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

GROUNDWATER FLOW MODELLING
The regional MODFLOW modelling indicated that a range in transmissivity (T) of between
400 and 750 m 2 d -1 is required in order to obtain realistic levels of discharge to the river of 8-
16 MLd -1 without significantly altering the boundary conditions. These estimates of T could
be low if significant abstractions are currently occurring within the model area. The values of
T are higher than expected for the bedrock sandstone indicating levels of hydraulic
conductivity >4 md -1 over a large effective aquifer thickness (>100 m) with limited impact
from impermeable mudstone layers. The high values of T may incorporate a contribution
from alluvial gravel on the flood plain. However, the average thickness of the gravel is 5 m
and values of conductivity would need to be considerable to reduce the contribution from the
bedrock aquifer. Limited field data suggest values of conductivity in the gravel are generally