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

GROUNDWATER FLOW MODELLING
boundary condition. Variations in other parameters, in conjunction with the expected dry
weather flow (DWF) river stage, yielded saturated thickness values of < 3m which are still
below the expected value. This implies the existence of a seepage face to increase the
calculated saturated thickness to a realistic level. The maximum likely vertical expression of
the seepage face is 37cm if a projection of the gradient between P10 and BH19 is used. If full
connection between the different aquifer units is assumed then a saturated thickness of >10m
is expected. This would require a minimum seepage face of 34 cm above the mean DWF river
stage under average conditions of head in the aquifer. With a seepage face of 37cm the
calculated saturated thickness is 65 m. The controls on the formation of the seepage face and
groundwater flow across it are examined in more detail in the next section.
6.6 Investigation of the controls upon groundwater flow across the seepage face.
6.6.1 Conceptual model
Groundwater discharge to the river occurs through a seepage face as a result of capillarity and
flow balancing when groundwater head gradients to the river are high and induce flow
through the sides of the channel above the river level. Seepage may occur under steady-state
conditions or following a river flood event after which ‘mounded’ groundwater and perhaps
infiltrated surface water is discharged. The size of the seepage face is dependent on the
conductivity values of each of the geological units through which flow to the river occurs. A
high ratio of anisotropy (Kx/Kz) is likely to increase discharge through the seepage face.
The significance of contaminant flux across the seepage face is unknown and in many parts of
the Tame it is difficult to measure directly the extent of the seepage face because of the
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