Storm tide frequency analysis for the open coast of Virginia, Maryland, and Delaware

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NOAA Technical Memorandum NWS HYDRO-32 '"'

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STORM TIDE FREQUENCY ANALYSIS

FOR THE OPEN COAST OF VIRGINIA,

MARYLAND, AND DELAWARE

Silver Spring, Md.
August 1976

QC
851
U6
H9
no. 32

NATIONAL OCEANIC AND N ational Weather
ATMOSPHERIC ADMINISTRATION Service

NOAA TECHNICAL MEMORANDA

National Weather Service, Office of Hydrology Series

The Office of Hydrology (HYDRO) of the National Weather Service (NWS) develops procedures for making
river and water supply forecasts, analyzes hydrometeorological data for planning and design criteria for
other agencies, and conducts pertinent research and development.

NOM Technical Memoranda in the NWS HYDRO series facilitate prompt distribution of scientific and
technical material by staff members, cooperators, and contractors. Information presented in this series
may be preliminary in nature and may be published formally elsewhere at a later date. Publication 1 is
in the former series, Weather Bureau Technical Notes (TN); publications 2 to 11 are in the former ser-
ies, ESSA Technical Memoranda, Weather Bureau Technical Memoranda (WBTM). Beginning with 12, publica-
tions are now part of the series, NOAA Technical Memoranda, NWS.

Publications listed below are available from the National Technical Information Service, U.S. Depart-
ment of Commerce, Sills Bldg., 5285 Port Royal Road, Springfield, Va. 22151. Price: $3.00 paper copy;
$1.45 microfiche. Order by accession number shown in parentheses at end of each entry.

Weather Bureau Technical Notes

TN 44 HYDRO 1 Infrared Radiation from Air to Underlying Surface. Vance A. Myers, May 1966. (PB-170-
664)

ESSA Technical Memoranda

WBTM HYDRO 2 Annotated Bibliography of ESSA Publications of Hydrological Interest. J. L. H. Paulhus,
February 1967. (Superseded by WBTM HYDRO 8)

WBTM HYDRO 3 The Role of Persistence, Instability, and Moisture in the Intense Rainstorms in Eastern
Colorado, June 14-17, 1965. F. K. Schwarz, February 1967. (PB-174-609)

WBTM HYDRO 4 Elements of River Forecasting. Marshall M. Richards and Joseph A. Strahl, October 1967.
(Superseded by WBTM HYDRO 9)

WBTM HYDRO 5 Meteorological Estimation of Extreme Precipitation for Spillway Design Floods. Vance A.
Myers, October 1967. (PB-177-687)

WBTM HYDRO 6 Annotated Bibliography of ESSA Publications of Hydrometeorological Interest. J. L. H.
Paulhus, November 1967. (Superseded by WBTM HYDRO 8)

WBTM HYDRO 7 Meteorology of Major Storms in Western Colorado and Eastern Utah. Robert L. Weaver,
January 1968. (PB-177-491)

WBTM HYDRO 8 Annotated Bibliography of ESSA Publications of Hydrometeorological Interest. J. L. H.
Paulhus, August 1968. (PB-179-855)

WBTM HYDRO 9 Elements of River Forecasting (Revised). Marshall M. Richards and Joseph A. Strahl,
March 1969. (PB-185-969)

DTTM HYDRO lC Flcoi Warning Eelefit ivalvation - Susquahanr.a River Basin (Urban Residences). darolU
J. Day, March 1970. (PB-190-984)

WBTM HYDRO 11 Joint Probability Method of Tide Frequency Analysis Applied to Atlantic City and Long
Beach Island, N.J. Vance A. Myers, April 1970. (PB-192-745)

NOAA Technical Memoranda

NWS HYDRO 12 Direct Search Optimization in Mathematical Modeling and a Watershed Model Application.
John C. Monro, April 1971. (COM-71-00616)

NNS HYDRO 13 Time Distribution of Precipitation in 4- to 10-nay Storms--Ohio River Basin. John F.
Miller and Ralph H. Frederick, May 1972. (COM-72-11139)

NWS HYDRO 14 National Weather Service River Forecast System Forecast Procedures. December, 1972.
COM-73-10517)

(Continued on inside back cover)

NOAA Technical Memorandum NWS HYDRO-32

STORM TIDE FREQUENCY ANALYSIS

FOR THE OPEN COAST OF VIRGINIA,

MARYLAND, AND DELAWARE

Francis P. Ho
Robert J. Tracey
Vance A. Myers
Normalee S. Foat Property of csc Library

Office of Hydrology
Silver Spring, Mdo
August 1976

t. S. DEPARTMENT OF COMMERCE NOAA
COASI AL SERVICES CENTER
1'34 SOUTH HOBSON AVENUE
nJhLESION, SC 29405-2413

At ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~~~~~~~~~~~~~N
--

UNITED STATES NATIONAL OCEANIC AND National Weather m
DEPARTMENT OF COMMERCE / ATMOSPHERIC ADMINISTRATION Service
Elliot L. Richordson, Secretory / Robert M White, Administrator George P Cressman. Director -__ ---
/~

CONTENTS

Page

Abstract.... . . .1.......................

1. Introduction .......................

1.1 Objective and scope ...................
1.2 Authorization ...................... 2
1.3 Study method ...................... 2

2. Summary of historical storms ...............

2.1 Hurricane tracks .................... 3
2.2 Historical notes on hurricanes ............. 3
2.3 Winter coastal storm characteristics .......... 8
2.4 Historical notes on winter storms . . . . ...... 9

3. Climatology of hurricane characteristics ... 10

3.1 North of Cape Charles... ......... 10
3.1.1 Probability distribution of hurricane intensity. . 10
3.1.2 Probability distribution of radius of maximum winds. 10
3.1.3 Probability distributions of speed and direction of
forward motion ................... 11
3.1.4 Frequency of hurricane tracks ............. 11
3.2 South of Cape Henry. . . . . ..... 11
3.2.1 Conditional probability question ...... 11
3.2.2 Separation of NE and SE landfalling hurricane
parameters ..................... 12
3.2.3 Exiting hurricanes .................. 12

4. Hurricane surge ...................... 12

4.1 Surge model ....................... 12
4.2 Shoaling factor ..................... 13

5. Hurricane tide frequencies ................ 14

5.1 The joint probability method .............. 14
5.2 Maximum hurricane surge computations .......... 14
5.2.1 Coastal surge envelopes from landfalling hurricanes -
north of Cape Charles ................ 14
5.2.2 Maximum surge for alongshore hurricanes - north of Cape
Charles ....................... 15
5.2.3 South of Cape Henry. ......... . . . .22
5.3 Astronomical tides ............. . . . 22
5.4 Hurricane tide frequencies at selected points ...... 23

6. Winter coastal storm tides ........ . .... 23

6.1 Evaluation of northeaster tide levels in study area. . . 23

iii

Page

6.2 Analysis of tide gage records .............. 23
6.2.1 Selection of data ................... 23
6.2.2 Adjustment for sea level trend ............. 24
6.2.3 Statistical analysis of maximum annual tides ...... 24
6.2.4 Coastal profile of tide frequencies .......... 25

7. Total storm tide frequency.. . . . . . . . . . ...... 25

7.1 Combination of hurricane and northeaster tide
frequencies . . . . . . . . ...... * 25
7.2 Comparison of frequency curve .............. 27

8. Reference datum.. . . ................. 28

9. Relation of this report to disaster planning ........ 29

References.. ... . . . . . ...... . . 30

TABLES

l.--Hurricane and tropical storm parameters - Rehoboth Beach, Del. 17

2.--Hurricane and tropical storm parameters - Ocean City, Md . . . 18

3.--Hurricane and tropical storm parameters - Parramore Island, Va. 19

4.--Hurricane and tropical storm parameters - Virginia Beach, Va . 20

5.-Hurricane and tropical storm parameters - N.C.-Va. border. . . 21

6.--Primary tide gages of the National Ocean Survey in and adjacent
to study area ........................24

7.-Maximum October - May tides from northeasters .........26

Illustrations

1. Location map. . . . . . . . . . ... . . . . 34

2a. Tracks of selected hurricanes affecting the study area... 35

2b. Tracks of selected hurricanes affecting the study area,
continued ........................ 36

3. Weather map for 1330E, November 25, 1950 .......... 37

4. Weather map for 1930E, April 11, 1956 ........... 37

5. Weather map for 0130E, March 7, 1962 ............ 38

6. Marigrams for winter coastal storms of November 1950, 39
April 1956, and March 1962 ................

7. Shoaling factor off Delmarva coasts. Adapted from Barrientos
and Chen (1975) ..................... 40

8. Peak surge heights (ft) at the coast produced by alongshore
hurricanes. The abscissa denotes distance of storm track
from coast... . . . . . . . . . . . .......... 40

9. Storm tracks for surge computations for alongshore storms . 41

10. Probability distrigution of astronomical high and low tides
for hurricane season, 1955-1973, for (a) Cape May, N.J.,
(b) Lewes, Del., (c) Wallops Island, Va., and (d) Virginia
Beach, Va .... . . . . .......42

11. Location of selected tide gage stations . . . .... 43

12. Sea level trends at Lewes, Del., illustrating adaptation
of Hicks and Crosby's (1974) values to this study . . . . 44

13a. Tide frequencies at Lewes, Del., from winter coastal
storms. Plotted points are seasonal (October-May)
maxima .......................... 45

13b. Same as figure 13a but for Kiptopeke Beach, Va ....... 45

13c. Same as figure 13a but for Hampton Roads, Va ........ 46

14. Coastal tide frequencies from winter coastal storms . . . . 47

15. Coastal tide heights observed in the storms of March 1962
and November 1950 ..... . 47

16. Mean normal tide range variation along the coast ...... 48

17. Tide frequencies at Rehoboth Beach, Del., for several classes
of storms: landfalling hurricanes and tropical storms,
alongshore hurricanes and tropical storms, winter storms,
and all storms. ......................49

18. Same as figure 17 but for Ocean City, Md. ..........49

19. Same as figure 17 but for Parramore Island, Va. .......50

20. Total tide frequencies on the open coast at (a) Virginia
Beach, Va., and (b) Va.-N.C. border. ...........50

21. Coastal tide frequencies. Delmarva coasts. . . . . . * 51

22. Comparison of tide frequency curve at Rehoboth Beach, Del., with
observations at Lewes, Del. Dots, annual maxima since 1948.
Circles, highest values since 1900. ............52

23. Comparison of tide frequency curve at Virginia Beach, Va. with
tide observations at Hampton Roads and Norfolk Navy Yard. 52

STORM TIDE FREQUENCY ANALYSIS FOR THE OPEN COAST OF
VIRGINIA, MARYLAND, AND DELAWARE

Francis P. Ho, Robert J. Tracey, Vance A. Myers, and Normalee S. Foat
Office of Hydrology
National Weather Service, NOAA, Silver Spring, Md.

A report on work for the Federal Insurance Administration, Department of
Housing and Urban Development by the National Oceanic and Atmospheric Admin-
istration, Department of Commerce.

ABSTRACT. Storm tide height frequency distributions are
developed on the coast of Virginia, Maryland and Delaware
for the National Flood Insurance Program. Storm tides
are computed from a full set of climatologically repre-
sentative hurricanes using the National Weather Service
numerical-dynamic storm surge model. Winter storm
effects are estimated from tide gage records. Storm
tide levels from all storms are shown in coastal profile
between annual frequencies of 0.10 and .002. This
report is intended for use in estimating actuarial
risk to buildings from coastal floods and in flood
plain management.

1. INTRODUCTION

1.1 Objective and Scope

The Federal Insurance Administration (FIA), Department of Housing and Urban
Development (HUD), requested the National Oceanic and Atmospheric Administra-
t-ion (NOAA) to study flood levels from storm tides on the open coast of
Virginia, Maryland and Delaware (fig. 1). This includes the Atlantic Ocean
coast of Sussex County, Del., Worcester County, Md., and Accomack County,
Northhampton County, and Virginia Beach, Va. The assignment is limited
to determining storm tide frequencies along the Atlantic Ocean coast on a
common regional basis. Modifications of the storm tide levels within Chesa-
peake Bay and Delaware Bay are not included. These modifications have
to be assessed by separate investigations, using the present study as
part of the relevant information.

The tide frequencies are of still water levels that would be measured
in a stilling well or tide gage house designed to exclude wave action. The
destructive effects of waves on the beach front must be taken into account
separately.

Storm tides in the study area are caused both by hurricanes -- which are
storms of tropical origin occurring in the summer and fall months -- and by a
winter type of coastal storm, commonly called northeasters. Both types of
storms are included in the study. The hurricane tide frequency analysis was
carried out primarily by the first two authors and the winter storm tide fre-
quency by the last two.

1.2 Authorization

The National Flood Insurance Act of 1968, Title XIII, Public Law 90-448,
enacted August 1, 1968, authorizes and directs the Secretary of Housing and
Urban Development to establish and carry out a National Flood Insurance
Program. The Secretary is authorized to secure the assistance of other
Federal Departments on a reimbursement basis in assessing flood frequencies.
Authorization for this particular study is Project Order No. 2, dated November
13, 1974, under agreement No. IAA-H-1975 between the Federal Insurance Ad-
ministration and NOAA, as amended.

1.3 Study Method

The technique used in this tide frequency analysis for the oceanic coast of
Virginia, Maryland, and Delaware (hereafter referred to as the Delmarva coast)
is basically the same as that applied earlier to the North Carolina coast
(Ho and Tracey 1975a, 1975b) and in other studies (e.g., Ho 1974).

Hurricanes and northeasters are studied separately, and the annual fre-
quencies from each at a given tide level summed to obtain the overall annual
frequency of that level. The northeasters are the most frequent, and in the
aggregate over the years have caused the largest dollar value of damage in.
the study area, but hurricanes are potentially the most severe. This is
clarified in the analysis. The hurricane tides are assessed from the clima-
tology of hurricanes, by a joint probability method to be described. Winter
storm tides are assessed directly by statistical analysis of tide records.

The first step is to assess the behavior of hurricanes along the coast from
past records. Factors analyzed included depression of the atmospheric pres-
sure at the storm center below the surrounding value, forward speed and
direction of motion of the storm, and distance from the storm center to the
band of maximum winds. All these factors relate to a storm's potential to
produce high tides.

The second step in the tide frequency analysis is to calculate the coastal
tide levels that each of a number of hypothetical but representative hurri-
canes from various combinations of the hurricane parameters would produce.
For this a dynamic calculation method is used that has been demonstrated to
reproduce storm tides of past hurricanes within acceptable tolerances. Each
hypothetical hurricane is defined by a particular combination of the hurri-
cane parameters determined in the first step.

Third, the computed hurricane surges are combined at several selected points
on the coast with the astronomical tide variation by using a joint probability
method to obtain a tide frequency distribution.

These three steps are amplified in sections 3, 4 and 5 of the report,
respectively.

Fourth, winter storm tide frequencies are estimated at tide gage sites
by a statistical analysis described in section 6.

Fifth, the tide frequencies are interpolated along the coast, separately
for hurricanes and winter storms, described in sections 5 and 6, respectively.
Finally, the hurricane and northeaster tide frequencies are summed. This is
described in section 7.

2. SUMMARY OF HISTORICAL STORMS

This section summarizes the major hurricanes that have affected the study
area since 1800 and selected recent severe winter-type coastal storms. Lesser
storms are omitted.

2.1 Hurricane Tracks

Selected tracks of damaging hurricanes affecting the study area since 1871
are shown in figures 2a and 2b. The information on hurricane tracks is taken
from the charts of North Atlantic tropical cyclones compiled by Cry (1965).
For 1964 through 1974, similar tracks are published in the Monthly Weather
Review.

2.2 Historical Notes on Hurricanes

Brief notes on the history of hurricanes and damages caused by them are
abstracted from published papers. Reported wind speeds are included to indi-
cate qualitatively the intensities of storms. Wind speeds from Weather Bureau
stations from storms before the 1920s have been adjusted by the anemometer
instrumental corrections developed by Harrison (1963). Since the 1920s,
official wind reports include the corrections. Prior to 1940, the highest
wind given for a storm was usually the "maximum velocity," an average wind
speed for a 5-mmn period. In recent years, the highest sustained wind is an
average over a 1-mmn period. The magnitude of storm surge is related to the
wind integrated over a longer period of time.

Maximum storm tide levels are quoted from the original reports. For the
1933 and later hurricanes, these are heights above the reference level now
known as the National Geodetic Vertical Datum, except for one or two instances
where another reference level is explicitly stated. Datums for heights are
discussed in section 8 of the report.

August 22-23, 1806

This large destructive hurricane crossed eastern North Carolina and moved
out to sea again near Norfolk, Va. Shipping suffered severely as the storm
picked up speed and moved up the Delmarva-New Jersey coast. The coastal ship
Rose in Bloom upset in a stiff northeast gale off Barnegat Inlet, on the
central Jersey coast, with the loss of 21 of 49 persons aboard (Ludlum 1963).

September 3, 1821

Shipping first reported the existence of this hurricane near Turks Island
in the southeastern Bahamas on September 1st. It moved rapidly to the north
and the center entered the North Carolina coast at daybreak on the 3rd. The
storm continued moving to the north toward Norfolk, Va., where it inflicted
great damage on shipping and installations, and high tides inundated the
wharves by 3 to 5 ft. It then moved northward over the Delmarva Peninsu-
la where the low-lying communities on Chesapeake Bay and the peninsula suf-
fered greatly. "The crops are laid low, and the country exhibits one scene
of widespread desolation and ruin," observed the American Commercial Beacon.
At Pungoteague the water rose 10 ft. The storm moved over Cape Henlopen
which experienced the eye and continued to the north-north-east over New
York City (Graham and Hudson 1960; Ludlum 1963; Corps of Engineers, New York,
N.Y. 1964).

October 13. 1846

Ludlum calls this "The Great Hurricane of 1846." The storm center passed
west of all the principal ports of the South Atlantic States, then moved
through east-central North Carolina and into the tidewater areas of Chesa-
peake Bay. The lowlands along the Delaware River near New Castle were over-
flowed in the greatest storm surge in 70 years. The waters rose high enough
to put out the fire in a locomotive which had been stalled by the rising
waters (Ludlum 1963).

August 18, 1879

A severe hurricane moved inland near Wilmington, N.C., on the 18th and back
out to sea near Norfolk with highest winds at Cape Lookout. The anemometer
cups at Cape Lookout were blown away indicating 138 mph. Anemometers were
also destroyed at Hatteras, Fort Macon, Kitty Hawk, Portsmouth, N.C., and
Cape 'Henry, Va., with speeds estimated at 100 mph or more. The schooner A.
J. Bently, about 90 mi off the coast of the lower Delmarva Peninsula reported
waves 40 ft from trough to crest. At Cape Henry the wind had reached a velo-
city of 76 mph when the anemometer cups were carried away. Lowest pressure
observed at Cape Henry was 983.8 mb (29.05 in). The damage to maritime
property was enormous. Over 100 large vessels were shipwrecked or suffered
serious injury while the number of yachts and smaller vessels which were
destroyed or seriously damaged exceeded 200 (U. S. Weather Bureau 1879).

August 23, 1933

This hurricane caused extensive damage in northeastern North Carolina,
eastern Virginia, the Delmarva Peninusla, and New Jersey. Most of the damage
was caused by high tides and waves. The storm passed over Norfolk, Va., dur-
ing the morning of August 23 and moved northward along Chesapeake Bay. Nor-
folk had a low pressure of 971.2 mb (28.68 in.) and a maximum wind velocity of
56 mph, while high tides flooded the business district with 4 to 6 ft of
water (Graham and Hudson 1960). Cape Henry had a maximum wind velocity of
68 mph. As the storm moved north of Norfolk, it caused great destruction
to resorts on the Delmarva Peninsula and New Jersey coasts. The greatest

damage occurred on the Delaware coast and at the tip of Cape May, N.J. The
wind at Cape Henlopen, Del., was estimated to have reached 75 mph. Damage
from the storm was estimated at $17,500,000 in Maryland and Delaware,
$10,000,000 in Virginia and $3,000,000 in New Jersey. The storm moved north-
ward through central Pennsylvania with decreasing intensity and then north-
eastward towards the St. Lawrence River Valley. In his chronicle of Mary-
* ~land's coastal hurricanes, Truitt gives the following description:

"The August 1933 storm did the greatest damage to the
seaside recorded up to that time, and statewide, per-
haps the greatest damage of all time. The state's
loss was estimated as high as $30 to $40 million and,
in Worcester County, the damage was placed at approxi-
mately $800,000 at a time when money values were much
higher than they are today. Of the 41 oyster houses
readied for seasonal operations, only 8 were left
usable though damaged. Farm crops were laid waste
and boardwalk, cottages, and many other buildings,
together with a new marina and machine shop at Ocean
City, were carried away. While this destruction was
vast, the accompanying winds were barely, if at all,
of hurricane strength. Rather over a long haul, or
fetch, they built up waves and tides that were highly
devastating. No lives were lost. The Ocean City inlet
was gained by the out-flow of pent-up high water in
Assawoman and Isle of Wight Bays, and later made perma-
nent" (Truitt 1976).

This storm caused the highest tide of record, 7.7 ft at Baltimore (Harris
and Lindsay, 1957). In the Portsmouth area of Virginia, high tide was 8
ft, while at Old Point Comfort, Va., the high tide reached 8.6 ft (corps
of Engineers, Norfolk, Va., 1963). At Breakwater, Del., the tide reached
6.1 ft (Corps of Engineers, Philadelphia, Pa., 1963), while at Atlantic City
the maximum wind reached 76 mph and the highest tide was 5.0 ft. At St.
George Ferry Terminal in New York City, the highest tide reached 4.9 ft (Corps
of Engineers, New York, N.Y., 1964). As stated in the introduction to this
section, tide hights here are above NGVD. Winds in this storm over coastal
waters and Chesapeake Bay have been reconstructed by Graham and Hudson (1960),
along with a detailed track.

September 18, 1936

This storm approached Cape Hatteras from the southeast, began recurving to
the north, and passed east of the Virginia Capes on September 18th. At Cape
Henry the full force of the hurricane was not recorded since the anemometer
cups were blown away but the wind was estimated at 75 mph (Tannehill 1936).
Tides in the Norfolk-Portsmouth area reached 6.0 to 7.5 ft (Corps of Engineers,
Norfolk, Va., 1963). This was a severe storm for the Delmarva Peninsula.
Late crops in Maryland were destroyed by wind and water to the extent of 60%
of their normal yield. This storm is known as the Morro Castle Storm because

of difficulties it placed in the way of aid to the stricken liner (Truitt
1967). The storm passed 100 miles southeast of New York City where much of
Ocean Avenue was flooded (Corps of Engineers, New York, N.Y., 1964).

September 14, 1944

This rapidly moving hurricane passed over Hatteras moving to the northnorth-
east. Of this storm Tannehill states: "There is no definite proof of a more
violent hurricane in the records." The storm has become known as the Great
Atlantic Hurricane and wrecked and sank 5 U.S. Navy vessels off North Caro-
lina. As the hurricane moved northeastward, it damaged coastal resorts along
the Delmarva Peninsula. The center passed about 30 mi east of Atlantic City,
N.J., where it destroyed the steel pier and most of the boardwalk. The storm
passed the New Jersey coast near time of high astronomical tide. This result-
ed in high storm tides with extensive flooding and great damage. The greatest
damage was done on Long Beach Is land and Absecon Island. The hurricane ap-
proached New York City, but passed well out at sea about 60 mi to the south-
east and moved across the eastern tip of Long Island and into New England
where it diminished in intensity. The total property damage 'has been estimat-
ed at $100 million (1944 prices). Three hundred and ninety people lost their
lives in this storm, the majority on the sunken vessels. The lowest report-
ed pressure of 947.2 mb (27.97 in) occurred at 8:20 a.m. on September 14 at
Hatteras, N.C., and the highest recorded wind speed of 134 mph at Cape Henry,
Va., on the same date. Maximum winds equalled or exceeded all previous records
at Hatteras, Cape Henry, Atlantic City, and Block Island. Some of the note-
worthy extreme winds (fastest mile) were: Hatteras, N.C., estimated 110 mph,
Norfolk, Va., 73 with gusts estimated to 90 mph, Cape Henry, Va., 134 mph with
gusts estimated to 150 mph, Cape May, N.J., gusts to 92 mph, Atlantic City,
91 mph, and New York City, 99 mph. Some of the high tides were: 8.0 ft at
Naval Air Station, Cape May, N.J., 7.6 ft at Atlantic City, N.J., and 7.4 ft
at Perth Amboy, N.J., (Corps of Engineers, New York, N.Y. 1964; Ludlum 1963;
Sumner 1944; Tannehill 1956).

October 15. 1954 (Hazel)

Hurricane Hazel moved inland near the South Carolina-North Carolina border
on October 15th. It moved northward very rapidly, passing near Washington,
D.C., through central Pennsylvania and western New York.,then across Lake
Ontario into Canada~maintaining its intensity most of the way. Peak wind
speeds of 90 mph or more were reached near and east of the center from the
Carolinas through New York. Along the Maryland coast considerable damage
was done to floating equipment, houses, and the boardwalk and cottages at
Ocean City. In "High Winds. . . . High Tides," Truitt states; "The
Chesapeake Bay and its tributaries bore the brunt of Hazel's fury in gale
and wind and tidal action with corresponding losses, though five-foot tides
were reported at Public Landing in Chincoteague Bay." At Breakwater, Del.,
the tide reached 4.6 ft and at Philadelphia, Pa., winds gusted to 94' mph
and the tide reached 7.5 ft. (Corps of Engineers, Philadelphia, Pa. 1963)
At Atlantic City, N.J., winds gusted to 80 mph and the tide rose to 4.6 ft

(Corps of Engineers 1965). Although the path of the storm was about 200
mi west of New York City, gusts to 100 mph were reported in the metropoli-
tan area (Corps of Engineers, New York, N.Y. 1964). Graham and Hudson
(1960) reconstruct the coastal and Chesapeake Bay wind fields in this storm
also.

August 12-13, 1955, (Connie)

Hurricane Connie entered the North Carolina coast-near Morehead City about
8:30 a.m. on August 12th. It continued moving northward across eastern North
Carolina, then over Norfolk, Va., along Chesapeake Bay, through central
Pennsylvania and western New York State into Canada. As the storm moved
north, it brought torrential rains all the way into Pennsylvania. Along
the Maryland coast, Connie brought high seas and tides that caused great
damage, although winds did not reach hurricane strength of 75 mph (Truitt
1967). At Breakwater, Del., the highest tide was 4.4 ft. Although the
hurricane passed 125 mi to the west, Atlantic City, N.J. had a maximum
wind of 65 mph and a high tide of 4.0 ft (Corps of Engineers 1965).

September 12, 1960 (Donna)

Hurricane Donna passed inland over the North Carolina coast between
Wilmington and Morehead City on September 11th. The storm moved northeast-
ward across North Carolina, then parallel to the Delaware-New Jersey coast,
across eastern Long Island and into New England. As the storm passed east
of the mouth of Chesapeake Bay, severe wind damage was sustained through-
out the area. A maximum wind velocity of 138 mph was recorded at the
mouth of Chesapeake Bay. At Norfolk Harbor the maximum tide reached
6.3 ft. Other measured tides in the area were: 5.5 ft at Sewells Point,
4.8 ft at Old Point Comfort, and 5.8 ft at Gloucester Point. Along the
Maryland coast, winds were estimated at 75 mph at Chincoteague and higher
at Ocean City. Only light damage was suffered on the Delmarva coast.
Donna was located about 80 to 100 mi east of Atlantic City, N.J., at
noon on the 12th, moving to the northeast at 40 mph. Along the Delaware
coast, low tide occurred during the peak of the storm and there was no
appreciable damage from flooding. But there was considerable damage from
medium to 'heavy wave action and flooding of low areas along the New Jersey
coast. Atlantic City reported a wind of 1-mmn duration of 60 mph, gusts up
to 83 mph, and a maximum tide of 6.1 ft. (Hardy and Carney 1962; Corps of
Engineers, Norfolk, Va. 1963; Truitt 1967; Corps of Engineers 1965).

September 16, 1967 (Doria)

Doria was one of the most erratic hurricanes ever observed. The storm,
centered 250 mi east of Jacksonville, Fla., on September 7th, moved slow-
ly and passed about 100 mi southeast of the North Carolina Capes on the
10th. It continued moving to the east-northeast for several hundred miles,
* ~~then on September 13th, reversed its course and moved westward. In its
westward movement it passed over colder water and encountered colder and
drier air which weakened the storm. The weakened center reached land near

the Virginia-North Carolina border and continued southward across the
North Carolina Capes and back to sea on September 17th. Doria attained
her lowest central pressure, 973 mb (28.73 in.), well at sea, midway be-
tween Nantucket and Bermuda, on September 14. The highest wind reported
by a land station near the center was 50 mph with gusts to 83 mph at Indian
River Inlet, Del. The highest tide, 6.5 ft above normal, also occurred
there (Sugg and Tanner 1968).

2.3 Winter Coastal Storm Characteristics

The study area is exposed to winter coastal storms, characterized by
strong winds from a northeast quadrant over long reaches of coast, hence,
the familiar name "northeaster." These winds are part of a counterclock-
wise cyclonic atmospheric circulation about a center of atmospheric low
pressure at sea. The proximity of warm gulf stream water to the colder
continent during winter and spring favors the development of such storms.
Most of these storms move rapidly to the north and northeast past the
coastal reach of the study area, but under favorable conditions of the
general atmospheric circulation they can stall and intensify with little
forward motion for a couple of days.

Another characteristic of those winter storms generating the highest
coastal surges is an unusually long fetch of strong winds directed toward
the coast. Surge-generating characteristics of winter storms are summarized
in a recent monograph by Pore and Barrientos (1976). The Earth's rotation
causes a rise in water level to the right of any current. The most critical
direction for the wind fetch is, therefore, an angle of less than 9Q0
to the coast, enabling this rotational effect and the direct wind and water
transport effect to combine in producing the coastal surge.

The critical surge-generating fetch is illustrated by sea level weather
charts for three winter storms significant to the study area. The isobars
on these charts may be construed as approximate wind streamlines, counter-
clockwise about the low pressure center. Contributing to the long fetch
in each case is either an unusual elongation of the low center or a double
center.

Figure 3 is for the storm of November 1950. This storm was most severe
in New York Harbor but also produced the third highest tide of record
in the northern part of the present study area (second highest northeaster
tide). The weather map may be compared with the storm marigrams at Atlantic
City, N.J., in figure 6 (marigrams not available at Lewes, Del., within
the study area). The datum reference in this figure is 1941-59 local
MSL (left-hand column of table 7).

Figure 4 is for the April 1956 storm that produced the second highest
northeaster tide of the last 40 years in the Norfolk-Hampton Roads area.
This was a more local storm, in terms of length of coast affected, than
the other two cited here. The wind fetch aimed at the mouth of Chesapeake
Bay is evident in the figure. The marigrams appear in figure 6.

The March 1962 northeaster produced the second highest tide of record
in most of the study area, being exceeded only by the 1944 hurricane in
the northern part and the 1933 hurricane in the Hampton Roads-Norfolk area.
The storm lasted through five high-tide cycles. The fetch directed at a
critical angle to the coast north of an elongated intense low center is
illustrated in figure 5. Marigramns are depicted in figure 6. It has not
been determined whether the 12.4-hr periodicity in the surge is a real
dynamic effect from storm surge-astronomical tide interaction or a spurious
effect from a timing discrepancy.

Further discussion is given below of local effects in the November 1950
and March 1962 storms. Wind velocities over the continental shelf in these
two storms have been reconstructed by Graham and Hudson (1960) and by
Goodyear (1963), respectively. Tide heights quoted from Corps of Engineers
reports are above National Geodetic Vertical Datum.

2.4 Historical Notes on Winter Storms

November 25-26, 1950

'The November 25-26, 1950, storm was considered the worst winter storm
on record for the eastern United States up to that time (Bristor 1951).
Destruction resulted primarily from high tides on the coast and flood-
producing rains inland, but local wind damage was also extensive. The
unusual SE fetch of winds directed toward the coast is indicated by figure
3. The storm struck the day following full moon, thus coincided with
spring tides. The highest tide reported at Lewes, Del., was 7.2 ft (Corps
of Engineers, Philadelphia, Pa. 1963). Effects were felt inland from the
southeast gales, Philadelphia (Pier 8) on the Delaware River and Cambridge,
Md., an Chesapeake Bay, observing the highest tide of record up to that
time (Pore et al. 1974).

March 6-8, 1962

The storm of March 6-8, 1962 was the worst northeaster of the present
generation in aggregate coastal damage. To the south the storm opened
a new inlet near Buxton, N.C., while to the north it breached Long Beach
Island, N.J. Two inlets were cut through Assateague Island 3 miles south
of Ocean City, Md. Tidal flooding was widespread in communities along
the entire coast of the study area. Five successive high tides over a
period of 48 hours carried the water inland to reach buildings and struc-
tures which would ordinarily be beyond the reach of such tides. Houses
and other structures were destroyed on sites where they had been safe
for 60 to 80 years. Some ocean front buildings were undermined and tilted,
while others were washed away. Boardwalks at Rehoboth Beach, Bethany
Beach, Del., and Ocean City, Md., were seriously damaged.

The tide gage at Lewes, Del., recorded a maximum of 7.4 ft, at Ocean
City, Md., 7.5 ft. This last tide was 1.5 ft higher than the previous
record high in the hurricane of August 1933. The gage at Fort Norfolk,
Norfolk, Va., recorded a highest tide of 7.4 ft,0.6 ft below the record

8.0 ft reached during the same hurricane (Corps of Engineers, North
Atlantic 1963). Along the south shore of Long Island, N.Y. the tides
reached elevations approaching record highs (Cooperman and Rosendal
1962).

3. CLIMATOLOGY OF HURRICANE CHARACTERISTICS

This section describes important characteristics of hurricane parameters
that are needed for calculating tide levels on the coast. Basic parameters
of hurricanes affecting the U.S. coast, including central pressure, radius
of maximum winds, speed of forward motion, and direction of forward motion,
all factors affecting storm tide producing capability, were published in
1959 (Graham and Nunn 1959). This compendium of hurricane characteristics
has been updated through 1973 and adapted to the needs of the Flood
Insurance Program, including specification of probability distributions
of the individual parameters. These data are published in a separate
report (Ho, Schwerdt, and Goodyear 1975), hereafter referred to as the
Climatology Report, and are the primary data source on hurricanes for the
present study. These data are used directly for the portion of the study
area north of Cape Charles, with certain refinements in alongshore hurri-
cane track count described later. The methods of the Climatology Report
were extended by certain additional analyses in the North Carolina study
(Ho and Tracey 1975b). These same methods, adopted in the present study
for the Virginia coast south of Cape Henry, are discussed in par. 3.2.

For the purpose of determining parameter probabilities in the Climato-
logy Report, hurricanes and tropical storms are grouped into three classes,
those that landfall on the coast, those that bypass alongshore with
the center remaining at sea, and those that exit the coast following an
earlier entry.

3.1 North of Cape Charles

3.1.1 Probability distribution of hurricane intensity

Storm surge magnitude varies approximately with the strength of the
windyother factors being constant. An index of the wind stress in hurri-
canes is the intensity of the storm as measured by the depression of the
storm's central pressure below representative peripheral pressure (D).
The assessment of probability distributions of this parameter for land-
f alling and alongshore storms is described in the Climatology Report.

3.1.2 Probability distribution of radius of maximum winds

Winds in all hurricanes increase from low values within the eye to
their most intense velocity just beyond the edge of the eye, then
decrease gradually. The average distance from the storm center to the
circle of the maximum wind speed is called the radius of maximum winds
(R) and is adopted as a convenient single number to be used as an
index to the size, or lateral extent, of the hurricane, a factor which
affects the surge profile along the coast. R values are taken from the
Climatology Report.

12.

3.1.3 Probability distributions Of speed and direction of forward motion

The speed (T) and direction (9) of forward motion of hurricanes also affect
surge height. The height of the surge on the coast increases with increasing
storm speed. Thus, the fastest moving storms, especially if they are large
and moving directly toward the coast, pose the greatest hazard. Probability
distributions of forward speed for the landfalling and alongshore storms are
given in the Climatology Report previously cited. The probability distribu-
tion of direction of forward motion for landfalling hurricanes and tropical
storms is also discussed in the Climatology Report.

3.1.4 Frequency of hurricane tracks

The overall frequency of hurricane occurrences is basic to calculating the
resulting tide frequencies. The frequency with which hurricanes and tropical
storms have entered or exited the coast and have moved approximately paral-
lel to the coast at sea (?'alongshore") based on 103 years of data smoothed
along the coast is given in the Climatology Report. These counts are used
in this study. Additional counts of alongshore storms immediately opposite
Ocean City, Md., and Parramore Island, Va., were made from Cry's (1965) annual
track charts to secure more detail. Hurricanes and tropical storms that by-
passed within 100 n.mi. off the coast or 30 n.mi. inland were assessed by
separate counts of storm tracks crossing lines normal to the coast at these
points. The cumulative track counts along each line were plotted and a
smooth curve fitted by eye to the data on each of these frequency plots. The
resultant track frequencies, as well as other hurricane parameters, are list-
ed in the parameter tables in section 5. Parameters for exiting storms are
not included in the tables. They are not significant here and are not in-
cluded in the tide frequency analysis for coastal stations north of Cape
Charles.

3.2 South of Cape Henry

Landfalling hurricanes and tropical storms in the study area south of Cape
Henry are further classified, as in the North Carolina report previously
cited (Ho and Tracey 1975b), to deal with the joint probability questions
referred to in chapter-6 of the Climatology Report, and to take account
of the effects on the coast of storms passing inland from the coast. These
are covered in detail in the North Carolina Report and briefly discussed
in the following paragraphs. Parameters not specifically mentioned are
treated in the same way as north of Cape Charles.

3.2.1 Conditional probability question

It will be explained in section 5 that assessing the probability of a
certain combination of hurricane parameters involves multiplying together
the probabilities of each of the parameters, on a scale of 0 to 1.0,
provided the distributions of the several parameters are independent in
the statistical sense (chapter 6 of the Climatology Report). If the dis-
tributions for any two parameters are not essentially independent, this
must be recognized by either using conditional probabilities or by segre-

gating the possible hurricane events into subsamples. An example in
the Climatology Report is the division of hurricanes into "landfalling"
and "alongshore". Separate forward speed distributions are then determined
for each subsample.

3.2.2 Separation of NE and SE landfalling hurricane parameters

South of Cape Henry we must deal with the correlation between hurricane
intensity and the direction of storm motion relative to the coast. This
is alluded to in par. 6.3 of the Climatology Report as an example of condi-
tional probability questions that may be expected in various regions, but
specific data are not developed. Hurricanes landfalling from the southeast
quadrant cover the full range of intensities from very severe to weak. From
time to time in this region a hurricane meanders and'strikes the coast from
the northeast quadrant. These storms are either of a weaker category ini-
tially or, if originally intense, have been weakened by transit over cold
water and other effects. The speed distribution for these storms is also
different from those moving from the southeast quadrant. These storms all
move at less than 15 kt. A separation for all parameters, including track
frequency, was made between landfalling storms from the SE and NE quadrants
south of Cape Henry.

3.2.3 Exiting hurricanes

Because of coastal configurations and the propensity of hurricanes to
recurve south of the study area and move northward, many hurricanes landfall
on the coast south of Cape Hatteras and then pass through Virginia on a
course approximately parallel to the coast. The central pressure for such
inland storms was estimated by applying an average filling rate after the
storm center landfalls. This filling rate was derived from an empirical
study of central pressure vs. time overland by Malkin (1959). The applica-
tion is described in detail in the North Carolina Report (Ho and Tracey
1975b).

The frequency with which hurricanes and tropical storms exited the coast
is given in the Climatology Report. Other parameters are adapted from
those for the landfalling and inland categories. Approximating the para-
meters and grouping into fewer class intervals suffices for these computa-
tions as exiting storms produce lower storm tides, and, as it turns out,
make an almost negligible contribution to the overall storm tide frequencies.

4. HURRICANE SURGE

4.1 Surge Model

The National Weather Service has developed a two-dimensional numerical-
dynamic surge model for calculating the water levels induced by hurricanes
on the continental shelf (Jelesnianski 1967, 1972, and 1974). The objective

of this work was to develop a tool to forecast open coast surges when hurri-
canes were approaching. The model has become the backbone of NOAA's tide-
frequency studies for the flood insurance program. The development of the
* ~model is described by Jelesnianski in the 1967 paper and operational appli-
cations (designated as SPLASH I and II) in the others. Both limitations
and verification of the model are described in the references. Replications
* ~~of surge profiles produced by past hurricanes agree well with observed
storm tides and high water marks adjusted to include astronomical tide. The
model computes the surge, the difference between the local storm-induced
level and the normal water levels for the area. Thus, the computed storm
surge m6ast be added to the predicted astronomical tide.

Inputs to a computer surge calculation are hurricane central pressure
deficit, radius of maximum winds, storm direction of motion and forward
speed, and ocean depths at a series of grid points. The hurricane climato-
logy just described is oriented toward providing these parameters. The
computer program generates the needed moving sea level pressure field and
moving wind field from the basic parameters by predetermined relations which
are part of the model.

The SPLASH I version is limited to storm moving forward at constant
velocity and intensity toward a specified landfall point while the earlier
version of SPLASH II has been expanded to accommodate storms with general-
ized motions of not too great complexity. Also, storm strength and size
are allowed to vary in a continuous monotonic manner with time. These
models were used for the Virginia coast south of Cape Henry. The later
version of SPLASH II further incorporates the dynamic effects of the curv-
ature of the coast and was used to compute surges generated by both classes
of hurricanes, landfalling and alongshore, in tide frequency analysis
north of Cape Charles.

4.2 Shoaling Factor

The capacity of a hurricane of given characteristics to produce a coast-
al surge depends on the profile of water depth. The shallower the coastal
water the higher the surge. This variation along the East coast is
depicted in a report by Barrientos and Chen (1975, fig. 3b) as the ratio
of the surge that would be produced locally at each coastal point by a stand-
ardized hurricane to the surge from the same hurricane moving over a conti-
nental shelf of average or standard slope. This ratio is called the shoal-
ing factor and is geperated by computing surges by the model that has
been described at the various coastal points and over the ''standard basin"
and taking ratios of the peak surges. The Delmarva portion of this dia-
gram is reproduced in figure 7. The shoaling factor is implicit in calcula-
tions of hurricane surge by the model at selected coastal points, since
sloping depths of the continental shelf are introduced to the calculation
as input data. The shoaling factor is a primary guide to interpolating
between coastal computation points. The shoaling factor curve of figure 7
reveals that a minimum factor is reached near Ocean City, Md. Compara-
tively higher factors appear to the north and south of the study area.

5. HURRICANE TIDE FREQUENCIES

5.l The Joint Probability Method

The joint probability method has been described in detail in a separate
report (Myers 1975, especially pp.'12-13). The first step is to define
the probability distributions of the several hurricane parameters, as
described in section 3. Each distribution is divided into class intervals,
and the mid-point values are read out for each class interval. The para-
meters derived in this way and used in the subsequent computations are
listed in tables 1 to 5 for the coast at Rehoboth Beach, Del., Ocean City,
Md., Parramore Island, Va., Virginia Beach, Va., and at the Virginia-North
Carolina border, respectively.

As the second step, calculations are made with the SPLASH computer program
of the coastal profile for representative hurricanes. The adjustment of
surge envelopes obtained by SPLASH computations to give other surge envelopes
is described in the next section. There are two kinds of adjustments, to
different hurricane parameters and to a shifted landfall point.

As the third step, all surge profiles including the ones obtained by
adjustment are added to the astronomical tide with random time phasing.
Handling this phasing in a probabilistic manner is described in the report
previously cited (Myers 1975). The requisite analysis of a 19-yr cycle of
the astronomical tide to obtain these ranges is further discussed in the
next section. Since each surge profile has a prescribed frequency, as have
the astronomical tides, the tides resulting from a combination have pre-
scribed frequencies.

As a fourth step, summing all 'hurricane possibilities yields the total
tide frequency from these storms.

5.2 Maximum Hurricane Surge Computations

Different variations of the second step of the above procedure were used
north of Cape Charles and south of Cape Henry. These are described in
the following paragraphs.

5.2.1 Coastal surge envelopes from landfalling hurricanes - north of Cape
Charles

Hurricanes landfalling on this stretch of the coast are described by
the parameters listed in tables IA to 3A. The possible combinations of
these parameters in each table give 160 hurricanes representing climato-
logically possible storms landfalling near the indicated coastal station
or in its vicinity. Potential surges that would be produced by the hurri-
canes were obtained from SPLASH computations and from adjustments. Surge
computations were made by using the later version of SPLASH II surge
prediction model with the possible combinations of assigned values of

R, T, and 0 (2Rs x 5Ts x 29s = 20 hurricanes), all at D = 62 mb. Each
surge profile generated in this way was adjusted by a predetermined surge-
pressure relation to each of the 8 Ds listed in the tables, yielding 160
potential surge profiles.

Another parameter required for a SPLASH computation is the landfall
point of the storm. 'Landfall points were spaced at approximately 48-mi
intervals for the SPLASH computations indicated above. Landfall points at
8-mi intervals in between were simulated by shoaling factor adjustment of
surge envelopes pertaining to the nearest primary computation track, as in
previous studies (e.g., Myers 1975).

5.2.2 Maximum surges for alongshore hurricanes - north of Cape Charles

Maximum surge heights produced by alongshore storms bypassing stations
north of Cape Charles were obtained by direct computations using the later
version of SPLASH II surge prediction program. Six storm tracks assigned to
hurricanes in the computations of alongshore surges (fig. 9), were spaced
at distances of 5, 15, 25, 40, 60 and 80 n.mi. from the coast off Cape
May, N.J. Surge computations were made for the 6 combinations of R and T
values in tables lB, 2B, and 3B, on each of the six tracks, all at D =
62 mb. Each of the 36 coastal surge profiles was adjusted to the eight D
classes by the same relation used for the landfalling storms, providing
288 surge values at each coastal point.

The direct computation of alongshore storm surges is a refinement of
the previous procedure in which surge values generated by alongshore storms
were read from prepared nomograms as cited in an earlier report (Myers
1975). The surge model incorporates dynamic effects on storm surges from
the curvature of the coast, and computed surge heights indicate more
distinct variations along the coast than values obtained,-by using the
cited nomograms.

The bathymetric effects on alongshore hurricane surges vary somewhat from
those of landfalling storms. To illustrate these points, peak surge values
at coastal points computed from one of the initial 6.representative hurricanes
(D =62 mb, R = 48 n.mi., T = 23.1 kt), moving along the several tracks, were
plotted against the distance of the storm center from the coast. This dis-
tance was measured from the coastal location as the storm center passed abeam.
These surge values were analyzed and contours joining equal surge heights
drawn. The resultant analysis, shown in figure 8, indicates a minimum area
near the coast in the vicinity of Ocean City, Md., and maximum near the south-
ern end of the Delmarva peninsula and near the entrance of Delaware Bay area.
These variations are partially caused by the curvature of the coast and the
gradient of the sloping continental shelf offshore, as indicated in the land-
falling storm shoaling factor curve in figure 7. Similar analyses (not shown)
made of the peak surges produced by the other five initial hurricanes indicate
the same features.

Legend for Tables 1 to 5

9
c = Orientation of coast, measured clockwise from north.

P = Central pressure (mb).
0
D = Central pressure deficit (mb)o

P. = Proportion of total storms with indicated D value.
1
R = Distance from center of storm to principal belt of maximum
winds (n.mi.).

P = Proportion of storms with indicated R value.
r
T = Forward speed of storm (kt).

P = Proportion of storms with indicated T value.
t
F = Frequency of storm tracks crossing coast (storm tracks per
~n n.mi. of coast per year).

0L = Direction of entry or exit, measured clockwise from the coast
~L ~ (deg.).

P = Proportion of storms with indicated 0L value.

L = Distance of storm track from coast inland or seaward (n.mi.).

F = Frequency of storm tracks crossing line normal to coast
~a (storm tracks per n.mio per year).

DL = Distance interval from coast (n.mi.).

LL = Effective distance of storm over land (n.mi.).

Table 1.--Hurricane and tropical storm parameters - Rehoboth Beach, Del.

A. Landfalling storms

F = .00016 0 = 030�
n c

P D P. R P T Pt P
o I r t L P

936.9 76.3 .02 30.5 10.0 .1 120 .5

944.8 68.4 .03 41.7 .5 13.5 .2 145 .5

950.4 62.8 .05 .5 18.0 .3

956.7 56.5 .10 24.1 .2

967.0 46.2 .20 31.9 .2

977.1 36.1 �20

985�6 27.6 .20

996.0 17.2 .20

B. Alongshore storms*

DL L F R P T P
L ar t

0 to 10 5 .00160 30.5 .5 16.5 o20

10 to 20 15 .00190 41.7 .5 23.1 .42

20 to 30 25 .00250 34.3 .38

30 to 50 40 .00280

50 to 70 60 .00350

70 to 90 80 .00320

*PO, D, and Pi are the same as those for landfalling storms.
o~ i~~

Table 2.-Hurricane and tropical storm parameters - Ocean City, Md.

A. Landfalling storms

F = .00019 0 = 030�
n c

P D Pi R P T Pt 0L P9

936.8 76.4 .02 30.5 .5 9.4 .1 120 .5

944.8 68.4 .03 41.7 .5 12.8 .2 145 .5

950.4 62.8 .05 17.2 .3

956.8 56.4 .10 23.4 .2

966.7 46.5 .20 31l1 .2

977.6 35.6 .20

986.2 27.0 .20

996.3 16.9 .20

B. Alongshore storms*

DL L F R P T Pt

-10 to 0 -5 .00200 30.5 .5 16.5 .32

0 to 10 5 .00240 41.7 .5 23.1 .40

10 to 20 15 .00260 34.3 .28

20 to 40 30 .00295

40 to 60 50 .00305

60 to 80 70 .00270

P D, and Pi are the same as those for landfalling storms.
0'~~

Table 3.--Hurricane and tropical storm parameters - Parramore Island, Va.

A. Landfalling storms

F = .00029 9 = 0300

o D P. R P T Pt P9
I r t L

936.4 76.8 .02 30.5 .5 8.1 .1 120 .5

944.7 68.5 .03 41.7 .5 11.2 .2 145 .5

950.2 63.0 .05 15.6 .3

956.7 56.5 .10 21.8 .2

966.2 47.0 .20 29.5 .2

977.8 35.4 .20

986.8 26.4 .20

996.6 16.6 .20

B. Alongshore storms*

DL L F R P T P
a r t

-15 to -5 -10 .00250 30.5 .5 16.5 .36

- 5 to 5 0 .00160 41.7 .5 23.1 .40

5 to 15 10 .00150 34.3 .24

15 to 35 25 .00265

35 to 55 45 .00320

55 to 75 65 .00265

*P0, D, and Pi are the same as those for landfalling storms.

Table 4.--Hurricane and tropical storm parameters - Virginia Beach, Va.
9 = 3450
C

Po D Pi R Pr T Pt Fn OL P0

935.4 77.8 .02 * * 7.9 .2 .00031 137 1.0
943.2 69.3 .03 * * 11.5 .2
H 949.8 63.4 .05 24.1 .33 11.5 .2
4 956.2 57.0 .10 37.0 .33 20.6 .2
a 965.6 47.6 .20 42.8 .33 25.9 .1
977.8 35.4 .20
987.2 26.0 .20
996,7 16.5 .20
0 962.0 51.2 .02 24.1 .33 6.1 .2 .00012 90 1.0
4 964.8 48.4 .03 37.0 .33 6.8 .2
H 968.8 44.4 .05 42.8 .33 7.5 .2
4 975.2 38.0 .10 8.7 .2
' 984.3 28.9 .20 10.4 .1
991.7 21.5 .20 12.9 .1
996.0 17.2 .20
999.6 13.6 .20
963.6 49.6 .1 24.1 .33 9.7 .3 .00212 230 .5
971.0 42.2 .1 37.0 .33 15.5 .4 263 .5
:4 978.0 35.2 .2 42.8 .33 25.9 .3
987.0 26.2 .2
x 994.0 19.2 .2
1001.0 12.2 .2

L F LL R P T P
L Fa LL R Pr t Remarks

5 .0004 * * 12.8 .2 Po, D, and Pi, are
15 .0008 24.1 .33 17.4 .2 the same as those
0
. 25 .0009 37.0 .33 20.5 .2 for SE landfalling
w 35 .0011 42.8 .33 24.9 .2 storms.
o 50 .0012 30.6 .1
70 .0012 36.5 .1

5 .0015 70 24.1 .33 11.2 .3 D's are adjusted
15 .0016 80 37.0 .33 25.1 .3 from landfalling
" 25 .0017 storms by eq (1)
i 35 .0017 100 using LL and T
a 50 .0013 120 values.

*SE landfalling and alongshore storms with P <945 mb:
R = 24.1 and 37.0 n.mi. are each assigned a probability of 0.5.

21
Table 5.--Hurricane and tropical storm parameters
N.C.-Va. border. e =342�
c

P D P R Pr T Pt Fn L

934.8 78.4 .02 * * 7.5 .2 .00033 140 1.0
n 942.9 70.3 .03 * * 11.3 .2
d 949.2 64.0 .05 23.8 .33 15.2 .2
r- 955.8 57.4 .10 36.9 .33 20.0 .2
Y 964.7 48.5 .20 42.8 .33 25.2 .1
r 975.2 38.0 .20 31.0 .1
985.0 28.2 .20
w 996.7 16.5 .20

962.0 51.2 .02 23..8 .33 6.1 .2 .00021 93 1.0
964.8 48.4 .03 36.9 .33 6.8 .2
'- 968.8 44.4 .05 42.8 .33 7.5 .2
975.2 38.0 .10 8.7 .2
1 984.3 28.9 .20 10.4 .1
0 991.7 21.5 .20 12.9 .1
996.0 17.2 .20
999.6 13.6 .20

959.7 53.5 .1 23.8 .33 9.4 .3 .00240 233 .5
967.9 45.3 .1 36.9 .33 15.2 .4 266 .5
975.4 37.8 .2 42.8 .33 25.2 .3
.' 985.1 28.1 .2
x 992.8 20.4 .2
1000.2 13.0 .2

L Fa LL R Pr T Pt Remarks

5 .0008 * * 12.5 .2 PO, D, and Pi are
15 .0008 23.8 .33 17.2 .2 the same as those
o 25 .0009 36.9 .33 19.9 .2 for SE landfalling
35 .0011 42.8 .33 24.4 .2 storms.
50 .0012 29.9 .1
0
�- 70 .0012 35.6 .1

5 .0015 50 23.8 .33 11.2 .3 D's are adjusted
15 .0016 60 36.9 .33 17.7 .4 from landfalling
0 25 .0017 65 42.8 .33 25.1 .3 storms by eq (3)
35 .0017 70 using LL and T
H 50 .0013 90 values.
* SE landfalling and alongshore storms with PO<945 mb:

R = 23.8 and 36.9 n.mi. are each assigned a probability of 0.5.

5.2.3 South of Cape Henry

older procedures were used here that differed from the foregoing in a few
details, and are identical with the procedure used in the North Carolina re-
port.. The earlier versions of the computer programs, SPLASH I and II, a
single primary landfall point, and more 8-mi step adjustments, were employed.

Surge computation SPLASH runs were made for all possible combinations of R
and 0 indicated in tables 4 and 5, with a standardized D and T value. Sepa-
rate computations were made to determine the relation of surge height to T,
this time at standard R and 0. Surge profiles that would be produced by all
possible combinations (D, T, R, and 0) were then obtained by adjustments, in-
cluding the usual adjustment for D from Jelesnianski (1972), Potential surges
that would be produced by alongshore and inland storms were obtained from
pre-prepared nomograms from the combinations of hurricane parameters in the
tables. The procedures are described in detail in an earlier report (Myers
1975).

5.3 Astronomical Tides

Most of the combinations of forces producing the astronomical tides are
experienced during a 19-yr cycle. There is also a seasonal variation in the
mean water level with a maximum in September-October. The months July,
August, Septembertand the first half of October are taken to represent the
hurricane season. Astronomical high and low tides at Cape May, N.J., Lewes,
Del.,, Wallops Island, and Virginia Beach, Va., for these representative months
were recomputed for a 19-yr period by running the standard tide computation
program written by Pore and Cummings (1967). The accumulated frequencies of
the high and low tides were calculated separately by months, then weighted
in proportion to hurricane occurrences in each month (July 13%, August 27%,
September 39%, October 21%). The weighted mean distributions are shown in
figure 10. The resulting probability distributions for Wallops Island are
almost the same as those for Virginia Beach, Va. The range of high and low
tides near the Delaware Bay entrance is slightly greater than those of the
southern stations. Interpolating from the probability curves of the stations
leads to distributions used in tide frequency analyses for locations along
the northern portion of the study area. As in previous studies, each distri-
bution is divided into four class i-I~tervals. The representative astronomical
tide marigrams needed to combine with each hurricane surge marigram were then
approximated as cosine waves with a period of 12.42 hours oscillating between
corresponding high and low tide class intervals. This assumes that the high-
est high tides occur with the lowest low tides, etc.

5.4 Hurricane Tide Frequencies at Selected Points

The hurricane tide frequencies are combined for all classes of storms:
landfalling and alongshore hurricanes for stations north of Cape Charles;
landfalling, alongshore,, exiting, and inland hurricanes for stations south
of Cape Henry. The complete detailed computation procedures were applied to
five selected stations mentioned in par. 5.1, and also at the Virginia-
Maryland State line, and Bethany Beach, Del. Hurricane tide frequencies for
other intermediate points were obtained by interpolations, described in
section 7.

6. WINTER COASTAL STORM TIDES

6.1 Evaluation of Northeaster Tide Levels in Study Area

Most of the 10-yr return period magnitude (10% probability of being
equalled or exceeded per year) storm tides in this study area are caused by
northeasters, as will be shown in section 7. The 1962 northeaster produced
the second highest tide of record and the largest damage in dollar value in
the study area. At the 100-yr return period magnitude (1% chance of being
equalled or exceeded in any year), the activating storms are hurricanes and
the additional contribution by northeasters is small by comparison.

For purposes of this study, the northeaster contribution to storm tide
frequency may be evaluated with sufficient precision by direct analysis of
long-period tide gage records and interpolation along the coast. For an
overall view, the northeaster tide frequency analysis was extended beyond the
study area to Sandy Hook, N.J., on the north. Northeaster tide frequencies
for contiguous coastal reaches to the south are contained in the previously
cited report (Ho and Tracey 1975b).

6.2 Analysis of Tide Gage Records'
6.2.1 Selection of data

The National Ocean Survey (NOS) primary gages that are maintained over
many years in and adjacent to the study area are listed in table 6 with their
periods of record. A selection of stations for analysis, indicated in the
table, was made considering spacing between stations, length of record, and
representing open coast as contrasted with estuarine conditions insofar as
possible. The locations of the selected stations are shown in figure 11.

To focus on northeasters and excluded hurricanes, at each station the maxi-
mum tide was abstracted for each October-through-May season, with an addi-
tional check of weather maps to exclude any hurricanes that might occur in
early October. These northeaster annual maxima are listed in table 7.

Table 6.-Primary tide gages of the National Ocean Survey in and adjacent to
study area.

Station Years of record

Willets Point, N.Y._ 1931-
The battery, N.Y. 1920-
*Sandy Hook, N.Y. 1932-
*Atlantic City, N.J. 1922-
Cape May, N.J. 1956-
Reedy Point, Del. 1956-66
*Lewes, Del. 1948-
*Kiptopeke Beach, Va. 1951-
*Hampton Roads, Va. 1927-
Norfolk, Va. 1935-

*Station selected for analysis.

6.2.2 Adjustment for sea level trend

Sea level with respect to the adjacent land has been rising more or less
steadily during the period of tide gage measurements in the study area. For
example, at New York City, where the longest record is available, sea level
has increased about 0.7 ft since 1890. In order to interpret the past expe-
rience in terms of present conditions, the annual tide maxima were adjusted
to 1970 conditions before performing a statistical frequency analysis. Hicks
and Crosby (1974) have analyzed secular variations in sea level at NOS pri-
mary gages. They also publish average trends in millimeters per year, based
on a linear regression fit to the period 1940-72 and to the entire series of
record at the particular station. Each maximum annual tide in table 7 during
or since 1940 was adjusted to 1970 by the latter trend. This is a statistical
estimate of the maximum annual tide that would have been observed from a com-
bination of the weather and solar and lunar gravitational forces during the
particular year but under 1970 mean sea level conditions. For years prior
to 1940, the annual trend was calculated for each station that, averaged with
the "since 1940" trend weighted by years, gives Hicks and Crosby's "entire
series" trend. The earlier records were then adjusted to 1940 by this trend
and again to 1970 by the later trend. An example of these statistical trends
is shown graphically in figure 12. This procedure was used in preference to
Hicks and Crosby's "entire series" trend at each station so as to not intro-
duce artificial distinctions between adjacent stations related to respective
length of record rather than geophysical factors. The maximum annual tides
thus adjusted are listed in table 7, marked "adj."

6.2.3 Statistical analysis of maximum annual tides

The tides adjusted to 1970 conditions in table 7 were treated as an annual
series and frequency curves fitted by the Gumbel method for Fisher-Tippett
type I. It was judged subjectively that this distribution fits the data
points as closely as several other standard distributions, including log

normal. The resulting curves for Lewes, Del., Kiptopeke Beach, Va., and
Hampton Roads, Va., are shown in figures 13a, 13b, and 13c, respectively.
Similar plots for Atlantic City and Sandy Hook, N.J. were used in the analysis
but are not shown.

The return period to assign to the most severe known storm events is always
a difficult question. It is known from historical accounts that the two high-
est winter tides of record at Lewes, in the 1962 and 1950 storms, have not
been equalled previously since 1900. Assuming a period of record of 76 years
(1900-75) leads to the supplementary plotting positions for these two storms,
shown in figure 13a as additional guidance in drawing conclusions on frequen-
cies. The frequency for equalling or exceeding these events implied by the
statistically fitted curve is 0.02 and 0.03 per year, respectively. These
seem reasonable, and the fitted curve is adopted. Similar considerations
apply to the 1962 storm at Kiptopeke Beach (fig. 13b) and Hampton Roads
(fig. 13c).

6.2.4 Coastal profile of tide frequencies

Coastal profiles of northeaster tide frequencies are shown in figure 14.
Elevations scaled from figures 13a, 13b, and 13c, and from similar curves for
Atlantic City and Sandy Hook are controlling points.

In constructing the curves an adjustment is made from Hampton Roads and
Keptopeke Beach gage locations to "open cat"

A limited amount of information was derived from each of several guides in
making the interpolation between stations shown on the figure. Hurricane
shoaling factor (fig. 7) is only suggestive. Northeasters, because of their
larger lateral extent, are less dominated by medium-scale bathymetric factors
than hurricanes. Specific "shoaling factor" curves have not been worked out
for northeasters. Historical storms should give a clue to prevailing storm
tide variations along the shore. This information is limited, however, by
the scarcity of tide reports, only a few more than the primary tide gages
between which interpolation is required. Coastal profiles of the maximum
tide in the November 1950 and March 1962 storms are depicted in figure 15.
Finally, the local mean range of the astronomical tide profiled in figure 16
from the large number of determinations in National Ocean Survey (1975) Tide
Tables is also suggestive. The astronomical tide range is more responsive
to very local bathymetric and coastal configuration effects than northeaster
tides, in which direct wind setup is a major factor.

7, TOTAL STORM TIDE FREQUENCY

7.1 Combination of Hurricane and Northeaster Tide Frequencies

The tide frequency curves for landfalling and alongshore hurricanes and
tropical storms, and winter coastal storms, are plotted together on figure
17 and combined to give an all-storm frequency curve for Rehoboth Beach, Del.
Similar tide frequency curves are shown in figure 18 for Ocean City, Md., and
figure 19 for Parramore Is land, Va. The all-storm curve is obtained by add-

'-v

Table 7.--Maximum October - May tides from northeasters

Hampton Roads Ktptopeke Beach Lewes Atlantic City Sandy Hook Montouk New London Newport
Va. Va. Bel. N.J. N.J. N.Y. Corm. R.I.
Season Max Date AdJ Max Date AdJ Max Date AdJ Max Date Adj Max Date AdJ Max Date AdJ Max Date AdJ Max Date Adj

1922-23 4.0 3-06 4.6
24 4.5 3-21' 5.1
25 4.0 10-30 4.6
26 3.9 2-10 4.5
27 4.6 2-20 5.1
28 2.7 5-08 3.4 4.1 12-05 4.6
29 3.0 4-16 3.7 4.0 4-16 4.5

1929-30 3.4 10-01 4.0 4.3 10-02 4.8
31 4.1 11-04 4.7 4.9 3-04 5.4 3.2 10-11 3.6
32 3.6 3-06 4.2 4.3 3-06 4.8 3.8 4-21' 4.2
33 3.8 1-26 4.4 5.2 11-10' 5.7 5.4 11-10 6.0 4.4 1-27 4.8
34 2.9 10-06 3.4 3.8 10-05 4.2 3.8 4-11 4.4 3.4 1-16
3.8
35 2.8 1-24 3.3 4.1 10-24 4.5 4.1 10-24 4.7 3.3 10-22
3.6
36 3.3 11-17 3.8 4.9 11-17 5.3 5.4 11-17 6.0 3.3 11-25' 3.6
37 3.6 1-29 4.1 4.5 4-26 4.9 4.6 10-01' 5.1 4.1 10-01 4.4
38 3.4 5-30 3.9 4.4 10-23 4.8 4.9 10-23 5.4 3.8 10-23, 4.1
39 3.1 4-29 3.5 5.0 5-03 5.4 4.7 5-03 5.2
3.0 4-02* 3.3 3.7 4-02 4.0

1939-40 4.1 1-26 4.5 4.7 1-24 5.0 4.5 4-20 5.0
3.0 4-21 3.3 3.9 4-21 4.2
41 3.6 10-01 4.0 4.8 10-01 5.1 4.7 10-01 5.2 3.4 11-27
3.6 3.9 11-02 4.1
42 3.0 3-28 3.4 4.8 3-03 5.1 4.7 3-03 5.2 4.3 3-03
4.5 4.6 3-03 4.8
43 4.2 12-19 4.5 4.9 3-06 5.3 4.0 12-02 4.2 -
44 2.7 12-29 3.1 5.1 10-26 5.4 5.4 10-26 5.8 3.3 10-27
3.5 3.9 2-23 4.1
45 3.0 11-18 3.3 5.4 11-30 5.7 5.3 11-30 5.7 4.2 11-30 4.4 5.3 11-30
5.5
46 3.9 12-05' 4.2 4.8 12-02 5.1 4.9 11-29 5.3 3.8 11-22 4.0 3.8 12-20
4.0
47 3.0 4-21 3.3 4.2 4-21 4.5 4.3 11-10' 4.7 3.2 3-03 3.4 4.8 3-03
5.0
48 3.7 11-02 4.0 5.2 11-01 5.4 5.5 11-01 5.8 5.0 10-31 5.4 4.7 11-12 4.9 4.5 11-12 4.7 4.6 11-12
4.8
49 4.6 10-05 4.9 4.9 10-05 5.1 4.9 10-06 5.1 4.8 10-06 5.2 3.2 13-31 3.4 3.4 12-31 3.6 3.9 12-30
4.1

1949-50 3.3 10-17' 3.6 4.4 10-18 4.6 4.4 10-18 4.6 4.5 10-22 4.8 2.9 10-21 3.0 2.9 10-21' 3.1 4.2 10-22 4.4
51 3.5 5-18 3.8 #?.2 11-25 6.6 11-25 6.8 6.9 11-25 7.2 5.4 11-25 5.5 6.3 11-25 6.5 4.5 2-07 4.7
52 3.5 2-27 3.7 3.4 2-27 3.6 4.8 11-01 5.0 5.0 11-01 5.3 3.5 11-03 3.6 3.9 11~03 4.1 4.4 11-03
4.6
53 3.3 11-21 3.5 3.7 11-21 3.9 4.5 12-22 4.7 4.4 12-22 4.6 4.6 12-23 4.9 3.3 12-23 3.4 3.2 2-15 3.3 4.3 2-15
4.4
54 3.9 10-23 4.1 3.9 10-23 4.1 5.5 10-23 5.7 5.7 10-23 5.9 7.6 11-07 7.9 5.1 11-07 5.2 5.5 11-07 5.6 5.0 11-O7
5.1
55 3.5 12-O6 3.7 3.1 4-25 3.3 4.4 4-24 4.6 4.5 4-24 4.7 5.0 4-24 5.3 3.0 3-22 3.1 3.4 3-22
3.5 - - -
56 5.5 4-11 5.7 3.7 1-11 3.9 5.2 1-10 5.4 4.8 1-10 5.0 5.9 10-14 6.1 4.5 3-16 4.6 4.1 3-16 4.2 4.2 10-16
4.3
57 3.5 10-28 3.7 3.2 10-25' 3.4 4.6 11-03 4.7 4.3 2-15 4.5 4.4 2-15' 4.6 3.0 11-26 3.1 3.1 11-26 3.2 3.5 1-16
3.6
58 4.8 10-O6 5.0 4.7 10-O6 4.9 4.6 4-03 4.7 4.7 4-03 4.8 5.6 3-20 5.8 4.6 2-16 4.7 4.2 2-16 4.3 4.5 4-03*
4.6
59 4.5 10-21 4.7 3.8 10-21 4.0 4.3 12-12' 4.4 4.2 12-12 4.3 5.2 3-27 5.4 3.5 10-26 3.6 3.6 10-26' 3.7 4.3 11-10
4.4

1959-60 3.4 2-01 3.5 3.1 12-29' 3.2 4.3 12-30' 4.4 4.9 12-29 5.0 5.3 12-29 5.5 4.3 2-19 4.4 4.6 2-19 4.7 4.6 2-19
61 4.7 't
3.1 1-16 3.2 3.3 1-16 3.4 5.1 1-16, 5.2 5.0 1-16 5.1 6.4 4-13 6.6 3.9 3-09 4.0 4.1 3-09 4.2 4.4 1-16 4.5
62 6.4 3-07 6.5 6.1 3-07 6.2 7.4 3-06 7.5 6.8 3-06* 6.9 7.3 3-06 7.4 4.3 3-07 4.4 4.1 3-07 4.2 4.9 3-07 5.0
63 4.0 11-27 4.1 3.8 11-27 3.9 5.6 11-03 5.7 4.6 11-03' 4.7 5.6 11-10 5.7 3.6 12-06 3.7 4.1 12-06 4.2 4.2 12-06 4.3
64 3.0 1-01 3.1 3.2 1-01' 3.3 5.4 1-13 5.5 4.5 11-07 4.6 4.6 1-13 4.7 3.6 11-30 3.6 4.2 11-30 4.3 5.7 11-30 5.8
65 4.0 1-16 4.1 3.7 1-17 3.8 4.8 1-17 4.9 4.5 1-17 4.6 5.0 1-17 5.1 2.9 1-17 2.9 3.1 1-17' 3.2 4.2 11-20 4.3
66 3.5 1-27 3.6 3.1 1-26 3.2 4.8 1-23 4.9 5.5 1-23 5.6 6.7 1-23 6.8 2.8 1-08 2.8 4.0 1-23 4.0 4.0 1-08 4.0
67 3.9 5-24 4.0 3.7 5-24 3.8 5.1 5-24 5.1 4.7 5-24* 4.7 5.0 4-27* 5.1 4.0 12-29 4.0 4.7 12-29 4.7 4.7 12-29 4.7
68 4.1 5-27 4.1 3.6 5-27 3.6 4.2 1-14 4.2 4.5 12-29 4.5 4.7 11-03' 4.7 3.0 10-31' 3.~ 2.7 10-31 2.7 4.0 11-03 4.0
69 4.1 3-02* 4.1 3.7 3-02 3.7 4.8 11-12' 4.8 5.3 11-12 5.3 6.7 11-12 6.7 5.0 11-12 5.0 5.1 11-12 5.1 4.3 11-12' 4.3

1969-70 3.3 11-10 3.3 3.6 11-10 3.6 5.3 11-10 5.3 5.8 12-26 5.8 3.4 12-26 3.4 3.7 12-26 3.7 4.0 11-11 4.0
71 4.2 3-26 4.2 3.6 3-26 3.6 4.7 3-27* 4.7 - 5.2 3-27 5.2 3.3 4-07 3.3 3.9 12-17 3.9 4.4 12-17 4.4
72 3.7 10-19 3.7 3.6 10-19 3.6 4.6 2-18 4.6 5.4 2--19 5.4 6.2 2-19 6.2 4.9 2-19 4.9 4.8 2-19 4.8 5.3 2-19 5.3
73 4.3 2-11 4.3 5.6 12-22 5.6 5.8 12-22 5.8 4.5 4-04 4.5

Legend:

Max = maximum observed at gage during October-May season, feet above local MSL based on 1941-59 epoch. Hurricanes excluded by inspection of
weather maps.

Ad] - maximum adjusted to 1970 sea-level conditions, using trends from Hicks and Crosby. (See text.)

* ~ same elevation attained on one or more additional dates. Date listed is simultaoeous with seasonal maximum at another station as first choice,
earliest in season as second choice.

# = High-water mark. Gage not in operation.

ing horizontally the frequencies (reciprocal of return period) for each tide
level. The overall frequency is reinverted to return period for plotting
on the diagram. The all-storm frequency curves for Virginia Beach, Va., and
at the Virginia-North Carolina border obtained in a similar manner are shown
in figure 20.

Tide frequencies for locations other than the above primary computation
points along this stretch of the coast were obtained in the same manner,
after interpolation of each storm type separately along the coast. The in-
terpolation of hurricane tide frequencies was based on consideration of the
frequency of storms, the variation in the shoaling factor (fig. 7), and the
trend in the hurricane climatology parameters along the coast. Analyzed peak
surge heights generated by alongshore storms, as shown in figure 8 for
example, were also used as an additional guide In the interpolation of along-
shore hurricane tide frequencies. Interpolation of winter coastal storm tide
frequencies is discussed in section 6.. Figure 21 shows the resulting varia-
tion of the total tide heights along the coast for the 10-, 50-, 100-, and
500-yr return period.

The tide levels are stated as heights above local mean sea level, adjusted
to the 1941-59 epoch. Datum levels and differences between datums in use are
covered in section 8. The "open coast" tide frequencies apply to ocean
beaches at or near the locations indicated. It should be emphasized that
these frequency values are of still-water levels on the open coast that
would be measured in a tide gage house or other enclosure, excluding wave
action. The destructive effects of waves on the beach front must be taken
into account separately. In insurance rating this is taken into account by
the ocean front '"velocity zone."~

Local effects can modify the elevation of the storm tide. Local features
diminishing "open coast" elevations in the landward direction include narrow
passes and inlets and obstructions to inundation such as dunes and swamp
vegetation. Converging shores of bays and strong winds over long fetches of
shallow water (wind setup) have the opposite effect. The net results of
these effects can result in either higher or lower storm-tide levels of a
given mean return period at estuarine, bay, and inland locations compared to
the open coast, These differences have to be determined by localized studies.

7.2 Comparison of Frequency Curves

The-derived frequency curves are compared with tide records, statistically
analyzed, at the two primary gages in the study area with the longest record
and with historical storm tide levels in the vicinity.

Figure 22 shows the frequency curve at Rehoboth Beach, Del., in comparison
to the 28-yr series of maximum annual tides at Lewes, Del., (inside the
breakwater) and also the four highest known tide levels at Lewes. The maxi-
mum annual series, unlike figure 13a, includes all storms and is not re-
stricted to hurricanes. The four historical values are known to be the high-
est since 1900 and are construed as a 76-yr record (1900-75) for computing
plotting positions. The 1944 value is from Cape May.

Figure 23 shows a similar comparison of the computed frequency curve at
Virginia Beach, Va., to the 47-yr series of maximum annual tides at the Hamp-
ton Roads gage. (Tides of less than 2-yr return period omitted from diagram.)
Virginia Beach storm tide levels are expected to be higher than Hampton Roads.
The six highest tides in Norfolk Harbor (Corps of Engineers 1959) since 1908,
construed as a 68-yr record, are also shown.

The annual maxima in figures 22 and 23 are adjusted for sea level trend
by the procedures of par. 6.2.2.

8. REFERENCE DATUM

The National Ocean Survey, NOAA, and its component, the National Geodetic
Survey, have developed the following standards for elevation control. Abbre-
viated definitions are given here for convenience in consistent application
of the results of this study. Further details are given in the Tide and Cur-
rent Glossary (Shureman 1975) and Variability of Tidal Datums and Accuracy in
Determining Datums from Short Series of Observations (Swanson 1974).

Mean sea level (MSL). A tidal datum for a specific location, also referred
to as local MSL. It is the arithmetic mean if sea-level heights over a speci-
fic 19-yr series of observations, or Metonic cycle. Boundaries and eleva-
tions of land adjacent to the sea are generally expressed with reference to
a tidal datum in legal definitions. The storm tide levels in this report,
by the manner in which they are derived, are heights above local MSL.

The National Geodetic Vertical Datum (NGVD). (Formerly known as "Sea Level
Datum of 1929.") A fixed reference adopted as a standard geodetic datum for
heights. NGVD coincides with the average height of the sea at 26 selected
tide gage sites in the United States and Canada, based on records available
in 1929. It does not reflect the changing stands in sea level since that
time nor non linear variations of mean sea level with respect to an equipoten-
tial surface along line segments between these stations. Elevation contours
on topographic maps are generally related to this datum.

The standard 19-yr epoch for tidal datum is currently 1941-59. Short-
period or recent tide gage records are adjusted to this standard epoch by
comparison to primary stations having at least 19 years of record. The
National Ocean Survey has an active program of establishing tidal bench
marks, based on such adjustments.

Differences between local MSL for the 1941-59 Metonic epoch and NGVD have
been established at primary gages and certain subordinate stations by differ-
ential leveling. Established differences on the outer coast applicable to
the study area are:
Atlantic City, N. J. . . 1941-59 local MSL 0.4 ft above NGVD

Virginia Beach, Va . . . 1941-59 local MSL 0.0 ft above NGVD

'Devised by Meton, an ancient Greek astronomer (Shureman 1975).

To adjust the coastal storm tide frequency levels of this report to heights
above NGVD from Cape Charles northwardpadd a difference obtained from the
above table by interpolation. From Cape Henry southward the difference be-
tween the two datums is negligible. Datum differences are under constant re-
view and differ somewhat in bays and estuaries from coastal values. Local
planners and engineers requiring datum differences in bays and estuaries
should obtain the latest information from the National Ocean Survey, Rock-
ville, Md., 20852.

MSL relative to land is increasing slowly on the east coast, at the rate of
about a foot a century. Data on trends in sea level relative to land are
given by Hicks and Crosby (1974). This trend is thought to be due to sub-
sidence of the land and change in volume of water in the sea from melting ice.
Adjustments of tide data for sea-level trend are described in par. 5.22. If
the base epoch for MSL is changed (Swanson 1974) the data of this study
should be used as elevations above the new MSL datum level, as an implicit
adjustment for sea-level trend.

9. RELATION OF THIS REPORT TO DISASTER PLANNING

The most disastrous display of hurricane force on the U.S. Coast in recent
years was by Camille, which struck the Bay St. Louis - Pass Christian - Gulf-
port - Biloxi, Miss., areas in 1969. According to high-water marks, the
storm tide reached a level of almost 25 ft MSL (Corps of Engineers 1969).
This is the most intense hurricane so far to strike the United States main-
land during the period of record keeping. Other diasasters could also be re-
counted, including Hazel at the North Carolina-South Carolina border in 1954
and the New England Hurricane of 1938. The high-water mark data for the New
England storm collected by the Corps of Engineers, Woods Hole Oceanographic
Institution, and others, were compiled by Harris (1963, fig. 8.3). The high-
est storm tides were about 12 ft MSL at the open coast and 14-16 ft MSL in
Narraganset Bay and Buzzards Bay. If a hurricane equal to the 1938 storm
were to strike the coast of the study area at a climatologically probable
speed and direction, a maximum surge of about 17 ft would be produced. Dis-
aster planning objectives should take into account such a possibility.

The central purpose of this report is to develop actuarial frequencies for
insurance rating and related uses; therefore, all frequencies, including the
coastal profiles of figure 21.are stated in terms of probabilities or mean
recurrence intervals at points. The likelihood of a severe storm tide of
any given level somewhere within the study area in any given year is much
greater than the point recurrence interval for the same storm, a difference
that needs to be taken into account in regional planning against disasters.
Regional disaster planning should be based on studies for that particular
purpose.

References

Barrientos, Celso S., and Jye Chen, 1975: "Storm Surge Shoaling Corrections
Along the East Coast of the United States," Techniques Development Labor-
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Spring, Md., Report to Dept. of Housing and Urban Development (to be
published).

Bristor, Charles L., 1951: "The Great Storm of November, 1950," Weatherwise,
Vol. 4, pp 10-16.

Cooperman, Arthur I., and Hans E. Rosendal, 1962: "Great Atlantic Coast
Storm, 1962," Mariners Weather Log, Vol. 6, No. 3, Weather Bureau, U.S.
Dept. of Commerce, Weather Bureau, Washington, D.C., pp. 79-85.

Corps of Engineers, 1959: U.S. Army Engineer District, Norfolk, Va.,
"Hurricane Survey, Norfolk, Virginia," Norfolk, Va.

Corps of Engineers, 1962 Rev. 1963: U.S. Army Engineer District, Norfolk,
Va., "Hurricane Survey, Middle and Lower Peninsulas of Virginia,"
Norfolk, Va.

Corps of Engineers, 1963: U.S. Army Engineer District, Philadelphia, Pa.,
"Report on Hurricane Study, Delaware River and Bay, Pennsylvania, New
Jersey, and Delaware," Philadelphia, Pa.

Corps of Engineers, 1963: U.S. Army Engineer Division, North Atlantic,
"Operation Five-High-March 1962 Storm," Washington, D.C.

Corps of Engineers, 1964: U.S. Army Engineer District, New York, N.Y.,
"Cooperative Beach Erosion Control and Interim Hurricane Study," New York,
N.Y.,

Corps of Engineers, 1965: "Atlantic Coast of Southern New Jersey and
Delaware," House Document No. 38, 89th Congress, 1st Session, U.S.
Congress, Washington, D.C.

Corps of Engineers, 1969: U.S. Army Engineer District, Mobile, Ala.,
"After Action Report -- Hurricane Camille/17-18 August 1969," Mobile
Ala.

Cry, George W., 1965: "Tropical Cyclones of the North Atlantic Ocean,"
Technical Paper No. 55, Weather Bureau, U.S. Dept. of Commerce, Washington,
D.C., 148 pp.

Graham, Howard E., and Georgina N. Hudson, 1960: "Surface Winds near the
Center of Hurricanes (and other Cyclones)," National Hurricane Research
Project Report No. 39, Weather Bureau, U.S. Dept. of Commerce, Washington,
D.C., 200 pp.

Graham, Howard E., and Dwight E. Nunn, 1959: "Meteorological Considerations
Pertinent to Standard Project Hurricane, Atlantic and Gulf Coasts of the
United States," National Hurricane Research Project Report No. 33, U.S.
Weather Bureau and Corps of Engineers, Washington, D.C., 76 pp.

Goodyear, Hugo V., 1963: "Reconstructed Surface Wind Fields for the East
Coast Storm of March 6-8, 1962," Paper presented at American Meteorological
Society Annual Meeting Jan. 21-24, 1963, available from National Weather
Service, U.S. Department of Commerce, Silver Spring, Md., 20910,
Attention W211.

Hardy, Albert V., and Charles B. Carney, 1962: "North Carolina Hurricane,"
Weather Bureau, U.S. Dept. of Commerce, Raleigh, N.C., 26 pp.

Harris, D. Lee, 1963: "Characteristics of the Hurricane Storm Surge,"
Technical Paper No. 48, Weather Bureau, U.S. Dept. of Commerce, Washington,
D.C., 139 pp.

Harris, D. Lee, and C. V. Lindsay, 1957: "An Index of Tide Gages and Tide
Gage Records for the Atlantic and Gulf Coasts of the United States,"
National Hurricane Research Project Report No. 7, Weather Bureau, U.S.
Dept. of Commerce, Washington, D.C., 104 pp.

Harrison, Louis P., 1963: "History of Weather Bureau Wind Measurements,"
Key to Meteorological Records Documentation No. 3.151, Weather Bureau,
U.S. Dept. of Commerce, Washington, D.C., 68 pp.

Hicks, Steacy, and James E. Crosby, 1974: "Trends and variability of
Yearly Mean Sea Level 1893-1972," NOAA Technical Memorandum NOS 13,
National Ocean Survey, NOAA, U.S. Dept. of Commerce, Rockville, Md.,
14 pp.

Ho, Francis P., 1974: "Storm Tide Frequency Analysis for the Coast of
Georgia," NOAA Technical Memorandum NWS Hydro-19, National Weather
Service, NOAA, U. S. Dept. of Commerce, Silver Spring, Md., 28 pp.

Ho, Francis P., Richard Schwerdt, and Hugo V. Goodyear, 1975: "Some
Climatological Characteristics of Hurricanes and Tropical Storms, Gulf and
East Coasts of the United States," NOAA Technical Report NWS 15, National
Weather Service, NOAA, U.S. Dept. of Commerce, Silver Spring, Md., 87 pp.

Ho, Francis P., and Robert J. Tracey, 1975a: "Storm Tide Frequency Analysis
for the Coast of North Carolina, South of Cape Lookout," NOAA Technical
Memorandum NWS HYDRO-21, National Weather Service, NOAA, U.S. Depto of
Commerce, Silver Spring, Md., 44 pp.

Ho, Francis P., and Robert J. Tracey, 1975b, "Storm Tide Frequency Analysis
for the Coast of North Carolina, North of Cape Lookout," NOAA Technical
Memorandum, NWS HYDRO-27, National Weather Service, NOAA, U.S. Dept. of
Commerce, Silver Spring, Md., 46 pp.

Jelesnianski, Chester P., 1967: "Numerical Computations of Storm Surges with
Bottom Stress," Monthly Weather Review, Vol. 95, pp. 740-756.

Jelesnianski, Chester P., 1972: "SPLASH - (Special Program to List Ampli-
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Memorandum NWS TDL-46, National Weather Service, NOAA, U.S. Dept. of
Commerce, Silver Spring, Md., 52 pp.

Jelesnianski, Chester P., 1974: "SPLASH (Special Program to List Amplitudes
of Surges from Hurricanes), Part Two: General Track and Variant Storm
Conditions," NOAA Technical Memorandum NWS TDL-52, National Weather
Service, NOAA, U.S. Dept. of Commerce, Silver Spring, Md., 55 pp.

Ludlum, David M., 1963: Early American Hurricanes 1492-1870, American
Meteorological Society, Boston, Mass., 198 pp.

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Land," National Hurricane Research Project Report No. 34, Weather Bureau,
U.S. Dept. of Commerce, Washington, D.C., 18 pp.

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Applied to Atlantic City and Long Beach Island, N.J.," ESSA Technical
Memorandum WBTM HYDRO 11, Weather Bureau, ESSA, U.S. Dept. of Commerce,
Silver Spring, Md., 109 pp.

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NOAA Technical Report NWS-16, National Weather Service, NOAA, U.S. Dept. of
Commerce, Silver Spring, Md., 133 pp.
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Bight Atlas Monograph 6, New York Sea Grant Institute, Albany, N.Y., 44 pp.

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tion of Hourly Values of Astronomical Tide and Time and Height of High and
Low Water," ESSA Technical Memorandum WBTM TDL-6, Weather Bureau, ESSA,
U.S. Dept. of Commerce, Silver Spring, Md., 17 pp.

Pore, N. A., W. S. Richarson, and H. P. Perrotti, 1974: "Forecasting Extra-
tropical Storm Surges for the Northeast Coast of the United States," NOAA
Technical Memorandum NWS TDL-50, U. S. Department of Commerce, Washington,
D.C., 70 pp.

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1944," Monthly Weather Review, Vol. 72, Washington, D.C., pp. 221-223.

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Monthly Weather Review, Vol. 96, Washington, D.C., pp. 242-250.

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Determining Datums from Short Series of Observations," NOAA Technical
Report, NOS 64, National Ocean Survey, NOAA, U.S. Dept. of Commerce,
Rockville, Md., 41 pp.

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Weather Review, Vol. 64, Washington, D.C., pp. 297-300.

Tannehill, Ivan R., 1956: Hurricanes (ninth edition), Princeton University
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Institute, University of Maryland, College Park, Md., 35 pp.

U.S. Weather Bureau, 1879, Monthly Weather Review and Annual Summary,
Washington, D.C., pp. 4-7.

Newburgh
Williamsport p593 OScranto GGr otan
Wilkes-Bane Bridgeport
Nantioe

L VAN JA Nei
Allentown Bethlehem _ n
Reading Yr
Harrisburg Reading (

PhiladelphiaN.C- Lakehurst I '40
I ~ Wilmington Camden'
Hagestown r
B 4~~~~~~~~~~~4

O Frederick4
Baltimore Alni city
4 ~c . , a I - o C a p e M a y
ashingto
uantico Rehoboth Beach
I I_

8 38
ncoteague Island

no <d 4
Petersburg' C ape Charles -
Newport Ne

Mount 36

o --,

Ca pe Hatleras
New BernC 74 p
F 4

Figure l.--Location map.

Newburgh
>~~~~~~~
OScrantoni
W ~~~~2593 r
tWilkes-Barre Bri rt
anticoke I.

A N I-Aw'
[iviliA I2h 3

Alleng ton
Philadeipia e-h

Wilmilfton C a n
Ha~wn \ -n -

F derick 4.

aSlingt >
D.C S o n bth

SEPT. 38

1967
Is E P T. gu ~S

Petersburg harles
Newport N

36-
SEPTA-, /

AUG.- 1954

AUG. -1933
194 ~c~pe Hat:-rab AU. 1893 SE.,T. 1903
Few B a rk slt r 7

Newburgh jraton

\Williameport 2593 WiOSkers-Barre oto
~,, Wiles-Baire Bridgeport
Nanticoke

L V A N 1, A' Newaiktt

Reading YNew York
Harrisburg I >rtc c1 it0

' , Phiadelphia . -Lakehurst j

gaden I
Wilmington dBarne/dt Inlet

o Fredericke a ne
Baltimore I Atlanti City
I'( a i CapeMay

| , ,~ , |
or 38
ashgto bc ./Chi1nc2ue Isu

OCTNhpo.eac / 7/

enceville "00

nb1a a 9

I J IU Idu
1893 E
o AU SEPLF.

n< t Cap Je C Hat ras
1 8Bern77 71 z g 1 -74.
Fiue2.-rcso ecteduricae afecin gtes u y a e , c n i u d

Figure3.--Wether mp for133 oebe 5 90

* ~~~~~~~~~~040.~** SaLve rsue(b
. .. 130,Api~l095

Figre4.-Waterma fr 93EApil11 156

-1024 1020 -%le1016

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~1101
.7 *SEA LEVEL PRESSURE (mb)~~~~~0

- ObOE. M~~10ARC .16

Fiu052-eahrmpfrO1Q~Mrh7 1962.

Ail-fol~ City, N.J,
Noo-nb-r 1950 - 6

6- --2~~~~~~~~~~~~~~~~~~~~~~~~
0

(3 12

04 08 12 16 20 24
25

Ilomplon Rood,. Vo.

13 ~ ~ ~ ~ ~ ~ ~ ~ 1
6- ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~P115

01~~~~~~~~~~~~~~~~~~~~~~~~2~

6 -2

24 12 24 12 24 12 24
II 12 13

Dee. 1. 6

A 44

0
24 12 24 12 24 12 24 12 24 12 24 12 24
5 6 7 a 9 10
TIME IESTI
DAY

Figure 6.--Marigrams for winter coastal storms of November 1950, April 1956,

and March 1962.

N.C.1 ~~~~~~~~~ Virginia Md D]

I~~~~~~~~~~~~~~~~~~~~~~~ CD
a~~~~~~~~~~~~~
~~~~~~~~~~a (D ' D a
I ~ ~~~~~~~ (D
1.0 -~~~I

10-

~~~~~~~DitneFonNC-VaIore In i.-

F~~~~~~~~~~~~~~igr 7.-haigfco f emra oss dpe rmBrin

an Che I17)

Cape~~ May

Metomk~~~~~~~ ~in Ine 4
I 8

CaeChre- I
40 60 8 0 20 140
Distance From NCoVast Borde nmi.)

Figure 7. --eksureheainghs factoof thelaa coasts prdapted byo Barientose
hriands Theabcsadnoe ditaceofstrmtrc

fro cost

Newburgh CC(O N
Williams 13t\OScrantOI roton
Wiaprt ,'PWilkes-Barre Bridgepo

)�anticoke d

L V ANA N
Allentown Bethlehem
Harrisburg :41
I ~a~ P~ ia renton
Phi lade Nt

Wilmington Camden

O Frederickk

Iing D.C. 5 15 25 40 60 8(1
Eastonh h

N 38

Petersburg eh
Newport Ne
enceville

~~;7~~~L Ne~~~~r C~~ity

36-

Cape Hatt-?ras
74

Figure 9.--Storm tracks for surge computations for alongshore storms.

4 4 I I I , I 4 I I I

3- 3-

2- - 2-

r 3:

' .
CD

-2- -2-

-3- a -3- c

-4
0 .2 .4 .6 .8 1.0 0 .2 .4 .6 .8 1.0
Accumulated Probability Accumulated Probability
4 , , , , , , I , , 4

3- 3-

2 2 ~~~~~High

=, O- -- Od

-2- -2-

-3- b - -3- d

-4 ' ' ' ' ' ' ' ' 4 * . . ,
0 .2 .4 .6 .8 1.0 0 .2 .4 .6 .8 1.0
Accumulated Probability Accumulated Probability

Figure 10.--ProbabilZity distribution of astronomical high and Zow tides for hurricane season,
1955-1973, for (a) Cape May, N.J., (b) Lewes, DeZ., (c) WaZZops Island, Va.,
and (d) Virginia Beach, Va.

; X ; 9 , \Ibrk~ andy Hook

tlantic City

ewes

750 70"

iptope' e Beach
Hampton R ads

"g1 '"'~--' l.~-;1 o" 350

Figure 11.--Location of selected tide gage stations.

0 - LEWES. DEL.

H & C 1940-72

,c ~ USED IN STUDY I
z

=+100 "'

H & C 1921-72

_ a./

+200 I
1920 1930 1940 1950 1960 1970 1980

YEAR

Figure 12.--Sea ZeveZ trends at Lewes, DeZ., iZZustrating adaptation of Hicks
and Crosby's (1974) values to this study.

I ''I I I I I ' ',

.3/62 /
� llo 0 (3/62)
- / � � � �(11/50)

X -

0 PLOTTING POSITION USING
2- N=76. i.e.. 1900-75

0 2 5 10 25 50 100 500

RETURN PERIOD (yr)

Figure 13a.--Tide frequencies at Lewes, Del., from winter coastal storms.
Plotted points are seasonal (October-May) maxima.

3/6 2
6-

_ /-

2- 1
~~~0 ~2 5 10 25 50 100 500

RETURN PERIOD (yr)

Figure 13b.--Same as figure 13a but for Kiptopeke Beach, Va.

.3/62

X1 _ /37

~ 4

I --

2 5 10 25 50 100 500
RETURN PERIOD lyr)

Figure 13c.--Same as figure 13a but for Hampton Roads, Va.

N.C.1 Virginia I Md. Del. New Jersey

3~~~~~~- 0
I ~~~~~~~~~~~~~~0
10- CD

8-1

Co I

0 ~ ~~~~ I I0 0 I1
-o~~~~~~~~~~~~~~ I I
1=~ ~~~~~~~~~~~~~C I I I
CD I 0 CDC

co 5r 0 En00 150 20 2 0

<C 0 i 01_C

CD. 1 9 6 2 .

48 ~ i~

2~~~~~~~I e

.10
I I010 10 0 5

~~~~~DsacfrmNC.-a ordr(m.

Figure~~ 15-CatZtd egt bevd ntesom fMrh16 n
Novmbe 1 9 0

N.C. Virginia I Md. I Del. New Jersey

< ci I o ow

I~U I I

a)~~~~ ~ CD -
I -3
_ I

g4 I

M 0) 7-r(id I z W m (D D CDCO C
coI _0 C. CD ICC
I I Ir
0 < 0 Q IDP" ~ co
W CD 0CD x Wr
13 r =r C D ~ o p
(DD I
In (a, a)

C I

r ~I\ I
_ID

3- -

0 50 100 150 200 250

Distance From N.C.-Va. Border (n.mi.)

Figure 16.--Mean normaL tide range variation along the coast.

12Rehoboth Beach, Dei."T-! 1 ii j 4

1~~~~~~~~ -
ii~~~~~~~~~~~~~~~~~4

5 10 50 100 500
Return Period (yr)

Figure 17.--Tide frequencies at Rehoboth Beach, Del., for severa" classes of
storms: (Al landfalling hurricanes and tropical storms, (B)
alongshore hurricanes and tropical storms, [C] winter storms,
and! ID) all storms. Datum reference is 1941-59 local MSL.

12 6Ocen City, Mu. Je li1:

I~~~~~ ~ ~~~~~~~~~~~~~~~~ I 1L 1A.

5~~~ ~ ~~~~~~ 110:. -010 0

Return Period (yr)

Figure 18.--Scane as figure 17 but for Ocean City., Md.

Parramor Island va.*>.-
1 ~ ~ ~ ~ i 2 --'

a~~~~~~~~~~~~~~~~~~~~~s

50 105 0 0
Return Period (yr)~~!V -

8~~~~~ -

60 - - .O
_4

~~~~~4 4

5 1050 10500
Return Period (yr)

Figur i0.- a tid frqece-nte pncata a Virginia Beach,Va
Va. -n b Va.-N.C. bode.iawnrefrnei19-9lca
MSL.~ ~ ~ ~ ~ ~~~~tati i

N.C. I Virginia Md. j Del.

o ~~~~~~~~~~CD 0 0 CD
C- -D w I

CD :3
CD~~~~~~~~0 0CD f 0C
0 : C 0 (
CL ~~~~~~0 z

12- 11.7
11.7
11.0
500-Yr.
- \\ 10.2
~19.9
1 09. 9.5

9.5~~~~~~~~~~~~~~1.
.o,~~ 8.8
I 00-Yr.
(D 18.2_
8 1 7.8
8- 10Y5 7

6.7
I ~ l I 6.2
6- 6.1 6.0 5.8
6- I 15.8

4-
I I

0 20 40 60 80 100 120 140

Distance From N.C.-Va. Border (n.mi.)

Figure 21.--Coastal tide frequencies. Delmarva coasts. Datum reference is 1941-59 local MSL.

1 2

4' 9338 ~~~ Legend
-o a~~~~~~~~~~ Maximum annual tide NOS gage,
Lewes, Del., 1948 -1973.
a Three highest above and 1 944 hurri-
cane tide (high-water mark) replotted

7 ~~~~~~~~Beach, Del., from fig. 1 7.

1 5 10 50 100 500
Return Period (yr

Figrure 22. --Comparison of tide frequency curve at Rehoboth Beach, Del., with
observations at Lewes, Del. Dots, annual maxima since 1948.
Circles, highest values since 1900.

:j 4 ~ 1.j :t7:.{:: ;10

193, Aug.
7~~~~~~~-1KT. :s:. >12

.. ~~~~~1956 ~~~Legend
a) 2:: 2: M1A : ~ aaximum annual tide, NSgae
w- [ Hampton Roads, Va.
___ Sept . Observed storm tide, Norfolk Navy
�iit ~ ~~~Yard for storms described in
4~~~~(:: - ... Chapter 2.
-Computed tide frequency, Virginia
2:!fl::.trL:::::~~~ ~ Beach, Va., from fig. 20.
__ [II .1K [ j..~ . :1]] U.4: T. I
1 5 10 50 100 500
Return Period (yr )

Figure 23. --Comparison of tide frequency curve at Virginia Beach, Va., with
tide observations at Hampton Roads and Norfolk Navy Yard.

(Continued from inside front cover)

NWS HYDRO 15 Time Distribution of Precipitation in 4- to 10-Day Storms--Arkansas-Canadian River Ba-
sins. Ralph H. Frederick, June 1973. (COM-73-11169)

NWS HYDRO 16 A Dynamic Model of Stage-Discharge Relations Affected by Changing Discharge. D. L.
Fread, December 1973. (COM-74-10818)

NWS HYDRO 17 National Weather Service River Forecast System--Snow Accumulation and Ablation MIodel.
Eric A. Anderson, November 1973. (COM-74-10728)

NWS HYDRO 18 Numerical Properties of Implicit Four-Point Finite Difference Equations of Unsteady
Flow. D. L. Fread, March 1974.

NWS HYDRO 19 Storm Tide Frequency Analysis for the Coast of Georgia. Francis P. Ho, September 1974.
(COM-74-11746/AS)

NWS HYDRO 20 Storm Tide Frequency for the Gulf Coast of Florida From Cape San Blas to St. Petersburg
Beach. Francis P. Ho and Robert J. Tracey, April 1975. (COM-75-10901/AS)

NWS HYDRO 21 Storm Tide Frequency Analysis for the Coast of North Carolina, South of Cape Lookout.
Francis P. Ho and Robert J. Tracey, May 1975. (COM-75-11000/AS)

NWS HYDRO 22 Annotated Bibliography of NOAA Publications of Hydrometeorological Interest. John F.
Miller, May 1975.

NWS HYDRO 23 Storm Tide Frequency Analysis for the Coast of Puerto Rico. Francis P. Ho, May 1975.
(COM-11001/AS)

NWS HYDRO 24 The Flood of April 1974 in Southern Mississippi and Southeastern Louisiana. Edwin H.
Chin, August 1975.

NWS HYDRO 25 The Use of a Multizone Hydrologic Model With Distributed Rainfall and Distributed Par-
ameters in the National Weather Service River Forecast System. David J. Morris, August
1975.

NWS HYDRO 26 Moisture Source for Three Extreme Local Rainfalls in the Southern Intermountain Region.
E. Marshall Hansen, October 1975.

NWS HYDRO 27 Storm Tide Frequency Analysis for the Coast of North Carolina, North of Cape Lookout.
Francis P. Ho and Robert J. Tracey. November 1975.

NWS HYDRO 28 Flood Damage Reduction Potential of River Forecast Services in the Connecticut River
Basin. Harold J. Day and Kwang K. Lee, February 1976.

NWS HYDRO 29 Water Available for Runoff for 4- to 15-Days Duration in the Snake River Basin in Idaho.
Ralph H. Frederick and Robert J. Tracey, June 1976.

NWS HYDRO 30 Meteor Burst Communication System--Alaska Winter Field Test Program. Henry S. Sante-
ford, in press, 1976.

NWS HYDRO 31 Catchment Modeling and Initial Parameter Estimation for the National Weather Service
River Forecast System. Eugene L. Peck, June 1976.

NOAA--S/T 76-2305

3 6668 00002 8789