Hydraulic structure safety: A hydraulic structure (e.g., a barrage or weir with floor and cutoffs) must be designed to withstand which of the following actions?

Introduction / Context:
Hydraulic structures interact continuously with flowing water and the underlying pervious foundations. Their safety depends on adequate resistance to multiple hydraulic actions, not just static head. Designers must consider seepage, surface flow transitions, and dynamic effects like hydraulic jumps.

Given Data / Assumptions:

• Typical barrage/weir with floor, cutoffs, and protection works.
• Variable flow regimes including low flows and flood flows.
• Pervious foundation where seepage is relevant.

Concept / Approach:
Key design actions include: (1) seepage forces causing uplift and exit gradients (piping risk); (2) hydraulic jump forces and turbulence on downstream glacis/apron; (3) hydrostatic and hydrodynamic pressures on structural faces and floors. Combined consideration ensures stability against uplift, sliding, overturning, and scour.

Step-by-Step Solution:
1) Identify seepage actions: uplift pressure distribution and exit gradient.2) Identify surface flow transitions: hydraulic jump impact and roller pressures.3) Identify hydrostatic/hydrodynamic pressures on faces and floors.4) Conclude that all listed actions must be resisted by structural and geotechnical design.

Verification / Alternative check:
Design codes and classical methodologies (e.g., Khosla’s theory, IS codes) explicitly require checks for uplift, sliding, overturning, structural stresses, and for adequate energy dissipation measures to manage hydraulic jumps and scour.

Why Other Options Are Wrong:

• Any single-action choice is incomplete and would lead to unsafe or uneconomical design.
• “Only static pressure” ignores the critical dynamic and seepage components.

Common Pitfalls:

• Underestimating dynamic loads during flood-induced jumps.
• Ignoring foundation permeability and exit gradient, leading to piping failures.

Final Answer:
All of the above.