Optimizing lift irrigation systems for mountain agriculture
Where water reaches and nourishes, food is abundant and life flourishes. Yet this simple truism is so hard to find in so many places; for example, in the mountainous regions of Bhutan, about two-thirds of arable land lacks irrigation water. This poses a major challenge to agriculture and, by extension, the livelihoods of many mountain farmers. Agriculture in hilly terrain is rain-fed, which, together with its unreliability, limits crop variety and production cycles. In response, lift irrigation systems are emerging as an innovative and affordable solution – supplying hillside farmland with water transported from a downstream source. More importantly, systems optimized for mountain agriculture are emerging, and these could be a game-changer for mountain farmers in Bhutan.
Suitable for mountain farming
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 delivered by gravity to farmland via a delivery system. Since the cost of the system increases with increasing delivery elevation and volume of water lifted, pushing a huge volume of water to the highest point is often not economical.
A more cost-effective design approach – optimized for mountain farming – is to take advantage of the natural slope and pyramid-shaped land structure of hills. The cultivation area is proportionally larger at the foot of the hill, and it decreases with increasing elevation. Thus, the need for irrigation is higher at the base and lower at the top. Unlike traditional lift irrigation of transporting water to higher points, a single lower capacity pump can be optimally designed to deliver the required volume of water at multiple elevations depending on the topography of the hill. Following this design principle can reduce the size of the pump by half or even less compared to traditional sump pumps. This naturally means lower capital and operating costs over the lifetime of the pump.
Promise to Gangri
In the village of Gangri, in 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 the agricultural land being laid fallow and a decrease in annual agricultural productivity. Mountain-optimized lift irrigation pumps could solve this problem.
Accordingly, the Ministry of Agriculture of the Royal Government of Bhutan is implementing a pilot project in Gangri, with technical assistance and co-financing from ICIMOD. The project is expected to be fully commissioned towards the end of 2022. The planned solar irrigation system will serve 38 households and improve water security and therefore agricultural productivity. The pilot project will also focus on building the capacity of community water user groups for the management, distribution and sustainable use of water from the system.
The figure below shows the planned irrigation control area (or area under irrigation) in the village, which has been strategically divided into four areas, each represented by the respective numbered outlets. Output 4 represents the highest delivery point while Output 1 represents the lowest. The lowest outlet covers 60% of the command area, which means that a large volume of water must be pumped at a relatively low altitude. Similarly, a lower volume of water must be pumped to the higher elevation as the command zone decreases as we climb higher. At this site, if the total water were to be pushed to the highest delivery point, a 30 HP pump would be required whereas with the optimized design, a 10 HP pump will suffice to supply the same water requirement, and thus reducing the capital investment for the system. by 75 percent.
At the pilot site, if the pump were to operate on the network, the optimized design will save an estimated Nu. 1.5 million over 10 years, based on the current electricity rate structure. Thus, this design approach enables the distribution of the same volume of water at the required delivery altitudes saving on capital investment as well as operating costs. This is a heavy burden for farmers, which minimizes their irrigation costs while increasing their agricultural yields. Additionally, the system is compatible to supply from a dual source – solar and utility – and in the future can be modified for grid-connected solar power to maximize utilization.
Safe and future-ready water
Reliable access to the irrigation system can serve as a cross-cutting adaptation strategy to mitigation, not only helping to build agricultural resilience and improving farmers’ livelihoods, but also contributing to the country’s economy. . The National Irrigation Master Plan of the Royal Government of Bhutan has identified 2,000 hectares of land for lift irrigation. This number is likely to quadruple as it is estimated that potentially 30% of the country’s cropland will require lift irrigation. Adopting the optimized lifting system therefore has the potential to save billions in capital and operating costs. In addition, it also encourages the productive use of domestic electricity consumption to offset agricultural imports; contributing to food security; and improve the fiscal trade deficit, local economy and water security – thus strengthening the climate resilience of agriculture.
Avishek Malla is an energy specialist at the International Center for Integrated Mountain Development (ICIMOD) working for the Renewable Energy and Energy Efficiency Initiative for the Hindu Kush Himalaya (REEECH) initiative.