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

GROUNDWATER FLOW MODELLING
in time only with groundwater level. The most likely explanation is that the S/T parameter
varies over time as a function of unsaturated flow and differences in the available storage as
the water table fluctuates. An additional factor may be that increased water levels and mass
loading on the river bed contributes to a reduction in the elastic storage. The unsaturated zone
is seen to be a major control on the groundwater and surface water interaction adjacent to the
river and further modeling was undertaken to investigate the processes associated with water
table fluctuation using the code UNSAT.
6.11 Investigate the control of unsaturated flow processes and the capillary
fringe on the fluctuation of the water table in response to changes in river stage.
6.11.1 Conceptual model
Variations in river stage cause a response in groundwater levels as observed in shallow
piezometers on the riverbank. The aquifer is unconfined and the observed fluctuations
represent variations in the level of the water table, the position at which pore pressure is equal
to atmospheric pressure. Above this level water is held under tension in pore spaces and as
grain coatings by the effect of soil-water attraction. The negative pressure created by the soil-
water (capillary) attraction draws water upward from the water table to form the capillary
fringe. This is a saturated zone with the upper limit defined as the point at which the gravity
head of the supported water column above the water table is equal to the capillary suction.
Above this point, the gravity head of the column of water will be greater than the suction and
gravity drainage will result.
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