Increasing access to groundwater is a key strategy for household water supply (both potable and nonpotable) during drought. Therefore, drought relief programs in rural areas typically incorporate drilling or deepening of tubewells and/or boreholes. However, these activities are often inefficient and may be unnecessary, as described below (Moss, 2003). This article describes options for increasing access to groundwater during drought and will provide references for pre-drought mitigation measures that reduce the need for emergency interventions.
Tubewells consist of a narrow, screened tube or casing driven into a water-bearing zone of the subsurface. The term tubewell is sometimes used synonymously with borehole. However, boreholes are more specifically defined as tubewells penetrating bedrock, with casing not extending below the interface between unconsolidated soil and bedrock. Tubewells can often be installed by hand-auguring; boreholes require a drilling method with an external power source. The choice of technology and drilling method depends on the cost, resources, groundwater table, desired yield and other factors (WaterAid, 2006). The distinctions between the tubewells and boreholes are not critical to this discussion and the terms are used interchangeably throughout.
A hand-powered or automated pump is used to draw water to the surface or, if the casing has penetrated a confined aquifer, pressure may bring water to the surface. The salient features of tubewells include: (1) plastic or metal casing (usually 100-150 mm diameter); (2) in unconsolidated soils, a “screened” portion of casing below the water table that is perforated; (3) a “sanitary seal” consisting of grout and clay to prevent water seeping around the casing; and (4) a pump to extract the water. Detailed information on tubewell construction options can be found in references including, for example, online resources from
WaterAid (WaterAid, 2006; WaterAid Bangladesh, 2006) and UN FAO (Sonou, 1997).
Three major strategies are employed for increasing borehole water supply during drought:
- Drilling new boreholes/deepening existing boreholes: These strategies form the basis of conventional approaches to improving groundwater access in rural areas during drought (Barker et al., 1992; Burdon, 1985). They are frequently appropriate for mitigating extreme symptoms of drought. However, they are often not the most efficient use of limited resources (Moss, 2003). Additionally, groundwater surveys and proper siting of boreholes are necessary for achieving maximum impact.
- Repairing damaged boreholes: In many droughts, regional groundwater depletion is not the main factor affecting domestic access to water. When individual boreholes fail during drought, the cause is often local drawdown or mechanical failure. During a recent drought in southern Africa, a survey of water points by Oxfam revealed that most non-functional boreholes had failed because of problems with hardware (e.g. pump failure) or demand management (e.g. localized drawdown). The failure of a water point (including traditional sources) increases pressure on boreholes, increasing demand, local drawdown and hardware failure. Repairing damaged boreholes is a quick and inexpensive way to prevent this cascade of water point failure (Moss, 2003; Calow et al., 1997).
- Relief boreholes with use restricted to drought periods: Many authors have proposed developing deep “relief boreholes” that remain capped when water supplies are adequate and are uncapped for use during drought (Burdon, 1985; Calow et al., 2009). There are reports that these have been implemented successfully in Botswana (WHO and DFID, 2010). However, discontinuing access following the drought can be problematic; this is discussed below in the section on barriers to implementation.
A warmer climate is highly likely to result in more frequent drought (IPCC, 2007). Deep tubewells, usually defined by engineers as those that penetrate at least one impermeable layer (WaterAid Bangladesh, 2006), generally have much greater resilience to drought than traditional water supplies including springs, hand dug wells and surface water sources. In many regions, groundwater is the only perennial source of water supply (Calow et al., 1997). However, a more nuanced understanding of drought is needed to formulate a proper response.
Drought is defined as “a temporary aberration” in a climate pattern and is driven by variability in precipitation and evapotranspiration. This is in contrast to aridity, which is the “ordinary” climatic condition for a given area, and water stress/scarcity, which reflects renewable water resources per capita (US National Drought Mitigation Center, 2006; Vörösmarty, 2000). Drought is further divided into three categories: meteorological drought, agricultural drought, and hydrological drought. The former two are experienced earliest, but hydrological drought is the drought-type associated with shortfalls in surface water and groundwater supply (US National Drought Mitigation Center, 2006). Groundwater drought is sometimes used to further distinguish cases in which the water table declines and some wells dry up (Calow et al., 1997). Many situations commonly described as drought can strongly impact rain-fed agriculture and other activities without having a direct impact on the availability of safe drinking water (Moss, 2003).
Discontinuity of water supply during drought can halt economic development and hinder human health and well-being (Gleick, 2002). Access to groundwater prevents reliance on poor quality alternative supplies and reduces expenditures for bottled and vended water.
The costs of drilling new boreholes vary widely depending many factors, so quoting ‘typical’ costs can be misleading. However, the average cost in much of Africa is $10,000-15,000; in contrast, the average cost in India is less than one-tenth as much (Carter, 2006; Doyen, 2003). A detailed methodology for costing borehole drilling operations in Ethiopia is available, incorporating (i) mobilisation/demobilisation, (ii) drilling, (iii) casing and completion, and (iv) development and test pumping (Carter et al., 2006). Repairing damaged wells can cost far less (sometimes by three or more orders of magnitude) than drilling new boreholes.
Determining the best strategy for improving groundwater access during drought requires knowledge of population distribution, groundwater resources, and water point locations/status. A broad review of the factors (including capacity building) that impact the success of groundwater programs in Ethiopia and India has been published by World Bank Water and Sanitation Program. These include recommendations of personnel training needs in the public and private well-drilling sectors (Carter, 2006).
In some settings, boreholes can be sited based on available maps and observation. Sometimes expensive geophysical techniques are necessary, but the success of a method will vary widely depending on the geological environment. Guidance on various methods, from simple and observational to technologically complex, is available (MacDonald et al., 2002; Barker et al., 1992).
A central groundwater database is essential to making informed decisions for groundwater access during drought (Calow et al., 1997). These data can be gathered through a central governmental initiative at great expense. Alternatively, governments can help to ensure that data from all major well-drilling entities (e.g. contractors, donors, NGOs, state enterprises) contribute to the database. Borehole logs, completion reports, test pumping data, and other useful information should be collected in a central repository for mutual benefit (Carter, 2006). In addition to data on groundwater resources, having a map of existing water points and population can greatly increase drought-alleviation program efficiency. WaterAid has reported on a methodology for water point mapping and lessons learned in Malawi and Tanzania (Welle, 2005).
Borehole drilling, deepening and repair are very dependent on access to international markets for drilling equipment, spare parts and consumables. Decreasing the difficulties and costs associated with international business (e.g tariffs, import restrictions) can help to mobilize the private sector to improve groundwater access. These and other institutional aspects are covered in detail in the references (Carter, 2006).
Proper pre-drought management can greatly increase the efficiency of these interventions and prevent costly and inefficient emergency activities. Broadly, these have been suggested to include groundwater resource assessment, groundwater drought vulnerability analysis, and building drought resistance into water supply programs.66 However, many of the critical functions that can improve their efficiency are not valued by key stakeholders. For example, attracting donor and government support for development of databases for mapping groundwater and water point access/status is generally difficult (Moss, 2003; Calow et al., 2009).
The cause of a “dry” borehole is usually unclear to users and is often assumed to be due to regional groundwater depletion caused by lack of rainfall. In reality, the cause of deep borehole failure is more often localized drawdown or mechanical breakdown, both of which are made more likely by the overuse (Moss, 2003; Calow et al., 2009).
Barriers for ‘relief boreholes’ include reported difficulties stopping access following the drought. UN FAO reports that informal settlements tend to spring up around relief boreholes76 and there are reports of threats of violence when the time comes to cap the borehole (Burdon, 1985).
Well-constructed deep tubewells generally yield water of good microbial quality. However, both deep and shallow aquifers can be contaminated with naturally occurring arsenic and fluoride. Although these waters can generally be used for non-potable domestic purposes, they should not be consumed without treatment. Arsenic is of particular concern in deltaic regions of South Asia and Southeast Asia (Fendorf et al., 2010). Fluoride concentrations in groundwater are generally higher at the foot of mountains. However, concentrations of these chemical species can vary widely by well location and depth, even at small geographic scales. Therefore, water testing for arsenic and fluoride should be conducted for each new well following construction and periodically during continued operation. If either is detected during sampling, numerous technical resources are available to help guide operational response (Feenstra et al., 2007; Petrusevski et al., 2006; World Bank, 2005; Qian, 1999).
The World Bank Water and Sanitation Program has disseminated a guide on cost-effective boreholes that covers technical, institutional and other aspects. It contrasts experiences in sub-Saharan Africa with those in India, using Ethiopia as a case study (Carter et al., 2006).
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