ZYNORIQUE

Shri Ram Newpane
Steep hills and mountains characterize approximately 86 percent of the Nepalese area. Elevation ranges from 60 m to 8,848 m (Mount Everest) within a radius of less than 200 km. The country comprises five distinct physiographic regions: the High Himalayas (23.7 percent of the total area), the High Mountains (19.7 percent), the Middle Mountains (29.5 percent), the Siwalik (12.7 percent) and the Terai (14.4 percent), (LRMP, 1986). Due to the presence of steep hills and mountains, frequently occurring erosion and landslides cause instability in slope. The rate of natural erosion in the geologically young and seismically active mountains is high. Laban (1979) estimated that approximately 74 percent of landslides occur under natural conditions and 26 percent of the occurring landslides in Nepal are caused by human activity. Landslides occur in Nepal due to toe cutting of the slope, deforestation in hills and mountains, intensive use of land resource for agriculture, grazing and fuel wood and development of infrastructure such as roads, without adequate conservation measures, and soil mass saturated with water.Control of slope instability caused by severe landslide and erosion usually requires the engineering of structures. However, structural measures involve high investment and a high degree of technology. When vegetative measures are combined with engineering measures, the end result can be effective for landslide protection and dramatic reduction of surface erosion, at relatively low cost and ensuring high sustainability. Bioengineering control measures have been observed in Nepal to be economically desirable and most effective for erosion control in degraded areas. Hence, planting local grasses, shrubs and trees becomes the successful use of vegetation along with engineering structures to increase slope stability against shallow landslide and to protect almost all slopes against erosion. On small sites, bioengineering techniques alone may be adequate. However, bioengineering is closely integrated with civil engineering structures.
The department of roads, through several donor-assisted projects had conducted experiments on bioengineering case studies in the history of Nepal such as:

a) Dharan-Dhankuta road (1988): A complicated failure occurred at certain portion of that road. Vegetative solutions along with engineering structures are applied there which provide support by planting bamboos above toe wall; seeding Khanyu, siris and tanki on all fill and loose debris areas; planting grass sito on critical sections of the middle slope; seeding grasses phurke, Bhujetro and sito at the upper section.

b) Dhankuta-Hile road (1990): An unstable slope in weak, deeply weathered gneiss was disturbed by road construction. Along with engineering structures, as a vegetative solution various plants such as asuro, amliso, simali, phurke, utis, large bamboos, kans, areri and keraukose were planted. Similarly, Amliso grass is planted at Phurke Khola on the Prithvi Highway, 67 km from Kathmandu and in Gajuri which is 73 km from Kathmandu. Asuro is planted at Kurintar on the Prithvi Highway and from Phisling to Benighat. Other examples are Jogbani-Dharan road (1991) and Baglung loop (1997). (Roadside bioengineering, reference manual, DOR). In the year 1991 to 1995 Dhading Development Project DDP/GTZ has widely planted Simali shrub at Dhading Besi-Salyantar road. An example of the ongoing project is DDC/GTZ, where Simali is planted in Tumlingtar-Chhyangkuti road in Sankhuwasabha District.

Vegetation greatly affects shallow soil mass stability mainly by increasing the shear strength of soil via root reinforcement. One major factor responsible for landslide is the role of roots. Roots mechanically reinforce a soil by transfer of shear stress in the soil to tensile resistance in the roots. Increase in soil shear strength due to root reinforcement is directly proportional to root tensile strength, root diameter and root density. Wide variations in the tensile strength of roots depend on species and on site; factors such as growing environment, season, root diameter and orientation. Roots of any deep penetrating vegetation (i.e. grass, shrub and tree) will increase the stability of the soil because all plant root systems hold the soil together. As explained earlier, Nepal is practicing roadside bioengineering from last two decades. Thus the prime attention should be given to an analytical study of some extensively used and abundantly available local grass and shrubs.

Nepal has been experiencing the use of grass and shrubs since the last two decades in roadside bioengineering. Various grasses, shrubs and trees have been used as bioengineering technique by different organizations on a number of highway slopes in Nepal. As far as roadside bio-engineering is concerned, the Department of Roads, HMG has published site handbook on various bio-engineering techniques in detail, covering planted grass lines, brush layers, palisades, live check dams, fascines and vegetated stone pitching walls, large bamboo planting, turfing, site seeding and planting grass, shrubs, small trees, large trees, their spacing and plant growing techniques etc. But it, however, does not cover the analytical part of root strength and root distribution and how it affects in landslide protection. Similarly, no literature concerning the experimental analysis of the strength of various grasses and shrubs roots, their root distribution, increase in soil shear strength due to root reinforcement and suitability of different grasses, shrubs for different soil and climatic condition were found in the Nepali context. Thus an attempt should be made to enhance the experimental analysis of mechanical properties of root. So it is high time for the study of mechanical properties of roots, their role in landslide protection in the context of rapid development of roadside bioengineering technology nationwide as well as worldwide. Considering the above facts a study is needed on an experimental analysis of strength of local grass and shrubs roots widely used for landslide protection in Nepal.