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~• ., ~. .~fp f ~ . ~'Ya v x `_ + f a ~^ • t:~ ~'y~'.j~.t•. ;~F.~ ji, y i lY... -.1 .f During the Great Flood of 1993, many home owners and businesses were surprised to find out that they were not protected from flood damage even though they were located above the designated 100-yeaz flood stage or behind flood control levees. The USGS (1993) reported that forty-six gaging stations in the Mississippi River watershed exceeded the 100-year flood reoccurrence interval. In the jazgon of the trade, we often use flood reoccurrence intervals to describe and forecast flood magnitudes and damage potential. It is increasingly appazent that the flood reoccurrence interval description of flooding is only a vaguely understood and often misinterpreted. concept by many. In addition, the use of reoccurrence flood frequency intervals to describe floods does not convey the inherent uncertainty associated with the stage height predictions or help to identify conditions and activities that contribute to the severity of flood damage. Most conventional methods for calculating flood magnitudes-and frequencies assume that the historic flood data constitutes a sample of random and independent events. Many standazd statistical techniques assume homogeneity of the mean and variance in estimating long-term potential magnitudes and s,. r .1'a~•"Y1a1:. i. .. ._ __ ~-. frequencies (Knox, 1993). The implied assump- tion is climate, land use, and floodplain activities have remained constant over the period of historic records and. will continue to be constant in the future. Paleohydrologists study physical evidence within floodplain deposits to reconstruct past hydrologic conditions. Their investigations have demonstrated that changing climatic conditions in the Holocene (post glacial) resulted in flood magnitudes ranging from 10-15% larger to 20- 30% smaller than contemporary floods. The reconstructed flood records show large flood periods to be nonrandom (Knox, 1983). A review by Knox (1993) of the 7000-yeaz geologic record suggests that modest climatic changes (even those smaller than predicted by global ...~ntlnued on next page Springfield Residents Receive Flood Relief........ 4 Plan for the Old Man: the Mighty Missssippi.......6 Climate Update Summer 1995 ........................... . 8 Heavy Rains Affect Chisago Chain of Lakes..... 10 Radar-Based Precipitation Estimates ................ i2 DNR Wetlands, Watersheds & Floodp/ain: Getting up to G/S Speed ................................ 13 Wetlands of Minnesota: How Much Do We Really Have ? .................................................. 14 Floodp/ain Report Available from USACE.......... 17 Court Camer ...................................................... 18 Announcements ................................................. 19 Only in California ? ............................................ 20