Project design flood
Encyclopedia
The project design flood is a hypothetical "maximum probable" flood of the Mississippi River
used by the United States Army Corps of Engineers
to aid in the design and execution of flood protection in the Mississippi Valley.
The current project design flood was developed in 1956 by the Mississippi River Commission with input from the Weather Bureau. 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 90 miles (144.8 km) 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 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
s need to be, how deep the dredging needs to be, and the flowrates at which flood control structures need to be used.
, 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 probably flood discharge of 2250000 cuft/s at Cairo, Illinois
that was greater than the 1927 flood but less than the 1927 flood combined with the maximum recorded discharge of the Ohio River
in 1913. In a separate analysis, the U.S. Weather Bureau determined that a "maximum possible" flood would result in a discharge of 2400000 cuft/s based on the maximum recorded flows of the upper Mississippi, Ohio, Cumberland
, and Tennessee River
s. In a combined analysis, the higher flow rate estimate was used.
Adding the flows of the Arkansas
and White River
s, the maximum flow farther downriver at Arkansas City, Arkansas
was estimated to be 2850000 cuft/s with a flood stage of 74 feet (22.6 m). Adding the flows of the Yazoo
and Red Rivers, the Weather Bureau estimated a flow of 3000000 cuft/s just North of Baton Rouge
at Red River Landing, Louisiana
.
caused the flood stage at Cairo to reach 59.5 feet (18.1 m) despite a flow of only 2100000 cuft/s. In response, the United States Congress
ordered the MR&T to review of the flood control plan. Maximum flows were changed to 2600000 cuft/s at Cairo, 3065000 cuft/s at Arkansas City with the White River backwater area levee overtopped, and Red River Landing unchanged at 3000000 cuft/s.
After the 1973 Mississippi River floods, the MRC reviewed the project design flood and found that it was still reliable based on current standards.
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...
used by the United States Army Corps of Engineers
United States Army Corps of Engineers
The United States Army Corps of Engineers is a federal agency and a major Army command made up of some 38,000 civilian and military personnel, making it the world's largest public engineering, design and construction management agency...
to aid in the design and execution of flood protection in the Mississippi Valley.
The current project design flood was developed in 1956 by the Mississippi River Commission with input from the Weather Bureau. 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 90 miles (144.8 km) 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 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
Levee
A levee, levée, dike , embankment, floodbank or stopbank is an elongated naturally occurring ridge or artificially constructed fill or wall, which regulates water levels...
s need to be, how deep the dredging 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 1927Great Mississippi Flood of 1927
The Great Mississippi Flood of 1927 was the most destructive river flood in the history of the United States.-Events:The flood began when heavy rains pounded the central basin of the Mississippi in the summer of 1926. By September, the Mississippi's tributaries in Kansas and Iowa were swollen to...
, the Flood Control Act of 1928
Flood Control Act of 1928
The Flood Control Act of 1928 authorized the U.S. Army Corps of Engineers to design and construct projects for the control of floods on the Mississippi River and its tributaries as well as the Sacramento River in California. It was sponsored by Sen. Wesley L. Jones of Washington and Rep. Frank R...
authorized the Mississippi River and Tributaries Project (MR&T), which is implemented by the Mississippi River Commission (MRC). The MRC estimated a maximum probably flood discharge of 2250000 cuft/s at Cairo, Illinois
Cairo, Illinois
Cairo is the southernmost city in the U.S. state of Illinois. It is the county seat of Alexander County. Cairo is located at the confluence of the Mississippi and Ohio rivers. The rivers converge at Fort Defiance State Park, an American Civil War fort that was commanded by General Ulysses S. Grant...
that was greater than the 1927 flood but less than the 1927 flood combined with the maximum recorded discharge of the Ohio River
Ohio River
The Ohio River is the largest tributary, by volume, of the Mississippi River. At the confluence, the Ohio is even bigger than the Mississippi and, thus, is hydrologically the main stream of the whole river system, including the Allegheny River further upstream...
in 1913. In a separate analysis, the U.S. Weather Bureau determined that a "maximum possible" flood would result in a discharge of 2400000 cuft/s based on the maximum recorded flows of the upper Mississippi, Ohio, Cumberland
Cumberland River
The Cumberland River is a waterway in the Southern United States. It is long. It starts in Harlan County in far southeastern Kentucky between Pine and Cumberland mountains, flows through southern Kentucky, crosses into northern Tennessee, and then curves back up into western Kentucky before...
, and Tennessee River
Tennessee River
The Tennessee River is the largest tributary of the Ohio River. It is approximately 652 miles 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 names...
s. In a combined analysis, the higher flow rate estimate was used.
Adding the flows of the Arkansas
Arkansas River
The Arkansas River is a major tributary of the Mississippi River. The Arkansas generally flows to the east and southeast as it traverses the U.S. states of Colorado, Kansas, Oklahoma, and Arkansas. The river's initial basin starts in the Western United States in Colorado, specifically the Arkansas...
and White River
White River (Arkansas)
The White River is a 722-mile long river that flows through the U.S. states of Arkansas and Missouri.-Course:The source of the White River is in the Boston Mountains of northwest Arkansas, in the Ozark-St. Francis National Forest southeast of Fayetteville...
s, the maximum flow farther downriver at Arkansas City, Arkansas
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.-Geography:According to the United States Census Bureau, the town has a total area of , all of it land....
was estimated to be 2850000 cuft/s with a flood stage of 74 feet (22.6 m). Adding the flows of the Yazoo
Yazoo River
The Yazoo River is a river in the U.S. state of Mississippi.The Yazoo River was named by French explorer La Salle in 1682 as "Rivière des Yazous" in reference to the Yazoo tribe living near the river's mouth. The exact meaning of the term is unclear...
and Red Rivers, the Weather Bureau estimated a flow of 3000000 cuft/s just North of Baton Rouge
Baton Rouge, Louisiana
Baton Rouge is the capital of the U.S. state of Louisiana. It is located in East Baton Rouge Parish and is the second-largest city in the state.Baton Rouge is a major industrial, petrochemical, medical, and research center of the American South...
at Red River Landing, Louisiana
Red River Landing, Louisiana
Red River Landing was the name of a community located in northern Pointe Coupee Parish, Louisiana, United States. The community was located near the Red River and the Mississippi River....
.
1941 project design flood
The Ohio River flood of 1937Ohio 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, one million persons were left homeless, with 385 dead and property losses reaching $500 million...
caused the flood stage at Cairo to reach 59.5 feet (18.1 m) despite a flow of only 2100000 cuft/s. In response, the United States Congress
United States Congress
The United States Congress is the bicameral legislature of the federal government of the United States, consisting of the Senate and the House of Representatives. The Congress meets in the United States Capitol in Washington, D.C....
ordered the MR&T to review of the flood control plan. Maximum flows were changed to 2600000 cuft/s at Cairo, 3065000 cuft/s at Arkansas City with the White River backwater area levee overtopped, and Red River Landing unchanged at 3000000 cuft/s.
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 2360000 cuft/s at Cairo, 2890000 cuft/s at Arkansas City, and 3030000 cuft/s at Red River Landing.After the 1973 Mississippi River floods, the MRC reviewed the project design flood and found that it was still reliable based on current standards.