The July 28 1997 Fort Collins Flood Putting

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 July 17, 2007 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 Radar View

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.

Spring Creek Discharge Estimates

NWS Radar Estimates vs. Actual Precipitation TOTAL 5. 9 10. 01 NOAA 100 -year, 6 -hour rainfall = 3. 5 inches

Timetable of Flood Events 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

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

The Runoff

Past Floods on Spring Creek • Prior to Horsetooth Reservoir 1902, 1904, 1938, 1949, 1951 • Recent Flooding 1975 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

Reduced Risk Because of Acquisition • 30 Mobile Homes 2 X 30 = 60 Assume 2 people per mobile home • 9 Residential Structures 2 X 9 = 18 Assume 2 people per home • 1 Retirement Home 15 15 residents • 1 Business 5 assume 3 workers, 2 customers TOTAL = 98

Our Trip There 5 2 1 4 3