1. Long Term Storage Long term storage means to store water during high inflows years for the benefit of low inflows years. 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: Hurst studied this problem and proposed the following equations:

2. R is the required capacity of the reservoir. R is the required capacity of the reservoir. σ is the standard deviation of the flow records. σ is the standard deviation of the flow records. N is the number of years. 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. 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.

3. 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: 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:

4. S is the live storage capacity. S is the live storage capacity. M is the mean yearly inflows. M is the mean yearly inflows. B is the guaranteed release. B is the guaranteed release. According to the available live capacity within the basin, one can calculate the guaranteed annual release from the reservoir. According to the available live capacity within the basin, one can calculate the guaranteed annual release from the reservoir.

5. Example: Example: For a wadi, if the annual mean discharge over 90 years is 92 mm 3 and the standard deviation is 19.2 mm 3, 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 mm 3 which must be divided into 30 mm 3 for sediment, 90 mm 3 for live storage and 44 mm 3 for flood control. Find the guaranteed annual release?

6. R = σ * 0.61 N 0.72 R= 19.2 * 0.61 * (90) 0.72 R ≈ 300 mm 3 This value exceeds the natural capacity of the basin log (90/300) = - 0.08 – (92-B)/19.2 B ≈ 84 mm 3