U.S. Floods of 1986

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

The first significant flooding of 1986 occurred in northern and central California and western Nevada as a result of rainstorms beginning February 11 and continuing through February 24. The storms produced widespread flooding and landslides. Record flooding occurred in three streams that drain to the southern part of the San Francisco Bay area. Large maximum discharges also occurred in the Feather and American River Basins in central California. Lake Tahoe rose 6 in/d as a result of high inflow. In California and Nevada the floods caused 14 deaths and $379 million in damages.

Flooding in South Dakota that began early in March was due to near-normal winter snowfall coupled with carryover moisture from the previous year, as fall precipitation was 150 to 200 percent of normal over most of the State. The third week in March, a wet spring storm produced precipitation that augmented the flooding. This was followed by the wettest April on record for South Dakota (the 5.13-in. precipitation total for April 1986 far surpassed the next largest 3.87-in. total received in 1941). Thunderstorm activity continued through May, June, and July, keeping rivers and streams at high stages. An unusually wet September (four times the usual rain for the area) again produced flooding in southeastern South Dakota and caused the highest stages of the year on the lower Vermillion and Big Sioux Rivers.

Intense rains, producing 8 in. in 2 hours, fell over the Pittsburgh, Pennsylvania, area on May 30. The rains caused severe flash floods in some Pittsburgh suburbs. The severity of the floods was increased by the area's high relief and many paved surfaces. The maximum discharge of Little Pine Creek near Etna, had a recurrence interval greater than 100 years.

Several intense thunderstorm systems moved through Texas, Louisiana, and Arkansas during the last week of May and the first week of June. On May 24, severe storms caused localized flood damage in the extreme northeastern corner of Arkansas. The San Antonio, Texas, area experienced recurring flash floods from thunderstorms from May 25 through June 4. Hurricane Bonnie made landfall at the Louisiana-Texas border on June 26, causing high storm surges and riverine flooding due to excessive rainfall.

Record snowmelt caused flooding along the eastern slopes of the Rocky Mountains from southwestern Montana to southern Wyoming during June. The maximum discharge of the Madison River near West Yellowstone, Montana, was the highest since records began in 1913 and had a recurrence interval greater than 100 years. Northern Utah also had flooding due to the snowmelt. Early in June, the Great Salt Lake reached its highest level in nearly 140 years of record.

Several severe thunderstorms occurred in Iowa, Nebraska, and Kansas from June 29 to July 8. The rains caused flash flooding in west-central Iowa. The Blue River and its tributaries, located in southern Nebraska and northern Kansas, had considerable flooding and exceeded flood stages by as much as 12 ft. Severe thunderstorms occurred in northeastern Kansas on July 6 and 7, produced about 10 in. of rain in 24 hours, and resulted in significant flash flooding.

A severe thunderstorm hit the Milwaukee, Wisconsin, area on August 6 causing major flash floods along the Menomonee and Kinnickinnic Rivers. Rainfall amounts for the 24-hour period totalled almost 7 in. During the most intense period of rainfall, 1.10 in. fell in 5 minutes. On the Menomonee River, the recurrence interval for the discharge was 40 to 50 years. Property damage totalled $30 million.

Recurring thunderstorms caused record-breaking rainfalls and floods during September in Minnesota, Wisconsin, Michigan, and Illinois. Severe floods occurred September 10-15 in eastern Wisconsin and across the central part of the Lower Peninsula of Michigan. Southeastern Minnesota and western Wisconsin were affected by floods from September 20 through September 22. Flash floods occurred September 25-28 in the Des Plaines River Basin in southeastern Wisconsin and northeastern Illinois. The Mississippi River was above flood stage from Wisconsin to southern Missouri as a result of excessive rainfall in the upper basin.

The South-Central States were affected by excessive rains and flooding between September 26 and October 5. The rains were the result of a nearly stationary front that extended from the Texas Panhandle, through Oklahoma and southeastern Kansas, and into central Missouri. The precipitation from the front was augmented as the remnants of Hurricane Paine from the Pacific Ocean moved northeastward along the frontal boundary on October 2 and 3. Hardest hit by the flooding were areas of north-central Oklahoma and southeastern Kansas, which received more than 20 in. of rain during the 8-day period. Severe floods also occurred in the Osage and Arkansas River Basins of Oklahoma, Missouri, and Kansas. Many streams in Oklahoma had maximum discharges with recurrence intervals of 50 to greater than 100 years, and many reservoirs were filled almost to capacity. The Marais des Cygnes and the Marmaton Rivers in Kansas had extremely high stages. Extensive flooding also occurred across much of Missouri as several streams in the Osage River Basin reached maximum flows that were greater than the 100-year recurrence interval. The high flow of the Missouri River, combined with the already high flow in the Mississippi River, produced the fifth highest stage of record for the Mississippi River at St. Louis.

Source: USGS.