Storm-Surge Hydrograph Development

database, which is archived at every 2.5 degrees of latitude and longitude at a

temporal period of 6 hr, was used as input to ADCIRC. The 16 winter season

(September-March) input files were prepared by archiving the data within the

area of 100 - 60 west longitude and 5 - 50 north latitude, which encom-

passes the east coast, Gulf of Mexico, and Caribbean Sea as part of ADCIRC's

20,000-node computational grid.

ADCIRC-generated surface elevation and current hydrographs for each

7-month period were archived at 686 locations at a sampling period of 1 hr. Of

the 686 stations, 340 correspond to locations (WIS) stations. As for the tropical

storms, extratropical storms impacting WIS Station 304 were selected for the

frequency analysis.

Storm-Surge Hydrograph Development

Tropical storms

Once identified, the selected tropical storms are retrieved from the DRP

database. However, each hydrograph represents the entire storm history, from

beginning to end, often a week or more in duration. Because only the erosional

effect of the event on the site being studied are of interest, each hydrograph was

constructed at a time step of 3 hr to be 99 hr in duration, measured as 48 hr

before the well-defined 3-hr duration peak and 48 hr after the peak, for example

see Figure G4. The time of peak is selected as the time when the eye of the

storm is closest site of interest.

Extratropical storms

For the extratropical storms, the storm event time periods of impact will not

be well defined at many locations, including the Mud Dump site. Examination

of surge elevation, current magnitude and wave height, and period records from

the Mud Dump site did not allow extratropical storms and their duration to be

readily identified.

One reason for this difficulty in identifying extratropical storms is the fact

that the surge currents accompanying each event are generally relatively small

(i.e., on the order of 20-30 cm/sec at the Mud Dump site), and their effects have

to be considered with respect to other environmental factors occurring at the

time of the storm. These factors include the local depth, the orbital velocities of

the wave field, the duration of the event, and the phase of the tide. Therefore, to

isolate significant events from the 7-month record, a more quantitative approach

to event parameterization is recommended and was developed for the Mud

Dump study. This second order parameterization approach is defined following

the descriptions of tide and wave field data accompanying the hydrodynamic

surge and current response.

G11

Appendix G Procedures for Conducting Frequency-of-Erosion Studies