I Salt-Water Encroachment

o 

ex

1 in the South Edisto River

3C

i ____

| Estuary, South Carolina

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1586-1

3 Prepared in cooperation with the

< South Carolina State Development

H Board
Salt-Water Encroachment 

in the South Edisto River 

Estuary, South Carolina

By T. RAY CUMMINGS

HYDROLOGY OF TIDAL STREAMS

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1586-1

Prepared in cooperation with the 

South Carolina State Development 

Board

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1968
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 15 (paper cover)
CONTENTS

Page

Abstract.______-______-___-------____________-___-____________-_- I 1

Introduction.______________________________________________________ 1

Purpose and scope of the investigation,__________________________ 1

Cooperation and collection of basic data________________________ 1

Characteristics of estuarine waters.._________________________________ 2

Description of the South Edisto River estuary._______________________ 2

Location and physical characteristics-.-----------.--------.----- 2

Fresh-water inflow___________________________________________ 4

Quantity of fresh-water inflow____________________________ 4

Quality of fresh-water inflow_______._____________________-__ 5

Tidal characteristics.__________________________________________ 5

Method of investigation.___________________________________________ 7

Chemical characteristics of the water______________________________ 8

Specific conductance__-____--_--_______-______-_______-_____-__ 8

Relation of specific conductance to fresh-water discharge. ______ 8

Relation of specific conductance to tidal height______________ 11

Relation of specific conductance to frequency of occurrence.____ 12

Dissolved-solids content and chloride__________________________ 13

Relation of dissolved-solids content and chloride to frequency of

occurrence.--__---___-----_-_____---_--_---------_-_---- 13

Composite sample analyses.____________________________________ 14

Temperature of water_________________________________________.____ 15

Suitability of water for use-_-_---__-___-____-_______-___--_-___--_- 16

Domestic use_______-_____--__-__-_-__-_-__________-_-_-_-_-__ 16

Industrial use.__-_-_-___--_----______________-_-_-_-___--_--_- 18

Conclusions_____________________________________________________ 18

References cited.__________________________________________________ 19

ILLUSTRATIONS

Page 

FIGURE 1. Map of the South Edisto River estuary. ________________ I 3

2. Graph showing mean monthly discharge at Edisto River

near Givhans______________________________________ 4

3. Flow-duration curves for Edisto River near Givhans______ 5

4. Frequency curve for height of high tide at Dawho River

entrance__ _______________________________________ 7

in
IV CONTENTS

Page 

FIGURES 5-8. Graphs showing 

5. Variations of specific conductance and discharge at 

high tide at Edisto River near Jacksonboro 

(lower station)_____________________________ I 8

6. Relation of specific conductance to discharge at 

high tide at Edisto River near Jacksonboro (lower 

station) _______ ____________________________ 9

7. Relation of specific conductance to discharge at 

high tide at Edisto River near Jacksonboro (upper 

station)_____________________ 10

8. Relation of specific conductance at high tide at 

Edisto River near Jacksonboro (lower station) to 

the height of high tide at Dawho River entrance- 11

9. Frequency curves for specific conductance at high tide at

Edisto River near Jacksonboro-__________________ 12

10. Graph showing relation of dissolved-solids content and 

chloride to specific conductance at high tide at Edisto 

River near Jacksonboro.___________________________ 14

11. Frequency curves for dissolved-solids content and chloride

at high tide at Edisto River near Jacksonboro_______ 15

12. Frequency curves for temperature of water at high tide at

Edisto River near Jacksonboro-________________ _ 17

TABLES

Page 

TABLE 1. Maximum and minimum values of dissolved substances and

physical properties of water at Edisto River near Givhans_ I 6 

2. Maximum and minimum values of dissolved substances and 

physical properties of fresh water at high tide at Edisto 

River near Jacksonboro________-________-_-__--__-__ 16
HYDROLOGY OF TIDAL STREAMS

SALT-WATER ENCROACHMENT IN THE SOUTH EDISTO 

RIVER ESTUARY, SOUTH CAROLINA

By T. RAY CUMMINGS

ABSTRACT

Salt-water encroachment in the South Edisto River estuary in South Carolina 

is related to river discharge, tidal heights, and weather. Encroachment alters the 

chemical characteristics of water for about 25 miles inland. At a Sampling station 4.5 miles southeast of Jacksonboro, S.C., salt water is detectable, but only 

on rare occasions. At a sampling station 7 miles southeast of Jacksonboro, however, the water has a specific conductance as great as 10,000 micromhos, and is 

unsuitable at times for most domestic and industrial uses.

INTRODUCTION

PURPOSE AND SCOPE OF THE INVESTIGATION

This report summarizes the results of an investigation of salt-water 

encroachment in the South Edisto Eiver estuary during the period 

January 1958 to September 1962. The principal purpose of the investigation was to determine how far salt water moves into the estuary and 

the chemical characteristics of water in the vicinity of the point of 

maximum inland movement.

COOPERATION AND COLLECTION OF BASIC DATA

The investigation was part of a cooperative program between the 

U.S. Geological Survey and the South Carolina State Development 

Board, Mr. W. W. Harper, Director. Mr. Harper was succeeded by 

Mr. J. D. Little, Jr. Water-quality data were collected and analyzed 

under the supervision of Granville A. Billingsley, District Chemist, 

U.S. Geological Survey, Ealeigh, N.C. Discharge records were collected 

under the supervision of Albert E. Johnson, District Engineer, U.S. 

Geological Survey, Columbia, S.C. Basic data used in preparing this 

report have been given by Harris (1962) and in the U.S. Geological 

Survey's series of water-supply papers (see "^References Cited," 

p. 119).

II
I 2 HYDROLOGY OF TIDAL STREAMS

CHARACTERISTICS OF ESTTJARINE WATERS

Sea water varies slightly in composition from place to place over 

the world, but compared to the water from most rivers, it is a highly 

mineralized solution.1 When sea and river water mix in an estuary, 

the body of salt water that results has a composition that reflects the 

quantity and the quality of the waters that mix and the manner in 

which they mix.

The movement inland of a body of salt water is called encroachment. 

Because salt water has a greater density than fresh water, it frequently 

moves inland as a density current along the bottom of a channel, while, 

at the same time, less dense fresh water moves seaward at the surface. 

At a given location in an estuary, the boundary between salt water in 

the bottom of the channel and overlying fresh water may be sharp and 

well defined, or the boundary may be absent and replaced by a gradual 

transition from fresh to salt water. Under other conditions, mixing of 

salt and fresh water may be complete, or nearly so, and the composition 

of the water moving inland may be homogeneous.

The manner in which sea and river water mix and the extent of saltwater encroachment depend on several factors. Among these are tides, 

currents, fresh-water discharge, sea level, winds, depth and configuration of an estuary, the rotation of the earth, temperature of both sea 

and fresh water, evaporation, and rainfall.

DESCRIPTION OF THE SOUTH EDISTO RIVER ESTUARY

LOCATION AND PHYSICAL CHARACTERISTICS

The Edisto Eiver drains an area of about 3,000 square miles in southcentral South Carolina. Drainage is generally in a southeasterly direction until the river reaches Givhans, in Dorchester County. Near 

Givhans the river turns south and flows about 60 miles to the Atlantic 

Ocean. Figure 1 is a map of the estuary.

Figure 1 shows that the Edisto River becomes the South Edisto 

River below the Dawho River entrance. In this report the estuary is 

referred to as the South Edisto River estuary, although a considerable 

reach of the estuarine channel is part of the Edisto River.

Near the mouth the estuary is li/^-2 miles wide, and at mean low 

water, it is about 35 feet deep at the deepest point. About 4 miles upstream from the mouth, the channel narrows to about a half a mile, 

and it is about 20 feet deep at mean low water. Twenty miles upstream

1 Normally, sea water contains about 35,000 ppm (parts per million) of dissolved solids, 

the most abundant constituents being sodium and chloride. A sample of sea water collected from the Atlantic Ocean near Miami, Fla., in 1941 had the following composition, 

In parts per million: Calcium, 423; magnesium, 1,324; sodium, 10,970; potassium, 429 ; 

bicarbonate, 147; sulfate, 2,750; chloride, 19,770; bromide, 49; and total dissolved solids, 

35,800 (Parker, Ferguson, Love, and others, 1955, p. 572).
COLLETON COUNTY
14 HYDROLOGY OF TIDAL STREAMS

from the mouth, the channel is one- to two-tenths mile wide and 

about 10 feet deep at mean low water.

FRESH-WATER INFLOW

QUANTITY OF FRESH-WATER INFLOW

Fresh-water discharge to the estuary is measured at a gaging station 

2.8 miles west of Givhans and about 18 miles northeast of Jacksonboro. 

Mean monthly discharge at the gaging station during the period 1939- 

65 is shown in figure 2. Discharge is normally highest in January, February, March, and April; lowest in June, July, and November. Average 

discharge near Givhans for the 1939-65 period was 2,652 cfs (cubic 

feet per second). Flow-duration curves for the period 1939-65 and the 

period of this investigation (1958-62) are shown in figure 3. Average 

discharge during the investigation was slightly higher than average 

discharge for the 1939-65 period.

Except during periods of heavy local runoff, there is no appreciable 

surface-water inflow between the gaging station and the Dawho Eiver 

entrance. For this investigation, discharge is assumed to have remained 

constant in this reach of the river.

Q 

O 4.0

3.0

2.0

/Average discharge, 1939-65

1.0

Oct. mmmm Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept.

FIGURE 2. Mean monthly discharge at Edisto River near Givhans, 1939-65.
SOUTH EDISTO RIVER ESTUARY, SOUTH CAROLINA 15

20

10

5.0

2.0 

1.0

uj 0.5

S

<

52 0.2 

O

0.1

-62

10 20 30 40 50 60 70 90 100

PERCENTAGE OF TIME DISCHARGE EQUALED 

OR EXCEEDED VALUE SHOWN

FIGURE 3. Flow-duration curves for Edisto Elver 

near Givhans, 1939-65 and 1958-62.

QUALITY OF FRESH-WATER INFLOW

The chemical characteristics of fresh-water discharge to the South 

Edisto River estnary are summarized in table 1. Maximum and minimum values given in the table are based on 13 samples collected during the period March 1946 to January 1965. Samples were obtained 

over a wide range of flow conditions from 705 to 7,690 cfs. The data 

in table 1 are thought, therefore, to be representative of the chemical 

charateristics of the water discharged to the estuary during most 

periods. The water is characterized by a low dissolved-solids content 

and low concentrations of individual dissolved substances. The water 

normally contains considerable organic matter, which, at times, causes 

the water to have a high color.

TIDAL CHARACTERISTICS

High- and low-tide predictions are published for locations along 

the Atlantic Coast by the U.S. Coast and Geodetic Survey. At a limited number of these locations, tides have been measured continuously 

over long periods of time. These tidal measuring stations are called 

reference stations, and daily predictions of height and time of tide

298 815 68 2
I 6 HYDROLOGY OF TIDAL STREAMS

TABLE 1. Maximum and minimum values of dissolved substances and physical 

properties of water at Edisto River near Givhans, S.C., March 1946 to January 

1965

[Concentrations in parts per million, except as indicated]

Minimum Maximum

Silica (SiO2)_._______________________________________ 0.9 7.3

Iron (Fe)____________ ___.____________ .03 .40

Calcium (Ca) __ _________________________ 3.0 5.9

Magnesium (Mg)_________.__________________________ .2 1.2

Sodium (Na)______________________________________ 1 2. 3 4.4

Potassium (K)__________________________________ .3 .9

Bicarbonate (HCO3)--______________._._____ 7 18

Sulfate(SO4).. _ __ ____ _ _ .8 4.4

Chloride (Cl)_____________________________________ 4.0 6.0

Fluoride (F)___________ _____ ________ __ _ .0 .1

Nitrate (NO3)----_______ _________________ .2 1.7

Dissolved solids (residue at 180°C)_ ______________ 30 2 62

Hardness (as CaC03)_--_______________________ 10 18

Noncarbonate hardness (as CaCO3 )____________________ 0 6

Specific conductance 3 (micromhos at 25°C)_____________ 33 55

pH (in pH units)-.__________________________ 5.7 7.2

Color (in color units 4)____.__________________________ 20 140

1 Includes small but undetermined amount of potassium (K).

2 Organic matter present; sum of dissolved substances 34 ppm.

3 Specific conductance is a measure of the ability of water to conduct an electric current and is related to 

the dissolved-solids content of water and to the type of individual ions in solution. Most natural waters, 

if freed of organic matter and sediment before analysis, have a dissolved-solids content to specific conductance 

ratio in the range of 0.5 to 0.8.

4 Based on platinum-cobalt scale (Hazen, 1892).

are published for each. At many other subordinate stations, tides may 

be predicted or determined by applying corrections to tidal predictions 

or measurements made at reference stations.

According to the U.S. Coast and Geodetic Survey (1966), the mean 

range of tide (the difference between mean high water and mean low 

water) at a subordinate tidal station at Edisto Beach on Edisto Island 

is 5.9 feet. About 20 miles upstream from the mouth, at a subordinate 

station at the Dawho River entrance, the mean range is 6.3 feet. About 

30 miles upstream from the mouth, at a subordinate station near Jacksonboro, the mean range is 1.9 feet. The maximum upstream point at 

which there is a tidal effect is about 38 miles from the river mouth 

(Col. Robert E. Rich, Corps of Engineers, U.S. Army, Charleston, 

S.C., written commun., 1966).

Tides that occur in the South Edisto River estuary may be computed 

from tidal measurements made by the Coast and Geodetic Survey at a 

reference station at Fort Pulaskie, Ga. (J. M. Symons, U.S. Coast 

and Geodetic Survey, Rockville, Md., written commun., 1967). Fort 

Pulaski is about 45 miles southwest of the estuary.

The frequency of occurrence of a high tide of given height at the 

Dawho River entrance during this investigation is shown in figure 4. 

Ninety percent of the time the high tide was 5.4 feet or greater; 10 

percent of the time the high tide was 7.6 feet or greater.
SOUTH EDISTO RIVER ESTUARY, SOUTH CAROLINA 17

10.0

9.0

8.0

ul

9 7.0

6.0

I 5.0

4.0

3.0

10 20 30 40 50 60 70 90 100

PERCENTAGE OF TIME HEIGHT OF HIGH TIDE 

EQUALED OR EXCEEDED VALUE SHOWN

FIGUEE 4. Frequency curve for height of high tide at Dawho River entrance, 

January 1958 to September 1962.

METHOD OP INVESTIGATION

Based on a field reconnaissance conducted in December 1957, daily 

sampling stations were established in January 1958 at two locations 

on the Edisto Kiver southeast of Jacksonboro. One station was located 

at the County Landing, 4.8 miles downstream from U.S. Highway 17 

and 4.5 miles southeast of Jacksonboro. The station is referred to as 

the "upper" station in this report. A second station, which is referred 

to as the "lower" station, was located at Hill's Fishing Camp, 8.7 miles 

downstream from U.S. Highway 17 and 7 miles southeast of Jacksonboro. (See fig. 1).

Daily samples were collected from boat docks at each station at 

high tide for chemical analysis. Each sample was depth integrated. 

The specific conductance of the individual daily samples was measured 

in the laboratory. If the specific conductance of samples collected on 

consecutive days indicated fresh water, these samples were composited 

and the composites analyzed. Composite periods ranged from 2 to 31 

days, depending on the length of time the water was fresh. Composite 

samples usually were analyzed for silica, iron, calcium, magnesium, 

sodium, potassium, bicarbonate, sulf ate, chloride, fluoride, nitrate, dissolved solids, hardness, pH, color, and specific conductance. At times
18 HYDROLOGY OF TIDAL STREAMS

when the specific conductance of individual daily samples indicated 

salt water, only chloride was determined.

CHEMICAL CHARACTERISTICS OP THE WATER

Fresh-water discharge, tides, and weather exert measurable influences on the chemical characteristics of water of the South Edisto 

River estuary. Because these factors act simultaneously, precise correlation of the chemical characteristics of the water with any one 

factor is not possible. General relations can be described, however, and 

information provided that is important to users of the water. The 

following section of this report discusses the relation of specific characteristics of the water to factors that affect these characteristics.

SPECIFIC CONDUCTANCE

RELATION OF SPECIFIC CONDUCTANCE TO FRESH-WATER DISCHARGE

Figure 5 shows the variations of daily specific conductance and the 

variations of daily mean discharge at the lower sampling station 

during July and August 1958. The variations shown are typical of 

those that occurred during the investigation. As long as discharge 

was 800 cfs or greater, specific conductance did not exceed 150

2500

« 2000 

o

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o

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2£1500

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500

s\ f N

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'Specific conductance

10 15 20 25 30

JULY

10 15 20 25

AUGUST

2500

2000

1500

500

1000 z

Li O

FIGUEE 5. Variations of specific conductance and discharge at liigli tide at 

Edisto River near Jacksonboro (lower station), July and August 1958.
SOUTH EDISTO RIVER ESTUARY, SOUTH CAROLINA 19

micromhos. As discharge decreased, specific conductance increased 

rapidly. On August 20, when discharge was about 600 cfs, specific 

conductance was 2,350 micromhos. In late August, specific conductance 

decreased rapidly as discharge increased.

Figure 6 illustrates the relation between daily specific conductance 

and discharge at the lower station from January 1958 to September 

1962. At average discharge (2,652 cfs), specific conductance varied 

from about 39 micromhos to about 250 micromhos. At a discharge of 

1,000 cfs, specific conductance varied from about 45 micromhos to 

about 3,500 micromhos. The variation in specific conductance at a given 

discharge may be attributed, in part, to the movement of water in and 

out of the estuary through the intercoastal waterway and through the 

Dawho River. It is probable that this movement of water causes

15,000

10,000

5000

2000

1000

500

 E 200

100

20

10

0.1 0.2 0.5 1.0 2.0 5.0 10 20

DISCHARGE, IN THOUSANDS OF CUBIC FEET PER SECOND

100

FIGTJEE 6. Relation of specific conductance to discharge at high tide at Edisto 

River near Jacksonboro (lower station), January 1958 to September 1962. 

(Shaded area includes all data except those affected by Hurricane Gracie. 

Points represent single days.)
110 HYDROLOGY OF TIDAL STREAMS

changes in the chemical composition of water that moves inland. Figure 6 shows, however, that salt water is more likely to reach the lower 

station when the discharge of the Edisto Eiver is low.

Storms, hurricanes, and heavy winds may alter even general relations between salt-water encroachment and fresh-water discharge. Although several storms or hurricanes occurred while this investigation 

was in progress, the effect of only Hurricane Gracie (September 29-30, 

1959) was easily separable from other factors affecting encroachment. 

(See fig. 6.) As Hurricane Gracie built up and approached the South 

Carolina coast, high tides 2 forced water inland and held it there almost independently of river discharge. As Hurricane Gracie moved 

inland and tides returned to normal, heavy rains increased the flow of 

the river, and salt water was gradually flushed seaward.

Figure 7 illustrates the relation of daily specific conductance to discharge at the upper station during the investigation. At average discharge (2,652 cfs), specific conductance ranged from 37 to 68 micromhos. At a discharge of 1,000 cfs, specific conductance ranged from 31 

to 55 micromhos. Points lying outside the shaded area in figure 7 

represent single days on which the effect of salt-water encroachment

. o i^ ii§1I" "ffi

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200 

100 

50

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10 20 50 100

DISCHARGE, IN THOUSANDS OF CUBIC FEET PER SECOND

FIGTJEB 7. Relation of specific conductance to discharge at high tide at Edisto 

River near Jacksonboro (upper station), January 1958 to September 1962. 

(Shaded area includes all data except those collected when salt water was 

detected. Points represent single days.)

2 According to the U.S. Weather Bureau (1959), the tide at Charleston (about 30 miles 

northeast of the South Edisto River estuary) was 8.2 feet above normal at the time of 

normal low water on September 29.
SOUTH EDISTO RIVER ESTUARY, SOUTH CAROLINA

was detectable. In the absence of salt-water encroachment, there is no 

significant relation between specific conductance and discharge. The 

lowest specific conductance values occur at less than average discharge, 

however. This is not normally expected. Heavy local rains which increase discharge may tend also to incrsase specific conductance by flushing more highly mineralized waters from swamp areas.

Hurricane Gracie had no measurable effect on the chemical characteristics of water at the upper station.

RELATION OF SPECIFIC CONDUCTANCE TO TIDAL HEIGHT

Ill

The tidal station at the Dawho Biver 

stream from the lower sampling sta 

illustrates the relation of daily specifi 

to the height of high tide at the Dawho 

of 5.0 feet a high tide equaled or ex 

4) the specific conductance ranged 

greater tide heights (those that occu 

specific conductance was greater.

entrance is 3% miles downion. The shaded area of figure 8 

c conductance at the lower station 

River entrance. At a high tide 

eeded 96 percent of the time (fig. 

from 38 to 700 micromhos. At 

?red less frequently) the range in

15,000

o

u> 10,000

5000

2000

1000

500

200

100

2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

HEIGHT OF HH3H TIDE, IN FEET

FIGURE 8. Relation of specific conductance 

Jacksonboro (lower station) to the he 

trance, January 1958 to September 

obtained.)

at high tide at Bdisto River near 

ght of high tide at Dawho River en1962 (Shaded area includes all data
112 HYDROLOGY OF TIDAL STREAMS

The poor correlation of specific conductance with tidal height is due 

probably to the variation in the chemical composition of water below 

the lower station, to variations in river discharge at a given tidal 

height, and to the fact that samples were not always collected at exactly high tide. It is evident, however, that the lower the high tide, the 

less likely salt water is to reach the lower station.

RELATION OF SPECIFIC CONDUCTANCE TO FREQUENCY OF OCCURRENCE

The frequency of occurrence of a specific conductance of a given 

value at both the upper and lower stations is shown in figure 9. The 

effect of salt-water encroachment is detectable about half the time at 

the lower station. At the upper station, however, salt-water encroachment is rarely detectable. The specific conductance equaled or exceeded 

10 percent of the time at the lower station (540 micromhos) is almost 

10 times as great as the specific conductance equaled or exceeded 10 

percent of the time at the upper station (57 micromhos).

Frequency curves indicate the severity and frequency of salt-water 

encroachment, but they do not indicate the length of time that en20,000

2000

1000

500

200

100

50

20

10

\

/Low* r stat on

NUp ser st stion

0 10 20 30 40 50 60 70 80 90 100

PERCENTAGE OF TIME SPECIFIC CONDUCTANCE 

EQUALED OR EXCEEDED VALUE SHOWN

FIGURE 9. Frequency curves for specific conductance at high tide at Edisto 

River near Jacksonboro, January 1958 to September 1962.
SOUTH EDISTO RIVER ESTUARY, SOUTH CAROLINA I 13

croachment of a given degree of severity occurred. The following table 

gives the average of the daily maximum specific conductance values 

for a specified period of consecutive days. For example, 7,960 micromhos was the highest such average for any 7-day period during the 

investigation.

Maximum average specific conductance 

(micromhos at 25° C)

Period of consecutive days

5___. _________________________

0___-__________________-_-__._.

0____________________-________.

o__._______________. ___________

20_________. ___________________

Lower station 

.__- 10,700

____ 7,960

___. 6,890

____ 6,360

____ 5,460

____ 4,520

_.__ 3,090

Upper station 

259

73

63

63

63

60

53

DISSOLVED-SOLIDS CONTENT AND CHLOBIDE

The dissolved-solids content of a water may be estimated from measurements of specific conductance if something is known about the 

chemical characteristics of the water. During this investigation, the 

dissolved-solids content of water usually was not determined when 

salt water was detected at the sampling stations. At such times only, 

specific conductance and chloride were determined. Fortunately, 

numerous studies have established the general relation between specific 

conductance and dissolved-solids content for waters containing principally sodium and chloride. Using data of Cox (1965) and data obtained during this investigation, the relations of specific conductance 

to dissolved-solids content and of specific conductance to chloride were 

developed. The relations are applicable to water at both the upper 

and lower stations. (See fig. 10.)

RELATION OF DISSOLVED-SOLIDS CONTENT AND CHLORIDE TO FREQUENCY OF

OCCURRENCE

Frequency curves for dissolved-solids content and chloride have 

been computed for both the upper and lower stations from frequency 

curves of specific conductance (fig. 9) and from the relations of dissolved-solids content and chloride to specific conductance (fig. 10). 

Frequency curves for dissolved-solids content and chloride are shown 

in figure 11. Fifty percent of the time at the upper station the dissolved-solids content equaled or exceeded 30 ppm. At the lower station, 

dissolved- solids content equaled or exceeded 40 ppm 50 percent of the 

time. Five percent of the time at the upper station the dissolved-solids 

content equaled or exceeded 37 ppm. At the lower station, however, the 

dissolved-solids content equaled or exceeded 850 ppm 5 percent of the
114

10,000 

5000

2000 

0 1000

ISSOLVED AND CHLORIDE, IN fvllLLI SOLIDS PARTSER 

tn "- o

moo M to o

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5

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HYDROLOGY OF TIDAL STREAMS

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10 20 50 100 200 500 1000 2000 5000 

SPECIFIC CONDUCTANCE, IN MICROMHOS PER CENTIMETER AT 25°C

10,000

FIGURE 10. Relation of dissolved-solids content and chloride to specific conductance at high tide at Edisto River near Jacksonboro, January 1958 to September 1962.

time. Five percent of the time chloride equaled or exceeded 8.6 ppm 

at the upper station, compared to 450 ppm 5 percent of the time at the 

lower station.

COMPOSITE SAMPLE ANALYSES

During periods when salt-water encroachment did not affect the 

chemical characteristics of water at the upper and lower stations, daily 

samples were composited, and complete chemical analyses were made
SOUTH EDISTO RIVER ESTUARY, SOUTH CAROLINA I 15

10,000 i 

5000

500

200

100

50

20

10

1.1-

/Dis iolved solid! (lowt

Chlori le (upper station)

r stat on)

Chloride 

flower station)

10 20 30 40 50 60 70 80 90 100

PERCENTAGE OF TIME CONCENTRATION EQUALED 

OR EXCEEDED VALUE SHOWN

FIGTJBE 11, Frequency curves for dissolved-solids content and chloride at high tide at Edisto River near 

Jacksonboro, January 1958 to September 1962.

on the composites (p. IT). Table 2 gives the maximum and minimum values of dissolved substances and physical properties found 

when composites of the fresh water were analyzed.

In the absence of salt-water encroachment, the concentration of most 

substances in the water is low. Iron, color, and organic matter, however, occur in amounts greater than are common in most streams.

TEMPERATURE OF WATER

The temperature of water at both the upper and lower stations on 

the Edisto River was measured at the time samples were collected. At 

the upper station the maximum temperature recorded during the 

investigation was 87°F; the minimum was 32°F. At the lower station
I 16 HYDROLOGY OF TIDAL STREAMS

TABLE 2. Maximum and minimum values of dissolved substances and physical 

properties of fresh water at high tide at Edisto River near Jacksonboro, S.C., 

January 1958 to September 1962.

[Concentrations In parts per million, except as indicated]

Upper Station Lower Station

Minimum

Silica (Si02)______________.______________

Iron (Fe)_ __ .-_-_-___---___________-__

Calcium (Ca)__ _____ ___ _______

Magnesium (Mg) ____ ____ _____

Sodium (Na)__ _______ ___ ._ ____ _

Potassium (K) ________ _ _ __

Bicarbonate (HCOg) _ _ __ ___________

Sulfate (SC>4)__ ___ __ _ ____ _ ___ _

Chloride (Cl)__________________. _______

Fluoride (F)___ ___ _____ _ _ _ _____ _

Nitrate (N03) _____ __ _ ______________

Dissolved solids (residue at 180°C) _ _ _

Hardness (as CaCOg)- _____ __ _________

Noncarbonate hardness (as CaC03) _ _

Specific conductance (micromhos at 25°C) _ _

pH (in pH units) ____ _ _ _ ____ _ ___

Color (in color units) __ _____ __ ____

1.3

. 03

2.4

.3

2.2

.2

7

.6

3.0

.0

. 1

28

9

0

35

6.0

30

Maximum Minimum

9.7

. 54

6.7

1.5

4.3

1.8

20

5.8

9.0

.2

1. 9

1 71

20

9

63

7.0

200

1.3

.02

3.0

.3

2.7

.3

9

.8

5.0

.0

. 1

32

12

2

43

6.2

50

Maximum

9.4

.51

7.4

2.0

6.6

2.0

20

7.0

10

.2

4.2

2 77

20

11

70

7.3

220

>Organic matter present; sum of dissolved substances 38 ppm.

 Organic matter present; sum of dissolved substances 45 ppm.

the maximum temperature was 89 °F; the minimum was 34° F. During 

the fall and winter the temperature of the water increased about 2°F 

between the upper and lower stations. During the spring and summer 

the temperature increased about 4°F. The average January temperature at the upper station was 45°F; the average July temperature was 

Y7.5°F. At the lower station the average January temperature was 

46°F; the average July temperature was 83°F. Frequency curves for 

temperatures at both station are shown in figure 12.

SUITABILITY OF WATER FOR USE

The suitability of a water for use depends largely on the chemical 

characteristics and physical properties of the water. Water suitable 

for one use may not be suitable for another, and thus water must be 

judged by criteria appropriate to the intended use. The degree to which 

a water fails to meet appropriate criteria usually determines the treatment required. If extensive treatment is necessary, use of a water supply may not be economically feasible.

DOMESTIC ITSE

Chemical-quality standards for water used for drinking and culinary purposes on interstate-commerce carriers have been established
SOUTH EDISTO RIVER ESTUARY, SOUTH CAROLINA I 17

100

90

80

70

2 60

50

40

30

2O

I pper s a ion"

Lower stat

0 10 20 30 40 50 60 70 80 90 100 

PERCENTAGE OF TIME TEMPERATURE EQUALED OR EXCEEDED VALUE SHOWN

FIGURE 12. Frequency curves for temperature of water at high tide at 

Edisto River near Jaeksonboro, January 1958 to September 1962.

by the U.S. Public Health Service (1962). These standards have been 

endorsed by the American Water Works Association, and are commonly used to evaluate water intended for human consumption. Some 

of the maximum concentration limits of significance to the evaluation 

of water in the report area are, in parts per million: iron, 0.3; chloride, 

250; and dissolved-solids content, 500. A maximum color of 15 units 

also has been recommended. Although specific limits have not been 

set for organic matter, even small amounts are unacceptable to most 

consumers.

Hardness, a measure of the ability of water to consume soap, has 

been arbitrarily classified in parts per million, as follows: 60 or less, 

soft; 61-120, moderately hard; 121-180, hard; and 181 or more, very 

hard.

Using these criteria, water at the upper station is suitable for domestic use at all times, providing the water is treated when necessary
I 18 HYDROLOGY OF TIDAL STREAMS

to remove iron, color, and organic matter. At the lower station, the 

dissolved-solids content of the water equals or exceeds the recommended maximum limit (500 ppm) Y percent of the time. (See fig. 11.) 

The recommended maximum limit for chloride (250 ppm) is also 

equaled or exceeded about Y percent of the time. The water is usually 

soft, except when salt water is detectable. Treatment to remove iron, 

color, and organic matter also will be necessary at the lower station.

INDUSTRIAL USE

The water-quality requirements of industry depend largely upon 

the specific use to be made of water. Reports by Moore (1940) and 

the California State Water Quality Control Board (1963) contain information on industrial water-quality standards and may be consulted for criteria applicable to a specific use. Generally, water that 

has a low dissolved-solids content and a low hardness, and does not 

vary greatly in quality or temperature, meets the requirements of 

many industries. Water ;at the upper station meets these general 

criteria at all times. At the lower station, water will be unsuitable for 

most industrial users on occasion, but the frequency can be determined 

only if the intended use is known. The iron, color, and organic matter 

characteristics of water at both stations are objectionable to many industries, particularly those that use water in a process. Treatment to 

remove these characteristics usually will be required.

CONCLUSIONS

Salt-water encroachment alters the chemical characteristics of water 

of the Edisto River about 25 miles upstream from the mouth. The 

distance that salt water moves inland depends on the discharge of the 

river, tidal heights, and weather. Precise correlations of these factors 

with specific chemical characteristics are not possible in the report 

area because water that moves inland varies in chemical composition 

from time to time.

The effect of salt-water encroachment is detectable on rare occasions 4.5 miles southeast of Jacksonboro (the upper station). Only 

minor changes in the characteristics of the water occur at this point, 

however. At a point Y miles southeast of Jacksonboro (the lower 

station), the effect of encroachment is detectable about half the time. 

Less frequently, the water is highly mineralized. Water is suitable 

for most uses at the upper station at all times, providing it is treated 

to remove iron, color, and organic material. If water at the lower 

station is similarly treated, it is suitable for domestic use about 

93 percent of the time. The water will be unsuitable for most industrial
SOUTH EDISTO RIVER ESTUARY, SOUTH CAROLINA I 19

uses at the lower station on occasion, but the intended use must be 

known to determine how frequently the water is unsuitable.

REFERENCES CITED

California State Water Quality Control Board, 1963, Water-quality criteria: 

California State Water Quality Control Board Pub. 3-A, 548 p.

Cox, B. A., 1965, The physical properties of sea water, in Riley, J.P., and Sklrrow, 

Geoffrey, Chemical oceanography: New York, Academic Press, v. 1, p. 105.

Harris, K. F., 1962, Chemical character of surface waters of South Carolina, 

1945-60: South Carolina State Devel. Board Bull. 16C, 123 p.

Hazen, Alien, 1892, A new color standard for natural waters: Am, Chem. Soc. 

Jour., v. 12, p. 427-428.

Moore, E. W., 1940, Progress report of the committee on quality tolerances of 

water for industrial uses: New England Water Works Assoc. Jour., v. 54, 

p. 271.

Parker, G. G., Fergusion, G. E., Ijove, S. K., and others, 1955, Watei resources of 

'southeastern Florida: U.S. Geol. Survey Water-Supply Paper 1255, 965 p.

U.S. COast and Geodetic Survey, 1966, High and low water predictions, east coast 

of North and South America, including Greenland: U.S. Coast and Geodetic 

Survey Tide Tables.

U.S. Geological Survey, Quality of surface waters of the United States, pts. 1 

and 2, North Atlantic Slope Basins and South Atlantic Slope and Eastern 

Gulf of Mexico Basins: U.S. Geol. Survey water-supply papers (published 

annually from 1941 through 1963; published periodically from 1964 to 

present).

 Surface water supply of the United States, pt. 2-A, South Atlantic 

Slope Basins, James River to Savannah River: U.S. Geol. Survey watersupply papers (published annually through 1960; published periodically 

from 1961 to present).

U.S. Public Health Service, 1962, Drinking water standards: U.S. Public Health 

Service Pub. 956,61 p,

U.S. Weather Bureau, 1959, Climatological data for South Carolina (issued 

monthly).

o