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

GROUNDWATER FLOW MODELLING
Average abstraction rates decrease groundwater discharge to the river by 30% (Table 6.5) and
maximum rates cause a 78% reduction.
Level of
abstraction
Abstraction rate
(m 3 d -1 )
River gain
(m 3 d -1 )
River loss
(m 3 d -1 )
None 0 9683 34
Average 4483 6824 381
Maximum 26907 2149 8320
Table 6.5 River gains and losses due to borehole abstractions
Under conditions of average abstraction, losses from the river are small and the river receives
a net gain in flow over the reach. At maximum abstraction rates the river loses over a large
proportion of its length, with a net loss in flow. If a dry weather river flow rate of 184 Mld -1 is
used from flow gauging, then total river flow would be reduced by 5%.
After abstraction and use in industrial processes the water may be discharged to sewer but in
many cases it is discharged directly to the river. This needs to be taken into account when
calculating the water balance and when considering whether contaminant flux to the river is a
result of the industrial process or the original contaminated groundwater. For example, in the
case of abstracted water containing chlorinated solvents (Rivett, 1989) discharged to the
Tame.
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