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

MONITORING NETWORKS AND METHODS
A specially constructed temperature probe was used for the survey. Difficulties were
encountered in driving the probe into some sections of the river and temperature readings
were slow to stabilise making the procedure time consuming. Unrealistic increases in
temperature for both the surface and groundwater were noted in one profile which may have
resulted from heating of the apparatus by direct solar radiation. Therefore, the most
meaningful data were thought to be the temperature gradient between the surface water and
the sediment water rather than the absolute temperature values. The method provided a
qualitative method that suggested the inflow of colder water through the bed sediments.
4.8.2 Construction of a temperature probe
The temperature probe was constructed from a 2m section of PVC pipe (ID 20mm) with a
steel drive point mounted on one end. A series of holes were drilled to form a screened
section between 5 and 10cm above the drive point. A K-type thermocouple with a 2m
extension was inserted into a protective plastic tube (2mm ID) leaving the two ends exposed.
The active end of the thermocouple was then located within the screened section and sealed
from the empty tube above using a waterproof sealant. The upper end of the thermocouple
was then connected via a plug to a hand-held thermocouple reader.
4.8.3 Estimating groundwater flow from vertical temperature profiles
Several workers have investigated the use of vertical temperature profiles within groundwater
to calculate vertical flow velocities. Bredehoft et al. (1965) developed a steady state analytical
solution describing the vertical flow of heat and groundwater through an isotropic
homogenous, fully saturated semiconfining layer by use of a type curve method. Silliman et
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