Canal Lining Studies
The Bureau of Reclamation - Pacific Northwest Region conducted a "Canal-Lining Demonstration Project" which began in 1992. Thirty-four canal lining test sections were constructed in 11 irrigation districts located in four states. The purpose of this extensive project was to assess the durability and effectiveness of various lining methods over severe rocky sub-grades.
The "The Year 10 Final Report" has been issued and is available at their website. There are also detailed reports of each installation and periodic inspection reports. Comparison charts of costs, durability, effectiveness and benefit/cost (B/C) ratios provide valuable insight into canal liner selection criteria.
Difficulties of Liner Installation
Liners must be installed late in the fall after the irrigation season or early in the spring before the water is sent down the canal. Some of the reports told of freezing cold temperatures, rain and wind which made liner installation and splicing difficult. One hot-melt splicing system was abandoned and hot tar was used. Another project encountered high winds and sand bags were used to hold the liner in place until it could be properly secured. One design using 200' sections required nineteen men to pull it into position on the side slopes. Many canals have limited access to one or both sides which eliminates liner methods like concrete that require access by heavy equipment.
The Executive Summary by the Bureau of Reclamation is very detailed and should be consulted for liner decision making information.
The final report rated each test installation by construction cost, durability, maintenance cost, and efficiency (seepage reduction). Then each was given a benefit/cost ratio. The B/C ratio estimates the number of dollars returned for each dollar invested using an average cost of water. Finally, the 34 lining methods were grouped into four major types and broad conclusions were given.
Fluid-applied Membrane - Received the lowest B/C ratio (0.2 to 1.5) and this group was considered to have potential only in niche applications. Most of the problems were related to poor quality control due to adverse weather conditions during installation.
Concrete - Was given a B/C ratio of 3.0 to 3.5. The initial cost is high but durability was 40 to 60 years. However, effectiveness of seepage reduction dropped to 70% because of random cracking.
Concrete with Geomembrane Underliner - This was given the highest B/C ratio of 3.5 to 3.7. Seepage reduction was 95%. The construction costs are nearly double those of exposed geomembrane liners and access for heavy equipment is necessary.
Exposed Geomembrane - Had the widest range of cost and durability. Consequently the B/C ratio also had a wide range, 1.9 to 3.2. Seepage effectiveness was rated at 90%. The reason for the wide B/C range is that some tests used thin membranes (30 - 40 mil) of various polymers, with and without geotextile backing, that did not score well. One test used a heavy (80 mil) HDPE that received a very good B/C ratio of 3.2.
The report stated that each lining alternative offered advantages and disadvantages.
Field splicing of geomembranes was usually a major liner design consideration and on some tests did not go as planned during installation. Further, liner materials expand and contract due to seasonal temperature change which can cause splice failure. There is an absence of information in the inspection reports regarding the success or failure of the field splices.