Planet WGSW-24010 User Manual page 52

Box 5 Exceptions to sur veying the full channel width
In all cases every reasonable attempt must be made to survey the full survey-length. There
are a few exceptional cases where it is acceptable to modify the approach.
1. Wide and deep r iver s
In some very wide and deep rivers it may be impractical to carry out a survey of the
full channel width on all surveying occasions. In such rivers, where the central channel
may be devoid of vegetation or cannot be accurately recorded due to depth/turbidity
even using an underwater camera, a 5m wide (minimum) strip down one side of the
channel (ideally with little tree shading) can be surveyed. Where the impact of a
discharge is being assessed, the downstream survey length must always be on the side
into which the effluent discharges. In watercourses where an effluent tracks along one
bank only for at least 500m downstream it may not be suitable to carry out a full width
survey on all occasions either and, therefore, a 5m (minimum) strip can be surveyed.
In such circumstances the whole river width must be surveyed initially so that results
from the whole channel can be compared with the selected 500m
2. Matur e islands
Where the impact of a discharge is being assessed and a mature island is located
within the survey length, only the side on which the discharge enters should be
surveyed.
3. 'Black holes'
No gaps/'black holes' must be left in a survey length except under the following
circumstances. If the majority (>80%) of a site can be surveyed by wading but the
remainder is deep or rapid and it is not practical to survey using a boat and
camera/glass-bottomed-bucket then this may have to be left as a 'black hole'. This
must be clearly mapped and discounted in all future surveys. The 'black hole' should
be totally excluded from the survey: it should not be included in estimations of plant
cover or physical attributes (except for width).
R&D Technical Report E38
2
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