INVESTIGATIONS AND ANALYSIS OF SEEPAGE FROM CANALS

Abstract

Seepage from canals is a problem of great economic importance. Large portions of water diverted into them are lost through seepage. Apart from loss of the valuable irrigation water, seepage also constitutes a great danger to the adjacent land,whieh may get waterlogged due to rise in water table in course of time. Accurate determination of seepage is a prerequisite to adequate control practices. Various empirical methods of its determination. have been used from time to time. These methods give. very erroneous results as some of the most important factors~affe- cting canal seepage have not been accounted for. Because of a very complex nature of the involved boundaries-and a number of factors involved, a satisfactory formula for computation of the seepage could never be evolved. The effect of the involved factors and boundaries should, however, be known for a correct evaluation and understanding of the problem of seepage. Some factors like posi-tion of impervious layer position of water table and depth of water in the canal have been studied by the author with the help of vis-cous fluid and electric analogy models. The results have shown that the seepage increases with depth of water table and impervious la-yer. However, other factors remaining the same, the position of impervious layer does not affect the position of phreatic line appreciably. It has also been found that comparatively more seepage occurs through the sides of a canal as compared to its bed. Seepage meters can be used with advantage for meas-urment of canal seepage as they are not associated with the limi-tations of other methods like ponding inflow outflow etc., which make them to be of less practical utility. But, results obtained by U-.S.B.R. with -the -use of seepage meter showed some inconsisten-cies. Attempts were, therefore, made by the author for its further development and calibration to make it handy and accurate for field use. Partial lining as an economic alternative to full lining of irrigation channels has also been experimentally inves-tigated. The results indicate that they are capable of reducing seepage losses appreciably, but do not prevent waterlogging of the adjacent land in areas of high original water table due to their inability to lower the phreatic line.