PROJ00492

• Contract/PO #: C153364
• Contractor Name: Beck, R. W. and Associates
• Water District: 0
• County: Garfield
• Bill Number: SB 81-439
• Loan Projects - Doc Type: Feasibility Study

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measUl"ements taken on the Colorado River near Cisco, Utah, the Colorado River
near De Eeque, and th<;l Cqlorl1do River at Glenwood Springs. The results ob-
tained from the suspended sediment measUl"ements were then checked against the
yield calculated on the basis of the State of Colorado Sediment Yield
(2)( 17)
Map prepared by the Colorado Land Use Canmission in 1974.

Da11y suspended sediment measUl"ements have been taken by the USGS
on the Colorado River near Cisco, Utah, since water year 1942. These meaSUl"e-
ments were correlated by ,linear regression with daily measUl"ements taken on
the Colorado HiveI' near De Beque in water years 1975 and 1976. The corre-
lation equation was also qhecj<:ed against miscellaneous measUl"ements taken near
De Beque and at Glenwood Springs. The correlation is excellent. The average
annual sedimenl~ load (tons per year) measUl"ed near Cisco, Utah and the esti-
mated load near De Beque, which is equivalent to the sediment inflow to Una
Reservoir, are shown in Table II-6. The average annual suspended load near
Cisco is 11,7'55,000 tons/year and the estimated load near De Beque is
1,615,000 tons/year. By increasing the suspended load value by 10% to reflect
the unmeasUl"ed bedload, the sediment inflow to Una Reservoir is estimated to
average 1,776,000 tons per year. This estimate is considered reliable since
it is based on 39 years of daily measUl"ements and results of similar magnitude
were obtained from the State Sediment Yield Map.

The average density of the sediments that would flow into the
reservoir was E!stimated based on various suspended sediment size distribution
measUl"ements tsLken by the USBR at Rulison Bridge on the Colorado River about
18 miles upstream of Parachute. Based on these measurements the average sedi-
ment load conststs of 46.6% bedload and sands, 30.3% silts, and 23.1% clays.
The average dEmsity of deposited sediments within the reservoir would be
approximately 80 1 b/ft. 3 (pef) after 50 years of consolidation based upon
this distribution of sediment sizes.

2. Reservoir Trap Efficiency and Sediment Deposition

The reservoir trap efficiency was estimated by means of Churchill's
(1)
method and would average 90% over the first 100 years of reservoir life.
The sediment volume that would be trapped in the reservoir over the first 100