Laserfiche WebLink
<br />7 <br /> <br /> Table 2. Change in River Stage as Flow Changes <br /> ChanQe in River StaQe (feet/hr) <br /> Location @ 2,500 cfsjhr @ 4,000 cfsjhr Difference <br /> USGS gauge below <br /> Glen Canyon Dam <br /> from 5,000 cfs 1.26 1.92 0.66 <br /> from 15,000 cfs 0.80 1.23 0.43 <br /> USGS gauge at <br /> Lees Ferry <br /> from 5,000 cfs 0.84 1.27 0.43 <br /> from 15,000 cfs 0.47 0.73 0.26 <br />Note: Lees Ferry calculations do not account for attenuation <br /> <br />To place this in perspective, it should be noted that the increased upramp <br />rate is still far below the upramp rate under the no action alternative which <br />was limited only by the physical capability of the powerplant. <br /> <br />B. IncreasinQ the Maximum Flow <br /> <br />The maximum flow cap of 20,000 cfs was established in 1991 based on the <br />preliminary information and results. It was agreed by the scientists that the <br />interim flow period should be a period of storing sediment. In order to store <br />sediment during this period, the maximum flow criteria of 20,000 cfs was <br />implemented, realizing that is was a conservative limit. <br /> <br />As shown in Table 3, increasing the maximum flow from 20,000 cfs to 25,000 cfs <br />will result in a 1.37 foot (16 inch) increase in river stage at Glen Canyon <br />Dam. At Lees Ferry, the increase in stage will be 0.76 feet (9 inches). <br /> <br />Table 3. River Stage and MaximUl Flow <br /> <br /> River StaQe (feet) <br />Location @ 20,000 cfs @ 25,000 cfs Difference <br />USGS gauge below <br />Glen Canyon Dam 35.53 36.90 1.37 <br />USGS gauge at <br />Lees Ferry 10.57 11. 33 0.76 <br /> <br />Evaluation of the direct and cumulative effects of increasing the maximum flow <br />focused on two critical elements: (1) duration; and (2) frequency. Of <br />primary use were the sand balance analysis by Randle, Strand, and Streifel <br />(1993), the flow and sediment model results of Smith and Wiele (1994), the <br />eddy model of Nelson, et. al. (1993) and the results of Budhu and Gobin (1994) <br />related to tractive force along the beach faces. Supporting documentation on <br />the status of the sediment deposits in the Grand Canyon based on ongoing <br />interim flow monitoring by Schmidt (1994), Cluer and Dexter (1994), Beus and <br />