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<br />000902 <br /> <br />may be because this range of flows provides a fairly continuous <br />wetted area within the channel. Field experience suggests that <br />below this range the wetted area within the channel diminishes <br />more rapidly as flow is reduced and wetted areas become more <br />discontinuous. IFIM hydraulic simulations conducted by the U.S. <br />Bureau of Reclamation confirm that as flow decreases the wetted <br />area gradually and uniformly decreases until about the 1200-1300 <br />level, then wetted channel area rapidly decreases (see Figure <br />D1) . <br /> <br />Table 1. Platte River discharge during the periods <br />used by whooping cranes groups, ranked from lowest to <br />hiqhest. <br /> <br />Flow (cfs) <br />580 <br /> <br />838 <br />842 <br />920 <br />1200 <br />1210 <br />1240 <br />1240 <br />1250 <br />1560 <br />1670 <br />1800 <br />1820 <br />1820 <br />1870 <br />1870 <br />2125 <br />2260 <br />2265 <br />2290 <br />2293 <br />2860 <br />3096 <br />5090 <br /> <br />Date <br />10/26-27/90 <br />808 4/16-17/89 <br />10/31-11/1/74 <br />11/4/89 <br />10/13-14/89 <br />10/20-21/66 <br />10/27/83 <br />4/18/75 <br />4/20/75 <br />3/24-4/14/89 <br />3/29/77 <br />10/21-22/87 <br />10/21/85 <br />4/10-11/92 <br />4/10/92 <br />4/10-11/92 <br />4/14/92 <br />4/1-11/88 <br />4/04/88 <br />3/24-26/88 <br />4/14-15/90 <br />3/26-4/7/88 <br />11/5/86 <br />3/17-4/15/87 <br />4/17-18/80 <br /> <br />No habitat factors are known that would account for the group of <br />four whooping crane sightings that have occurred in the 800-920 <br />cfs range. <br /> <br />Use of the river by a group of whooping cranes for an extended <br />period of time are as follows: 30 days/2420-5070 cfs; 13 <br />days/2150-2680 cfs; 11 days/1970-2290 cfs; 22 days/745-1710 cfs. <br />All four instances occurred during the spring. Reasons for the <br />prevalence of spring sightings (16 of the 25 confirmed sightings) <br /> <br />5 <br />