U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 01–4097

Hydrologic and Salinity Characteristics of Currituck 

Sound and Selected Tributaries in North Carolina 

and Virginia, 1998–99

Prepared in cooperation with the

NORTH CAROLINA DIVISION OF WATER RESOURCES and the

NORTH CAROLINA DIVISION OF MARINE FISHERIES

By William S. Caldwell

Raleigh, North Carolina

2001
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

CHARLES G. GROAT, Director

For additional information write to: Copies of this report can be purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

3916 Sunset Ridge Road Box 25286, Federal Center

Raleigh, NC 27607 Denver, CO 80225

dc_nc@usgs.gov 1-888-ASK-USGS

The use of firm, trade, and brand names in this report is for identification purposes 

only and does not constitute endorsement by the U.S. Geological Survey.

Information about water resources in North Carolina is available on the World Wide Web 

at http://nc.water.usgs.gov.
Cover photograph: Data-collection site in Currituck Sound at Poplar Branch, North Carolina, August 31, 1998, 

following Hurricane Bonnie. Taken by William S. Caldwell, U.S. Geological Survey.
Contents III

CONTENTS

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

Introduction .......................................................................................................................................................................... 2

Purpose and scope ...................................................................................................................................................... 3

Study area ................................................................................................................................................................... 3

Previous studies........................................................................................................................................................... 5

Acknowledgments....................................................................................................................................................... 5

Data collection ..................................................................................................................................................................... 6

Water levels ................................................................................................................................................................ 6

Water velocity and discharge ..................................................................................................................................... 6

Salinity ....................................................................................................................................................................... 7

Precipitation and wind ................................................................................................................................................ 7

Hydrologic characteristics .................................................................................................................................................... 7

Drainage system ......................................................................................................................................................... 7

Water-level fluctuations ............................................................................................................................................. 8

Flow ............................................................................................................................................................................ 10

Salinity characteristics ......................................................................................................................................................... 19

Spatial patterns ........................................................................................................................................................... 19

Seasonal patterns ........................................................................................................................................................ 25

Effects of flow and wind ............................................................................................................................................ 25

Salt loads .................................................................................................................................................................... 31

Summary ............................................................................................................................................................................... 34

References ............................................................................................................................................................................ 35

FIGURES

1. Map showing locations of study sites in the Currituck Sound study area, North Carolina and Virginia, 

March 1, 1998, through February 28, 1999............................................................................................................. 4

2–11. Graphs showing:

2. Daily maximum and minimum water leve1s at the Currituck Sound and tributary study sites from 

March 1, 1998, to February 28, 1999............................................................................................................... 9

 3. Cumulative frequency distribution of flows at (A) West Neck Creek (site WN2) 

and (B) Coinjock (site CU2) from March 1, 1998, to February 28, 1999 ....................................................... 11

4. Flow at (A) West Neck Creek (site WN2) and (B) Coinjock (site CU2),

May 21–28, 1998 ............................................................................................................................................. 13

5. (A) Daily net flow volume and (B) cumulative flow volume at West Neck Creek (site WN2)

from March 1, 1998, to February 28, 1999...................................................................................................... 14

6. (A) Daily net flow volume and (B) cumulative flow volume at Coinjock (site CU2) 

from March 1, 1998, to February 28, 1999...................................................................................................... 15

7. (A) Percentage of time wind blew from indicated direction and (B) frequency of 

occurrence of measured hourly wind speed at site WS1 from March 1, 1998, to January 3, 1999, 

and (C) percentage of time wind blew from indicated direction and (D) frequency of occurrence 

of measured hourly wind speed at site WS1 for the period January 1979 through May 1998 ........................ 17

8. Relation of hourly flow to hourly wind direction at West Neck Creek (site WN2) and 

Coinjock (site CU2) for the periods (A) April 21–29, 1998, and (B) August 17–25, 1998 ............................ 18

9. Daily maximum salinity at the Currituck Sound and tributary study sites from 

March 1, 1998, to February 28, 1999............................................................................................................... 20

10. Cumulative frequency distribution of salinity at the Currituck Sound and tributary study sites 

from March 1, 1998, to February 28, 1999...................................................................................................... 21

11. Comparison of daily maximum salinity at sites WN2, AC1, and CU4 from 

March 1, 1998, to February 28, 1999............................................................................................................... 22
IV Contents

12–13. Maps showing:

12. Locations of transects and salinity profile data at selected Currituck Sound 

study sites, June 9, 1998 ................................................................................................................................... 23

13. Prevailing wind direction resulting in (A) increased salinities and (B) decreased salinities 

at Currituck Sound and tributary study sites, March 1, 1998, to February 28, 1999 ....................................... 27

14–19. Graphs showing:

14. Relation of the direction of prevailing winds and daily maximum salinities 

at West Neck Creek (site WN2) during selected periods ................................................................................. 28

15. Relation of the direction of prevailing winds and daily maximum salinities 

at Coinjock (site CU2) during selected periods................................................................................................ 29

16. Relation of the direction of prevailing winds and daily maximum salinities 

at Point Harbor (site CU4) during selected periods.......................................................................................... 29

17. Comparison of daily maximum salinity and daily maximum water level at the 

Currituck Sound and tributary sites for the period March 1, 1998, to February 28, 1999 ............................... 30

18. Daily and cumulative daily salt loads, in tons, at West Neck Creek (site WN2) for the period 

March 1998 through February 1999................................................................................................................. 32

19. Daily and cumulative daily salt loads, in tons, at Coinjock (site CU2) for the period 

March 1998 through February 1999................................................................................................................. 33

Tables

1. Data-collection sites in the Currituck Sound study area, North Carolina and Virginia, 1998–99 .......................... 6

2. Water-level characteristics at the Currituck Sound and tributary study sites based on measurements 

made from March 1, 1998, to February 28, 1999 .................................................................................................... 8

3. Summary of flow characteristics at West Neck Creek (site WN2) and Coinjock (site CU2) based 

on 15-minute interval measurements made from March 1, 1998, to February 28, 1999......................................... 12

4. Largest precipitation events and associated winds and daily net flows at West Neck Creek (site WN2) 

and Coinjock (site CU2) .......................................................................................................................................... 16

5. Highest daily net flow volumes at West Neck Creek (site WN2) and Coinjock 

(site CU2) and associated precipitation and winds .................................................................................................. 16

6. Salinity characteristics at the Currituck Sound and tributary study sites based on 

measurements made from March 1, 1998, to February 28, 1999 ............................................................................ 19

7. Selected water-quality values measured along three transects in Currituck Sound, June 9, 1998 .......................... 24

8. Summary of events associated with the highest daily maximum salinities at the Currituck Sound 

and tributary study sites from March 1, 1998, to February 28, 1999....................................................................... 26

9. Summary of the highest daily salt loads at West Neck Creek (site WN2) and Coinjock (site CU2), 

and the relation of precipitation, flow, and wind direction and speed ..................................................................... 34
Contents V

CONVERSION FACTORS, VERTICAL DATUM, SPECIFIC CONDUCTANCE, 

TEMPERATURE, AND DEFINITIONS

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NDVD

of 1929)—a geodetic datum derived from a general adjustment of the first-order level nets of the

United States and Canada, formerly called Sea Level Datum of 1929.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 25 °C).

Temperature: Water temperature is given in degrees Celsius (°C), which can be converted to

degrees Fahrenheit (°F) as follows:

°F = (1.8 x °C) + 32

Definitions:

AIWW Atlantic Intracoastal Waterway

AVM acoustic velocity meter

DENR North Carolina Department of Environment and Natural Resources (formerly

known as the North Carolina Department of Environment, Health, and Natural

Resources [DEHNR])

EC electrical conductivity

hrs hours

ppt parts per thousand

USACE U.S. Army Corps of Engineers

USGS U.S. Geological Survey

VDEQ Virginia Department of Environmental Quality

Multiply by To obtain

Length

inch (in.) 2.54 centimeter

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

Area

acre 0.4047 hectare

acre-foot (acre-ft) 1,233 cubic meter

square mile (mi2) 2.590 square kilometer

Volume

cubic foot (ft3

) 0.02832 cubic meter

Flow

cubic foot per second (ft3/s) 0.02832 cubic meter per second

inch per year (in/yr) 25.4 millimeter per year

mile per hour (mph) 1.609 kilometer per hour

Mass

ton per day (ton/d) 0.9072 megagram per year
Abstract 1

Hydrologic and Salinity Characteristics of Currituck 

Sound and Selected Tributaries in North Carolina 

and Virginia, 1998–99

By William S. Caldwell

ABSTRACT

Data collected at three sites in Currituck 

Sound and three tributary sites between March 1, 

1998, and February 28, 1999, were used to 

describe hydrologic and salinity characteristics of 

Currituck Sound. Water levels and salinity were 

measured at West Neck Creek at Pungo and at 

Albemarle and Chesapeake Canal near Princess 

Anne in Virginia, and at Coinjock, Bell Island, 

Poplar Branch, and Point Harbor in North 

Carolina. Flow velocity also was measured at the 

West Neck Creek and Coinjock sites.

The maximum water-level range during the 

study period was observed near the lower 

midpoint of Currituck Sound at Poplar Branch. 

Generally, water levels at all sites were highest 

during March and April, and lowest during 

November and December. Winds from the south 

typically produced higher water levels in 

Currituck Sound, whereas winds from the north 

typically produced lower water levels. Although 

wind over Currituck Sound is associated with 

fluctuations in water level within the sound, other 

mechanisms, such as the effects of wind on 

Albemarle Sound and on other water bodies south 

of Currituck Sound, likely affect low-frequency 

water-level variations in Currituck Sound.

Flow in West Neck Creek ranged from 

313 cubic feet per second to the south to 

-227 cubic feet per second to the north (negative 

indicates flow to the north). Flow at the Coinjock 

site ranged from 15,300 cubic feet per second to 

the south to -11,700 cubic feet per second to the 

north. Flow was to the south 68 percent of the time 

at the West Neck Creek site and 44 percent of the 

time at the Coinjock site. Daily flow volumes were 

calculated as the sum of the instantaneous flow 

volumes. The West Neck Creek site had a 

cumulative flow volume to the south of 

7.69 x 108 cubic feet for the period March 1, 1998, 

to February 28, 1999; the Coinjock site had a 

cumulative flow volume to the north of 

-1.33 x 1010 cubic feet for the same study period. 

Wind direction and speed influence flow at 

the West Neck Creek and Coinjock sites, whereas 

precipitation alone has little effect on flow at these 

sites. Flow at the West Neck Creek site is 

semidiurnal but is affected by wind direction and 

speed. Flow to the south (positive flow) was 

associated with wind speeds averaging more than 

15 miles per hour from the northwest; flow to the 

north (negative flow) was associated with wind 

speeds averaging more than 15 miles per hour 

from the south and southwest. Flow at the 

Coinjock site reacted in a more unpredictable 

manner and was not affected by winds or tides in 

the same manner as West Neck Creek, with few 

tidal characteristics evident in the record.

Throughout the study period, maximum 

salinity exceeded 3.5 parts per thousand at all 

sites; however, mean and median salinities were 

below 3.5 parts per thousand at all sites except the 

Point Harbor site (3.6 and 4.2 parts per thousand, 

respectively) at the southern end of the sound. 

Salinities were less than or equal to 3.5 parts per 

thousand nearly 100 percent of the time at the Bell 
2 Hydrologic and Salinity Characteristics of Currituck Sound and Selected Tributaries in North Carolina and Virginia, 1998–99

Island and Poplar Branch sites in Currituck Sound 

and about 86 percent of the time at the Albemarle 

and Chesapeake Canal site north of the sound. 

Salinity at the West Neck Creek and Coinjock sites 

was less than or equal to 3.5 parts per thousand 

about 82 percent of the time.

During this study, prevailing winds from the 

north were associated with flow to the south and 

tended to increase salinity at the West Neck Creek 

and the Albemarle and Chesapeake Canal sites. 

Conversely, these same winds tended to decrease 

salinity at the other sites. Prevailing winds from 

the south and southwest were associated with flow 

to the north and tended to increase salinity at the 

Poplar Branch and Point Harbor sites in Currituck 

Sound and at the Coinjock site, but these same 

winds tended to decrease salinity at the West Neck 

Creek and the Albemarle and Chesapeake Canal 

sites. The greatest variations in salinity were 

observed at the northernmost site, West Neck 

Creek, and the southernmost site, Point Harbor. 

The least variation in salinity was observed at the 

upper midpoint of the sound at the Bell Island site.

Daily salt loads were computed for 364 days 

at the West Neck Creek site and 348 days at the 

Coinjock site from March 1, 1998, to February 28, 

1999. The cumulative salt load at West Neck 

Creek was 28,170 tons to the south, and the 

cumulative salt load at the Coinjock site was 

-872,750 tons to the north.

The cumulative salt load passing the West 

Neck Creek site during the study period would be 

0.01 part per thousand if uniformly distributed 

throughout the sound (approximately 489,600 

acre-feet in North Carolina). If the cumulative salt 

load passing the Coinjock site were uniformly 

distributed throughout the sound, the salinity in the 

sound would be 0.32 part per thousand. The net 

transport at the West Neck Creek and Coinjock 

sites indicates inflow of salt into the sound. A 

constant inflow of freshwater from tributaries and 

ground-water sources also occurs; however, the 

net flow volumes from these freshwater sources 

are not documented, and the significance of these 

freshwater inflows toward diluting the net import 

of salt into the sound is beyond the scope of this 

study.

INTRODUCTION

During the 1970’s, Currituck Sound was well 

known for its freshwater fisheries (Venters, 1995). By 

the late 1980’s, however, comparisons of fishpopulation surveys revealed a notable change from 

freshwater species to estuarine species in the sound—a 

change that was attributed to an increase in salinity in 

Currituck Sound (Kornegay, 1989). 

Previous studies by Kornegay (1989) and the 

Hampton Roads Planning District Commission (1992) 

documented periodic fluctuations of salinity and the 

effects of salinity on freshwater fisheries in Currituck 

Sound. Increased salinity in the sound has been 

attributed to droughts and the pumping of seawater into 

Back Bay, which occurred between 1965 and 1987 

(Y. Barber, Currituck County volunteer, written 

commun., 1993). Salt also moves into Currituck Sound 

from the north by way of West Neck Creek through 

North Landing River or the Albemarle and Chesapeake 

Canal, or from the south by way of Albemarle Sound 

through the Atlantic Intracoastal Waterway (AIWW) or 

through the mouth of the sound (Bales and 

Skrobialowski, 1994). Thus, the causes of changes in 

salinity in Currituck Sound are complex and seem to be 

the result of both natural and human-induced 

mechanisms, prompting the need for further 

investigation.

The total fluxes of water and salt into and out of 

Currituck Sound remain undocumented. Moreover, the 

conditions under which these fluxes occur are not well 

understood. Management plans for the sound and 

surrounding watershed are being considered; however, 

development of effective management plans is 

dependent on good characterization of transport 

processes affecting the sound and its response to 

influxes of salt.

In 1997, the U.S. Geological Survey (USGS), in 

cooperation with the North Carolina Divisions of Water 

Resources and Marine Fisheries, began a 23-month 

investigation of salinity and flow into and within 

Currituck Sound. The objectives of the study were to 

(1) quantify selected major fluxes of water and salt into 

and out of Currituck Sound, (2) document salinity 

variations at selected sites within the sound, and 

(3) characterize conditions under which major fluxes 

occur. This investigation complements the findings of 

a USGS study conducted during 1989–92 (Bales and 

Skrobialowski, 1994). Interstate water issues and 

coastal hydrology are a key part of the USGS mission 

(U.S. Geological Survey, 1999). 
Introduction 3

Purpose and Scope

The purpose of this report is to summarize 

selected hydrologic and salinity characteristics of 

Currituck Sound and three of its tributaries, document 

water and salt fluxes in two tributaries to the sound, and 

describe variations in salinity within the sound. Data 

were collected at three locations in Currituck Sound 

and at three tributary locations to the sound from 

March 1, 1998, to February 28, 1999. These data 

include water level, velocity, flow, salinity, and 

temperature. Selected climatological data were 

obtained from the National Climatic Data Center 

(National Oceanic and Atmospheric Administration, 

written commun., 1999).

Study Area

Currituck Sound is in northeastern North 

Carolina in the Coastal Plain Physiographic Province 

(fig. 1). The North Carolina portion of the sound has a 

surface area of about 97,900 acres, or about 153 square 

miles (mi2). Currituck Sound is a brackish-water 

estuary that extends 40 miles (mi) from the VirginiaNorth Carolina State line to its confluence with 

Albemarle Sound (Eagleson, 1994). The average depth 

of the sound is about 5 feet (ft). The drainage area of 

Currituck Sound, including tributaries from both North 

Carolina and Virginia and Back Bay, is estimated to be 

733 mi2 (Rideout, 1990), of which almost one-third is 

open water. The cities of Virginia Beach and 

Chesapeake compose most of the land area in Virginia 

that drains to Currituck Sound; in North Carolina, the 

land in northwest Currituck County drains to the sound. 

The exact delineation of the Currituck Sound 

contributing drainage area is not well defined because 

of (1) low topographic relief, which ranges from 0 to 

30 ft in the basin (Malcolm Pirnie Engineers, Inc., 

1980); (2) several canals that connect Currituck Sound 

to Chesapeake Bay; and (3) bidirectional flow that 

moves to the north and south. 

The climate of the study area is humid 

subtropical (Trewartha and Horn, 1980). The annual 

average precipitation is about 45 inches (in.), and 

monthly totals typically are greatest during the 

summer. Flood-producing rainfall and high winds 

generally are associated with hurricanes or tropical 

storms and(or) convective thunderstorms during the 

summer or fall. In addition, northeasters can generate 

strong winds, heavy rainfalls, and high water levels or 

flooding during the fall and winter. 

Three major tributaries supply most of the 

freshwater to Currituck Sound—North Landing River, 

Northwest River, and Tull Creek (fig. 1). The drainage 

area of North Landing River at the Virginia-North 

Carolina State line is about 117 mi2

; in 1990, 

44 percent of the drainage area was used for 

agriculture, 35 percent was undeveloped, 17 percent 

was developed, and 4 percent was water (Hampton 

Roads Planning District Commission, 1992). North 

Landing River is channelized over its entire length as a 

part of the AIWW and joins the Albemarle and 

Chesapeake Canal about 12 river mi north of the State 

line and 3.2 river mi north of the confluence with West 

Neck Creek. Great Bridge Lock (fig. 1) at the western 

end of the Albemarle and Chesapeake Canal and about 

21 river mi from the State line prevents continuous 

inflow of water with high salinity from Elizabeth River 

into the canal and, thus, into Currituck Sound.

From Great Bridge Lock, the AIWW extends 

east through the Albemarle and Chesapeake Canal and 

south through North Landing River and into Currituck 

Sound. About 14 river mi south of the Virginia-North 

Carolina State line, the AIWW is routed through a land 

cut near Coinjock to the confluence of North River 

where the AIWW continues south through the North 

River, parallel to Currituck Sound, to the confluence 

with Albemarle Sound (fig. 1).

Before the 1960’s, a natural hydraulic 

connection existed between Lynnhaven Bay in Virginia 

and Currituck Sound in North Carolina through 

London Bridge Creek to West Neck Creek (fig. 1; 

U.S. Army Corps of Engineers, 1996). In the early 

1960’s, a drainage canal, used primarily for flood 

control for rural agricultural land, was constructed by 

the U.S. Soil Conservation Service, currently known as 

the Natural Resources Conservation Service. This 

drainage canal bypasses part of London Bridge Creek 

and is known as Canal No. 2. Over time, flood flows 

carried by Canal No. 2 increased, and the capacity of 

the canal often was exceeded because of intensive 

residential and commercial land development and 

altered runoff patterns. The West Neck Creek 

watershed is heavily developed and drains about 37 mi2

(U.S. Army Corps of Engineers, 1980). Consequently, 

a segment of Canal No. 2 was enlarged in 1989 based 

on recommendations by the U.S. Army Corps of 

Engineers (USACE). This modification is referred to as 

the Canal No. 2 Project in this report.
4 Hydrologic and Salinity Characteristics of Currituck Sound and Selected Tributaries in North Carolina and Virginia, 1998–99

Figure 1. Locations of study sites in the Currituck Sound study area, North Carolina and Virginia, 

March 1, 1998, through February 28, 1999.
Acknowledgments 5

Previous Studies

Overton and McAllister (1993) applied a salttransport model to London Bridge Creek, the Canal 

No. 2 system, and North Landing River. They 

concluded that salinity entering Canal No. 2 from the 

north potentially can be transported southward to the 

mouth of North Landing River under extreme tidal 

conditions (6.6-ft wind tide) that persist for 5 days or 

more. Under normal tidal conditions (1.7-ft range), 

simulation results indicated that salt was not 

transported southward from Lynnhaven River to the 

mouth of North Landing River. The model was 

calibrated by using data collected during the Bales and 

Skrobialowski (1994) study.

From August 1991 to May 1994, the USACE 

measured salinity at monthly intervals at selected sites, 

including Lynnhaven Bay at Trants Point (located near 

the northern confluence of London Bridge Creek and 

Canal No. 2; fig. 1) and at the West Neck Creek and 

Shipps Corner Road crossing (located near the 

southern confluence of London Bridge Creek and 

Canal No. 2; fig. 1). These data were compared with 

data collected by the Virginia Department of 

Environmental Quality (VDEQ) at the West Neck 

Creek and West Neck Road crossing before (January 

1983–May 1989) and after (June 1989–September 

1994) the Canal No. 2 Project. The West Neck Creek 

and West Neck Road crossing site is located about 

1.5 mi east of the confluence of West Neck Creek and 

North Landing River (fig. 1). 

In February 1996, the North Carolina 

Department of Environment, Health, and Natural 

resources (currently known as the North Carolina 

Department of Environment and Natural Resources 

[DENR]) requested the USACE, Norfolk District, to 

perform a Section 1135 (Water Resources 

Development Act of 1986, P.L. 99-662, as amended) 

study of the Canal No. 2 Project (U.S. Army Corps of 

Engineers, 1996) to determine if the Canal No. 2 

Project had resulted in increased salinity in the northern 

part of Currituck Sound. The USACE (1996) 

concluded that the causes of increased salinity in 

Currituck Sound are complex and could be produced 

by a variety of mechanisms. The USACE (1996) also 

concluded that the Canal No. 2 Project had not 

increased salinity in this area beyond levels that would 

have occurred prior to the Canal No. 2 Project. The 

occasional elevated readings in Canal No. 2 were 

consistent with expected variations as a result of tidal 

fluctuations; however, salinity readings made at 

monthly intervals during the 1991–94 study are 

insufficient to reach conclusions about changes in the 

Currituck Sound regime. These studies did not 

conclude how far south the occasional elevated salinity, 

such as that observed in the southern portion of West 

Neck Creek, extended into Currituck Sound.

The USGS conducted an investigation to 

determine flow rates and predominant flow direction in 

West Neck Creek during 1989–92, and to characterize 

the salinity in West Neck Creek and North Landing 

River near the Virginia-North Carolina State line 

during 1991–92 (Bales and Skrobialowski, 1994). The 

highest salinity observed was at West Neck Creek 

during periods of sustained north to northeasterly 

winds. Simultaneous measurements of flow and 

salinity were used to compute transport of salt in West 

Neck Creek. For 294 days, during which simultaneous 

flow and salinity data were available at West Neck 

Creek, the net salt transport was 34,510 tons to the 

south or 0.01 part per thousand (ppt) if uniformly 

distributed throughout the sound. Southward salt 

transport ranged from 0.3 to 4,500 tons per day 

(tons/d), and northward transport ranged from 0.2 to 

302 tons/d (Bales and Skrobialowski, 1994). 

From January 1989 through June 1998, staff 

from the North Carolina Wildlife Resources 

Commission made monthly salinity measurements at 

four locations in Currituck Sound—Currituck Ferry 

Landing, Church Island, Poplar Branch, and at the 

southern end of the sound near Point Harbor (Thomas, 

1996). During November 1994 to June 1998, 

measurements also were made at a fifth site, AIWW at 

Coinjock (Thomas, 1998). Considering all 

measurements, salinity ranged from 0.0 to 9.0 ppt. The 

lowest salinity was at Currituck Ferry Landing, and the 

highest was at the southern end of the sound. Monthly 

salinity at all sites exceeded 3.5 ppt less than 5 percent 

of the time. The approximate upper threshold at which 

largemouth bass can successfully reproduce is 3.5 ppt 

(Tebo and McCoy, 1964), and is an indicator of the 

status of the fishery resource.

Acknowledgments

The USGS thanks the private property owners 

for their graciousness in allowing access and use of 

their property for data-collection activities. 

Specifically, appreciation is extended to Ms. Sarah 

Roney, Mr. Robert Boyd, and Ms. DeLoise 

Stonecypher. Also, appreciation is extended to the 
6 Hydrologic and Salinity Characteristics of Currituck Sound and Selected Tributaries in North Carolina and Virginia, 1998–99

North Carolina Wildlife Resources Commission, the 

Norfolk District of the U.S. Army Corps of Engineers, 

and the City of Virginia Beach for their cooperation. A 

special thank you to Mr. Jerad Bales and Ms. Jeanne 

Robbins of the USGS, both of whom contributed 

significantly to this report.

DATA COLLECTION

Data for this investigation were collected at six 

locations (fig. 1; table 1)—West Neck Creek at Pungo 

(WN2); the Albemarle and Chesapeake Canal near 

Princess Anne (AC1); the AIWW at Coinjock (CU2); 

and in Currituck Sound at Bell Island (CU1), Poplar 

Branch (CU3), and Point Harbor (CU4). Salinity, water 

level, and temperature data were recorded at sites AC1, 

CU1, CU2, and CU3 from July 1997 through June 

1999; at site CU4 from July 1997 through March 1999; 

and at site WN2 from December 1997 through June 

1999. Flow data were collected at sites WN2 and CU2 

from February 1998 through June 1999. Data collected 

from March 1, 1998, to February 28, 1999, were used 

for the interpretations presented in this report. All data 

were published in the USGS annual water-resources 

data report for North Carolina (Ragland and others, 

2000).

The northernmost data-collection site was West 

Neck Creek at Pungo, Va. (site WN2), located about 

3 mi south of a site that was used in the 1989–92 study 

(Bales and Skrobialowski, 1994) and about 7 mi south 

of the southern confluence of West Neck Creek with 

London Bridge Creek. The northernmost site in the 

1989–92 study could not be used for this study because 

of bridge construction that was underway during 1997.

Water Levels

Water levels were measured by using a float 

mounted in a stilling well. Data were recorded by 

electronic data loggers to the nearest 0.01 ft at 

15-minute intervals. Gage datums were referenced to 

sea level by leveling to the nearest benchmark. All 

reported water levels are referenced to sea level. 

Water Velocity and Discharge 

Water velocity was measured at sites WN2 and 

CU2 at 15-minute intervals by using acoustic velocity 

meters (AVM), sometimes referred to as ultrasonic 

velocity meters. The AVM determines the magnitude 

and longitudinal direction of the laterally averaged 

flow velocity at a specific elevation in the channel (line 

velocity) by measuring the travel time of an acoustic 

pulse through the water body. Velocity measurements 

made by the acoustic method are recognized as reliable 

and accurate (International Organization for 

Standardization, 1985). Details on the theory and 

operation of the AVM system were documented by 

Laenen (1985). A relation was developed between the 

cross-sectional mean velocity and AVM-measured line 

velocity by making standard discharge measurements 

for a range of flow conditions. A relation also was 

developed between stage and cross-sectional area. 

Instantaneous discharge was then computed from 

Table 1. Data-collection sites in the Currituck Sound study area, North Carolina and Virginia, 1998–99

[na, not applicable. Latitude and longitude coordinates are referenced to the North American Datum of 1927]

Site

(fig. 1)

USGS 

station 

number

Site name Latitude Longitude

Salinity 

probe 

location 

(feet 

above 

channel 

bottom)

WN2 02043200 West Neck Creek at Indian River Road at Pungo, Va. 36°43'16" 76°02'03" 3

AC1 02043120 Albemarle and Chesapeake Canal near Princess Anne, Va. 36°43'04" 76°06'02" 4

CU1 0204342510 Currituck Sound at Bell Island, N.C. 36°25'43" 75°58'02" 1

CU2 0204343500 Atlantic Intracoastal Waterway at Coinjock, N.C. 36°20'34" 75°57'15" 3

CU3 0204345010 Currituck Sound at Poplar Branch, N.C. 36°17'14" 75°53'02" 1.5

CU4 0204347490 Currituck Sound near Point Harbor, N.C. 36°04'52" 75°47'28" 1

WS1 na Oceana Naval Air Station weather station, Va. 36°49' 76°02' na

WS2 na Elizabeth City weather station, N.C. 36°19' 76°12' na
Hydrologic Characteristics 7

measurements of line velocity and stage, and 

application of the line velocity cross-sectional mean 

velocity and stage area relations.

Salinity

Specific conductance and water temperature 

were measured at 15-minute intervals at all sites by 

using a conductivity/temperature probe (Campbell 

Scientific, Inc., 1996). Specific conductance and 

temperature data were collected at approximately 

midwater depth at each site (table 1). The temperature 

sensor range is 0 to 50 degrees Celsius (°C) with 

an accuracy error of +0.4 °C. The electrical 

conductivity (EC) sensor range is approximately 5 to 

7,500 microsiemens per centimeter at 25 °C (μS/cm at 

25 °C) with an accuracy of +5 percent of the reading 

range of 440 to 7,000 μS/cm. Specific conductance was 

converted to salinity by using the algorithm given by 

Miller and others (1988).

Measured specific conductance values exceeded 

the manufacturer-specified EC sensor range for 

extended periods of time at sites WN2 and CU4. 

During each visit to these two sites, the EC readings 

were checked against four specific conductance 

standards that ranged from 10,000 to 49,400 μS/cm. 

Adjustments of less than 5 percent typically were 

required to correct the EC sensor data that were outside 

the specified range.

The sites were visited at approximately monthly 

intervals, at which time data were retrieved, and each 

sensor was cleaned and checked against appropriate 

specific conductance standards. A vertical profile of 

specific conductance and water temperature was 

measured during each visit to ensure that the 

measurements at the sensor were representative of 

conditions over the full depth of flow. Methods similar 

to those reported by Garrett and Bales (1991) and 

Robinson and others (1996) were used for servicing the 

sensors and processing the data.

Precipitation and Wind

Precipitation and wind data used in this study 

were provided by the National Climatic Data Center in 

Asheville, N.C. Only data through January 3, 1999, 

were available at the time this report was prepared. 

Precipitation and wind data were measured at the 

weather station (WS1) at Oceana Naval Air Station in 

Virginia Beach, Va., located about 8 mi north of site 

WN2 (fig. 1). Precipitation accumulations were 

recorded each day at 0700 hours (hrs) for the previous 

24 hrs. Wind speed and direction were recorded hourly. 

Daily precipitation also was measured at the 

climatological weather station (WS2) in Elizabeth City, 

N.C., located about 15 mi west of site CU2 (fig. 1).

HYDROLOGIC CHARACTERISTICS

Currituck Sound is a coastal system 

characterized by the mixing of freshwater and 

saltwater. The sound has two hydraulic connections 

with Chesapeake Bay in Virginia—Canal No. 2 and 

London Bridge Creek by way of West Neck Creek, and 

the AIWW by way of the Albemarle and Chesapeake 

Canal (fig. 1). Currituck Sound also has two hydraulic 

connections to Albemarle Sound in North 

Carolina—North River by way of Coinjock Canal and 

the confluence of Currituck Sound with Albemarle 

Sound (fig. 1). Thus, flows at these hydraulic 

connections can move to the south or north depending 

on prevailing conditions, such as winds and tides.

Wind speed and direction and tides tend to 

change seasonally and are event driven. Events of low 

magnitude (astronomical tides) tend to cause flows to 

move back and forth with little net transport along the 

northern and southern boundaries of the sound. Events 

of greater magnitude (strong winds and wind-induced 

tides) tend to override astronomical tides and push 

flows farther into the middle of the sound (site CU1) 

and are associated with increased net transport in and 

out of the northern and southern boundaries of the 

sound. Regardless of the magnitude of the prevailing 

conditions, the least amount of variation in water level 

and flow over time is near the central portion of the 

sound.

Drainage System

The Currituck Sound Basin lies completely 

within hydrologic unit 03010205, a 3,750-mi2 unit that 

includes the coastal drainage and associated waters of 

the Back Bay drainage system to the north and parts of 

Dare County to the south (Seaber and others, 1987). 

Currituck Sound has a complex drainage system. The 

drainage basin, composed of tributaries from North 

Carolina and Virginia, including Back Bay, is estimated 

to be 733 mi2

. An accurate drainage area is difficult to 
8 Hydrologic and Salinity Characteristics of Currituck Sound and Selected Tributaries in North Carolina and Virginia, 1998–99

delineate because of ambiguous relief, drainage canals 

that cross topographic divides, and tributaries where 

water can move toward or away from Currituck Sound.

The tributary having the largest drainage area in 

the Currituck Sound Basin is North Landing River. The 

Virginia portion of the North Landing River Basin has 

a drainage area of about 117 mi2

 (Hampton Roads 

Planning District Commission, 1992). Tributaries to 

North Landing River in Virginia include Pocaty River, 

Blackwater Creek, Milldam Creek, Oakum Creek, 

Walnut Creek, and West Neck Creek (fig. 1). 

Back Bay is a 25,600-acre (40-mi2

) estuary 

located east of the North Landing River Basin 

(Eagleson, 1994; fig. 1). Back Bay tributaries include 

Beggars Bridge Creek, Hell Point Creek, Muddy 

Creek, and Nawney Creek, most of which drain the city 

of Virginia Beach. Major tributaries to Currituck Sound 

in North Carolina include Northwest River and Tull 

Creek (fig. 1).

An estimated 56 percent of the Currituck Sound 

Basin is in North Carolina; the remaining 44 percent of 

the basin is in Virginia. Approximately 30 percent of 

the entire basin is open water.

Average annual rainfall on the sound is 

approximately 45 in. In general, annual surface runoff 

volume in northeastern North Carolina is about onethird the amount of rainfall, and annual ground-water 

runoff is about two-thirds the amount of rainfall 

(Wilder and others, 1978; Krug and others, 1990). If the 

average depth of open water in the basin is 5 ft, then the 

total volume of open water in the entire basin is about 

3.07 x 1010 cubic feet (ft3

). The sum of the average 

annual rainfall volume and the average annual runoff 

volume is about 4.1 x 1010 ft3. Hence, the average 

hydraulic residence time of water in Currituck Sound 

and adjacent open waters is about three-fourths of a 

year.

Water-Level Fluctuations

Water levels fluctuated between -1.79 and 2.66 ft 

above sea level at site WN2, a range of 4.45 ft (table 2; 

fig. 2). The same general range was observed by Bales 

and Skrobialowski (1994) approximately 3 mi north of 

site WN2, at West Neck Creek at State Road 149 during 

294 days of record from September 1990 through 

March 1992. Common measurements in table 2 and 

subsequent tables refer to the set of data recorded 

simultaneously at all sites during the period March 1, 

1998, through February 28, 1999. The highest water 

levels consistently were observed near the lower 

midpoint of the sound at site CU3. There was no 

apparent hydraulic explanation for this phenomenon. 

Further investigation, including a flow model of the 

sound, might provide insight into these observations. 

The maximum water-level range was observed at 

site CU3; the lowest water-level ranges were near the 

upper midpoint of the sound at site CU1 and at site CU2 

(table 2).

Water levels at all sites generally were higher 

during March and April and lower during November 

and December throughout the study period. This 

observation is different from previous observations at 

two sites on West Neck Creek (Bales and 

Skrobialowski, 1994). Minimum water levels during 

1991–92 generally occurred in winter and spring 

months, and maximum water levels generally occurred 

Table 2. Water-level characteristics at the Currituck Sound and tributary study sites based on measurements made from 

March 1, 1998, to February 28, 1999

Site

(fig. 1)

All measurements

(feet above sea level)

Common measurementsa

(feet above sea level)

a

Data recorded simultaneously at all sites.

Mean Median Maximum 

observed

Minimum 

observed

Number 

of 

measurements 

analyzed

Mean Median Maximum 

observed

Minimum 

observed

Number 

of 

measurements 

analyzed

WN2 0.80 0.88 2.66 -1.79 35,040 0.71 0.76 2.66 -1.79 25,683

AC1 .90 .98 2.73 -1.90 35,040 .82 .87 2.73 -1.90 25,683

CU1 1.07 1.12 3.00 -.75 34,937 .98 1.00 3.00 -.75 25,683

CU2 .97 1.00 2.91 -.79 35,040 .90 .90 2.91 -.79 25,683

CU3 1.34 1.33 4.82 -.20 25,786 1.35 1.33 4.82 -.20 25,683

CU4 .98 .98 3.86 -.48 33,193 .92 .90 3.86 -.48 25,683
Hydrologic Characteristics 9

Figure 2. Daily maximum and minimum water levels at the Currituck Sound and tributary study sites from 

March 1, 1998, to February 28, 1999.
10 Hydrologic and Salinity Characteristics of Currituck Sound and Selected Tributaries in North Carolina and Virginia, 1998–99

in summer months. The difference between the 

1991–92 and 1998–99 data suggests that water levels in 

the study area are influenced by mechanisms, such as 

wind and tides, that vary from year to year as well as 

daily and seasonally.

During this investigation, maximum water levels 

observed at sites WN2 and AC1 occurred on March 9, 

1998, and minimum water levels occurred at these sites 

on February 22, 1999 (fig. 2). Maximum water levels 

at sites CU1, CU2, CU3, and CU4 occurred on 

August 28, 1998, and minimum water levels at these 

four sites occurred on December 16, 1998 (fig. 2). 

Winds, averaging between 8 and 12 miles per hour 

(mph) out of the south and southwest (August 21–25, 

1998) several days prior to the passage of Hurricane 

Bonnie, generated the high water levels in Currituck 

Sound on August 28, 1998; however, Hurricane Bonnie 

did not produce high water levels at sites WN2 and 

AC1, probably because these waters are somewhat 

shielded from winds by surrounding land (fig. 1) and 

because of minimal effects of Hurricane Bonnie on 

Chesapeake Bay. High winds from the south produced 

the highest water levels at sites WN2 and AC1 on 

March 9, 1998 (fig. 2), when the mean wind speed was 

17 mph.

No statistical correlation was identified between 

water levels and precipitation. Generally, the common 

factor associated with high water levels at all study 

sites during the study period was prevailing southerly 

winds (winds from the south) that averaged 12 mph or 

greater, excluding atypical conditions, such as those 

generated by a hurricane. Lower water levels generally 

were associated with prevailing northerly winds (winds 

from the north). 

The times of occurrence of daily maximum and 

minimum water levels observed at each site were 

compared for selected days. When winds were from the 

south, maximum water levels occurred first at sites 

WN2 and AC1. Within 4 hrs, the maximum water level 

occurred at site CU4; within 8 hrs, maximum water 

levels were observed at the remaining sites. This 

pattern changed slightly, however, when wind was 

predominantly from the southwest. When wind was 

from the southwest, maximum water levels occurred 

first at sites AC1 and CU2 nearly simultaneously. 

Within 2 to 6 hrs, maximum water levels occurred at 

the remaining four sites. 

Low water levels typically occurred when winds 

were predominantly from the north with sustained 

speeds greater than 10 mph. When winds were from the 

northwest, daily minimum water levels typically 

occurred first at sites WN2, AC1, CU2, and CU4 nearly 

simultaneously. Minimum water levels then occurred 

at sites CU1 and CU3 between 5 and 7 hrs later. When 

wind was from the northeast, minimum water levels 

typically occurred first at site CU4 followed by 

minimum water levels at sites WN2, AC1, and CU3 

nearly a day later. Minimum water levels occurred at 

sites CU1 and CU2 as much as 2 days after the 

minimum water level was observed at site CU4. 

Although wind direction and speed over 

Currituck Sound is associated with changes in water 

level within the sound, other mechanisms may be 

important. The effects of wind on Albemarle and other 

water bodies south of Currituck Sound likely affect 

low-frequency water-level variations in Currituck 

Sound. Also, the movement of water in the sound may 

be a result of a recovery process following a previous 

event. For example, several days of northerly winds 

may produce a water-level gradient within the sound. 

When these winds cease or become calm or moderate 

(2–5 mph), the sound may recover in a day or two 

whether or not winds are from the south. This reversal 

or recovery process may produce brief high water, and 

southerly winds may sustain this high water even if the 

winds were not strong enough to initiate the higher 

water levels.

Flow

Flow at site WN2 was to the south 68 percent of 

the time (fig. 3) and ranged from 313 cubic feet per 

second (ft3

/s) to the south to -227 ft3/s to the north 

(table 3). (For this report, positive flows are to the south 

and negative flows are to the north.) Flow at site CU2 

was to the south 44 percent of the time (fig. 3) and 

ranged from 15,300 ft3

/s to the south to -11,700 ft3/s to 

the north (table 3). On average, the net daily flow 

volume to the south at site CU2 was 55 times greater 

than at site WN2. Likewise, the net daily flow volume 

to the north at site CU2 was 140 times greater than at 

site WN2 (table 3).

Bales and Skrobialowski (1994) reported that 

daily mean flow at West Neck Creek was to the south 

64 percent of the time during 1991–92, which is 

comparable to the amount of time (68 percent) flow 

was to the south at site WN2 during this study (fig. 3). 

Flow at site WN2 was between 100 ft3/s to the south 

and -100 ft3

/s to the north nearly 90 percent of the time 
Flow 11

Figure 3. Cumulative frequency distribution of flows at (A) West Neck Creek (site WN2) and (B) Coinjock 

(site CU2) from March 1, 1998, to February 28, 1999.
12 Hydrologic and Salinity Characteristics of Currituck Sound and Selected Tributaries in North Carolina and Virginia, 1998–99

(fig. 3), and typically double-peaked over a 24-hour 

period due to tidal influence (fig. 4).

Flow was much greater at site CU2 than at 

site WN2 and showed less distinct tidal characteristics 

(fig. 4). Flow at site CU2 was affected more by wind 

than by tides and, therefore, was less predictable. Flow 

at site CU2 was between 6,000 ft3

/s to the south and 

-6,000 ft3/s to the north about 90 percent of the time 

and between 0 and -6,000 ft3/s to the north about 

50 percent of the time (fig. 3).

Daily net flow volume was calculated as the 

sum of the instantaneous flow volumes (measured 

15-minute interval flow, in cubic feet per second, 

integrated over time) for each day at sites WN2 and 

CU2. Days of missing record (fewer than 5 percent of 

the days) were assigned a null value that did not 

increase or decrease the cumulative flow volume. For 

the period March 1, 1998, to February 28, 1999, the 

cumulative flow volume at site WN2 was 7.69 x 108

 ft3

with a net flow to the south (fig. 5). For the same 

period, the cumulative flow volume at site CU2 was 

-1.33 x 1010 ft3

 with a net flow to the north (fig. 6).

Winds associated with rainfall events make it 

difficult to determine the effects of precipitation alone 

on daily flow volumes at sites WN2 and CU2. Data 

from weather station WS1, approximately 8 mi north of 

site WN2, and weather station WS2, approximately 

15 mi west of site CU2 (fig. 1), were summarized for 

the days having the largest precipitation totals (table 4) 

during the study period (National Oceanic and 

Atmospheric Administration, 1998, 1999). The total 

rainfall of 43.09 in. at site WS1 for the study period was 

representative of the long-term average (January 1979 

to May 1998) of about 45 inches per year (in/yr). The 

precipitation totals given in table 4 are for the previous 

24 hours for each of the dates shown. When 

Table 3. Summary of flow characteristics at West Neck Creek (site WN2) and 

Coinjock (site CU2) based on 15-minute interval measurements made from 

March 1, 1998, to February 28, 1999

[ft3/s, cubic feet per second; ft3, cubic feet. Positive values are to the south; negative (-) values 

are to the north. Locations of sites are shown in figure 1]

Flow characteristics Site WN2 Site CU2

All 15-minute interval flow

Mean, in ft3/s 24.8 -448

Median, in ft3

/s 20.1 -767

Maximum observed, in ft3/s 313 15,300

Minimum observed, in ft3/s -227 -11,700

Number of measurements analyzed 34,407 32,991

Common daily net flow volumea

a

Data recorded simultaneously at all sites.

Mean, in ft3 2.11 x 106 3.66 x 107

Median, in ft3 1.77 x 106 -4.69 x 107

Maximum observed, in ft3 1.83 x 107 6.34 x 108

Minimum observed, in ft3 -9.88 x 106 -7.31 x 108

Number of measurements analyzed 348 348

All days for which net flow volume was to the south

Mean, in ft3 3.39 x 106 1.87 x 108

Median, in ft3 2.50 x 106 1.60 x 108

Maximum observed, in ft3 1.83 x 107 6.34 x 108

Minimum observed, in ft3 1.40 x 104 9.44 x 105

Number of measurements analyzed 271 157

All days for which net flow volume was to the north

Mean, in ft3 -1.59 x 106 -2.23 x 108

Median, in ft3 -9.22 x 105 -2.13 x 108

Maximum observed, in ft3 -9.88 x 106 -7.31 x 108

Minimum observed, in ft3 -9.61 x 103 -8.43 x 106

Number of measurements analyzed 93 191
Flow 13

Figure 4. Flow at (A) West Neck Creek (site WN2) and (B) Coinjock (site CU2), May 21–28, 1998.
14 Hydrologic and Salinity Characteristics of Currituck Sound and Selected Tributaries in North Carolina and Virginia, 1998–99

Figure 5. (A) Daily net flow volume and (B) cumulative flow volume at West Neck Creek 

(site WN2) from March 1, 1998, to February 28, 1999.
Flow 15

Figure 6. (A) Daily net flow volume and (B) cumulative flow volume at Coinjock (site CU2) 

from March 1, 1998, to February 28, 1999.
16 Hydrologic and Salinity Characteristics of Currituck Sound and Selected Tributaries in North Carolina and Virginia, 1998–99

precipitation totals were greater than 1 in., net flows at 

site WN2 increased relative to the median flow to the 

north or south at the site (table 4). Such a response was 

not evident at site CU2 where the largest daily 

precipitation totals did not necessarily produce the 

highest daily net flows during the study period. No 

rainfall occurred during most of the days having the 

greatest net flow (table 5). 

Prevailing (northerly) winds and daily average 

wind speeds greater than 9 mph were associated with 

flow to the south at sites WN2 and CU2 (table 5). 

Conversely, prevailing winds from the south-southwest 

were associated with increased flow to the north at 

these sites. From March 1, 1998, to January 3, 1999, the 

wind was from the southwest 22 percent of the time and 

from the north 15 percent of the time (fig. 7A). This is 

consistent with long-term wind patterns observed 

during January 1979 through May 1998 when winds 

were mostly from the southwest or from the north or 

northeast (fig. 7C).

Table 4. Largest precipitation events and associated winds and daily net flows at West Neck Creek (site WN2) and 

Coinjock (site CU2)

[mph, miles per hour; ft3, cubic feet; —, no data. Positive values are to the south; negative (-) values are to the north]

Date

Daily 

average 

wind 

speed 

(mph)

Prevailing 

wind 

direction 

(from)

24-hour 

precipitation 

at WS1

(inches)

WN2 24-hour 

precipitation 

at WS2

(inches)

CU2

Daily net 

flow 

volume 

(ft3)

Percentage 

of 

median

Daily net 

flow 

volume 

(ft3)

Percentage 

of 

median

3-9-98 17 South 1.69 -9.88 x 106 -1,071 0.50 -5.67 x 108 266

4-23-98 11 North 1.14 8.87 x 106 355 .01 -4.06 x 107 19

7-17-98 5 West 2.80 1.17 x 107 468 2.50 1.42 x 108 89

8-27-98 27 East .08 -9.74 x 105 -106 1.10 -3.29 x 108 154

8-28-98 12 Northwesta

a

Winds prevailed from the south and southwest August 23–25, 1998, and from the east August 26–27, 1998.

3.27 9.00 x 106 360 .45 1.11 x 108 70

8-30-98 6 Variable 1.73 8.89 x 106 355 1.45 — —

8-31-98 5 Variable 0 8.06 x 106 322 1.95 — —

10-5-98 8 North 1.06 2.42 x 106 97 0 — —

Table 5. Highest daily net flow volumes at West Neck Creek (site WN2) and 

Coinjock (site CU2) and associated precipitation and winds

[ft3, cubic feet; mph, miles per hour. Positive values are to the south; negative (-) values are to the north]

Site 

(fig. 1) Date

Daily net flow 

volume 

(ft3)

24-hour 

precipitation 

(inches)

Prevailing 

wind 

direction 

(from)

Daily 

average 

wind 

speed 

(mph) WS1 WS2

WN2

3-10-98 1.58 x 107 0 0 Northwest 17

3-11-98 1.83 x 107 0 0 Northwest 16

5-9-98 1.66 x 107 .55 Trace Northwest 15

3-9-98 -9.88 x 106 1.69 .50 South 17

4-1-98 -9.06 x 106 0 0 South 15

4-17-98 -9.01 x 106 0 0 Southwest 15

CU2

3-11-98 5.36 x 108 0 0 Northwest 16

4-3-98 5.44 x 108 0 0 Northeast 9

4-18-98 6.34 x 108 0 0 Northeast 13

4-24-98 -5.69 x 108 0 0 Southwest 9

5-15-98 -3.63 x 108 0 0 Southwest 4

5-16-98 -7.31 x 108 0 0 Southwest 5
Flow 17

4%

Figure 7. (A) Percentage of time wind blew from indicated direction and (B) frequency of 

occurrence of measured hourly wind speed at site WS1 from March 1, 1998, to January 3, 1999, 

and (C) percentage of time wind blew from indicated direction and (D) frequency of occurrence of 

measured hourly wind speed at site WS1 for the period January 1979 through May 1998.
18 Hydrologic and Salinity Characteristics of Currituck Sound and Selected Tributaries in North Carolina and Virginia, 1998–99

At site WN2, the largest flows to the south were 

associated with wind speeds averaging more than 

15 mph from the northwest, and flows to the north were 

associated with wind speeds averaging more than 

15 mph from the south and southwest (table 5). When 

winds prevailed from the north, waters in the 

Chesapeake Bay presumably were pushed southward 

against the land in Lynnhaven Bay (fig. 1), and water in 

Currituck Sound was pushed south reducing the 

elevation at the north end, thus creating a slope in the 

water-level surface causing flow to move toward the 

south through London Bridge Creek and Canal No. 2 to 

West Neck Creek. 

During April 21–29, 1998 (a period typical of 

spring conditions), flow was predominantly to the 

south at site WN2, regardless of wind direction 

(fig. 8A); however, winds from the west-southwest to 

the east-southeast were associated with the only time 

that flow was to the north at site WN2 during this 

period. Generally, this same pattern also was present 

during August 17–25, 1998 (a period typical of 

summer conditions; fig. 8B). Flow was most likely to 

the north at site WN2 when winds were from the south 

to southwest, although winds from this direction do not 

always coincide with flows to the north because of 

fairly strong tidal effects at the site. 

Figure 8. Relation of hourly flow to hourly wind direction at West Neck Creek (site WN2) and Coinjock (site CU2) for the 

periods (A) April 21–29, 1998, and (B) August 17–25, 1998.
Salinity Characteristics 19

Winds from the south and west forced waters 

from the North River into the AIWW (fig. 1), resulting 

in flow to the north at site CU2. Likewise, when winds 

were from the west-northwest to the east-northeast, 

flow was almost always to the south (fig. 8). Flows at 

site CU2 were seldom to the south when winds were 

from the south (fig. 8), unlike conditions at site WN2. 

A stronger association between wind direction and 

flow direction occurred at site CU2 than at site WN2.

On June 9, 1998, two discharge measurements of 

-16,400 ft3/s and -22,500 ft3/s to the north were made 

at site CU4 in Currituck Sound. The average of these 

measurements is -19,500 ft3

/s to the north—more than 

eight times the flow to the north at site CU2 during the 

time of these measurements. Simultaneous 

measurements of discharge at sites CU4 and CU2 may 

provide insight into the relation of flows at the two 

sites. A flow model of Currituck Sound would provide 

needed detail on flow patterns in and out of the sound, 

as well as flow within the sound.

SALINITY CHARACTERISTICS

Salinity characteristics identified during this 

study include spatial patterns, seasonal variations in 

salinity, and effects of flow and wind on salinity at all 

six study sites. Salt loads at sites WN2 and CU2 also 

are presented for the study period.

The magnitude of prevailing seasonal and eventdriven conditions, such as winds and tides, are 

associated with variations in salinity within the sound. 

Events of low magnitude are associated with little 

variation in salinity along the northern and southern 

boundaries of the sound. Conversely, events of greater 

magnitude (strong winds and large tide variations) tend 

to increase salinity variations along the northern and 

southern boundaries of the sound. Salinity variations 

remained the lowest within the central portion of the 

sound (site CU1) throughout the study period.

Spatial Patterns

The mean and median salinities at all sites except 

site CU4 were below 3.5 ppt, 10 percent of typical 

ocean salinity and the level at which adverse effects can 

occur in freshwater fish reproduction (table 6; 

Kornegay, 1989). The maximum salinity observed at 

all sites exceeded 3.5 ppt (fig. 9). The largest ranges in 

salinity were observed at sites WN2 and CU4 (17.4 and 

20.0 ppt, respectively). These large ranges may be due 

to proximity to a salt source. Interestingly, site AC1 had 

the third largest salinity range (7.1 ppt), which may 

indicate that the Albemarle and Chesapeake Canal is a 

source of salt to Currituck Sound. The two sites in the 

interior of Currituck Sound (sites CU1 and CU3) had 

the smallest ranges in salinity (3.1 and 3.2 ppt, 

respectively). 

The highest salinities were at sites WN2 and 

CU4 (table 6; fig. 9); however, the lowest salinities also 

were at site WN2 and at site AC1. Salinity at sites AC1, 

CU1, CU2, and CU3 was always less than or equal to 

7.2 ppt (table 6). Salinity was less than or equal to 

3.5 ppt at all study sites more than 80 percent of the 

time, except at site CU4 where salinities were less than 

or equal to 3.5 ppt less than 50 percent of the time 

(fig. 10). Salinity at site CU4 is trimodal—less than 

Table 6. Salinity characteristics at the Currituck Sound and tributary study sites based on measurements made from 

March 1, 1998, to February 28, 1999

[ppt, parts per thousand]

Site

(fig. 1)

All measurements (ppt) Common measurementsa (ppt)

a

Data recorded simultaneously at all sites.

Mean Median Maximum

 observed

Minimum 

observed

Number of 

measurements 

analyzed

Mean Median Maximum

observed

Minimum 

observed

Number of 

measurements 

analyzed

WN2 2.1 0.7 17.5 0.1 35,040 2.1 0.7 17.5 0.1 32,889

AC1 1.6 1.3 7.2 .1 35,040 1.6 1.4 7.2 .1 32,889

CU1 1.3 1.0 3.6 .5 35,040 1.3 1.0 3.6 .5 32,889

CU2 2.0 1.3 5.1 .5 35,040 2.0 1.3 5.1 .5 32,889

CU3 1.6 1.6 3.7 .5 34,153 1.6 1.7 3.7 .5 32,889

CU4 3.6 4.2 20.3 .3 33,196 3.6 4.1 20.3 .3 32,889
20 Hydrologic and Salinity Characteristics of Currituck Sound and Selected Tributaries in North Carolina and Virginia, 1998–99

2 ppt about 40 percent of the time, between 2 and 8 ppt 

about 55 percent of the time, and greater than 8 ppt 

5 percent of the time. Salinity was less than or 

equal to 3.5 ppt at sites CU1 and CU3 (in Currituck 

Sound) nearly 100 percent of the time (99.96 and 

99.82 percent, respectively), and at site AC1 (in the 

Albemarle and Chesapeake Canal about 10 mi north of 

the sound) about 86 percent of the time. Salinities at 

sites CU2 and WN2 were less than or equal to 3.5 ppt 

about 82 percent of the time (fig. 10). 

The daily maximum salinity at site WN2 was 

less than or equal to 1 ppt about 54 percent of the time 

Figure 9. Daily maximum salinity at the Currituck Sound and tributary study sites from March 1, 1998, to 

February 28, 1999.
Salinity Characteristics 21

and less than or equal to 10 ppt about 92 percent of the 

time. These percentages are consistent with those 

observed in West Neck Creek by Bales and 

Skrobialowski (1994; 50 and 94 percent, respectively).

During the period from the occurrence of 

Hurricane Bonnie (August 28, 1998) to the end of the 

study (February 28, 1999), daily maximum salinity at 

sites WN2, AC1, and CU4 exceeded daily maximum 

salinity at the other sites most of the time (fig. 11). 

Figure 11 contains the same data as figure 9 except that 

the comparison of daily maximum salinity is shown 

only for sites WN2, AC1, and CU4 for simplicity. 

Daily maximum salinities at the remaining sites (CU1, 

CU2, and CU3) were less than or equal to 5.1 ppt 

(baseline shown in fig. 11). The highest salinities were 

observed at the sites farthest north (WN2) and farthest 

south (CU4). These two sites are closest to sources of 

seawater. During much of November and December 

1998, salinity at site AC1 was higher than the salinity 

at site WN2 and briefly higher than the salinity at 

site CU4 (fig. 11), whereas salinity at site CU1 

remained low (about 2 ppt; fig. 9). This suggests that 

the source of salt at that time may have been southward 

flow through Great Bridge Lock (fig. 1) rather than the 

northward movement of salt through Currituck Sound.

Daily maximum salinity throughout the study 

area differed by as much as 19.3 ppt and as little as 

0.8 ppt during the study period. The largest spatial 

difference in daily maximum salinities occurred on 

August 28, 1998, following Hurricane Bonnie (fig. 9). 

The daily maximum salinity at site CU4 was 20.3 ppt 

(figs. 9, 11) but only 1.0 ppt at site CU1 (fig. 9). The 

smallest spatial difference in daily maximum salinities 

among the sites occurred on May 11, 1998, when the 

daily maximum salinity at site CU3 was 1.0 ppt, and 

the daily maximum salinity at site WN2 was 0.2 ppt 

(fig. 9). 

Figure 10. Cumulative frequency distribution of salinity at the Currituck Sound and tributary 

study sites from March 1, 1998, to February 28, 1999.
22 Hydrologic and Salinity Characteristics of Currituck Sound and Selected Tributaries in North Carolina and Virginia, 1998–99

Figure 11. Comparison of daily maximum salinity at sites WN2, AC1, and CU4 from March 1, 1998, 

to February 28, 1999.

On June 9, 1998, salinity measurements were 

made along three transects beginning at sites CU1, 

CU3, and CU4 (fig. 12; table 7). These measurements 

were made to compare data from shore-based monitoring sites to conditions across the sound. Little lateral 

or vertical variations in salinity were observed (fig. 12; 

table 7). On this date, a salt gradient was observed that 

decreased from the southernmost site (CU4) to the 

northernmost site (CU1) within the sound, implying a 

salt source from the south (Albemarle Sound).
Salinity Characteristics 23

Figure 12. Locations of transects and salinity profile data at selected Currituck Sound study sites, June 9, 1998.
24 Hydrologic and Salinity Characteristics of Currituck Sound and Selected Tributaries in North Carolina and Virginia, 1998–99

Table 7. Selected water-quality values measured along three transects in Currituck Sound, 

June 9, 1998

[ft, feet; μS/cm, microsiemens per centimeter at 25 °C; ppt, parts per thousand; °C, degrees Celsius; mg/L, milligrams per liter. 

Locations of transects are shown in figure 12]

Estimated 

distance 

from west 

bank 

(ft)

Time

Sampling 

depth 

(ft)

Specific 

conductance 

(μS/cm)

pH 

(standard 

units)

Salinity 

(ppt)

Water 

temperature 

(°C)

Dissolved 

oxygen 

(percent 

saturation)

Dissolved 

oxygen 

(mg/L)

Recorded

instantaneous 

salinity 

values at 

study site

(ppt)

CU1 transect

50 1407 1.20 1700 9.0 0.9 23.5 128 10.9 0.8

750

1420 7.10 1770 8.2 .9 21.6 101 9.0

.8 1421 5.00 1770 8.2 .9 21.7 104 9.2

1422 3.00 1780 8.3 .9 21.8 105 9.2

1423 .90 1770 8.3 .9 21.8 105 9.3

850

1425 8.30 1770 8.1 .9 21.5 100 8.9

1426 6.30 1770 8.2 .9 21.6 103 9.1 .8

1427 1.10 1770 8.2 .9 21.9 105 9.3

950

1429 5.40 1770 8.1 .9 21.2 95 8.4

1430 3.00 1780 8.2 .9 21.8 105 9.3 .8

1431 1.20 1780 8.3 .9 21.8 105 9.3

9,600 1437 6.30 1780 8.4 1.0 21.7 104 9.2 .8 1438 1.00 1780 8.4 1.0 21.8 107 9.4

17,000

1444 6.50 1870 8.3 1.0 21.6 100 8.9

.8 1445 4.60 1890 8.3 1.0 21.7 102 9.0

1446 2.70 1880 8.4 1.0 21.7 103 9.1

1447 1.10 1880 8.3 1.0 21.7 102 9.0

CU3 transect

50 1243 3.10 2090 8.0 1.1 22.3 105 9.1 1.1

1244 1.20 2100 8.1 1.1 23.5 107 9.1

3,400 1253 1.30 1890 8.6 1.0 22.5 111 9.6 1.1 1254 1.20 1900 8.6 1.0 22.4 111 9.6

6,800 1257 4.20 2050 8.4 1.1 21.8 104 9.1 1.1 1258 1.20 2050 8.4 1.1 22.9 104 8.9

10,200 1302 3.70 2110 8.1 1.1 21.5 96 8.5 1.1 1303 1.00 2070 8.2 1.1 23.0 101 8.7

CU4 transect

50 1035 2.20 2420 7.8 1.3 22.0 99 8.7 1.2

1036 1.00 2420 7.8 1.3 22.1 99 8.7

800

1039 5.00 2480 7.8 1.3 21.8 99 8.7

1040 2.90 2450 7.9 1.3 22.1 99 8.6 1.2

1041 1.20 2440 7.9 1.3 22.2 99 8.7

3,200

1045 6.80 2280 8.0 1.2 22.2 98 8.6

1.2 1046 4.80 2280 8.0 1.2 22.2 99 8.6

1047 2.90 2270 8.1 1.2 22.4 99 8.6

1048 .90 2270 8.1 1.2 22.4 99 8.6

5,600

1050 7.40 2310 8.0 1.2 22.3 98 8.6

1.2

1051 5.70 2310 8.0 1.2 22.3 98 8.6

1052 4.50 2300 8.0 1.2 22.3 98 8.6

1053 3.10 2300 8.0 1.2 22.4 99 8.6

1054 1.20 2300 8.0 1.2 22.5 99 8.6

8,000

1058 7.90 2720 7.9 1.5 22.4 97 8.4

1.2 1059 5.90 2720 7.9 1.5 22.5 98 8.5

1100 3.00 2700 8.0 1.5 22.6 99 8.6

1101 1.10 2700 8.0 1.5 22.7 99 8.6

10,400

1104 8.60 2810 7.8 1.5 22.4 95 8.3

1.2

1105 6.20 2810 7.9 1.5 22.4 96 8.3

1106 3.70 2680 7.9 1.4 22.5 98 8.5

1107 3.40 2660 7.9 1.4 22.5 98 8.5

1108 1.10 2630 7.9 1.4 22.6 99 8.5

12,800 1109 2.80 2390 8.0 1.3 22.3 100 8.7 1.2 1110 1.00 2390 8.0 1.3 22.3 100 8.7
Effects of Flow and Wind 25

Seasonal Patterns

Daily maximum salinities in the sound generally 

were low from March to July 1998, but increased from 

August 1998 to February 1999 (fig. 9). At sites CU1, 

CU2, and CU3, salinities were low from spring through 

mid-summer (April–July) and then higher during the 

remainder of the study period (including March 1998). 

At sites WN2, AC1, and CU4, salinities were low from 

late winter through mid-summer (March–July) and 

generally higher from August 1998 through February 

1999 (fig. 9). Bales and Skrobialowski (1994) observed 

high salinities during periods of sustained north to 

northeasterly winds during late October to early 

November 1991.

Additional long-term data during a nonhurricane year are needed to determine if the slow 

increase in salinity in the sound during August to 

February 1998 was a typical seasonal response or a 

direct result of Hurricane Bonnie, which made landfall 

along the North Carolina coast during the early 

morning hours of August 27, 1998. The increase in 

salinity occurred first in the south followed by 

subsequent increases to the north. Within the sound, 

increases in salinity at site CU3 preceded increases in 

salinity at site CU2, which in turn preceded increases in 

salinity at site CU1, suggesting some northward 

movement of salt through the sound.

Daily maximum salinities at site AC1 were 

greater than 3.5 ppt only during November and 

December (figs. 9, 11). Salinity at site CU4 was less 

than or equal to 2 ppt during the spring and increased, 

for the most part, to between 3.5 and more than 8 ppt 

during the summer, fall, and winter. Salinity measured 

near site CU4 from January 1990 through September 

1991 exhibited similar seasonal patterns, except that 

salinity less than 2 ppt also occurred occasionally 

during the winter (Garrett, 1993). Daily maximum 

salinity at site CU4 was greater than 8 ppt during three 

separate events in August (9 days) and one event in 

November (4 days). Occurrences on August 11, 17, and 

28, 1998, were likely a result of the effects of Hurricane 

Bonnie (fig. 11).

Effects of Flow and Wind

Little correlation was evident between flow 

volume and salinity at sites WN2 and CU2 (table 8). 

Days when the highest flows occurred at sites WN2 

and CU2 during this investigation (table 5) did not 

coincide with days on which the highest salinities were 

recorded at these sites. The highest observed salinities 

at site WN2, however, were associated with net flow to 

the south. Daily net flows at site WN2 during these 

events were low—less than 3.75 x 106 ft3

, which is 

equal to a daily mean flow of about 45 ft3

/s, or 

approximately the mean daily net flow volume to the 

south (table 3). The highest observed salinities at site 

CU2 were associated with daily net flows ranging from 

-1.6 x 108 ft3 to -3.5 x 108 ft3 to the north, or daily mean 

flows ranging from -1,850 to -4,050 ft3

/s to the north 

(fig. 3; table 3).

Northerly winds were associated with increased 

salinity at sites WN2 and AC1 (fig. 13A). The relation 

of increased salinity at site AC1 to the occurrence of 

northerly winds is consistent with the previous 

suggestion that Great Bridge Lock is a source of salt to 

the waters of Currituck Sound. However, the salt 

source from the Great Bridge Lock may be negligible 

because the salt is diluted as it moves into Currituck 

Sound through North Landing River. Conversely, 

northerly winds tended to lower salinity at sites CU1, 

CU2, CU3, and CU4 (fig. 13B). Prevailing winds from 

the south and southwest tended to increase salinity at 

sites CU2, CU3, and CU4. Conversely, these same 

winds tended to lower salinity at sites WN2 and AC1. 

Also, winds from the northwest and west were 

associated with increased salinity at sites CU1 and CU2 

(fig. 13A).

The magnitude of change in salinity was 

dependent upon the length of time the wind blew from 

a particular direction. For example, the largest increase 

in salinity at site WN2 occurred during August 1–9 

when winds were from the northeast (fig. 11; table 8) 

for the entire period and the daily maximum salinity 

increased 14.3 ppt. The data indicate that the longer the 

wind blew from a particular direction, the more salinity 

was affected. Another example was when the lowest 

spatial difference in salinity among the study sites 

occurred on May 11 and was preceded by 7 days of 

southerly winds averaging 9 mph (May 2–8) and 3 days 

of northerly winds averaging 13 mph (May 9–11). 

Winds from the south caused low salinity at site WN2 

(<0.3 ppt) to slowly decrease further, whereas these 

same winds caused low salinity at site CU3 (<1.2 ppt) 

to slowly increase. Conversely, winds from the north 

caused salinity at site WN2 to slowly increase, but 

caused salinity at site CU3 to slowly decrease. 

Typically, when winds changed direction on a daily 
26 Hydrologic and Salinity Characteristics of Currituck Sound and Selected Tributaries in North Carolina and Virginia, 1998–99

Table 8. Summary of events associated with the highest daily maximum salinities at the 

Currituck Sound and tributary study sites from March 1, 1998, to February 28, 1999

[ppt, parts per thousand; ft3/s, cubic feet per second; ft3, cubic feet; mph, miles per hour; na, not applicable. Positive 

values are to the south; negative (-) values are to the north]

Site 

(fig. 1) Date

Daily 

maximum 

salinity 

(ppt)

Daily 

instantaneous 

flow

maximum /

minimum

(ft3/s)

Daily 

net 

flow 

volume 

(ft3)

Daily 

average 

wind 

speed 

(mph)

Prevailing 

wind 

direction 

(from)

WN2

8-8-98 14.4 +69 / -18 +2.30 x 106 8 Northeast

8-9-98 15 +72 / -22 +2.29 x 106 7 Northeast

8-20-98 11.6 +90 / +7 +3.74 x 106 8 Northeast

8-21-98 12.8 +61 / -32 +1.42 x 106 9 Northeast

11-1-98 17.3 +36 / -25 +1.08 x 106 5 Northwest

11-2-98 17.4 +40 / -17 +1.24 x 106 4 West

11-3-98 17.5 +75 / -12 +2.16 x 106 8 Northeast

AC1

11-5-98 4.7 na / na na 12 North

11-6-98 5.3 na / na na 13 Northwest

12-15-98 6.6 na / na na 9 Northeast

12-16-98 7.2 na / na na 15 Northwest

12-18-98 2.6 na / na na 12 Northwest

12-19-98 3.5 na / na na 7 West

CU1

12-29-98 1.9 na / na na 6 North

12-30-98 3.6 na / na na 15 West-Northwest

CU2

11-10-98 4.8 +1,083 / -5,059 -1.59 x 108 10 Southeast

11-11-98 5.1 +3,925 / -8,697 -2.13 x 108 15 Southwest

12-18-98 4.8 +1,617 / -5,287 -2.74 x 108 12 West-Northwest

12-19-98 5.0 -2,745 / -5,293 -3.52 x 108 7 West

CU3

8-28-98 2.8 na / na na 12 Northwest

8-29-98 3.7 na / na na 6 Southwest

9-26-98 3.5 na / na na 7 South

9-27-98 3.5 na / na na 12 Southwest

CU4

8-10-98 7.5 na / na na 10 South

8-11-98 11.5 na / na na 8 South

8-17-98 10.9 na / na na 10 Southwest

8-27-98 12.5 na / na na 27 East

8-28-98 20.3 na / na na 12 Northwesta

a

Winds prevailed from the south and southwest August 23–25, 1998, and from the east August 26–27, 1998.

11-14-98 10.0 na / na na 9 Southwest

11-15-98 11.2 na / na na 16 Southwest
Effects of Flow and Wind 27

basis, fluctuations in salinity in the sound were 

minimized. 

Events that produced the largest daily maximum 

salinities were evaluated to determine the relation 

between prevailing wind direction and salinity. Twelve 

events, which lasted from 2 to 9 days, were evaluated 

for site WN2; daily maximum salinity ranges for these 

events differed by as little as 2.1 ppt to as much as 

14.3 ppt (fig. 14). All daily net flow during these events 

was to the south. Winds from the north and associated 

flows to the south tended to increase salinity at 

site WN2.

The largest daily maximum salinities at site CU2 

occurred between October and December 1998 (fig. 9). 

Six events, which lasted from 2 to 6 days, were evaluated for site CU2; daily maximum salinity ranges for 

Figure 13. Prevailing wind direction resulting in (A) increased salinities and (B) decreased 

salinities at Currituck Sound and tributary study sites, March 1, 1998, to February 28, 1999.
28 Hydrologic and Salinity Characteristics of Currituck Sound and Selected Tributaries in North Carolina and Virginia, 1998–99

these events differed by as little as 0.7 ppt to as much 

as 2.3 ppt (fig. 15). Winds during these selected events 

were generally from the west or south, generating 

flows to the north.

The smallest salinity variations were observed at 

sites CU1 and CU3, where salinity remained less than 

4 ppt throughout the study period (fig. 9). The highest 

salinities at site CU1 were associated with winds from 

the west and northwest. The highest salinities at site 

CU3 were associated with winds from the south and 

southwest (table 8).

Five events, which lasted from 2 to 6 days, were 

evaluated for site CU4; daily maximum salinity ranges 

for these events differed by as little as 1.2 ppt to as 

much as 15.4 ppt (fig. 16). Winds from the south and 

southwest tended to increase salinity at site CU4. 

During the period August 23–28, winds associated with 

Hurricane Bonnie first blew from the south and 

southwest for 3 consecutive days, causing an increase 

in salinity; the winds then shifted from the east for the 

3 remaining days of the period (fig. 16). During the 

last 3 days, winds from the east ranged between 12 and 

27 mph. On August 28, salinity peaked and then began 

to decrease.

There was a statistically significant correlation 

between water level and salinity at all sites during the 

study period (fig. 17). This correlation was positive for 

sites CU3 and CU4 when salinities were greater than or 

equal to 2 ppt (fig. 17). Salinity increased at sites WN2, 

AC1, CU1, and CU2 as daily maximum water level 

decreased (correlations between -0.34 and -0.61). 

Conversely, salinity increased at sites CU3 and CU4 as 

daily maximum water level increased (correlations 

between 0.45 and 0.53, respectively).

Figure 14. Relation of the direction of prevailing winds and daily maximum salinities at West Neck 

Creek (site WN2) during selected periods.
Effects of Flow and Wind 29

Figure 15. Relation of the direction of prevailing winds and daily maximum salinities at Coinjock 

(site CU2) during selected periods.

Figure 16. Relation of the direction of prevailing winds and daily maximum salinities at Point 

Harbor (site CU4) during selected periods.
30 Hydrologic and Salinity Characteristics of Currituck Sound and Selected Tributaries in North Carolina and Virginia, 1998–99

Figure 17. Comparison of daily maximum salinity and daily maximum water level at the Currituck Sound and tributary 

sites for the period March 1, 1998, to February 28, 1999.
Salt Loads 31

Salt Loads

Daily salt loads were computed for sites WN2 

(fig. 18) and CU2 (fig. 19) by using salinity and flow 

data measured in 15-minute intervals. Data were 

available to compute loads for 364 days at site WN2 

and 348 days at site CU2 from March 1, 1998, to 

February 28, 1999. As mentioned previously, days of 

missing record were assigned a null value that did not 

increase or decrease the cumulative salt load. The 

cumulative salt loads at sites WN2 and CU2 were 

28,170 tons to the south and -872,750 tons to the north, 

respectively (figs. 18, 19).

If all of the salt load at WN2 were transported 

into Currituck Sound (volume of approximately 

489,600 acre-ft in North Carolina) and uniformly 

distributed through the sound and no additional salt left 

the sound, salinity in the sound would be 0.01 ppt. If 

the total salt load at site CU2 were transported into the 

sound and uniformly distributed throughout the sound, 

salinity in the sound would be 0.32 ppt. The net 

transport at sites WN2 and CU2 indicates inflow of salt 

into the sound. In addition, the sound receives a 

constant inflow of freshwater from tributaries and 

ground-water sources; however, the net flow volumes 

from these freshwater sources are not documented, and 

the significance of these freshwater inflows toward 

diluting the net import of salt into the sound is beyond 

the scope of this study.

Bales and Skrobialowski (1994) computed 

cumulative salt loads at West Neck Creek at State 

Road 149 (approximately 3 mi north of site WN2) for 

294 days during September 1990 through March 1992. 

The cumulative salt load at site WN2 for 364 days 

during the current study (fig. 18) was 18 percent less 

than the cumulative salt load observed by Bales and 

Skrobialowski (1994). The difference in cumulative 

salt load between these two sites could be due to natural 

year-to-year variation in salt loads. 

For the majority of time at site WN2, salt 

transport was small. The mean daily salt load was 

77 tons to the south, and the median daily transport was 

30 tons to the south. The largest part of the salt load at 

this site occurred during four distinct events (May, 

August, October, and February; fig. 18). The maximum 

observed daily salt load to the south was 989 tons, 

which occurred on August 6, 1998. The maximum 

observed daily salt load to the north was -586 tons, 

which occurred on November 11, 1998, following the 

late October–early November transport of salt to the 

south (fig. 18; table 9). 

At site CU2, the mean daily salt load was 

-2,510 tons to the north, and the median daily transport 

was -1,530 tons to the north. The largest part of the salt 

load at this site occurred during five distinct events 

(May, August, October, December, and February; 

fig. 19). The maximum observed daily salt load to the 

south was 55,257 tons, which occurred on 

November 12, 1998. The maximum observed daily 

salt load to the north was -65,709 tons, which occurred 

on January 3, 1999 (fig. 19; table 9). 

The maximum daily salt load to the south at 

site WN2 was associated with daily average wind 

speeds of 12 mph from the northeast and no 

accumulation of precipitation (table 9). Total daily flow 

was near average (98 percent of mean daily total flow 

to the south; table 3). The maximum daily salt load to 

the north at site WN2 was associated with daily 

average wind speeds of 15 mph from the southwest and 

no accumulation of precipitation (table 9). Total daily 

flow was three times greater than average (308 percent 

of mean daily total flow to the north; table 3). 

The maximum daily salt load to the south at site 

CU2 was associated with 10-mph winds from the north 

and no recorded precipitation at site WS2 (table 9). 

Total daily flow was more than double the average 

flow. The maximum daily salt load to the north at site 

CU2 was associated with 18-mph winds from the 

southwest and no recorded precipitation. Total daily 

flow was more than double the average flow 

(244 percent of mean daily total flow to the north; 

table 3). 

Flow models would be useful in quantifying the 

salt loads from sites AC1 and CU4. As discussed 

previously, the salt source from site AC1 seems to be 

negligible as the salt is diluted while flow is moving 

south into North Landing River. Salt loads at site CU4 

from the Albemarle Sound are not well defined. The 

increasing salinity trend within the sound may not be 

due to an increased input of salt but rather to a decrease 

in freshwater input as a result of channelization and 

rerouting of surface runoff inflows into the sound. 

Further investigation would help to determine a trend 

in freshwater inputs into the sound.
32 Hydrologic and Salinity Characteristics of Currituck Sound and Selected Tributaries in North Carolina and Virginia, 1998–99

Figure 18. Daily and cumulative daily salt loads, in tons, at West Neck Creek (site WN2) for the 

period March 1998 through February 1999.
Salt Loads 33

Figure 19. Daily and cumulative daily salt loads, in tons, at Coinjock (site CU2) for the period March 1998 

through February 1999.
34 Hydrologic and Salinity Characteristics of Currituck Sound and Selected Tributaries in North Carolina and Virginia, 1998–99

SUMMARY

Currituck Sound is a brackish-water estuary that 

lies in the northeastern part of North Carolina in the 

Coastal Plain Physiographic Province. The sound has a 

surface area of about 97,900 acres, or about 153 mi2

, 

and has an average depth of about 5 ft. The sound 

extends 40 mi southward from the Virginia-North 

Carolina State line to its confluence with the Albemarle 

Sound. The drainage basin, composed of tributaries 

from both North Carolina and Virginia, including Back 

Bay, is estimated to be 733 mi2

, of which almost onethird is open water. Most of the land that drains to 

Currituck Sound is located in the cities of Virginia 

Beach and Chesapeake, Virginia, and in northwest 

Currituck County, North Carolina.

During March 1, 1998, to February 28, 1999, 

data were collected at three sites in Currituck Sound 

and at three tributary sites. Data were used to 

characterize the hydrologic and salinity regime of 

Currituck Sound to better identify potential sources of 

salt to the sound. The Currituck Sound sites were 

located at Bell Island, Poplar Branch, and Point Harbor, 

and the tributary sites were on West Neck Creek at 

Pungo, the Albemarle and Chesapeake Canal near 

Princess Anne, and the Atlantic Intracoastal Waterway 

at Coinjock. The data collected included measurements 

of water level, velocity, flow, salinity, and temperature.

The maximum water-level range was observed 

near the lower midpoint of Currituck Sound at Poplar 

Branch (site CU3); the lowest water-level ranges were 

near the upper midpoint of the sound at Bell Island and 

Coinjock (sites CU1 and CU2, respectively). Water 

levels at all sites generally were higher during March 

and April and lower during November and December, 

and varied daily, seasonally, and annually.

Flow at West Neck Creek (site WN2) ranged 

from 313 ft3

/s to the south to -227 ft3/s to the north. 

Flow at Coinjock (site CU2) ranged from 15,300 ft3

/s 

to the south to -11,700 ft3/s to the north. Flow was to 

the south 68 percent of the time at site WN2 and 

44 percent of the time at site CU2. During March 1, 

1998, to February 28, 1999, the cumulative flow 

volume was 7.69 x 108

 ft3 to the south at site WN2 and 

-1.33 x 1010 ft3

 to the north at site CU2.

Precipitation alone had little effect on flow at 

sites WN2 and CU2, whereas wind direction and speed 

had a greater effect on flow at these sites. Flow at 

site WN2 was most likely to be to the north when 

winds were from the south to southwest, although 

winds from this direction do not always coincide with 

flows to the north because of fairly strong tidal effects 

at the site. At site CU2, flow was almost always to the 

south when winds were from the west-northwest to 

east-northeast.

On June 9, 1998, flow in Currituck Sound was 

measured at Point Harbor (site CU4). Two discharge 

measurements were made, and the average flow of the 

two measurements was -19,500 ft3

/s to the north—

more than eight times the flow to the north at site CU2 

during the time of these measurements.

The mean and median salinities at each site were 

less than 3.5 ppt for the study period except at site CU4; 

however, the maximum salinity exceeded 3.5 ppt at all 

sites. Salinities were less than or equal to 3.5 ppt at 

all sites more than 80 percent of the time, except at 

Table 9. Summary of the highest daily salt loads at West Neck Creek (site WN2) and Coinjock 

(site CU2) and the relation of precipitation, flow, and wind direction and speed

[ft3, cubic feet; mph, miles per hour; —, no data. Positive values are to the south; negative (-) values are to the north]

Site 

(fig. 1) Date

Daily

salt 

load 

(tons)

24-hour precipitation 

(inches)

Daily 

net 

flow 

volume 

(ft3)

Prevailing 

wind 

direction 

(from)

Daily 

average 

wind 

speed 

(mph)

WS1 WS2

WN2

8-6-98 +989 0 0 +3.33 x 106 Northeast 12

8-17-98 -454 .12 .03 -2.10 x 106 Southwest 10

11-2-98 +940 0 — +1.24 x 106 North 2

11-11-98 -586 0 — -4.92 x 106 Southwest 15

CU2

11-12-98 +55,257 0 — +4.22 x 108 North 10

12-17-98 -60,605 .2 0 -5.66 x 108 West 10

12-23-98 +52,506 0 .5 +4.47 x 108 North 15

1-3-99 -65,709 0 — -5.45 x 108 Southwest 18
References 35

site CU4 where salinities were less than or equal to 

3.5 ppt less than 50 percent of the time. Salinities were 

less than or equal to 3.5 ppt in Currituck Sound at Bell 

Island (site CU1) and Poplar Branch (site CU3) nearly 

100 percent of the time, and in the Albemarle and 

Chesapeake Canal (site AC1) about 86 percent of the 

time. Salinities at sites CU2 and WN2 were less than or 

equal to 3.5 ppt about 82 percent of the time. Daily 

maximum salinities throughout the study area differed 

by as much as 19.3 ppt to as little as 0.8 ppt during the 

study period.

Daily maximum salinities in the sound generally 

were lower from March to July 1998 but increased 

from August 1998 to February 1999. At sites CU1, 

CU2, and CU3, salinities were low from spring through 

mid-summer (April–July) and higher during the 

remainder of the study period (including March 1998). 

At sites WN2, AC1, and CU4, salinities were low from 

late winter through mid-summer (March–July) and 

generally higher from August 1998 through February 

1999. More long-term data would be needed to 

determine if the slow increase in salinity in the sound 

following Hurricane Bonnie, which made landfall 

along the North Carolina coast during the early 

morning hours of August 27, 1998, was a typical 

seasonal response or a direct result of the storm.

Little association exists between flow volume 

and salinity at sites WN2 and CU2. Days when highest 

flows occurred did not coincide with days when highest 

salinities were observed. Prevailing northerly winds 

were associated with increased salinity at sites WN2 

and AC1. At site WN2, daily net flows were to the 

south during the days with the highest salinities. At 

site CU2, prevailing winds from the south and 

southwest were associated with the highest salinities, 

and daily net flows were to the north. 

Winds from the north generated flow to the south 

and, therefore, tended to increase salinities at 

sites WN2 and AC1. This indicates a salt source from 

Chesapeake Bay for site WN2 and from Great Bridge 

Lock for site AC1. Conversely, these same winds 

tended to lower salinities at sites CU1, CU2, CU3, and 

CU4. Prevailing winds from the south and southwest 

were associated with flow to the north and, therefore, 

tended to increase salinities at sites CU2, CU3, and 

CU4. This indicates a salt source from the Albemarle 

Sound. Southerly winds tended to lower salinities at 

sites WN2 and AC1.

The cumulative salt loads at sites WN2 and CU2 

for the study period were 28,170 tons to the south and 

-872,750 tons to the north, respectively. If all of the salt 

passing site WN2 were transported to Currituck Sound 

(approximately 489,600 acre-feet in North Carolina) 

and uniformly distributed throughout the sound, the 

salinity in the sound would be 0.01 ppt. Similarly, if the 

cumulative salt load at site CU2 were uniformly 

distributed throughout the sound, the salinity in the 

sound would be 0.32 ppt. The net transport at sites 

WN2 and CU2 indicates inflow of salt into the sound. 

There also is a constant inflow of freshwater from 

tributaries and ground-water sources; however, the net 

flow volumes from these freshwater sources are not 

documented, and the significance of these freshwater 

inflows in diluting the net import of salt into the sound 

is beyond the scope of this study.

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