Geomorphic Assessment of Channel Systems
18.104.22.168 Field Equipment for Stream Reconnaissance
Stream reconnaissance involves both qualitative observation and quantitative
measurement of key dimensions and geometric parameters of the channel and its
morphological features. It is important that the measured dimensions and parameters are
representative of the study site or reach but, given the nature of stream reconnaissance, it is
not necessary that they are of great precision. Hence, there is no justification for the use of
sophisticated instrumentation capable of millimeter accuracy. Also, the need to make
observations and measurements in inaccessible locations quickly, and with assistance from
only one or two field assistants prescribes the use of equipment that is suited to the purpose
and which is convenient to use. As any fieldwork near a waterway carries with it unavoidable
hazards, it is essential that individuals performing stream reconnaissance carry basic safety
equipment. Finally, the equipment must be portable. Ideally, it should fit into a backpack or
rucksack and weigh under 50 pounds.
During development and testing of the approach presented here, a field backpack
containing the equipment necessary to perform stream reconnaissance in a wide variety of
environments was assembled. The actual contents evolved over time based on the suitability
of each instrument or tool, and the need to add or delete some items in order to produce a
fieldpack that was versatile, but of manageable size and weight. The final product was a set
of equipment that would fit into a single backpack and could easily be carried long distances.
Rangefinder. This is an optical distance measuring device based on the `coincidence'
method of rangefinding. It uses a binocular system to produce twin images of a distant
object. The observer uses an adjustment knob to make the images coincide and then reads
the distance from the instrument to the object on a graduated scale. When properly calibrated
and used by an experienced observer, distances can be measured to about two percent
accuracy. The range of distances that can be measured varies with the type and cost of the
rangefinder. The instrument can be used for distances up to 500 meters. In field tests,
accuracy was found to be 3% at 300 meters, rising to 1% at 100 meters.
The rangefinder has the enormous advantages that it is operated by a single person
and that it measures distances without the operator having to traverse the intervening
landscape. For example, this allows water surface and channel widths to be measured without
crossing the stream, saving time and reducing the hazards encountered in field reconnaissance.
String-operated Pedometer. This instrument measures the distance walked by the
operator by using fine, biodegradable string to spin an odometer as the string is pulled out.
The string is broken off at the end of the measured section and left to decompose. The device
allows a marked improvement in accuracy over simple pacing, but with no added
inconvenience. Like the rangefinder, a single person can measure distance quickly and
accurately, but unlike the rangefinder the pedometer does require the operator to traverse the
section being measured. Available proprietary brands of string pedometer include "Hip
Chain," "Walk-Tax" and "Field Ranger."