Reservoir operation – lowest outlet sluice level:\r At what vertical level is the lowest outlet sluice of a dam typically provided relative to the dead storage zone?

Introduction / Context:
Reservoir storage is partitioned into dead storage and useful or live storage. Outlet works must deliver acceptable quality water and avoid excessive sediment withdrawal. The elevation of the lowest outlet sluice is set with these objectives in mind.

Given Data / Assumptions:

• Dead storage near the bottom accumulates settled sediments over time.
• Useful storage contains better quality water for supply, irrigation, or power.
• Question concerns the typical level of the lowest outlet sluice.

Concept / Approach:
Placing the lowest outlet at the top of the dead storage minimizes sediment entry while still allowing drawdown to the designed minimum operating level. Outlets below dead storage would entrain heavily silted water and risk blockage. Outlets too high would strand part of the intended useful storage and reduce dependable yield.

Step-by-Step Reasoning:
Define storage zones and their purposes.Balance water quality and operating flexibility by setting the outlet just above the sediment accumulation zone.Conclude that the appropriate elevation is at the top of dead storage.

Verification / Alternative check:
Design drawings typically show multi level outlets or selective withdrawal structures, but the lowest service outlet aligns with the live storage floor to avoid silt laden draw, consistent with this selection.

Why Other Options Are Wrong:

• Below dead storage increases sediment entrainment and blockage risk.
• At useful storage top or center of dam height would waste live storage and reduce supply reliability.

Common Pitfalls:

• Confusing sediment sluices or bottom outlets for flushing with service outlets for regular delivery. Flushing conduits may be lower but are not the service outlet referenced here.

Final Answer:
At the top level of dead storage