AU-Irrigation Engineering [22CEPESCN] : 4. Unit IV Canal Irrigation

1. Introduction to Canal Regulation

Definition:

Canal regulation refers to the methods and structures used to control and manage the flow of water in irrigation canals. Effective regulation ensures the efficient delivery of water to fields, prevents wastage, and minimizes erosion and flooding.

Purpose of Canal Regulation:

Water Distribution: Ensure equitable and controlled distribution of water to different sections of the canal system and ultimately to the fields.
Flow Control: Maintain the desired flow rates to match the irrigation needs and prevent excess water delivery.
Safety: Prevent overflow, breaches, and flooding that can damage agricultural lands and infrastructure.
Efficiency: Minimize water losses due to seepage, evaporation, and unauthorized withdrawal.
Sediment Control: Manage sediment deposition and scouring in the canal to maintain capacity and reduce maintenance needs.

Scope of Canal Regulation:

Main Canals: Large canals that carry water from the source (like a river or reservoir) to the distribution network.
Branch Canals: Offshoots from the main canals that distribute water to smaller areas.
Distributaries: Smaller channels that deliver water directly to the fields.

2. Key Components of Canal Regulation

A. Canal Regulation Structures

Head Regulators:
- Function: Control the flow of water from a river or reservoir into the main canal.
- Components: Typically include gates or sluices that can be adjusted to regulate flow rates.
- Location: At the head of the main canal, where it begins.
Example:
The head regulator of the Narmada Canal in India controls the water flow into the extensive Narmada Canal network, which irrigates vast agricultural areas in Gujarat.
Cross Regulators:
- Function: Control water levels and flow rates in different sections of a canal, especially in main and branch canals.
- Components: Include gates, sluices, and sometimes a bridge to allow the crossing of roads or railways.
- Location: Installed at strategic points along the canal, often near junctions or where water levels need to be managed.
Example:
The cross regulators in the Indira Gandhi Canal, India, help maintain desired water levels and manage distribution to various branches and distributaries.
Distributary Head Regulators:
- Function: Control the flow of water from main or branch canals into smaller distributaries.
- Components: Generally consist of a gate or a sluice to regulate the flow.
- Location: At the junction where water is diverted from a main or branch canal into a distributary.
Example:
In the Krishna Delta System, distributary head regulators manage the flow of water into smaller channels, ensuring equitable distribution among different farming regions.
Escape Structures:
- Function: Provide a safety outlet for excess water during floods or when the canal system needs to be relieved of water.
- Components: Includes gates or weirs that allow water to spill out of the canal into a drainage channel or natural watercourse.
- Location: Located at points where overflow might occur or where controlled release is necessary.
Example:
The Mettur Canal system in Tamil Nadu, India, includes escape structures that protect the canal from overflow during heavy rains.

B. Canal Operation Mechanisms

Gates and Sluices:
- Types: Vertical lift gates, radial gates, sluice gates.
- Operation: Manually or automatically operated to control the flow rate and water levels.
- Material: Commonly made of steel or reinforced concrete for durability and strength.
Flow Measurement Devices:
- Types: Staff gauges, float-operated devices, electronic sensors.
- Purpose: Measure flow rates and water levels to assist in managing the distribution and ensuring accurate water delivery.
- Location: Installed at key points such as head regulators, cross regulators, and distributary heads.
Control Room Operations:
- Function: Centralized monitoring and control of canal operations using real-time data.
- Components: Includes computers, sensors, and communication systems to operate gates and monitor water levels remotely.
Example:
The Sutlej-Yamuna Link (SYL) Canal uses modern control room operations for managing water distribution across Punjab and Haryana, India, ensuring precise water delivery.

C. Sediment Control Mechanisms

Sediment Traps and Desilting Basins:
- Function: Capture and remove sediment from the water before it enters the main canal or distributary.
- Location: Positioned near the headworks or at specific points where sediment load is high.
- Design: Large basins or tanks that slow down the water flow, allowing sediment to settle out.
Example:
The Nagarjuna Sagar Right Canal in India uses desilting basins to manage sediment, ensuring cleaner water reaches the agricultural fields.
Bed Slope and Velocity Control:
- Function: Design the canal bed with a slope that maintains a self-cleaning velocity, preventing sediment deposition.
- Implementation: The slope and cross-section of the canal are carefully calculated to maintain the desired flow velocity.
Example:
The Bhakra Canal System in India has carefully engineered slopes to maintain flow velocities that minimize sedimentation.

D. Lining and Maintenance

Canal Lining:
- Function: Reduces seepage losses and prevents erosion.
- Materials: Concrete, brick, plastic, or geomembranes.
- Benefits: Increases water use efficiency and reduces maintenance costs.
Example:
The lined sections of the Sardar Sarovar Canal in Gujarat, India, help conserve water by reducing seepage losses.
Maintenance Activities:
- Inspection: Regular inspections to identify and repair cracks, leaks, or blockages.
- Desilting: Periodic removal of accumulated silt and debris to maintain flow capacity.
- Vegetation Control: Removing vegetation growth along canal banks to prevent obstruction and maintain water flow.
Example:
The Grand Canal in China undergoes regular maintenance to keep it free from silt and vegetation, ensuring its continued operation as a major waterway.

3. Canal Regulation Techniques

A. Manual Regulation

Description: Using manual labor to operate gates and other control structures.
Advantages: Low cost, simple technology, suitable for small-scale systems.
Disadvantages: Labor-intensive, less precise control, slower response to changing conditions.

B. Semi-Automatic Regulation

Description: Combines manual and automatic systems, with some remote control or mechanized gates.
Advantages: Improved control, reduced labor, faster response.
Disadvantages: Requires some level of infrastructure and technical knowledge.

C. Automatic Regulation

Description: Fully automated systems using sensors, actuators, and control systems to manage water flow.
Advantages: Highly efficient, precise control, real-time adjustments, reduced water losses.
Disadvantages: High initial cost, requires skilled personnel for operation and maintenance, complex technology.
Example:
The modern canal automation system used in the California State Water Project, USA, automatically adjusts water deliveries based on real-time data from sensors and weather forecasts.

4. Case Studies

A. Narmada Canal, India

Background:

Part of the Sardar Sarovar Project in Gujarat, India.
Designed to provide irrigation and drinking water to drought-prone areas.

Canal Regulation Features:

Head Regulator: Controls the flow from the Sardar Sarovar Dam into the main canal.
Cross Regulators: Installed at various points to manage water levels and flows.
Distributary Head Regulators: Ensure controlled water distribution to various distributaries and minor canals.
Lining: Concrete lining to minimize seepage and improve efficiency.

Impact:

Provides irrigation to over 1.8 million hectares of land.
Supplies drinking water to thousands of villages and towns.
Improved agricultural productivity and water availability in the region.

B. California State Water Project (SWP), USA