Canal irrigation is the second most important source of irrigation in India after groundwater, accounting for approximately 24% of the total net irrigated area. It involves the diversion of water from rivers or reservoirs through man-made channels to agricultural fields. While geographically concentrated in the Indo-Gangetic plains and deltaic regions, it remains the backbone of the “Command Area Development” strategy in Indian economic planning.
Classification of Canals
In the Indian context, canals are primarily categorized based on the nature of water supply and their functional hierarchy.
Based on Water Availability
- Perennial Canals: Fed by permanent reservoirs or perennial rivers (mostly Himalayan). They maintain a constant water flow throughout the year. Examples include the Upper Bari Doab Canal and the Indira Gandhi Canal.
- Inundation (Non-Perennial) Canals: These do not have a barrage or dam at the head. They draw water from rivers only when the river level rises during floods or the monsoon. Many of these have been converted into perennial systems post-independence.
Based on Functional Hierarchy
- Main Canal: Carries water directly from the source (river/dam). Not used for direct irrigation.
- Branch Canal: Sub-divisions of the main canal with a discharge usually over $5$ m³/sec.
- Major/Minor Distributaries: Smaller channels that take water from branches to the vicinity of the fields.
- Field Channels (Watercourses): The last mile connectivity constructed and maintained by farmers to carry water to individual plots.
Geographic Distribution and Regional Dominance
The development of canal irrigation is governed by topography and soil characteristics.
| Region | Dominant Features | Major Canal Systems |
| Northern Plains | Level land, soft alluvial soil, perennial rivers. High canal density. | Upper Ganga Canal, Western Yamuna Canal, Sirhind Canal. |
| Peninsular India | Rocky terrain, non-perennial rivers. Limited to deltas. | Krishna-Godavari Delta canals, Cauvery Coleroon system. |
| Coastal Plains | High rainfall but utilizes canals for second crops. | Mahanadi Delta canals, Kurnool-Cuddapah (KC) Canal. |
Major Canal Projects and Economic Impact
Major canal systems are often part of Multi-Purpose River Valley Projects (MPRVPs) that contribute significantly to the GDP through agricultural surplus.
- Indira Gandhi Canal (Rajasthan): Originally known as the Rajasthan Canal. It starts from the Harike Barrage (confluence of Satlej and Beas) and covers about 650 km. It has revolutionized the economy of the Thar Desert, enabling the cultivation of wheat, cotton, and mustard in arid districts like Ganganagar and Jaisalmer.
- Buckingham Canal: A 796 km long freshwater navigation and irrigation canal running parallel to the Coromandel Coast.
- Sarda Canal: One of the longest canal systems in Uttar Pradesh, irrigating the Rohilkhand and Oudh regions.
Institutional Framework and Management
- Command Area Development and Water Management (CADWM): Launched in 1974 to bridge the gap between Irrigation Potential Created (IPC) and Irrigation Potential Utilized (IPU). It focuses on constructing field channels and land leveling.
- Participatory Irrigation Management (PIM): Involves the formation of Water User Associations (WUAs) where farmers are given the responsibility of managing and distributing water at the local level to ensure equity.
- National Projects: Canals like the Polavaram (Andhra Pradesh) are designated as National Projects, where the Central Government provides 90% of the funding for the irrigation component.
Advantages and Economic Constraints
Advantages
- Low Operating Cost: Once constructed, the flow is mostly gravity-based, requiring less energy than groundwater pumping.
- Recharge Factor: Seepage from unlined canals often helps in recharging local groundwater tables.
- Multi-utility: Large canals also serve as sources for rural drinking water and inland navigation (e.g., National Waterway 4).
Constraints and Issues
- Waterlogging and Salinity: Excessive seepage and lack of proper drainage in canal commands (especially in Punjab and Haryana) lead to “Reh” or “Kallar” (saline efflorescence) on the soil surface.
- Head-Tail Disparity: Farmers at the “head” of the canal often over-irrigate, leaving those at the “tail-end” with insufficient water.
- Siltation: Accumulation of silt reduces the carrying capacity of canals, requiring frequent and expensive desilting.
Facts and Trivia for Prelims
- Highest Net Canal Irrigated Area: Uttar Pradesh has the largest area under canal irrigation in India.
- Highest Percentage of Canal Irrigation: Mizoram and Manipur (due to the absence of groundwater infrastructure), followed by Jammu & Kashmir.
- The “Grand Anicut” (Kallanai): Built by Karikala Chola on the River Cauvery in the 2nd century AD, it is one of the oldest water-regulatory structures in the world still in use.
- Warabandi System: A rotational method for equitable distribution of available water in the canal command area by fixed time slots for each farmer.
- Lining of Canals: The process of surfacing the bed and sides of a canal with concrete or tiles to prevent seepage; a key focus under PMKSY.