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

GROUNDWATER FLOW TO THE RIVER TAME
Diffuse and unknown sources are seen to increase dry weather flow by 22% between Bescot
and Water Orton gauging stations. These unknown sources incorporate the groundwater
contribution derived directly from the main channel between the two gauging stations. The
total catchment groundwater component of the river flow may be even higher, up to 61%, if
flow from tributaries is considered primarily groundwater derived. The unknown inputs are
likely to include interflow and minor discharges from field drains and sewer overflow,
although groundwater is thought to provide the main contribution. Over the entire 23.8km of
the reach an average groundwater flow of up to 2.2 m 3 d -1 per metre of channel may be
discharging through the river bed. This equates to a specific discharge of 0.18 md -1 through an
average wetted channel perimeter of 12 m. This is an average figure for the entire reach and
takes no account of variations in the underlying geology. The Birmingham Aquifer would be
expected to provide a larger groundwater contribution to dry weather flow than the adjacent
and less permeable Coal Measures and mudstones. However the presence of old coal mining
voids and shafts may considerably increase the relative groundwater contribution from the
Coal Measures. River flow measurements were undertaken to define the baseflow accretion as
a result of groundwater discharge specifically from the aquifer and are discussed later
(Section 5.3.3).
The Environment Agency estimates are for an average set of dry weather flow conditions, but
both surface water flows and the groundwater discharge are time variant. Therefore, an
investigation was undertaken to establish the range of baseflow conditions and groundwater
discharge to the river.
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