For a flood control reservoir, the effective storage is equal to A. Useful storage – valley storage B. Useful storage + surcharge storage C. Useful storage + surcharge storage + valley storage D. Useful storage + surcharge storage – valley storage

The correct answer is: B. Useful storage + surcharge storage

Effective storage is the amount of water that can be stored in a reservoir for flood control purposes. It is equal to the useful storage plus the surcharge storage.

Useful storage is the volume of water that can be stored in the reservoir for beneficial uses, such as irrigation, drinking water, and power generation. Surcharge storage is the volume of water that is stored in the reservoir above the useful storage level. This water is not available for beneficial uses, but it can be used to control floods.

The following is a brief explanation of each option:

• Option A: Useful storage – valley storage. This is not the correct answer because valley storage is not included in the definition of effective storage. Valley storage is the volume of water that is stored in the valley below the reservoir. This water is not available for beneficial uses or flood control.
• Option B: Useful storage + surcharge storage. This is the correct answer because it includes both the useful storage and the surcharge storage.
• Option C: Useful storage + surcharge storage + valley storage. This is not the correct answer because valley storage is not included in the definition of effective storage.
• Option D: Useful storage + surcharge storage – valley storage. This is not the correct answer because valley storage is not included in the definition of effective storage.