Geomorphic Assessment of Channel Systems
channel dimensions can be measured using a tape. Usually, two people are required, but if
survey pins are used to secure the end of the tape, one person can manage. Banklines and
other channel features can be mapped using a compass and tape with surprising accuracy. If
repeat reconnaissance surveys are performed, these maps can be useful in establishing rates
of bankline migration or channel shifting. Flagging tape is used to mark near-bank objects or
vegetation near reference points to aid relocation of repeat sections or transect lines.
Hand-Level and Pocket Rod or Surveying Staff. Cross-sections and, on steep
streams, longitudinal channel bed and water surface profiles can be surveyed using a hand
level and pocket rod. The hand level has a five time magnification and can be used for
leveling over distances up to about 20 meters with centimeter accuracy. If shorter distances
are acceptable, an Abney Level can be used in place of the hand level.
The pocket rod resembles a 2 meter (or 6 foot) long steel tape which is substituted
for a conventional surveying staff. Its advantage is that it retracts into a 50 mm square case
that fits easily into the fieldpack. If transportability is not a problem, a telescopic surveying
staff may be used instead of the pocket rod.
Clinometer. The clinometer is used to measure angles and heights. It works on the
principle of a spirit level and can be used to measure the slope or inclination of a bank surface
or tree trunk to within one degree. It can also be used together with simple trigonometry to
measure the height of objects such as trees, engineering structures or flood marks on
buildings.
Estimating bank slopes is notoriously difficult and most untrained observers tend to
seriously over-estimate bank angles. The inclinometer can be used in conjunction with the
pocket rod or survey staff laid along a bank profile to measure the slope angle of different
segments of the bank profile quickly and conveniently and so avoid subjectivity.
Folding Trenching Tool, Plastic Bags and Marker Pen. These items constitute the
basic equipment for collecting field samples of any sediment finer than coarse gravel. The
trenching tool is a type of folding spade used for digging into the bed, bank or bar to extract
a sample, examine the stratigraphy or gain access to the substrate. Its advantage over a
conventional spade is that it is more compact and fits easily into the fieldpack.
Samples of clay, silt, sand or pea-gravel of sufficient size for particle size analysis can
be packed in plastic "zip-lock" bags and labeled using a water-proof marker pen. Bulk
sampling of coarse gravels or cobbles requires samples that are too large to carry by hand
over all but the shortest distances. Consequently, a size-by-number sampling strategy is
preferable when dealing with gravel, cobble or boulder-bed rivers. The necessary equipment
is described in the next section.
59
Previous Page
