Criss applied his equation to the well-recorded history of peak water levels or “stages” that occur as a flood reaches its highest crest of the year. “Many factors such as climate change and in-channel structures are causing flood levels to rise, so realistic estimation of future flood levels must take these changes into account.”Ĭriss’ study proposes a new statistical equation for the analysis of environmental variables that are changing over time. “Such outcomes are far too unlikely to be attributed to a nearly continuous succession of statistical flukes, and instead must be attributed to faulty calculation of flood risk,” Criss said. Since the publication of that study, floods at Hannibal have exceeded the “10-year” flood levels in 2009, 20 in both 20, the area experienced stages that were officially designated as “50-year” floods, he said. In a 2008 study, he showed that flooding patterns along the Mississippi River near Hannibal, Missouri, were already in an extreme range - far beyond what would be expected using the official federal flood risk calculations. In his study, Criss argues that the statistical formulas now used to set federally-recognized official levels for 100-year flood events are grossly inaccurate because they assume conditions are the same as they were many decades ago, when the rivers were relatively untamed and global weather patterns were more consistent. Global warming and the resulting increase in extreme weather cycles has only added to the flooding risk in recent years, he said. Levees are commonly designed to withstand floods at “100-year” levels and “100-year” flood zones are delineated on detailed flood insurance maps produced by FEMA.Ĭriss, a hydrogeologist who has studied water flows on major rivers for decades, has long argued that man-made river control systems, such as levees, locks, dams and navigation-enhancing dikes, have gradually increased the odds of catastrophic flooding by tightly constricting river channels and preventing floodwaters from flowing naturally into surrounding wetlands and floodplains. ![]() Army Corps of Engineers (USACE), the official 100-year flood level is a key national index of potential flood severity. CrissĪny flood that rises even a few inches over the top of a 100-year levee has the potential to cause a catastrophic breach of the flood control system, he warns.īased on complicated equations currently used by key federal agencies, such as the Federal Emergency Management Agency (FEMA) and the U.S. ![]() Published this month in an advance online issue of the Journal of Earth Science, the findings are important, Criss said, because many of the nation’s flood-control river levee systems are not engineered to withstand floods that rise much higher than the projected 100-year flood level. “This analysis shows that average high-water marks on these river systems are rising about an inch per year - that’s a rate ten times greater than the annual rise in sea levels now occurring due to climate change,” said Robert Criss, PhD, professor of geology in the Department of Earth and Planetary Sciences in Arts & Sciences and author of the study. ![]() Louis suggests federal agencies are underestimating historic 100-year flood levels on these rivers by as much as five feet, a miscalculation that has serious implications for future flood risks, flood insurance and business development in an expanding floodplain. Flood waters inundated parts of Jefferson City, Missouri, and threatened the Missouri State Capitol during the “Great Flood of 1993.” (Credit: Wikipedia / Creative Commons)Īs floodwaters surge along major rivers in the midwestern United States, a new study from Washington University in St.
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