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The July 28,1997 Fort Collins Flood: Putting the Stormwater System to the Test How Did it Serve to Minimize Societal Impact?. Matt Kelsch Hydrometeorologist Field Trip Leader UCAR/COMET August 12, 2008. Material Contributed by: Marsha Hilmes-Robinson Floodplain Administrator
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The July 28,1997 Fort Collins Flood:Putting the Stormwater System to the TestHow Did it Serve to Minimize Societal Impact? Matt KelschHydrometeorologistField Trip LeaderUCAR/COMET August 12, 2008 Material Contributed by: Marsha Hilmes-Robinson Floodplain Administrator City of Fort Collins, Colorado
Stormwater Utility • System Repair and Maintenance • System Construction • Development Review • Floodplain Administration • Water Quality • Master Planning Annual budget is approx. $6 million.
What is a 100-year flood? • The 100-year flood is a statistical designation for a specific streamflow that has a 1% chance of being equaled or exceeded in any given year. • The 500-year flood has a 0.2% chance of being equaled or exceeded in any given year. • Short period-of-record and urbanization greatly affect the accuracy of these measures.
Floodplains FEMA: Poudre River, Spring Creek, Dry Creek, Boxelder Creek, Cooper Slough Locally Designated: Fossil Creek, Old Town, West Vine
The Meteorology Low level flow into the terrain (upslope). Dewpoints of 60+ ( a big deal for Colorado).
The Localized Nature Rainfall 5:30-11:00 PM 28 July 1997 Localized area of extreme rain on SW side of town. Spring Creek watershed (13 sq miles) takes the bulk. Water surges eastward along west-east roads.
NWS Radar Estimatesvs. Actual Precipitation TOTAL 5.9 10.01 NOAA 100-year, 6-hour rainfall = 3.5 inches
5:30 8:00 8:30 9:00 9:40 10:30 10:55 1:20 Rain begins, Flash Flood Watch is in Effect EOC Activated Ponds Overflowing, rapid water rescues begin Most intense rain commences NWS Flash Flood Warning Storm begins to dissipate and move northeast Trailer Park Flooding, Fires, Train Derailment Declared City Disaster Timetable of Flood Events
The Impact 5 dead, dozens injured, major destruction along Spring Creek Over $100 million in damages at CSU.
Building Damages Destroyed: 97 mobile homes, 5 houses Damaged: 1,988 properties
Past Floods on Spring Creek • Prior to Horsetooth Reservoir1902, 1904, 1938, 1949,1951 • Recent Flooding1975 and 1977 Spring Creek Improvements:$5 Million spent since 1989 • Acquisition and Relocation of Structures • Channelization • Storm Drainage Improvements • Reinforcement of Burlington-Northern Railroad Embankment • Bridge Improvements
30 Mobile Homes Assume 2 people per mobile home 9 Residential Structures Assume 2 people per home 1 Retirement Home 15 residents 1 Business assume 3 workers, 2 customers 2 X 30 = 60 2 X 9 = 18 15 5 TOTAL = 98 Reduced RiskBecause of Acquisition
Flash Flood Field Trip Route Fort Collins Rocky Mountain National Park Lawn Lake Big Thompson Canyon Boulder