The project design flood is a hypothetical "maximum probable" flood of the

Mississippi River The Mississippi River is the List of longest rivers of the United States (by main stem), second-longest river and chief river of the second-largest Drainage system (geomorphology), drainage system in North America, second only to the Hudson B ...

used by the

United States Army Corps of Engineers , colors = , anniversaries = 16 June (Organization Day) , battles = , battles_label = Wars , website = , commander1 = ...

to aid in the design and execution of flood protection in the

Mississippi Valley The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it ...

. The current project design flood was developed in 1956 by the Mississippi River Commission with input from the

Weather Bureau The National Weather Service (NWS) is an agency of the United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weather-related products to organizations and the public for the ...

. It is based on a scenario of three rain events in the lower Mississippi Valley occurring 3 days apart: the January 1937 (increased by 10%), January 1950, and then the February 1938 rain event with its center adjusted to the north and rainfall pattern rotated to achieve a hypothetical worst-case flood of the tributaries of the Mississippi River. Assumptions were made based on the completion of tributary reservoirs and dams by 1960. When the Commission reviewed the plan after the

1973 Mississippi River floods The Mississippi flood of 1973 occurred between March and May 1973 on the lower Mississippi River. The flooding was the third most severe along the U.S.'s Mississippi River during the 20th century. Winter of 1972-1973 A series of unusually cold w ...

, the Project Design Flood in use was determined to be "based on sound technology that was still reliable by current standards. The project design flood peak discharges remained unchanged." Once the project design flood was developed, flow rates at critical points are used to determine how high

levee A levee (), dike (American English), dyke (Commonwealth English), embankment, floodbank, or stop bank is a structure that is usually earthen and that often runs parallel to the course of a river in its floodplain or along low-lying coastli ...

s need to be, how deep the

dredging Dredging is the excavation of material from a water environment. Possible reasons for dredging include improving existing water features; reshaping land and water features to alter drainage, navigability, and commercial use; constructing d ...

needs to be, and the flowrates at which flood control structures need to be used.

1928 project design flood

In response to the

Great Mississippi Flood of 1927 The Great Mississippi Flood of 1927 was the most destructive river flood in the history of the United States, with inundated in depths of up to over the course of several months in early 1927. The uninflated cost of the damage has been estimat ...

, the Flood Control Act of 1928 authorized the Mississippi River and Tributaries Project (MR&T), which is implemented by the Mississippi River Commission (MRC). The MRC estimated a maximum probable flood discharge of at

Cairo, Illinois Cairo ( ) is the southernmost city in Illinois and the county seat of Alexander County. The city is located at the confluence of the Ohio and Mississippi rivers. Fort Defiance, a Civil War camp, was built here in 1862 by Union General Ulysse ...

that was greater than the 1927 flood but less than the 1927 flood combined with the maximum recorded discharge of the

Ohio River The Ohio River is a long river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing southwesterly from western Pennsylvania to its mouth on the Mississippi River at the southern tip of ...

in 1913. In a separate analysis, the

U.S. Weather Bureau The National Weather Service (NWS) is an agency of the United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weather-related products to organizations and the public for the ...

determined that a "maximum possible" flood would result in a discharge of based on the maximum recorded flows of the upper Mississippi, Ohio,

Cumberland Cumberland ( ) is a historic counties of England, historic county in the far North West England. It covers part of the Lake District as well as the north Pennines and Solway Firth coast. Cumberland had an administrative function from the 12th c ...

, and

Tennessee River The Tennessee River is the largest tributary of the Ohio River. It is approximately long and is located in the southeastern United States in the Tennessee Valley. The river was once popularly known as the Cherokee River, among other name ...

s. In a combined analysis, the higher flow rate estimate was used. Adding the flows of the

Arkansas Arkansas ( ) is a landlocked state in the South Central United States. It is bordered by Missouri to the north, Tennessee and Mississippi to the east, Louisiana to the south, and Texas and Oklahoma to the west. Its name is from the O ...

and White Rivers, the maximum flow farther downriver at

Arkansas City, Arkansas Arkansas City is a town in Desha County, Arkansas, United States. The population was 366 at the 2010 census. The town is the county seat of Desha County. Arkansas City's historic Commercial District, located at Desoto Avenue and Sprague Stree ...

was estimated to be with a flood stage of . Adding the flows of the Yazoo and Red Rivers, the Weather Bureau estimated a flow of just north of

Baton Rouge Baton Rouge ( ; ) is a city in and the capital of the U.S. state of Louisiana. Located the eastern bank of the Mississippi River, it is the parish seat of East Baton Rouge Parish, Louisiana's most populous parish—the equivalent of counti ...

at Red River Landing, Louisiana.

1941 project design flood

The

Ohio River flood of 1937 The Ohio River flood of 1937 took place in late January and February 1937. With damage stretching from Pittsburgh to Cairo, Illinois, 385 people died, one million people were left homeless and property losses reached $500 million ($10.2 billion ...

caused the flood stage at Cairo to reach despite a flow of only . In response, the

United States Congress The United States Congress is the legislature of the federal government of the United States. It is Bicameralism, bicameral, composed of a lower body, the United States House of Representatives, House of Representatives, and an upper body, ...

ordered the MR&T to review of the flood control plan. Maximum flows were changed to at Cairo, at Arkansas City with the White River backwater area levee overtopped, and Red River Landing unchanged at .

Current project design flood

The current project design flood was developed at the request of the Senate Public Works Committee in 1954. The Mississippi River Commission and the Weather Bureau worked together to investigate hypothetical flood conditions. The study of a set of 35 combinations of actual storms resulted in the selection of combination called "Hypo-Flood 58A," a combination of previous storms in 1937, 1938, and 1950. The peak discharges were found to be at Cairo, at Arkansas City, and at Red River Landing. After the

, the MRC reviewed the project design flood and found that it was still reliable based on current standards.

1928 project design flood

1941 project design flood

Current project design flood

See also

References

Further reading