Threats to Wildlife and the Platte River

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WILDLIFE p. 37 will probably continue to decline, even with the 1100 cfs" (p 5), he recommended this flow rate. FWS followed Boudreaux's suggestion, dutifully quoting (though not citing) the original report's contention that the meadows will probably continue to decline, while still recom- mending 1100 cfs ( USFWS 1983, p 9). Subsequent reports continue to rely on this figure (i.e., USFWS 1987b, p 16). N This number seems to have been arrived at by compromise: "According to studies conducted by Currier, VanDerwalker, and Lingle (1982), an average of 25 percent of the channels would have a width of 500 feet or greater at a flow of 2,020 cfs (average based on analysis at three different sites between Overton and Grand Island). At a flow of 1,070 cfs, no channels of 500 feet or greater would be present. At a flow of 2,020 cfs, the percentage of channels 500 feet or greater increases from 17 percent at the Grand Island site, to 27 percent at the Wood River site to 30 percent at the Audubon site. Percentage of channel width 500 foot [sic] or greater that would be present with 2,020 cfs at the Audubon and Wood River sites would appear adequate for whooping cranes. Flows at Grand Island of between 1,070 cfs and 1,500 cfs could reduce the percentage of channel width 500 feet or greater to 0 percent and approximately 8 percent respectively, which in our opinion would be insufficient for the needs of whooping cranes in that area ... Flows of 1,700 cfs in the river between Overton and Grand Island should be adequate for whooping cranes during the migration periods, provided vegetative encroachment is controlled with mechanical cleaning and/or scouring flows." (NGPC 1985a, p 19). O Based on empirical measurements at eight segments of the Big Bend area of the river, and assuming that channels must be at least 500 feet wide in order to be acceptable to Whooping Cranes. This flow is based on average channel widths at all measured sites under present conditions. No assumptions are made about possible future changes in river morphology. Ziewitz' model "uses physical measurements of the river collected according to the Instream Flow Incremental Methodology (Bovee 1982)" during 1983 -1986 (p 1). "The purpose of the model is to quantify the relationship between river discharge and roost habitat" (p 3). To assess the amount of roosting habitat available at different flows, Weighted Usable Area criteria- -which were arrived at by consensus during a Whooping Crane habitat criteria workshop (Shenk and Armbruster 1986)- -were used. A flow of "approximately 2000 cfs provides the most roost habitat of the highest quality at all sites" (Ziewitz 1987, p 10). However, criteria in Shenk and Armbruster are not necessarily definitive; e.g. aspects have been criti- cized by the USFWS (1987a, p 4). P Ninety percent of Whooping Crane sightings since 1966 occurred at flows "no lower" than 1200 cfs. In spring, "the minimum flow used by whooping cranes was 1240 cfs... 15 of the 34 whooping cranes sighted on the Platte between 1966 and [early] 1987 were on the river when flows were within the narrow range of 1,200 to 1,240 cfs" ( USFWS 1987b). Note that the recommended flow is lower than the flow that actually occurred when Whooping Cranes used the river in spring. Q Least Terns and Piping Plovers have similar nesting site requirements, often breeding together in the same colonies. R This number was developed by consensus opinion by NGPC fisheries biologists (R. Lock 1988, pers. comm.). It appears in a 1983 draft of the Little Blue - Catherland Opinion, and in the final version (NGPC 1985a), where it is not referenced nor is its derivation explained. This number, like several other proposed target flow numbers, has been widely cited. No data were collected specifically to determine minimum flows for the maintenance of fish for Least Terns. It was meant as an absolute minimum fish survival flow. NGPC no longer supports this figure,