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

GROUNDWATER FLOW MODELLING
and frequency of the piezometer hydrograph are independent of changes in the regional head
gradient. This indicates that it is valid to compare the analytical model results of S/T for
boreholes from different locations with different regional head gradient conditions. Full
details of the modelling carried out are given in Appendix 22.
The 1-D analytical model provided a simple and rapid estimate of average S/T over a 5-10
day period incorporating several flood events. More detailed 2D modelling incorporating
complex geology was undertaken for a single event using FAT3D.
6.10.3 Application of the FAT3D cross sectional model
The FAT3D cross sectional model was used to simulate groundwater-surface water
interactions across the channel during a single flood event lasting a period of 1.2 days with the
peak in stage, 0.5 m above dry weather flow conditions. The calibrated steady-state model
was subjected to varying river boundary head conditions based upon field data (6-7 th March
2001). A general specific storativity of 0.00001 was assigned to all geological units. In
addition, the gravel unit was assigned a value of specific yield, as it was known to contain the
free surface of the water table. The transient model was calibrated on a trial and error basis by
varying values of specific yield in the gravel unit and comparing modelled heads with field
data for piezometers P10 and P11. The model was run under steady-state conditions to obtain
the initial head conditions prior to each transient run.
A sensitivity analysis was undertaken to gauge the effect of variation in hydraulic parameters
on groundwater discharge to the river and hydrograph amplitude in piezometer P10. An
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