Canal Enclosure with HDPE Pipes

What is a canal enclosure, and why is it important? It all starts with water.

Irrigation is one of the most demanding uses of water worldwide. A Utah geological survey has reported that about 33% (other estimates as high as 42%) of the United States water use goes toward irrigation activities such as crop production and recreational lands (1). In 2018 alone, there were about 55.9 million acres of irrigated land in the United States (2). Surface water is the primary withdrawal source for irrigation in the United States (3). One of the primary methods for transporting this water is canals due to their cost efficiency in long distances scenarios. However, the major drawback of open canals is direct contact with the surrounding environment, resulting in multiple problems such as water evaporation and seepage loss (4).

A canal lining solution is typically adopted to limit seepage loss (5). Nevertheless, it lacks control over water evaporation while reducing the canal carrying capacity, mainly when thick concrete layers are utilized. On the other hand, recently, a solution known as “canal enclosure” has gained popularity as a means to prevent water loss while addressing public safety concerns associated with open canals in urbanized areas by improving water quality, eliminating contamination from external sources, providing redundancy for drinking water supplies, and in some cases allowing for the development of recreational projects inside the enclosed canal (6–8).

This article highlights the benefits of a canal enclosure, explores how high-density polyethylene (HDPE) pipes support better outcomes for a canal enclosure, and outlines examples of successful canal enclosures using HDPE pipes.

Benefits of Canal Enclosure

Transporting irrigation water in bare canals is susceptible to multiple problems, such as water loss due to seepage and evaporation and the impact of critical periodic droughts. For instance, seepage loss is a function of the canal discharge rate and depth (Figure 1), accounting for about 20% to 30% of the total flow volume in unlined earthen canals (9). To limit this water loss, engineers suggest applying lining material. However, this solution does not address water lost to evaporation (Figure 2).

Additionally, linings in irrigation canals are often seen as a poor stopgap to water loss (10). A survey revealed that most organizations did not view linings as a viable long-term solution (Figure 3). These issues in open canals negatively affect shareholders, local communities, and the local economy. Therefore, the canal enclosure technique is typically applied to prevent seepage and evaporation losses while addressing drought-associated concerns (11).

Canal enclosures can also improve water quality by preventing contact with the canal surface and the surrounding environment (8). Besides, it restores and increases the water transportation system’s reliability and capacity through the ability to pressurize water (12). Another advantage of canal enclosure is allowing for potential recreational projects such as the active transportation infrastructure in the case of the Provo Reservoir canal enclosure project, where pipes were used to save space in the canal corridors while restoring and increasing its capacity (6, 13).

A summary and case study about the importance and benefits of canal enclosure from the Provo Reservoir canal project are shown in Table 1.

Table 1. Benefits of canal enclosure projects to shareholders, local communities, and the local economy (6).

Advantage	Description	Example from the Provo Reservoir canal enclosure project
Water Savings	Water loss is typically caused by seepage and evaporation. Accordingly, enclosing canals with pipes helps preserve water	The project saves approximately 2.6 billion gallons of water per year since the unlined canal was losing 8% to 10% due to seepage and evaporation.
Environmental Benefits	The saved water is kept in the original river or lack which helps fish species and can be used for any environmentally friendly project.	The saved water remains in the Provo River to provide in-stream flows to recover fish species listed as endangered in April 1986.
Improving Water Quality	The water flowing in open canals is kept in direct contact with the surrounding environment, which causes contamination.	The open canal system receives unwanted storm drainage runoff from the surrounding communities along the canal, which reduces the quality of the water. Using a canal enclosure can solve this issue.
Restore and Increase Canal Capacity	Sediment deposits and vegetation growth are among the major problems that cause a reduction in the effective canal capacity.	Enclosing the Provo Reservoir canal helps increase the canal’s maximum capacity from 550 cfs to 630 cfs.
Increase Reliability	Canal enclosure with pipes allows the development of a pressurized system that increases the reliability of the canal.	Before the canal enclosing, its demand for delivering irrigation and secondary water was 85%. The enclosure project is expected to increase the long-term reliability of the system.
Enhance Safety and Security	Providing security and public safety by preventing drowning deaths through enclosing canal water with pipes.	A total of 22 deaths were associated with the open canal due to drowning. This project will help ensure no such accidents in the future.
Recreational Trail	Canals enclosures save space in the canal’s corridor while transporting the volume of water through the pressurized system.	Upon completing the project, a $17 million project will start to build a trail within the canal right-of-way by Utah County to provide an aesthetically pleasing recreational facility.

Canal Enclosure with HDPE Pipes

Pipeline material selection is among the most critical factors that affect the performance and success of any canal enclosure project (6). Typically, various design considerations must be addressed when selecting the appropriate pipe material, including the pipe type, load-carrying system, corrosion protection, leakage rate, and suitability for pumping water.

A comparison between concrete, steel, and HDPE pipes emphasizing design considerations is shown in Table 2. It can be seen that, unlike concrete and steel pipes, HDPE pipes present greater flexibility and durability and lower seismic susceptibility. Moreover, it provides a low leakage rate and biofilm’s formation potential, highlighting its capability to preserve water quality while transporting it.

Table 2. Advantages of HDPE pipes over the steel and concrete pipes (15–19).

	Concrete	Steel	HDPE
Pipe type	Rigid	Rigid	Flexible
Load-carrying system	Pipe-soil system	Pipe-soil system	Soil-pipe system
Seismic vulnerability	High	High	Low
Corrosion resistance	Low	Low	High
Oxidation resistance	Low	Low	High
Leakage rate	High	Low	Low
Biofilms’ formation potential	Low	High	Low
Overall suitability for pumping water	Less	Less	More

Enclosing or covering the canals is challenging owing to the irrigation rotation, low depths, and widths of irrigation canals (20). Hence, HDPE pipes are suitable for canal enclosure projects, owning the flexibility that helps in very winding canals. Furthermore, HDPE pipes’ advantages in minimizing the impact due to operating pressure and the potential of possible seismic activity have motivated decision makers to adopt HDPE pipes in enclosing canals such as the recent Steinaker service canal (21).

This paper has focused on discussing the benefits of canal enclosure and highlights the advantages of using HDPE pipes over other alternatives. On the bases of the statements above, the following conclusions are drawn:

Summary

• Water loss due to evaporation is a critical factor that can go up to 30% of the seepage. This issue can be effectively prevented by adopting a canal enclosure solution.
• A canal enclosure provides a better alternative to lining when issues such as total water savings, canal reliability, and safety and security concerns.
• HDPE pipes provide a better alternative to rigid pipes in winding canals due to the material’s enhanced flexibility.
• The service life expectancy of an HDPE pipe is higher than that of steel and bare concrete due to its improved durability and chemical resistance.

Figures

Figure 1. Relation between canal parameters and water losses (14).

Figure 2. The ratio of seepage loss to evaporation loss over 50 different canals (14).

Figure 3. Percentage of organizations citing differing reasons for not lining conveyance infrastructure (10). Organizations can cite multiple reasons for not lining main and lateral canals.