Understanding Weir Components and River Division

A weir is a type of low dam built across a river to raise the water level upstream or to divert water into a canal. Weirs have several important components, each serving a specific purpose in managing river flow and water diversion.

The question asks about the component that divides the river width into two distinct areas: the weir portion and the under sluices pocket. Let's examine the options provided:

• Canal head regulator: This structure is located at the head of the canal and controls the flow of water from the river (or reservoir) into the canal. Its primary function is regulating flow, not dividing the river width itself.
• Divide wall: This is a long wall constructed parallel to the river flow, extending downstream from the upstream end of the weir. Its main function is to separate the weir proper from the under sluices portion (also known as the scouring sluices pocket). This separation helps in concentrating flow near the under sluices for sediment removal and maintains a sufficient water level near the canal head regulator located in the under sluices pocket.
• Weirs ancillary work: This is a broad term referring to various supporting structures associated with a weir, such as guide banks, marginal bunds, and perhaps even fish ladders. These works support the overall function but do not specifically perform the function of dividing the river width into the weir and under sluices sections.
• Weir proper: This is the main body of the weir constructed across the river, designed to raise the water level. While it spans the river width, it doesn't divide the width into separate sections; rather, the divide wall separates an area *alongside* the weir proper.

Based on the functions of these components, the structure specifically responsible for dividing the river width into the weir portion and the under sluices pocket is the Divide wall.

Therefore, the component that performs the function of dividing the river width into the weir portion and under sluices pocket is the Divide wall.

Revision Table: Key Weir Components

Additional Information on River Diversion Works

Weirs and barrages are common river diversion structures. While both raise water levels and divert water, barrages typically have gates across their entire width, allowing better control over upstream water levels and downstream flow compared to fixed-crest weirs. The principles of separating the sediment-laden flow (via under sluices) from the clear water flow (for the canal) are crucial in the design of both weirs and barrages to ensure the efficient and sustainable operation of irrigation canals.

The Divide wall plays a vital role in directing the main flow away from the canal head regulator during floods, thereby reducing sediment entry into the canal. It also helps in scouring deposited silt near the regulator by concentrating flow through the under sluices during low flow periods.