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Page 2 WATER TALK Summer/Fall 1995 ...continued from page 1 circulation models for greenhouse gas increases) caused. large and sometimes abrupt changes in magnitude and frequency of floods in the Upper Mississippi River Valley. Knox (1988) observed that in the historic record, large floods were more frequent prior to 1895 and after 1950. The Red Wing gage on the Upper Mississippi River clearly shows the post- 1950 rise in frequency in floods greater than the 5-year flood event (Figure 1). Knox associates the greater frequency of larger floods to time periods when mean temperature was slightly below the long-term temperature mean and annual precipitation was above. the long-term mean. The Illinois State Water Survey (1992) found slight to moderate flood frequencies and heavy precipitation events trending upward in Minnesota. Land use changes from European settlement to the present in the B1ufllands Landscape of Minnesota, Wisconsin, Iowa, and Illinois have been well documented by Trimble and. Lund (1982) and Knox (1977). Their findings are generally applicable to most of the state. The conversion of prairie and forest to cropland and pasture resulted in reduced infiltration and increased surface water runoff. Associated with these changes were reduced base flows, more frequent flood events, accelerated upland erosion, and changes in floodplain geomorphology. Statewide, Minne- sota has drained approximately 45% of its wetlands (Robinson and Mazks, 1994). In the Mississippi and Missouri watersheds above St. Louis, the nation has lost 19 million acres of wetlands (World Wildlife, 1993). Illinois is a state that has lost better than 80% of its original wetlands. 'The Illinois State Water Survey (1993) determined quantitatively that wetland area and flood flow volumes are inversely related. Belt (1975) concluded that the combination of navigation works and levees caused significant rises in stage and that the 1973 flood's record stage (the pre-1993 record. flood) was man-made. The 1973 flood was a 30-year discharge event but represented a 200-year flood stage.. The 1.993 flood crest at Keokuk, Iowa, had a higher stage but less discharge than the 1973 flood suggesting significant floodplain encroachment over the past 20 years. Within the Upper Mississippi River Pool 2 floodplain, no new projects that encroach on the designated floodway can be approved because all allowable stage increases are already earmarked. for future projects. The Great Flood of 1993 compels us to contemplate how to better communicate flood risk and account for human activities that affect. flooding conditions. The discussion above suggests that climate, land use, and floodplain activities have not and will not remain constant. Assumptions used in the calculation of flood frequency events should take into account this bmader and longer term perspective. If current trends continue, it is reasonable to expect more frequent flooding throughout the Upper Mississippi River Watershed. The federal government's tab for disaster relief for the Great Flood of 1993 included $4.2 billion in direct .expenditures, $1.3 billion on insurance claims, and $621 million in loans (Hanson and Lemanski, 1995). The federal government's attention remains focused on the 1993 flooding disaster. The Clinton Administration appointed an Interagency Floodplain Management Review Committee to study flood impacts and make policy recommendations. Completed in 1994, the Interagency Committee's report recommends far reaching policy changes (Galloyway, 1994). The Corps of Engineers will complete a Congressionally funded study of their own on the -Great Flood of 1993 this summer. It remains to be seen how many of the recommendations will be translated into federal policy changes. The Reforms to the Flood Insurance Act, which have been outlined in past Water Talk articles, is a very good start. ...~ntinued on page 3