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Flashcards in Darcys Law Deck (10):
1

Darcys law

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

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

symbol: K
Units: m/s

4

Hydraulic conductivity can be written mathematically as

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

a) properties of the rocks/sediments

increase in porosity = increase in K

b) properties of the fluids in the aquifers

6

Hydraulic gradient

symbol: i or >h/>l
units: unitless

7

2 major driving forces to groundwater flow

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

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

units: q

formula: q= v . n

n= porosity

10

Flow velocity

units: v