Understanding Weir Structure Components

Weirs are hydraulic structures built across rivers or channels to raise the water level upstream and regulate flow. They consist of several key parts, each serving a specific function in managing water flow and energy.

What is a Glacis?

The question asks about the specific name given to the slopping floor located below and in continuation of the raised crest of a weir. This particular component is crucial for the performance of the weir, especially on the downstream side.

Let's look at the term 'glacis'. In the context of a weir, the glacis refers to the downstream sloping floor that extends from the crest of the weir. Its primary purpose is often to guide the flow and assist in dissipating the energy of the water flowing over the crest, preventing erosion downstream.

Considering the definition, the description "the slopping floor below and in continuation of the raised crest of a weir" perfectly matches the definition of a glacis.

Analyzing Other Options

Let's briefly consider the other options provided:

• DS slope: This term typically refers to the overall slope of the channel bed downstream (DS) of the structure, not a specific structural component of the weir itself.
• DS grade: Similar to DS slope, this refers to the gradient or inclination of the downstream channel bed.
• DS fall: This could refer to a drop in the water surface level or channel bed elevation downstream, but it doesn't name the specific sloped floor structure built as part of the weir.

Based on the standard terminology used in hydraulic engineering for weir components, none of the other options accurately describe the slopping floor immediately downstream of the raised crest.

Revision Table: Key Weir Terms

Additional Information: Weir Function and Parts

Weirs serve various functions, including water level control for irrigation, navigation, flow measurement, and creating head for hydropower. A typical weir structure includes:

• The Body or Wall: The main barrier across the channel.
• The Crest: The top edge where water flows over.
• The Upstream Apron: A paved floor extending upstream from the weir body.
• The Glacis: The downstream sloping floor starting from the crest.
• The Downstream Apron: A paved floor extending downstream from the glacis or weir body, often incorporating energy dissipators like baffle walls or blocks.
• Cut-off Walls: Walls extending into the bed below the structure to prevent undermining due to seepage.

The glacis plays a vital role in safely conveying water from the crest down to the downstream level, controlling flow velocity, and assisting energy dissipation, which is critical for the stability and longevity of the structure and the downstream channel.