U.S. Floods of 1980

By C.A. Perry, B.N. Aldridge, and H.C. Ross of the USGS

The first significant floods of 1980 occurred February 13 to 21 in southern California and Arizona. The floods were a result of six Pacific storms hitting the Southwest and creating an extended period of rainfall. This extended period of rainfall, not an excessive amount in one storm, caused the severe flooding. The resulting volumes of runoff in many streams south of Los Angeles, California, during February were the highest ever recorded. The 7-day volumes on the Salt and Verde Rivers in Arizona were the second and third highest, respectively, recorded since 1906. These excessive volumes caused all the reservoirs in southern California, except Lake Henshaw in San Diego County, to have spillway releases. Seven reservoirs in Arizona on the Salt, Verde, and Agua Fria Rivers had spillway releases. The floods caused 18 deaths and $350 million in damages.

Intense rains hit Louisiana, Mississippi, and Alabama in two consecutive storms in March and April. The first storm occurred from March 26 to April 2 and struck southeastern Louisiana and scattered areas in Mississippi. The second storm lasted from April 11 to April 13 and affected most of Mississippi and was especially intense in the area from Baton Rouge and New Orleans, Louisiana, to Mobile, Alabama. The 2-hour rainfall in Mobile on April 13 had a recurrence interval of 100 years. As a result of this rainfall, Mobile experienced the worst flash floods in the city's history.

The most devastating hydrologic event during the year occurred on May 18 with the eruption of Mount St. Helens in Washington. The eruption caused very rapid melting of the mountain's snow and ice, creating severe mudflows along the North Fork Toutle, South Fork Toutle, and lower Cowlitz Rivers and throughout the Lewis River Basin in Washington. The mudflows had substantial effects on the streams and flood plains as large quantities of sediment were deposited. The mudflows deposited about 11,000 acre-ft of water, mud, and debris in Swift Reservoir on the Lewis River. The sediment that was deposited from these mudflows caused changes in the characteristics of flow in many of the streams in the area and required flood profiles to be reworked in the affected areas.

The month of August brought almost continuous rain to West Virginia, southwestern Pennsylvania, and eastern Ohio. Many precipitation stations reported rain during almost every day from August 2 to 22, and daily totals of 2 in. or more were very common. On August 9, thunderstorms produced 3.0 to 3.5 in. of rain in 1 hour over Clarksburg, West Virginia . Flooding was particularly severe in the town of Lost Creek, West Virginia.

Hurricanes and tropical storms ravaged the coastal areas of Texas in August and September. Hurricane Allen, the first of the season, was the most intense ever recorded in both the eastern and western parts of the Caribbean Sea. The storm made landfall on August 9 in Texas, and tidal surges 10 to 20 ft above sea level were recorded along the southern coast. The tidal flooding was the worst since 1919. Tropical Storm Danielle, which made landfall in eastern Texas on September 5, did not produce the high winds and tidal flooding that Hurricane Allen did, but the storm did produce torrential rains. Urban flooding caused by the excessive rainfall was the most destructive element of this storm. Tropical Storm Jeanne in mid-November also caused coastal flooding along the entire coast of Texas with the worst flooding near Galveston.

Source: USGS.