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<br />Changes in Channel Capacity With Time <br /> <br />For comparison, changes in the Sacramento River near Ord Bend channel between <br /> <br />1972 and 1984 have been documented for a discharge of 10,000 ft3/s (283 m3/s) <br /> <br />(table 6). Based on data collected over this period, the channel thalweg has <br /> <br />moved laterally over 100 feet (80.5 m). Unlike Pinole Creek, the channel is <br /> <br />not confined and is therefore able to migrate laterally, and a point bar on <br /> <br />the right bank is subject to continual scour and fill. For a constant <br /> <br />discharge, hydraulic properties such as area, hydraulic radius, water-surface <br /> <br />width, and depth, changed up to 87 percent from the mean for the period. The <br /> <br />changes noted are related to both low and high flows that occurred during the <br /> <br />study period. Because the comparative discharge of the study period is <br /> <br />constant but the cross-sectional area shows variations of +40 percent, the <br /> <br />mean velocity must also vary in order to maintain continuity of flow <br /> <br />Q - AlVi - A2V2 - ....AnVn <br /> <br />The changes in velocity evidently are related to local changes in slope for a <br /> <br />short reach near the site. In general, changes in channel slope are localized <br /> <br />in terms of length of reach and are for short periods of time. The subject of <br /> <br />channel slope stability is discussed in a later section of this report. <br /> <br />20 <br />