A curve was manually fit to the data in figure 8. A rating table was made from the curve (fig. 9). The rating table, which is included as Appendix A, was used as a lookup table to calculate the stages (gage heights) for the nearly 10,000 ‘run of the river’ daily discharges provided by USACE. It is realized that the stage- discharge relation even before anthropogenic affects relating to the channel changing form in response to the channel responding to the last high flood event. However, on the average, a typical flow discharge relation existed. For analysis purposes, the 1938-1939 relation was used to back calculate the river probable gage heights at Sioux City. The gage heights can be considered as the gage heights that would have existed if the 1938-1939 stage-discharge relationship were constant from 1929-1955. This is especially useful as it allows comparison of different discharge scenarios during the interval of study. For example, it may be desirable to ascertain how much flooding would likely occur at a particular discharge during the interval of interest.
1938- 1939 RATING TABLE DATA
Figure 9. 1938-1939 Stage-discharge relation for the Missouri River at Sioux City. Based on 1938- 1939 USGS measurements with supplemental 1952 high flow measurements.
It is also useful to investigate the ‘natural’ hydrograph in relation to water temperature. For example, it has been stated that a spring rise is essential to cue the pallid sturgeon to spawn. Historical water-temperature data for the Missouri River prior to 1980 is non-existent or sparse at most locations. However, in 1948 the USGS initiated water-temperature measurements at Sioux City in addition to making stage measurements to correspond to the water-discharge measurements. Typically, the USGS measured water temperature and air temperature twice weekly, especially from spring to winter. These periodic measurements form a valuable record; however, the records do not exist from 1929 to 1948, and also, they are not daily measurements, which are desirable. Inspection of the