Question

Which of the following stream bank control measure is used especially when stream takes a sharp bend and bed scour is not deep?

• A. Revetment
• B. Sodding
• C. Brushwood edging
• D. Brushwood rollers

Hint:

______Brushwood rollers______ act as a highly flexible "toe armor".
Because the live brushwood eventually takes root in the bank, it transforms from a temporary physical barrier into a ______permanent, self-reinforcing biological root network______.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Stream bank erosion is highly pronounced along sharp curves due to centrifugal forces acting on the water flow, which increases shear stress on the outer banks.
Bio-engineering measures are cost-effective, ecological solutions used to stabilize these vulnerable zones.

Step 2: Detailed Explanation:
Let us analyze the specific applications of the listed stream bank control measures:
- Sodding (B): Involves establishing a grass cover on the bank slopes. It is suited only for gentle slopes and straight reaches with low-velocity flows.
- Revetment (A): Consists of hard armor (like stone rip-rap or concrete blocks) placed on the bank. It is highly effective but expensive, typically reserved for deep bed scour or critical infrastructure protection.
- Brushwood edging (C): Involves placing brushwood along the edge of the bank. It is used primarily on small, shallow streams with straight channels.
- Brushwood rollers (D): These are constructed by wrapping bundles of live brushwood around a core of gravel or stones, tied tightly with wire.
These rollers are laid along the toe of the stream bank at the outer curve of a sharp bend.
Because they are flexible, they conform easily to the shape of the bend.
The rocky core provides ballast, while the brushwood dissipates energy and traps sediment.
Since they are placed at the toe where bed scour is not deep, they prevent undermining and protect the bank from high-velocity currents.

Step 3: Final Answer:
The stream bank control measure used for sharp bends with shallow bed scour is brushwood rollers, which corresponds to option (D).