Transcript Long Term Storage

Long Term Storage
• Long term storage means to store water
during high inflows years for the benefit of
low inflows years.
• Hurst studied this problem and proposed
the following equations:
(
•
•
•
•
R

)  0 . 61 N
0 . 72
R is the required capacity of the reservoir.
σ is the standard deviation of the flow records.
N is the number of years.
This equation is used to determine the required
capacity of the reservoir in order to insure the
release of the mean value of the inflows every
year.
• If the basin capacity is less than the
required capacity then, one may calculate
the annual guaranteed release based on
the available life storage within the basin
using the following equation:
•
log(
S
R
)   0 . 08  1 . 05 (
M B

)
• S is the live storage capacity.
• M is the mean yearly inflows.
• B is the guaranteed release.
• According to the available live capacity
within the basin, one can calculate the
guaranteed annual release from the
reservoir.
• Example:
For a wadi, if the annual mean discharge
over 90 years is 92 mm3 and the standard
deviation is 19.2 mm3, find the reservoir capacity
required to guarantee a yearly release equal to
the annual mean flow. If the natural basin has a
maximum capacity of 164 mm3 which must be
divided into 30 mm3 for sediment, 90 mm3 for
live storage and 44 mm3 for flood control. Find
the guaranteed annual release?
R = σ * 0.61 N0.72
R= 19.2 * 0.61 * (90)0.72
R ≈ 300 mm3
This value exceeds the natural capacity of
the basin
log (90/300) = - 0.08 – (92-B)/19.2
B ≈ 84 mm3