Difference between revisions of "Groundwater development techniques"

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[[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Additional resources | Additional resources]] >> Groundwater Development Techniques
==What does Groundwater Development involve?==
Developing groundwater resources sustainably is easier in some hydrogeological environments than others. If good supplies of groundwater can't be found everywhere - for example, if the local aquifers are low permeability and/or complex, or there are groundwater quality issues - then 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.
The main stages of a groundwater exploration programme which will allow you to assess groundwater resources are summarised in the table below, with an indication of costs. Some more detail is given in the sections below, but this page is not a comprehensive guide to groundwater development. Many resources are available which do provide detailed guidance and support, including a detailed book by MacDonald et al. (2005); a report with less detail by [http://nora.nerc.ac.uk/501046/ MacDonald et al. (2001)], but which is available online; and other references listed at the bottom of this page.
{| class = "wikitable"
|+ Stages of groundwater exploration and an indication of the costs of each
|'''Stage'''||''' Notes on costs'''
|'''Reconnaissance''': gathering maps and information (eg 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 (eg from satellite images or field mapping), costs will increase, but not prohibitively so.
|'''Siting boreholes & wells: Hydrogeological fieldwork''': assessing the groundwater potential of an area using an experienced eye (eg by someone who has developed boreholes in the area, or similar areas, before); examining local rocks and geomorphology; discussions with local communities on traditional water sources. This helps to 'ground-truth' the information gathered from the reconnaissance stage.
||Requires a well-trained engineer or hydrogeologist to visit the area.
|'''Siting boreholes & wells: Geophysical surveying''': eg 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.
|'''Collecting information during borehole drilling''': gathering information on geology (eg from logging drilled rock chips and measuring penetration rates) and hydrogeology (eg from water strikes). Borehole 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 supervise the drilling and collect good data.
|'''Assessing source yield''': assessing the sustainable yield of a borehole/well by carrying out a pumping test. 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.
===Types of Groundwater Sources===
Groundwater can be abstracted from the ground in different ways. Many resources are available to support the choice of which abstraction method  to use in different environments - there are some references at the bottom of this page.
Groundwater is most often accessed through '''springs''', '''hand-dug wells''', or drilled '''boreholes'''. (Drilled boreholes are also sometimes called wells!).
* '''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.
===Siting boreholes and wells===
===Drilling boreholes and wells===
====Drilling with a rig====
Most drilling methods use a motorised drilling rig (a different method is manual drilling - see next section). There are different types of drilling rig and methods of drilling, and these should be chosen to suit the local hydrogeology. The main types are cable tool percussion (also known as shell and auger), and rotary drilling. Rotary drilling can be air flush, sometimes with down-the-hole hammer; mud flush; or reverse circulation. Some more detail is available in [http://nora.nerc.ac.uk/501046/ MacDonald et al. (2001)].
====Manual drilling====
Manual drilling is an approach that is appropriate in some hydrogeological environments, particularly in shallow unconsolidated aquifers with shallow water tables. It can reduce drilling costs and increase cost-effectiveness of groundwater development programmes. Manual drilling methods are being used to provide water for drinking and other domestic needs in at least 36 countries around the world, and in some places are already well established.
[http://www.unicef.org/wash/index_49090.html UNICEF] has worked with a range of partners to develop a toolkit for African countries wishing to embark on the professionalisation of manual drilling. This toolkit includes technical notes and technical manuals, advocacy materials, case studies, and implementation and training manuals for manual drilling. There is also a series of [http://www.unicef.org/wash/index_54332.html maps]showing areas suitable for manual drilling in 12 countries in West Africa, and a report on the mapping methodologies used.
The Rural Water Supply Network (RWSN) has produced a [http://www.rural-water-supply.net/en/resources-top/details/653 Manual Drilling Compendium], which provides a useful overview of the impacts and challenges of manual drilling, and support for improving practices on the ground. 
===Pump type===
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. Mechanical or electrical pumps are most appropriate for higher yielding wells or boreholes. 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 [http://www.rural-water-supply.net/en/search?searchword=handpump&searchphrase=all hand pumps], including technical manuals and a number of discussion documents on practice and policy.
===Test pumping===
==References and links to more information==
Danert, K. 2015. [http://www.rural-water-supply.net/en/resources-top/details/653 Manual Drilling Compendium 2015]. RWSN Publication 2015-2, Skat, St Gallen, Switzerland.
Danert, K. 2015. [http://www.rural-water-supply.net/en/resources-top/details/656 Chad’s Growing Manual Drilling Industry]. , Skat Foundation, St Gallen, Switzerland.
MacDonald, A.M., Davies, J. & Ó Dochartaigh, B.É.. 2001. [http://www.bgs.ac.uk/africagroundwateratlas/fulldetails.cfm?id=AGLA000031 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. & Chilton, J. 2005. [http://www.bgs.ac.uk/africagroundwateratlas/fulldetails.cfm?id=AGLA500019 Developing groundwater: a guide for rural water supply]. ITDG Publishing, NERC 2005.
MacDonald, A.M. & Calow, R.C.. 2009. [http://nora.nerc.ac.uk/8460/    Developing groundwater for secure rural water supplies in Africa]. Desalination, 248 (1-3), 546-556. doi: 10.1016/j.desal.2008.05.100
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Latest revision as of 16:07, 7 May 2019