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

rivers. Whi I e less sediment load Is beneficial to maintaining substrate
conditions for viable spawning, an adequate sediment supply must be
maintained for beach replenishment and riparian vegetation In the canyon.
Important to the canyon ecology is the relationship of endemic phreatophytes
(wiI lows and cottonwoods) and their confrontation with invading tamarisks
over available sandy beaches for seed germination. The cottonwoods in the
riparian zone require moist, sandy substrate during seed deposition and high
flows to scour years i ng growth of tamarisks. The substrate must be
relatively free of al ten vegetation for cottonwood seed germination and
growth. Further, the beaches are important to the aesthetic and
recreational resource values In the canyon. The interaction of all the
biological and physical processes occurring in the canyon require thorough
understanding before peak flows and annual water volumes are reduced in the
upstream tributary systems.
The effect of reducing the discharge In the Little Snake w i l l be to
reduce the sediment load to the canyon. Concomitantly, reducing the water
supply In the Yampa River upstream of the confluence with the Little Snake
River will have the effect of limiting the river's abil ity to transport the
sediment load In the canyon. The possible options for water development
must be evaluated in terms of quantifying how the equi l ibr i um of the
hydrologic system is disrupted.
To Initiate the project, the daily flow discharge and sediment load
data base was reviewed, this included reviewing data from the reports by the
NPS (O'Brien, 1982 FI ug, O'Brien, et al., 1983 O'Brien, 1984) and the USGS
(El I lott, et al . , 1984), and reviewing the USGS gaging station data In
computer fit es. It was discovered during this review that there were
missing data In the USG S da i I y f I ow records, that the most recent years
(exceedI ngly wet years) had not yet been processed i nto the f II es, and that
the sediment dl sch arge rel ati onsh i ps req ui red f urther evai uati on. The
fol I ow i ng tasks were performed to remedy these probl ems.
1 . Seventy-two random bl ocks of el ght day, da i I y L i ttl a Snake w ater
discharges were missing from the computer data base. Most of
missing data were extracted from the pub) fished USGS water supply
records in the library and added to computer files. Several blocks
of missing data from the period 1928 to 1934 had to be obtained
from the Colorado State records as the USGS relinquished
responsibility for taking the Little Snake discharge measurements
during this period.
2. The water years of 1983 and 1984 were added to the computer f i I es
completing the current published USGS database (64 years dating
from 1921). These years constitute very high vol ume water years
with 1983 the highest volume water year on record.
3. Al I three databases (USGS gaging station USGS, El I iott data and
the NPS O'Brien data) had water-sediment discharge regressed
relationships based log-log data transformation using a
mathematical I east squares best f it to the data. This regression
method underestimates predicted sediment I oads and the
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