Laserfiche WebLink
<br />11 <br /> <br />The SCS repo.eses a value of 1.62 ac. ft./a.Jr. for the "nresent <br /> <br /> <br />condi tion" comnosi te acre (approoriate mix of various crops ~rown) and 1.90 <br /> <br /> <br />for the "future >rithout" and "future '.lith" conditons. The 1.90 fL:;ure is <br /> <br /> <br />aoparently a,dry year fi~ure in so far as the desicn charts ~e concerned. <br /> <br /> <br />IISBR's reoort states that they used 1.81 for the 1978-80 3 'rear avera''(e ideal <br /> <br /> <br />crop re~uirement. The 1980-81 ,Annual Reoort for the ~esearch Demonstration <br /> <br /> <br />farm, San Juan 3asin Research Center, Cortez Unit, showed that they aoplied <br /> <br /> <br />an avera~e of 1.0 over a 3 year ~eriod and noted that this ,ras not as much as <br /> <br /> <br />was really neerted. They also noted that rains "rere of Ii ttle value. One <br /> <br /> <br />farmer told me that he ~as anolyin~ 25 to 30 inches ~er year for alfalfa and <br /> <br /> <br />this was not enough. Con~ideri~~ a 75% effeciency for snrinklers, this would <br /> <br />be 1.5 to 1.9 for the crop. <br /> <br />Rased on the ahove, the "KRK "-ater bud'!et" uses 1.~ for "nresent", 1.75 <br /> <br /> <br />for "future '.'/ithout" an,: 1.9 for "future ',rith". r did not increase to 1.9 <br /> <br /> <br />for "future '.li thout", as SCS ,'lid, since I 'luestion that t":e e:dstin" onf:1rr.l <br /> <br /> <br />systems can effectively use all water that is made available. <br /> <br />Sprinkler Evaporation <br /> <br />Evaporation from the operating sprinklers is a loss that should probably be <br /> <br /> <br />considered in the water budget. Air temperature, wind and operating pressure <br /> <br /> <br />are factors affectin~ the quantity. SCS basic data uses an effeciency of 75% <br /> <br /> <br />for sprinkler systems. this effeciency takes into account losses due to <br /> <br /> <br />evaporation, wind drift, leaching fraction, and uneven distribution. To get <br /> <br /> <br />the gross application required, the crop irrigation re~uirement is divided by <br /> <br /> <br />the effeciency. The 75% value is a rather high figure and it is questioned <br /> <br /> <br />that this can be achieved for an average condition. How much of the remaini;ng <br /> <br /> <br />25% should be charged to evaporation is another question. So far, I dO not <br /> <br /> <br />have a good reference. For the "KRK water bud.~et". 750~ is u<::ed' for sprinkler <br /> <br />system effeciency and 5% of the gross application is allocated to evaporation <br />for all three condi tions ; evaporation in excess of that for the surface systems. <br /> <br />i <br />, <br />___.J . <br />