Table 8. Elevation range for each
elevation range, at 2-ft intervals, were then inter-
multitemporal class.
polated from the 11 difference values; these differ-
ences were then subtracted from the 1985 area vs.
Elevation range
elevation curve to create the updated 1993 area vs.
Multitemporal
Scene date
represented
class
(1993)
(ft)
elevation curve. Areas for reservoir elevations
above 665.86 ft were not computed because there
1
2 Nov
< 578.51
were no Landsat data with higher elevation.
2
1 Oct
578.51594.65
3
30 Aug
594.65604.88
4
29 Jul
604.88612.32
Updated elevation vs. storage capacity curve
5
27 Jun
612.32620.61
The updated elevation vs. storage capacity
6
26 May
620.61631.06
curve was computed by integrating under the up-
7
10 May
631.06637.75
dated elevation vs. area curve. Capacity of each 2-
8
24 Apr
637.75644.22
9
8 Apr
644.22651.68
ft elevation interval was computed by multiplying
10
31 Mar
651.68655.24
the elevation difference (2 ft) by the average area of
11
7 Mar
655.24665.86
the upper and lower elevations for that interval. To
compute the total reservoir capacity for each ele-
does not include the shoreline classes. Each class
vation, the capacities of all intervals up to that ele-
represents a range of elevation (Table 8).
vation were summed. Capacity values for eleva-
tions above 665.86 ft. were not computed.
Verification comparison
To make an assessment of the Landsat classifi-
cation, the ground survey profile points from
Sediment depth estimation procedure
1993 were superimposed on the 1993 multitem-
If it is assumed that the volume of sediment de-
poral water classification. Each survey point was
posited between 1985 and 1993 is equal to the res-
located in an image pixel and its class was noted.
ervoir capacity lost in that time period, then the
Then the elevation as measured at each survey
average depth of the sediment deposited can be
point was compared with the elevation range of
computed. This is done by dividing the volume
the class it fell into. If the class is correct, the sur-
lost (acre-ft) by the area over which the loss is dis-
vey elevation should lie within the elevation
tributed (acres), yielding the average depth of sed-
range of the class. Profile cross sections were cre-
iment (ft). The depth can be computed for different
ated, showing ground survey elevation and
parts of the reservoir as follows.
Landsat elevation range.
The range of reservoir elevations can be divided
into elevation increments--in this case, according
Storage capacity procedure
to the elevation of the reservoir at the time of the
A two-step procedure was used to make an up-
Landsat overpasses. The first elevation increment
dated estimate of the elevation vs. storage capaci-
is 530 ft (empty) to 578.51 ft, then 578.51 ft to 594.65
ty curve for the Painted Rock Reservoir. First, the
ft, 594.65 ft to 604.88 ft, etc., with the last increment
elevation vs. water surface area curve resulting
being 655.24 ft to 665.86 ft.
from the 1985 survey was updated using the 11
As the reservoir elevation increases from a low-
area estimates derived from the 1993 Landsat
er level to a higher one, the surface area of the res-
data, and then an updated capacity vs. elevation
ervoir increases. The area at the higher level in-
curve was computed from the updated area
cludes the same area as that of the lower elevation
curve.
plus an extra incremental ring of area. Each new
higher elevation level adds an incremental ring of
area. The area at any elevation can be considered
Updated elevation vs. surface area curve
the sum of the area for the lowest level plus the
Water surface area values from the 1985 survey
area of each subsequent incremental area ring.
were available from the Los Angeles District in
The reservoir capacity (water volume) also in-
hard copy for 0.1-ft intervals, from elevation 525
creases with increasing reservoir elevation. As ele-
ft to 705 ft; these were transcribed to digital form
vation increases, the reservoir capacity includes all
for 2-ft intervals. By interpolating from the 0.1-ft
the capacity of the lower level plus a layer of water
data, 1985 area values were determined for the
volume as thick as the elevation increment. Each
same 11 reservoir elevations as the 1993 Landsat
higher elevation adds an incremental volume lay-
passes. The difference between the 1985 and 1993
er. The reservoir capacity at any elevation there-
surface area values was computed for these 11
fore can be thought of as the sum of the volume of
reservoir elevations. Difference values for the full
8
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