Reservoir zoning: The storage capacity of a reservoir is divided into three zones. Which is the lowest zone by elevation?

Introduction / Context:
Reservoir capacity is partitioned to plan sediment accommodation, water-supply reliability, and flood routing. Identifying each zone helps evaluate how sedimentation and drawdown affect operations over time.

Given Data / Assumptions:

• Three standard zones: dead, useful (live), and surcharge storage.
• Elevation increases upward from the dam base.

Concept / Approach:

Dead storage is the lowest zone, allocated primarily to contain sediment and cannot be released by gravity under normal outlet invert elevations. Above it lies useful (live) storage, actively managed for supply and power. The topmost (above full-supply level) is surcharge storage used temporarily during floods.

Step-by-Step Solution:

Verification / Alternative check:

Operating rule curves and reservoir capacity–elevation charts consistently show dead storage at the bottom of the pool.

Why Other Options Are Wrong:

• Useful storage and surcharge storage occupy higher elevations.
• “Inactive sediment wedge only” is not a standard capacity designation in operating charts.

Common Pitfalls:

• Confusing inactive (dead) storage with live storage below minimum operating level.

Final Answer:

Dead storage.