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GWD2 1
WASH Cluster – Emergency Training GWD
1
Groundwater Development and Drilling
Session 2
Characteristics of Groundwater Systems
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GWD2 2
WASH Cluster – Emergency Training GWD
• You can’t drill anywhere and get groundwater
• Groundwater is not static – it flows through
pores in rocks
• Aquifers are not underground rivers – only
really in caves
• Not all groundwater obtained will be drinkable
Debunking Groundwater Myths
2
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GWD2 3
WASH Cluster – Emergency Training GWD
Interconnection and Flow
3
Interconnection of the pores in rock or soil allows water to:
•enter the groundwater,
•be stored in an aquifer below ground,
•flow through the subsurface,
•discharge naturally to a river, swamp, spring
or the sea,
•be recovered in a well or boreThis all relates to the geology of the area and the different types of soil and rock.
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GWD2 4
WASH Cluster – Emergency Training GWD
Groundwater Recharge
4
Recharge is the process by which water gets into an aquifer.
Recharge quiz
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GWD2 5
WASH Cluster – Emergency Training GWD
Rainfall to Groundwater
Water entering the soil is used by plants
(Evapotranspiration)
Water that isn’t used or stored in the soil seeps down below water table
– becomes Groundwater
- known as recharge Aquifer
RAINFALL
Some rainfall runs off across ground surface,
Some evaporates at the surface
Remainder enters soil
Storage of water in the soil (unsaturated zone) Becoming wetter closer to water table
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GWD2 6
WASH Cluster – Emergency Training GWD
• Groundwater flows through an aquifer under an hydraulic gradient
• effectively the difference in potential energy of the water – (hydrogeologists and groundwater engineers refer to the
potential as the “head”).
• Groundwater flows from areas of higher to lower head
Groundwater Flow
6
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GWD2 7
WASH Cluster – Emergency Training GWD
EXERCISE 1
7
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GWD2 8
WASH Cluster – Emergency Training GWD
EXERCISE 1 Cross section
8
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GWD2 9
WASH Cluster – Emergency Training GWD
Rate of groundwater flow is a function of the hydraulic gradient
Flow through the soil and within aquifers occurs by different pathways through different types of rocks
Rate of groundwater flow
9
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GWD2 10
WASH Cluster – Emergency Training GWD
Permeability
10
K (cm/s) 10² 101 100=1 10−1 10−2 10−3 10−4 10−5 10−6 10−7 10−8 10−9 10−10
Permeability Pervious Semi-Pervious Impervious
Aquifer potential Good Poor None
Unconsolidated sediments / Soils
Clean Gravel
Clean Sand or Sand & Gravel
Very Fine Sand, Silt, Loess, Loam
Peat Stratified clay Unweathered Clay
Consolidated Rocks* Oil Reservoir Rocks Sandstone Limestone, Dolomite
Granite
Rock permeability governs the ease at which groundwater flows
after Bear and Verruijt, 1987
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GWD2 11
WASH Cluster – Emergency Training GWD
Impact on well supply
11
After: Don Armstrong, Australian Groundwater School, AMF course notes 1987 (unpublished)
Extraction Potential
high
lowhighlow
high in fractures
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GWD2 12
WASH Cluster – Emergency Training GWD
Aquifers and Aquitards
12
Aquifer: A layer of soil or rock that has relatively higher porosity and permeability than the surrounding layers, enabling usable quantities of water to be extracted.
Aquitard: A layer of soil or rock that has relatively lower porosity and/or permeability than the surrounding layers, limiting the movement of groundwater through it and the capacity to extract useable quantities of water.
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WASH Cluster – Emergency Training GWD
Activity
• Fill the kettle• Plug spout with cork• Keep filling• Use different things to plug spout• Time how long it takes for water to
come out
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GWD2 14
WASH Cluster – Emergency Training GWD
Confined and Unconfined aquifers
14
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GWD2 15
WASH Cluster – Emergency Training GWD
• Water flows preferentially through higher permeability zones
• Water will move to areas that have least restriction to flow
• Groundwater will discharge at a point where constraints are released
Groundwater Discharge
15
DISCHARGE QUIZ
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GWD2 16
WASH Cluster – Emergency Training GWD
Discharge sites
16
after Bear and Verruijt, 1987
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GWD2 17
WASH Cluster – Emergency Training GWD
EXERCISE 2 cross section
17
Seepage - springs or soaks
Seepage - springs or soaks
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GWD2 18
WASH Cluster – Emergency Training GWD
Climatic influence on Groundwater occurrence
18
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GWD2 19
WASH Cluster – Emergency Training GWD
Springs
19
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GWD2 20
WASH Cluster – Emergency Training GWD
Interaction with Rivers
• Water table above river
• Groundwater discharge to river
20
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GWD2 21
WASH Cluster – Emergency Training GWD
Interaction with Rivers
High flow in the river can lead to seepage into the groundwater
21
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GWD2 22
WASH Cluster – Emergency Training GWD
• River above the water table
• Downward seepage into groundwater
22
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GWD2 23
WASH Cluster – Emergency Training GWD
Coastal Zones
23
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GWD2 24
WASH Cluster – Emergency Training GWD
Variability of Water Quality
24From Elrail et al 2009
Groundwater salinity can vary within the same aquifer