Storm Selection

Storm Selection

The first step in a frequency-of-erosion study is to identify storms that have

impacted the site of interest. For sites on the east coast, particularly the north-

east coast, both tropical storms (hurricanes) and extratropical storms (north-

easters) have to be included. While the tropical storms often have higher winds,

the longer duration of the extratropical storms allows them to produce vertical

erosion of equal or greater magnitude than hurricanes. Also, northeasters occur

much more frequently than hurricanes. For sites on the Gulf coast, northeasters

will generally not be a major problem; hurricanes will most likely be the only

storms of concern.

Tropical storm selection

The tropical storm database of the National Hurricane Center's HURricane

DAT (HURDAT) database (Jarvinen, Neuman, and Davis 1988) is the recom-

mended source of historical events that have impacted the east and Gulf coasts

(and therefore the Mud Dump site). The tropical storm database generated by

the DRP (Scheffner et al. 1994) contains an atlas of 134 storm events, as well as

their respective tracks, that impacted the east and Gulf coasts of the United

States. The database contains maximum computed storm surge elevations at up

to 486 discrete locations impacted by each event according to the criteria that

(a) the minimum pressure of the storm was less than or equal to 995 mb, (b) the

eye of the storm passed within 200 statute miles of the location of interest (the

Mud Dump site in this application), and (c) the storm generated a surge of at

least 1 ft above mean sea level (MSL). The published atlas in Scheffner et al.

(1994) tabulates maximum storm surges that have impacted each station and the

respective storm events responsible for that surge. Cross-referencing is also

provided to show which stations were impacted by each of the 134 events and

the respective maximum surge at those stations.

This dual tabulation should be used to identify potential storms impacting the

site of interest, the Mud Dump site in this example. Elevation and current

hydrographs corresponding to each event and impacted location are available

from the DRP database.

The DRP tropical storm database was constructed by simulating the

134 historically based storm events as they propagated over the east coast, Gulf

of Mexico, and Caribbean Sea computational domain shown in Figure G1 using

the numerical hydrodynamic model ADCIRC described earlier. The DRP data-

base of storm-surge hydrographs and currents was archived at 240 east and Gulf

coast Wave Information Study (WIS) stations (Hubertz et al. 1993) with addi-

tional locations prescribed for Puerto Rico. To use the DRP tropical storm

database information, the WIS station nearest the disposal site of interest is

selected. WIS Station 304 (DRP numbering system) is nearest to the Mud Dump

site; therefore, storm events impacting this station were selected for the fre-

quency analysis (Figure G3). Station 304 has a depth of approximately 108 ft.

Appendix G Procedures for Conducting Frequency-of-Erosion Studies