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Canal designers usually specify the use of some kind of lining to reduce seepage and the resultant water loss. Lining materi- als typically consist of compacted clay, concrete, or geomembranes (plastic liners). 25 reduce irrigation water shortages, and bene- fit recreation, fish, and wildlife. Reclamation serves as the technical lead in a cooperative program to develop low- cost, durable canal linings suitable for Alternative Canal Linings - Deschutes Demonstration Project JAY SWIHART Materials Engineering Branch Older canals are often unlined, and can have high seepage rates depending on the permeability of the native soil. The north- western United States has extremely permeable soil and severe (angular) geo- logic conditions, including highly fractured basalt, loose pumice stone, and other porous materials. These angular subgrades often cause damage to geomembrane liners that are susceptible to sharp objects. A 1972 Reclamation report estimated that unlined irrigation canals in the upper Deschutes River basin, Oregon, lose about 500,000 acre-feet of water per year through seepage. To put that loss in per- spective, the average household uses between If2 and 1 acre foot of water per year. In some canal reaches, seepage causes up to 50 percent of the irrigation water loss. Recent ponding tests found av- erage seepage rates on sections of the Arnold and the North Unit canals of the Deschutes Project ranging from 0.64 to 4.20 ft3fft2fday. These rates represent increases of one to two orders ofmagni- tude over the average seepage rate of 0.07 ft3fft2fday for a well-built, concrete- lined canal. Water saved through lining can enhance and stabilize river flows, installation over severe subgrade condi- tions. Collaborators include Reclamation's Denver Office and Pacific Northwest Region, Arnold Irrigation District, North Unit Irrigation District, Oregon Water Resources Department, and about a dozen material suppliers and installation contrac- tors. Other Reclamation Regional Offices and irrigation districts are expected to join in the effort beginning in Fiscal Year 1994. Material suppliers and installation con- tractors were encouraged to provide new materials and installation techniques that could accommodate severe subgrades, form a watertight membrane, resist weath- ering, provide slope stability, accommodate subgrade movement, and resist animal damage and vandalism. Effectiveness of the canal linings will be determined by comparing the seepage data from the ponding tests performed both before and after installation. Durability will be assessed from future (years 5 and 10) ponding tests, annual O&M reports, visual inspections, and periodic coupon testing. Initial construction costs, O&M costs, seepage costs, and durability (life expectancy) will determine life-cycle costs.