The great flood of 1965 on the Mississippi River, along the eastern border if the State, exceeded any flood known in 139 years. It cause damages probably in excess of ten millions of dollars in the State of Iowa. Studied now in progress will more thoroughly cover this and other phases of the flood.
The underlying cause of the flood was an abnormally cold winter which prevented the melting of an excessive snow cover in the upper reaches of the basin. Heavy rains late in March followed by rapid melting triggered the runoff which caused the floods. Peak discharges experienced ranged from 276,000 cfs (cubic feet per second) at McGregor near the northern boundary of the State to 327,000 cfs at Keokuk near the southern boundary. Tributary streams in Iowa were receding as the main-stem flood peak passed their mouths. The discharge they contributed was generally insignificant except for the larger streams.
Flood data compiled for the part of the River along the eastern border include flood discharges, flood elevations, and the frequency of floods of varying magnitudes. They also include the daily or more frequent stage and discharge data for both the Mississippi River and the downstream gaging stations on Iowa tributaries for the period March-May 1965. Sufficient data are presented to permit studied for preparation of plans for protective works and plans for zoning or for flood plain regulation.
