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Missouri River has been an important site for successful spawning of the pallid sturgeon. Not withstanding that numerous existing observation indicate that important sturgeon spawning grounds are in the tributaries and not in the main stem, a purpose of this investigation is to study the relation between water temperature and the natural Missouri River hydrograph, which has been previously reported as forming a coupled cue for pallid sturgeon and other fish to spawn.

The author wishes to acknowledge the U.S. Geological Survey and the U.S. Army Engineers in making available information and data essential to the successful completion of the investigation. The review and suggestions by many individuals was useful and appreciated. The reviews of John Drew (Mo. Dept. Natural Resources), Robert Vincze (attorney and biologist) and William Beacom, (Missouri River naturalist and navigation consultant) were especially insightful.

B)

HYDROGRAPHS AT SIOUX CITY

The Sioux City hydrograph was selected for analysis because it is the closest downstream gaging station to the non-channeled river reach between Gavins Point and Ponca, Nebraska. A significant record of daily flow (66-years) exists for the gaging station at Yankton. However, this station is above most of the Ponca to Gavins Point reach. A USGS daily flow record at Sioux City exists from 1928 through 1931, and from1938 to present.

The USACE and the USGS created a synthetic discharge record from 1898 to 1928 and from 1931 to 1938. The annual average-daily discharges for the 101- year period from 1898 to 1998 in cfs (cubic feet per second) at Sioux City are shown in figure 2. The large droughts of the upper Missouri River basin are easily seen. The synthetic historical record was created because Missouri River planning during the 1940s, if based only on the record that started in 1929 and included the lengthy drought of the 30’s, would have been greatly skewed toward non-typical drought flows (McAllister, 2003, written com.)

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