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Structural Anadromous Fishery Habitat Improvement
on the Siskiyou National Forest 1
Bruce D. Sims and Lee D. Johnson 2
Abstract.--Three separate strategies for allowing
fish Passage through culverts are discussed.
These include: 1) construction of stepped log weirs to
raise the pool level at the culvert outlet; 2) retrofitting
circular culverts with a baffle system; and 3) use of an
open-bottomed arch-type culvert. In addition, several log
and gabion structures used to create pool habitat are
discussed. All examples presented have survived several
seasons and have achieved their fishery enhancement
obiectives.
anadromou~
INTRODUCTION
The Siskiyou National Forest. which has the
highest value fishery of any National Forest outside Alaska, has been involved in anadromous fish
habitat imorovement since 1967. Thi~ paper
presents three different anproaches the Siskiyou
has taken to allow fish passage through obstructive
culverts and describes three structures which have
been constructed to create deen pools for rearing
habitat and for trapping spawning gravel.
CULVERT PASSAGE BARRIERS
Velocity Barriers
Figure 1.--Pipe arch used to allow fish
In 1981, an 8~-foot circular corrugated steel
culvert was replaced with a 6-~ foot rise, 13-foot
SJ?an pipe arch. Although this pipe arch allowed
easy fish passage, the inlet end footing was undercut during the first high flows: the arch constricted the water flow, thereby accelerating its
velocity over the native channel bed material.
Grout was subsequently pumped under the exposed
footing, but it too was soon undercut. Riprap was
then placed at the arch outlet to create a stable
base level which more nearly matched the original
channel's level. This second strategy induced
backfilling through the pipe arch and created a
passable channel (fig.l).
Another approach used to correct a velocity
barrier is the addition of a baffle system to the
floor of an in-place corrugated circular culvert.
Rather than replacing worn culverts. it has become
common practice on the Siskiyou N.F. to protect
tl~ worn culvert bottom with a reinforced concrete
apron. When the concrete is poured, it is relatively easy to embed baffle supports 'cut from
steel 1-beamf, into the concrete. These !-beams
are precut to desired dimensions and holes predrilled to allow wooden baffles to be easily
bolted into place (fig.2). Adjusting the system
in the field is a simple matter of raising or
lowering the wooden baffles if observation deems
it necessary. To date, two large culverts have
been successfully fitted with these wooden baffles.
One of these, a 7-foot-diameter by 80-foot-long
culvert, is sloped at 6.5 percent.
1
Poster session naper, 1985 North American
Riparian Conference.
University of Arizona,
Tucson, April 16-18, 1985.
2Bruce D. Sims is a Hydrologist, Siskiyou
National Forest, Gold Beach, Oregon and Lee D.
Johnson is a Fishery Biologist. Siskivou National
Forest, Brookings, Oregon.
502
During the second spawning season after construction of these five stair-stepped log weirs,
over 42 chinook (King) salmon were counted above
the culvert. This quanitiy of fish above the
culvert--even before the stream's run has fully
recovered--indicates high oassage success.
HABITAT IMPROVEMENT
Instream structures have been built in a
variety of configurations, using gabions or logs
that are available at or near the site. The most
effective structures to date have been the wing
deflector gabion in large streams and the reverse
V or perpendicular log weir in smaller streams
(fig.4-fig.6).
Figure 2.--Retrofitted culvert baffles.
Culvert Entry Barriers
Culvert outlets that are higher than three
feet above the plunge pool generally inhibit
anadromous fish entry into the pipe. Jumn success
depends on both pool depth and location of the
standing wave (reversals) below the culvert.
Plunge pool elevations below culverts can be
raised by a series of log weirs. In the example
shown below (fig.3), the nool was raised three
feet by a series of five large log weirs. Jumps
between the structures ranged from about twelve
inches to a maximum of twenty-eight inches.
Figure 4.--Wing deflector gabion.
Figure 3.--Log weirs used to correct a culvert
entry barrier.
Following placement of the log weirs,chainlink fence was tacked to the unstream edge of the
logs and snread upstream along the channel bed.
The fencing catches bedload and organic debris,
which holds the structures in place and reduces
the potential for water scouring beneath the
weir. Riprap was placed at the ends of each
structure to create the log weir's lateral
boundaries and protect the alluvial channel banks.
Figure 5.--Reverse V gabion.
A notch was cut in each log weir and sized to
insure several inches of water depth, during
low flow, to allow smolt migration downstream.
The notches also concentrate flow and can set up
favorable standing waves, which encourage fish
jumps. A wooden weir was also fitted in therulvert
outlets to create favorable standing waves below
the pipe and deeper water inside the lower end of
the culvert where the fish land.
Figure 6.--Small log weir.
503
Log structures in small streams can be built
with ten-to-twenty-inch-diameter logs, cabled
together to achieve the desired height, without
heavy equipment. A twenty-foot small log
structure can be built by a crew of three in half
a day.
sufficient height to induce pool scour. Wing
deflector gabions with a total height of three
fee&, placed at approximately a 35 degree angle
from. the stream bank, have been built with good
success. A three-by-three-foot hand-constructed
gabion (including bed leveling) can generallv be
built at one-and-a-half-feet per man hour.
Gabions built in small streams are wired together and filled with three-to-eight-inch rocks
from the stream. Half-inch cable through the
center of the gabion provides strength and
integrity to the overall structure. Gabions are
generallv twelve to eighteen inches high at the
weir to minimize the reduction of channel gradient
above the structure, while creating a fall of
The babjtat im~rovement structures presented
herein have been excensively used for spawning
and rearing habitat. Sampling (by electroshocking) in im~roved areas and control areas has
revealed an increase of greater than 300 percent
in iuvenile fish oopulations.
504