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CHAMP Application - Open Ocean Wave Dominated V Zone Case

This and the previous (August 2002) Coastal Hazard Listserv bulletins will address the CHAMP modeling and coastal engineering data preparation techniques typically associated with determining coastal flood hazards for a non-restricted fetch (open ocean) wave height-dominated case. A general description of data requirements for coastal flood hazard analyses was provided in the July 2002 bulletin, and should be referred to prior to starting this exercise.

In this month's bulletin we will discuss the methodologies for determining several coastal parameters for this non-restricted fetch (open ocean) wave height dominated case, including:

  • Wave Height Analysis for Flood Insurance Studies (WHAFIS)
  • Primary Frontal Dune
  • Mapping

This information will then be applied to the following modules in CHAMP, including:

  • Module 4 - Wave Height Analysis (WHAFIS)
  • Module 6 - Summary Tables and Graphics for Mapping

The complete inundation of the barrier island during the 1% annual chance coastal flood does not allow for the development of wave runup. As a result, wave runup will not be considered in the mapping of the coastal flooding.

Previously, several coastal modeling methodologies were discussed for this case in the August 2002 bulletin, including:

  • Geomorphic Setting
  • Topographic Data Source
  • Stillwater Elevation (SWEL) Determination
  • Initial Wave Height and Period Determination
  • Wave Setup Determination
  • Erosion Treatment

Please download the zipped file named 'ch_sep02.zip' by clicking here. It includes a CHAMP database which has been developed in entirety. This completes the zipped file of the same name presented in the August 2002 bulletin. For this month's bulletin:

  • extract the file named 'openoceancase.mdb' from 'ch_sep02.zip', and save it directly to your local directory (C:\Program Files\Champ)
  • extract the files named 7.dxf, mg.dat, w7.dat, and W7.out from 'ch_sep02.zip', and save them in a folder named 'openoceancase' to be located in your local directory (C:\Program Files\Champ)

In both cases, the previously named files of the same name should be overwritten. The openoceancase.mdb database can be opened by clicking on the 'Open' button on the CHAMP main menu button bar.

  • WHAFIS - The WHAFIS input specifically for this case study in Franklin County, Florida considers the following information which is entered into the CHAMP 'Module 1 -Transect Description/Parameter Entry' module, including:
    • 1% SWEL - 8.1 ft
    • 10% SWEL - 5.1 ft
    • Fetch length - unlimited, non-restricted fetch as the transect is subject to open ocean conditions
    • Significant wave height - 27.2 ft.
    • Deepwater wave period - 11.02 sec
    • Wave setup - 1.8 sec

Additional WHAFIS input information is included in the CHAMP Module 4 - Wave Height Analysis data input window, including:

  • Card Type
    • IF cards were used for open fetches over inland areas such as beaches and shallow inland water bodies.
    • A DU card was used to compute wave dissipation over the flooded sand dune which is a consistent feature at the barrier islands of Franklin County, FL.
    • VE cards were used to compute wave dissipation associated with vegetation. In this case, vegetation coefficients were used to characterize trees which are characteristic of Franklin County, FL., barrier islands, and include the following parameters:
      • Mean stem diameter - 0.44ft
      • Average height of vegetation - 30ft
      • Average spacing - 35ft
      • Drag coefficient - 0.65 (on a scale of 1.0 where 1.0 = dense forest, and 0.35 = single stand of trees).
  • SWEL (plus wave setup) - The 1% annual chance SWEL plus wave setup as an additional flood component was applied at the beginning of the transect due to non-restricted fetch conditions. Wave setup was reduced in a landward manner landward of the dune crest and was approximated by reducing the wave setup elevation for every 1,000' of linear distance.

The results of the WHAFIS modeling include the following: a Zone VE to Station 233 (i.e., 233 ft landward of Station 0); a Zone AE to Station 1303. Landward of Station 1303, the transect crosses the backbay which is not being modeled in this case.

Primary Frontal Dune (PFD)

The landward limit of the PFD, also known as the toe of the dune, occurs at a point where there is a distinct change from a relatively steep slope to a relatively mild slope. The PFD toe represents the landward extension of the Zone VE high hazard velocity zone. In the CHAMP database, the PFD toe can be selected in the 'Adjusted Graph' section of 'Module 2 - Transect Data Entry and Editing'. In this section, select 'Landward Toe (PFD)' from the 'Graph' drop down menu. The Landward Toe of the PFD for this transect is situated at Station 377.

Mapping

As discussed above and shown in Figure 1 below, the PFD landward toe of the PFD is located at Station 377, which is the controlling factor of the Zone VE (the wave-based Zone VE as determined from WHAFIS is located at Station 235, which is seaward of the PFD toe). Thus, a Zone VE will be mapped to Station 377. A base (1% annual chance) flood elevation of 12 feet (based on WHAFIS) will be used for this zone. The remainder of the coastal flood hazard mapping will be based on the WHAFIS output as shown in Figure 2, and will include:

  • Zone VE, Elevation 15 to Station 25
  • Zone VE, Elevation 13 to Station 189
  • Zone VE, Elevation 12 to Station 377
  • Zone AE, Elevation 12 to Station 438
  • Zone AE, Elevation 11 to Station 1303
Figure 1. Summary Graphic from CHAMP
Figure 2. WHAFIS Output (Part 6) from CHAMP

Hot Topic #1 - Hurricane information on the FEMA web site

Available FEMA web site links regarding hurricane information are provided below:

Hot Topic #2 - FEMA Coastal Flood Hazard Technical Resources Page

The Coastal Flood Hazard Technical Resources Page is now available via the internet at: http://www.fema.gov/plan/prevent/fhm/en_cfhtr.shtm. This page is a resource for all coastal flood hazard information pertinent to FEMA and the NFIP, including technical modeling and mapping applications such as FEMA Guidelines and Specifications, FEMA accepted coastal models, and the Coastal Hazard Analysis Modeling Program (CHAMP). This site will be updated with additional topics in the near future.

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Last Modified: Friday, 22-Jun-2007 11:57:20 EDT