WRC HURRICANE DAMAGE POTENTIAL SCALE GULF OF MEXICO HURRICANES PAST – PRESENT – FUTURE MMS ITM
Morganza to the Gulf Hurricane Protection Feasibility Report March 2002 Hydraulic Analysis.
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Transcript of Morganza to the Gulf Hurricane Protection Feasibility Report March 2002 Hydraulic Analysis.
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
• Datum errors as much as 1 foot in both topography and measured water levels.
• Calibration - Hurricane Andrew (1992) and 1991 rainfall event
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
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
Table 2.5.1 Exterior Stage Frequencies
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
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
Morganza to the Gulf Hurricane Protection Restudy
2008
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
‘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
Frequency Analysis
• JPM-OS (Joint probability-optimum sampling technique)
• Products will be 50-, 100-, 500- & 1000-yr frequency stages
• & Confidence bands
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
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