By Gary Vert, PE, CFM

Many irrigation districts have converted their earthen canals to pipelines to modernize today’s irrigation water delivery systems. From durable, long-lasting materials to reduced operation and maintenance, pipelines can help conserve water and improve efficiencies. Achieving these project benefits takes careful planning. From our experience, there are five important considerations for canal-to-pipeline conversion projects.

My last article discussed why converting open irrigation channels into pipelines may be the most feasible, sustainable, and practical solution to address irrigation system inefficiencies. But irrigation districts should also think about the five following considerations:

1. Cost

Project costs will largely be driven by pipe type, required diameter, and the canal length to be converted. Typical costs for pipeline conversion projects include site grading, trenching, bedding installation, backfilling, and pipe material and installation costs. Additional costs include any pipe appurtenances or fittings, service connections, and end treatments such as flared end sections, riprap armoring, or grated ends. Modernization efficiencies, such as a more effective pipeline alignment compared to the existing canal (See “Location”), could contribute to project cost savings.

2. Location

Determining the location of a proposed pipeline conversion project can be influenced by several factors. Oftentimes, the end goal or objective for the project is what dictates the location. For example, converting canal to pipelines at more upstream locations within the irrigation delivery system will impact more water users than downstream locations.

Additionally, converting areas with high seepage or evapotranspiration losses will result in more water conserved. Problem areas within the delivery system—areas where washouts or erosion are common or homes proximate to a canal that experience flooding—can dictate the proposed project’s location.

Other considerations for pipeline locations include the existing right of way (ROW) or easements. In some cases, the existing canal alignments do not provide the most efficient layout. Therefore, consideration should be given to the potential need for ROW or easement changes.

3. Material

There are many good options available for pipe material in an irrigation application. Common pipe materials include reinforced concrete pipe (RCP), polyvinyl chloride pipe (PVC), steel reinforced polyethylene pipe (SRPE), or high-density polyethylene pipe (HDPE).

  • Reinforced Concrete Pipe (RCP) – RCP is common in irrigation pipe because of its strength and durability. RCP comes in various sizes, typically 12” to 144” diameters. The pipe can be lined or coated, depending on the project conditions. RCP is common in areas with traffic loading.
  • PVC – PVC is more popular in smaller sizes, typically available in 4” to 36” diameters. PVC has a smooth interior surface that provides superior hydraulic function. PVC is lightweight, making it easy to install. PVC is resistant to abrasion and scour and will not corrode, making it a durable, long-lasting pipe option.
  • SRPE – SRPE provides the strength of steel and the durability of plastic. Pipe sizes range from 30” to 120″ in diameter. SRPE is lightweight and comes in longer sections, providing cost savings during construction. SRPE is corrosion and abrasion resistant and is hydraulically efficient because of its smooth interior.
  • HDPE – Corrugated double-wall HDPE is typically available in 4” to 60” diameters. Like PVC and SRPE, HDPE has a smooth interior surface that improves hydraulic function. HDPE pipe is lightweight; easy and cost-effective to install; and resistant to abrasion, corrosion, and chemicals.
  • Other Materials – Other pipe material options could include corrugated metal pipe (CMP) or high-pressure pipe such as single-wall fusion-welded HDPE. These pipe materials can be used for unique situations. CMP could be used in steep areas to reduce velocities within the pipe. In pressurized pipe situations such as a sag pipe, single-wall fusion-welded HDPE could be used to accommodate high pressures.

4. Operation and Maintenance

Operation and maintenance of pipeline systems will require routine inspections, regular clearing of debris, removal of any sediment buildup, pipe flushing, and dewatering during the irrigation off-season. When designing the irrigation pipeline, regular access points should be included with manholes every 300-500 linear feet. End treatments such as grates should be included at the inlet to prevent debris from entering the pipe and reduce safety hazards.

5. Size

Irrigation pipe has a range of sizes, generally starting at 12” and increasing in half-foot increments up to 144” diameters. Pipe size can differ from material to material, with larger pipes (>60”) more commonly found in RCP. For pipeline conversion projects, pipes should be sized to handle the maximum capacity of the canal or the full water right for the irrigation district. Desired flow rates, velocities, and pressure should all be considered when sizing pipelines.

The Extra Work is Worth It

For your next canal-to-pipeline conversion project, take the extra time and effort to consider these five things and how they might best serve your project. This is the best bet for a successful project and to achieve the most benefits for your irrigation system, the users, and those responsible for operating and maintaining the system.