Reservoir storage zoning in hydrology In a reservoir capacity diagram, which zone is termed the “surcharge storage” (i.e., the flood storage above the normal or useful storage)?

Introduction / Context:
Reservoir capacity is commonly subdivided into dead storage, useful (live) storage, and surcharge storage. Understanding these zones is essential for flood routing, dam safety checks, and operation policies.

Given Data / Assumptions:

• Surcharge storage is the temporary flood-storage space above the full reservoir level (FRL).
• Useful (live) storage lies between minimum drawdown level and FRL.
• Dead storage lies below the minimum drawdown level and cannot be routinely used.

Concept / Approach:
Surcharge storage provides capacity exclusively for attenuating floods. It is not intended for regular water-supply withdrawals and is normally empty under conservation operation. Hence it must be located above the useful (live) storage zone.

Step-by-Step Solution:

Verification / Alternative check:
Reservoir elevation–capacity curves and dam operation manuals show surcharge space between FRL and maximum water level, confirming the position of this zone.

Why Other Options Are Wrong:

• Below dead storage: incorrect—surcharge is never below dead storage.
• Between dead and useful: that is the live storage, not surcharge.
• Valley storage: a different concept relating to natural valley volume, not a reservoir zone term.

Common Pitfalls:
Confusing “live/usable storage” with “surcharge storage.” Live storage is for supply regulation; surcharge is for flood moderation.

Final Answer:
Above useful (live) storage