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0757 Effective river miles represent the length of theoretical channel. having specific values of T and S which produce the same bank storage effects as the natural channel. Table 3 gave calculated bank storage after 16 hours as 116 and 90 ft~/s for the reservoir releases of August 29, 1970, and August 22, 1972, respectively. For the antecedent river conditions and release discharge of these two releases, equation 1 with T=4,760 ft2 per day: S=0.15, and t=16 hours, gives bank st01:age r.ates of about 1.4 and 1.7 ft3/s per mile, respectively. Consequently, the number of effective river miles would be 83 (116 ft3s-l/l.4 ft3s-1 mi-I) and 53 (90 ft3s-l/l.7 ft3s-1 mi-I), or an average of about 65 miles (the. release of August 22, 1972, was weighted slightly more due to the favorable conditions at this time).. . ~;. By combining selected So yalues with equation 1 for 65 effective river miles, bank storage along the Arkansas River .from Twin Lakes Reservoir to Colorado Canal was determined for various antecedent river conditions (flows at Wellsville,. 07093700) and release discharges. The results from the calculations are summarized in table 4. Figure 6 is a nomograph developed from table 4 and shows average rate of bank storage during selected time intervals measured from the time of arrival of the release at the Colorado Canal. The nomograph shows that although the rate at which reservoir-release water enters bank storage decreases rapidly, large amounts of release water continue to enter bank storage days after the release has arrived at Colorado Canal. Early in the release period,. all release water may enter bank. stora"ge. Inadvertent Diversions It has long been recognized that the increase in river stage during a reservoir release caused ditches along the river to divert more water. This additional water which ditches divert during a release is termed inadvertent diversion. Ditches upstream from Salida, Colo., are especially subject to inadvertent diversions. Ditch systems along this reach of the Arkansas River typically consist of a manmade rock and gravel diversion dike, a .wooden sluicing structure some distance down the ditch, and a Parshall measuring flume downstream from the sluicing structure. As a result of the unsophisticated nature of these diversion structures, many of the ditches are unable to divert their legal water right when the river stage is low. When the stage of the river rises during a reservoir release, the ditch diverts additional water, but since the total diver- sion is usually less than the ditch's legal right no attempt is made to reduce the diversion to the original rate. Although diversions downstream from Salida are also subject to inadvertent diversions, these ditches generally have .elaborate diversion structures which reduce the magnitude of the inadvertent diversion. 17