Time of Travel of Water 

3 in the Ohio River

Pittsburgh to Cincinnati

'I 1 II «'

GEOLOGICAL SURVEY 

CIRCULAR 439

fu
Time of Travel of Water

in the Ohio River 

Pittsburgh to Cincinnati

By R. E. Steacy

GEOLOGICAL SURVEY QRCULAR 439

Washington, D. C. 

1961
United States Department of the Interior

STEWART L. UDALL, SECRETARY

Geological Survey

THOMAS B. NOLAN, DIRECTOR

Free on application to fhe U.S. Geological Survey, Washington 25, D. C
CONTENTS

Page Page

Abstract____________________________ 1 Examples of application Continued

Introduction _________________________ 1 Time of travel of Ohio River water

Description of the reach ______________ 2 from Pittsburgh to Cincinnati _____ 13

Dispersal effect _____________________ 5 Time of travel of water from any

Basic data and computational point on the Ohio River___________ 14

procedures _______________________ 6 Time of travel of water during low -

Computed time of travel of water______ 9 flow periods ____________________ 14

Examples of application ______________ 13 Reference cited _____________________ 14

ILLUSTRATIONS

Page 

Figure 1. Index map of the Ohio River showing cities, principal tributary streams, and

stream -gaging stations referred to in this report ____________________________ 2

2. Duration curve of daily flow, Ohio River at Cincinnati, Ohio, water years

1948-57 _________________________________________________________________ 3

3. Frequency of daily flow, by months, Ohio River at Cincinnati, Ohio, 1948 57______ 4

4. Schematic diagram of dispersal effect _______________________________________ 5

5. Average time of travel of Ohio River water for discharges at Cincinnati, Ohio,

of 50,000 or more cubic feet per second ____________________________________ 10

6. Average time of travel of Ohio River water for discharges at Cincinnati, Ohio,

between 10,000 and 80,000 cubic feet per second_____________________________ 11

7. Relation of discharge at Cincinnati, Ohio, to average time of travel of water

from Pittsburgh, Pa., to selected downstream points___________-------------- 12

8. Stage-discharge relation, Ohio River at Cincinnati, Ohio. ______________________ 13

TABLES

Page 

Table 1. Locks and dams on the Ohio River between Pittsburgh, Pa., and Cincinnati,

Ohio -________--_____________-_________----___--_-_---------------------- 5

2. River mileage and catchment drainage area at selected points on the Ohio River--- 6

3. Relation of discharge at Ohio River gaging stations---------------------------- 7

4. Computation of time of travel of Ohio River water from Pittsburgh to Cincinnati__ 8

5. Time of travel of Ohio River water from Pittsburgh to Cincinnati ______---______ 12

III
Time of Travel of Water in the Ohio River 

Pittsburgh to Cincinnati

By R. E. Steacy

ABSTRACT

This report presents a procedure for estimating the time of 

travel of water in the Ohio River from Pittsburgh, Pa., to 

Cincinnati, Ohio, under various rivei\ stage conditions. This 

information is primarily for use by civil defense officials and 

by others concerned with problems involving travel time of 

river water.

Tables and charts are presented to show, for a particular 

stage or discharge at Cincinnati, the average time it would 

take for water to travel through the entire reach from Pittsburgh, or through successive intermediate segments of the 

reach. For example, when the discharge at Cincinnati is 

200,000 cfs, travel time from Pittsburgh to Cincinnati, a 

distance of 470 miles, averages about 7 days; and for discharges of more than 200,000 cfs, the travel time decreases 

very slowly with increasing discharge. When the discharge is 

30,000 cfs, travel time is about 28 days; and for discharges 

of less than 30,000 cfs, the travel time increases very rapidly with decreasing discharge. Estimates of travel time at 

low discharge are subject to large errors.

Statistical analysis of the possible variations of upstream discharge for a given discharge at Cincinnati indicates that the shortest probable travel time from Pittsburgh to Cincinnati ranges from 56 percent of that under 

average conditions when the discharge at Cincinnati is 

15,000 cfs to 93 percent of that under average conditions 

when the discharge at Cincinnati is 894,000 cfs.

A chart showing the time distribution of flow at Cincinnati is presented so that the probable travel time of 

Ohio River water can be determined for any time of the 

year. This chart provides information which, when applied 

to the time-of-travel chart, shows that the most probable 

travel time of water from Pittsburgh to Cincinnati ranges 

from 160 hours in February to 1,250 hours in September. Also 

presented is a flow-duration curve that can be used to predict future discharges and, subsequently, times of travel, 

for use in long-range planning. The procedure used to compute time of travel is described in sufficient detail to make 

it usable as a guide for similar studies on other rivers that 

have dams and pools in the reach being studied.

The computations for the time-of-travel charts were made 

as follows: (a) by dividing the reach between Pittsburgh and 

Cincinnati into four subreaches with a full-range streamgaging station at or near the ends of each; (b) by computing 

for each subreach mean velocities corresponding to various 

discharges at Cincinnati, using data obtained from river survey maps and data available from gaging station operations; 

(c) by assuming that any mass of contaminated water would 

travel at a rate equal to that of the mean velocity of the river 

water.

INTRODUCTION

The report presents a. procedure by which 

the time of travel of water in the reach of the 

Ohio River between Pittsburgh, Pa., and

Cincinnati, Ohio, can be estimated, provided 

that the river stage at Cincinnati is known. 

The gage at Cincinnati is used as an index of 

flow, and if the stage ana the subsequent discharge at Cincinnati are not known, a. special 

flow-frequency chart can be used to estimate 

the probable discharge at any time of year. 

For long-range planning, a flow-duration 

curve is presented for use in predicting the 

percent of time during which various flows 

will occur in the future.

The time-of-travel procedures in this report can be used to estimate the arrival time 

of possible accidental contamination from an 

upstream source, because dissolved contamination travels at the same speed as a unit 

mass of water. If a harmful contaminant were 

suddenly introduced in the reach of river under study, it might be necessary to stop diverting and using water downstream until the 

contamination drops to a harmless level. The 

time available before arrival of the contamination front at downstream critical points 

can be used to store emergency water supplies or to arrange for obtaining supplies 

from substitute sources. The time required 

for the contamination to drop to a harmless 

level cannot be estimated from this report 

because contaminants moving as suspended 

material travel more slowly than the water 

and the dissolved contamination. The study 

of the movement of suspended contaminants 

is outside the scope of this report. Other 

possible uses of information on time of travel 

of water are in quality-of-water studies of 

biochemical oxygen demand and in determining the optimum time for release of waste 

materials such as radioactive wastes.

The reach of river used in this study contains numerous navigation locks and dams 

that affect the natural velocity of flow. The 

data presented herein are based on the condition of the locks and dams in June 1958.
TIME OF TRAVEL OF WATER IN THE-OHIO RIVER. PITTSBURGH TO CINCINNATI

Three higher dams are presently under construction in the reach, and five additional 

high dams are tentatively proposed. Each of 

these will replace several old, low-head dams 

and will provide a much deeper channel. One 

of the effects of these new dams will be to increase the time of travel of water, particularly at low stages.

River survey maps prepared by the Louis - 

ville district of the Corps of Engineers were 

used in drawing the low-flow profile and in 

determining cross-sectional areas.

The methods used in developing the timeof-travel charts were based in part on suggestions by the Washington office staff of the 

Geological Survey, particularly J. K. Searcy 

and C. H. Hardison.

DESCRIPTION OF THE REACH

The Ohio River is formed by the confluence 

of the Monongahela and Allegheny Rivers at

Pittsburgh, Pa., (fig. 1). The river flows 

southwestward to Cincinnati, augmented enroute by inflow from many tributaries. Several of these tributaries drain areas larger 

than 1,000 square miles; thus, the discharge' 

varies at successive locations along the 

reach. The average discharge is about 32,000 

cfs (cubic feet per second) at Pittsburgh and 

about 97,000 cfs at Cincinnati. The distribution of daily flow for the period 1948 57 at 

Cincinnati is shown by a flow-duration curve 

(fig. 2), and a breakdown of the same data by 

months is shown in figure 3.

The Ohio River has a series of locks and 

dams that provide a navigation channel 500 

feet wide whose minimum depth is 9 feet. 

Table 1 shows the location of each lock and 

dam between Pittsburgh and Cincinnati, and 

the elevations of their pools. Most of the 

dams have movable crests that consist of 

hinged wickets supported by a sill near 

streambed level. At low flows, some or all 

of the wickets are raised to an erect position 

so that the dam thus formed creates a pool

85

EXPLANATION 

U. S. Geological Survey stream-gaging station

w

Partialwrange gage 

Highjlows only

ilNCINNATI

Maysville

Ashland 

KENTUC KY V I R G I

25 25 i

5Q 75 100 125 MILES _I

Figure 1. Index map of Ohio River showing cities, principal tributary streams, and stream-gaging stations referred to in this report.
DESCRIPTION OF THE REACH

with sufficient depth for navigation. When at 

extremely low flows all the wickets of each 

dam are raised, the river becomes a series 

of nearly level pools, and the velocity of flow 

is very low.

Most of the cities and industries adjacent 

to the river divert water from the river for 

domestic, commerical, and industrial uses, 

but much of this water is returned to the 

river.

THOUSANDS DISCHARGE, IN OFCUBIC FEETPER SECOND

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PERCENT OF TIME DISCHARGE EQUALED OF EXCEEDED THAT SHOWN

Figure 2. Duration curve of daily flow, Ohio River at Cincinnati, Ohio, water years 1948 57.
TIME OF TRAVEL OF WATER IN THE OHIO RIVER, PITTSBURGH TO CINCINNATI

1,000,000

Maximum

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

Figure 3. Frequency of daily flow, by months, Ohio River at Cincinnati, Ohio, 1948-57.
DISPERSAL EFFECT 

Table 1. Locks and dams on the Ohio River between Pittsburgh, Pa., and Cincinnati, Ohio

Lpck. 

designation

Emsworth-..---

Dashields _ ____

Montgomery-. o </ __

7 ..........

8..........

9..........

10...... __ .

11....... __

12. .........

13... ____ .

14. ...._....

15...... __ .

16..........

17... .......

18_. __ ....

19..........

Distance downstream from 

Pittsburgh, Pa. 

(miles)

6.2

13.3

31.7

36.5

46.4

56.1

66.2

76.9

87.4

96.1

114.0

129.1

146.5

167.5

179.9

192.2

Upper pool 

elevation 

(feet above 

mean sea 

level)

710.0

692.0

682.0

662.6

655.7

649.3

641.9

633.5

626.2

617.8

610.5

602.2

^QA A

586.6

578.4

572.2

Lock 

designation

20. ___ ...

21. ......._

22.........

23 .........

Gallipolis .......

27.........

28 __ .. ...

29 .........

30 ____ ...

31.........

32. ________

33 __ .. ___

34___-______

35. ___ ___

36 __ .. ___

37_. .......

Distance downstream from 

Pittsburgh, Pa. 

(miles)

202.5

214.6

220.9

231.4

279.2

301.0

311.6

319.9

339.4

359.3

382.6

405.1

434.1

451.0

460.9

483.2

Upper pool 

elevation 

(feet above 

mean sea 

level)

564.5

557.0

551.4

543.6

538.0

512.0

505.6

498.5

490.5

483.0

475.5

468.0

461.0

455.4

449.0

441.1

DISPERSAL EFFECT

The use of the time-of-travel data in this 

report to estimate the time of arrival of hypothetical contaminants depends on the assumption that the rate of travel of contaminants is the same as the mean velocity of 

water in the river channel. Actually, in some

parts of the channel the flow rate exceeds the 

mean rate; in other parts the flow is less 

than the mean. The general results of this 

variation are shown schematically in figure 

4. The diagram for point A represents the 

initial time distribution for a hypothetical 

contaminant in solution, and the diagrams for 

points B and C show the longitudinal variation

Point A

2

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oo

00

Point B Point C

TIME TIME TIME

Figure 4. Schematic diagram of dispersal effect.
TIME OF TRAVEL OF WATER IN THE OHIO RIVER. PITTSBURGH TO CINCINNATI

in the concentration of the contaminant at 

given downstream cross sections of the 

stream channel. The distance between the 

two vertical lines at point A represents the 

time during which the contaminant is released. The height of the two lines indicates 

the concentration. The diagram for point B 

represents the redistribution of the contaminant after it has traveled some distance 

downstream from point A. The diagram for 

point C shows the more pronounced redistribution farther downstream. The widths between the bottom of the legs in the diagrams 

for points B and C represent the time interval between the first appearance and the disappearance of the contaminant at the given 

cross section, assuming that the contaminant 

was introduced at a uniform rate for a short 

period of time. According to these diagrams, 

a small concentration of the contaminant will 

arrive at a point downstream somewhat 

sooner than will the maximum concentration. 

Nevertheless, owing to the lack of detailed 

knowledge about the contributing variables, 

the dispersal effect is disregarded in this 

report, and the main mass of the contaminationis assumed to travel at the mean velocity 

of the water.

BASIC DATA AND COMPUTATIONAL PROCEDURES

Various kinds of data on the Ohio River 

have been collected during many years, so 

that in th'e absence of direct observations of 

the time it takes water to travel through long 

reaches, the approximate time of travel can 

be estimated by computing the velocity of 

flow from data collected for other purposes.

Records of stage and discharge at 5 fullrange and 5 partial-range stations operated 

by the U.S. Geological Survey on the Ohio 

River between Pittsburgh and Cincinnati were 

used in this study. The river miles below 

Pittsburgh and the drainage area for each of 

these stations are listed in table 2. Data collected at the gaging station at Sewickley, 11.8 

miles below Pittsburgh were assumed to 

represent flow conditions at Pittsburgh.

The procedure used in this report for computing the time of travel of river water was 

to obtain (a) correlations between discharges 

at adjacent full-range gaging stations, (b) 

stage profiles showing the water surface elevation for selected flow conditions, (c) a

Table 2. River mileage and catchment drainage area at selected points on the Ohio River

Point

Pittsburgh, Pa. _______

Sewickley, Pa, 1 ______

Bellaire, Ohio 1 ______

St. Marys, W.Va. 2 _._

Parkersburg,W. Va. 1 _

Pomeroy, */ * Ohio 2 ______

Point Pleasant,

W.Va. 2 ___ ___ _

Huntington, W. Va. 1 ___

Ashland, Ky.2 __ __ __

Maysville,Ky.

(near) 2 ___________

Cincinnati, Ohio 1 ____

Distance

from

Pittsburgh,

Pa.

(miles)

0

11.8

96.4

155.0

184.4

265.4

265.4

311.6

319.9

405.1

470.5

Drainage

area

(sq mi)

19,050

19,500

25,170

26,850

35,600

40,500

' 8 52,760

55,900

60,750

70,130

76,580

1 Full-range stream-gaging station. 

2 Partial-range stream-gaging station 

(high flows only).

3 Below Kanawha River.

weighted cross-sectional area at each of several stages in the reach between each pair of 

full-range gaging stations, and (d) the weighted 

mean velocity applicable to each of these 

reaches for each flow condition.

The correlations between the discharges 

were obtained by plotting the monthly mean 

discharge for simultaneous months for the 

period 1951 55 at adjacent full-range streamgaging stations as described by Searcy (1960, 

p. 80). The correlations were very good. The 

top half of table 3 shows discharge figures 

computed from these correlations for selected Cincinnati discharges. These discharges are an estimate of the most probable 

simultaneous discharges tobe expected at the 

upstream stations. For example, when the 

discharge at Cincinnati is 10,000 cfs, the 

most probable discharge at Huntington is 

8,500 cfs and at Sewickley 4,150 cfs. The 

bottom half of table 3 shows the greatest discharge that would be expected 99 times out 

of 100. This discharge was computed from 

the standard error of estimate (Searcy, 1960, 

p. 74, 84), as explained in table 3, and was 

used to .compute the discharge shown in the 

greatest discharge columms of table 4.
BASIC DATA AND COMPUTATIONAL PROCEDURES

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COMPUTED TIME OF TRAVEL OF WATER

Stage profiles for the entire distance, Pitts - 

burgh to Cincinnati, were obtained by plotting 

stages for selected flow conditions against 

stream locations expressed as river mileages 

downstream from Pittsburgh. For medium 

and high flows, the profiles were based on 

maximum daily stages recorded at all 10 

gaging stations between Pittsburgh and Cincinnati during rises in March and October 

1954. The rise of January 1954 was also 

used, but for the Huntington to Cincinnati 

reach only. For low flow, the profile was 

based on pool stage and thus shows the level 

water surface between dams and the abrupt 

drop of water surface at the dams.

Cross sections at 32 points midwaybetween 

navigation dams were plotted from elevations 

on river survey maps of the Corps of Engineers. Elevations obtained from the appropriate profile were plotted on each of these 

32 cross sections and the cross-sectional 

areas were measured. From these measured cross-sectional areas, weighted crosssectional areas applicable to each of the 4 

reaches between full-range gaging stations 

were obtained. The weighting factor was the 

distance between navigation dams, as each 

cross section was assumed to apply throughout the length of the pool of which it was. 

the midpoint. In measuring cross-sectional 

areas, only the area of the main channel was 

used when overbank flow existed.

Mean velocities for the rise corresponding 

to each profile were obtained for each of the 

four reaches by averaging the peak discharges at the ends of the reach and by dividing the average discharge by the corresponding weighted cross-sectional area. For lowflow, or pool condition, the weighted crosssectional area was divided by the monthly 

mean discharge for October 1953, a typical 

low-flow month.

The results of these computations were 

used to plot a curve of relation between discharge and mean velocity for each of the four 

reaches between full-range gaging stations. 

The mean velocities picked from these curves 

for selected discharges are shown in the top 

part of table 4. The selected discharges are 

the average of the discharges for the adjacent 

gaging stations shown in table 3 for arbitrary 

discharges at Cincinnati.

The final step was to compute the time of 

travel in the four reaches, Pittsburgh to

Bellaire, Bellaire to Parkersburg, Parkersburg to Huntington and Huntington to Cincinnati, using the distance in miles and the velocities in feet per second. The results are 

shown in the top part of table 4.

COMPUTED TIME OF TRAVEL OF WATER

For convenience, the information in table 4 

is plotted in figures 5 and 6. If the time of 

contamination at any point in the river and 

the discharge at Cincinnati are known, the 

time of arrival at any point in the reach can 

be estimated. Examples are given in the following section. The curves shown in figure 

7, which are also based on data in table 4, 

can be used to interpolate bet we en the curves 

shown in figures 5 and 6.

The average times of travel of water shown 

in figures 5, 6, and 7 contain errors from two 

sources. The first source is that the discharges at the four upstream gaging stations 

were estimated from correlations of monthly 

values. The estimated mean velocities, in 

turn, were based on results of these correlations. Thus, figures 5, 6, and 7 represent the 

average time of arrival fora given discharge. 

The bottom part of table 4 shows the time of 

travel under the condition that has only one 

chance in a hundred of being exceeded (labeled fastest probable conditions). This fastest probable condition is based on the possibility of error in estimating upstream discharge when only the discharge at Cincinnati 

is known. For a given discharge at Cincinnati, there is only one chance in a hundred 

that the upstream discharge will exceed the 

discharge obtained from the average relation 

by enough to give a time of travel shorter 

than that shown for the fastest probable conditions. These results are summarized in 

table 5. It is apparent from this table that a 

more precise prediction can be made at high 

flows than at low flows.

The second source of error is the variable 

velocity of the water in a given mass: not all 

of it travels at the mean velocity. For example, water delayed in stagnant and sluggish 

areas travels considerably slower than mean 

velocity; whereas, water at or near the surface in the main current travels faster than 

mean velocity.

So far as the movement of contaminants is 

concerned, time-of-travel estimates apply
10 TIME OF TRAVEL OF WATER IN THE OHIO RIVER, PITTSBURGH TO CINCINNATI

320

300

20

100 200 300 400 

DISTANCE DOWNSTREAM FROM PITTSBURGH, IN MILES

500

Figure 5. Average time of travel of Ohio River water for discharges at Cincinnati, Ohio, of 50,000 or more cubic feet per second.
COMPUTED TIME OF TRAVEL OF WATER 11

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DISTANCE DOWNSTREAM FROM PITTSBURGH, IN MILES

Figure 6. Average time of travel of Ohio River water for discharges at Cincinnati, Ohio, between 10,000 and 80,000 cubic feet per second.
12 TIME OF TRAVEL OF WATER IN THE OHIO RIVER, PITTSBURGH TO CINCINNATI

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AVERAGE TIME OF TRAVEL FROM PITTSBURGH, IN HOURS

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Figure 7. Relation of discharge at Cincinnati, Ohio, to average time of travel of water from Pittsburgh, Pa., to selected downstream poinls. 

Table 5. Time of travel of Ohio River water from Pittsburgh to Cincinnati

Time of travel of water

at Cincinnati Suspension Bridge

Discharge 

(cfs)

894,000 __ ___ ____

250,000 __ __ __ __ __

150,000.. ____ ____

80,000 ______ ___

30,000___ __ __ __ __

15,000__ ___ _ __ __

Stage 

(feet)

78.8 

36.9 

25.9 

16.6 

12.5 

12.0

Hours

106 

154 

193 

285 

673 

1,331

Average conditions

Days

4.4 

6.4 

8.0 

12 

28 

55

Hours

99 

128 

152 

200. 

390 

748

Fastest probable 

conditions 1

Days

4.1 

5.3 

6.3 

8.3 

16 

31

Percent of 

average

93 

83 

79 

70 

58 

56

1There is a 1-percent chance that travel time will be faster than that shown for fastest probable 

conditions.
EXAMPLES OF APPLICATION 13

only to contaminants in solution or suspension in the flowing water. Contaminants absorbed on sediment might be delayed in 

transit indefinitely, depending on whether the 

sediment is carried in suspension or as bedload, or whether it is deposited in the channel 

during a falling stage. Thus, only by making 

direct tests of the water could a completely 

reliable estimate be made of the time of arrival and the concentration of contamination 

or of the time required for the water to recover to a satisfactory quality.

EXAMPLES OF APPLICATION

TIME OF TRAVEL OF OHIO RIVER WATER FROM PITTSBURGH 

TO CINCINNATI

Table 5 and figures 5, 6, and 7 show that 

the average time of travel of water from 

Pittsburgh to Cincinnati may range from less 

than 5 days to more than 50, depending on the 

-discharge If. the discharge at Cincinnati is

known, an approximate discharge can be obtained by entering figure 8 with readings 

from the gage at the downstream side of the 

Covington-Cincinnati suspension bridge. For 

example, at a gage-height reading of 30 feet, 

figure 8 shows the discharge to be 180,000 

cfs. Figure 5 shows the time of travel corresponding to Cincinnati discharges of 150,000 

cfs and 250,000cfs. The discharge of 180,000 

cfs is about one-third of the difference between these two discharges, for which the 

times shown on figure 5 are 193 hours and 

154 hours respectively. The time required 

at 180,000 cfs is therefore 193 hours less 

one-third of the difference between 193 hours 

and 154 hours, or 180 hours. Figure 7 shows 

about the same travel time when the Cincinnati curve is entered with a discharge of 

180,000 cfs.

The fastest probable travel time can be 

computed by using the information shown in 

table 5. For 150,000 cfs the fastest probable 

travel time is 79percent of the average time.

80

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100 200 300 400 500 600 700

APPROXIMATE DISCHARGE, IN THOUSANDS OF CUBIC FEET PER SECOND

800 900

Figure 8. Stage-discharge relation, Ohio River at Cincinnati, Ohio. The curve gives average discharge in cubic feet per second corresponding to gage readings from the suspension bridge at Cincinnati; a rating using water-surface slope must be used to obtain more accurate 

evaluations of discharge.
14 TIME OF TRAVEL OF WATER IN THE OHIO RIVER, PITTSBURGH TO CINCINNATI

By interpolation, a value of 81 percent is obtained for 180,000 cfs,and the resulting fastest probable travel time is computed as 146 

hours (0.81x180 equals 146 hours).

The information on the distribution of daily 

flow at Cincinnati shown in figures 2 and 3 

can be combined with information in figures 

5, 6, and 7 to give the probability of various 

times of travel. For example, from figure 2 

the median discharge (at the 50-percent line) 

at Cincinnati is 60,000 cfs, and from figure 7 

the corresponding travel time from Pittsburgh to Cincinnati is about 360 hours. Thus, 

for 50 percent of the time, the travel time 

from Pittsburgh to Cincinnati is at least 360 

hours.

Similarly, from figure 3 the discharge that 

is exceeded 10 percent of the time during 

February is 380,000 cfs. For this discharge, 

figure 6 or figure 7 indicates that about 135 

hours, or roughly 5 5 days, will be the travel 

time. This .means that there is a 90-percent 

probability that in February there will be at 

least a 5| days delay between the introduction 

of a contaminant at Pittsburgh and its arrival 

at Cincinnati. By the same process, it can be 

seen that there is a 90-percent probability 

that there will be more than 20 days delay 

during October.

TIME OF TRAVEL OF WATER FROM ANY POINT ON THE 

OHIO RIVER

The average time of travel of water between 

other points on the Ohio River and Cincinnati 

canbe readily computed. Assume an influx of 

contamination at Huntington, W. Va., and a 

gage reading of 30.0 feet at Cincinnati. According to figure 8, the discharge at Cincinnati would be 180,000 cfs. From figure 5, by 

interpolation, travel times between Pittsburgh 

and Cincinnati and between Pittsburgh and 

Huntington are 180 hours and 118-hours, respectively. The difference of 62 hours is the 

travel time from Huntington to Cincinnati. 

By similar computations, the travel time of 

water between other points can be determined. 

A more direct way to obtain the travel time 

of water between the cities at the ends of the 

four reaches is to use figure 7; for a discharge of 180,000 cfs, the travel times from 

Pittsburgh to Cincinnati and to Huntington are

shown to be about 173 hours and 117 hours, 

respectively a difference of 56 hours.

TIME OF TRAVEL OF WATER DURING LOW-FLOW PERIODS

Under low-flow conditions, when the Ohio 

River forms a series of pools through which 

flow is very slow, time of travel of water 

estimated by the procedure presented in this 

report maybe substantially in error. Factors 

that affect travel time during pooled conditions are diffusion, wind action, lock operation, and changes in wicket settings. When 

-the discharge at Cincinnati is less than 30,000 

cfs, the time of travel from Pittsburgh is 

more than 600 hours under average conditions. Estimates of travel time of such great 

length are inaccurate, and the probability is 

great that there will ,be marked changes in 

discharge during the intervening period. With 

these uncertainties, frequent monitoring is 

advisable, to ensure that the downstream 

progress of a possible contaminant is known, 

and to aid in revising estimates of the time 

of arrival of the contaminant at critical 

points.

Revision of estimated travel time of water 

is illustrated in the following example. Assume that the accidental introduction of a 

contaminant at Pittsburgh takes place when 

the discharge at Cincinnati is 30,000 cfs. 

From table 4, the corresponding travel time 

from Pittsburgh to Cincinnati is 673 hours, 

and from Pittsburgh to Huntington is 511 

hours. The actual time of travel to Huntington, however, is found by field observation to 

be 550 hours. The initial estimate of travel 

time from Pittsburgh to Cincinnati can now 

be improved as follows: The observed time 

to Huntington is plotted on figure 6 and its 

position is computed to be 16-percent of the 

distance from the 30,000 cfs line to the 20,000 

cfs line. Then by projecting a line downstream 

at this percentage, a revised time of travel 

estimate of 720 hours from Pittsburgh to 

Cincinnati is obtained.

REFERENCE CITED

Searcy, J. K., 1960, Graphical correlation of 

gaging-station records, Manual of hydrology* pt. 1, General surface-water techniques: U.S. Geol. Survey Water-Supply 

Paper 1541-C, p. 67-100.