Planet WGSW-24010 User Manual page 38

Surveys should not be undertaken when survey conditions are atypical for the site or prevent an
adequate survey, or when the suitability of the site has otherwise been compromised. Some
examples of unsuitable survey conditions are listed in Box 3.
Box 2 Factor s to consider when selecting MTR sites and sur vey lengths
1. Oper ator health and safety
Follow health and safety guidelines in selecting the location of survey lengths.
2. Gener al physical char acter
The survey lengths chosen should be typical of the river, within the other constraints
listed. If local knowledge is not available look further upstream and downstream of the
proposed survey length to determine this.
3. Water clar ity
Try to avoid locating survey lengths where the visibility of the river bed is significantly
impaired either because the water is deep or turbid. If the survey length is usually
turbid or too deep to see the bottom of the channel then a 'best attempt' at surveying
for macrophytes can be made (see guidance on sampling aids, 4.5.3).
Shade
4.
Although the degree of shade does not appear to influence the performance of the MTR
at assessing trophic status (Dawson et al 1999b), it is advisable to avoid heavily shaded
areas when selecting survey lengths.
5. Water flow and velocity
Survey lengths should not be situated where water flows and/or current velocity
compromise operator safety (refer to health and safety guidelines). Careful
consideration should be given before undertaking surveys in circumstances where the
flow from a point-discharge maintains river flows greater than would be expected, ie
significantly more flow downstream of the discharge than upstream. In this situation,
the physical conditions may affect the MTR score more than water chemistry.
River management
6.
Weed cutting and other associated maintenance activities including dredging will often
have a major effect on the cover and biomass of plant communities. Over time, this
may alter and maintain the dominance of different plant species from those naturally
present. The frequency and timing of river maintenance should be considered when
selecting sites and survey lengths, and the effects of the maintenance taken into
account when interpreting results.
7. Ar tificial str uctur es
Survey lengths are often located in the vicinity of bridges for ease of access. It is
preferable, however, if the length selected is situated so that it does not include
structures such as bridges, gauging/syphon weirs, locks and concrete-lined channels
within the survey length itself as these may affect the substrate type, marginal area type
and flow pattern. Local trampling effects may also occur near such structures so an
atypical vegetation pattern may be observed. Any structure is potentially dangerous to
the surveyor(s). Where structures cause change in the flow regime of the river the
survey length should be situated at a location most typical of the rest of the river.
8. Location of the sur vey length in r elation to a dischar ge being assessed
R&D Technical Report E38 24