Flashcards in Darcys Law Deck (10):

1

## Darcys law

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Q=q.A

Q= volumetric ground water flow rate (m3/s)

q= the specific discharge/darcys flux (m/s)

A= cross sectional area (m2)

2

## Darcys law can also be written as

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Q= -k . >h/>l . A

Q= volumetric flowrate (m3/s)

K= hydraulic conductivity (m/s)

>h/>l= hydraulic gradient (i) unitless

A= the cross sectional (m2)

3

## Hydraulic conductivity

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symbol: K

Units: m/s

4

## Hydraulic conductivity can be written mathematically as

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K= k. (pw.g/uw)

k= permeability (m2)

pw= density of water (1000kg/m3)

g= gravity at 9.8 m/s2

uw= the viscosity if fresh water at 20c = 1E-3 kg/m.s

5

## Hydraulic conductivity is dependent on

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a) properties of the rocks/sediments

increase in porosity = increase in K

b) properties of the fluids in the aquifers

6

## Hydraulic gradient

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symbol: i or >h/>l

units: unitless

7

## 2 major driving forces to groundwater flow

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a) gravitational force -- water will flow from high elev to low elev

b) pressure force (see photo in notes)

8

## The head at a particular point is defined mathematically as

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h= z + P/pw.g or h= z + (psy)

h= head (m)

z= elevation head (m)

P= pressure (PA or Kg/m.s2)

pw= density of water (1000 kg/m3)

g= gravity at 9.8 m/s2

9

## Specific discharge

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units: q

formula: q= v . n

n= porosity

10