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

WATER QUALITY INTERACTIONS
Underlying the fluctuations due to anthropogenic inputs and rainfall is a general progressive
increase in EC during the baseflow recession. This indicates that low levels of baseflow are
associated with poorer surface water quality. For example, EC increases from 900 μScm -1 on
23/1/98 to 1000 μScm -1 on 20/2/98 as baseflow declines (Figure 7.2b). Thus, if EC increases
as the groundwater contribution to surface water decreases, and if anthropogenic inputs are
assumed to remain relatively constant through baseflow periods, the implication is that, on the
catchment scale (400 km 2 ), groundwater discharge improves the quality of the river by
diluting anthropogenic inputs. The results from the riverbed piezometers indicate a higher EC
in the groundwater but these results are specific to discharge from the Birmingham Aquifer
whereas the gauging station data reflect the larger catchment scale.
The level of industrial discharges will limit the extent to which groundwater affects the
quality of surface water, but even without industrial discharges, the levels of EC of surface
water in urban areas are still likely to remain higher than in rural areas.
The poorest levels of water quality occur in the river during the initial phase of a flood event.
Previous workers (O’Connor, 1976, Pinder et al.,1969) have found that groundwater forms a
significant component of flow in a natural catchment during these events (up to 80%, Sklash
et al., 1979). Although it is generally considered most important in upland catchments the
effect of groundwater dilution may be significant in mitigating the effects of first flush run-off
and CSO discharges in the Tame.
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