9521

• UCREFRP Catalog Number: 9521
• Author: Liebermann, T. D., D. K. Mueller, J. E. Kircher and A. F. Choquette.
• Title: Characteristics and Trends of Streamflow and Dissolved Solids in the Upper Colorado River Basin, Arizona, Colorado, New Mexico, Utah, and Wyoming.
• USFW Year: 1989.
• USFW - Doc Type: Denver.
• Copyright Material: NO

1400
Z 1200
O
<tr
w
Z J 1000
U OC
Zw
a
OC) to 800
pQ
J cc
OJ
w 600
OZ
In
25 400
200
?1 --- INFLOW
- OUTFLOW
it
P
I
1 it
I I I?i
+ + i 1 Iti t i ? ? ?? ? ? t
I I I 1 1 1 1 1 1 ? 11 1 1 tI 1{ 1 { 11 I
1 I 1 1 1? 1+ h { II I I p 11 1
1 + 1 I I 1+ 11 1) 11 I I Il I ?1 1 1\ I 1+?= Ir
I 1 ? I I I 1 11 11 11 ? M I I! 1{ 1'nl 1 1 1 I IVI ? 1
1 1 1 1 I 1 11 ? I{ 11 11 I JI 1 1 1 1 11 I 1 1 1 I 1 1
11 i ! i? l I I I ! I I !l I It 1I V11 1 l i 1 1 1 1 I 1 IJ 11 I 1 1
1 1 ! 1
11 11 1 1{ 1 I I I\ 1 11 1 1 1 1 1 I li 1
11 1 1 1 1 1 1 1 1 1 \ 1 1 1 1 ?i 1 1 1 I I ? 1 }1 l Iii !
II I I 1 1 1 1 1 1 I 1 I 1 1 1 1 1 I 1 1 I !
1j 1 1 1 1 I 11 I ! 1 1 I I {{ I
11 11 1 11 II 11 11 1 1 II 11 1 I I II 11 I I ! 11 1 1
I 11 1 11 11 I 11 1
I 1 11 1 If 'III I I I I 11 11 11 11 I I I I I I 11 I
11. 11 I II II 1
1 11 II
11
I! I II II I1 11 II 11 11 1! II 1 1j 1 1
11 1 N 11 II I1 11 11 II 11 II 11 1 11 11 11
11 I ' ? ? II 11 ? II 11 11 V Ij 11 11 I; +
1+ I l1 ? y fl Al 1963

1970
1977
1984
WATER YEAR
Figure 27. Monthly dissolved-solids concentration in Lake Powell inflow and outflow.
Qo, m = the outflow volume during month m;
UV, m = the unexplained change in volume during month
m;
Cm = the flow-weighted mean dissolved-solids concen-
tration in the outflow during month m;
Cm -I = the flow-weighted mean dissolved-solids concen-
tration in the outflow during the previous month
(m -1);
L1, m = the total inflow dissolved-solids load during month
m;
Lo, m = the outflow dissolved-solids load during month m;
UL, m = the unexplained change in load during month m.
The unexplained changes in volume (Up m) and load (UL, m)
were defined to be negative if there was a loss in the reser-
voir during the month and positive if there was a gain. Unex-
plained losses of volume could be caused by evaporation or
bank storage. Unexplained volume gains could be due to
return flow from bank storage or unmeasured inflow. Over
a long period, evaporation probably has the greatest effect.
If equation 6 is accurate, the long-term mean value of UV
should be negative and approximately equal to the mean
monthly evaporation. Monthly values of UV are plotted in
figure 28 for the period of record after July 1965, when the
normal release program was implemented. The mean
monthly unexplained change in volume for that period was
-45,111 acre-ft, which indicates an annual loss of about
541,000 acre-ft from Lake Powell. A smoothed curve
through the monthly values shows the annual deviation about
this mean during the period. This loss closely corresponds
to U.S. Bureau of Reclamation estimates of evaporation from
the reservoir, which averaged about 517,000 acre-ft per year
for 1973-82 (U.S. Bureau of Reclamation, 1982; J.
Osterberg, U.S. Bureau of Reclamation, oral commun.,
1986). Therefore, equation 6 seems appropriate for com-
puting reservoir storage.
If the primary source of water loss in Lake Powell is
actually evaporation, the dissolved-solids load would not be
affected. A long-term gain or loss identified by the mean
monthly unexplained change in load would indicate that a
chemical process, such as salt dissolution or precipitation,
was occurring in the reservoir. However, no consistent
departure from zero was found in the values of UL (fig. 29).
The values were evenly distributed around zero, which in-
dicates short-term fluctuations in mixing or inaccuracy of
the mass balance given by equation 7. The mean monthly
value was not significantly different from zero, and a
smoothed curve showed no trend during the period. There-
Lake Powell and Dissolved-Solids Outflow 59