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AVERAGE- ANNUAL MISSOURI RIVER DISCHARGE AT SIOUX CITY

60000

50000

40000

Discharge (cfs)

30000

20000

10000

0

06/01/1898 06/01/01 06/01/04 06/01/07 06/01/10 06/01/13 06/01/16 06/01/19 06/01/22 06/01/25 06/01/28 06/01/31 06/01/34 06/01/37 06/01/40 06/01/43 06/01/46 06/01/48 06/01/51 06/01/54 06/01/58 06/01/61 06/01/64 06/01/67 06/01/70 06/01/73 06/01/76 06/01/79 06/01/82 06/01/85 06/01/88 06/01/91 06/01/94 06/01/97

Figure 2. Average Annual Missouri River Discharges at Sioux City, Iowa. Data from USACE and USGS. Synthetic record from 1898 to1928 and from 1931-1938.

B1) Discharge hydrographs.

The discharge hydrograph for the USGS gage at Sioux City from 1929 through 1955 is shown in figure 3. Note that from 1931 through 1938 no discharge measurements were made, and thus, daily discharge values were not ascertained (Gorman, 2003, pers. com.).

Factors that affect the discharge hydrograph in Sioux City as compared to the ‘natural’ hydrograph include but are not limited to large scale land-use change that started about 1850, the closure of Fort Peck Dam in 1937, the closure of Fort Randall Dam in 1952, the closure of Garrison Dam in 1953, the closure of Gavins Point Dam in 1955, the bank stabilization at Sioux City about 1960, the closure of Oahe Dam in 1962, and the closure of Big Bend in 1963. From the previous information, it is apparent that it is not possible to directly quantify the natural discharge hydrograph. However, ignoring the effects of land use, the record at

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