Difference between revisions of "Groundwater development techniques"

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World Health Organisation. 2011. [http://www.who.int/water_sanitation_health/publications/dwq_guidelines/en/ Guidelines for drinking-water quality, 4th edition]. ISBN: 978 92 4 154815 1
 
World Health Organisation. 2011. [http://www.who.int/water_sanitation_health/publications/dwq_guidelines/en/ Guidelines for drinking-water quality, 4th edition]. ISBN: 978 92 4 154815 1
  
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Revision as of 12:27, 6 March 2019

Africa Groundwater Atlas >> Resource pages >> Developing groundwater resources >> Groundwater Development Procedures

  This page is still in development - please check back soon for updates.


What does groundwater development involve?

Developing groundwater for water supply can involve various different activities, depending on the hydrogeological environment, how much groundwater is needed and what it will be used for. It is usually also important to develop groundwater sources sustainably, so that the groundwater resource is protected and maintained for future supplies.

At its simplest, groundwater flowing naturally from a spring can be directly tapped with very little effort, although protecting that spring, so that the water doesn't become polluted, can be more difficult. In another simple example, where groundwater levels are shallow and the aquifer is easy to dig through (e.g. sand or gravel), hand dug wells can be quite easily constructed to allow groundwater to be abstracted - but again, protecting the groundwater in the well from pollution can be more difficult.

Where the aquifer and/or groundwater levels are deeper, or the aquifer can't be easily dug through by hand, developing groundwater resources is more complicated. It is likely to need some kind of mechanical drilling - either manual drilling, or using a drilling rig.

In areas where the aquifers are all permeable and productive, water boreholes can often be drilled just about anywhere. But in areas with low permeability and/or complex aquifers, or where there are groundwater quality issues, new boreholes and wells must be sited and designed carefully if they are to be successful. To do this, it's important to understand how groundwater exists and behaves in the area.

Stages in a groundwater exploration programme

The main stages of a groundwater exploration programme - which will allow you to assess and sustainably develop groundwater resources - are summarised in the table below, with an indication of costs. Some more detail on each stage is given in the sections below, but this page is not a comprehensive guide to groundwater development. Many other resources are available which do provide detailed guidance and support for groundwater exploration and development, and some of these are listed at the bottom of this page, under Links to more information.

Stages of groundwater exploration and an indication of the costs of each
Stage Notes on costs
Project Management
Project management is an essential part of projects to develop groundwater. A borehole drilling project can include sensitisation of and training of end users; borehole siting, design, drilling, development and completion; borehole testing (yield and water quality); and pump installation. Each part needs to be professionally run if it is to be successful. RWSN provide guidance in this area, including this guide to Procurement and Contract Management of Drilled Well Construction. An experienced project manager may be needed to oversee a borehole drilling project.
Siting Boreholes
Reconnaissance: gathering maps and information (e.g. from existing reports, academic papers etc) on geological and hydrogeological conditions. This is an essential first step for understanding groundwater resources. A one-off cost: several weeks time of a project staff member or consultant. If new data have to be bought or generated (e.g. from satellite images or field mapping), costs will increase, but not prohibitively so.
Hydrogeological fieldwork: making field observations of the local geology (e.g. from rock exposures or chippings/cuttings from any local hand-dug wells or previously drilled boreholes); hydrogeology; and existing water sources (both dry and wet season sources), and gathering relevant information from discussions with the local community: e.g. how much do existing sources yield; do yields fall or dry up in the dry season; are there water quality problems? Also observe any local pollution sources, such as pit latrines, burial grounds, cattle pens or market areas. This should be done by someone experienced (e.g. who has developed boreholes in this area, or similar areas, before). Requires a well-trained engineer or hydrogeologist to visit the area.
Geophysical surveying: e.g. resistivity or electromagnetic (EM) techniques. Must be combined with reconnaissance data and hydrogeological fieldwork. It is important to analyse geophysical data correctly so that it gives good information. Investment in training staff is often beneficial. Geophysical equipment varies in price, but for a single technique (eg resistivity) is generally less than $US20 000. A well-trained geophysics team will need to spend at least 1 day in each area targetted for a new borehole.
Borehole Drilling
Drilling Supervision: experienced supervision of drilling is essential for the provision of successful and long-lasting water boreholes. A well-trained hydrogeologist or engineer should be onsite during drilling to supervise the drilling.
Collecting information during drilling: gathering information on geology (e.g. from logging drilled rock chips and measuring penetration rates) and hydrogeology (e.g. from water strikes). Drilling is a unique opportunity to collect useful geological and hydrogeological data from deep underground - data that are not otherwise available. A well-trained hydrogeologist or engineer should be onsite during drilling to collect good data.
Designing and constructing suitable boreholes. The design of every borehole should be adapted to the particular geology found at the drilling site, based on the information collected during drilling. An introduction to some types of borehole design that are suitable for many hydrogeological environments found in Africa can be found in the chapter Designing and constructing water points in MacDonald et al. (2001), which can be freely downloaded online. A well-trained hydrogeologist or engineer should be onsite during drilling to design the final borehole construction.
Borehole Testing
Assessing source yield: in most cases, this means assessing the sustainable yield of a borehole or well by carrying out a pumping test. For springs, it may mean measuring spring flow in different seasons. It is important to measure how much the source will yield sustainably in order to know how many people it can serve. A well-trained hydrogeologist or engineer is needed to carry out a pumping test, and normally they need at least 1 day per borehole. For higher yielding boreholes, an electric pump and generator are likely to be needed.
Assessing water quality: measuring the most important chemical and biological parameters that can impact human health. Some parameters can be measured quickly in the field using relatively simple equipment, but most need to be collected and sent to a laboratory. A well-trained field technician may be needed to carry out sampling.

Groundwater source types

The most common groundwater source types are springs, hand-dug wells, or drilled boreholes. (Drilled boreholes are often also called wells!).

Many resources are available to support the choice of which groundwater source type to use in different environments or for different purposes. Some of these are shown in the section Links to more information at the bottom of this page.

  • Springs are natural flows of groundwater from the underlying rock or unconsolidated sediment. Springs are dependent on the characteristics of the rocks, and their nature and yields are hugely variable. They often occur in specific hydrogeological environments. Because they are open at their source, springs are vulnerable to contamination. No equipment is needed to make a spring, but springs can be improved and made less vulnerable to contamination and drought by various developments, such as constructing a collection tank to store spring water, and installing a protective cover over the spring head.
  • Hand-dug wells have been dug to access groundwater for thousands of years. They can only be dug in soft material, such as unconsolidated sediment like sand and gravel, weathered basement, or limestone. They are only appropriate where the groundwater level (water table) is shallow. They are usually less than 20 m deep and 1–2 m in diameter, but can be wider and much deeper. Little or no specialised equipment is needed to construct a well – just something to dig with, and a way of removing the spoil. Wells often need to be lined to keep them open, using materials like brick, stones, concrete rings or even lorry tyres. Open wells are vulnerable to contamination from the surface, and can be improved by installing a concrete apron around the top. Wells have large storage, which helps make them less vulnerable to drought, but because they typically tap only shallow groundwater, they can dry up in dry seasons or longer droughts.
  • Boreholes are narrow diameter tubes drilled into the ground, usually vertically. Boreholes are also called tube wells or simply wells. They can be drilled more quickly and go deeper than hand-dug wells, and so can tap deeper, often more sustainable groundwater; they can be drilled though hard rocks and they can be more easily protected from contamination. There are many different techniques for drilling boreholes, some of which are more suited to certain hydrogeological environments. Usually, a motorised drilling rig is used, operated by specialist drillers. There are also manual drilling techniques.

Other, less common ways of accessing groundwater are by:

  • Collector wells, which are vertical boreholes or wells modified by drilling horizontally out radially below the water table to increase the collection area for groundwater into the central well, from where water is abstracted. They are often constructed in alluvium, next to ephemerally dry ('sand') rivers, with the horizontal radials drilled into the river bed deposits; or in weathered basement.
  • Infiltration gallery, which is a horizontal trench or drain dug below the water table to abstract shallow groundwater, usually from unconsolidated alluvium, including sand rivers, or windblown deposits. The trench drains into a sump from where water is abstracted. The gallery may have to be lined to keep it open.
  • Qanats, which are an ancient method of tapping and transporting groundwater in many parts of North African and the Middle East. A qanat comprises a mother well, often in alluvial deposits at the edge of a mountain range, and a gently inclined covered, underground channel which allows groundwater to flow downhill to a village.

Groundwater Abstraction Methods

Groundwater can be abstracted from boreholes and hand-dug wells by traditional methods (buckets, etc); by hand pumps; or by mechanical (e.g. diesel) or electrical submersible pump. Many resources are available to support the choice of which abstraction method to use, and some of these are shown in the section Links to more information at the bottom of this page.

Most rural water supply boreholes and wells in Africa are installed with hand pumps. There are many different types of hand pump, and the choice of which to use will depend on national standards, ease of maintenance and local expertise, availability of spare parts, the depth of water lift required, the groundwater chemistry (mild steel can corrode), and cost. RWSN provides many resources on hand pumps, including technical manuals and a number of discussion documents on practice and policy.

Mechanical or electrical pumps may be most appropriate for higher yielding wells or boreholes.


Links to more information

Danert, K. 2015. Manual Drilling Compendium 2015. RWSN Publication 2015-2, Skat, St Gallen, Switzerland.

Danert, K. 2015. Chad’s Growing Manual Drilling Industry. , Skat Foundation, St Gallen, Switzerland.

MacDonald, A M, Davies, J, and Ó Dochartaigh, B É. 2001. Simple methods for assessing groundwater resources in low permeability areas of Africa. British Geological Survey Commissioned Report, CR/01/168N.

MacDonald, A M, Davies, J, Calow, R, and Chilton, J. 2005. Developing groundwater: a guide for rural water supply. ITDG Publishing, NERC 2005. This book is a comprehensive manual for how to develop groundwater for rural water supply, based on extensive experience in Africa. Each chapter of the book can be freely downloaded from the Practical Action Publishing website.

MacDonald, A M, and Calow, R C. 2009. Developing groundwater for secure rural water supplies in Africa. Desalination, 248 (1-3), 546-556. doi: 10.1016/j.desal.2008.05.100

World Health Organisation. 2011. Guidelines for drinking-water quality, 4th edition. ISBN: 978 92 4 154815 1


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