2 Groundwater Hydraulics

Question 1

Hydraulic conductivity: heterogeneity & anisotropy

Answer 1

Heterogeneity:
kf-values of natural rocks are spatially very variable (in all three dimensions): e.g. bedding, fractures, schistosity

Anisotropy: directional dependence of hydraulic properties

In sediments horizontal permeability is often 10 x higher as vertikal permeabilty

Question 2

Determination of permeability in the lab

Answer 2

• Permeameter (Darcy-Experiment)
• Falling head permeameter for impermeable sediment

Sample:

• Undisturbed samples (drillcores)
• Disturbed samples

Question 3

Integral permeability: transmissivity

T = kf . m

Answer 3

kf-values of natural rocks are spatially quite variable -> heterogeneity

Representative Elementary Volumen?

Transmissivity T as integral of the permeability kf (here: over depth)

Question 4

Fractured aquifers: parameters

Answer 4

• aperture (opening width)
• density (number per length)
• asperity (roughness)
• length
• interconnectivity
• anisotropy (direction, orientation)
• distribution
• fracture systems
• REV

Question 5

Fractured aquifers: conductivity

Answer 5

Variation in hydraulic conductivity with fracture frequency and conducting aperture

Question 6

Fractured aquifers: aperture and stress

Answer 6

The aperture decreased as the depth increase because more rocks on top of it which gives more weight and compact the sediment below

Question 7

Fractured aquifers:

Permeability over depth

Answer 7

Permeability decreases as the depth increases, hydraulic conductivity decreases

Question 8

A proper aquifer needs to have 2 properties

Answer 8

1. Transmit water -> Hydraulic conductivity (K)

2. Volume of water that we can actually store in that aquifer -> Storage coefficient (S)

Question 9

Storage coefficient, storativity

Answer 9

For unconfined aquifers:
S = ne
ne= 0,05 -0,35

For confined aquifers:
S = 10^-3 - 10^-5

Question 10

Groundwater levels: natural influences (1)

Answer 10

•Surface of groundwater
pressure equals air pressure

-> groundwater levels react upon changes in atmospheric pressure

Barometric coefficient=
Proportionality factor between change in air pressure and groundwater level
(0 % < BC < 100 %)

Question 11

Groundwater levels: natural influences (2)

Answer 11

• precipitation
(delayed by transit time through the unsaturated zone)

• tides (ocean, earth)
• water levels in rivers, lakes etc.