Table 13. Error bars for Landsat storage cap-
would have to be less than the 48,633 acres actu-
acity estimate at spillway elevation (661 ft).
ally measured with the Landsat data at the next
lower elevation, 655.24 ft. This is visualized in
Error source
Upper error bar
Lower error bar
Figure 7, which shows the image from 7 March
#1 Mudflats
40,000
30,000
1993 (elevation 665.86 ft) overlaid with the water
15,000
15,000
surface classification from 31 March 1993 (eleva-
#3 Wind setup
8,000
8,000
tion 655.24 ft). If as much as 500,000 acre-ft had
#4 Threshold
15,000
16,000
been lost, the 7 March water surface classification
#5 Masking
5,000
8,000
would have extended not quite as far as the light
#6 Depth reading
400
400
#7 Lowest levels
2,000
0
blue area in this figure. However, this would
clearly leave rather extensive areas of water un-
classified, as seen in the dark rim around the edge
The area ring for the 594.65- to 604.88-ft elevation
of reservoir. This rim is larger than just uncertain-
range (medium blue color in Fig. 4) has the larg-
ties in the classification procedure. This leads us
est sediment depth estimate (4.73 ft).
to be reasonably sure that not as much as 500,000
acre-ft of storage capacity have been lost.
Error analysis results
Table 13 lists approximate error bars for the
Landsat estimate of storage capacity at spillway
APPLICABILITY TO OTHER RESERVOIRS
elevation. Appendix D explains the error approx-
Given that the techniques described in this
imations in more detail and gives error estimates
report prove useful for the Painted Rock Reser-
for each reservoir elevation level.
voir, the question arises whether it would be pos-
500,000-acre-ft-loss scenario results
sible to use the same techniques to update area
The estimate of the water surface area and
and capacity curves for other reservoirs. The fol-
capacity for the elevations of the Landsat over-
lowing conditions must be met for the techniques
passes, given a loss of 500,000 acre-ft from 1953 to
to work:
1993 (instead of the 157,000-acre-ft loss meas-
There must be a record of the water surface
ured), is listed in Table 14. Estimates for the full
elevation of the reservoir at the exact times
range of elevations are given in Tables C1 and C2
of the remote sensing data acquisition.
in Appendix C.
Remote sensing data must be available for
According to Table 13, if the 500,000-acre-ft-
the full range of reservoir elevations, prefer-
loss scenario were true, then the surface area of
ably as the reservoir is drawn down rather
the reservoir at elevation 665.86 ft (47,038 acres)
than as it fills up, because additional sedi-
Table 14. Painted Rock Reservoir surface area and storage cap-
acity estimates for 500,000 acre-ft loss.
1993 area if
1993 capacity if
Measured
500,000 acre-ft
500,000 acre-ft
Reservoir
1993 area
had been lost
had been lost
elevation
(Landsat)
since 1953
since 1953
Date
(ft above MSL)
(acres)
(acres)
(acre-ft)
4 Dec 93
532.10
0
0
0
2 Nov 93
578.51
7,779
6,636
85,171
1 Oct 93
594.65
13,328
11,369
229,709
30 Aug 93
604.88
17,623
15,033
365,044
29 Jul 93
612.32
21,455
18,302
488,873
27 Jun 93
620.61
25,888
22,084
656,247
26 May93
631.06
32,303
27,556
915,097
10 May93
637.75
36,485
31,123
1,111,370
24 Apr 93
644.22
40,934
34,919
1,325,133
8 Apr 93
651.68
45,795
39,066
1,600,896
31 Mar 93
655.24
48,633
41,486
1,744,278
7 Mar 93
665.86
55,141
47,038
2,214,001
Spillway
661.00
52,101
44,444
1,991,700
15
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