Erosion and Sediment Yield: Global and Regional Perspectives (Proceedings of the Exeter Symposium July 1996). IAHS Publ. no. 236, 1996.
Sediment management of the Kosi River basin in Nepal
JIT NARAYAN NAYAK
Department of Civil Engineering, Institute of Engineering, Tribhuvan University GPO Box 1175, Kathmandu, Nepal
Abstract The Kosi River is one of the biggest in south Asia. It accounts for about 25% of the county's total river runoff and causes soil erosion equivalent to nearly 50% of Nepal's total sediment loss. Meandering of this river has caused shifting of the channel from east to west of over 110 km spreading devastation and laying waste an area of about 770 km2. The Sunkosi storage dam at Kurale would possibly store about 50% of the Kosi sediment and nearly 40% of its flood flow. The Tamor-I storage dam would also hold about 20% of the Kosi sediment. Altogether 70% of the Kosi sediments will be stored and the remaining 30% will probably be required to sustain the turbidity of the Kosi River flow. These two storage dams would control 60% of the Kosi flood flow.
INTRODUCTION The Kosi River with a length of 720 km is one of the biggest in south Asia, and its drainage area of 92 538 km2 lies in Tibet, Nepal and India. The Kosi River has three main tributaries, comprising the Sunkosi, Arun and Tamor Rivers, which meet at Tribeni 5 km upstream of Barahkshetra. After this confluence, the river is called "Spat Kosi" or Kosi. The hydrological characteristics of the Kosi River and its tributaries (Thapa, 1993) are given in Table 1. It is quite clear that the flood flow of the Kosi River during the monsoon season historically has been creating serious problems of widespread destruction and devastation. Cities and villages have been ruined, along with damage to agricultural land in Nepal as well as India. Chitale et al. (1966) have commented on the meandering nature of the Kosi River: "The Kosi is known as the river of sorrow of north Bihar.. .the...