Flooding in Iowa, May 16 to 20, 1999

May of 1999 saw several significant flooding episodes across the Des Moines CWA. For the most part, central Iowa was spared the extremely heavy rainfall that caused major, and at several locations record, flooding along rivers in the northeast and east parts of the state. The most serious flooding was caused by heavy rains during the overnight hours of May 16. The heaviest rains fell in the counties just to the northeast of the Des Moines CWA. Up to 8 inches of rain fell over parts of Fayette County with anywhere from 2 to 6 inches falling over parts of Butler, Bremer, and Black Hawk Counties. Most of the rain fell in the Cedar River basin, which includes the West Fork Cedar River, Shell Rock River, Beaver Creek, and Black Hawk Creek. Among the largest 24-hour rain gage reports within the basin were the 5.18 inches at Kesley in the upper West Fork Cedar basin and 4.75 inches at Shell Rock in the Shell Rock basin. An isohyetal analysis of the storm produced by Harry Hillaker, the State Climatologist of Iowa, showed the heavy rainfall pattern extended across north central and northeast Iowa, with much less, but still significant, rain over central and northwest Iowa. Flooding was widespread across portions of Black Hawk, Butler, and Bremer Counties, with many smaller streams and creeks spilling out of their banks. A Flash Flood Warning was issued for Butler County late on the 16th and for Black Hawk County during the morning hours of the 17th. The runoff into the tributaries of the Cedar River from all of this rainfall led to the cresting of rivers from midday on the 17th to early on the 18th. Among the most notable crests were: 16.07 feet (flood stage is 12 feet) at Finchford on the West Fork Cedar River, which was the 5th highest on record and the highest since 1993. On the Beaver Creek at New Hartford the crest of 12.89 feet (flood stage is 8 feet) late on the 17th was the 7th highest on record, and again the highest since 1993. Much of the town of New Hartford was under water and many roads closed during a site visit by the Hydrologist on the 18th. Fortunately for the residents of Cedar Falls and Waterloo, rainfall in the upper portions of the mainstem Cedar River above Charles City was less than one half inch, helping to reduce the flow on the river through these locations. The contributions from the major tributaries above was still enough to bring about a crest of 19.20 feet (flood stage is 12 feet) at Waterloo, the 9th highest on record and also the highest since 1993. With levee protection to 26 feet, the city of Waterloo was not seriously impacted by this flood. Upstream in the Cedar Falls area, there was substantial impacts, with flooding and evacuations in several residential areas. In addition to property and public damages caused by the flooding, there was considerable damage to agricultural lands. Many areas had to replant crops and over the northeast part of the state soil erosion was very serious with some farmers reporting as much as a foot loss of top soil. It is very difficult to calculate the cost of that as its effect will go on for hundreds of years.