Tubewell Irrigation in Nepal's Terai: Shallow vs Deep Boring Explained

The Terai — the flat southern plain that grows most of Nepal's rice and wheat — sits on thick layers of water-bearing sand and gravel (aquifers), recharged every monsoon by rain and by rivers descending from the Chure (Siwalik) hills. Because surface canals cannot reach every field, and many canal systems run low exactly when winter and spring crops need water, hundreds of thousands of farm households pump groundwater through tubewells, locally called 'boring'. According to the Government of Nepal's Irrigation Master Plan 2019 (Updated 2024), groundwater contributes about one third of the country's irrigated area: 152,766 shallow tubewells and 1,278 deep tubewells together irrigate about 493,830 hectares.

This is overwhelmingly a Terai story: 149,521 shallow tubewells irrigating 437,388 hectares and 1,250 deep tubewells irrigating 48,489 hectares are in the plains, with only a few thousand wells in the hills. The Department of Water Resources and Irrigation (DWRI) plans and builds public irrigation, while the Groundwater Resources Development Board (GWRDB), established in 2033 BS (1976 AD), maps aquifers, drills investigation wells and runs groundwater projects through nine branch offices from Biratnagar to Dhangadhi.

The distinction that matters most to anyone searching 'boring for irrigation' is between shallow tubewells (STWs) and deep tubewells (DTWs). They differ in depth, cost, pump technology and command area — and, critically, in management: shallow tubewells are private, farmer-managed assets, while deep tubewells are drilled and operated by government agencies or organised water-user groups because of their high cost and complexity.

A tubewell is a bored hole fitted with a pipe (casing) that reaches an aquifer. Along the water-bearing layer, a slotted 'screen' lets water enter while keeping sand out; a pump then lifts the water to field channels or hoses. In much of the Terai the shallow water table lies only a few metres below the surface, which is why even simple, locally drilled wells can supply a smallholding.

Shallow tubewells are usually sunk by local drilling teams with hand-percussion or small mechanical rigs in a matter of days, then paired with a centrifugal suction pump — most commonly a portable 5-horsepower diesel set, increasingly electric or solar. Deep tubewells are drilled by heavy truck-mounted rigs, cased with larger-diameter pipe, test-pumped, and fitted with electric submersible pumps that push water up from far below the suction limit. The Master Plan's model design for new small groundwater schemes uses a submersible pump delivering about 10 litres per second to each 10-hectare block, four blocks per well.

A shallow tubewell is conventionally defined in Nepal as a well up to about 50 metres deep with a casing under 10 centimetres in diameter, tapping the unconfined shallow aquifer. Its advantage is affordability: drilling is cheap and fast, pumps are portable and can be rented or shared, and no large civil works are needed. A typical STW commands roughly 1.5 to 3 hectares — the Master Plan's Terai figures average just under 3 hectares per well — matching Nepal's small landholdings.

Government and donor programmes drove much of the expansion. The IFAD-supported Community Shallow Tubewell Irrigation Project (FY 2051/52 BS, 1994/95 AD, to 2000) worked in five flood- and drought-prone districts, and the Asian Development Bank–financed Community Groundwater Irrigation Sector Project (CGISP), launched in FY 2054/55 BS (1997/98 AD) in 12 eastern and central Terai districts, installed 19,767 shallow tubewells irrigating 37,685 hectares according to GWRDB — beating its 15,000-well target by lending to organised farmer groups. ADB's independent evaluation found the model raised cropping intensity and smallholder incomes where electricity or affordable diesel was available.

Running costs depend almost entirely on energy. Diesel pumping is flexible but expensive, so many wells are used only for high-value crops or rescue irrigation. Rural electrification and subsidised solar pumps are lowering the cost per watering and encouraging fuller dry-season use of existing wells.

A deep tubewell exceeds the shallow-well limits — deeper than about 50 metres, and in the Terai drilled to as much as 300 metres — tapping confined aquifers sealed beneath clay layers. A single DTW yields enough to command 40 hectares or more; GWRDB's farmer-managed deep-tubewell schemes in the eastern Terai were designed at about 40 hectares per well. The trade-off is cost: CGIAR researchers put a grid-connected deep tubewell installation at roughly NPR 10 million (about USD 75,000), far beyond an individual household, which is why DTWs are drilled by agencies and handed to water-user associations to operate.

Deep-well development began early. USAID supported the first systematic deep-tubewell investigations in seven western Terai districts, and Nepal's groundwater investigation programme formally started in FY 2026/27 BS (1969/70 AD). The flagship Bhairahawa Lumbini Groundwater Project, begun in Rupandehi in FY 2033/34 BS (1976/77 AD) with World Bank credit, constructed 181 deep tubewells plus 272 km of farm roads and 287 km of electrification, irrigating 20,309 hectares. A later India-grant project in Jhapa, Sunsari, Saptari and Siraha aimed to build 22 farmer-managed DTW systems covering about 880 hectares.

Performance has been mixed: roughly 30 percent of the Terai's deep tubewells have been reported non-functional at any given time, owing to unreliable electricity, pump breakdowns or weak user committees. Yet the untapped potential is large — GWRDB estimates about 190,000 hectares of Terai farmland could be irrigated from deep aquifers, about three times current development — and pilot programmes are now 'solarising' existing DTWs (around NPR 3 million per well) to cut running costs and revive idle systems.

For anyone weighing a 'shallow tubewell' against 'deep boring' in the Terai, the choice comes down to the depth of the productive aquifer, how much land needs water, and who will pay for and manage the system.

The Master Plan notes that groundwater schemes cost about 1.5 times more to build than equivalent surface canals and four to five times more to operate — mainly electricity and asset replacement — but deliver water on demand, reliably and exactly where needed. Its analysis found an extra hectare under groundwater or conjunctive (canal-plus-well) irrigation raises a district's net production value by around USD 2,044, versus about USD 560 for an extra surface-irrigated hectare.

Groundwater's real value shows in the dry season. Most rain falls between June and September; from October to May, rivers shrink and many canals deliver little water. The Master Plan estimates that surface water can reliably irrigate only about 0.75 million hectares in the dry season — far below the Terai's irrigable land — so year-round cropping depends on storage dams or groundwater. Only about 39 percent of Nepal's irrigated area currently has year-round irrigation, and the plan counts every groundwater-irrigated hectare toward its target of 100 percent year-round irrigation by 2045, precisely because a tubewell works in Chaitra as well as in Saun.

The resource is substantial. The Master Plan puts the Terai's average annual renewable groundwater at about 13,215 million cubic metres (13.2 billion m³) across the Koshi, Narayani and Karnali basin plains — enough, at a typical demand of 18,400 m³ per hectare, to irrigate more than 725,000 hectares. Independent studies cite a more conservative recharge of around 8.8 billion m³ a year, against current extraction estimated at under 2 billion m³. GWRDB's mapping identifies about 726,000 hectares with good shallow-aquifer potential, another 305,000 hectares of marginal potential, and about 190,000 hectares suited to deep-aquifer irrigation.

On paper, then, the Terai still pumps far less than nature returns each year; the binding constraints are energy prices, well siting, dry-season water depth in particular pockets, and the institutions needed to keep deep tubewells running.

Aggregate abundance hides local stress. Parts of the central and eastern Terai — Madhes Province in particular — report falling water tables, dry ponds and hand pumps, and even deep tubewells yielding less than designed. Reporting in Nepali Times (July 2025) linked the Madhes crisis to denudation of the fragile Chure hills, which cuts the infiltration that recharges Terai aquifers, along with riverbed mining, the loss of traditional ponds and wetlands to construction, and heavy pumping on both sides of the Nepal–India border. A failed monsoon that year — only around a fifth of normal rainfall in parts of the eastern Terai — exposed how thin the buffer has become.

Monitoring and regulation remain works in progress. GWRDB has measured water levels since 1991 at a network of around 400 shallow observation wells across the Terai, but Nepal still has no comprehensive licensing regime for private borings, and most shallow tubewells are drilled without hydrogeological assessment. Experts caution that promoting deep borings as a quick fix for drying shallow wells can worsen the problem, since deep aquifers recharge far more slowly; they urge conjunctive use — canal water in the monsoon, wells in the dry season — plus Chure conservation, pond restoration and managed aquifer recharge.

The practical guidance from DWRI, GWRDB and development partners is consistent: prefer shallow tubewells where the shallow aquifer is productive, site wells using GWRDB district groundwater maps, adopt electric or solar pumping to cut costs, and organise water-user groups so that deep tubewells stay maintained and financially sustainable.