On the slippery slope

- SUSAN THAPA, Kathmandu

Oct 9, 2015-

The Food and Agriculture Organisation of the United Nations is celebrating this year as International Year of Soils. Every year, the productivity of soil has been deteriorating due to many reasons, one of them is erosion. Soil is a non-renewable resource, as it takes thousands of years for soil to form by the weathering of rocks. Thus, soil conservation is very important. During the Gorkha earthquake, many hills in Nepal were shaken which triggered erosion and landslides in many hilly regions, costing many lives and forcing people to shift to safer places. The erosion not only took lives but also affected the regular flow of motor vehicles.

A similar problem used to persist on the Prithvi Highway at Krishna Bhir, 83 km to the west of Kathmandu. The movement of people along the route used to be a nightmare, and local people lived in fear during the rainy season. Even a low-intensity rainfall used to trigger landslides. As a result, the only route in and out of the Kathmandu Valley on the western side used to be blocked for several hours. But now the scenario has changed, thanks to bio-engineering techniques that have helped to prevent landslides and which suffered no damage even during the catastrophic quake.

Recently, our soil science teacher took our class on a day trip to observe the conservation method at Krishna Bhir. Located on the banks of the Trishuli River, Krishna Bhir is battered by the river current that has made a deep gash in its side. The hill itself has a steep slope, and the loose aggregated gravel and soil are easily washed down by the rain. A bioengineering technique which consists of constructing small dams, retaining walls, stone masonry, proper drainage system  and grass water ways has made it more stable. In addition, a combination of vegetation, herbs, shrubs and trees like Napaire grass, khayer, bamboo, epilipil and amliso have been extensively planted which helped to stop downward debris movement.

In a bid to decrease the impact of raindrops and protect the soil from surface sealing and crusting, which decreases clogging of soil pores and increases the infiltration rate, broad leaf plants like bhojetro which grow in harsh conditions on rocks were extensively planted. Bhojetro has a unique property of expanding the leaves during the monsoon season. This moderately deep rooted vegetation holds the soil and makes it stronger to support structures and helps to reduce landslips in the hills. On a geological time scale, Nepal’s hills and mountains are considered to be young as they are believed to have been formed by the collision of two tectonic plates. In the hills, highways and side roads built without proper engineering studies are at risk of landslide. To prevent erosion on hills, simple techniques of planting vegetation at the right time with some engineering practice can be effective.

Published: 09-10-2015 09:01

User's Feedback

Click here for your comments

Comment via Facebook

Don't have facebook account? Use this form to comment