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

5.2 Groundwater in the Tame Valley
GROUNDWATER FLOW TO THE RIVER TAME
Previous investigations indicate that the River Tame is the natural sink for groundwater
discharge from the Birmingham Aquifer. The kriged contour map of groundwater head in the
Tame Valley (Figure 5.1a, Appendix 8) constructed using mean head data for shallow
groundwater and river level indicates that groundwater flow is directed towards the river. The
present course of the river lies close to the northern (left) side of the valley where flow
through the aquifer is generally directly towards the river or the major tributary and high
gradients are apparent associated with steep slopes in the topography. To the south of the river
data are limited except for a detailed profile of shallow piezometers through the flood plain
within the river meander centred (OS co-ordinates SP 0750091500). Here groundwater
appears to flow across the flood plain away from the upper bend in the river indicating the
possibility of a losing section in the river. The depth to the water table (Figure 5.1b) decreases
from ~19 m on the sides to ~2 m at the base of the valley where flow will occur through the
shallow alluvial gravel as well as the deeper sandstone aquifer. The reduced thickness of the
unsaturated zone in the valley bottom may increase the risk of groundwater pollution from
industry in this region.
The results of a MODFLOW model of the aquifer for the year 1989 indicate 22.3 Mld -1 of
groundwater discharging to rivers and streams, 16.4 Mld -1 being abstracted and 13.6 Mld -1
entering storage (Knipe et al, 1993). The large amount shown to be entering storage in 1989 is
a result of the groundwater rebound occurring after a reduction in the previously high levels
of abstraction. The current reduced levels of pumping from the aquifer fluctuate about a
generally stable trend of around 13.3 Mld -1 (Figure 5.2) estimated from Environment Agency
borehole return data. Historically, during the period of peak abstraction from the aquifer
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