Planet WGSW-24010 User Manual page 88

Standar d 'r ules': use of flowchar t 'decision tr ees'
The trophic status of each site and the magnitude of impact of QDs should be assessed by
following the steps below, these steps referring to the flowcharts shown in Figures 4 and 5. The
flowcharts must only be used in conjunction with the information contained within this manual
and not used in isolation.
The flow charts are devised for use where there is one site upstream of a qualifying discharge and
one site downstream. If there is more than one site upstream or downstream, then the same
overall principles and descriptors of trophic status and significance of impact apply.
The steps are as follows.
1. Determine the standard 'descriptor' for the trophic status of each site, using the Stage I
'decision tree' flowchart (Figure 4). These descriptors are in given in the shaded boxes
and are each assigned a reference number. This descriptor is intended to determine
whether a reach is a suitable case for submission as a potential candidate for SA(E)
designation.
2. a) If the final descriptor is 1 or 2 there is no significant evidence for eutrophication and
the MTR cannot be used to support the designation of a SA(E).
b) If the final descriptor is 3–5 then the evidence can be used to support the
designation of a SA(E) and the Stage II flow chart should be used to assess the
impact of the qualifying discharge (proceed to 3 below).
c) If the final descriptor is 6 then there is little evidence from the MTR which can be
used to support the designation of a SA(E) but other evidence may prove useful in
supporting the designation.
3. For reaches including sites with standard descriptors 3–5:
For each pair of sites upstream and downstream a qualifying
discharge calculate the percentage change in MTR downstream
compared to upstream of the discharge.
NB % change = (Y - X)/X
values at the upstream and downstream sites respectively.
Downstream reductions in MTR will thus always be denoted
by a negative value.
Determine whether the discharge is having a significant
impact by using the Stage II 'decision tree' flow chart
(Figure 5) to determine the standard descriptor for the
significance of the impact, these descriptors again being
given in the shaded boxes with a reference number.
For each QD/potential candidate SA(E) there will be a number of
sets of results (3–4 over 3 years for most).
should be followed separately for each set of survey results
R&D Technical Report E38
´ 100, where X and Y are the MTR
The above steps
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