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

GROUNDWATER FLOW TO THE RIVER TAME
and both the surface water and groundwater temperatures at each point were taken in quick
succession, therefore the data can be used to estimate the temperature contrast for each
location. Each of the lateral profiles display the largest temperature difference close to the
bank edge, indicating a zone of high groundwater flow. Points at which the temperature
difference is zero suggest flow of surface water through the upper 10 cm of the riverbed. The
data indicate the hyporheic zone to be deeper and more extensive in the central portions of the
channel than adjacent to the banks. The variation in temperature contrast for the longitudinal
profile indicates the river is gaining, with variable groundwater discharge over the section.
The data also suggest that significant surface water flow does not occur through the riverbed
sediments at depths greater than 10cm within 2 m of the riverbank in this area. Groundwater
discharge is seen to occur through the riverbed and a major control on the rate of flow is the
conductivity of the riverbed sediment. An investigation was therefore undertaken to
characterise the riverbed sediments.
5.5 Characterisation of the Riverbed Sediments
Falling head tests in the riverbed piezometers and sieve analyses of riverbed core material
were carried out to determine the hydraulic conductivity of the riverbed sediments.
5.5.1 Falling Head Test Permeability Data
The results of 45 falling head tests in the riverbed piezometers were analysed using the
Hvorslev method and gave conductivity ranging between 0.08 md -1 and 23 md -1 with an
average of 3.13 md -1 and a geometric mean of 1.26 md -1 (Appendix 15). Three of the tests
were repeated immediately and showed a variation from the original value of between 0.25
and 1.6 md -1 . The poor repeatability is a result of errors in the manual measurement process,
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