Laserfiche WebLink
<br />that SOllIe lands east Qf U.S. Jl'1ghway 285 beClll.Dle seeped. . 'fl4s led ta <br />the famat10n €If the :Elia Grande Drainage Distnct in 1920. ' <br /> <br />Fazmers in this general area are callfronted with the unsatis- <br />factary situatian €If practiciDg subirr1gation. with illadequate- late season <br />water. III the past, during Jleriods €If drought, :f'amers in the area have <br />constnlcted pump wells as a survival measure. 'l'l1e P\lD\'Ping €If, wells, <br />tapping the shallOW water aquifer, precludes subirrigatian in this area. <br />This results in reduced crop productica caupled with increased productian <br />costs ta the extent that fanning in the general area has becOll1e a marginal <br />ape ration except in years €If good Yater supply. <br /> <br />Solutians Considered <br /> <br />Artificial barriers. Recellt drought periods have magnified the <br />problems €If the area and proposals haVe been made to explare methods of <br />reducing ar restricting ground water mavement. ' <br /> <br />Figure 9 shows schematically the ground water conditians that <br />wauld prevail during periods €If plentiful water supply. In this iutaJlce, <br />the inflow is equal ta the aut:flow plus crop consumptive use. As lcng as <br />this cGlIlditian prevails, there is na clum.ge in ground. water s1;crage. <br />Figure 10 is a schematicdie.g:ram of the conditicns that would develop <br />with reduced in:flow if a barrier were constructlltd. Under thos. ccn- <br />ditions, a waterlogged ZC:lle would be formed '1IIlmediatlltly upstream. :f'l"OIII the <br />barriers, falloved by a narrow bud €If' land where the water table wauld be <br />at a depth suitable far SUbi,rrigatioll, and this llaad would l.?e fallowed by <br />a drought zone. Even though the ia1'low and out:flow are appruimate1y <br />equal, the quaati1;ies illvalved are too SllIIIlll tc maintain the ground water <br />gradients shOll'll. in Figure 9 which are :IleCelisary far successful sub- <br />irrigatiaa practices. <br /> <br />The cost €If Sealing off or restricting the movement of ground <br />water from a 160-acre tract in this general area is, estimated ta be about <br />$1.0,000. It was COJl.cluded that canstructian o:e a 'barrier ta restrict <br />or retard the movemelllt €If ground water to aid subsurf'ace irrigatian would <br />aot be practical. <br /> <br />Resumptiall. of histaric practices. .Alla1yses of rates and <br />quantities of ground. water movement are possible mathElllll!l.tie&lJ.y by use <br />of Darcy's Lawwhieh ,was developed from. IlI8Jly studies €If the :flow €If <br />:fluids through porous IlUll.terials. The law is stated eoneise1y as <br />Q = O.OOll2'fIL. . <br /> <br />Q is the volUllll!l €If water ill acre-feet per year that Will move <br />through a plane, per,pelildicuJ..e.r to the directian €If ground water movement. <br />. , <br /> <br />T is a mea.sure €If tl1e rate €If water mavement through a unit <br />portion of the aquifer e.ad. is gellerally detenniaedby pllIIql tests or in <br />the laboratary. ,Far these analyses.a range €If values was US.f.'a. Yh:1~ is <br />estimated ta illclll.de aettie.l values. . C.... ... . <br /> <br />Rev. 10-29-64 <br /> <br />46 <br />