Santa Maria River Levee Failure Analysis

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Santa Maria River Levee Failure Analysis
MAP IX-Mainland
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BACKGROUND

• Santa Maria Valley levees are part of a flood
  control and water conservation project which
  includes the Twitchell Reservoir.
• Twitchell Reservoir was constructed by the BOR in
  1958 and Santa Maria Valley levees were completed
  by USACE in 1963.
• Project was developed to provide protection
  against floods and debris for the City of Santa
  Maria, and agricultural areas.

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DAMAGE HISTORY

• Due to natural channel width of approx 2,000,
  the floods do not fill the channel but meandered
  and impinged against the existing levees.
• Impingement undermined the levee toe and erode
  the levee demonstrating that the levees are
  vulnerable to smaller discharges and as a result
  would not provide the protection as designed.

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MEANDERING LOW FLOW
?
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PUBLICATIONS

• USACE (1980) East of Landfill Breach

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PUBLICATIONS

• USACE (1980) Suey Road Breach

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1998 Levee Breach

• Levee sustained break near Guadalupe and the
  Bonita School Crossing The break washed away
  approximately 1,000 feet of levee. It was
  estimated that over 20,000 cfs of water was
  flowing down the river. With flood control
  employees and contractors working 24 hours
  straight, it took 61 truckloads of rock and
  concrete rubble to fill in the breach.

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SANTA MARIA ANALYSIS

• Previous analysis included five segments for the
  left levee
• Fulgers point to Bradley Canyon (most upstream
  segment)
• Bradley Canyon to landfill
• Landfill to Suey Bridge
• Suey Bridge to U.S. Highway 101 Bridge
• U.S. Highway 101 Bridge to State Highway 1 Bridge

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SANTA MARIA ANALYSIS

• FEMA asked MAPIX-M for a revised analysis that
  used a single levee segment for the left levee
  from Bradley Canyon to State Highway 1 Bridge
  as prescribed by Appendix H

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SANTA MARIA ANALYSIS - Terrain

• 2 ft contour data and IFSAR topographic data were
  combined to cover entire study reach

IFSAR
2 ft contours
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SANTA MARIA ANALYSIS - Terrain
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SANTA MARIA ANALYSIS - Hydrology
Discharges from Supplement to Design Memorandum
No. 1 (1980)


Proposed Updated Discharges from Santa Maria
River
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SANTA MARIA ANALYSIS - Hydraulics
Lateral Weirs in Hydraulic Model
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SANTA MARIA ANALYSIS - Hydraulics

• Consideration of US Hwy 101
• Use of US Hwy 101 as-builts provided by
• Santa Barbara County
• Flow through underpasses
• Main Street
• Jones Street
• Flow over US Hwy 101 near
• Santa Maria River

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SANTA MARIA ANALYSIS - Flows
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SANTA MARIA ANALYSIS - Results
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SANTA MARIA ANALYSIS - Results
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FIS TIMELINE
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QUESTIONS