WSP07706

• File Number: 8200.765
• Description: White River General
• State: CO
• Basin: Yampa/White
• Water Division: 6
• Date: 1/1/1993
• Author: USGS
• Title: Sediment Transport and Water-Quality Characteristics and Loads - White River - Northwestern Colorado - Water Years 1975 through 1988
• Water Supply Pro - Doc Type: Report/Study

A total of five samples for size analyses were
coUected during a stream-discharge range from 1,840
to 2,470 ft3/s at sites 3, 4, and 5 during water years
1987-88. Size analyses of suspended sediment were
determined for 22 samples collected during a stream-
discharge range from 599 to 6,090 ft3/s at site 6 during
water years 1984-88. The sand, silt, and clay composi-
tions are listed below:

Number Average percentage
Site of
aamplea Sand Slit Clay
3 t 27 48 25
4 2 26 44 30
5 2 37 41 22
6 22 30 46 24
Total: 3-6 Total: 27 Average: 30 45 25

In addition, a total of 174 suspended-sediment
samples collected for sediment concentrations at
sites 1-6 were analyzed for sand percentages (greater
than 0.062 mm). The percentage variation of sand
among samples was great and ranged from 2 to
64 percent. Data correlations of size composition with
stream discharge and suspended-sediment concentra-
tions were poor, and definable patterns of suspended-
sediment size with subbasin geology were
inconclusive.

Retention In Reservoirs

Retention of fluvial-sediment loads will occur in
reservoirs that are constructed on the main stem of the
White River. The efficiency of sediment retention is a
function of reservoir capacity, inflow volume, mean
velocity of flow through the reservoir, and size compo-
sition of the sediment load (Churchill, 1948; Brune,
1953). Generally, reservoir retention of sediment will
increase as the ratio of the reservoir capacity to inflow
volume increases or the percent composition of silt and
clay in the sediment load decreases, or both. Based on
sediment data collected at site 6 during water years
1985-87, sediment retention in Kenney Reservoir,
about 8 mi downstream from site 6, was estimated at 91
to 98 percent (Tobin and Hollowed, 1990). Proposed
reservoirs constructed on the White River that have
capacities larger than Kenney Reservoir (13,800 acre-
ft) could have sediment-retention values that exceed
98 percent.
Assuming 98-percent sediment retention and an
average sediment size composition of 30 percent sand,
45 percent silt, and 25 percent clay, original and 20-
year compacted volumes of sediment deposits for two
ranges of sediment loads (fig. 11) were calculated from
methods of Strand and Pemberton (1982). In order to
assess the sensitivity of sediment loads on capacity loss
in reservoirs, annual capacity losses in a hypothetical
50,000 acre-ft reservoir on the White River were deter-
mined for a range of annual sediment loads (table 6),
Annual capacity losses calculated using average annual
suspended-sediment loads at sites 1 through 6 (table 5)
for a range of hypothetical reservoir sizes constructed
on the White River at or near each site are shown in
figure 12. If values of maximum and minimum annual
suspended-sediment loads (table 5) are used, then the
annual capacity losses in a 50,000 acre-ft reservoir
could range from less than 0,01 percent near sites 1
and 2 to about 2.5 percent near site 6. Because the
variability in annual sediment loads at each site (fig. 10
and table 5) is substantial, the curves in figure 12 are
general estimates only.

28 Sediment Tranaport and Water-Quality Characterlatlca and Loada, White River, Northweatern Colorado, Water Vea..
1975-88