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

GROUNDWATER FLOW TO THE RIVER TAME
rainfall. In the same way, catchment recharge was calculated as 29% at Bescot and 20% at
Calthorpe. These values will incorporate leakage from water mains in addition to recharge
from precipitation. The 1999 yearly discharge to the main channel, derived from the
Birmingham Aquifer directly, was approximated as 8.86 x10 6 m 3 yr -1 based on the sandstone
underlying a reach length of 7.4 km from the total of 23.8km. The total contribution from the
aquifer as a whole may be significantly larger with a flow of 1.66 x10 7 m 3 yr -1 from the Rea
and 8.32 x10 6 m 3 yr -1 from the lesser tributaries, which drain the aquifer and are groundwater
fed.
5.3.3 River Flow Gauging
In order to determine the level of baseflow accretion, river flow gauging was undertaken.
Measurements were carried out on ten separate days of dry weather flow during the period
7/7/99 to 23/5/01 at different points on the river between Bescot and Water Orton. An
increase in flow across the reach is evident (Figure 5.8, Appendix 9) with base flow accretion
ranging from 1x10 -4 m 3 s -1 (8.6 m 3 d -1 ) to 3x10 -5 m 3 s -1 (2.6 m 3 d -1 ) per metre length of channel.
Taking into account known DWF discharges of 10.3 Mld -1 , groundwater discharge from the
aquifer directly to the channel ranges between 1.2 m 3 d -1 and 7.2 m 3 d -1 per metre of channel.
Several of the data series (e.g.02/06/00) fluctuate, sometimes displaying a fall in discharge
levels downstream, indicating either that the river is not under steady dry weather flow
conditions or an error in the flow measurements. There does not appear to be any obvious rise
in accretion levels across the aquifer compared with the other types of bedrock geology (coal
measures and the mudstones). This may be due to insufficient data coverage or perhaps it is
an indication that the drift, in particular the alluvial gravel which is present along the entire
length of the study reach, is controlling groundwater flow to the river. The most recent data
were recorded on consecutive days (22 nd - 23 rd May 2001) and exhibit consistent discharges
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