U.S. Floods of 1975

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

Nearly constant flood conditions plagued the eastern half of the United States from January to April 1975. Cycles of snow, rain, and snowmelt contributed to many floods. The floods continued to compound through time; by April, many streams in the Mississippi and Ohio River Basins exceeded flood stages. The 1975 floods caused damages of $44 million along the lower Mississippi. In addition to the Mississippi and Ohio River floods, several other floods occurred in Alabama, Michigan, Minnesota, Wisconsin, and North Dakota during the month of April.

Ten inches of rainfall, most of which fell within a 24-hour period, caused significant flooding in central Tennessee from March 12 to 14. The Cumberland River Basin, including the Nashville metropolitan area, was most affected by the flooding. The Cumberland River at Nashville crested at 47.6 ft, the highest regulated stage on record.

On March 22, warm temperatures and about 1 in. of rainfall caused 10 to 20 in. of snow in northern Illinois to melt quickly and caused severe flooding in the Rock, Pecatonica, and Illinois Rivers. Record flooding was also reported in southern Wisconsin. High water in the Pecatonica River caused record flooding on the Rock River at Rockton and Rockford, Illinois. The crest at Rockton exceeded the previous record crest recorded in 1937.

Significant flooding occurred in parts of lower Michigan as a result of intense rainfall on April 18 and 19. Flooding was intensified by the already swollen streams and saturated ground that resulted from the snowpack melting 2 weeks earlier. The area around and including the city of Lansing was the worst hit by the floods, with many streams having 100-year or greater recurrence-interval floods. U.S. Geological Survey streamflow-gaging stations recorded maximum stages on the Thornapple River, the highest since the record-setting flood in 1947.

Ice jams created extensive flooding in Alaska in May. An ice jam near Holycross on the Yukon River caused the worst flooding known at the village of Anvik. The ice jam created a lake with an area of about 1,000 mi². The Yukon River remained in overbank flow until June 26 while the huge lake drained.

Snowmelt and ample rainfall caused significant flooding in the upper Missouri River Basin from May to July. The Sun River crested 6 ft above flood stage at Great Falls, Montana. A record stage was recorded on the Musselshell River at Harlowton, Montana. Record-setting floods plagued the Red River of the North Basin in North Dakota and Minnesota during the month of July. Eleven streamflow-gaging stations recorded maximum-of-record flows. The flood was one of the most damaging to occur in the region and unusual because it was caused entirely by rainfall; snowmelt usually plays a role in flooding in the region. An estimated $245 million in damage was attributed to the flood.

Thirteen counties were declared eligible for Federal disaster aid, and one death and $12 million in damages were caused by the July 13-15 flood in New Jersey. The second highest stage of record was recorded on the Millstone River at Blackwells Mills, New Jersey. The flood was caused by a storm that had rainfall totals of more than 10 in. at several locations. On July 20-21, a second storm caused greater than 100-year recurrence-interval flooding along Assunpink Creek in the Trenton, New Jersey, area.

Hurricane Eloise caused flooding in Puerto Rico and the Eastern States during September. The hurricane passed near the north coast of Puerto Rico causing torrential rains across the island. As much as 23 in. fell in Maricao during a 24-hour period. Several rivers had maximum discharges that were the highest of record and had recurrence intervals of 50 to 100 years. Hurricane Eloise made landfall in southeastern Louisiana on September 22. The hurricane then followed a northeasterly path across Mississippi and Alabama and along the East Coast. Floods occurred from Louisana to Maryland. Damages were estimated at $415 million. Counties in New York, Pennsylvania, Maryland, Florida, and Alabama were declared disaster areas.

Sources: USGS.