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

GROUNDWATER FLUX
measured concentration and flow (chemical mass flux) to the lateral position of the
piezometer within the channel. The greatest groundwater discharge is likely to occur close to
the riverbank and comprises shallow perhaps more contaminated groundwater than older
water discharging through the centre of the channel and this is significant to the mass flux
estimation.
The contribution to surface water mass flux from the Birmingham Aquifer is estimated as
6.7% of the total dissolved mass flux in the surface water at Water Orton downstream of the
study area. This estimate is based upon a mean baseflow discharge of 308 Mld -1 at Water
Orton, a mean groundwater discharge of 19 Mld -1 from the aquifer and TDS in the surface
water, and groundwater of 1,014 mgl -1 and 1,101 mgl -1 respectively. The effect of discharge
from the aquifer is therefore relatively minor owing to the dilution effect and the fact that the
TDS content of the water moving downstream is already high. The impact of discharge from
the aquifer is dependent on conditions within the overlying river system. The Tame rises in an
urban catchment and receives numerous discharges from sewage treatment works and other
industry that significantly increases contaminant loading in the river before it reaches the
Birmingham Aquifer. However if the aquifer were located immediately downstream of a rural
catchment then the impact would be more significant. For example, using a surface water
TDS content of 245 mgl -1 from Sutton Park, the contribution of the aquifer to total mass flux
at Water Orton would increase to 23%.
Calculations of the groundwater contribution to surface water mass flux using gauging station
data on discharge and EC indicate that on the catchment scale groundwater (mean estimated
TDS 809 mgl -1 ) is diluting the surface water (mean estimated TDS 924 mgl -1 ) implying an
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