Santa Maria River Levee Failure Analysis

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Santa Maria River Levee Failure Analysis
MAP IX-Mainland
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BACKGROUND

• The Santa Maria Valley levee is a part of a flood
  control and water conservation project consisting
  of the Twitchell Reservoir and the Santa Maria
  Valley Levees.
• Twitchell Reservoir was constructed by the Bureau
  of Reclamation in 1958 and construction of the
  Santa Maria Valley levee was completed by the
  USACE in 1963.
• The project was developed to provide protection
  against floods and debris for the City of Santa
  Maria, agricultural lands in the Santa Maria
  Valley, and residential, commercial, industrial,
  and public properties. It would also protect US
  Highway 101, State Highway 1, Southern Pacific
  Railroad, Santa Maria Valley Railroad, three
  highway bridges, and one railroad bridge.

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BACKGROUND
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BACKGROUND

• Construction included
• Approximately 17 miles of revetted levee along
  the left bank of the Santa Maria River from
  Fugler Point (at the junction of the Cuyama and
  Sisquoc Rivers) to approximately 600 downstream
  to the State Highway 1 Bridge at Guadalupe
• About 5 miles of revetted levee along the right
  bank of the Santa Maria River from a point about
  1 ¼ miles downstream from US Highway 101 to a
  point about 1 ½ miles upstream from the Southern
  Pacific Railroad Bridge at Guadalupe and
• Around 1.8-2.06 miles of channel and revetted
  levees from the mouth of Bradley Canyon to Santa
  Maria River to divert floods from Bradley Canyon
  to the Santa Maria River.

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BACKGROUND
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DAMAGE HISTORY

• A number of floods have occurred since the levees
  were constructed, each with relatively low peak
  discharges. Because the natural channel averages
  about 2,000 in width, the floods did not fill
  the channel but meandered and impinged against
  the existing levees.
• This impingement undermined the levee toe causing
  considerable damage and jeopardized adjacent
  properties, demonstrating that the project was
  vulnerable to smaller discharges and as a result
  would not provide the protection for which it was
  designed.

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DAMAGE HISTORY

• Following is the Santa Maria River damage history
  since its construction
• 1966 Revetment damages
• 1969 Near breach
• 1978 Near breach
• 1983 Revetment damages
• 1995 Revetment damages
• 1998 Total breach, other revetment damage
• 2001 Revetment damage

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MEANDERING LOW FLOW
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MEANDERING LOW FLOW
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PUBLICATIONS

• Design memorandum No.1, General Design for Santa
  Maria Valley, Levees and Channel Improvements,
  dated December 1958, prepared by USACE. This
  document described the purpose and scope of the
  flood control project and included pertinent
  technical data such as composite quantities,
  drainage areas and design discharges, levee
  dimensions, cost and benefit-cost ratio etc.
• Operation and Maintenance Manual for Santa Maria
  Valley Levees and Channel Improvements, dated
  January 1964, prepared by the USACE. This manual
  prescribed standard procedures for the operation
  and maintenance of the federally constructed
  Santa Maria Valley levees and channel
  improvements. It superseded all previously issued
  operation and maintenance manuals.

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PUBLICATIONS

• Santa Maria Levees Investigation Report, dated
  August 1970, prepared by USACE. The purpose of
  this report was to present the results of
  investigations conducted to determine the
  foundation and facing stone properties of the
  existing levees to determine the cause of facing
  stone disturbance and to provide a basis for
  restoration design. This investigation was
  initiated because during the storm period of
  February 25 and 26, 1969, serious embankment
  erosion occurred at several locations on the
  Santa Maria levees and the district had reported
  four areas of apparent levee failure and two
  areas of possible disturbances.

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PUBLICATIONS

• Design Deficiency Report of the Santa Maria
  Valley Levees, dated August 1974, prepared by
  USACE. This report was submitted to present
  proposed revisions to the existing project. The
  supplemental design provided for changes in
  design concept to ensure the safety and integrity
  of the levees and to provide adequate hydraulic
  capacity near the Southern Pacific Railway and
  State Highway 1 bridges. It was stated in this
  report that when levees were subjected to flows
  ranging from 10 to 17 percent of the design
  capacity (1966 and 1969 floods), the levees did
  not provide the protection as intended by the
  original design. It was also noted that flows
  with such magnitude do not occupy the entire
  channel but tend to meander. Damage in all cases
  was at points where flows impinged on levees.

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PUBLICATIONS

• Supplement to Design Memorandum No.1 for Santa
  Maria Valley Levees and Channel Improvements,
  dated March 1980, prepared by USACE. The purpose
  of this report was to evaluate and recommend
  designs for remedial construction, which would
  protect the levees and permit the levees to
  function as authorized by Congress. As in the
  previous reports it was noted here that since
  completion of this project a number of floods
  with relatively low peak discharges have occurred
  and because the natural channel averages about
  2,000 in width, these floods did not fill the
  channel but meandered and impinged against the
  existing levees undermining the levee toe causing
  considerable damage and jeopardizing adjacent
  properties. Five reaches were identified in this
  report as being subject to impingement and
  failure on the occurrence of flood in the river

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PUBLICATIONS

• Along the upper end of the left bank levee at
  Fuglers Point
• Along the left bank levee downstream from the
  mouth of Bradley Canyon
• Along the left bank levee downstream from Suey
  Road crossing
• Along the right bank at its upper end
• Along the left bank upstream from the Southern
  Pacific Railroad bridge

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PUBLICATIONS

• East of Landfill Breach

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PUBLICATIONS

• Suey Road Breach

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PUBLICATIONS

• It was indicated in the report that based on
  levee performance during past flood events, the
  levee embankment is estimated to undergo serious
  undermining at about 10,000 cfs. As the discharge
  increases, the levee would progressively erode,
  so that an expected breach length of 1,200 feet
  would result on the occurrence of an SPF. It was
  noted that overflow of developed lands, in Santa
  Maria Valley would take place on occurrence of
  breaches in the levees the extent of overflow
  and the magnitude of resultant damage would
  depend on the location of the breach and would
  include the city of Santa Maria and the
  agricultural area in Santa Maria Valley. It was
  estimated that property valued at over
  800,000,000 (1980 value) would be subject to
  damage as a result of breaching of the levees.

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PUBLICATIONS

• Santa Maria River Levees Condition Survey,
  dated May 1988, prepared by USACE. This report
  evaluated the condition of the embankments and
  facing stone on the Santa Maria levees from the
  upstream end near Fuglers Point to the downstream
  end at Guadalupe based on visual examination
  relative to those observed in 1980-1981
  inspections. It was concluded in this report that
  the gradation of the facing stone had not changed
  significantly and was recommended that the
  performance of all stone facing should be
  monitored after a major flood, especially for
  areas where the stone is smaller than 5 inches.

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PUBLICATIONS

• Santa Maria Levees, Study on Adequacy of Levee
  Stone, dated May 1996, prepared by USACE. The
  report summarized the findings and drew
  conclusions from field investigations of the
  stone protection for Santa Maria River Levees
  conducted in July 1995. The purpose of the
  investigation was to identify the locations along
  the levees where the mean diameter of the facing
  stone is less than 6 inches, determine the
  thickness of the layers with undersized stones,
  and develop an approximate guide to assess
  degradation and to evaluate the existing rock
  sizes. The conclusions of the report were
• The mean diameter was between approximately 8-12
  inches
• If the stone on the surface is small, it is
  generally of appropriate size at depth however,
  in limited areas due to segregation or placing
  thin layers during original construction, small
  stones were found below the surface
• Two reaches on the left levee had median size
  less than 6 inches
• Degradation was negligible
• Typically the thickness of the riprap is greater
  than 18 inches
• The existing riprap layer would require some
  additional riprap in limited areas to meet the
  1952 design criteria and substantial additional
  riprap to meet current (1994) design criteria

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PUBLICATIONS

• Santa Maria Levee, Storm and Damage History and
  Reinforcement Recommendations, dated January
  2006 prepared by the District. It is the most
  comprehensive report on Santa Maria Levee
  construction and damage history with
  recommendations and a reinforcement construction
  cost estimate.

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INSPECTIONS SINCE 1993

• the Santa Barbara County Flood Control District
  (District) is responsible for the operations and
  maintenance of the flood-control levees and
  channel improvements. After the USACE completed
  construction of the levee (1963), the District
  assumed Operation and Maintenance responsibility.
  Following is a summary of a few critical
  observations during some inspections since 1993
• August 1993 Personnel from the USACE and
  District performed an inspection of the levee and
  found it had one major problem namely
  deterioration of the rock facing. At several
  locations the rock had turned to gravel with a
  maximum size of approximately 4.

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INSPECTIONS SINCE 1993

• June 1999 Erosion had destroyed several places
  along the slope of the lower access road and
  along the landside slope of the levee.
• October 1999 It was restated that there were
  several places along the slope of the lower
  access road and along the landside slope of the
  levee itself which sustained some surface
  erosion.
• January 2002 Staff from the District met with
  USACE staff to inspect the levee. At several
  locations along the levee a closer inspection of
  the riprap was conducted. Significant breakdown
  of the surface stone was observed

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INSPECTIONS SINCE 1993

• - November 2003 The entire south levee and a
  portion of the north levee, which had been
  rebuilt following storm damage sustained in March
  2001, were both inspected. Observed and
  discussed was the breakdown of stone which
  occurred primarily downstream of US Highway 101.
• The key maintenance issues seemed to be the rock
  facing and the potential low flow damages. Rock
  facing is important because the levee is a sand
  core levee. Failure of the rock armoring will
  result in a rapid dissipation and erosion of the
  sand core resulting in total levee failure.
  Additionally, the Santa Maria River being wide
  and shallow results in drastic meanders in lower
  flows. The low flows can hit the levee at an
  angle, almost perpendicular in some cases
  impinging strong dynamic forces of the rock
  facing and causing failure.

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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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1998 Levee Breach (Courtesy of Santa Barbara
County Flood Control District)
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1998 Levee Breach
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TOPOGRAPHY AND TERRAIN

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

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TOPOGRAPHY AND TERRAIN
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UPDATED HYDROLOGY
Discharges from Supplement to Design Memorandum
No. 1 (1980)


Proposed Updated Discharges from Santa Maria
River
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PRELIMINARY RESULTS
150,000 cfs
80,000 cfs
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APPENDIX H
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MAPIX-MAINLAND MEMO
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SANTA MARIA ANALYSIS

• Traditionally, the without levee analysis
  entails removing the levee system completely and
  including the entire cross sectional area in the
  water surface computations and delineating a
  continuous floodplain that consists of the
  riverside and landside areas.
• The topography of the area behind the Santa Maria
  levee is such that in case of a failure, the
  portion of the flood entering the landside of the
  levee will take its own path (overland flow) and
  flow parallel to Santa Maria River and will
  re-join the main river somewhere downstream.

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SANTA MARIA ANALYSIS

• The failure analysis entails
• Replacing each segment with a lateral weir, one
  segment at a time.
• Computing the magnitude of the diverted flow
  through each lateral weir for each segment
  individually.
• Performing an overland flow analysis using
  HEC-RAS and determining the Base Flood Elevations
  (BFEs) along the flow paths individually.
• Mapping the corresponding floodplains.
• Once one segment fails, it is assumed that other
  segments will remain in place. Simultaneous
  failure scenarios will not be considered when
  running HEC-RAS. This assumption is consistent
  with historical events and the USACE analysis.
• Once the floodplain for each segment failure is
  mapped, they will be merged into one floodplain
  and the highest BFEs will be placed on it.

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SANTA MARIA ANALYSIS

• Santa Maria levee along the left bank (looking
  from upstream to downstream) can be divided into
  five different segments as follows
• 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
• The levee along the right bank consists of only
  one segment
• From a point approximately 17,600 feet upstream
  of Bonita School road to a point approximately
  7,900 feet upstream of Southern Pacific Railroad

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SANTA MARIA ANALYSIS
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SANTA MARIA ANALYSIS
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SANTA MARIA ANALYSIS
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SANTA MARIA ANALYSIS
US 101
Suey Road
Landfill
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SANTA MARIA ANALYSIS
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SANTA MARIA ANALYSIS

• Levee Breach 2 modeled as a lateral weir
• HEC-RAS computes about 10,000 cfs (100-yr Q)
  leaves the Santa Maria River
• Levee Breach 3 modeled as a lateral weir
• HEC-RAS computes about 19,000 cfs (100-yr Q)
  leaves the Santa Maria River

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SANTA MARIA ANALYSIS
Breach 6
Breach 4
Breach 2 Northern Flowpath
Breach 1
Breach 3 Southern Flowpath
Breach 2 Southern Flowpath
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COORDINATION

• Coordination Process
• Initial Community Coordination meeting (April,
  2006)
• Define scope and coordinate timeframe
• Follow-up meeting and field reconnaissance (July,
  2006)
• Better understand physical conditions
• Coordinate technical approach and data
  requirements
• MAPIX-Mainland Memorandum (August, 2006)
• Community meeting to present technical
  methodology for the failure analysis (October,
  2006)
• Community meeting to present preliminary results
  (April, 2007)

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QUESTIONS