the july 28,1997 fort collins flood: putting the stormwater system to the test how did it serve to...
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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 KelschMatt KelschHydrometeorologistHydrometeorologistField Trip LeaderField Trip LeaderUCAR/COMETUCAR/COMET
August 12, 2008August 12, 2008
Material Contributed by:Material Contributed by:Marsha Hilmes-RobinsonMarsha Hilmes-RobinsonFloodplain AdministratorFloodplain AdministratorCity of Fort Collins, ColoradoCity 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.
FloodplainsFEMA:
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
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.
Rainfall 5:30-11:00 PM 28 July 1997
Spring Creek Discharge Estimates
Location 100-year Discharge
(cfs)
500-year Discharge
(cfs)
July 28, 1997 Discharge
(cfs) Taft Hill Rd. 1,492 2,347 3,500
Drake Rd. 1,635 2,575 4,200
Shields St. 2,135 3,325 8,250
Remington St. 1,528 1,846 5,000
Riverside St. 2,187 2,920 5,500
NWS Radar Estimatesvs. Actual Precipitation
Time NWS Actual 6-7 pm 0.6 1.02 7-8 pm 0.6 1.02 8-9 pm 1.2 2.03
9-10 pm 2.5 4.24 10-11 pm 0.6 1.02 11-12 pm 0.4 0.68
TOTAL 5.9 10.01
NOAA 100-year, 6-hour rainfall = 3.5 inches
Timetable of Flood Events5:30
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 Impact5 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 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 RiskBecause of Acquisition
• 30 Mobile HomesAssume 2 people per mobile home
• 9 Residential StructuresAssume 2 people per home
• 1 Retirement Home15 residents
• 1 Businessassume 3 workers, 2 customers
2 X 30 = 60
2 X 9 = 18
15
5
TOTAL = 98
Flash Flood Field Trip Route
18Boulder
Fort Collins
Big Thompson Canyon
Rocky Mountain National Park
Lawn Lake
Lunch in the Big Thompson Canyon
19
Rocky Mountain national Park
20