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<br />siderable drop or loss of head to function accurately. .fuen such a head <br />loss cannot be tolerated, a flow meter or trapozoidal flume na.y be used. <br />Usually large canal systems have a measuring device built into the head- <br />gate. Some pumping installations are equipped with meters on the discharge <br />line. <br /> <br />Improved Methods of Irrigation <br /> <br />Level Borders or Basins - The level border method of irrigation con- <br />sists of surrounding a nearly level area with a long narrow low dike, <br />which can be filled with the desired amount of water. A temporary pond <br />is created until 'the water infiltrates the soil. Level basins are similar <br />to level borders except that the basins are generally as wide as they are <br />long, while level borders are several times longer than they are wide. <br />These systems can be adapted to automation easily or can be operated <br />efficiently by inexperienced labor. High application efficiency can be <br />obtained and runoff is eliminated. <br /> <br />~ <br /> <br />Both row crops and close grown crops are adapted to use with level <br />borders or basins as long as the crop is not affected by temporary inun- <br />dation or is planted on beds so that it will remain above the water level. <br />The area within the border must be carefully leveled. Preferably there <br />should be no cross slope and the total fall within the length of the <br />border should not exceed one-half the normal net water application depth. <br /> <br />As the intake rate of the soil increases, the stream size must be <br />increased or the run lengths shortened in order for water to cover the <br />area within the correct period of time. Large irrigation streams usually <br />require higher border ridges. Level borders are useful when leaching is <br />required to remove salts from the soil profile. <br /> <br />Graded Borders - With graded border method of irrigation, the field <br />is divided into rectangular parallel strips separated by small earth <br />dikes called border ridges. These ridges are broad and low enough so that <br />they can be planted and harvested with the rest of the field. Borders <br />are usually level or nearly level across the border strip, but have slope <br />in the direction of irrigation run. <br /> <br />d <br /> <br />o <br /> <br />The graded border method is adapted to close growing crops. A stream <br />of water is introduced into the upper end and it flows across the field in <br />a sheet between the border dikes. By selecting the proper stream size, <br />efficient irrigation application results. <br /> <br />Ideally, graded borders should have a uniform slope in a downfield <br />direction. When this is not pOSSible, the steepest slope should not be <br />greater than twice the flattest and the slope should either steadily <br />increase or decrease in a downstream direction. Undulating slopes are <br />inefficient. <br /> <br />Sprinkler Irrigation - The sprinkler method applies the irrigation <br />water by means of a spray somewhat resembling rainfall. Sprinkler systems <br />must be designed to meet specific conditions. The Nevada SCS Irrigation <br />Guide gives the required information concerning: <br /> <br />B-2 <br /> <br />r r ~~ ~ <br />00~~~~ <br />