wash cluster – emergency training gwd gwd2 1 1 groundwater development and drilling session 2...
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Groundwater Development and Drilling
Session 2
Characteristics of Groundwater Systems
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• 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
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Interconnection and Flow
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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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Groundwater Recharge
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Recharge is the process by which water gets into an aquifer.
Recharge quiz
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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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• 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
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EXERCISE 1
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EXERCISE 1 Cross section
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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
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Permeability
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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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Impact on well supply
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After: Don Armstrong, Australian Groundwater School, AMF course notes 1987 (unpublished)
Extraction Potential
high
lowhighlow
high in fractures
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Aquifers and Aquitards
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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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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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Confined and Unconfined aquifers
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• 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
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DISCHARGE QUIZ
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Discharge sites
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after Bear and Verruijt, 1987
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EXERCISE 2 cross section
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Seepage - springs or soaks
Seepage - springs or soaks
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Climatic influence on Groundwater occurrence
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Springs
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Interaction with Rivers
• Water table above river
• Groundwater discharge to river
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Interaction with Rivers
High flow in the river can lead to seepage into the groundwater
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• River above the water table
• Downward seepage into groundwater
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Coastal Zones
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Variability of Water Quality
24From Elrail et al 2009
Groundwater salinity can vary within the same aquifer