Principles of Siphons 

With Respect to the 

Artificial-Recharge Studies 

in the Grand Prairie Region 

Arkansas

By R. T. SNIEGOCKI and J. E. REED

ARTIFICIAL RECHARGE OF GROUND WATER GRAND PRAIRIE REGIONj 

ARKANSAS

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1615-D

Prepared in cooperation with the 

U.S. Army, Corps of Engineers, 

and the University of Arkansas

UNITED STATES GOVERNMENT PRINTING OFjFlJCE, WASHINGTON : 1963
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

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

Washington 25, D.C.
CONTENTS

Page

Abstract __ ______________________________________________________ Dl

Introduction._____________________________________________________ 1

Principles of siphons____--_________________________________________ 2

Theoretical concepts___________________________________________ 2

The artificial-recharge system_______________________________________ 4

General description____________________________________________ 4

Hydraulic-gradeline analysis____________________________________ 6

Siphon effects on recharge.._________________________________________ 12

Air entrainment-._-_-_____------___________-_-____-------_____ 12

Cavitation and release of dissolved gases_________________________ 12

Chemical changes____________________________________________ 12

Filter operation-____________________________________________ 13

Water transference ________________ _ _________________________ 13

Injection rates._______________________________________________ 14

Minimizing siphon effects on the recharge system____________________ 17

Summary and conclusions__________________________________________ 18

References cited___________________________________________________ 19

ILLUSTRATIONS

Page

FIGTJBE 1. Map showing location of the Grand Prairie region, Arkansas. _ D2

2. Simplified sketch of a siphon____________________________ 3

3. Sketch showing injection of water from the canal into the

recharge well________________________________________ 5

4. Sketch of recharge well when filter is used to treat injected

water._______________________________________________ 5

5. Schematic representation of gradelines as applied to recharge

system_______________________________________________ 7

6. Scaled plots of hydraulic gradelines when recharging is done

with water from canal________________________________ 8

7. Scaled plots of hydraulic gradelines when recharging is done

with water from filter_______________________-__-_______ 11

8. Hydrograph of water level in observation well 20 feet from

recharge well________________________________________ 15

9. Scaled plot of hydraulic gradelines when recharging is done

with butterfly valve partly closed______________________ 18

m

ARTIFICIAL RECHARGE OF GROUND WATER GRAND PRAIRIE REGION

ARKANSAS

PRINCIPLES OF SIPHONS WITH RESPECT TO THE ARTIFICIAL-RECHARGE STUDIES IN THE GRAND PRAIRIE 

REGION, ARKANSAS

By R. T. SNIEGOCKI and J. E. REED

ABSTRACT

In artificial-recharge experiments in the Grand Prairie region, siphoning has 

caused both favorable and adverse effects. This report discusses these effects 

and methods of utilizing or minimizing them. For any recharge rate, negative 

pressure exists in the injection line when water is siphoned into the recharge 

well. The length of the injection line in which the vapor-pressure limit prevails 

is principally controlled by the depth to water in the recharge well. Filtering 

through a closed system into the recharge well allows the negative head to 

increase normal filter-head loss and destroys filter effectiveness. A valve at the 

discharge end of the injection line provides a means of eliminating negative 

pressure in the line.

INTRODUCTION

In 1953 the Grand Prairie region of Arkansas was -elected for an 

investigation of the principles or artificially rechargrn,? ground-water 

reservoirs in alluvial deposits through wells. This arra (fig. 1) in the 

Coastal Plain of east-central Arkansas provided a large natural 

laboratory in which studies of general interest could be made. The 

U.S. Army, Corps of Engineers, and the University of Arkansas have 

actively participated with the U.S. Geological Survey in these studies. 

State and local agencies, companies, and individuals have given invaluable advice and assistance.

The general plan of study has involved controlled experiments to 

determine the feasibility of artificial recharge using various types of 

wells and water. Two experimental recharge wells were constructed, 

and 22 recharge tests were completed; in the first test ground water 

was used and in the others surface water treated in several ways was 

used. In many of the tests, there have been favorable and adverse 

effects because of siphoning. The purpose of this report is to discuss 

these effects and methods for utilizing or minimizing them.

Dl
D2

r

ARTIFICIAL RECHARGE, GRAND PRAIRIE REGION

7"

FIGURE 1. Map of Arkansas showing the location of the Grand Prairie region.

PRINCIPLES OF SIPHONS 

THEORETICAL CONCEPTS

Physics textbooks commonly refer to a siphon as a conduit that 

conveys liquid from one point to another of lower elevation after 

raising the liquid to a higher elevation at an intermediate point. Negative pressures exist in siphons and are greatest at the summit of the 

conduit; if the negative pressure approaches the vapor pressure of the 

liquid conveyed, the siphon will not flow full. The limiting height 

of the apex of the siphon is the barometric height of a column of the 

liquid conveyed.

These and other siphon characteristics may be comprehended more 

easily by examining the siphon shown in figure 2 and by considering 

the following mathematical relationships. Vessels A and B are subject to virtually the same atmospheric pressure, pa.
PRINCIPLES OF SIPHONS D3

FIGURE 2. Simplified sketch of a siphon. Modified from Weber, White, and Manning

(1952, p. 218).

The atmospheric pressure forcing liquid from A to B is diminished in 

the conduit by the pressure, pgh, of the column of liquid in 

the conduit, where h is the height of the conduit apex above 

the liquid level in A (the maximum value of h in an operative siphon 

transferring water is approximately 34 feet) p is the density of the 

liquid, and g is the acceleration due to gravity. The atmospheric 

pressure forcing liquid from B to A is diminished by the pressure, 

o#Ai, of the column of liquid in the conduit, where &i is the height of 

the conduit apex above the liquid level in B. The net pressure effect 

operating between vessels A and B then becomes

hipg hpg.
D4 ARTIFICIAL RECHARGE, GRAND PRAIRIE REGION

If A becomes greater than the height of a column of liquid that the 

atmosphere can support (h=pa/pg)') the siphon will not operate.

The velocity of flow in a full siphon may be expressed as follows 

(Engineering Hydraulics, 1949, p. 429) :

where h^ is the difference in inflow and outflow elevation and K represents the sum of the loss coefficients in terms of velocity head. 

The quantity, $, flowing through a siphon is expressed as

in which A is the cross-sectional area of the conduit.

The pressure at the summit of a siphon cannot approach absolute 

zero without the formation of discontinuities, and because pa is the 

atmospheric pressure, the maximum value of A for water is about 34 

feet. Dissolved gases always present in natural water, however, come 

out of solution at pressures well above the vapor pressure and collect 

at the apex of the conduit. Thus, A must be appreciably less than 34 

feet or the siphon will not flow full.

A siphon not flowing full may still discharge at a useful rate. 

Surges, however, will occur as intermittent discontinuities develop at 

the summit. This important aspect of siphon operation is discussed 

in a later section of this report.

THE ARTIFICIAL-RECHARGE SYSTEM

GENERAL DESCRIPTION

It is not the purpose of this report to describe in detail the physical 

layout of the equipment used in this study of artificial recharge 

through wells. Under certain conditions, however, the recharge system is analogous to a siphon, and a brief description of the equipment layout is necessary to show this analogy. A diagrammatic 

sketch of the recharge well and attendant water facilities is shown in 

figures 3 and 4.

During the recharge tests at least two siphon conditions existed 

in the recharge system. Consider first a test in which water is taken 

from the canal through a pipeline and injected directly into the recharge well through the pump column (fig. 3) . The canal corresponds 

to A in figure 2, the pipeline corresponds to the conduit, and the recharge well represents B. Thus, the field layout is the equivalent of 

a siphon.
PRINCIPLES OF SIPHONS D5

FIGURE 3. Diagrammatic sketch showing injection of water from the canal into the

recharge well.

Water supply in canal Pump Meter Recharge well and pump

A

a

FIGURE 4. Diagrammatic sketch of the recharge well when a filter is used to treat the

injected water.

681385 63 2
D6 ARTIFICIAL RECHARGE, GRAND PRAIRIE REGION

The following approximate relationships apply to the recharge 

system shown in figure 3: A=4 feet, hi=100 feet, and A2 = 96 feet.

Although the water level in the canal declines slightly as water is 

withdrawn, A is considered to be constant for all practical purposes, 

because the canal conveying water to the project site is in direct connection with a large surface-water reservoir.

The dimensions given for li-i and A2 apply for one period of time at 

a given recharge rate. Buildup of water level in the recharge well 

changes with time because of hydraulic conditions imposed on the 

aquifer by injection. Additional changes in AI and h2 may be caused 

by plugging of the well screen and aquifer.

A siphon condition also exists when a filter is used (fig. 4). Water 

is pumped from the canal to the top of the filter tank. The water 

passes through the filter medium into an uiiderdrain and then through 

the pump column into the recharge well. Under these conditions of 

injection, the filter corresponds to A in figure 2, the underdrain and 

pump column correspond to the conduit, and the recharge well represents B.

The following approximate relationships apply to the recharge 

system shown in figure 4 for one period of time at a fixed recharge 

rate: h=8 feet, A^lOO feet, A^IOS feet.

When water is transmitted from the filter into the recharge well 

under gravity head, the usual definition of a siphon does not apply, 

because the liquid has not been raised to a higher elevation at an intermediate point. The pressure in the injection line, however, becomes negative at some point in the system when flow from the filter 

is restricted, and this negative pressure has the same effect as negative 

pressure created by a siphon. Therefore, in this report, siphon effect 

and siphon conditions refer to negative pressure created in the pipes 

by pipe geometry and head conditions, although the system may not 

meet the usual definition of a siphon. The definition of a siphon may 

be applied algebraically to the foregoing relationships if A is considered to be negative.

HYDRAtTLIC-GEADELINE ANALYSIS

It is generally advantageous to plot hydraulic gradelines to scale 

to aid in visualizing and solving complex problems of pipe flow. A 

hydraulic gradeline is the line of piezometric head and is the plot of 

the resulting sum of pressure head and position for each point along 

the pipe. The method by which siphon-effect gradelines may be 

applied to the recharge system is shown schematically in figure 5. 

It is inconvenient to superimpose scaled gradelines on a scaled drawing of the recharge system; hence, in subsequent representations of
PRINCIPLES OF SIPHONS D7

- 9'H /

FIGURE 5. Schematic representation of hypothetical gradelines as applied to the recharge

system.

siphon effects only the scaled hydraulic situation is plotted. Further simplification is achieved by assuming that the injection line has 

uniform friction loss throughout, no friction loss at elbows and connections, and no entrance and exit losses. Although these assumptions are not valid during recharge, their use does not significantly 

alter the interpretation.

The hydraulic gradelines in the recharge system when water is 

siphoned from the canal into the recharge well are shown in figure 6 

for two different water levels in the well. Construction of the plots 

was based on the following approximate dimensions of the recharge 

system. (See fig. 3.)

Feet

Lift from water level in canal to summit of injection line (h) 4 

Distance from water level in recharge well to summit of injection line at

beginning of injection period (7ti) 100 

Difference between the water level in canal and water level in the recharge

well at beginning of injection period (h2 ) 96 

Distance from water level in recharge well to summit of injection line

(hi), after 50 feet of buildup of water level in recharge well 50 

Difference between water level in canal and water level in the recharge

well (7^), after 50 feet of buildup of water level in the recharge well 46 

Length of pipe from canal to valve _ 70 

Length of pipe from valve to top of well 5 

Length of pipe from top of well to end of tailpipe 125
D8 ARTIFICIAL RECHARGE, GRAND PRAIRIE REGION

140

120'<

100

80

60

40

20

140 

120' 

100

J 

J 

.

80

60

40

20

140

'^i&l&^^il:

>e'

Valve completely open

Zone of positive pressure / _ . , , . ... 

 B ^ ~ Projected pips profile

 Absolute vapor-pressure line

 - Hydraulic gradeline

Head loss caused by 

approaching vapor 

pressure of water V(X: 

and flow of a partly ' 

full pipe

A. Hydraulic-gradeline plot when rscharge rats is 1200 gpm and ths 

water level in the well is 100 feet below the top of the injection line

100

40 -

20 -

Valve partly closed 

Zone of positive pressure J

Head loss caused by 

flow through valve

Head loss caused by 

approaching vapor 

pressure of water 

and flow of a partly 

full pipe

__Atmospheric pressure, pa , at ! 

Ex"Fa|3o7atio~nliiTe"

B. Hydraulic-gradeline plot when re 

charge rate is 500 gpm and the water 

level in the well is 100 feet below 

the top of the injection line

/, Extrapolation line

Valve partly closed

Zone of positive pressure,/ 120 &x^2£££gg^'''-'~'-'

Head loss caused by 

flow through valve

^Atmospheric pressure, /?,,at n 

Extrapolation" line"

Head loss caused by 

80 - approaching vapor 

pressure of water 

and flow of a partly 

60 - full pipe

Extrapolation line

C. Hydraulic-gradeline plot when recharge rate is 500 gpm and the water 

level in the well is 50 feet below the 

top of the injection line

20 40 60 80 100 120 

LENGTH, IN FEET

140 160 180 200

FIGURE 6. Scaled plots of hydraulic gradelines when recharging is done 

with water siphoned from the canal. A, Hydraulic-gradeline plot 

when recharge rate is 1,200 gpm and the water level in the well is 

100 feet below the top of the injection line; B, Hydraulic-gradeline 

plot when recharge rate is 500 gpm and the water level in the well is 

100 feet below the top of the injection line ; G, Hydraulic-gradeline 

plot when recharge rate is 500 gpm and the water level in the well is 

50 feet below the top of the injection line.
PRINCIPLES OF SIPHONS D9

The smoothness and continuity of the lines on the plots (figs. 6^4, 

65, and 6(7) are the result of the assumptions regarding head losses 

in the recharge system. The slopes of the lines were determined by 

use of three factors the physical dimensions of the recharge system, 

a maximum observed rate of flow of the siphon of about 1,200 gpm 

(valve completely open), and a negative head in the pipe of 34 feet 

or less.

In figure 6A the difference in head (elevation) between a and 5 represents the head loss between the two points in the pipe when the flow 

is 1,200 gpm. The head loss throughout the length of the pipe would 

be 80 feet. Differences in the water level in the canal and in the well 

(A2 ) show an available head of 96 feet. The difference of 16 feet between the available head and the head loss was caused by pressure in 

parts of the injection line approaching the vapor pressure of water 

when the siphon was operated at 1,200 gpm. The valve controlling 

flow into the recharge wel] was completely open at this flow rate.

The hydraulic-gradeline plot (fig. 6A) was constructed to determine the amount of head loss caused by pressure approaching the 

vapor pressure of water when the pipe is flowing partly full. Because 

recharge tests generally were made at 500 gpm or less, no further 

consideration will be given figure 6A in interpretation of the siphon 

effects.

The rate of flow through a pipe is approximately proportional to 

the square root of head. A flow of 500 gpm through the recharge 

system would require a head loss of 14 feet, which is represented by 

ee' in figure 65 and jj' in figure QC, Because 96 feet of head is available, the valve must be closed if flow is to be reduced. Closing the 

valve so that the siphon discharges at 500 gpm causes a head loss 

through the valve of about 24 feet (fg and kl, figs. 65 and 6(7, respectively) . The resultant additional head loss (loss in excess of that 

in a full pipe) must be accounted for, but, as shown in figures 65 and 

66', it is dependent upon the water level in the recharge well. Accordingly, the head loss at a recharge rate of 500 gpm is 58 feet when 

the water level is 100 feet (gh, fig. 65). When the water level is 50 

feet, the head loss is 8 feet (Zm, fig. 6(7). These losses are caused by 

negative pressure in the line approaching the vapor pressure of water 

when the pipe is flowing partly full, as when water is siphoned at 

1,200 gpm.

The plots show that for any recharge rate, negative pressure will 

exist in the injection line when water is siphoned into the recharge 

well, and the water level in the recharge well controls the length of 

pipe in which negative pressure prevails. Furthermore, the valve 

must be opened as the depth to water in the well decreases, if a con-
D10 ARTIFICIAL RECHARGE, GRAND PRAIRIE REGION

stant recharge rate is to be maintained. The following table shows 

the decline in injection rate recorded when water was siphoned into 

the well without changing the valve setting.

Injection rates and depths to water, recharge test 20, March 10,1959

Time (minutes)

0-.. .....................

6... .... .. _ ___

7_ __

10 .... .

15 __

30 

45-. 

Injection

rate

(gpm)

(')

320

316

315

313

Depth to

water in

recharge

well (feet

below

measuring

point)

97. 8

83.1

80.3

79.9

Time (minutes)

90 

180 

305 . -- -

31S1,355-... - ..

1,360 

Injection

rate

(gpm)

311

302

305

238

Depth to

water in

recharge

well (feet

below

measuring

point)

78.fi

77.6

74.9

51.7

1 Begin recharge.

The hydraulic gradelines in the recharge system when recharging 

is done with water from the filter at two different water levels in the 

recharge well are shown in figure 7. Construction of the plots was 

based on the following approximate dimensions of the recharge system 

(fig. 4) and the simplifying assumptions used in constructing the 

gradeline analyses in figure 6.

Feet

Height of water level in filter above injection line (70 ____________ 8 

Distance from water level in the recharge well to summit of injection

line at beginning of injection period (h^ ___________________ 100 

Difference between water level in filter and water level in the recharge

well at beginning of injection period (h2 ) ___________________________ 108

Distance from water level in the recharge well to summit of injection

line (lii), after 50 feet of buildup of water level in the recharge well___ 50 

Difference between water level in filter and water level in the recharge

well (h3 ), after 50 feet of buildup of water level in the recharge well___ 58 

Length of pipe from filter to valve________________________ 20 

Length of pipe from valve to top of well_____________________ 5 

Length of pipe from top of well to end of tailpipe_______________ 125

When recharging under closed-system conditions between the filter 

and the recharge well, the length of pipe over which negative pressures occur becomes less with a buildup of water level in the well. 

The injection rate decreases unless the valve controlling the flow is 

opened. This is demonstrated by the data shown in the following 

table.
PRINCIPLES OF SIPHONS Dll

140

120

100

80

60

40

20

Water level 

in filter

Head loss caused by < 

flow through valve

Filter base

Valve partly closed

Projected pipe profile

 Absolute vapor-pressure line 

_._._._ Hydraulic gradeline through filter

 Hydraulic gradeline through pipe

!|f!

Head loss caused by Ng>

approaching vapor 

pressure of water 

and flow of a partly 

full pipe

A. Hydraulic-gradeline plot when recharge rate is 500 gpm and the water 

level in the well is 100 feet below 

the top of the injection line

Valve opened more than in figure 7A

Head loss caused by 

flow through valve

Head loss caused by approaching 

vapor pressure of water and 

flow of a partly full pipe

B. Hydraulic-gradeline plot when recharge rate is 500 gpm and the water 

level in the well is 50 feet below the 

top of the injection line

100 120 140 160 180 200

LENGTH, IN FEET

FIGURE 7. Scaled plots of hydraulic gradelines when recharging is done 

with water from the filter. A, Hydraulic-gradeline plot when recharge rate is 500 gpm and the water level in the well is 100 feet 

below the top of the injection line ; B Hydraulic-gradeline plot when 

recharge rate is 500 gpm and the water level in the well is 50 feet 

below the top of the injection line.

Injection rates and depths to water, recharge test 2, March 28,1956

Time (minutes)

0 ..... . _. _ -. .

3

28..........................

31 . 

66-.. ._.__ _ .-__._--.

Injection

rate 

(gpm)

(')

600

520

500

Depth to

water in

recharge

well (feet 

below

measuring

point)

290

n

o

Time (minutes)

79_--_ -.. ._._, 

119-..- _ _____ -

131-.. ._.._ _. . 

163 _ _. _ 

203 _ . ........

Injection

rate 

(gpm)

500

495

495

495

Depth to

water in

recharge

well (feet 

below

measuring

point)

67.2

J Begin recharge. 

' Estimated.
D12 ARTIFICIAL RECHARGE, GRAND PRAIRIE REGION

A similar condition of flow decline can be observed when filtering 

to waste. If interstices of the filter bed become clogged, the filter 

output decreases. If the effluent valve is opened, the head loss through 

the filter is increased and the flow is maintained; however, if the 

valve is opened to maintain flow when filtering through a closed 

system into the recharge well, the negative head caused by the siphon 

effect increases the normal filter head loss and the total head loss 

through the filter soon exceeds the physical limitations of filter depth. 

(Compare the length of filter gradelines in figs. 1A and IB.)

SIPHON EFFECTS ON RECHARGE

AIR ENTRAINMENT

When the pressure inside the injection line is less than the atmospheric pressure, air enters the line if there are any leaks, however 

small. Pinhole leaks in welded joints, loose valve shafts, worn grease 

seals, and improperly connected couplings provide entrances for air 

that are difficult to eliminate. Ordinarily, such leaks cannot be detected when the pipeline is under positive pressure, but they will 

allow air to enter when the pressure is less than the atmospheric 

pressure.

The arrangement of the injection line, controlled injection rates, 

and the resultant siphon condition make air entrainment a major 

cause of clogging in the recharge well and aquifer. Air entrainment 

as a clogging factor was discussed in another report (Sniegocki, 

1959).

CAVITATION AND RELEASE OF DISSOLVED GASES

Pressure reduction in the injection line due to the siphon effect 

causes the release of dissolved gases and cavitation of the recharge 

water. This is another possible cause of air binding and may be 

more difficult to control. Water vapor formed in the area of negative pressure condenses to water when positive pressure is restored. 

The released gases, however, do not go back into solution instantaneously and could reduce aquifer permeability, as when air is introduced from an outside source. No data have been collected to 

support the possibility of clogging of the recharge well by air 

released from solution in the injected water.

CHEMICAL CHANGES

Pressure effects also alter the chemical balance of dissolved solids 

in the recharge water. Chemical precipitates are formed by reduction in solubility caused by reduced pressure and by increased 

dissolved-solids contents when part of the water is vaporized. The
PRINCIPLES OF SIPHONS D13

iron content of the water is especially affected by the reduction of 

pressure to less than atmospheric pressure and by subsequent cavitation of the water, which causes iron to precipitate. Such changes 

have been observed in laboratory tests and, consequently, must be 

considered possible in the recharge studies, even though no supporting data have been collected.

FILTER OPERATION

When the increased head loss allowed by the siphon effect exceeds 

the height of the filter (figs. 7A and 75), flow lines through the filter 

medium are altered and the throughput of water per square foot 

over part of the filter-bed surface is increased. During a test in which 

a closed-system injection line was used between the filter and the 

recharge well, a negative pressure of 7.5 inches of mercury was measured at the bottom of the filter tank. As the negative pressure caused 

part of the filter mat (floe mat) to be pulled through the filter medium, water of inferior physical quality resulted. The filter medium 

also may have been downwarped; this condition would have decreased 

the thickness of the filter medium and allowed water to move down the 

sides of the filter tank. An increase in turbidity of as much as 30 

ppm was noted in the filter effluent when the head loss through the 

filter was allowed to exceed the filter height.

WATER TRANSFERENCE

The siphon effect (negative pressure) created by recharge under 

closed-system conditions was used to advantage in several recharge 

tests. When transferring water from the canal directly into the 

recharge well, the siphon was primed by filling the injection line 

with water pumped from the recharge well. When the pump was 

stopped, the direction of water movement reversed and water flowed 

from the canal to the well.

A clear well was constructed to receive the filter effluent. The 

siphon was primed as above and used to move water from the clear 

well into the recharge well. The length of pipe from the clear well 

to the top of the recharge well was only about 8 feet, resulting in fewer 

joints and fewer chances for pinhole leaks, whereas there was more 

than 100 feet of pipeline from the canal to the recharge well. Although the siphon effect was of some use in recharge operations, the 

benefits derived may have been seriously offset by problems created 

when operating with negative pressure in the injection line.
D14 ARTIFICIAL RECHARGE, GRAND PRAIRIE REGION

INJECTION BATES

Water was transferred from the canal to the recharge well by 

siphoning during one of the recharge tests (test 20). Daily observations were made on all equipment and control points as the test 

progressed. The injected water ranged in turbidity from 40 to more 

than 150 ppm. The water temperature ranged from 48° to 66° F 

and averaged 54.1° F. The water was injected at a rate ranging 

from 47 to 367 gpm and averaged about 240 gpm. Chlorination, at 

a rate ranging from 0 to 20 pounds of chlorine, per day, was the only 

water treatment used. The specific capacity of the recharge well was 

20 gpm per ft of drawdown at the beginning of the test and 2 gpm 

per ft at the end; these data indicate severe plugging of the well and 

aquifer. Apparently, suspended solids were the principal cause of 

clogging, but there was a possibility of air entrainment.

An automatic water-level recording gage was maintained in an 

observation well 20 feet from the recharge well througout the test 

period (March 10-29, 1959). A typical part of the hydrograph for 

the period of recharge from March 24 through March 28, 1959, is 

shown in figure 8.

Injection of water was stopped periodically, and the deep-well turbine pump was used to redevelop the recharge well by surging and 

pumping. The redevelopment periods are conspicuous in the hydrograph (fig. 8). Upon completion of the surging and pumping, recharge was resumed. If the recharge rate was too low, the valve in 

the injection line at the recharge well was opened slightly. The 

change in injection rate caused by valve adjustment is indicated by 

a characteristic "pip," or an abrupt change in the water level shown 

in the hydrograph. These pips are indicated in figure 8 as rate 

increases caused by opening the valve.

As the water level in the recharge well rose during each cycle of 

injection, the negative head in the injection line decreased. The 

resulting gradual decline in injection rate (recorded to be as much as 

150 gpm) is apparent in the hydrograph as an increase in depth to 

water between the beginning and end of a recharge cycle. For 

example, on March 24, 1959, the depth to water in the observation 

well was about 92.4 feet at 1200 when the injection rate was about 

300 gpm. Near the end of the same cycle of recharge at 0800 on 

March 25, 1959, the depth to water in the observation well was 93.0 

feet and the injection rate was about 190 gpm. The overall decline 

in water level in the observation well during the next three cycles of 

recharge (fig. 8) is not as great as it would have been if the recharge 

rate had not been increased by opening the valve after 4 or 5 hours 

of injection.
1959

Recharge rate 

increased by 

opening valve

FIGURE 8. Hydrograph of the water leyel in an obseryation well 20 feet from the recharge well.
D16 ARTIFICIAL RECHARGE, GRAND PRAIRIE REGION

The changes in water level recorded in the observation well (see 

examples designated "X" during first cycle of recharge in fig. 8) are 

not as readily explained as the changes caused by opening the valve 

and increasing the rate of recharge. The recording gage was checked 

and was operating satisfactorily, and none of the water-level changes 

could be attributed to malfunctioning of the observation well. No 

correlation existed between changes in atmospheric pressure and 

changes in water level. Once, however, a temporary increase in the 

injection rate was observed, and the water level in the recharge and 

observation well rose in response. Furthermore, the shape of each pip 

suggests a sudden but temporary rate change which quickly reverts 

to the previous rate. It was assumed, therefore, that each pip was 

caused by rate changes within the injection line, causing more water 

to enter the recharge well.

The anomalous change in water level in the observation well originally was throught to be related to plugging of the recharge well and 

the aquifer by air entrainment and suspended solids. As plugging 

occurred in and near the recharge well, the head in the well rose and 

may have caused the plugging material to break and let a sudden 

surge of water into the aquifer. The depth to water in the recharge 

well, however, did not become greater as the water level in the observation well rose. It was concluded tentatively that a breaking 

up of clogging material was not related to the pips in the hydrograph 

shown in figure 8.

Dissolved gases in natural water come out of solution at pressures 

greater than the vapor pressure of water. These gases collect at 

high points in a conduit and cause discontinuities and surges in flow. 

It was concluded that cavitation resulting from the siphoning of 

water from the canal into the recharge well caused temporary changes 

in the injection rate, these changes in rate affecting the water level in 

the observation well.

Another recharge test (test 21) was set up to collect additional data 

on the anomalous changes in water level in the observation well. An 

electric pump with a valve on its discharge side was installed in the 

injection line to permit water transference from the canal into the 

recharge well without using a siphon. The pump was placed near 

the water supply to make the suction side of the line as short as possible 

and to thereby reduce the possibility of air entrainment. By operating the pump, pressure would be increased in the injection line. During test 20 (before the electric pump was installed), water did not flow 

from a sample valve in the injection line located about 18 feet from the 

recharge well; instead, the valve allowed air to enter the line. This 

behavior indicated that pressure in the system was less than atmos-
PRINCIPLES OF SIPHONS D17

pheric pressure at that point. When the electric pump was operated 

during test 21, water flowed from the sample valve when opened; this 

behavior indicated that pressure was positive at that point. Although 

all possible causes of the anomalous water-level changes in the observation well were though to have been eliminated, they were still in 

evidence during test 21. Test 22 was made in the same manner as 

test 21 but at an average recharge rate of 37 gpm. Similar pips were 

observed on the hydrograph but at a much reduced amplitude.

Hydraulic-gradeline analysis showed that even though the pump 

was used in water transference during tests 21 and 22, negative pressure could exist in the system at some point between the pump and the 

the end of injection line. The point of negative pressure must have 

been located in the injection line near the top or inside of the recharge 

well or water would not have flowed through the sample valve when 

it was opened.

It was concluded that discontinuities of flow in the system would be 

virtually impossible to eliminate as long as the layout of the injection 

line was not changed.

Hydraulic-gradeline analysis showed that the pump used to transfer 

recharge water should be near the recharge well and that the valve on 

the discharge side of the pump should not be used to control injection 

rates if negative pressure on the discharge side of the pump is to be 

eliminated.

MINIMIZING SIPHON EFFECT ON THE RECHARGE

SYSTEM

Several methods may be used to minimize or eliminate siphon effects when recharging under the conditions mentioned in this study.

The simplest method is to place a large opening or vent in the injection line between the source of water and the recharge well. This 

provides for entrance of air so that the line pressure is in equilibrium 

with atmospheric pressure. Air-entrainment problems, however, may 

be intensified greatly unless care is taken to select a pipe whose diameter is large enough to deliver the flow required but is small enough to 

create enough friction to cause positive pressure in the line.

If a clear well is used to receive the filter effluent, the siphon effect 

will be prevented from operating on the filter by providing an interruption in the hydraulic continuity of- the pipeline between the filter 

and the recharge well. Siphoning of water from the clear well into 

the recharge well would permit more efficient filter operation. Cavitation effects, possible air leaks, and consequent air entrainment would 

not be eliminated, however.
D18 ARTIFICIAL RECHARGE, GRAND PRAIRIE REGION

By recharging under constant-head conditions with the water level 

in the well at the land surface and allowing the injection rate to 

change, the siphon effect and possible air entrainment can be eliminated. In the High Plains near Lubbock, Tex., water was injected into 

wells at a rate sufficient to raise the water level in the recharge well to 

the elevation of the source of water. This method of introduction of 

water into a recharge well was considered in this study; however, less 

experimental variation is possible and treatment of water in various 

ways becomes more difficult by this method. Furthermore, because 

water velocity through the screen is undesirably high and injection 

heads are greatest, redevelopment of the recharge well is made more 

difficult.

The most satisfactory method for eliminating the siphon effect used 

in this study was the installation of a butterfly valve at the bottom of 

the injection line inside the recharge well. The valve was rigged for 

manual operation at the surface by means of a long shaft. The 

hydraulic-gradeline plot shown in figure 9 demonstrates the effectiveness of the valve in creating positive pressure throughout the 

injection line.

140

120

100 

j 

; so

j

! 60

j 

c

40

20

Water levelin filter

/Filter base

i Projected pipe profile 

~ " Absolute vapor-pressure line 

_._._.. Hydraulic gradeline through filter 

 Hydraulic gradeline through pipe

Head loss through partly 

closed butterfly valve \ 

\\>

\

II.

vValve

\___L

20 40 60 80 100 120 140 160 180 200 

LENGTH, IN FEET

FIGURE 9. Scaled plot of hydraulic gradelines when recharging is done 

with the butterfly valve partly closed.

SUMMARY AND CONCLUSIONS

Siphon conditions may cause difficulty in artificial-recharge operations by creating negative pressure in the injection line. Air entrainment, caused by the entrance of air through pinhole leaks due to 

negative pressure in the pipeline is a major cause of clogging in the
PRINCIPLES OF SIPHONS D19

recharge well and the aquifer. Another source of air binding is the 

release of dissolved gases and cavitation of the recharge water. Pressure effect may cause the formation of chemical precipitates 'by the reduction in solubility and increased dissolved-solids content. Also, the 

effectiveness of the filter operation is reduced by the increased head 

loss allowed by the siphon effect.

REFERENCES CITED

Bouse, Hunter, ed., Engineering hydraulics, Proceedings of the Fourth Hydraulics Conference, Iowa Institute of Hydraulic Research, June 12-15, 

1949, Engineering hydraulics: New York, John Wiley and Sons, Inc., 1,039 p.

Sniegocki, R. T., 1959, Plugging by air entrainment in artificial-recharge tests: 

Water Well Jour., v. 13, no. 6, p. 17-18, 43.

Weber, R. L., White, M. W., and Manning, K. V., 1952, College physics: New 

York, McGraw-Hill Book Co., Inc., 820 p.

U.S. GOVERNMENT PRINTING OFFICE: 1963