Stream transects are established to collect the
information required to complete items 13 through 35. Six transects, as a
minimum, are established throughout the reach with two transects
established at or near each boundary (fig. 6). If the reach is established
on the basis of the presence of two examples of each of two types
of geomorphic channel units, the remaining four transects are established
at the middle of each geomorphic channel unit. If the reach is defined on
the basis of channel width, then the remaining four transects are evenly
spaced throughout the reach. Transects are oriented perpendicular to
streamflow. Drawing a simple map, as shown in figure 6, and marking
transect locations when establishing the locations of the reach boundaries
and transects facilitate subsequent sampling efforts.
- 13. Distance from the reach boundary nearest to the reference location:
This distance is measured as the channel distance from the transects
to the reach boundary nearest to the reference location.
- 14. Channel width:Measure the channel width along the
transect from left edge of water to right edge of water.
- 15. Bank width: Banks include geomorphic features, such as
some channel shelves, and are flooded on average more than once every 1 to
3 years (Hupp, 1986). Banks are bounded by the channel bed and the flood
plain (fig. 7). Thus, bank width is the distance between the channel bed
and the flood plain. This distance is measured with a tape measure or
rangefinder.
- 16. Flood-plain width: The
flood plain is a relatively flat surface that is flooded on average once
every 1 to 3 years (Leopold and others, 1964). The flood plain is bounded
by higher features, such as terraces, that are flooded on average once
every 3 or more years, and riparian features that are flooded more than
once every 1 to 3 years (Hupp, 1986). Thus, flood-plain width is measured
as the distance between the significant changes in slope that distinguish
the flood plain from terraces and riparian features (fig. 7). If this
distance is less than 50 m, it can be measured with a tape measure or
rangefinder. However, if the flood-plain width is greater than 50 m, it
is determined from maps or aerial photographs, and indicated as greater
than 50 m on the form.
For items 17 through 20, data are collected at three points along each transect. These points should
correspond to the thalweg, and to two locations that are equally spaced
along the transect (or three equally spaced locations if no thalweg is
apparent). At each point, record the distance from the left edge of water and note
if the point is located in the thalweg by including the letter "T" next to
the distance.
- 17. Depth: In wadeable reaches, water
depth between the water surface and the bed substrate is measured with a
wading rod and recorded. In nonwadeable reaches, a sounding line or
hydroacoustic depth meter may be necessary to determine d epth. When
using a hydroacoustic depth meter, the investigator maneuvers the boat
along the transect with the meter operating, so as to produce a continuous
recording of water depth along the transect. Three depth measurements,
one at the thalweg and two at locations equally spaced along the
transect, can be determined from the hydroacoustic chart.