Feasibility study by Ben C. Gerwick, Inc. New Orleans East Land Bridge Study LPV 111 to Chef Menteur, Chef Menteur to Rigolets Presentation to the SLFPA.E by Dale E. Berner, PhD PE and Jean O. Toilliez, PhD, PE THURSDAY, DECEMBER 20, 2012 1 EAST LAND BRIDGE
East Land Bridge feasibility study Outline › Existing Studies › Published research and body of results available › Background information and key vulnerable locations › Met ocean assessment and coastal state of the art › Plan formulation › Definition of goals, constraints, performance criteria and screening › Preliminary levee design parameters › Rationale for numerical model tests › Hydrodynamic model test results › Definition of test cases, goals of the modeling efforts › Proposed plan and analysis › Proposition for immediate implementation and concept design, draft cost analysis › Conclusions and recommendations › Action plan, recommendations for immediate implementations and future efforts THURSDAY, DECEMBER 20, 2012 2 EAST LAND BRIDGE
East Land Bridge feasibility study Chapter 2 Existing studies THURSDAY, DECEMBER 20, 2012 3 EAST LAND BRIDGE
Existing studies Background References › Louisiana Draft Master Plan (2007 and 2012) › General framework; use it to define objectives and constraints for plan formulation › UNO Report on Hydrodynamic Modeling of the Tidal Prism in the Pontchartrain Basin › Optimal pass opening widths study using FVCOM model › Recommend wide openings at both passes to minimize disruption on tidal hydrodynamics (tidal prism and hydro.period) › Louisiana Coastal Protection and Restoration (LACPR) Final Technical Report › Very large database available directly applicable to current study, with information on: › Storm surge › Present day/future condition hazard › Future projects › Large collection of case studies directly connected to the East Land Bridge › Major basis for future work; this study to draw on these results › Framework for Environmental Assessment of Alternative Flood Control Structures on Chef Menteur and Rigolets Passes › Rigorous assessment of pass impact on ecosystem; framework for future installations › NRC Review of the LACPR Technical Report › Others: see report for complete list of references THURSDAY, DECEMBER 20, 2012 4 EAST LAND BRIDGE
LACPR Technical Report // CPRA ELB as Critical Feature and Location for Future Flood Protection System › Land bridges › " ����������������������������������������� ������������������������������������� ���������������������������������������� ��������������������������������� ����������������������������������� ����������������������������������� ������������������������������ ������������������������������ ��������� " › ELB as Strategic Location for Flood Defense System › Several alignment directly on ELB path › CPRA (2007) states: › " ������������������������������������ ��������������������������������������� ��������������������������������������� �������������������������������������� ������������������������ " THURSDAY, DECEMBER 20, 2012 5 EAST LAND BRIDGE
LACPR Technical Report Levee at ELB – Overtopping vs. Non.overtopping and Consequences › In LACPR Technical Report › Two solutions were envisaged for the partial or complete hydraulic closure of Lake Pontchartrain. › Both solutions dismissed based on cursory review of engineering feasibility issues › This report to investigate this matter in greater depth and scope › Barriers and levees considered along US 90 alignment in LACPR against various design storm surge cases › Use this information when devising additional cases to evaluate ���������������� ���������������������� "���������������� �������������� ������������� ! ����������� ������ ! 100.YRP 25 12.5 400.YRP 32 12.5 1000.YRP 36 12.5 Added value: design basis for flood control system to be investigated in this study THURSDAY, DECEMBER 20, 2012 6 EAST LAND BRIDGE
LACPR Technical Report // FEMA Present Day and Estimated Future Condition Storm Surge Hazard at ELB › In LACPR Technical Report › Include high estimates for future sea. level rise conditions › Estimates provide a good reference for the existing flood risk in the South Lake Pontchartrain region, in the absence of a flood control system › Return periods: 100, 400 and 1000. YRP › Double check with most recently (1984) FEMA FIRM stating 18ft. NGVD29 storm surge elevation #������$����% &������� ������� ���%�������'����� ���%����������! Added value: design basis for flood control system ����(����! to be investigated in this study 100.YRP 14.6 17.9 400.YRP 17.8 21.5 1000.YRP 19.4 23.8 THURSDAY, DECEMBER 20, 2012 7 EAST LAND BRIDGE
LACPR Technical Report Structures at ELB: Existing Results › Alternative EA › Full closure at US.90 with presence of closed flood control structures at the Chef Menteur and Rigolets passes. The levee is non.overtopping, with a design crest elevation of 27ft. This option is the most effective at reducing storm surge near Slidell. › Alternative EB › Same as EA but with an overtopping levee, with top crest elevation of 12.5ft. Again, the two passes at ELB Are in a closed position. › Alternative EC › This alternative is identical to EB, however in this case the two passes are in an open position (i.e. no flood control structures). THURSDAY, DECEMBER 20, 2012 8 EAST LAND BRIDGE
LACPR Technical Report Effect of Structures: Value of High.Crested Levee System Alt. EA Alt. EB Alt. EC THURSDAY, DECEMBER 20, 2012 9 EAST LAND BRIDGE
LACPR Technical Report Effect of Alternatives on MEOW and MWLD at Key Locations at and Near ELB MEOW (left) and MWLD (right) bar charts show the impact of hard overtopping and non.overtopping structures at different sites near the ELB for various alternatives. The massively non.overtopping flood control structure (Alt. EA) diverts some amount of storm surge toward neighboring areas, in exchange for a large reduction in storm surge near Slidell, LA. Undeniable value of high.crested levee system to reduce storm surge )������������*+%����������%���������%��+��*����+����, THURSDAY, DECEMBER 20, 2012 10 EAST LAND BRIDGE
East Land Bridge feasibility study Chapter 3 Background information THURSDAY, DECEMBER 20, 2012 11 EAST LAND BRIDGE
NOAA DEM Timeline for study: 2060 Regional influence: St. Tammany, Orleans, St. Bernard parishes and State of Mississippi Critical location: direct line of defense against storm surge THURSDAY, DECEMBER 20, 2012 12 EAST LAND BRIDGE
Federal Levee Lake Pontchartrain and Vicinity (LPV) 111 to Rigolets Pass. As delineated in the project, the area of considered here covers approximately 40 square miles. THURSDAY, DECEMBER 20, 2012 13 EAST LAND BRIDGE
&��-������� ���.#&����! ��.#&����! /���.#&����! ���.#&����! Subject to frequent, severe Maximum water 15.4 10 11.6 12.7 flooding level Source: Shell Minimum water .2.3 Beach, LA .1.8 .2.0 .2.1 level Estimated wind "��%��$��% � �.#&���$*! ��.#&���$*! /���.#&���$*! ���.#&���$*! speeds: exposed Bay Waveland, MS 74 77 79 82 location Shell Beach, LA 82 88 94 107 "01�1������ "�����%�$�* 1�����������2���� &��3�&����% Large waves near *���*� Chandeleur Islands capable 73145 15 m 6.5 m (21 ft) 12.50 s of entering into 73143 20 m 7.3 m (24 ft) 12.50 s Lake Borgne and vicinity 73142 20 m 8.0 m (26 ft) 12.50 s 73141 21 m 8.8 m (29 ft) 12.50 s THURSDAY, DECEMBER 20, 2012 14 EAST LAND BRIDGE
LACPR Technical Report Local wave climate Evidence of value of marhsland in wave attenuation Degraded Chandeleur Islands still provide significant reduction in wave height (breaking/friction) 6.8 ft significant wave height expected near ELB STWAVE maximum wave height spatial distribution for 150 storms evaluated for the 2007 (current) conditions near the ELB, per (USACE 2009) THURSDAY, DECEMBER 20, 2012 15 EAST LAND BRIDGE
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