The impact of urban groundwater upon surface water - eTheses ...

GROUNDWATER FLOW MODELLING
Using an Excel spreadsheet, Equation 6.1 was used to calculate the base of the aquifer (b),
given input values for h, h1, h2, l, and x obtained from field measurements (Appendix 22). The
aim was to compare the effective thickness of the aquifer beneath the river with the expected
thickness based on geological data. An investigation was also carried out to see whether h1
was equal to the river stage, or contained an additional head component i.e. a seepage face.
6.2.2 Analytical Model, Transient Solution
Transient analytical solutions have been applied successfully in practical studies of ocean-
aquifer (Erskine, 1991) and river-aquifer interactions (Reynolds, 1987). De Marsily (1986)
presents the following analytical solution for aquifer heads given a sudden step change in
river stage.
h ( x , t ) = h 0 . erfc
( x
S
4Tt
h = change in head at distance x from the river at time t. [L]
t = time after the stage increment has occurred [T]
h0 = sudden rise in stream stage at time t=0 [L]
S = Storage [-]
)
Equation 6.2
This solution fits the case of a semi-infinite confined aquifer initially in equilibrium with the
stream at one boundary. It may be applied to the case of an unconfined aquifer if the stage
change is small enough that the saturated thickness can be considered constant
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