U.S. Floods of 1981

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

The first significant flood of 1981 was a result of rain falling on deep snow in the area from New Hampshire to eastern Pennsylvania. Rainfall of 1 to 4 in. occurred over the area and, along with temperatures in the 50- to 60-°F range, caused 6 to 12 in. of snow to melt. Ice jams were the major factor causing the flooding. The highest recorded stage (26.6 ft) on the Delaware River at Matamoras, Pennsylvania, was a result of a massive ice jam.

Considerable spring flooding occurred in Montana during May when four extensive storms created conditions that resulted in flooding in the Helena and Continental Divide areas. Flooding occurred when excessive precipitation combined with snowmelt. At 13 streamflow-gaging stations, recurrence intervals of greater than 100 years were recorded. Near Boulder, Montana, the maximum discharge of the Boulder River was twice the previous maximum of record. These floods were some of the costliest in Montana's history, with total damages exceeding $30 million (Paulson and others, 1991).

A deadly flash flood struck Austin, Texas, during the night of May 24. A short, intense rainfall produced as much as 10 in. of rain in 4 hours. Streams rose rapidly, beginning about 10:00 p.m. and peaking about midnight. The floods receded just as quickly, so most streams were at preflood levels by 3:00 a.m. The flood resulted in 13 deaths and $40 million in damages. The speed at which the streams rose to flood levels contributed to the number of deaths as the floods probably caught many people unaware of the danger.

The summer months were plagued with floods in the North-Central States. Illinois and Indiana were the hardest hit, as rains began in May and continued through July. Flooding was widespread from Wisconsin to Kentucky, with the most severe floods in scattered areas. Thirteen counties dispersed over Illinois, Ohio, and western Pennsylvania were declared Federal disaster areas because of flooding in mid-June. Agriculture in Illinois and Indiana suffered substantially from the storms and resulting floods.

On August 29, a tropical depression moved inland at Brownsville, Texas, and continued to move up the Rio Grande Valley. By August 30, the depression reached San Antonio and, during the evening, created a line of thunderstorms that produced 8 to 12 in. of rain in the area. Water levels on many rivers in the region were near record highs.

October brought excessive rains and flooding to Texas and Oklahoma. On October 5, rainfall amounts totaling 8 in. caused severe urban flooding in Houston. A storm produced 11 in. of rain in southern Texas on October 6 through 7. Record floods were produced in Oklahoma and Texas from a storm that lasted from October 11 to 16. In a 3-day period from October 11 to 14, 17 to 20 in. of rain fell in south-central Oklahoma and north-central Texas. As a result, floods that exceeded the 100-year recurrence interval occurred in central Texas. The damage totals exceeded $115 million in Texas and Oklahoma combined.

Source: USGS.