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

MONITORING NETWORKS AND METHODS
borehole locations. Environment Agency maps were available at a scale of 1:1000 showing
the River Tame and environs and marking the location of surveyed river sections and flood
defence boreholes.
4.6.3 Pressure Transducer Logging System
To obtain information on groundwater and river interaction it was necessary to collect
continuous head data from both the river and adjacent bank-side piezometers. The cost and
the size restrictions of the piezometers (ID 20mm) precluded most of the commercially
available pressure logging systems. The urban setting meant a high risk of theft /vandalism
necessitating the concealment of all equipment beneath a standard size 13x13 cm metal stop-
cock cover. It was decided to construct a pressure transducer and logging system that would
meet the space requirements and have low component cost in case of loss. A benefit of in-
house construction was the ability to adjust the transducer range and resolution to each
individual site.
The voltage recording data loggers and pressure transducers were readily available from parts
catalogues and construction was simple (Figure 4.5) and achieved by soldering on to single-
sided circuit board. Surface components consisted of the power source (two 9V batteries) and
the voltage data logger (either an 8-bit or 16-bit device) housed in accessible waterproof
containers. Downhole components comprising the transducer unit were waterproofed by
encasing in heat-shrunk plastic and sealing with polyurethane potting compound. After
construction, the transducers were calibrated by plotting voltage versus head which showed a
linear relationship. Sensitivities of 1cm to 1mm over a 3m range in water level depending on
whether the 8-bit or the 16-bit data logger was used. The 8-bit logger had a trigger output
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