7198

• UCREFRP Catalog Number: 7198
• Author: O'Brien, J. S.
• Title: Analysis of Minimum Streamflow and Sediment Transport in the Yampa River, Dinosaur National Monument.
• USFW Year: 1987.
• USFW - Doc Type: Fort Collins, Colorado.
• Copyright Material: NO

Table 6 shows the Impacts of so reducing f laws In the Yampa River on
the sediment balance in the Yampa Canyon. The initial trial indicates that
the sediment budget i s excel I ent empl oy i ng the h i stor i c f I ow s of the Yampa
and the slight depletions from the Little Snake. The remainder of the tests
employ the NPS minimum streamflow hydrograph or an altered form of it for
the daily discharges. In all cases, the reductions in daily flow are
considered as depletions from the Yampa River. The second test in Table 6
with the NPS minimum streamflow hydrograph represents a storage of sediment
In the canyon of approximately 38 percent of the sediment load predicted at
Mathers Hole.
To restore some of the sediment balance to the analysis where the NPS
minimum streamflow is used, flows greater than 95 percent of actual peak for
each year of record are added to the hydrograph. These higher flows are
added to the hydrograph by increasing only the Yampa River (Maybe) I)
discharge. Subsequent tests (5-7) are performed adding more of the peak
flows until flows greater than 50 percent of peak f I ow for that year are
Included in the hydrograph. This results In a sediment budget in which the
sediment storage In the canyon Is only 9 percent of the sediment load at
Mathers. Adding peak flow days to the minimum streamflow hydrograph has the
advantage of keep) ng the cobbl a bed mobs I e w ith bankf ul I di scharges. This
physical process is important to keeping the channel morphology active and
the cobble bed conditions Ideal for Colorado squawfish spawning (O'Brien,
1984).
Table 7 is similar in concept to Table 6 except that the minimum
streamf I ow hydrograph is altered to attempt to deplete additional water from
the Yampa and sti I I maintain the sediment balance. Th I s is accomplished by
decreasing the minimum streamflow hydrograph on the rising and recession
I imbs and increasing the number of peak f I ow days. Al I the computer runs
involving flow reductions in the Yampa are displayed in Appendix C. in
these tests, minimum base flow for the Yampa at Maybel I is 297 cfs or the
historic flow, whichever is less. The minimum streamfIow hydrographs for
the runs In Table 7 are presented and compared with the NPS minimum
streamfl ow hydrograph in Table 8. These depl eti ons from the Yampa River are
made when the historical water discharge has been above the minimum
streamf I ow and peak f I ow criteria. No assumptions are made on haw the water
may be allocated or at what rate it may be consumptively used.
The minimum streamflow hydrograph is reduced in runs 1 through 3 in
Table 7 while the peak f I ow criteria Is reduced from 50 percent to 35
percent increasing the number of high flow days (and discharge) in the
analysis. In the remaining runs 4 through 7, only the peak flow criteria is
changed from 35 percent to 20 percent. Increasing the number of peak f I ow
days results in a computed hydrograph that is closer to the historic flow
condition. When the peak f I ow cr 1 ter i a i s 35 percent or I ess, reduc i ng the
m i nimum streamf I ow hydrograph has I ittl a of fect on the amount of f I ow
depletion from the Yampa or the sediment budget. Increasing the number of
high f I ow days with discharges In excess of 35 percent of the peak f I ow has
the result of negating most of the minimum streamflow hydrograph. Enough
high flow days are incorporated in the analysis to override the minimum
streamflow criteria greater than 1260 cfs. The same minimum streamfIow
hydrograph is used for runs 4 through 7 in Table 7.
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