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1935

11-Jun

23-May

-19

5-Jun

21-Jul Trivial ?

94

1936

21-May

5-May

-16

24-May

19-Jun Marginal?

95

1937

25-May

20-May

-5

20-Jun

25-Jun Marginal?

93 1.8' rise 22-Jul

1938

30-May

28-Apr

-32

5-Jun

24-Jul Trivial ?

70

1939

3-May

6-May

3

29-May

4-Jul Trivial ?

86

1940

31-May

21-May

-10

12-Jun

26-Jun Trivial ?

99

1941

15-May

21-May

6

6-Jun

2-Jul Trivial ?

89

1942

26-May

21-Apr

-37

3-May

26-Jun Trivial ?

49

1943

5-Jun

2-Jun

-3

5-May

29-Jul Trivial ?

22

1944

13-Apr

22-May

9

25-May

31-Jul Trivial ?

29

1945

21-Jun

13-May

-39

10-Jun

31-Jul Trivial ?

62

1946

16-Jun

28-Apr

-39

7-Jun

27-Jul Trivial ?

73

1947

22-Jun

16-May

-37

12-May

31-Jul Trivial ?

37

1948

3-Jun

27-May

-7

29-May

1-AugTrivial ?

36

1949

12-May

19-May

7

24-May

3-Jul Trivial ?

64

1950

6-Jun

14-Jun

8

18-Jun

7-Jul Trivial ?

33

1951

14-Jun

6-May

-39

12-May

29-Jul Trivial ?

34

1952

29-Apr

10-May

11

29-Mar

15-Jul Trivial ?

11

1953

26-May

30-May

4

4-May

7-Jul Trivial ?

48

1954

7-Jun

17-May

-21

30-May

9-Jul Trivial ?

80

1955

16-May

23-May

7

31-May

7-Jul Trivial ?

91

Table 1. Evaluation of 1929 -1955 ‘natural’ hydrographs for the Missouri River at Sioux City.

Since the construction of the main stem dams, the hydrograph has been significantly changed. Large flood events associated with the June rise, in general, have been moderated. In reference to the sandbars in the Gavins Point to Ponca, Nebraska, reach, the moderation of the spring rise has resulted in the sandbars not typically being completely flooded during the reproduction season for the birds. For two decades, the USACE has implemented a ‘flat’ hydrograph by strictly controlling the discharges from Gavins Point Dam. This management

Year

Date

Date

Days

Date

Date Success

1929

1-Jun

16-May

-16

18-May

29-Jul Trivial ?

50 Trivial/non existent

1930

26-Jun

5-May

-52

18-May

6-Jul Trivial ?

83 Weak June Rise

1931

2-Jun

31-May

-2

2-Jun

9-Jul Trivial ?

101

1932

19-May

30-Apr

-19

7-May

15-Jul Trivial ?

77

1933

17-May

26-Apr

-21

17-May

9-SepTrivial ?

84

1934

29-Apr

5-May

6 N.A.

N.A.

Marginal?

100 <7’,2.8' rise 16-Jun

entire record would likely be more negative toward the least tern and piping plover successful nesting as compared to the1929-1955 period. The natural hydrograph was very inhospitable to the least terns and piping plovers.

June 18 deg. C Rise

Offset > 7 Feet

< 7 Feet

Reprod.

Rank Remarks

22

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