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

GROUNDWATER FLOW TO THE RIVER TAME
channel (61 Mld -1 , 20% of flow), after the mean values of known discharges have been
subtracted. On the catchment scale if tributary flow is considered as groundwater derived,
then flow at Water Orton comprises between 40 and 67% groundwater. Clearly, the influence
of groundwater contaminants on the dry weather surface water concentrations will vary
considerably and will be dependent on the baseflow conditions and changing levels of
industrial (STW) discharge. The mean values of baseflow derived using the filter technique
were compared with values based on the analyses (Section 4.9.1, Appendix 17) of seven
periods (54 days total) of baseflow recession during 1999. The results (Table 5.2) show a
reasonable correlation with the recession estimates generally 14 to 18 % lower than the filter
estimates.
Gauging Station
Average Baseflow – Recession
Method (Mld -1 )
Average Baseflow – Filter
Method
(Mld -1 )
Bescot 113 131
Calthorpe 31 38
Water Orton 260 308
Table 5.2 Comparison of mean baseflow obtained using filter and recession analyses methods.
The effect of industrial discharges was subtracted from the mean baseflow to provide an
estimate of diffuse baseflow discharge per unit of catchment area (Table 5.3). The values for
Water Orton and Calthorpe are higher than Bescot and may reflect high levels of groundwater
discharge from the sandstone and drift, though differences in recharge rates and land use will
also be significant. A difference between catchments is also evident from the variation
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