Flash Floods in the Region

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Flash Floods in the Region

• Hurricane Ike and Impact of Localized Flooding on
  September 14, 2008
• Board of Directors Meeting
• October 29, 2008

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Basin Average Precipitation St. Louis City and
County Watersheds in MSD
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Radar Tracked Total Precipitation
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City of St. Louis Damage Report
Homes Affected 690 MSD Covered 469 FEMA
Declaration Homes Major 186 Homes Minor
4 Businesses Minor 30 Non-Profit Major 1
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Eighty-nine Percent of 302 Affected Commercial
Properties In St. Louis County Were in Just
Seven Municipalities
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St. Louis County Ninety-one Percent of 1,932
Affected Residences in 11 Municipalities
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Deer Creek
Litzsinger Road West McKnight, East of Lindbergh
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Deer Creek in Rock Hill and Maplewood

• McKnight Road at Litzsinger

• Ladue 76 Homes (19 Major Damage)
• Brentwood 97 Homes, (36 Major Damage)
• 136 Businesses (53 Major Damage)
• Webster Groves 32 Homes (2 Major)

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Flood Damage in Floodplain Apartments
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North County Coldwater Creek

• Most Affected North County Communities
• Bellefontaine 116 Homes, 7 businesses
• Breckenridge Hills 176 Homes
• Ferguson 130 Homes (27 major)
• Florissant 184 Homes, 52 Businesses
• Hazelwood 273 Homes

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Fishpot Creek
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Fox Creek At Allenton
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Other parts of the region

• Jefferson County
• Residences 8 Major 40 Minor
• Franklin County Damage to Bridge Near Meramec
  River
• St. Clair County Some Flood Damage in East St.
  Louis
• Madison County Some Flash Flooding, but no
  significant damages

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Judys Branch Indian Creek, IL
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Silver Creek, Freeburg, IL

• Larger Stream, Rural Area, Less Development
• Peak Flow reached on 9/18
• Over 17 feet Gage Height
• Discharge (Volume) of more than 5000 cfs
• Average Discharge below 10 cfs

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MSD and Flood Liability

• The public tends to blame MSD, or the local Sewer
  District when flash flooding occurs, but the real
  source is development in the floodplain
• MSD does not cover overland flooding, only sewer
  back-ups, and only for 2400
• (This coverage is rare among any sewer districts
  nationally.)

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Observations

• Flooding can best be understood at a watershed
  level
• The current FEMA 100Year Flood zone may need to
  be revised.
• Impervious surfaces exacerbate flash flooding
• Even properties built above the 100 year flood
  zone, but still in the flood plan may be
  vulnerable in these unusual storm events
• Flood insurance is extremely important, even for
  properties not in the 100 year flood zone