8065

• UCREFRP Catalog Number: 8065
• Author: Vaill, J. E.
• Title: Computation of Selected Hydraulic Variables for the Lower Yampa River in Northwestern Colorado.
• USFW Year: 1997.
• USFW - Doc Type: Denver, Colorado.
• Copyright Material: NO

The Maybell Canal diversion structure is
located in Juniper Canyon about 20 mi upstream from
Cross Mountain Canyon. Juniper Canyon is about 2 mi
long, and the channel slope is less than 13.3 ftlmi. The
canyon rim ranges in height from 200 to 400 ft above
the river. Vegetation type and coverage is similar to
that of the other study reaches.
Cross Mountain Canyon is the farthest
downstream study reach and contains two subreaches.
One subreach is located at the downstream end of the
canyon and the other is located at the upstream end
of the canyon. The Yampa River has a channel slope
of about 4.0 ftlmi before entering the canyon and
increases to about 57 ftlmi within the canyon. The
canyon side slopes are very steep and are vertical in
some places. The canyon is about 3.5 mi long, and the
rim of the canyon ranges in height from 800 ft to more
than 1,000 ft above the river. Vegetation within the
canyon consists of sparse grasses, sagebrush, and
occasional clumps of willows. The banks and
streambed consist of rock fragments ranging in size
from coarse gravel to room-sized boulders that create
a very turbulent and irregular water surface at most
streamflows.

METHODS OF DATA COLLECTION

Cross-section geometry of the reaches selected
for study was obtained by using standard field-
surveying techniques (Benson and Dalrymple, 1967),
with modifications for the extreme velocities in Cross
Mountain Canyon, or by using detailed topographic
information for the Patrick Sweeney and the Maybell
Canal diversion structures. Cross-section information
used for WSPRO input at the Patrick Sweeney and the
Maybell Canal diversion structures was obtained from
I-ft contour maps provided by CRWCD. The critical
cross sections at the diversion structures were
determined to be the cross sections along the top
of the structures. This determination was based on
the fact that diversion structures act as weirs and that
shallower depths and greater velocities generally occur
along the crest of the weir rather than in the natural
stream channel. The critical cross section for the
Patrick Sweeney diversion structure is shown in
figure 2, and the critical cross section for the Maybell
Canal diversion structure is shown in figure 3.

Aerial reconnaissance of Cross Mountain
Canyon at a medium streamflow of about 2,500 ft3 Is
and ground reconnaissance at a high streamflow of
about 6,000 ft3/s indicated that two subreaches located
at the downstream and upstream ends of the canyon
might impede squawfish migration. Within these two
subreaches, critical cross sections having hydraulic
properties of minimum depths and maximum veloci-
ties at lower streamflows that could impede squawfish
migration were selected for detailed surveys. Selection
was based on cross sections that had high velocities
and large falls or drops in the water surface. Selection
of the critical cross sections in Cross Mountain
Canyon was verified during a ground reconnaissance
at a streamflow of about 200 ft3 Is. The two subreaches
within Cross Mountain Canyon were surveyed using a
chart-recording fathometer and transducer mounted on
a standard kneeboard used for water skiing. The
kneeboard was suspended from one bank using 7-rom
static rope and from the other bank using a Kevlar-
wrapped transducer cable. The Kevlar wrapping
provided the tensile strength to maintain the
kneeboard on line during the cross-section traverse
and prevented excessive strain on the transducer
cable. The kneeboard was moved across the channel
by hand, and stream depths were marked on the
fathometer chart at known distances from the
bank.
Five cross sections were surveyed in the
subreach at the upstream end of Cross Mountain
Canyon (fig. 4). Cross section 2 shown in figure 4
was located at the first major water-surface drop into
the canyon and was determined to be the critical cross
section, based on observation and verification by
WSPRO computations. Three additional cross
sections located downstream, about one channel
width apart, were surveyed to aid in WSPRO
computations and to verify selection of the critical
cross section.
Two cross sections (6 and 7) were surveyed in
the subreach at the downstream end of the canyon,
about 0.25 mi upstream from the mouth of the canyon
and are shown in figure 5. Cross section 7 (fig. 5)
was determined to be the critical section in the
downstream reach based on observation at the time
of the survey. The WSPRO computations confirmed
this determination.

METHODS OF DATA COLLECTION 3