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Irrigation and drainage
Evolution of irrigation development
Irrigation development in Nepal has a long history. Numerous small raj kulos (canals) in the government sector first appeared in and around Kathmandu valley in the seventeenth and eighteenth centuries. The first large public sector irrigation canal system (the Chandra Canal System) with a net command area of 10 000 ha was constructed in 1922 and is still in operation.
The irrigation potential of the country is an estimated 2 177 800 ha (Table 4). This potential is mainly for irrigation using surface water, but some 352 050 ha are potentially irrigable from groundwater in the terai region; 292 600 ha from shallow tubewells (83 percent) and 59 450 ha from deep tubewells (17 percent).
In 2002, the area equipped for irrigation was an estimated 1 168 300 ha, of which 79.5 percent was irrigated by surface water, 19.2 percent by groundwater and 1.3 percent by mixed surface water and groundwater (Figure 2). Seasonal canals accounted for 58 percent of the area irrigated by surface water, permanent canals accounted for 39 percent, and ponds for 3 percent. In 1992, the area equipped for irrigation accounted for 882 400 ha and in 1982 for 583 900 ha.
In 1994, 73.9 percent of the area equipped for irrigation was irrigated by surface water, 12.4 percent by groundwater and 13.8 percent by not fully identified irrigation systems. Almost all areas using surface water are dependent on transit flow availability at the sources. Therefore, the irrigated area varies from season to season and from region to region. As far as the public schemes are concerned, 91 percent were dependent on surface water in 1994 and 9 percent on groundwater. Only 67.7 percent of the public schemes was irrigated in summer, 31.1 percent in spring and 1.2 percent in winter.
Many irrigation systems use surface irrigation (basin, furrow). Some areas in the hills and mountains use sprinkler irrigation, but no figures are available.
Irrigated areas are often classified as public irrigation systems and farmer-managed irrigation systems (FMIS). Non-formal associations have existed for a long time in almost all FMIS. Water user associations (WUAs) received legal status after the promulgation of the 1992 Water Resources Act. The WUA has now become a prerequisite for the transfer of public schemes to users. In 2008, 70 percent of the country’s irrigated area fell under FMIS. In the remaining areas, some systems are being transferred completely to the WUAs for management, whereas some are being jointly managed by the government and WUAs. Farmer- and community-managed systems are found to be more efficiently managed than government-managed systems. However, the government plays a crucial role in research and development, extension services and other regulatory fiscal and non-fiscal mechanisms. At the same time, essential and emergency assistance from the government to the communities in the rehabilitation and repair of irrigation systems has to be continued to sustain the farmer-managed systems (MOIR, 2005).
FMIS can be either entirely managed by farmers or assisted by specialized agencies. In FMIS, most diversion structures are constructed from brushwood and boulders and are, therefore, temporary and often washed away during monsoon season. The canals are generally unlined and prone to damage. There is, typically, a large expenditure of labour every year to restore the systems or to maintain them. In spite of these physical limitations, FMIS have demonstrated managerial skills (at community level) that have kept them functioning and contributing significantly to Nepal’s food supply.
Modernization of irrigation systems and improved water management practices could lead to a reduction in irrigation water withdrawal. On the other hand, a higher cropping intensity on the irrigated areas, which would be desirable because of the increasing need for food supply, could result in increased agricultural water withdrawal.
The Sunari Morang Irrigation Project (SMIP) was implemented in the terai of southeastern Nepal in the 1990s. It has about 65 000 ha under command of the Chatra Main Canal (CMC), which is fed from the Kosi river. The CMC, which runs from west to east, gives a gross water delivery of about 0.9 litres/s/ha, or rather less than 0.5 litres/s/ha at the plant root. This is because it was designed for supplementary irrigation, i.e. to supply enough water to supplement (by 80 percent) the monsoon rainfall, thus guaranteeing one crop of rice a year over the entire area. A series of secondary canals, running north-to-south, take the water from the CMC into the command area, which extends almost to the Nepal-India border some 20 km to the south. There is considerable conjunctive use of groundwater (STWs) and low lift pumping from drainage lines to supplement supplies from the CMC, particularly towards the tail end of the system.
The Sikta Irrigation Project is situated in the Banke district of the mid-western development region. The project, with a command area of 33 766 ha, including the rehabilitation of the Dunduwa irrigation system constructed by Indian Cooperation Mission in 1964, would irrigate almost all the lowlands of the Banke district and its economic impact could be significant for this development region. The irrigated area can be further extended by 9 000 ha. Based on the Feasibility Study Report 2004, the Government of Nepal decided to implement the project in three phases: Phase I - Construction of headworks and desilting basin; Phase II - Construction of main canal and branch canals; and Phase III - Command area development.
The Community Managed Irrigated Agriculture Sector Project (CMIASP) is the follow-up programme to the Irrigation Sector Project (ISP) and the Second Irrigation Sector Project (SISP) in 35 districts of the eastern and central development regions. The overall goal of the project is to promote inclusive economic growth while reducing poverty in the rural areas. Its specific objective is to improve agricultural productivity and sustainability of existing small- and medium-size FMIS suffering from low productivity and incidence of high poverty. To achieve the objective, the project will (i) provide improved means to empower WUAs, for irrigation facilities, agricultural extension, and targeted livelihood enhancement to build the human capital of the poor, including women and traditionally neglected disadvantaged groups; and (ii) strengthen policies, plans, and institutions for more responsive service delivery and sustained impacts. The irrigation facilities will be provided in about 210 FMIS covering the total command area of 34 000 ha (including 8 500 ha expanded command area).
In 1999, the average cost of irrigation development varied from US$2 900 to 3 700/ha for the large schemes, and from US$850 to 4 300/ha for small hill schemes. The average cost of irrigation rehabilitation varies from US$1 000 to 1 800/ha. The average cost of operation and maintenance (O&M) was about US$42/ha in the smaller schemes, and US$8-14/ha in the larger schemes.
In 2002, there were 1 997 600 households that practiced irrigation, while in 1992 there were 1 377 500.
Role of irrigation in agricultural production, the economy and society
In 2006, the harvested irrigated crop area covered around 1 926 000 ha, of which 37 percent was for rice, 33 percent wheat, 22 percent maize, 2 percent vegetables, 2 percent oil crops, 2 percent sugarcane and 3 percent other annual crops (Table 4 and Figure 3).