U.S. Floods of 1974

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

The most significant floods during 1974 occurred in January in Montana, Idaho, Washington, Oregon, and northern California and caused as much as $250 million in damage. Significant floods occurred on the west slopes of the Cascade and Sierra Nevada Ranges, and in western Montana, western Idaho, and small parts of eastern Washington. New maximums of record were established at many gaging stations in the Spokane River Basin of Idaho. Flooding was severe on small streams in the Kootenai River Basin in Montana and on streams in the Kootenai and Pend Oreille River Basins in Idaho. Ice jams caused most flooding in the Snake River Basin. The Salmon River, a tributary to the Snake River, had record high floods enhanced by ice jams. Record and near-record flooding also occurred in southwestern Oregon and northwestern California.

The Verdigris and Neosho Rivers, tributaries to the Arkansas River in Kansas and Oklahoma, had record flooding in March, and other streams in eastern Kansas and Oklahoma had near-record flooding in March and April. Flooding from basins in western Mississippi kept the Mississippi River high through much of April. Rains of May 13-20 in the upper Mississippi, Illinois, and lower Missouri River Basins caused another flood on the Mississippi River. The May flood in the Missouri River Basin produced few extreme discharges but still caused considerable damage.

Snowmelt during April, May, and June produced significantly high discharges in the Souris and Pembina River Basins of North Dakota, the Yellowstone, Gallatin, Bitterroot, Swan Rivers, and other basins of northwestern Wyoming and southwestern Montana, and the Salmon River Basin of Idaho. Northern Maine also had record high floods from snowmelt and ice jams.

Nationwide, thunderstorm floods during the summer of 1974 generally did less damage than usual. The absence of severe thunderstorm floods was particularly obvious in the Midwest where floods of this type generally occur frequently. Only two Federal disaster declarations resulted from floods in the conterminous States from July through October. One disaster declaration resulted from flash floods in central New York. The second was for Hurricane Carmen in Louisiana. Hurricane Carmen, which came ashore on September 7, was the only hurricane to make landfall in the United States in 1974. Hurricane Carmen did about $150 million in damage (U.S. Army Corps of Engineers, 1975a) but produced excessive rain in only a few areas and caused little riverine flooding. Much of the damage resulted from flooding in the Mississippi Delta area.

Southeastern Alaska had nearly continuous rainfall in September and October. A few streams near Ketchikan had the second or third highest discharges of record on October 8-9. Elsewhere in Alaska, a glacial lake outburst caused record high discharges on the Kenai River on September 14-15.

The southern Great Plains from Kansas to northeast Texas received excessive rainfall from late August to late November. Flooding occurred in Texas on August 28, September 13-14, September 17-18, September 20-21, October 30-November 10, and November 23. Most of the rains produced widespread, low-magnitude floods, but there were a few isolated areas of high runoff. Other than moderately high discharges at a few gaging stations, most of the floods were not unusual.

Sources: USGS.