Colorado Water Resources Circular No. 20

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0754 Channel Storage Even if no losses or ains occur in a reach o ha g f channel, the shape of an upstream hydrograph will be modified downstream by the storage characteristics of the channel. The effect of channel storage can be determined by various routing methods. In a recent study, Sauer (1971) successfully used the unit - hydrograph technique to route releases from Toledo Bend Reservoir to three locations as far as 50 miles down the Sabine River on the Texas - Louisiana State line. As part of the Sabine River study, a computer program was developed which routes reservoir releases by the unit - hydrograph technique. This program was used to determine the effects of channel storage along the Arkansas River from Granite to Avondale (fig. 2). The hydrographs at the Granite gaging station for eight actual reservoir releases were routed approximately 170 miles downstream by means of the program. The releases selected for study included a variety of release discharges and antecedent river conditions. The results of this analysis were used to define channel storage as a function of time. This relationship is shown in figure 4. Figure 4 shows that although the rate at which release water enters channel storage is initially high, it decreases rapidly with time and ceases in from 7 to 31 hours depending on the amount of the release. Figure 4 also gives a table which summarizes the average channel storage for selected time intervals. Bank Storage If the alluvium and river are hydraulically connected, an inter- change of water is possible. For example, if the stage of a river increases, flow which normally occurs from the alluvium to the river may be reversed, and bank storage occurs. Two approaches to define bank storage during reservoir releases were investigated. The first approach was to study streamflow gains and losses before and during a reservoir release. The second approach was to monitor head changes in observation wells near the river as a release passed. Gain -loss studies During August 28 -31, 1970, in the reach from Turquoise Lake to the Arkansas River at Nepesta gaging station, gain -loss investigations were conducted within 36 hours before and 24 hours after the passage of a 392 -ft /s release to Colorado Canal. The study involved measurement of 235 inflows, 58 outflows, 15 miscellaneous mainstem sites, and 12 main- stem gaging stations. The flow at each mainstem gaging station was inde- pendently measured by two hydrographers to insure accurate determination of river flow. The same procedure was used during a second series of 11