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The Effects of Starting Wave Conditions on Coastal Flood Hazards: A Sensitivity Analysis for the Texas Coast Katrina Myers, PE, CFM Guillermo Simn, PE, CFM

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Outline BackgroundWHAFIS Setup Starting Wave Conditions Findings

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Past FEMA Projects

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Texas Coastal Projects Subcontractor to Halff & Associates Aransas County Calhoun County Jackson County Matagorda County Refugio County Victoria County Prime Contractor Galveston County Subcontractor to Halff & Associates Aransas County Calhoun County Jackson County Matagorda County Refugio County Victoria County Prime Contractor Galveston County

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FIS and DFIRM Coastal mapping WHAFIS modeling

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Welcome to Galveston

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Development Coastal Structures Welcome to Galveston Bays

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Long History of Storms Ike 2008 1915 1900 Carla 1961 Carla 1961 Alicia 1983 Alicia 1983

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Long History of Storms

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WHAFIS Overview

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Transects

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USACE Storm Surge

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Land Cover

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Topography/Bathymetry

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Starting wave conditions Fetch STWAVE Hindcast Data Options

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Starting Wave Conditions: Fetch

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Starting Wave Conditions: STWAVE U.S. Army Corps of Engineers, (2010). Flood Insurance Study: Coastal Counties, Texas. Intermediate Submission 1: Scoping and Data Review. STWAVE WAM ADCIRC

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Starting Wave Conditions: STWAVE 2D wave model, uses output from model surface as WHAFIS starting wave height and period.

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STWAVE T p

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Starting Wave Conditions: Hindcast Data Hourly wave data from WIS stations

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Starting Wave Conditions: Hindcast Data

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Relationship Between T p and H mo

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Overview Map

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Coastal Analyst Taylor Engineering-developed GIS tool for WHAFIS modeling and mapping

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Transect 18

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Gulf T18, Starting Conditions T p (sec)H c (ft) Fetch6.449.48 Hindcast Data12.2110.45 STWAVE11.4510.45 Ground0 ft NAVD Stillwater13.40 ft NAVD Depth Limited Wave Height 10.45 ft

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Gulf T18, Buildings Wave Crest Elevation

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Gulf T18, Open Water Wave Crest Elevation

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Gulf T18, Marsh Wave Crest Elevation

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Transect 18

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Bay T18, Bay Shoreline T p (sec)H c (ft) Fetch6.928.89 Bay Fetch3.877.34 Hindcast Data12.219.26 STWAVE11.459.22 Bay STWAVE5.38.45 Stillwater14.05 ft NAVD Depth Limited Wave Height 10.96 ft Fetch Length3.16 miles

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Bay T18, Bay Shoreline Wave Crest Elevation

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Conclusions Higher Wave Period from STWAVE and Hindcast Data compared to fetch No difference after transect crosses high ground/ above surge areas Very little difference on wave crest elevation for areas where wave is dampened by buildings or trees

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Conclusions Less than 0.5ft difference in areas where wave is regenerating in marsh and open water Larger differences between transects originating in the bay compared to the Gulf Potential impact on wave runup

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Thank you