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. >> In the above equation, the term 0.2..tVV approximates the wetted area eT mile of the canal. This approximation is relatively accurate for ~opezoidal earth-lined canals. The main problem in estimating seepage lpsses in water delivery canals ies in the proper selection (adaption) or measurement of the term C in ~uation 2.6. Research results give diverse values of the seepage rate C. elected publications containing applied data include Lining for Irrigation lOals (USBR, 1961), Irrigation Canal Lining (Kraatz, 1971), Estimation of eepage Losses from Lined Channels, Canals and Related Structures (USBR Design . tandard No.3, 1967), and Earth Lining for Seepage Control: Evaluation of Ffectiveness and Durability (Dedrick and Lauritzen, 1974). The Dedrick and Lauritzen (1974) publication is at present unique and )$t useful in that it presents information on the durability.of earth materials led for seepage control in earth canals. Dedrick and Lauritzen, summarized Lta and analysis relative to the performance of earth-lining materials ~r a l4-year period. Additionally, the effectiveness of.materials has en tested each year for four successive 25-day periods of observation. Two classes of USBR lining materials--clay loam and silt clay loam-- .3 2 re found to have a 14-year average seepage rate of 0.32 ft 1ft Iday. Silt, . .3 2 am averaged 0.48 ft 1ft Iday. These values are averages of the four 25- , successive periods of flow in the canals each year. The seepage rate during the first year for all these materials was , .3 2 Lerally 0.15 oft 1ft Iday or less which appears to be consistent with USBR . ldings for such short periods. However, these initial rates increase eral fold with age. For example, the rate ros~ to an average of 0.46 ;ft2/day in 10 years for the silt clay loam (Dedrick and Lauritzen, 1974). " Ii