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1931 DISCHARGES AT SIOUX CITY

60.00

50.00

40.00

Discharge (kcfs

30.00

20.00

10.00

0.00

1/1/1931 1/8/1931 1/15/1931 1/22/1931 1/29/1931 2/5/1931 2/12/1931 2/19/1931 2/26/1931 3/5/1931 3/12/1931 3/19/1931 3/26/1931 4/2/1931 4/9/1931 4/16/1931 4/23/1931 4/30/1931 5/7/1931 5/14/1931 5/21/1931 5/28/1931 6/4/1931 6/11/1931 6/18/1931 6/25/1931 7/2/1931 7/9/1931 7/16/1931 7/23/1931 7/30/1931 8/6/1931 8/13/1931 8/20/1931 8/27/1931

USGS

Run of the River

Figure 6. 1931 USGS and ‘run of the river’ discharges of the Missouri River at Sioux City. Data from USGS and USACE.

The comparison is considered adequate, and, thus, the ‘run of the river’ flow hydrograph was used as a surrogate natural flow hydrograph. The surrogate flow hydrograph is essential to complete the flow record at Sioux City after 1931 when measurements were terminated for a multiyear duration. The hydrograph based on measured flow after 1938 was affected by construction of the main stem dams. The ‘run of the river’ flow hydrograph can be used to help reconstruct other types of ‘natural’ hydrographs.

B2) Stage and temperature hydrographs

Stage is the elevation of the water surface above a datum. At Sioux City, as at most other gage sites, an arbitrary datum is selected and river water levels are referenced to that datum. Measurements of discharge are made at different times at gaging stations. At Sioux City, the discharge and gage height measurements are typically made twice a week when surface ice is not present. The gage height and discharge value measured at the gage are referenced to the stage of the water level. At a gage site, the stage is the gage height. Gage height data are collected at least daily and generally continuously at the gaging station. The gage height and discharge measurements are used to create a rating curve for the station. The

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