Planet WGSW-24010 User Manual page 66

4.6.2 Width
The width is the channel width for which macrophyte species have been recorded, as defined
in section 4.4.2, including any area of substratum above the actual water level that has been
surveyed.
The first time a survey length is surveyed the width of the channel should be measured using
a tape measure/rope with 0.5m divisions or an optical range finder (Appendix 4). If the
width varies noticeably along the survey length then several width measurements should be
made.
Record varying widths by entering the actual percentage in the appropriate boxes on the standard
sheet. More than one category may be recorded. For repeat surveys it should be sufficient to
estimate the width by one of the methods described below.
i) Use of a calibrated optical range-finder.
ii) If the survey length is easily/safely wadeable or a convenient bridge is present at a deep
water survey length, pace out the width.
iii) If (i) or (ii) are not practical, determine channel width using the following method. Place
a reference point on the ground, estimate by eye the distance across the channel then pace
a greater distance than the estimate of channel width from the reference point along the
riverbank. Turn and face the reference point, compare the distance to the reference point
with the channel width and decrease the distance to the reference point until it matches
the channel width.
Quality assurance
Optical range finders are designed to measure certain ranges so check that the one used
is suitable for the width being estimated. Check the calibration regularly.
If the width estimates vary greatly from the original width measurements it is necessary
to use a measuring device to check the data recorded for present and future surveys.
If a bridge is used to pace out channel width make sure that the channel under the bridge
is the same width as the channel in the length surveyed.
Pace-to-metre ratios should be calculated as under section 4.4.1 and regularly checked.
Ratios when wading in water should be calculated separately from ratios determined on
the bank, but pacing in water should be avoided if at all possible. All ratios are person-
specific (non-transferable!).
4.6.3 Depth
R&D Technical Report E38 52