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

MONITORING NETWORKS AND METHODS
Water level was calculated for the set-up by subtracting the depth of the transducer from the
collar elevation and then adding the recorded head value from the transducer. The dipped
level recorded at the start was taken as the actual water level and if necessary used to apply a
correction to the transducer reading. The correction was sometimes necessary because the
transducer does not hang freely within the narrow piezometer.
Transient water levels within the river were monitored using the pressure transducer clamped
securely inside a 30 mm ID section of polyethene pipe with nylon cable ties. This pipe was
fixed securely to the wire gabions that reinforce the channel sides in many places. Owing to
the possibility of theft or vandalism it was necessary to make the equipment as unobtrusive as
possible. The data logger and power pack for the system were concealed within dense
undergrowth on the channel side.
Head measurements within the riverbed piezometers were possible by direct observation of
the water level through the semitransparent HDPE tubing. Relative differences between
piezometer head and river level were measured by placing a section of 20 cm ID clear plastic
tube around the piezometer to isolate the river surface and reduce the effect of river flow and
surface ripples. River levels and hence piezometer levels were calculated by comparing them
with a known benchmark on the riverbank.
4.6.2 Borehole locations and survey data
The details of the Severn Trent piezometers included collar locations and elevations according
to ordnance datum. These boreholes were used as fixed reference points from which to survey
in the flood defence boreholes, riverbed piezometers and river stage markers using a tape and
prismatic level with stadia. Maps at 1:1250 scale were available from Severn Trent showing
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