- 14. Segment length: Using a map wheel (or GIS), record the approximate
length of the stream segment.
- 15. Elevation: Record the elevation at the reference location. Also
record source of data, for example, a 7.5' map or a benchmark on a bridge.
- 16. Sideslope gradient: Sideslope gradient is based on the
cross-sectional profile of the valley segment. Make three gradient
measurements within 300 m horizontal distance of the channel at positions
representative of the sideslope gradient along the segment. These
measurements and their mean are recorded.
- 17. Segment gradient: Determine the gradient of the segment
from a 7.5' map.
- 18. Channel sinuosity: Channel sinuosity is the ratio of channel
length between two points on a channel to the straight-line distance between the same
two points (Schumm, 1963; Platts and others, 1983). The value is useful for comparisons
of habitat conditions among or within streams. In general, low sinuosity indicates
steeper channel gradient, uniform cross sections, limited bank cutting, and limited pools.
High sinuosity is associated with less steep gradients, asymmetrical cross sections,
overhanging banks, and bank pools on the outside of meanders.
Channel sinuosity reflects the amount of meandering and, hence, the
diversity of habitat. Using a map wheel (or GIS), measure the sinuous and
straight-line distances of the entire segment. If the segment is less
than 2 km, a minimum distance of 2 km is measured starting at the
downstream node of the segment and proceeding upstream.
- 19. Stream order: Stream order is a classification of
streams based on tributary junctions (Horton, 1945) and has proven to be a
useful indicator of stream size, discharge, and drainage area (Strahler, 1957).
On a topographic map sho wing all intermittent and perennial
streams in a basin, the smallest unbranched tributaries are designated order 1.
Where two first-order streams join, a second-order stream
segment is formed; where two second-order segments join, a third-order
segment is formed, and so on. The major difficulty in determining stream
order is deciding what constitutes a first-order stream. Leopold and
others (1964) defined a first-order stream as the smallest unbranched
tributary that appeared on a 7.5' map. Using a 7.5' map, find the
smallest unbranched tributary upstream of the reference location,
designate it as first order, and record the appropriate stream order for
the segment. For irrigation canals and other "artificial" systems, "NA"
is recorded for stream order.
- 20. Downstream link: Record the downstream link number of the
segment. The downstream link number describes the relation of a given stream segment to
upstream and downstream influences within a basin and, therefore,
indicates the spatial location of a stream within a basin (Osborne and
Wiley, 1992). Downstream link number is the magnitude of the link of the
next downstream confluence. For example, the segment immediately
downstream from the confluence of two headwater tributaries has a
downstream link of 2. If a headwater tributary flows into a stream with a
downstream link of 2, then the segment immediately downstream from the
confluence of these two streams has a downstream link of 3, and so on.
For irrigation canals and other " artificial" systems, "NA" is recorded
for downstream link.