Discharge equivalence of an ogee weir Under free-flow (non-drowned) conditions, the discharge over an ogee weir is effectively the same as that over which type of weir?

Introduction / Context:
Ogee crests are shaped to match the lower nappe of a sharp-crested weir to minimize separation and maintain accurate discharge characteristics. Hence, their discharge relation mirrors that of sharp-crested weirs when flow is not submerged.

Given Data / Assumptions:

• Free overflow (no submergence from downstream water level).
• Standard ogee profile correctly shaped for approach velocity.
• Head measured over the crest as in sharp-crested calibrations.

Concept / Approach:

Because an ogee is designed to conform to the nappe trajectory, it behaves hydraulically like a sharp edge for free overflow. Thus, Q ∝ H^(3/2) with a similar coefficient of discharge, subject to approach and aeration conditions.

Step-by-Step Solution:

Verification / Alternative check:

Empirical calibrations show close agreement of discharge coefficients between ogee and sharp-crested weirs under free flow.

Why Other Options Are Wrong:

V-notch and Cipoletti use different head–discharge relations; drowned weirs involve submergence corrections; broad-crested weirs have different flow regimes and coefficients.

Common Pitfalls:

Applying free-flow formula when downstream submergence exists; neglecting approach velocity corrections.

Final Answer:

Sharp-crested weir