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Bayou Chene Flood Protection & Diversion Structure and Levee System Evaluation Report (LSER)

Bayou Chene Flood Protection & Diversion Structure and Levee System Evaluation Report (LSER). Bayou Chene Flood Protection and Diversion Structure. Background. 2011 Flood Fight. May 2011. Background. Bayou Chene Flood Control Structure. Bayou Boeuf Locks. Avoca Levee Alignment.

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Bayou Chene Flood Protection & Diversion Structure and Levee System Evaluation Report (LSER)

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  1. Bayou CheneFlood Protection & • Diversion Structure and • Levee System Evaluation Report (LSER)

  2. Bayou Chene Flood Protection and Diversion Structure

  3. Background

  4. 2011 Flood Fight May 2011

  5. Background

  6. Bayou Chene Flood Control Structure Bayou Boeuf Locks Avoca Levee Alignment Avoca Borrow Canal Alignment Bayou Chene Flood Control Structure Proposed Closure Structures Tabor Canal Levee

  7. ProposedBayou Chene Flood Control Structure

  8. Preliminary Report Recommendation The recommended solution consists of the following: • Steel receiving structure, +10.0’ • Steel swing barge gate to +10.0’ • Braced steel sheet pile floodwalls to +10.0’ • Elevate the existing Avoca Road to +8.0’ • A earthen levee from Avoca Road to the Structure along the existing borrow canal to elev. +8.0’ • An earthen levee with geotextile fabric from the south side of the closure structure to Tabor Canal to +8.0’ • Earthen levees along Tabor Canal utilizing the existing berm and geotextile fabric to. +8.0’ • A weir structure at the end of Tabor Canal to an of +6.0’ The features above were chosen based on cost, maintenance and operation advantages, the ease of construction, and the construction schedule.

  9. USACE Levee System Evaluation Report (LSER) Summary

  10. St. Mary Parish DFIRM & FEMA • FEMA’s preliminary DFIRM analysis (2008) assumed that all Federal (MR&T) levees under Corps jurisdiction were certifiable and provided protection from the 1% (100 year) event • Areas protected by these Levees were only subject to flooding from interior rainfall and many BFE’s in St. Mary Parish were shown to be reduced from the 1996 Maps • The final Flood Insurance Study and resulting Flood Maps are still pending; FEMA is re-evaluating parish wide levee systems based on new policy (LAMP) • The new maps are expected to be complete by the end of 2014

  11. LSER Background • SMLD was requested by FEMA to provide evidence of certification of Levees under their jurisdiction (previously assumed to be certified) • SMLD requested assistance from the USACE – NOD for all federal levee systems. • 5 flood protection systems analyzed and reports were presented in February • Morgan City Ring Levee • Terrebonne Basin Levee System (Avoca Island Cutoff) • Wax Lake East Area Levee System (Berwick - Patterson) • Wax Lake West Area Levee System • Bayou Sale Levee System (Gordy) • Results were sent to FEMA for incorporation into their DFIRM analysis for St. Mary Parish

  12. LSER Results • Each of the 5 Systems failed to meet the USACE HSDRRS criteria for providing protection from the 1% annual flood event • The controlling flood event was found to be the 1% Hurricane Surge event not the 1% Riverine Flood Event (1% Flow Line) • USACE is only authorized to maintain MR&T levees to the 1% Riverine Flow Line • Summary • For Southernmost Levee Reaches – 1% Storm Surge exceeds 1% Riverine event by an average of 6 feet • Required Hurricane Design Elevations in deficient areas range from +17’ to +21’ • Largest deficiency was 15’ on Bayou Sale Levee • Largest deficiency north of GIWW was 12.5’ on Wax Lake West Levee

  13. LSER Results • Summary Cont. • Levee Runup Analysis not based on actual field data (based on theoretical design, LIDAR, etc.) • 1% Riverine SWL was reduced in some areas (why?) • Morgan City Backwater Levees should not have been included in the LSER (not a Federal Levee System) • Currently in process of evaluating hurricane design evaluation in reports based on data sent from USACE

  14. LSER Deficient Areas • RED = Existing Elevation more than 1’ below Design Elevation

  15. LSER Profiles Station 900+00 1% Riverine Flow Line = 5.2’ 1% Storm Surge Still Water Level = 9.3’ 1% Hurricane Design Elevation = 19.0’ Existing Levee Elevation = 11.5’

  16. Implications / Path Forward • USACE will no longer provide certification for MR&T Levees in St. Mary • FEMA’s revised Flood Maps will incorporate results and BFE’s will be based on Storm Surge Elevations (much higher BFE’s than previously proposed) OPTIONS • Elevate / Reconstruct Deficient Levees • Large Costly Construction Project • Funding? • Can it be done before new flood maps are issued? • No Action • Higher Flood Insurance Premiums for Residents • New Structures must be built to higher elevations (increased construction cost) • Reduction in Economic Growth and Development Parish wide

  17. South Central Project - Proposed Path Forward • Continue working with the Iberia and St. Mary Levee Boards • Coordinate interaction of projects between Southwest Coastal and South Central (determine optimum junction points for levee tie ins on west and east sides) • Further develop restoration measures in State Master Plan • Advance specific hydrologic modeling; preliminary engineering; and permitting • Work to incorporate South Central funding in future Annual Plan budgets

  18. Questions/Comments?

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