9596

• UCREFRP Catalog Number: 9596
• Author: Ayers Associates.
• Title: Yampa River Basin Research Final Synthesis Report.
• USFW Year: 1999.
• USFW - Doc Type: Fort Collins, CO.
• Copyright Material: NO

Appendix B

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these flows is to combine daily data from the diversion record of the Maybell Canal with the
concurrent record of the Maybell gage. The latter method was selected for this analysis.

Existing human water use in the Yampa Basin depletes about 120,000 acre-feet (AF) annually
out of an average annual yield of 1.13 million acre-feet (MAP). Future water development for
human consumption in the Yampa River Basin is expected to deplete up to -50,000 AF more
(-170,000 AF total) from the river by the year 20451,2. By modeling the estimated human water
demand against an historical set of hydrologic and atmospheric conditions, CRDSS can predict
the magnitude and monthly distribution of discharge in AF under similar conditions in the future.

The Recovery Program funded a study by Modde et a1.3 (1999) to determine stream flow needs
of endangered fishes in the Yampa River, The study focused on riffle habitat due to its
importance to production of invertebrate biomass and its sensitivity to changes in flow. Based
on a series of physical habitat variables (e.g., depth, velocity, wetted width, etc.), the authors
found that the rate of loss of riffle habitat was greatest at flows below 93 cfs. Historically, at
times river flows have fallen below 93 cfs with no apparent harm to the Colorado pikeminnow.
Moreover, native fishes in the Colorado River Basin have evolved under highly variable flow
conditions. Therefore, the authors concluded that these fish can tolerate and may benefit from
"transgressions" below this 93 cfs flow target at their historic frequency, magnitude and duration.
This hydrologic analysis was designed to compare CRDSS calculated historic with CRDSS
modeled future (ca. 2025 and 2045) supply and demand conditions within the context of this 93
cfs flow target.

CRDSS modeling assumptions for the Yam?a River

1. Modeled four different levels of demand4
a. Natural (no demand)
b. Calculated historic
c. Near-term future (ca. 2025)
d. Long-term future (ca. 2045)

2. Functions as if the river were under water rights administration; water is delivered in
priority to satisfy individual demands served by water rights as needed and available. 5

3. Explicitly includes all water diversions and return flows.

4. Functions on a database with a 17-year period of record which serves as a hydrologic
template for modeling an overlay of alternative water supply and demand scenarios.

lBBC Research & Consulting. 1998. Yampa Valley Water Demand Study. Final Report. Denver, CO.

2Hydrosphere Resource Consultants. 1995. Yampa River Basin Recommended Alternative Detailed Feasibility
Study. Final Report. Boulder, CO.

3 Modde,T., W.J. Miller, and R. Anderson (eds.). 1999. Determination of habitat availability, habitat use, andflow
needs of endangered fishes in the Yampa River between August and October. Final Report submitted to the
Recovery Implementation Program, U.S. Fish and Wildlife Service, Denver, Colorado. 134 pp.

4Calculated historic = natural flow minus historic consumption estimate; 2025 and 2045 = natural flow minus 2025
or 2045 predicted consumption.

sBased on historic hydrologic and atmospheric data, using Blaney-Criddle to estimate irrigation demand, and
assuming that Stagecoach Reservoir initially was full.