Introduction to Surface Irrigation
Surface irrigation is the oldest and most widely used method of irrigation worldwide. It involves distributing water across the land surface by gravity flow. This method has been practiced for thousands of years, dating back to ancient civilizations in Mesopotamia, Egypt, and the Indus Valley. Today, surface irrigation accounts for approximately 85% of all irrigated land globally, especially in developing nations. The method is simple in concept but requires careful management to be efficient and avoid water losses.
In surface irrigation systems, water is applied to the field by flowing over the soil surface, and then infiltrates into the soil profile. The effectiveness of this method depends on soil characteristics, field slope, water availability, and management practices. While often criticized for lower water use efficiency compared to pressurized irrigation systems, surface irrigation can be very efficient when properly designed and managed.
Types of Surface Irrigation Methods
Border Irrigation
Border irrigation involves dividing fields into long, parallel strips (borders) bounded by low earth ridges. Water is applied at the upper end of each border and flows down the slope to the lower end, spreading across the strip as it advances. This method is particularly suitable for close-growing crops like cereals, fodder crops, and legumes on relatively flat slopes (0.2-2%).
The effectiveness of border irrigation depends on proper border dimensions, slope, and flow rate. Borders typically range from 10 to 30 meters wide and 100 to 400 meters long, depending on soil type, slope, and available water flow. Excessive slopes can cause erosion, while insufficient slopes may lead to poor water distribution.
Furrow Irrigation
Furrow irrigation applies water to small trenches (furrows) between crop rows. This method is commonly used for row crops such as corn, cotton, potatoes, sugar beets, and vegetables. By wetting only a portion of the soil surface (typically 1/3 to 1/2), furrow irrigation reduces evaporation losses compared to flooding methods.
Furrows are usually 0.2 to 0.5 meters deep with spacing varying according to crop requirements (typically 0.5 to 1.5 meters). The method can be adapted to variable field topographies and is particularly suitable where labor is relatively inexpensive. Modern improvements include gated pipe supply systems and surge flow irrigation.
Basin Irrigation
Basin irrigation involves surrounding level areas with earth dikes to contain irrigation water. This method is commonly used for orchards, rice paddies, and fields with crops requiring standing water. The entire basin is flooded to a predetermined depth, which then infiltrates into the soil.
Basins can be of various sizes, from small tree basins to large rectangular fields covering several hectares. This method is particularly suitable for flat lands with soils having low to moderate infiltration rates. Basin irrigation is very common in rice production but can also be effective for other crops when proper land leveling is implemented.
Check Basin Irrigation
A variation of basin irrigation, check basin method divides fields into smaller, square or rectangular compartments (checks) separated by low levees. Water enters each check through small openings in the levees. This method provides better control over water application, particularly in fields with minor slope variations.
Corrugation Irrigation
Corrugation irrigation is a combination of border and furrow methods, where small V-shaped channels or corrugations are made in the soil surface between crop rows. Water flows through these small channels and spreads laterally into the soil. This method works well on relatively flat lands with medium-textured soils and close-growing crops.
Advantages of Surface Irrigation
- Lower initial cost and energy requirements compared to pressurized systems
- Minimal technical expertise needed for basic implementation
- Compatible with a wide range of crops and field conditions
- Can utilize runoff water effectively in some designs
- Less sensitive to water quality issues like sediment
- Can be improved with modern management techniques
- Has minimal risk of clogging since no emitters are used
Disadvantages of Surface Irrigation
- Generally lower water use efficiency than pressurized systems
- Requires relatively flat land or proper land leveling
- Potential for significant water loss through deep percolation and runoff
- Limited control over water application rates and uniformity
- May lead to waterlogging and salinity problems if not managed properly
- Higher labor requirements for water management in some systems
- Less suitable for uneven or steep terrain
Design Considerations
Effective surface irrigation requires careful consideration of several factors:
- Soil Type: Soils with faster infiltration rates require longer stream durations or larger stream sizes to achieve adequate water infiltration. Clay soils with slow infiltration may need smaller streams applied more frequently.
- Field Slope: Proper slope is essential for uniform water distribution. Excessive slope causes runoff before adequate infiltration, while insufficient slope results in poor water advance.
- Crop Requirements: Different crops have specific water needs and tolerance to waterlogging, which influence irrigation scheduling and method selection.
- Stream Size: The flow rate must be matched to field conditions for uniform application. Too much water leads to runoff losses, while too little results in inadequate application at the field end.
- Cutoff Time: The duration of water application significantly impacts efficiency and must be determined based on soil infiltration characteristics and desired application depth.
- Field Length and Width: Smaller fields typically achieve higher uniformity but require more control structures and management.
Modern Improvements
Traditional surface irrigation has evolved significantly with technological advances improving efficiency and management:
- Laser Land Leveling: Precise field grading with laser-guided equipment dramatically improves water distribution uniformity.
- Surge Flow Irrigation: Intermittent water application reduces infiltration rate, leading to better water distribution and reduced deep percolation.
- Gated Pipe Systems: Distributing water through pipes with adjustable gates provides better control than traditional earthen canals.
- Automation: Modern control systems can automate water delivery using sensors and computer programs, improving efficiency.
- Drip-Micro Integration: Combining surface irrigation with supplementary drip systems can optimize water use.
- CIGR (Continuously Intermittent Graded Regular): A variation of furrow irrigation that alternates flow between multiple furrows to improve efficiency.
Best Practices for Surface Irrigation
- Implement proper land preparation and leveling for uniform water distribution
- Adjust stream size and application duration based on soil moisture conditions
- Use cutoff schedules tailored to specific field conditions and crop needs
- Monitor soil moisture to avoid over-irrigation
- Maintain distribution systems to control leaks and ensure proper function
- Consider runoff recovery systems where appropriate
- Implement irrigation scheduling based on crop evapotranspiration requirements
- Train personnel in proper irrigation management techniques
- Regularly evaluate system performance and make adjustments as needed
- Incorporate water measurement to track application efficiency
Sustainability and Water Conservation
Surface irrigation can contribute to sustainable water management when implemented thoughtfully. Modern approaches focus on improving efficiency through better management and technology. Simple improvements like reducing field lengths, improving water control structures, and implementing proper scheduling can significantly reduce water losses.
Many irrigation districts and farmers are adopting deficit irrigation strategies with surface systems, applying less water than full crop requirements during non-critical growth stages while maintaining yields. This approach, combined with improved scheduling and better field preparation, can optimize water productivity.
Recirculation systems that collect and reuse surface runoff water are another sustainability enhancement, particularly valuable in water-scarce regions. These systems, combined with improved distribution uniformity, can raise surface irrigation efficiency from traditional 40-60% levels to 70-80% or higher.
Conclusion
Surface irrigation remains a fundamental agricultural water delivery system worldwide, offering simplicity and cost-effectiveness. While traditional methods have limitations, modern improvements and proper management can significantly enhance water application efficiency. The continued evolution of surface irrigation technology, combined with sustainable management practices, ensures this ancient method will remain relevant in contemporary agriculture, particularly for farmers with limited resources or those operating in regions where pressurized irrigation systems are impractical.
