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FLOOD SEASONS AND DURATIONS OF FLOODS Average number of days by calendar months for period 1900-46, inclusive, that the flood stage shown was equaled or exceeded.

Gages

Flood
stage Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.
(feet)

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The table below shows the maximum number of consecutive days that the flood stage was equaled or exceeded at the gages given during thirteen selected high-water years.

Maximum number of consecutive days flood stage was equaled or

exceeded

Gages

Flood
stage
(feet)

1908 1915 1922 1927 1929 1935 1937 1938 1942 1943 1944 1945 1946

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Duration of water above flood stage at certain gages is shown in the table below:

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1900 1901. 1902. 1903. 1904 1905. 1906. 1907 1908 1909 1910. 1911 1912 1913. 1914. 1915. 1916. 1917 1918. 1919. 1920 1921 1922. 1923 1924. 1925 1926. 1927 1928 1929 1930. 1931. 1932.. 1933 1934. 1935. 1936. 1937. 1938. 1939. 1940. 1941. 1942. 1943 1944. 1945. 1946.

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67

0
62
35
22

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136

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69
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0 13 0 3 4 12 0 9 17 42 58 62 25

7 0 2 14 48 33 72 6

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12 36 26 42 0

103
97
97
59

CURRENT VELOCITIES IN CHANNEL In general, velocities of about 1 mile per hour at usual pool stages may be expected above the mouth of Wisconsin River, with velocities of 3 miles per hour when dams are fully opened at high discharges. Open-river velocities of 4 to 5 miles per hour may occur in pools 1 and 4 at extreme high water. Between Wisconsin River and Alton, Ill., velocities may vary from about 2 miles per hour at usual pool stages to about 4 miles per hour at high water. In the open-river section below Alton, Ill., velocities range from 2.0 to 7.5 miles per hour except through the Chain of Rocks, above St. Louis, Mo., in which velocities as high as 8 miles per hour may occur at both extreme high and extreme

low stages.

NAVIGATION SEASON

OHIO RIVER TO ST. LOUIS. MO,

During the period 1865 to 1946, ice was present in the river at St. Louis an average of 36 days per year. The earliest and latest dates on which ice was present were November 18, 1880, and March 15, 1932. During the period 1909 to 1946 the river was gorged or frozen at St. Louis an average of 10 days per year. The longest open navigation season has been 365 days and the shortest 282 days. The average navigation season is considered as February 15 to December 15. However, in recent years navigation has been active throughout the year.

ST. LOUIS, MO., TO ROCK ISLAND, ILL.

In the usual year, closure of navigation occurs from December 1 to March 1. There have been years when closures occurred November 15 and lasted to April 1.

ROCK ISLAND, ILL., TO MINNEAPOLIS, MINN. The average period of closure by ice is from December 1 to April 10. During a very severe winter, the river may be closed as early as November 10 and may not open until April 25.

LOW WATER AND NAVIGABLE DEPTHS

Moderate and high flows sufficient to assure depths of 9 feet are to be expected during the spring and early summer. Inadequate summer flows due to deficient rainfall have occurred as early as July. Low flows are to be expected in late summer and autumn, and particularly during the winter, because of the effects of freezing temperatures. Deficient flows have occurred as late as March. The system of locks and dams between Minneapolis, Minn., and Alton, Ill., now complete, provides a generally dependable 9-foot channel depth in that section throughout the ice-free season. Between Alton and the Ohio River, a channel depth of 9 feet may be depended upon with stages on the St. Louis (Market St.) gage in excess of 3 feet above zero. Between stages of 3 feet and zero a satisfactory channel, although not dependably 9 feet deep, may be expected. In this section a channel depth of 9 feet can generally be depended upon from the beginning of the navigation season to about August 15. After that date a satisfactory channel may be available with usual low water stages, but occasionally during unfavorable navigation seasons controlling depths may be as little as 5 to 5.5 feet in the Chain of Rocks section and only slightly better between St. Louis and Cairo. However, such deficient depths may be expected to be of infrequent occurrence, particularly outside the Chain of Rocks section and below St. Louis, where progressive improvement is to be anticipated as regulating works are completed and become more effective. Further improvement by means of a lateral canal and locks around the Chain of Rocks section has been authorized by Congress and funds to initiate construc

IMPROVEMENT BY THE UNITED STATES FOR NAVIGATION OF THE

MIDDLE AND UPPER MISSISSIPPI RIVER

WAR DEPARTMENT SUPERVISION

The Secretary of War and the Chief of Engineers, War Department, whose of es are in Washington, D. C., have general supervision of river improvements executed under Congressional authority. The improvement of the Middle and Upper Mississippi River is in charge of the Division Engineer, Upper Mississippi Valley Division, St. Louis, Mo., who is an officer of the Corps of Engineers, War Department. For immediate supervision of the work, this reach of the river is divided into three districts, each in direct charge of a District Engineer, who is also an Army officer. Information concerning the river may be obtained from these District Engineers. Their addresses and the limits and lengths of their districts are listed below:

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HISTORY OF IMPROVEMENT The Mississippi River in its original condition consisted of a series of relatively deep pools separated by shoal bars and rapids. The channel was obstructed by rocks and snags, and during the low-water season the flow through the shoals divided into several chutes with narrow widths and depths as little as 30 inches. Some rapids were impossible to navigate at low water. At higher stages the river was navigable to St. Paul, Minn.

The first step toward improvement was taken in 1820, when Congress authorized a reconnaissance survey of the Ohio and Mississippi Rivers. As a result of this survey, Congress, by act approved May 24, 1824, authorized improvement of the Mississippi River between New Orleans and the mouth of Missouri River by snagging, and appropriated $75,000 for this purpose. This snagging service has been extended and continued to the present day. The first work in the nature of permanent improvement, "a pier to give direction to the current of the Mississippi River near the City of St. Louis," was authorized by acts of July 4, 1836, and March 3, 1837. For a number of years thereafter, Federal improvement consisted of removal of snags and wrecks and improvement of the Des Moines (Keokuk) and Rock Island Rapids by lateral canal with locks and rock dredging, respectively.

À project for general improvement of the Middle Mississippi was adopted by the act of June 10, 1872, which authorized improvement between Alton and the Meramec River to secure greater channel depths by means of revetment, solid dikes, and closing dams. The act of March 31, 1881, approved a more comprehensive project for continuous improvement between St. Louis, Mo., and the Ohio River to secure a minimum depth of 8 feet by means of revetment, permeable dikes and contraction of the low-water channel to an approximately uniform width of 2,500 feet. The acts of March 2, 1895, and June 3, 1896, modified the project by providing for maintenance of a channel 250 feet wide and 9 feet deep by regulating works and dredging. The act of March 3, 1905, again modified the project by providing that extensive dredging instead of regulating works be adopted as the principal means of improvement. Improvement by dredging alone proved unsatisfactory, and regulating works were again authorized by the act of June 25, 1910, which authorized depths of 8 feet from the Ohio River to St. Louis and 6 feet from St. Louis to the Missouri River. The acts of January 21, 1927, and July 3, 1930, respectively, authorized channels 9 feet deep and 300 feet wide from the Ohio River to St. Louis and 9 feet deep and 200 feet wide from St. Louis to the Illinois River. By the act of March 2, 1945, a lateral canal and locks around the difficult Chain of Rocks reach just above St. Louis were authorized. Construction of the regulating works considered necessary for the 9-foot channel and of the lateral canal and lock in the reach between the Missouri and Ohio Rivers is about 71 percent complete (1946).

A project for general improvement between St. Paul and the Missouri River by means of wing dams and closure of chutes to secure a depth of 4% feet, eventually to be increased to 6 feet, was initiated by the act of June 18, 1878. The rock cut through Rock Island Rapids was improved to a width of 400 feet and depth of 6 feet in the period 1888 to 1906. The improvement was extended to Minneapolis by act of September 19, 1890, which provided for dredging and removal of boulders between St. Paul and Minneapolis. The method of improvement in that section was later modified to include two lowlift dams with locks. An act of February 9, 1905, permitted construction of the Keokuk power dam with a navigation lock to replace the locks and lateral canal previously built by the United States. The act of March 3, 1905, provided for construction of the Moline Lock at the lower end of Rock Island Rapids. The act of March 2, 1907, authorized provision of a 6-foot channel from the Missouri River to Minneapolis by contraction works as in the project of 1878, supplemented by dredging, and a lateral canal with navigation lock around the upper portion of the Rock Island Rapids at Le Claire, Iowa. The acts of June 25, 1910, and January 21, 1927, provided respectively for construction of a single high dam to replace the two old dams between St. Paul and Minneapolis and for a dam at Hastings, Minnesota. The act of July 3, 1930, as modified by the act of August 30, 1935, authorized improvement by means of locks and dams supplemented by dredging to provide a 9-foot channel from Minneapolis to the Missouri River. The act of August 26, 1937, authorized extension of the 9-foot project to above the Falls of St. Anthony at Minneapolis. The locks and dams between the Missouri River and Minneapolis are described in detail in the table on page 185.

A bibliography of the more important surveys and reports pertaining to improvement of the Upper and Middle Mississippi River, together with acts of Congress relating to these reports, follows:

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