Developing Ground Water For Secure Rural Water Supplies in Africa
Developing Ground Water For Secure Rural Water Supplies in Africa
Developing Ground Water For Secure Rural Water Supplies in Africa
Abstract
In sub-Saharan Africa 85% of those without access to safe water live in rural areas where the consequent poverty and ill health
disproportionately affect women and children. The widespread development of groundwater is the most affordable and sustainable
way of improving access to secure water for the rural poor on the scale required to achieve current coverage targets. However,
groundwater resources vary considerably across the continent, and the sustainable development of the resource depends on an
accurate understanding of the hydrogeology. To develop secure water supplies, the quantity, quality and sustainability of ground-
water resources must be known to ensure that key decisions are informed by knowledge of resource conditions. Communities must
also be involved at every stage of the process and given the authority to manage and maintain sources. There is a danger that the
current pressure to achieve ambitious coverage targets will result in short cuts being taken and, although many new sources are
constructed, they will not be secure.
Keywords: Groundwater; Africa; Water supply
Presented at the Water and Sanitation in International Development and Disaster Relief (WSIDDR) International
Workshop Edinburgh, Scotland, UK, 28–30 May 2008.
0011-9164/09/$– See front matter © 2009 Natural Environment Research Council (NERC). Published by Elsevier B.V.
All rights reserved.
doi:10.1016/j.desal.2008.05.100
A.M. MacDonald, R.C. Calow / Desalination 248 (2009) 546–556 547
Table 1
Advantages and limitations of groundwater [4]
Groundwater is often available close to where it is Considerable effort may be needed in some situations to
required locate suitable sites
Groundwater can be developed relatively cheaply and As overall coverage increases, the more difficult areas
progressively to meet demand with lower capital which are left can become more costly to supply
investment than many surface water schemes
Groundwater generally has excellent natural quality, Naturally-occurring quality constraints are becoming more
and is usually adequate for potable supply with widely observed
little or no treatment
Groundwater generally has a protective cover As development increases more rapidly, the threat of
provided by the soil and unsaturated zone pollution from human activities needs to be assessed in
relation to the nature of the protective cover
rural demand [3]. Alternative water resources can be quantity, quality, ease of access and renewability of
unreliable and expensive to develop: surface water groundwater resources.
(if available) is prone to contamination and often sea- Rainfall is highly variable across Africa. Annual
sonal; rainwater harvesting can be expensive and rainfall varies from negligible over parts of the
requires good rainfall throughout the year. Ground- Sahara, to almost 10,000 mm in the Gulf of Guinea
water, however, can be found in most environments. (Fig. 1). As a consequence of this great variability, the
It generally requires no prior treatment since it is natu- hydrology of Africa is probably the most variable and
rally protected from contamination; it does not vary challenging of all populated continents – demon-
significantly seasonally and is often drought resistant. strated by the low runoff/rainfall coefficient (0.23)
Also it lends itself to the principles of community [5]. This illustrates the high evaporation, and low
management – it can be found close to the point volume of water flowing in rivers. The great varia-
of demand and be developed incrementally (and bility in rainfall, and in particular the long dry season
often at low cost). However, the resource is not (>5 months) over much of Africa, increases reliance
invulnerable: with the ability to pump out large quan- on groundwater storage for water supply. Recharge
tities of water, and the advent of particularly persis- to groundwater in wet periods is naturally stored, and
tent contaminants, the resource needs to protected can be abstracted in times of drought. There is no
and managed. Table 1 summarises the advantages simple direct relationship between average annual
of groundwater for rural water supply, with some rainfall and recharge, and significant recharge
qualifications. (10–50 mm) can still occur where annual rainfall is
In this paper, we discuss the groundwater resources less than 500 mm [6–8].
in Africa, and the steps required to develop secure The available groundwater resources are best
rural water supplies. described by considering the geology and construct-
ing a hydrogeological map – which classifies the
geology into units in which groundwater is likely to
occur in a similar way. A simplified hydrogeological
2. Groundwater resources in Africa
map for Africa is shown in Fig. 2 based on a synthesis
Groundwater occurrence depends primarily on of studies [10–14] and using the 1:5,000,000 scale
geology, geomorphology/weathering and rainfall geological map of Africa as a base [15,16]. The four
(both current and historic). The interplay of these different environments are: Precambrian ‘‘basement’’
three factors gives rise to complex hydrogeological rocks, volcanic rocks, unconsolidated sediments, and
environments with countless variations in the consolidated sedimentary rocks. Roughly 34% of the
548 A.M. MacDonald, R.C. Calow / Desalination 248 (2009) 546–556
Fig. 1. Average annual rainfall for Africa for the period 1951–1995 [9].
land surface is underlain by heterogeneous Precam- Consolidated sedimentary rocks, particularly large
brian basement; 37% by consolidated sedimentary sandstone basins, can store considerable volumes of
rocks; 25% by unconsolidated sediments; and 4% groundwater, but in arid regions, much of the ground-
by volcanic rocks [17]. Groundwater occurrence in water can be non-renewable, having been recharged
each hydrogeological environment is described below when the area received considerably more rainfall.
and illustrated in Fig. 3. Also, sedimentary rocks are highly variable and can
Precambrian basement rocks comprise crystalline comprise low permeability mudstone and shale as
igneous and metamorphic rocks over 550 million well as more permeable sandstones and limestones
years old. Unweathered and non-fractured basement [14,19].
rocks contain negligible quantities of groundwater. Unconsolidated sediments form some of the most
Significant aquifers however, develop within the productive aquifers in Africa. They cover approxi-
weathered overburden and fractured bedrock [18]. mately 25% of the land surface of Africa (Fig. 2).
A.M. MacDonald, R.C. Calow / Desalination 248 (2009) 546–556 549
• the supply is reliable all year round, and also in times constructed, providing valuable information on how
of drought, when demand can be high; the source will behave during drought [21]. If a single
• the water is accessible to all in a community and source cannot meet peak dry season or drought
within a reasonable distance of all households demand, further village sources may need to be devel-
(usually within 1 km) and oped. In the longer term this is more cost effective
• the supply is affordable and can be easily than trying to cope with water shortage when drought
maintained. arrives [22].
In some areas, for example on major alluvial
To achieve a secure groundwater supply the fol-
plains with abundant rainfall, groundwater may be
lowing factors must be incorporated into any rural
widely available at relatively shallow depths. In these
water supply project or programme.
areas, little or no hydrogeological investigation is
necessary as wells or boreholes may be successful
wherever they are developed. Siting can therefore
3.1. Boreholes or wells should be sited effectively
be determined by the local population alone. In envir-
Any groundwater source should be located where onments which are more geologically heterogeneous,
the groundwater resources are sufficient and able to however, investigations ranging from simple field
meet the demands put upon it. Modest investment observation to more costly exploratory drilling and
in resource assessment and siting techniques can surveying may be necessary to ensure success (see
pay dividends in terms of higher drilling success rates Table 2). Where investigations help reduce the num-
and higher yielding (more reliable) sources [4]. Sim- ber of unsuccessful wells drilled, cost savings may
ple tests can also be carried out to assess the perfor- be significant, more than covering the cost of the
mance of a well or borehole once it has been investigation procedure (Fig. 4).
Table 2
The costs and benefits of different borehole siting methods
One off cost Reconnaissance: Gathering background A one off cost – several weeks time of a Essential first step for understanding the
maps and information on the project member or consultant groundwater resources
geological and hydrogeological More expensive (but not prohibitively
conditions so) if data have to be generated from
satellite images, field mapping, etc.
; increasing costs per Hydrogeological fieldwork: Siting Requires a well trained engineer to visit Objective is to ‘ground-truth’ results
borehole using an experienced eye by the community gathered from reconnaissance
examining the rocks and
geomorphology in an area
Discussion with local communities
Geophysical surveying: Resistivity, Equipment varies in price but is Important to have good analysis of the
electromagnetic, seismic, etc. generally <$US 20 k. A well trained data. Investment in training staff
(see [4] overview) geophysics team will need at least 1 often beneficial
Must be combined with reconnaissance day in each community
data and hydrogeological fieldwork
Exploratory drilling: Drill exploratory Costs equivalent to drilling a dry The only way to ‘prove’ that
boreholes in a community – often borehole, but considerably reduced if groundwater occurs in an area
combined with hydrogeological the team has control over their own Requires careful facilitation to ensure
fieldwork and geophysics rig that communities do not get
A.M. MacDonald, R.C. Calow / Desalination 248 (2009) 546–556
As a general guideline, boreholes should be Nine major chemical constituents – sodium (Na),
designed to meet the following criteria: calcium (Ca), magnesium (Mg), potassium (K), bicar-
bonate (HCO3), chloride (Cl), sulphate (SO4), nitrate
• borehole efficiency is maximized (high pumping
(NO3) and silicon (Si) – make up about 99% of the
from small boreholes can lead to friction losses and
solute content of natural groundwaters. The concen-
deep drawdowns);
trations of these constituents give groundwaters their
• sand inflow to the borehole is kept to a minimum
hydrochemical characterisation, and the proportions
(this can quickly wear out pumps);
reflect the geological origin and groundwater flow
• materials are of sufficient quality to last at least
regime [25]. However, it is the presence (or absence)
25 years and
of the remaining 1% – the minor and trace elements –
• any contaminated sources or aquifers, or zones of
that can occasionally give rise to health problems or
undesirable water quality, should be sealed off from
make the water unacceptable for human use. Fig. 5
the borehole.
indicates which chemicals are essential for humans
Obviously these factors have to be balanced with and which are harmful. Of particular concern in East
the cost of the borehole. Drilling a large diameter Africa are elevated concentrations of fluoride [26].
borehole to 100 m and lining it with expensive stain- Although arsenic has not yet been widely detected,
less steel screen could cost as much as 10 narrow dia- the lack of monitoring may mean that this is a pro-
meter boreholes drilled to 50 m and completed with blem yet to surface [25,27].
uPVC screen and casing. Also, it is important to know To ensure secure water supplies, the quality of the
whether the borehole is likely to be successful before water must be assessed at the time of construction and
installing expensive screen and casing. some method of regular monitoring for a selection of
There have been recent moves to make borehole boreholes to identify any degradation. Currently in
drilling and more cost effective and fit for purpose Africa this does not occur, and without a major incen-
[24]. This involves using smaller less costly drilling tive from donors or government it is unlikely that
rigs to drill reduced (100–150 mm) diameter bore- thorough groundwater quality monitoring will be
holes completed with plastic screens and casing. taken seriously.
These designs, where coupled with a good under-
standing of the groundwater resources and good siting
techniques (see above) can give high quality sources 3.5. Supplies and groundwater resources must be
at much reduced cost. protected from contamination
Water quality can deteriorate through contamina-
tion of the local groundwater, or direct contamination
3.4. The quality of the water must be known
of the water supply itself. Rural water supplies can be
Groundwater has traditionally been regarded as particularly vulnerable since they are often shallow
having good natural quality. For most of the geologi- and have hazards close by – such as pit latrines, or
cal environments this is true, but this does not mean animal watering troughs, etc. (Fig. 6).
that natural groundwater quality is always good. The To minimise the risk of contamination of the water
natural quality can vary from one rock type to another supply, the supply must be well constructed, and
and also within aquifers along groundwater flow sources of contamination kept away. Community
paths. Because groundwater movement can be so management of a source using simple guidelines can
slow, and residence times long, there is scope for che- help to keep animals away from a supply and mini-
mical interaction between the water and the rock mised any standing water. Sanitary inspections
material through which it passes. Natural ground- provide an easy but effective, risk-based approach
water quality changes start in the soil, where infiltrat- to monitoring wellhead protection [28]. The use of
ing rainfall equilibrates with carbon dioxide to standardised and quantifiable approaches makes it
produce weak carbonic acid which can remove solu- possible to compare the results obtained by differ-
ble minerals from the underlying rocks. ent inspectors, allows an overall risk score to be
554 A.M. MacDonald, R.C. Calow / Desalination 248 (2009) 546–556
developed, identifies priority sites for remedial techniques are difficult to apply on an African context
actions and permits comparisons between different due to a general absence of government legislation
supply types. enforcement [17,30].
In rural Africa, the increase in the use and con-
struction of household latrines poses a considerable
4. Conclusions
threat to the groundwater supplies. Contaminants can
migrate vertically to the aquifer and then to the bore- Over much of Africa, developing groundwater
hole, or more dangerously, horizontally through offers the only realistic and affordable way to meet
permeable soils to poorly constructed supplies (see coverage targets and improve access to water. How-
Fig. 6). Some methods are available to help site ever, to build secure groundwater supplies takes time.
latrines an appropriate distance from water supplies The groundwater resources must be understood, and
to help reduce contamination [29]. boreholes/wells developed in a way that is appropriate
Groundwater vulnerable techniques are well to the hydrogeology – to ensure long term availability
developed in most northern countries to help inform of the water. It is also important to know the quality of
land use planning and exclude the most polluting the water (to ensure it is fit to drink) and protect the
activities from vulnerable aquifers. However, such water supply and local groundwater resource from
A.M. MacDonald, R.C. Calow / Desalination 248 (2009) 546–556 555
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