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Morganza to the Gulf Hurricane Protection Feasibility Report March 2002

Morganza to the Gulf Hurricane Protection Feasibility Report March 2002. Hydraulic Analysis. Interior Drainage Analysis. UNET (gradually varied unsteady flow 1D model that conserves energy & volume) Geometry - mixed, some new & some from earlier studies back to 1987, datum to NGVD

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Morganza to the Gulf Hurricane Protection Feasibility Report March 2002

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  1. Morganza to the Gulf Hurricane Protection Feasibility Report March 2002 Hydraulic Analysis

  2. Interior Drainage Analysis • UNET (gradually varied unsteady flow 1D model that conserves energy & volume) • Geometry - mixed, some new & some from earlier studies back to 1987, datum to NGVD • Datum errors as much as 1 foot in both topography and measured water levels. • Calibration - Hurricane Andrew (1992) and 1991 rainfall event

  3. ADCIRC Modeling • Grid developed from surveys, nautical charts & quadrangle maps • Verification – Carmen(1974), Juan (1985) & Andrew (1992) • 17 experienced storms from 1893 to 1992 used to generate data set • Storms experienced prior to ~1945 produced unacceptable results. Sparse storm data during this earlier period did not permit accurate computation of surge elevations

  4. Frequency Analysis • EST (Emperical sampling technique) – not used to analyze ADCIRC results due to the lack of data during the 100 year storm analysis period, but used for UNET results with some smoothing • Plotting position formulation – used to generate exterior frequencies at gage locations and interpolated between. • HEC-FDA used to compute confidence bands based on estimated record length

  5. Table 2.5.1 Exterior Stage Frequencies

  6. Levee Design • Windspeeds from GM – Larose GDM, 1972 (77mph = 100-yr frequency) • ACES used to determine Hs, T & Levee Height • Runup from Hs & T added to SWL determined levee height

  7. Table 2.6.5. 100 Year Frequency Hurricane, Wave Characteristics And Design Wave Runup And Design Elevations Of Protective Structures, Highway 57 Alignment – Base Conditions

  8. Morganza to the Gulf Hurricane Protection Restudy 2008

  9. Interior Drainage • HEC-RAS • Geometry – from ADCIRC grid • Grid composed of ~ 10-year old Lidar • Original datum adjusted to NAVD88(2004.65) • May 2008 - Corrections grid datum using latest survey data • Calibration - Hurricane Rita (2005) and a recent rainfall event

  10. ‘New’ ADCIRC Modeling • Preliminary stages generated in LACPR study not used due to errors in grid datum and recent availability of new survey data • Restudy will use a sub-set, 54 hypothetical storms, specifically for Morganza region • Verification – Rita(2005) • Model - base & future, w & w/o levee alignments

  11. Frequency Analysis • JPM-OS (Joint probability-optimum sampling technique) • Products will be 50-, 100-, 500- & 1000-yr frequency stages • & Confidence bands

  12. Levee Design • Waves – STWAVE (using ADCIRC grid) Hs & T plus confidence bands generated for required frequencies • Standard deviations (std) for SWL, Hs, & T • Runup & overtopping at 50% confidence from PCOverslag determines levee slope. • Design Height determined at overtopping limit of 0.1 cfs/linear foot at 90% confidence for base & future conditions

  13. Structure Design • Waves – STWAVE (using ADCIRC grid) Hs & T plus confidence bands generated for required frequencies • Standard deviations (std) for SWL, Hs, & T • Design Heights determined for vertical walls by overtopping limit of 0.1 cfs/linear foot at 90% confidence for future conditions

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