WSP07478

• File Number: 8272.600.60
• Description: Colorado River Basin Salinity Control Program - Basin Member State Info - Utah
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 3/1/1982
• Title: Salt Uptake in Natural Channels Traversing Mancos Shales in the Price River Basin - Utah
• Water Supply Pro - Doc Type: Report/Study

sepsrsting sslt pickup from within the
surface channels from salt brought into
the channel by overland flows. In order to
collect dsta for this separation, a small
ephemeral chsnnel was supplied with water
from an irrigation ditch, a situation where
no overland flow occurs. The instrumentation
ia deacribed in Chapter III. The experimental
channel i 8 referred to 8S the mact'ochannel
(Figure 3.3), and the results are listed in
Appendix C (Figures C.3, C.4, and C.S and
Tables C.7 snd C.8).

N
o
00
o

Flow was induced on August 26 and
September 9, 1976, for 7 and 4 hours respec-
tively. The mean flow was 0.1 cfs but
amounts were highly variable (Appendix C,
Figures C.4 and C.S). Flow was monitored
at four flumes approximately 400 feet
apart (Figure 3,3). A typical TDS curve of
salt concentration as a function of time
after the induced flow began at the most
upstream flume is illustrated in Figure 4.18.
TDS was estimated by the following relation-
ship previously derived for Coal Creek
data.

TDS = 0.746 C . . . . . . . . . . (4.4)

in which

TDS Total dissolved solids (mg/l)
C Conductivity (umhos/cm @ 2S'C)

The salt concentration of the induced flow
was initially high, as would be expected, and
then declined as the more exposed or highly
soluble salts in the channel dissolved.

750
~
..."
,
'"
~
'" 500
'"
...
~
...,
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250

1000

A plot of accumulated salt load versus
accumulated flow (Figure 4.19) at the three
downstream flumes supports linear loading
during the first few hundred cubic-feet of
flow. Such an initial linear response
was also reported by White (1977a) in com-
paring accumulated salt load versus accumu-
lsted sediment. The later decrease in the
slope of esch curve is produced by a fslling
rate of sslt pickup after the more expos'ed
salts have been dissolved from the channel
sections.

Plots for the two induced flow tests of
accumulated salt load versus the square root
of time (Figures 4.20 and 4.21) indicate that
the data plot as straight lines with high
correlation (Table 4.10). The salt loading
responae is similsr to thst observed in the
laborstory jar tests of the Coal Creek
channel sediments. The Coal Creek sediment
analysis showed a break in the square root
linear relationship at about 60 hours (65
minO.S on Figure 4.16). The curves of
Figures 4.20 for August 26 and 4.21 for
September 9 cover only 6 hours and thus are
entirely in the initial steep section of
Figure 4.16.

Assuming a uniform channel geometry, an
average salt loading rate per unit of channel
length may be calculated for the mean wetted
perimeter (Table 4.11). Figure 4.19 shows
that the rate of release declines downstream.
Some differences in the rate of salt pickup
between channel sections can be explained
on the basis of nonuniformities in the
salinity potential of the streambed. How-

.1-__
6

o

2 3 4
Time (hours) After Induced Flow Began

5'

Figure 4.18. Illustrative mac~ochannel salt concentration response.

38