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High Flows
Under high flow conditions, faecal indicator concentrations exhibit a strong seasonal
pattern with much higher levels in the summer period. In the unmodified ‘control’
catchment, the increase in mean bathing water compliance parameters between the
pre- ‘autumn/winter’ and the post- ‘summer’ sampling periods were as follows:
a. total coliform 10.6 -fold increase
b. Escherichia coli 6.8-fold increase
c. Intestinal enterocci 3.5-fold increase.
Commonly, over 95% of the faecal indicator flux in the bathing season occurs during
storm periods, thus, the elevation in concentration in high flows is very significant.
Analysis
This observed seasonality made direct comparison of the high flow water quality data
acquired pre- and post-remediation meaningless. However, the control catchment
facilitated comparisons between the pre-remediation difference between ‘test’
and ‘control’ catchments (a) and the post-remediation difference (b). The value (b)
minus (a) gives the magnitude of water quality improvement in the post-remediation
period.
Two measures of subcatchment remediation intensity were calculated:
i. the additional percentage of the stream bank length fenced and,
ii. the additional percentage of subcatchment land area from which the stream was
‘protected’, by the new fencing.
While this inferred relationship will always be ‘confounded’ by subcatchment factors
such as, (a) the exact positioning of the fencing in relation to the sampling point
and (b) locations of hardstandings and their ‘connectivity’ within the subcatchment,
there does seem to be a clear improvement in the catchments where a significant
proportion of the stream bank has been fenced.
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