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Santa Maria River Levee Failure Analysis

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Title: Santa Maria River Levee Failure Analysis


1
Santa Maria River Levee Failure Analysis
MAP IX-Mainland
2
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.

3
BACKGROUND
4
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.

5
BACKGROUND
6
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.

7
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

8
MEANDERING LOW FLOW
9
MEANDERING LOW FLOW
?
10
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.

11
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.

12
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.

13
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

14
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

15
PUBLICATIONS
  • East of Landfill Breach

16
PUBLICATIONS
  • Suey Road Breach

17
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.

18
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.

19
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

20
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.

21
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.

22
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

23
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.

24
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.

25
1998 Levee Breach (Courtesy of Santa Barbara
County Flood Control District)
26
1998 Levee Breach
?
27
TOPOGRAPHY AND TERRAIN
  • 2 ft contour data and IFSAR topographic data were
    combined to cover entire study reach

28
TOPOGRAPHY AND TERRAIN
29
UPDATED HYDROLOGY
Discharges from Supplement to Design Memorandum
No. 1 (1980)


Proposed Updated Discharges from Santa Maria
River
30
PRELIMINARY RESULTS
150,000 cfs
80,000 cfs
31
APPENDIX H
32
MAPIX-MAINLAND MEMO
33
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.

34
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.

35
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

36
SANTA MARIA ANALYSIS
37
SANTA MARIA ANALYSIS
38
SANTA MARIA ANALYSIS
?
39
SANTA MARIA ANALYSIS
US 101
Suey Road
Landfill
40
SANTA MARIA ANALYSIS
41
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

42
SANTA MARIA ANALYSIS
Breach 6
Breach 4
Breach 2 Northern Flowpath
Breach 1
Breach 3 Southern Flowpath
Breach 2 Southern Flowpath
43
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)

44
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