WSP09917

• File Number: 8143.600.30B
• Description: John Martin Reservoir - Other Studies
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 10/1/1967
• Title: Report on Sedimentation - John Martin Reservoir - Arkansas River Basin Colorado -- Resurvey of September 1966
• Water Supply Pro - Doc Type: Report/Study

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32. The temperature of the water did not vary more than a few
degrees during and after density flow observations.. The dissolved
solids did not vary from those of normal flows. Samples were taken
and analyzed for size. They averaged 99 percent finer than sand
(.06.' mm). Outflows from the reservoir normally average only 82 per-
cent"' finer than sand. The reservoir water surface elevation was
above 3,830 feet during periods of observations. Data on density
flow observations below John Martin Dam are presented in table 12.
Although the'sediment concentration increased greatly with the release
of the density flows, the total volume of sediment carried by the _-I
density flows was insignificant when compared with the average annual
sediment deposition in the reservoir.

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ANALYSIS OF SEDIMENTATION

33. Vol.wne of sediment in John Martin Reservoir. The volume of
sediment deposited in John Martin Reservoir during the 24.3 years of
reservoir operation has been 70,654 acre-feet or 2,908 acre-feet per
year. During the period between resurveys, from March 1962 to Sep-
tember 1966 (4.5 years), a total of 11,269 acre-feet of sediment was
deposited or 2,504 acre-feet per year> Detailed data are shown in
table 4, Reservoir Sediment Data Summary, ENG Form 1787. The sediment
retention computed on basis of the difference between inflow and out-
flow, using a dry weight of sediment of 75.7 pounds per cubic foot, --i--
is 16,414 acre-feet for the period between the latest resurveys. This
figure is the retention for the entire period and must be adjusted
for consolidation of the older deposits to give a comparative amount
with the deposition calculated by survey methods. After the 1962
resurvey and prior to the 1965 flood, the reservoir was emptied sev-
eral times. This caused a considerable drying out and consolidation
of the deposits in the lower reaches of the reservoir. It can be
concluded that some of the sediment deposition was offset by shrinkage
of previous deposits and resulted in the difference between sediment .
inflow and sediment deposition volumes.

34. Gradation of reservoir deposits. The grain size of the
sediment deposited in the reservoir is dependent on the grain size
of the inflow. Once the inflow enters the reservoir the sediment
particles are segregated and distributed in so many ways that the
original size distribution is lost. Samples of suspended sediment
were taken for the period March 1962 to September 1966 at the two
inflow stations and the average gradation for this period, weighted
for the difference of inflow, is as follows:

Suspended sediment inflow

Sand
10

Percent
Silt
71

Clay
19

9