WASH Cluster – Groundwater Development and Drilling
GWD1
Handout
GWD1 – Occurrence
CASE STUDY 1: GEOLOGY AND GROUNDWATER FOR REFUGEES AND IDPs IN EASTERN CHAD
Summary
The relationship between geological features and groundwater sources is well observed in the
supply of groundwater at a number of locations in eastern Chad, where refugees from neighbouring
Darfur have been living since around 2003.
 The geology was assessed to see if possible aquifers were present.
 The two key aquifers identified from geological maps, air photos, topographic maps and field
observation are wadi sands and fractured bedrock.
 The location and extent of wadis was mapped to indicate a significant groundwater resource
that was readily developed. T.ese deposits are relatively continuous and homogeneous
 In areas where there were no significant wadis, groundwater supplies were found in
fractures in crystalline rocks – the groundwater zones were investigated by mapping of rock
geological structures, topography and geophysics. The sources found were isolated and
localised. Not all areas investigated in the bedrock yielded successful wells due to the
irregular distribution of fractures
Humanitarian Situation:
In 2005 there were three refugee camps in the Eastern border of Chad where refugees from Darfur
were located. Up to 20,000 people were residing in each of the three camps at Treguine, Breidjing
and Farchana, around 40-50 km from the border with Sudan. As the crisis in Sudan escalated,
refugees continued to enter the country. This led to stress on resources in the existing camps with
the potential for another refugee camp to be established at Gaga further inside Chad.
Further south around Goz Beida, there were additional refugees in the Djabal refugee camp, and by
2007 large numbers of Internally Displaced People (IDPs) were also in this area requiring aid.
The needs of large numbers of people as well as possible impacts of climate requiring water at
much large volumes than existing sources were able to provide pointed to a potential water crisis.
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WASH Cluster – Groundwater Development and Drilling
GWD1
Indicative refugee situation in
Eastern Chad, 2004 – from UNHCR records
Water supply situation
Rainfall records for Abeche, a city around 100km from the border indicates a average maximum of
nearly 400 mm in August from September to March with some falls in April and May. Water supply
in this dry environment is thus largely provided by groundwater.
Prior to the influx of refugees and IDPs many local communities sourced their water supply from
shallow wells often in the wadis or wadi margins. Water was also recovered from wadi sands, that
are often at risk of contamination from surface pollution, including the impact of animal waste.
Water levels in the larger wadis are commonly shallow (around 1-3m depth to water) although this
will vary seasonally and with use.
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WASH Cluster – Groundwater Development and Drilling
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Camel herds on Wadi – water in the wadi sediments
potentially damaged by animal waste.
Further south around Goz Beida, a borefield was operating supplying groundwater from bedrock
fractured rock aquifers to the town of Goz Beida. As the Djabal refugee camp was established
nearby, this source was used to provide water to the refugees. Stress on the fractured rock aquifer
increased.
The need for sustainable sources of groundwater to meet the demands of the rapidly increasing
population was evident. The aquifer systems were not well documented and knowledge of existing
wells limited.
Adopted options to meet emergency needs
A range of water supply options focussed on groundwater have been developed for these areas for
water supply.
1. WadiSands: It was recognised that the wadi sands are potentially large sources of
groundwater that has the potential to be recharged annually during teh wet season.
Estimates of thickness in some of the larger wadis (eg teh Wadi Hamra at Treguine and
Breidjing) are in excess of 40m (Salas, 2004). Assuming a wadi width of around 200m,
saturated thickness of say 20m and porosity of 30% for the coarse sand, - along a 100m
length of wadi there may be sufficient water stored in the wadi sands to supply 20,000
people for a year (assuming 15L/p/day, the Sphere Standard). However it must be noted
that this volume would need to be replenished by recharge from flooding if the entire
volume were extracted
Wadi sands have been developed at Treguine and Breidjing using shallow wells with suction
pumps attached. Lytton et al (2007) report pumping volumes of 6L/sec.
Wadi within fractured crystalline
rocks can be a major source of groundwater
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WASH Cluster – Groundwater Development and Drilling
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Rocky outcrop of crystalline metamorphic
basement rock containing quartz veins forming a hill. A wadi containing sandy sediment is visible in
the left background.
MDPE Discharge line from 6m deep tube well in the sands in
the bed of the Wadi Hamra. Water pumped by petrol powered suction pump to 70,000L water
tanks. Water was treated with Chlorine before disctribution through the network to tapstand
tapstands.
2. In the Farchana camp to the north east, the Wadi Hamra is thinner and narrower than at
Breidjing and does not present the same potential for high yields, so bedrock was the
available target aquifer . In this location, two wells up to around 40m deep are located
around 3km from the camp and the water pumped by submersible pump to the camp.
These are drilled into fractured bedrock and have yielded 2.3 and 3 L/sec although there
has been significant drawdown of water levels. There was a need to provide additional yield
to this camp and further sources were investigated.
The diagrammatic section across the wadi shows how mapping the extent of different
aquifer types can help in the search for a groundwater source. The extent of the Wadi
sediments was obtained by mapping the width of the wadis and drilling of shallow bores.
Shallow drilling of wells in the wadi was undertaken for short term assistance, while in the
meantime investigation using geophysics of potential sites for drilling in the bedrock was
undertaken. A well adjacent to the wadi but not in the wadi bed was drilled with a yield of
5L/sec.
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Diagrammatic cross section across a Wadi in Chad.
3. At Goz Beida in Southeast Chad, up to 5 existing Government wells more than 50m deep
were supplying the community at GozBeida. The wells equipped with submersible pumps
were drilled into fractured bedrock. As the increased demand was placed on these wells
from the refugee camp, careful monitoring and pump scheduling was required to maintain
supply to users.
4. The bedrock aquifers were investigated in the area around Goz Beida to provide water for
IDPs. There was a serious water shortage, geophysical surveys (resistivity) coupled with
examination of geological maps and air photos targeted drilling sites. Bores up to 60m
deep were drilled and installed as production wells. Not every interpreted site provided a
successful bore.
Developing a successful bore at Gouroukun
drilled in bedrock with PAT Drill (mud rotary) to approximately 60m
References:
Lytton, L., Arafan, S. and Hazell, R. 2007. A low-tech drilling method for refugee water supplies.
WaterLines Vol 26, No 1, pp 5 – 7
Salas, G. 2004. Groundwater Resources for Refugees in Eastern Chad. Reprt to UNHCR and RedR
Australia.
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