Flood data out of date; Runoff, weather patterns have changed since risk standard was calculatedSacramento Bee - September 07, 2005 By Matt Weiser Flood data out of date; Runoff, weather patterns have changed since risk standard was calculated Sacramento Bee – 9/8/05 By Matt Weiser, staff writer Flood management experts from three states on Wednesday in Sacramento confronted a cold reality: Our risk of deadly floods is probably much higher than we think. That's because the tools for estimating and mapping flood risk are based on weather and stream-flow data that are almost 40 years old. The foundation of the system for estimating floods fails to consider wetter weather that exists in many places today, increased runoff caused by urbanization in many watersheds, and decades of sediment accumulation in waterways. In short, when the Federal Emergency Management Agency says a city like Sacramento has a 1 percent chance of flooding in any 100-year period, it relies on data that have little relevance today. And when FEMA releases maps showing areas of the city that will be flooded by such a "100-year" storm, the submerged areas noted by colorful blobs are merely an approximation. "There's a tremendous amount of uncertainty in the calculations," said Ricardo Pineda, floodplain management branch chief at the California Department of Water Resources. The issue was the focus of a panel discussion Wednesday at the Floodplain Management Association's annual conference, which continues through Friday. It draws experts from throughout California, Nevada and Hawaii. It is a coincidence that the conference occurs while corpses are being pulled from floodwaters in New Orleans in the aftermath of Hurricane Katrina. But that reality gave the conference extra urgency, and a serious tone. A moment of silence was held for New Orleans flood victims before the day's sessions began. New Orleans was said to have 1-in-250 protection, meaning it was considered able to withstand the worst flood that could be expected in any 250-year period, a higher standard of protection than Sacramento enjoys. "Unfortunately, you're here at a very sad time in our history," Sacramento Mayor Heather Fargo said in opening remarks to the group of about 250. Fargo urged the flood experts to lobby for more money for flood planning nationwide, noting it has been chronically underfunded. "Some of our priorities are wrong, and people have lost their lives because of it. What you do matters, and we need you to do it really, really well," she said. The so-called "1 percent standard" for measuring flood risk has been debated in the scientific community ever since it was first adopted in California in 1923. It is now used worldwide, but the public has remained largely unaware of its limitations. Today, one of the biggest limitations is that the standard is based on weather and streamflow data gathered in the late 1960s by the U.S. Geological Survey, said David Ford, a former Sacramento State professor and now a water resources consultant. Ford was part of a panel of experts who analyzed the 1 percent standard for a National Academy of Sciences review last year. They found that while the standard has had a number of benefits, such as encouraging safer home construction, it has many shortcomings. In addition to old weather data, the standard relies on equations and "model storms," published by the National Oceanic and Atmospheric Administration, that also have not been updated since the late 1960s, Ford said. USGS and NOAA recognize these weaknesses, but have no money to update the data. Other new variables include changes in runoff and debris flow caused by catastrophic wildfires, now more common near urbanized areas; changes in runoff volume from so-called "Pineapple Express" storms, which quickly melt mountain snowpack; and what Pineda called "tremendous uncertainties" about the structural integrity of levees. The academy's report recommended gathering new data. It also proposed steps to improve the 1 percent standard, including: new standards for levee safety; requiring flood calculations in development decisions; requiring national flood insurance but setting rates based on flood elevation; or making new development cover its own flood losses, to encourage less risky land uses. Absent such changes, the result is that today's mapping of flood risk causes many people to think they are safe from flooding. Others may face deeper or more frequent flooding than they now expect. "If you're wrong, you may find yourself under 20 feet of water, and that is a significant error," said Ronald Stork, another panelist and a senior policy advocate with the nonprofit Friends of the River. "It's time communities like Sacramento begin to have some moral outrage about that." Another key shortfall of the 1 percent standard is that it had the effect of clustering urban development just outside the mapped flood zone. And these may be the areas most at risk when flooding exceeds current maps. "I hope in the months ahead, we will see government stake out an ambitious position to move these flood management issues forward," said Assemblywoman Lois Wolk, D-Davis, who also addressed the group. "We know there is a crisis pending, and we need to do more." #
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