The next information needed to evaluate the flood routing is the volume of
storage in the reservoir at any elevation. This may be determined by measuring the
area under water at a series of different elevations. The volume then becomes the
sum of the calculations of the mean area times the difference in elevation between
any two area measurements. The calculations for the storage are shown in Fig. 6.12.
The upper portion of the figure indicates the method for calculating the volume at a
given elevation, and this may be applied to the total storage available at any given
elevation, as shown in the lower diagram. In this figure, English units of area and
volume are indicated because of the simplified relationship between ac-ft and cfs.
Calculate storage for each interval of elevation
S
458
a.
b.
454
450
446
442
438
434
430
458
454
450
446
442
438
434
430
0
40
5
30
75
125
180
240
305
375
total storage to any elevation = Σ S to that elevation
80
120
160
200
240
280
320
STORAGE THOUSAND ACRE - Ft
360
400
Outlet
5,000
7,500
12,000
13,000
14,500
15,500
17,000
18,000
Elevation, ft
Elevation, ft
S 7
S 6
S 5
S 4
S 3
S 2
S 1
Surface Area,
Acres
2
x (elevation 1 – elevation 0 )
A 0 + A 1
=
Fig. 6.12 Illustration of calculation of reservoir storage at any depth
6 Basic Hydrology, Water Resources, and DAF Boat Plant for Lake Restoration
259