9671

• UCREFRP Catalog Number: 9671
• Author: Rees, D. E., W. J. Miller and J. A. Ptacek.
• Title: Volume 1 Draft Final Report - Ecological and Physical Processes During Spring Peak Flow and Summer Base Flows in the Colorado River.
• USFW Year: 2003.
• USFW - Doc Type: Fort Collins, CO.
• Copyright Material: NO

. Is there a relationship between turbidity produced by summer thunderstorms and standing
crop of macroinvertebrates and periphyton?

There were significant relationships between changes in mean daily turbidity and all
aspects of periphyton and macroinvertebrate community structure that were statistically
analyzed.

· Is there a difference in primary and secondary production between two major habitat
types (run and riffle) in the 15-Mile-Reach of the Colorado River?

Periphyton and macro invertebrate standing crop was much greater in habitats with higher
current velocities. Aquatic communities in the 15-MR are dynamic and dependent on a
variety of physical variables. Attributes of available habitat types result in differences in
structure and function of the benthic communities that inhabit them. Evidence from three
years of seasonal sampling suggests that periphyton and macroinvertebrate communities
exhibit some predictable seasonal change, have specific habitat preferences or
requirements, and are also dependant on physical processes. These results suggest that
much of the biological variability can be attributed to physical processes that occur after
snowmelt runoff.

Discussion

Physical Investigations

Water resource development projects in the Upper Colorado River basin upstream of the 15-MR
commenced in the 1920's and by about 1950 approximately 45 percent of the annual streamflow
was controlled (Pitlick et aI., 1999). Suspended sediment concentrations at the UCR gages have:
not changed appreciably (Pitlick and Wilcock, 2001) as a result of the upstream dam
construction in the last 50 years because of the high supply of sediment from the lower elevation
portions of the basin that are underlain by highly erodible sedimentary rocks (Iorns, et aI., 1965;
Van Steeter and Pitlick, 1998; Liebermann et aI., 1989; Spahr et aI., 2000).

The Clifton Water Treatment Plant site (Clifton Site) was chosen as the location for micro-and
meso-scale investigations after reconnaissance of the 15 MR in 1999. This site is representative:
of the 15 MR channel characteristics, is approximately 2,200 feet long with a mid-channel bar,
large cross-channel riffles and cobble bars. A 2-D hydrodynamic model of the site was
constructed from topographic and bathymetric data. The 2-D model output is better than a 1- D
model at evaluating meso- and microscale habitat analyses of incipient motion and sediment
transport.

Investigation of the relationships between flows, sediment loads and habitat requires that the
temporal nature of the relationships be recognized and incorporated. In general terms, the annual
hydrograph can be divided into low- and high-flow periods (Figure ES-2). The low-flow periods
include late-summer and fall baseflows, as well as the winter base flows that extend from about
August to the end of April. The high-flow period includes the rising, peak, and falling limbs of
the annual snowmelt hydro graph that usually extends from May to the end of July.

Draft Final Report - 15 Mile Reach Studies
Miller Ecological Consultants, Inc.

Page ES-5
October 24, 2003