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<br />COO:68 <br /> <br />. <br /> <br />. <br /> <br />The losses along the farm conveyance system are of several kinds, <br /> <br /> <br />but perhaps the greatest is seepage from ditches, Although seepage can <br /> <br /> <br />be reduced by lining or surface treatment, it is not usually done because <br /> <br />of high initial costs of lining material and the labor for installation. <br /> <br /> <br />Another loss, that of overtopping (spillage), can occur if ditch <br /> <br /> <br />banks are not properly maintained. These losses can cause bank erosion <br /> <br /> <br />and eventual bank failure with an associated loss. The problem is exacer- <br /> <br /> <br />bated if weeds are allowed to grow in the ditch, thus causing higher <br /> <br /> <br />resistance to flow resulting in an increased flow for a constant <br /> <br /> <br />depth for a given discharge. <br /> <br /> <br />Weeds outside the ditch cause an additional 10ss--that due to phreato- <br /> <br /> <br />phytic water use. Their removal of seepage water can increase the hydraulic <br /> <br /> <br />gradient between the canal and the surrounding soil and thus increase <br /> <br /> <br />seepage losses. They also prevent seep water from reaching the ground <br /> <br /> <br />water for later pumping or return to the river. <br /> <br /> <br />Because one turnout may serve more than one field, additional losses <br /> <br /> <br />may occur if there are leaks at farm gates. A neighbor may receive <br /> <br />leakage water, or the farmer may have some of his water delivered where <br /> <br /> <br />it is not needed or can not be used effectively. <br /> <br /> <br />A most important factor is the timing of water delivery to the farm. <br /> <br /> <br />If sprinklers are used, economics dictate a relatively constant delivery <br /> <br /> <br />rate during the irrigation season, If surface irrigation is used, it <br /> <br /> <br />is necessary to have high flow rates, but unless the farm is quite large, <br /> <br /> <br />only periodic deliveries are needed or can be used, If surface deliveries <br /> <br /> <br />occur when water is not needed, such as after a substantial rain or during <br /> <br /> <br />periods of low crop demand, that water which is not used by the system <br /> <br /> <br />is wasted whether by diversion down a drain gulch or through application <br /> <br /> <br />and subsequent deep seepage or runoff. Thus, it behooves the farmer to <br /> <br /> <br />select cropping patterns with requirements which will in some way match <br /> <br /> <br />his expected water delivery schedule. <br /> <br /> <br />The above comments pertain principally to farms and fields irrigated <br /> <br /> <br />with surface water from mutual canal and reservoir systems. Some of the <br /> <br /> <br />factors causing reduced efficiencies are overcome on farms and fields <br /> <br /> <br />irrigated from wells because of shorter delivery canals and the capability <br /> <br /> <br />of applying water on demand according to crop needs, <br /> <br />. <br /> <br />-11- <br />