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- 154. GROUNDWATER HYDROLOGY <br /> GROU, <br /> 60 <br /> t 50 <br /> { <br /> i as <br /> e _ <br /> 3 30 <br /> p ''Drawdown I blhZe: <br /> 20 series <br /> I. , <br /> 4 'Increr. <br /> proxii <br /> s 10 ' k <br /> shoulc. <br /> Well loss' r." in Ord' <br /> con , k <br /> _ Fror,. <br /> 00 5 10 15 <br /> Well discharge, Q,1000 meter!s3lday <br /> Fig:4.30 . Variation of total drawdown s;. aquifer.Ioss BQ, Theref <br /> and well loss CQ"'with well discharge (after Rorabaugh55). -r straight <br /> by the 1 <br /> increases the discharge'"only 10 percent..When the comparison is <br /> "=' ' interce <br /> extended to include well loss, however, the effect is significant. Rorab <br /> Doubling the well radius doubles the intake area, reduces entrance determ� <br /> velocities to almost half, and (if,n = 2)cuts the frictional loss to less <br /> than a third For axial flow within the well;,the .area.increases four <br /> times, reducing this loss an even greater extent.' <br /> Itis apparent that the well loss can be a substantial fraction of :.. :: If disc <br /> J total drawdown wheni,pumping rates are 'large, as illustrated by copacit <br /> Fig.'4.30. With proper design:and development of new wells (see tivity 01 <br /> f „Chapter 5), well losses can be minimized. Clogging or deterioration - the well <br /> of well screens can increase well losses in old wells.36 Based on field .(.Eq. 4.4i <br /> experience Walton70 suggested criteria for the well loss coefficient C <br /> in Eq 4.67. These are presente.d.in Table 4.4'to aid in evaluating the <br /> condition of a well <br /> v Loss. To evaluate well loss aste -drawdown so that t <br /> E aluadon of Well a •, p r <br /> pumping test is required. This consists of pumping a.well initially <br /> at a.low rate until the'drawdown within the.well essentially sta- " <br />