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

GROUNDWATER FLUX
an urban setting. Direct measurement of changes in discharge and concentration along the
river provides mass flux in the surface water but includes inputs from sources other than the
groundwater and is susceptible to the temporal variations in pipe discharges. Riverbed
piezometers directly measure the concentrations in the groundwater discharging to the river
and are useful for delineating localised areas of plume discharge which surface water
sampling does not. However, the mass flux calculation relies on estimates of groundwater
flow rather than direct measurements, and a wide range in estimated flows may be calculated
depending on the method used (Chapters 6 and 7). River baseflow and groundwater discharge
display considerable temporal variation through the year and it is necessary to take this into
account by using continuous discharge monitoring. This may be combined with continuous
EC measurements so as to estimate the variability in surface water mass flux.
Ideally, continuous discharge and EC data would be available from the upstream and
downstream boundary of the aquifer and from the major surface discharges such as tributaries
and sewage treatment works. Regular surface water sampling could be conducted at the
gauged points and converted directly to a surface water chemical mass flux. The increase in
surface water mass flux at points across the aquifer could be determined more accurately from
the combined sampling and discharge measurements if the temporal variations in mass flux
entering the upstream limit of the study reach were known. These measurements could be
combined with a surface water tracer test (Kimball et al., 2002) to reduce the uncertainty in
the results. The riverbed piezometer monitoring network should be extended to identify any
narrow, high concentration, plumes that may have been missed, and to provide more reliable
mean groundwater concentrations. Geostatistical analyses should be performed to determine
the optimum sample density. Further investigation is necessary on the sensitivity of the
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