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<br />0:)13 Jf <br /> <br />.->' <br /> <br />h = H <br /> <br />n=CiJ <br /> <br />~e <br />rrLn <br /> <br />n""':l ~ 3, 5. . . <br /> <br />nZrrZ crt <br />L' <br /> <br />S. nrr <br />m~x <br /> <br />. . . (6) <br /> <br />The part of the drainable volume remaining can be obtained from this expression <br />in the form: <br /> <br />\>dX <br /> <br />HoL <br /> <br />n= 00 <br /> <br />= <br /> <br />8 <br />rrz <br /> <br />e <br />7 <br /> <br />nZrrZ cr t <br />L' <br /> <br />. . . (7) <br /> <br />n=I,3,5... <br /> <br />A plot of this expression is shown on figure 3. These expressions may be used <br />to estimate drainage rates to parallel drains a distance L apart. or. since <br />there is no flow across the plane at x = L /2 they may be used to estimate the <br />return flow due to deep percolation losses from irrigation in an irrigated river <br />valley of width L with the river in the middle of the valley. <br /> <br />I <br />I <br />I <br /> <br />Nature of the solutions <br /> <br />The condition of continuity described above is of a budgetary nature and <br />imposes the requirement that the total flow across the boundaries and the water <br />remaining in storage must equal the volume originally present in the aquifer. <br />This condition is imposed upon the solutions and it follows that the amounts of <br />water involved are exactly accounted for even though the differential equation is <br />an exact expression of the physical conditions only if the rise or fall of the water <br />table is infinitesimally small when compared with the original saturated depth. <br />Whatever inaccuracies there may be will then appear only in the estimate of the <br />time required for the changes to take place. The movements of ground water are <br />treated as transient phenomena by these methods. This idealization will be <br />found to accord well with the conditions to be found in the field. <br /> <br />Comments: <br /> <br />I <br />I' <br /> <br />I, <br /> <br />Plans for engineering works to promote the conservation of water and to <br />provide for its effective use have generally been concerned with surface waters <br />only. Such plans are usually based upon studies utilizing the records of runoff <br /> <br />" <br /> <br />-5- <br />