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

GROUNDWATER FLOW MODELLING
across the river doubtful. Subsequent modelling and sensitivity analyses were based on the
calibration against P10 with specific yield = 0.005.
Piezometer Distance from river (m) Period Modelled Best fit value of S/T
P10 13.27 6/3/01 – 10/3/01 0.000399
P10 13.27 11/5/01 – 22/5/01 0.000321
P11 8.9 6/3/01 – 10/3/01 0.001934
P11 8.9 11/5/01 – 22/5/01 0.001069
P13 9 9/6/01 – 18/6/01 0.001457
P8 13.25 27/6/01 – 3/7/01 0.004 – poor fit
BH39 13.96 3/7/01 – 12/7/01 0.006092
Table 6.8 Values of S/T derived for the transient analytical model.
The FAT3D transient calibration was performed by varying specific yield (Sy) alone, as
transmissivity had been set previously in the steady-state calibration. It was possible to obtain
the same calibration hydrograph for higher values of Sy if Kx and Kz were also increased by
the same factor. Any possible increase in Sy is limited by the expected groundwater discharge
to the river. The values of Sy derived in the calibration are therefore thought to be
representative of the actual field parameters.
Using the results of the analytical modelling to derive a meaningful value of storage is
problematic. Straight use of values of horizontal transmissivity from the MODFLOW (450
m 2 d -1 ) and FAT3D (206 m 2 d -1 ) models yields storage values well in excess of those derived
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