Case Study Groundwater Irrigation Northeast Ghana
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Small scale groundwater irrigation in northeast Ghana
In the Upper East Region of Ghana, shallow groundwater is used by many small scale vegetable farmers for dry season irrigation. This use of groundwater is not always reflected in official statistics, which focus on larger-scale, often state-run irrigation schemes, and which don’t report groundwater irrigation independently from surface water irrigation figures.
Nevertheless, groundwater irrigation makes an important contribution to household incomes in parts of northeast Ghana. Bawku West and Talensi Nabdam are two districts in the Upper East Region where groundwater plays an important role in dry season irrigated vegetable cropping. A study by Namara et al. (2011) in three sub-catchments of the White Volta basin showed that about 61% of 4,576 households they surveyed practice irrigation, and of these, most – about 90% - use shallow groundwater, mostly from alluvial aquifers. Tomatoes and onions are some of the main crops produced: tomatoes can be sold as part of cross-border trade with Burkina Faso, and onions have a relatively long shelf life.
The farmers’ choice of groundwater abstraction, conveyance and application technology helps them manage irrigation costs. They mainly use low-technology infrastructure.
- - One groundwater abstraction point type is seasonal hand-dug wells, which are dug into alluvial aquifers in dry river beds. Because these are often relatively distant from the farmers’ fields, they are often used with transportable motorised pumps.
- - In-field hand-dug wells are also constructed in some cases, where there is a shallow unconsolidated and/or weathered aquifer that can be exploited using manual digging. Because the distances to crops are shorter, motorised pumping isn’t needed, and cheaper rope-and-bucket techniques can be used.
- - In several areas, farmers dig seasonal wells on land they do not own, filling in the well at the end of the dry season when the landowner returns to cultivate rainfed crops.
- - Deeper and/or lined, (semi-) permanent hand-dug wells are also used where farmers own their land, with either motorised pumps or rope-and-buckets, or with mechanical pumps: there are a few cases of treadle pump use.
- - Permanent mechanically drilled boreholes are also used in some cases, with either motorised or mechanical pumps.
The use of mechanical and/or motorised pumps incurs capital and fuel costs, and so relying on river bed hand-dug wells, which are far from the cropped fields and therefore can’t practically be used with rope-and-bucket technology, is often less profitable. Permanent drilled boreholes also incur high fixed costs for construction, and often ongoing pump and fuel expenses. By contrast, in-field hand-dug shallow wells using buckets minimise pump and fuel costs, indicating why many farmers opt to retain this low-technology option, where it is hydrogeologically possible.
Economics and income benefits
Incomes from this small scale irrigated agriculture can be up to 1.5 to 4.9 times as profitable as rainfed agriculture, depending on the technology used to abstract the groundwater (electric pumps, mechanical pumps or buckets). So, irrigated dry season farming can provide more than half the annual cropping income of irrigating households. Irrigation is associated with increased asset ownership. This may just be because wealthier people are more able to invest in irrigation technology, but if irrigation then increases incomes, there could be a positive cycle of accumulation.
In Bawku West and Talensi Nabdam, the most economically efficient irrigation system, with the highest profits per hectare, is in-field hand dug shallow wells using rope-and-bucket. However, the total area that can be watered in this way is just 0.3 hectares, so households using this option can struggle to earn a minimum income. Constraints on access to land due to other reasons, including relatively high population densities, is another limiting factor.
The Namara et al. (2011) study found that the costs of constructing mechanically drilled boreholes are low compared to the costs of other agricultural inputs, especially paying for labour at average day rates. However, in reality, because dry season employment is low in northeast Ghana, most agricultural work is done by family labour, for which there is little opportunity cost. This explains why dry season groundwater irrigated vegetable production remains an attractive livelihood activity.
Most of the farmers in this study use shallow groundwater from alluvial aquifers in river valleys. These aquifers are formed of sand and gravel, deposited by rivers in floodplains. The aquifer is unconsolidated, and the groundwater level is usually relatively shallow, even in the dry season, so that it relatively easy to find and abstract groundwater by hand digging shallow wells. Because relatively small volumes of groundwater are used for irrigation by small scale farmers, there have been few reported problems up till now of over-abstraction and falling groundwater levels. However, a recent study suggested that if groundwater abstraction increases in future, this could have a significant effect on the groundwater level in alluvial aquifers, and could lead to local over-abstraction (Barry and Forkuor 2010).
It is also possible to hand dig shallow wells into weathered basement (regolith) aquifers, where fracturing and weathering has changed the hard basement rocks into sands, gravels, silts and clays. These weathered zone aquifers can be up to about 20 m thick. These aquifers may be present below farms away from river valleys.
Find out more about the hydrogeology of different aquifers in Ghana on the Hydrogeology of Ghana page.
If the local aquifer isn’t suitable for hand digging shallow wells, then the options for shallow groundwater use by farmers for irrigation are far more limited. If the local aquifers are formed of unweathered rock – e.g. consolidated sandstone – then mechanically drilled boreholes are likely to be the only option for groundwater abstraction.
Remote sensing studies have indicated that there is good potential for groundwater use from basement and consolidated sandstone and other sedimentary aquifers across parts of northeast Ghana (Forkuor et al. 2013, Gumma & Pavelic 2013). However, as mechanically drilled boreholes and mechanical or motorised pumps are likely to be needed in most cases in these aquifers, the costs of accessing and using this groundwater are higher than for the informal technologies currently used by most small scale farmers in the region.
In some areas, poor groundwater quality can limit its use. In nitrate concentrations in groundwater have been measured and are too high for drinking – for example, around Bawku and Zalerigu – but this groundwater can be, and is, used for irrigation. In other parts of the White Volta Basin, groundwater with naturally high salinity is found in basement aquifers, making it unsuitable for irrigation (Namara et al. 2011).
Barry B and Forkuor G. 2010. Contribution of informal shallow groundwater irrigation to livelihoods security and poverty reduction in the White Volta Basin (WVB): Current status and future sustainability. CPWF Project Report. Colombo, Sri Lanka: CGIAR Challenge Program on Water and Food (CPWF). www.waterandfood.org
Evans AEV, Giordano M and Clayton T (Eds.). 2012. Investing in agricultural water management to benefit smallholder farmers in Ghana. AgWater Solutions Project country synthesis report. Colombo, Sri Lanka: International Water Management Institute (IWMI) 37p. IWMI Working Paper 147. doi: 10.5337/2012.209
Forkuor G, Pavelic P, Asare E and Obuobie E. 2013. Modelling potential areas of groundwater development for agriculture in northern Ghana using GIS/RS, Hydrological Sciences Journal, 58:2, 437-451, DOI: 10.1080/02626667.2012.754101
Gumma MK and Pavelic P. 2013. Mapping of groundwater potential zones across Ghana using remote sensing, geographic information systems, and spatial modeling. Environmental Monitoring and Assessment 185 (4), 3561-3579
Namara RE, Awuni JA, Barry B, Giordano M, Hope L, Owusu ES and Forkuor G. 2011. Smallholder shallow groundwater irrigation development in the upper east region of Ghana. Colombo, Sri Lanka: International Water Management Institute. 35p. IWMI Research Report 143. doi: 10.5337/2011.214
Saa Dittoh JAA. and Akuriba MA. 2013. Small pumps and the poor: a field survey in the Upper East Region of Ghana, Water International, 38:4, 449-464, doi: 10.1080/02508060.2013.819454