Sedimentation control for reservoirs and dams Before constructing a dam and planning the reservoir, which measures are considered for controlling siltation and sediment entry into the pool?

Introduction / Context:
Sedimentation is a primary life-cycle risk for reservoirs. If unmanaged, deposited silt reduces live storage, affects intakes, and shortens project life. Designers therefore integrate catchment and hydraulic measures to control the sediment load that reaches and remains in the reservoir.

Given Data / Assumptions:

• New storage project in a sediment-bearing catchment.
• Typical riverine sediments (sands, silts, clays).
• Conventional gravity or embankment dam with bottom outlets.

Concept / Approach:
Controls act at three levels: (1) catchment treatment to reduce erosion and sediment yield, (2) in-stream structures (check dams) to trap coarse fractions before they reach the pool, and (3) hydraulic provisions at the dam (under-sluices) to flush deposited material from near the intake and thalweg when flows are available.

Step-by-Step Solution:
Identify catchment-level actions → vegetation screens, afforestation, contour bunds reduce soil loss.Add in-channel traps → check dams slow flow, promote deposition of sand/gravel upstream.Provide dam-level features → under-sluices at low level allow density current and bottom flushing during high flows.Site selection → choose alignment and site with lower specific sediment yield (geology/land use), and with feasible flushing hydraulics.

Verification / Alternative check:
Reservoir sediment management guidelines consistently recommend a portfolio approach: watershed treatment + structural traps + sluicing / flushing through low-level outlets when hydrology permits.

Why Other Options Are Wrong:

• Each of (a)–(d) is indeed a recognized measure; none alone is sufficient. Hence the comprehensive option is correct.

Common Pitfalls:
Relying solely on under-sluices without catchment treatment; ignoring density currents; providing bottom outlets but without adequate discharge capacity during floods.

Final Answer:
All the above