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<br />E:1.60 <br /> <br />Notes <br /> <br />Monitoring <br />Specific Project Features <br /> <br />, <br /> <br />The smallest scale normally considered within the salinity <br />control program is a specific project feature or onfarm <br />practice, Specific features/practices, such as canal lining <br />or reduction of deep percolation, require monitoring to <br />prove ihe feature or practice can, or has, achieved a ' <br />specific purpose, usually a reduction in seepage to either <br />ground water or a surface channel. <br /> <br />Canal Seepage <br />Canal seepage is often one of the major sources contribut- <br />ing to the dissolution and movement of mineral salts from <br />subsurface strata to natural drainages, A determination of <br />how much water is actually leaking from a canal is <br />important in estimating the salt loading caused by canal <br />seepage and the potential reduction in loading if the canal <br />is lined, <br /> <br />! <br />, <br />, <br /> <br />The methods for estimating canal seepage were originally <br />developed for application to canals where seepage loss <br />was a substantial fraction of the conveyed water. <br />However, the canals of interest in salinity studies are often <br />located in massive geologic fO\llllltions, such as the <br />Mancos shale, or in low-permeability soils derived from <br />these formations, Consequently, canals in salinity control <br />project areas may have lower seepage rates than cana1S for <br />which the seepage-estimation methods were developed, <br />and the difference between prelining and postlining <br />seepage may be small. Therefore, the accuracy of seepage <br />estimates is an important consideration. Application of <br />traditional methods of seepage estimation in salinity con- <br />trol studies requires special attention to measurement tech- <br />nique, estimation uncertainty, and site characterization. <br /> <br />I <br />. <br /> <br />12 <br /> <br />13 <br /> <br />