wash cluster – emergency training gwd gwd2 1 1 groundwater development and drilling session 2...

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WASH Cluster – Emergency Training GWD

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Groundwater Development and Drilling

Session 2

Characteristics of Groundwater Systems

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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

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WASH Cluster – Emergency Training GWD

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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WASH Cluster – Emergency Training GWD

Groundwater Recharge

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Recharge is the process by which water gets into an aquifer.

Recharge quiz

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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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• 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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WASH Cluster – Emergency Training GWD

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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WASH Cluster – Emergency Training GWD

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