.
The controlling mechanism applied in this landslide involves the integration of mechanical and bio-engineering. This achievement was done by the special technicians of bioengineering. There are a number of frequent landslide prone areas along the road as well as near the settlements. Only 17 per cent of total land area of Nepal is in the plains. The remaining 83 per cent of land cover is mountainous and hilly. Generally the land area with more than 150 degree slant angle have landslide prone characteristics while the plains area are prone to flooding and inundation.
Almost 68,000 km of roads in Nepal has been built by the local agencies of the concerned ministry. The Department of Roads (DoR) has constructed the roads with length of 28,000 km. The DoR has formulated the provision of bio-engineering as mandatory tool to design and construction roads.
But there is a serious question asked about the local level roads constructed with poor technical evaluation. Almost 50 per cent of the local roads are built with the fund of the local agencies without technical evaluation and environmental assessment. Due to low budget, the tracks opened by the local agencies have no engineering design. Due to this, most of the rural roads are deteriorating the environment and causing gradual soil erosion. The soil lost from Nepal is collecting at the Bay of Bengal.
Bio-engineering is an integral part of Green Road concept. It uses living vegetation, either alone or in conjunction with civil engineering structure and non-living plant material to reduce instability and erosion on slopes. Positive mechanical and hydrological properties of plants are utilised to control erosion and stabilise the slope. This is the most effective and low-cost measure. It can also be applied as a curative means for reducing the risks of future slope failure as a preventive measure.
Bio-engineering is a sustainable approach where the combination of live and dead plants and plant parts are used as building materials for erosion reduction and landslip prevention. The combination of vegetative engineering and civil engineering systems normally offers the most complete natural and cost effective solution to the variety of instability problems affecting a site.
Under most circumstances, bio-engineering can be effectively combined with appropriate and low cost geotechnical applications to provide the most cost-effective, integrated solution to slope stability problems. This is important for mountainous country like Nepal.
Bio-engineering is the most affordable and effective way of enhancing civil engineering structures to increase stability as far as possible. The vegetative structures are flexible and capable of absorbing movement and reducing damage. In this respect, bio-engineering is a sustainable method of management since it helps to ensure the life of physical structures, and reduces overall maintenance costs. On roadsides, plants reduce the accumulation of debris from degraded slopes, which is one of the greatest contributors to road maintenance costs.
Road bio-engineering is totally labour based approach providing benefits to the local people. It focuses on minimising the damage to the natural environment as well as reducing maintenance costs. Major portion of the cost of the road construction in this mode goes as wages to the local labours.
Road construction approach incorporates social, environmental and technical issues. Due to these facts, this method is getting prioritised by national and international organisations in hill road construction. People’s participation is most essential for the success of slope conservation works. The use of local materials motivates local people’s participation.
The use of bio-engineering in Nepal has been developed since its introduction in the Dharan-Dhankuta road project in the mid-1980s for the protection of roadside slopes. More importantly, bio-engineering approaches were adopted in projects not as an alternative to civil engineering but as an additional combination of vegetative methods.
The operation of bioengineering techniques brings considerable cost saving from 50-70 percent in road maintenance. The Department of Roads has published Roadside Bio-engineering Reference Manual and Site Handbook which are used to design such works. Bio-engineering work is proposed for roads, more emphatically for major slide areas.
The DOR is formally incorporating these techniques to construct roads in safe way. But there are a numbers of problems associated with the rural roads. These roads should follow strict measures to make development sustainable. Roads provide access for development in rural area but the construction activities should not be creating problems such as soil erosion, loss of fertile soil, landslides and catastrophic imbalance in natural ecosystem.
In reality the rural roads that were constructed by the local agencies are not in operational condition. Most of them were opened with dozers.
Construction of rural roads itself is a challenging task and the additional challenge is to make them sustainable and environmentally friendly.
So, the incorporation of bio-engineering should be an integral part for the rural as well as any other road construction.

(Pokharel is an environmental specialist. navarajp@gmail.com)