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

5.9 Concluding Discussion
GROUNDWATER FLOW TO THE RIVER TAME
Baseflow analyses of river hydrographs indicate that 40-60% of dry weather flow at the lower
end ( Water Orton ) of the study reach is derived from unknown sources including a major
groundwater component. An estimated 20-25% of this is derived from groundwater
discharging directly to the 7.4 km of channel that overlies the Birmingham Aquifer. Baseflow
accretion also takes place as the river flows over the less permeable mudstone and coal
measure bedrock formations, and it is suspected that a significant component of baseflow is
derived from flow through surficial deposits of sand and gravel. Sewage Treatment Works
provide a major contribution to river discharge and comprise 30% of the total dry weather
flow at the end of the study reach. The Tame is estimated to be under dry weather flow
conditions for between 39% and 68% of the year, during which time the groundwater
component of river flow is most significant.
Groundwater levels in the Tame Valley have recovered from historical lows that occurred
during the period of peak abstraction 1900 –1950 when considerable loss of surface water to
the aquifer occurred. The Tame is now primarily, a gaining river with a very few localised
areas displaying surface water loss.
Groundwater discharge to the river is both spatially and temporally variable. The river
baseflow is at its lowest during the summer due to a reduction in groundwater discharge in
response to lower levels of recharge. Baseflow analyses for the entire 23.8 km study reach
estimated groundwater discharge to vary between 1.7 and 5.5 m 3 d -1 per metre of channel
during 1999 with a mean of 3.6 m 3 d -1 . River flow gauging measurements taken across the
aquifer indicate groundwater discharge in the range between 1.2 m 3 d -1 and 7.2 m 3 d -1 per metre
147