国外在发展灌溉方面,都面临着水源严重缺乏的问题。如美国计划到2,000年时的灌溉面积要比1954年增加1倍,但引水总量只能增加5%,主要靠提高灌溉效率,节约水量;而搞好渠道防渗是节约水量的一个重要途径。美国以往对灌区建设的一般方针,除肯定有大量渗漏、影响渠道或建筑物安全以及为了保护邻近土地不受水浸等严重情况外,一 Abroad in the development of irrigation, are facing a serious lack of water problems. For example, if the United States plans to increase the irrigated area by 2,000 years compared with 1954, the total water diversion can only increase by 5%, mainly by increasing irrigation efficiency and saving water; and improving channel seepage prevention is an important way to save water . In the past, the general guideline for the construction of irrigated areas in the United States, apart from affirming a great deal of leakage and affecting the safety of channels and buildings, as well as protecting the neighboring land from flooding and other serious situations,