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

GROUNDWATER FLOW MODELLING
conditions. A variable pressure boundary condition may be applied at the base of the model to
induce upward flow or downward gravity drainage simulating changes in the level of the
water table. The model provides information on the flow across the boundary condition that
may be used in conjunction with the change in applied head to calculate storage values.
6.11.2.1 Boundaries and grid layout
The 1-D model comprised a 2 m column of 100 cells with boundary conditions applied at the
top and bottom. A no flow condition was assigned as the upper boundary. The lower
boundary at the base of the column was assigned a pressure head that was held either constant
or varied sinusoidally over time.
6.11.2.2 Procedure adopted, starting conditions and modelling periods
The model was used to investigate the occurrence of the capillary fringe under stable
conditions for sand and clay - the two extremes of the materials likely to occur adjacent to the
river. In the initial experiment, conditions for the column were set as dry with residual
moisture content. The model was run for a period of 10 days with the lower boundary
condition set as zero pressure to wet the column. A second experiment was carried out in
which a saturated column was allowed to drain for 10 days with a pressure of zero applied at
the base.
To simulate the aquifer response to river level fluctuations, a pressure head varying in the
form of a sine function was applied at the base. The amplitude and wavelength were varied
for different model runs over the ranges seen in field observations (wavelength 0.5-2 days,
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