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

GROUNDWATER FLOW TO THE RIVER TAME
which could be overcome if a pressure transducer and logging system were used. The
frequency distribution (Figure 5.14) shows the large heterogeneity in the system and suggests
a log normal distribution. This implies that the geometric mean is representative of the general
conductivity of the sediments. This value contains both vertical and horizontal components
and the vertical conductivity that controls the groundwater flow through the riverbed is likely
to be lower. However the volume sampled is small (~200 cm 3 ) and other investigations
(Bradbury et al., 1990) have suggested that hydraulic conductivity increases with the scale of
measurement. In addition other studies (Cey et al., 1998) have recognised that clogging of the
riverbed piezometer screen may reduce the estimated conductivity.
The conductivity estimates are very site specific and show large heterogeneity that requires a
high sample density to determine average conductivity adequately. The spatial variation in
conductivities along the study reach (Figure 5.15) may reflect changes in the sediment type
but sample density is too limited to confirm this. High values at Profile 8 may be associated
with coarse gravels.
5.5.2 Riverbed Sediment Core Data and Sieve Analyses
A total of 23 riverbed cores were taken to depths of up to 0.5m from Profiles 1,2,8,and 17
across the aquifer. The sediments typically comprised a 10 cm section of coarse gravel
containing cobbles 60% of the samples were classified as gravel. In general, (Figure 5.17) particles < 10
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