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0757 <br />Effective river miles represent the length of theoretical channel_ <br />having specific values of T and 'S which produce the same bank storage <br />effects as the natural channel. 'Table 3 gave calculated bank storage <br />after 16 hours as 116 and 90 ft /s.for the reservoir releases of August <br />29,.1970, and August 22, 1972, respectively. For the antecedent river <br />conditions and release discharge of these two releases, equation 1 with <br />T =4,760 ft per day, S =0.15, and t =16 hours, gives bank storage rates <br />of about 1.4 and 1.7 ft /s per mile, respectively. Consequently, the <br />number of effective river miles would be 83 (116 ft -1 /1.4 ft -1 mi -1 ) <br />and 53 (90 ft 3 S -1 /1.7 ft -1 mi -1 ), or an average of about 65 miles <br />(the release of August 22, 1972, was weighted slightly more due to the <br />favorable conditions at this time). <br />By combining selected s values with equation 1 for 65 effective <br />river miles, bank storage along the Arkansas River.from Twin.Lakes <br />Reservoir to Colorado Canal was determined for various antecedent river <br />conditions (flows at Wellsville,:07093700) and release discharges. The <br />results from the calculations are summarized in table 4. Figure 6 is a <br />nomograph developed from table 4 and shows average rate of bank storage <br />during selected time intervals measured from the time of arrival of the <br />release at the Colorado Canal. The nomograph shows that although the <br />rate at which reservoir - release water enters bank storage decreases <br />rapidly, large amounts of release water continue to 'enter bank storage <br />days after the release has arrived at Colorado Canal. Early in the <br />release period,, all release water may enter bank storage. <br />Inadvertent Diversions <br />It has long been recognized that the increase in river stage during <br />a reservoir release caused ditches along the river to divert more water. <br />This additional water which ditches divert during a release is termed <br />inadvertent <br />Ditches upstream from Salida, Colo., are especially subject to <br />inadvertent diversions. Ditch systems along this reach of the Arkansas <br />River typically consist of a manmade rock and gravel diversion dike, a <br />wooden sluicing structure some distance down the ditch, and a Parshall <br />measuring flume downstream from the sluicing structure. As a result of <br />the unsophisticated nature of these diversion structures, many of the <br />ditches are unable to divert their legal water.right when the river <br />stage is low. When the stage of the river rises during a reservoir <br />release, the ditch diverts additional water_, but since the total diver- <br />sion i"s usually less than the ditch's legal right no attempt is made-to <br />reduce the diversion to the original rate. <br />Although diversions downstream from Salida are also subject to' <br />inadvertent diversions, these ditches generally have,elaborate diversion <br />structures which reduce the magnitude of the inadvertent diversion. <br />17 <br />