Abstract
Although Nepal has been implementing conventional soil bioengineering measures to protect and stabilize bare roadcut slopes, it is still seeking a perennial strategy to combat the instability and destabilization of slopes. A case study was carried out at a Churiya Pass roadcut slope, which had been a serious issue for the Department of Roads(DOR), to protect and stabilize the slope from severe deterioration. The study area lies in the Siwalik region, which is very fragile and has a high erosion capacity. The DOR was unable to solve the problem through conventional soil bioengineering measures, as evidenced by the results of a revegetation project in 1993. This case study was carried out to investigate the adaptability and feasibility of a Rapid Afforestation Seeding(RAS)method by a soil seeder in Nepal. With the use of Japan’s hydro-seeder, soil-seeder technology was implemented to protect and stabilize roadcut slopes perpetually, principally by establishing a woody vegetation colony. Most of the basic materials used in the study were imported from Japan. Only half of the soil and organic matter used for preparing the carrying soil was locally prepared and arranged; it was mixed with carrying soil imported from Japan a 1:1 ratio. Local and imported plant species were used in the study. A year after the vegetation was introduced, the entire degraded study area was covered by the introduced Nepalese as well as Japanese species, showing excellent growth of more than 2 m in height. The established vegetation colony successfully prevented the development and formation of ephemeral gullies that would have resulted from concentrated flows, and protected the roadcut slope from further deterioration from severe erosion. The findings of the study show that a 3-cm growth-foundation layer is ample for growing both native and introduced vegetation in the Siwalik region.
