Nepal faces a great challenge to enhance agricultural production by improving and increasing eliable and adequate irrigation facility to meet food requirement of its ever increasing population. Development of reliable year-round-irrigation system, especially in the rural area to increase agricultural productivity is the pressing need of the country to ensure food security and to lower down level of poverty. However, Nepal's achievement in irrigation development is far less compared to the huge potential provided by nature in terms of water resource and geography.
It is estimated that more than 225 billion m3 of surface water available every year in the country. Considered on annual basis, this water resource is abundant for irrigation development needs of the nation. However, due to non-uniform temporal and spatial distribution of the resource, less than 10 % of available water has so far been utilized in the country for irrigation purpose.
Most of the irrigation systems in Nepal draw water from small and medium rivers which have abundant flow during wet months of June to September but have little discharges or even dry up during remaining months. As a result of this non uniformity, farmers of most of the irrigated area are unable to apply irrigation water to their field at the time when the need is critical, thus adversely affecting productivity. This unreliable situation is attributed as one of the main cause for disinterest in agriculture among the rural community resulting in low income and poverty. In other words, irrigated cropping intensity is so low that for many farmers in Nepal, net income from agriculture is just enough for sustenance, i. e to live with own productions for a whole year. This situation has ultimately resulted in general lack of interest of the people in agricultural farming, thus endangering food security of the country. Therefore, there is a need to develop facilities that can draw water from perennial sources and supplement the numerous existing irrigation systems.
Harnessing perennial sources to create uniformity in temporal and spatial availability of water can only be achieved by developing infrastructures for inter-basin transfer and storage schemes on large rivers. Towards this end, Government of Nepal has started implementing projects for inter-basin transfer in Nepal, among which Bheri Babai Diversion Multipurpose Project (BBDMP) is the leading one.
Initially, a reconnaissance study of BBDMP was conducted in 1977 as a part of study on Babai Irrigation Project. After that Master Plan study for Karnali and Mahakali conducted in 1992 by JICA considered Bheri Babai Diversion Project as a priority project for Hydropower development in Karnali Basin. Later in 1998, JICA further carried out study at feasibility level and studied various options.
Based on overall analysis project size was optimized for a diversion discharge of 40 m³/s which was determined mainly on environmental considerations of minimum potential long term environmental effects on the aquatic ecosystem of Bheri and Babai Rivers. Besides, augmentation of 40 m3/s to Babai River is found to be adequate to provide year round irrigation to about 51,000 ha of agricultural land. Average monthly discharge of Bheri river is about 332 m3/s and 40 m3/s of flow is available 99.8% of the time in a year which means assured water and power would be available practically throughout the year. Thus, in terms of utilization of water resources, this is one of the most attractive multi-purpose projects in Nepal.
Recognizing this fact, National Water Plan has emphasized implementation of BBDMP from 2012; subsequently the Interim Plan (2010-2013) has included BBDMP as one of the new projects in irrigation sector for implementation during the plan period. To realize this plan, Government of Nepal has allocated budget for implementation of project from FY 2068/69. Accordingly, detailed engineering design and other study for various aspects of the project has been carried out.
Bheri Babai Diversion Multipurpose Project (BBDMP) is the first of its kind of inter-basin water transfer project conceptualized to provide round the year irrigation facility to 51,000 A of land of Banke and Bardiya district. Therefore, it has two components i.e. Hydropower and Irrigation. It involves construction of intake at Chiple of Ramghat VDC in Surkhet, 12 km long tunnel across the youngest mountain chain, i.e. Siwaliks, surge shaft and powerhouse at Hattikhal, Bardiya. For the first time in Nepal, Tunnel Boring Machine (TBM) is used to excavate the tunnel through fragile rocks of Siwaliks. Seeing its importance for the overall development of Nepal, Government of Nepal has nominated it for Project of National Pride.