Richard Patton,
Hydrologist,
George Washington & Jefferson
National Forests
Harrisonburg, Virginia
With decreasing budgets and reductions in personnel, it is becoming increasingly
difficult to put together field survey teams -- or even to find one person to accompany
you in the field. So I have developed procedures to go it alone -- to take measurements
of physical stream parameters without an assistant.
These procedures are not intended for stream channel reference sites or similar situations
where precision is essential, but rather for general surveys where stream measurements
are desired to classify streams (Rosgen classes, etc.) or otherwise characterize
a large number of streams quickly.
Working alone in the field requires extra safety precautions. These might include
taking proper clothing and equipment, including emergency and first aid items; carrying
a radio; and telling someone where you will be and when you will return. In some
locations and some situations, safety concerns may preclude solo surveying.
Pebble Counts -- Use of a voice-actuated pocket-size tape recorder, fastened in a
shirt pocket, makes this simple. The tape is started by your voice and turns off
a few seconds after you quit speaking. The recorder's sensitivity can be adjusted
so that background noises will not activate it. Since the first word spoken will
be somewhat garbled as the tape starts up, I always preface the size class with a
preparatory word, such as "and...", so that the tape is in motion before
the size class is spoken. After each measurement, I click a tally counter to keep
track of the number of pebbles measured. After I have taken the desired number of
measurements, I replay the tape and tally the measurements on a data sheet. This
procedure takes only 25-30% longer than with another person as recorder. A suitable
tape recorder can be purchased for about $60.
Cross-Section -- A laser level will allow solo surveying of cross-sections and gradients,
but these instruments are expensive, bulky, heavy, and relatively fragile -- not
very appropriate for back country measurements.
In my approach to measuring cross-sections, I stretch a measuring tape, attaching
it to a survey pin at each end of the cross-section (see figure on next page). I
then set up a folding rod or a pocket rod. At appropriate points along the tape,
I then set a 5X magnification hand level on top of a vertical stick (I use a five-foot
folding rule) and take readings on the rod ("A" in figure). If, as I move
along the tape, the rod becomes obscured or too distant, I move the rod, taking from
one location a reading on the rod both before and after moving it, thus establishing
a turning point. Or I set up a second rod, again taking from one location a reading
on both rods ("B" in figure).
Here, also, I use the voice-actuated tape recorder to record distances along the
tape and readings on the rod, writing these down on a data sheet as soon as I finish
all the measurements.
The rod should be set as vertical as possible. To keep it upright, it can be secured
to a tree or limb. A range pole tripod can also be used to hold the rod upright.
Leaning the rod against a tree or limb gives acceptable results if the lean is kept
to 4 degrees or less. This introduces an error of less than 0.2 percent.
Another method for taking cross-section measurements quickly is to stretch a string
(a mason's chalk line works well) or tape across the channel. Check to see that the
string or tape is truly horizontal across the channel. A folding rule or rod can
then be used to measure distances from the string or tape to the channel bottom.
Another approach that works well for wide channels is the sag-tape method. Verticals
are measured from a metal tape stretched across the cross-section. This tape will
have a moderate sag in it. The computer program R2-CROSS compensates for the sag,
based on a measure of tape tension from a spring scale attached to the tape, and
computes corrected depths. For details of the sag-tap procedure, refer to: Measuring
Cross Sections Using a Sag-Tape: A Generalized Procedure, USDA Forest Service General
Technical Report INT-47, Ogden, UT, by Gary Ray and Walter Megahan, 1979.
Gradient -- I set up a rod near the middle of the reach over which gradient is to
be measured. At an appropriate point upstream, I set my vertical stick at the water
surface, place the hand level on top of the stick, and take a reading on the rod.
I then go downstream, below the rod, and take another reading. The difference between
the two readings is the drop of the stream between the two points. I measure distance
with a tape or hipchain. Where the gradient needs to be measured over longer distances,
turning points should be used, as described above.
Sinuosity -- For field measurements of sinuosity, I walk up the channel pulling a
hipchain. I keep the string on one side of the channel, looping it around twigs,
etc. along the bank. Measuring sinuosity along one bank should not be significantly
different from measuring it up the center of the channel as long as full meander
wavelengths are measured. After measuring the channel length, I use the hipchain
to measure valley length.
