ure profiles and gradients, they require line of sight and
are frequently cumbersome in small stream measurements. We adopted a
builders level to measure gradients and channel profiles, which eliminates
many of the requirements of other methods.

The instrument is easy to use, inexpensive, and simple to build. Based on
the principle that water seeks its own level, it is precise and accurate to
1 cm. The instrument we describe will measure a vertical drop up to 1 m.
Larger drops and distances can be measured by constructing a larger
instrument than the one described here.

U.S. DEPARTMENT OF AGRICULTURE FOREST SERVICE


This file was created by scanning the printed publication.
Text errors identified by the software have been corrected;
however, some errors may remain. The waterlevel (fig. 1) is constructed from a pair of 2-m � 1/2-in
1
type "L" or "M" copper water pipes, a pair of 1-m � 1/2-in O.D., 1/4-in
I.D. plastic tubes, pipe fittings, and 1/4-in flexible plastic tubing.
Each pipe is cut into a 1-m upper scale assembly section and a 1-m lower
support section. The scale assembly receives the scale and the clear
plastic pipe. The scale assemblies are prepared by removing two thirds
of the diameter of 1-m length of each pipe with a table saw. Use a non-
ferrous cutting blade and the fence set to guide the pipe.
2
The finished
pipe is cleaned with a file to remove all sharp edges.
1
English measurements are used to correspond to commonly available
materials on the U.S. market.
2
Caution: A face shield and heavy gloves should be worn during this
operation. The cutting generates heat and metal chips; and until filed,
the cut edges are very sharp.
Figure 1.--The waterlevel device.
2 We used a calcomp plotter to draw the 1-m scale strip in 1-cm incre-
ments from 0 to 100 cm on waterproof mylar paper. The strip is placed
inside the 1-m opening cut out of the copper pipe.
We sealed the scale strip between the clear plastic tube and the open
copper pipe with a clear leak-tight sealer to maintain a closed water
system inside the pipe and tube. The pipe and tube are clamped together
until the sealer is set. Enough sealer should be used to insure a good
bond between components. Excess sealer is easily removed from the face
of the scale sight tube.
The scale assembly (1) is soldered into a tee connection (2) (fig. 2 ) .
A 1/2-in sweat to a 3/4-in NPT (National Pipe Thread) fitting (3) is
soldered into the tee. A 3/4-in to 1/4-in NPT bushing (4) is connected
to the 3/4-in NPT fitting. A 1/4-in thermoplastic tube fitting is
mounted in the 1/4-in NPT bushing ( 5 ) . The thermoplastic fitting is
fitted with a short length of 1/4-in polyethylene tubing (6). The two
level tubes are connected with a length of 1/4-in I.D. flexible plastic
tubing. The length is optional, but we use a 10-m length. The flexible
tubing is clamped onto the polyethylene tubing. The lower copper support
section is sealed water tight and connected to the lower opening of the
tee fitting. A threaded adapter between the tee and the support allows
the two sections to be separated for transportation and storage.
Figure 2.--Detail of tee, tubing connection, and top of waterlevel.
Scale assembly (1), Tee connection (2), 1/2-in sweat to 3/4-in
NPT fitting (3), 3/4-in to 1/4-in NPT bushing (4), thermoplastic
fitting (5) with a short length of 1/4-in polyethylene tubing (6),
lower support section (7), top fitted with a rubber stopper (8).
3 Both scale tubes must be the same height when finished so readings will
be the same when the water tube assembly is vertical. Care must be taken
to insure that all parts are made the same length and the scale strips
are matched for each pair of scale tubes.
The water level system is filled with water to 40 or 50 centimeters on
both sight tubes with both tubes held vertically on the same level. The
water filled tubes must be free of air bubbles. An uneven water level
indicates air bubbles, plugged or restricted tubes, or stoppers left in
the top of the level tube. Stoppers are placed in the reducers (8) in
the top of each level tube after filling and are removed during use
(fig. 2 ) . The connecting tube may be coiled for transportation to the
stream site.
To calculate gradient, the horizontal distance (d) and the vertical
drop (v) must be measured. The length of the flexible plastic tube
represents horizontal distance (d), and the difference between the water
level in the two scales h
1
and h
2
represent vertical drop (v). For
example, let d = 10 m, the downstream reading h
1
= 87 cm, and the
downstream reading h
2
= 17 cm, then gradient in percent (g) can be cal-
culated from the general equation:
In the above example the gradient is 7.0 percent.
Stream cross-sections are measured in the same manner, but the water
level on the bank (reference station) will change as the depth across the
transect changes because there is a constant volume of water in the tube
(fig. 3 ) . The difference between the two readings is the vertical drop
from the streambank to the stream bottom h
i
(fig. 3 ) . Let y =
reference station reading, x = transect station reading, h = actual depth
with respect to the reference station, and i = transect point. For the
first transect point depth (h
i
, i = 1) take both readings on the bank.
At this point x
i
- y
i
= 0; thereafter h
i
= x
i
- y
i
.
Figure 3.Stream channel cross-
section showing operation of a
water level device to measure
channel profile.
4 The stoppers should be replaced to prevent water loss during transpor-
tation. After the stoppers are removed, the water will oscillate for a
few seconds. Oscillations are also set up if the flexible tube is placed
in a turbulent current. Readings can be taken with the tubing over,
under, and around obstructions, even if the tubing is higher than the
sight tubes. Line of sight is not necessary. The limit for vertical
drop to be measured is 1 m.
G P O 989-965
5 The mission of the PACIFIC NORTHWEST FOREST AND
RANGE EXPERIMENT STATION is to provide the knowl
edge, technology, and alternatives for present and future
protection, management, and use of forest, range, and related
environments.
Within this overall mission, the Station conducts and
stimulates research to facilitate and to accelerate progress
toward the following goals:
1. Providing safe and efficient technology for inventory,
protection, and use of resources.
2. Developing and evaluating alternative methods and levels
of resource management.
3. Achieving optimum sustained resource productivity
consistent with maintaining a high quality forest
environment.
The area of research encompasses Oregon, Washington,
Alaska, and, in some cases, California, Hawaii, the Western
States, and the Nation. Results of the research are made
available promptly. Project headquarters are at:
Anchorage, Alaska La Grande, Oregon
Fairbanks, Alaska Portland, Oregon
Juneau, Alaska Olympia, Washington
Bend, Oregon Seattle, Washington
Corvallis, Oregon Wenatchee, Washington
Mailing address: Pacific Northwest Forest and Range
Experiment Station
809 N.E. 6th Ave.
Portland, Oregon 97232 The FOREST SERVICE of the U.S. Department of Agriculture is dedicated
to the principle of multiple use management of the Nation's forest resources
for sustained yields of wood, water, forage, wildlife, and recreation.
Through forestry research, cooperation with the States and private forest
owners, and management of the National Forests and National Grasslands, it
strives as directed by Congress to provide increasingly greater service to
a growing Nation.
The U.S. Department Of Agriculture is an Equal Opportunity Employer.
Applicants for all Department programs will be given equal consideration
without regard to age, race, color, sex, religion, or national origin.