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<br />Q()1951
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<br />Operative Areas
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<br />The concept of operative areas identifies specific processes and areas where the processes are
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<br />operative. Some processes, such as the effects of leakage from the Arkansas River or the Fort Lyon
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<br />Canal may be limited to general zones. For instance, the relatively widespread occurrence of areas
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<br />where the depth to water is less than 5 feet and the knowledge that increases in river elevations affect
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<br />increases in ground-water levels leads to the question "How far-reaching can the effecAts of the river
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<br />be?" The depth to water map shown in figure 3 is a convenient, although generl\k:irrw~sm t(1gener-
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<br />ally evaluate such a question. /""" \/.,~::--:::..,/
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<br />The depth to water map (fig. 3) generally delineates the area, cjUdhg ~\~:hiias(\r'ek'ent~riod,
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<br />where the water table is within 5 feet of the land surface. In an,.e'~anlPJ(~xer~is.e,:Sut5p<;lse that the
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<br />Arkansas River elevation increases 5 feet, compared to CP'tditio~((U::~:~~~imaOf water-level
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<br />measurements on which the depth to water map i~J:>~~"Q:'B~~s:d}'lL~~\i~ated average discharge of
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<br />100 cubic feet per second during the measuri~g'R€!~> stich arf'~cf~a~e would represent an instanta-
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<br />neous discharge of about 5,000 cubic fe~~''P~r"Sec\lnd, TI(e'lh;>'\y-duration statistics listed in table 5 indi-
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<br />cate that a daily mean discharge qf; , \ ~gpitud{pT.Qhl!:biy"~ccurs less than 1 percent of the time.
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<br />Assuming that the ArI\~s~S\~~~t it~~kt to affect its surface elevation in the surrounding aquifer,
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<br />a 5-foot increase in st!l~~~\!~J~ry~\ \~e,t}ire area on the depth to water map that is within 10 feet of
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<br />the land surface t6'b~'I!6"nlor'?'~?fe~ above the water table. In the western one-half of the study
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<br />area such a ~h~ryg~)'0~)1~a'y~i~igespread effects; in the eastern one-half of the study area, the effects
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<br />would be liJrtile'dlll\?stlt'tptre"lativeIy narrow strip.
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<br />This e"e~ci'se illustrates that the Arkansas River has the potential to effect a large part of the study
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<br />area. For instance;ln the example, if the land surface being within 5 feet of the water table is the crite-
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<br />rion used to evaluate whether or not an area is affected by the river, then the river would influence,
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<br />according to the frequency information in table 2, about 65 percent of the study area.
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<br />19
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