Where water reaches and nurtures, food is plentiful and life flourishes. Yet, this simple truism is so difficult to find in so many places; for instance, in the mountain regions of Bhutan, around two-thirds of cultivable land lacks irrigation water supply. This poses a major challenge for agriculture – and by extension the livelihoods of many mountain farmers. Agriculture in the hilly terrains is rain fed, which with its unreliability limits the variety and production cycles of crops. In response, lift irrigation systems are emerging as an innovative, affordable solution – feeding hill farmlands with water transported from a source downhill. More importantly, systems optimised for mountain farming are emerging, and these could be a game changer for mountain farmers in Bhutan.
Suited for mountain agriculture
In a traditional lift irrigation system, a pump pushes water from a source to the highest delivery point (with or without storage), from where the water is gravity fed to the farmlands through a distribution system. Since the system cost increases with the increase of delivery elevation and the volume of water lifted, pushing a huge volume of water to the highest point is often not economical.
A more cost-effective design approach – optimised for mountain agriculture – is to capitalise on the natural slope and pyramid-shaped land structure of hills. The cropping area is proportionally larger at the hill base, and it decreases with the increase in elevation. Thus, the irrigation requirement is higher at the base and lower at the top. Contrary to the traditional lift irrigation of transporting water to the highest points, a single pump with lower capacity can be optimally designed to deliver the required water volume at multiple elevations to suit the hill topography. Following this design principle can reduce the pump size to half or even less when compared with traditional lift pumps. This naturally means a reduction in the capital and operations expenditure over the pump’s service life.
Promise in Gangri
In Gangri Village of Bhutan’s Paro District, springs are drying up and traditional irrigation canals have proven unreliable. Villagers share that irrigation water shortages have resulted in more than half of farmlands turning fallow and a decrease in annual agricultural productivity. Mountain-optimised lift irrigation pumps could address this problem.
Accordingly, the Department of Agriculture, Royal Government of Bhutan, is implementing a pilot in Gangri, with technical assistance and co-funding by ICIMOD. The project is expected to be fully commissioned towards the end of 2022. The intended solar lift irrigation system will serve 38 households and improve water security and consequently agriculture productivity. The pilot will also focus on capacity building of the community water user groups for water management, distribution, and sustainable operation of the system.
The figure below shows the planned command area for irrigation (or the area under irrigation) in the village, which has been strategically divided into four zones, each represented by the respective numbered outlets. Outlet 4 represents the highest delivery point while outlet 1 represents the lowest. The lowest outlet covers 60% of the command area, which means a high volume of water needs to be pumped at a relatively low elevation. Similarly, a lower volume of water needs to be pumped to the higher elevation as the command area decreases as we move up higher. In this site, if total water had to be pushed to the highest delivery point it would require a 30 hp rated pump while with the optimised design a 10hp pump will suffice to deliver the same water requirement, and thus reduce capital investment for the system by 45 percent.
At the pilot site, if the pump were to be operated on grid, the optimised design will save an estimated Nu. 1.5 million over 10 years, as per the current electricity tariff structure. Thus, this design approach allows distribution of the same volume of water at the required delivery elevations by saving on capital investment as well as operational costs. This is a great burden off farmers’ shoulders, minimising their irrigation costs while augmenting their agricultural yields. Further, the system is compatible to supply from dual source – solar and utility – and in the future can be modified for grid-connected solar to maximise utilisation.
Water secure and future ready
Reliable access to irrigation system can serve as an adaptation strategy cross-cutting into mitigation, not only helping build agricultural resilience and improving farmer’s livelihoods but also contributing to the country’s economy. The Royal Government of Bhutan’s national irrigation master plan has identified 2,000 hectares of land for lift irrigation. This number is likely to increase four folds as it is estimated that potentially 30% of the cultivable land in the country will require lift irrigation. The adoption of the optimised lift system thus has the potential to save billions in capital and operation costs. Further, it also promotes productive use of domestic electricity consumption to offset agriculture imports; contribute towards food security; and improve fiscal trade deficit, local economy, and water security – thereby building climate resilience in agriculture.
Avishek Malla is an Energy Specialist at the International Centre for Integrated Mountain Development (ICIMOD) working for the Renewable Energy and Energy Efficiency Capability for the Hindu Kush Himalaya (REEECH) Initiative.