Alluvial Aquifer in 

Northeastern Louisiana 

A Large Source of Water

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1619-V

Prepared in cooperation with the 

Louisiana Department of Public ff^orks 

and the Department of Conservation, 

Louisiana Geological Survey
Alluvial Aquifer in 

Northeastern Louisiana 

A Large Source of Water

By A. N. TURCAN, JR., and R. R. MEYER

CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1619-V

Prepared in cooperation with the 

Louisiana Department of Public ff^orks 

and the Department of Conservation, 

Louisiana Geological Survey

UNITED STATES GOVERNMENT PRINTING OFFICER WASHINGTON : 1962
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. __________________________________________________________ VI

Introduction-______________________________________________________ 1

Purpose and scope________-___________-_______-_-_--___--_-.__- 1

Acknowledgments- __-______________-._________---___-___-__-__- 2

Physiography.________________________________________________ 2

Geology. __________________________________________________________ 4

Tertiary bedrock._-____-_______________-__-____-___--____-_-__ 4

Quaternary alluvium____-___________._-_____-___-___-_-_____,-,_ 6

Pleistocene series.-_____.._-._-.___-__-_-_-_-_--_-_-____-___- 6

Recent series._________-.__--__-.-_____-______-_-_--__-.___^ _ _ 8

Hydrology___--__-____._.___________________ _____________________ 9

Occurrence.__________________________________________________ 9

Pumping tests_____________-________-__-_____---_--_____.___ 10

Theoretical effects of pumping._________--_______-_____-___-__-._ 16

Nonequilibrium method.________-______-____-_-.____---____ 17

Equilibrium method-___________________-_-_-_-__--_---._-_ 18

Water wells____._______.._-__.-____.____._.__________________-_- 20.

Test drilling._________________________________ ______.________ 20

Well construction._____________________________________________ 21

Drilling problems________________________________________ 22

Screen selection._____-__-___.____-__-_--___--_----_.-_____ 22

Development--__---___- ________________________________________ 23

Specific capacity...._____---__--__-______-___-__--___--___- 25

Pumps. ---__._____-.-_--_____________--___-__-__-._--_.___-_-_ 25

Potential supply summarized-.--.-------.--------------.-.---------- 26

Selected references.________________________________________________ 27

in
IV CONTENTS

ILLUSTRATIONS

Page

FIGUBE 1. Isopach, structure, and location map of the Tallulah area_... V5

2. Geologic section of the Quaternary alluvial deposits _________ 6

3. Hydrograph showing effect of barometric pressure changes on

water level in well Ma-12, May 1957________________ 10

4. Hydrograph showing effect of barometric pressure changes on

water level in well Ma-12, November-December 1956_____ 11

5. Location and construction data of pumped and observation

wells_____________________________________________ 12

6. Logarithmic time-drawdown plot for well Ma-25-2________ 13

7. Relation of apparent storage coefficient to time _____________ 14

8. Semilogarithmic time-drawdown plot of water levels in well

Ma-25-2__________._____---___-__-____-_____- 15

9. Semilogarithmic time-drawdown plot of water levels in well

Ma-25----__._._________----__----_-____--_-_-- 17

10. Semilogarithmic distance-drawdown relation for alluvial

aquifer.---__-_______-_-__ _______-_____-__--___-____-- 19

TABLES

Page

TABLE 1. Measured operating yield and specific capacity of experimental

irrigation wells in the Tallulah area__________-___--___-_ V25

2. Specific capacity of irrigation wells in northeastern Louisiana and

northwestern Mississippi-------------------------------- 26
CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

ALLUVIAL AQUIFER IN NORTHEASTERN LOUISIANAA LARGE SOURCE OF WATER

By A. N. TURCAN, JR., and E. E. METER

ABSTRACT

A properly constructed and developed well screened in the alluvial aquifer 

in the Mississippi River valley in northeastern Louisiana, especially in the 

vicinity of Tallulah in Madison Parish, would be capable of pumping as much 

as 7,000 gpm (gallons per minute) without causing excessive water-level declines. To induce recharge from the Mississippi River, which also serves as 

a drain for the aquifer, large quantities (more than 100 million gallons per 

day) of water would have to be pumped from wells near the river.

To determine the optimum yield of wells and to provide a relatively economical 

source of irrigation waters in the Tallulah area, the Louisiana Department of 

Public Works installed three experimental wells in the alluvial aquifer. During 

the drilling, installation, and testing of these wells, hydrologic and geologic 

data on the aquifer were obtained. The permeability of the semiconfined alluvial aquifer is 1,700 gpd (gallons per day) per sq ft. Calculations were 

made using the nonequilibrium method of analysis and the data obtained in 

the early part of the test when water was released instantaneously from storage.

Observed pumping-test data and the equilibrium method of analysis were 

used to approximate the theoretical effect of pumping; that is, when the cone 

of depression reaches equilibrium in form, and drainage from the semiconfining 

material is relatively uniform.

INTRODUCTION

PURPOSE AND SCOPE

The agricultural growth in the Mississippi Kiver alluvial valley 

of northeastern Louisiana, where Tallulah is located (fig. 1), depends 

largely upon the availability of water and an inexpensive means of 

water transmission. The Mississippi River and the alluvial deposits 

underlying the area are sources of large amounts of water for irrigation; however, the use of river water would require large pumping 

plants and a costly distribution system. Streams in the Tallulah area, 

such as Eoundaway and Walnut Bayous, which bisect most of the 

agricultural land, are sources of irrigation water except during dry

VI
V2 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

periods. These bayous and the large quantities of ground water in 

the interstream areas offer an economical solution to the problem of 

having irrigation water available when and where it is needed.

The Louisiana Department of Public Works made plans, based on 

sound hydrologic and engineering principles, for the proper recovery 

of ground water. In the spring and summer of 1956, four test holes 

were drilled to locate favorable sites for wells along either Roundaway 

or Walnut Bayous. Three experimental wells were designed, installed, and developed on the basis of the quantity of water needed 

and the analysis of test-drilling data. The results were considered 

excellent in that the wells, whose yield was the highest on record in 

that part of the Mississippi River alluvial valley, provide an adequate 

quantity of water to supplement the flow of streams during the irrigation season.

As a part of the ground-water investigation being made in cooperation with the Louisiana Department of Public Works and the Louisiana Department of Conservation, data were collected and analyzed. 

This paper contains a brief discussion of physiographic and geologic 

conditions in the area; an analysis of data gathered during the drilling of the test holes and the testing of the experimental irrigation 

wells; a summary of well construction and development methods; and 

a summary of the analyses of data obtained during a pumping test 

made at one of the well sites.

ACKNOWLEDGMENTS

Most of the field data were gathered by personnel from the northeastern district of the Louisiana Department of Public Works under 

the supervision of S. C. Smith, District Engineer, and George Johns, 

Area Engineer. Acknowledgment also is given the Madison Parish 

Police Jury who permitted tests to be made on the experimental wells. 

Special thanks are given Mr. A. Kell on whose property observation 

wells were installed.

PHYSIOGRAPHY

The Tallulah area is in the Mississippi Alluvial Plain section of the 

Coastal Plain province (Fenneman, 1938, p. 65-99). The relief in the 

area is about 20 feet; the crest of the natural levee is at an altitude of 

about 90 feet and the lowest backswamp area at about 70 feet. The 

principal topographic features are natural levees and swamps.

The natural levees are restricted to the areas that border existing 

or abandoned stream channels. They are asymmetrical in profile; 

their crests border the stream, and their surfaces slope gently away 

from the river and merge into the backswamps. The maximum width 

of the natural levees adjacent to the Mississippi River is approximately
ALLUVIAL AQUIFEE, NORTHEASTERN LOUISIANA V3

2 miles, but the width of those adjacent to the small streams is about 

half a mile. Both the width and the height of the natural levees have 

adjusted to the flood heights of the parent streams. The altitude of 

the levees gradually decreases downstream; for example, the crest of 

the natural levee along Walnut and Eoundaway Bayous declines about 

5 feet in 35 miles.

The origin of the natural levees is ascribed to the decrease in velocity of the river water when it overflows the banks. The lower velocity causes deposition of load in decreasing amounts away from the 

stream until the landward slope of the levee reaches approximate 

equilibrium with the volume of water that overflows the crest of the 

levee.

In the Tallulah area, swamps generally are restricted to the interstream areas beyond the landward limit of the natural levees. The 

forested swamps are replete with concentric meander scars which are 

remains of the parent stream. Many of the scars contain shallow 

lakes, which are bordered by low ridges. The distribution of these 

lakes and ridges depicts the history of lateral cutting and deposition 

by former streams in the area.

The streams in the Tallulah area contrast greatly in amount of 

flow, depth, and other characteristics. The Mississippi Eiver, which 

bounds the area on the east, is the largest river on the North American 

continent, whereas the Walnut-Eoundaway Bayou system, which 

meanders through the heart of the area, contains little or no water 

during dry periods. The Mississippi Eiver above Vicksburg, Miss., 

which is just a few miles downriver from the Tallulah area, drains an 

area of 1,144,500 square miles. The maximum flow is estimated to be 

2,278,000 cfs (cubic feet per second) and the minimum flow is 91,800 

cfs (U.S. Army Corps of Engineers, 1950). The average channel 

width is about 2,500 feet, but where the course of the river has been 

altered by artificial means, the channel is narrower; for example, 

the width of the channel at the Marshall cutoff is approximately 1,600 

feet. Although the Tallulah area is about 450 river miles upstream 

from the mouth of the Mississippi Eiver, the river has scoured its 

channel to as much as 50 feet below sea level on the outside of meanders (U.S. Army Corps of Engineers, 1950, sheet 73). Between 

meanders the maximum depth of the channel is about at sea level.

The principal streams west of the Mississippi Eiver are Walnut and 

Eoundaway Bayous. Walnut Bayou begins near the artificial levee 

bordering the Mississippi Eiver northwest of Tallulah and follows 

a meandering course for about 10 miles roughly parallel to the Mississippi Eiver, whence it reverses direction and flows northwestward 

through Tallulah and enters Eoundaway Bayou. Eoundaway Bayou
V4 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

flows southeastward out of the area and eventually enters the Tensas 

Eiver. The natural levees bounding the Walnut-Boundaway Bayou 

system have long been areas of habitation, as shown by the numerous 

Indian mounds. Today the natural levees form the principal agricultural land of the area. The importance of these landf orms to the 

economy of the area is indicated also by the division of the townships 

into sections. South of Tallulah, the sections have not been surveyed 

into the normal plots of 1 square mile but rather into narrow strips, 

normal to the stream, that have a minimum width of about 500 feet 

and a maximum length of about l1/^ miles. Division of the land into 

narrow sections is probably the result of the desirability of the high 

area of the natural levee bordering the streams.

Artificial levees have been constructed to a height of about 25 feet 

adjacent to the west bank of the river. Gradual shifting of the river 

channel has breached the old levees in some places, and new levees 

have been constructed more distant from the river.

The natural levees of the Walnut-Roundaway Bayou system perform an important hydrologic function in that most of the water 

from precipitation flows down the slope of the levees toward the backswamps and not toward the bayous. Only a few short tributaries and 

some drainage ditches enter the streams; consequently, the flow of 

the bayous depends chiefly on water from precipitation on the relatively narrow strip between natural-levee crests. If the flow of the 

Walnut-Roundaway Bayou system was adequate, it would form an 

ideal source of irrigation water, as the natural levees slope gently 

away from the bayous, and the course of the bayous bisects most of the 

potential irrigable land.

GEOLOGY

Viewed broadly, the general geology of the Tallulah area is very 

simple. The Tertiary bedrock in the area is considered to be of Eocene 

or Oligocene age. The bedrock is overlain unconf ormably by Quaternary alluvium deposited by the Mississippi River and its 

distributaries.

TEBTIABY BEDBOCK

The Tertiary bedrock immediately underlying the alluvium is 

composed principally of clay of the Jackson group of Eocene age 

and of the Vicksburg group of Oligocene age. South of the Tallulah 

area, where their full thickness is represented on electrical logs, the 

two groups are composed chiefly of clay and, consequently, are difficult 

to distinguish on the basis of rock type. The full thickness of the 

Vicksburg and Jackson groups, as shown by electrical logs, is about 

550 feet. The groups have been beveled by erosion in the Tallulah 

area, and 1 mile north of Tallulah their thickness is only 150 feet.
ALLUVIAL AQUIFER, NORTHEASTERN LOUISIANA V5 

R.I2E. i R.I3E. R.IE. ,R,2E. R.I4E.

Map source: Army Map Service, 

Talla Bena Quadrangle, 1939

EXPLANATION

 75 

Thickness of

alluvial aquifer,

in feet

Contour drawn on

base of alluvium

Contour interval, 25 feet

Datum is mean sea level

Revetment

Levee

Lake

0

Experimental irrigation well

o 

Control point

1234 MILI

FIGURE 1. Location map of the Tallulah area showing physiographic features; location of 

experimental irrigation wells; the base of the alluvium and the thickness of aquifer, 

by contours; and location of generalized section A A'. (See fig. 2.)

643873 62 2
V6 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

The irregularities in the eroded surface beneath the Quaternary alluvium are illustrated in figures 1 and 2.

Although electrical logs of oil test wells indicate that deep sands 

underlying the Jackson and Vicksburg groups in the eastern part of 

the Tallulah area may contain relatively fresh water, the principal 

hydrologic significance of the Tertiary bedrock is its function as an 

effective confining bed below the principal aquifer of the area.

120'

80 L

£ 

^.^J J.

FIGURE 2. Generalized geologic section of the Quaternary alluvial deposits near

Tallulah.

QUATEBNABY ALLUVIUM 

PLEISTOCENE SERIES

The Quaternary alluvium is composed of two distinct but graditional rock types the basal sand and gravel and the overlying silt 

and clay. The sand and gravel overlying Tertiary rocks in the principal stream valleys of Louisiana has been interpreted as Pleistocene 

in age by some geologists and as Recent by others. J. L. Poole (1961) 

gives reference to and a brief history of the various interpretations 

and concludes that in East Carroll Parish the sand and gravel phase 

of the alluvium is Pleistocene in age and the overlying silt and clay 

is Recent. East Carroll Parish is adjacent to the northern boundary 

of the Tallulah area, and the sand and gravel can be correlated easily 

from one area to the other. In addition to the evidence given by 

Poole, carbon-14 determinations show the age of the sand in the upper 

part of the alluvium in West Baton Rouge Parish to be about 21,000 

years (U.S. Army Corps of Engineers, 1950). Thus the age inter-
ALLUVIAL AQUIFER, NORTHEASTERN LOUISIANA V7

pretation in this report conforms to that used by Poole; namely, in 

the Tallulah area the alluvial sand and gravel is considered Pleistocene, and the overlying silt and clay is Recent.

One of the most distinctive features of the Pleistocene deposits is 

the upward, gradation in grain size from the large gravel near the 

base of the deposits to the very fine sand underlying the silt. The 

material near the base of the deposit ranges in grain size from very 

coarse sand to small boulders. One small limestone boulder having 

a maximum dimension of lO1/^ inches was brought to the surface by 

drilling along the upper reaches of Walnut Bayou. The material 

overlying the sand and gravel grades in grain size from coarse sand 

to very fine sand at the top of the unit. The upper fine-grained sand 

merges into the silt of the overlying natural levee and backswamp 

deposits.

In Louisiana, the alluvial sand and gravel extends along the Mississippi River valley from the Arkansas State line southward, where it 

merges with marine sediments near the Gulf of Mexico. At the latitude of Tallulah, the sand and gravel was deposited on the eroded surface of the Tertiary bedrock from the highlands east of the Mississippi River to the bluff forming1 the west bank of the Ouachita River.

Although the base of the Pleistocene deposits is easily defined because of the change in material from sand and gravel to clay, the 

upper contact is difficult to determine precisely because of the upward 

gradation in grain size from very fine sand to silt. Because of this illdefined upper contact, the aquifer thickness reported in drillers' logs 

for a group of wells that have been drilled in one area may differ considerably. For example, the reported aquifer thickness at Tallulah 

ranges from 40 to 118 feet. Although there may be some difference in 

the thickness of the deposits within a small area, the wide range in 

reported thickness is probably due to differences in drilling techniques 

and interpretation of the upper contact of the Pleistocene deposits. 

The contours on figure 1 showing the aquifer thickness are based on 

the data that are interpreted as being the most nearly correct.

The Pleistocene sand and gravel lies unconformably on the eroded 

surface of the Tertiary rocks (fig. 2). The contours in figure 1 show 

the surface of the Tertiary rocks in the area to range from about 50 

feet to slightly more than 100 feet below sea level. The surface, which 

is irregular and shows the effect of scour by the ancestral Mississippi 

River, has a general southward dip. During the Pleistocene epoch, 

the deepest scours in the Tertiary surface were filled with sand and 

gravel. Therefore, as shown in figure 2, the thickness of the sand and 

gravel is affected principally by the depth of the Tertiary rocks. The 

thickness ranges from about 50 feet in the northern part of the area 

to 170 feet in the southern part. (See fig. 2.)
V8 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

The sand and gravel is the most productive aquifer in the entire 

Mississippi River valley, and in the Tallulah area it is the only developed source of ground water. The great potential yield from this 

aquifer results not only from the high permeability of the sand and 

gravel but also from the large amount of water available from recharge or potential recharge. The channel of the Mississippi River 

incises the aquifer from south of Baton Rouge northward to beyond 

the State line, and the river is hydraulically connected with the 

aquifer. Therefore, if ground-water levels are lowered by pumping, 

water from the river would be induced to flow into the aquifer and 

would greatly increase recharge to the aquifer.

RECENT SERIES

The silt and clay overlying the sand and gravel of Pleistocene age 

correlates with the material in East Carroll Parish described as Recent in age by Poole (1961). Silt and clay deposited during periodic 

floods of the Mississippi River formed the natural levees and gradually filled the backswamps. Recent deposits range in thickness from 

about 10 to 90 feet in most of the area. Near Lake Providence, about 

30 miles north of Tallulah, silt and clay of Recent age has been 

deposited in a cutoff meander loop of the Mississippi River, forming 

an oxbow lake. In places the channel of this abandoned meander 

had been scoured deeply, and only a thin bed of Pleistocene sand and 

gravel underlies the silt and clay. Fisk (1944, p. 19) referred to 

these clay- and silt-filled abandoned channels as "clay plugs." He 

includes within the same term arcuate "lows" or swales that have 

been filled with silt and sandy clay. Logs of wells indicate no deeply 

filled clay plugs in the Tallulah area. Many of the minor irregularities in thickness of the Recent deposits may reflect the filling of 

relatively shallow, low areas by silt during floods.

The silt and clay control to a large extent the occurrence of ground 

water in the area. These Recent deposits have not been compacted 

by overburden and consequently are relatively permeable. Thus some 

of the water from local precipitation is transmitted directly downward 

to the underlying sand and gravel. This recharge normally maintains 

the water levels above that in the Mississippi River, and consequently 

the river functions as a drain of the aquifer. In areas underlain principally by clay, such as the upper reaches of Walnut Bayou, the 

smaller streams are not connected hydraulically with the aquifer. 

The permeability of the Recent silt is much less than that of the 

underlying sand and gravel. Therefore, where the water level in 

wells is above the aquifer, the silt functions as a semiconfining layer 

when the well is pumped. If the well is pumped continuously and the
ALLUVIAL AQUIFER, NORTHEASTERN LOUISIANA V9

water level in the vicinity declines below the silt zone, the confining 

effect gradually diminishes as the water drains slowly from the silt.

HYDROLOGY

OCCURRENCE

As discussed in the section "Geology," the sand and gravel phase, 

which is considered to be the aquifer, is overlain by silt and clay (fig. 

2). Because these fine-grained sediments imperfectly confine the 

water in the underlying coarser sediments and the piezometric surface is usually in the fine-grained sediments in much of the area, 

ground water in the alluvial deposits in the Tallulah area is considered 

to be semiconfined.

Ground water generally occurs either under unconfined (watertable) or confined (artesian) conditions. In the alluvial deposits, 

confinement is usually a matter of degree and varies with the static 

water level and the rate and period of pumping. The magnitude of 

the water-level fluctuations in the alluvial aquifer due to atmospheric 

pressure changes indicates the variation in degree of confinement of 

the alluvial aquifer. The piezometric surface (an imaginary surface 

that coincides with the static water level in wells) of a perfectly confined aquifer fluctuates normally in response to barometric, loading, 

and other pressure changes that may be exerted on the aquifer. In an 

unconfined aquifer, however, the water table usually is affected only 

slightly, if at all, by these forces. As shown by figures 3 and 4, the 

magnitude of the effect of changes in barometric pressure varies with 

the position of the static water level. When the static water level is 

in the upper part of the semiconfining layer, the fine-grained material 

functions as a confining bed, and the water level readily responds to 

barometric pressure changes (fig. 3); but, as the water level declines, 

the effect of pressure changes becomes small. (See fig. 4.) The high 

ratio of the vertical permeability of the aquifer to that of the semiconfining material allows the release of water instantaneously from 

storage during an initial period of pumping, and, during this time 

only, the aquifer functions as an artesian system. After an initial 

period of pumping, water from the sand in the upper part of the 

aquifer, especially in the vicinity of the pumped well, drains toward 

the piezometric pumping surface and becomes a significant part of 

the total withdrawal. As pumping continues, the effect of this vertical 

percolation becomes less. However, water from the less permeable 

semiconfining material overlying the aquifer drains slowly and at a 

relatively uniform rate throughout the pumping cone of influence.
VlO CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

17.0

!7.6H->

7 8 9 10 II 12 13 14 15 16 18 19 20 21 22 23 

MAY 1957

FIGURE 3. Hydrograph showing effect of barometric-pressure changes on water level In 

observation well Ma-12, May 1957.

PUMPING TESTS

A pumping test was made in the Tallulah area during the time of 

year (November-December 1956) when the requirement for ground 

water was at its minimum. This test was terminated unexpectedly
ALLUVIAL AQUIFER, NORTHEASTERN LOUISIANA Vll

UJ

^27.7

2 

o:

(O

< 27.8

UJ 

CD

H 

UJ 

UJ 

U_

27.9

UJ

_J

UJ

&28.I

28.2^

26

Barometric effects

30 2 ' 3 ' 4 ' 5 ' 6 ' 7 ' 8 ' 9 ' lO 1 I I

NOVEMBER AND DECEMBER 1956

FIGURE 4. Hydrograph showing effect of barometric-pressure changes on water level in 

well Ma-12, November-December 1956.

at 1:00 p.m. on December 9, 1956, after about 18,000 minutes of continuous pumping, and therefore recovery measurements were not 

made. Well Ma-25 was used as the pumped well during the test, 

and observation wells, their locations dependent upon the availability 

of space in a cultivated field, were installed at various distances from
VI2 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

1.9 MILES TO 

Ma-12

TO US 80

25-3

EXPLANATION 

Pumped well

Observation well

I 

TO US 80

1000 1000 FEET

FIGOKB 5. Location and construction data of pumped and observation wells.

well Ma-25. The construction data for and the location of these 

wells are given in figure 5. The rate of pumping was measured with 

a 12- x 10-inch open-end orifice and regulated with a valve. The 

well was pumped at an average rate of 3,200 gpm. Water levels were 

measured in the pumped and observation wells with an electrical tape. 

Changes in barometric pressure were recorded before and during the 

test periods, and the necessary corrections were made to the observedtrend data. Water-level-trend corrections also were applied.

Well

Ma 25... .. . 

25-1 _ . ________ ...

25-2 _ . _ . _______ .

25-3. 

25-4 _ . _______ .....

12....... .......

Distance 

from 

pumped 

well 

(feet)

250 

375 

500 

100 

11,000

Depth to 

bottom of 

screen 

(feet)

166 

63 

63 

63 

70 

75

Diameter 

of well 

casing 

(inches)

18 

1.25 

1.25 

1.25 

3-1.25 

3

Screen

Length 

(feet)

52.5 

3 

3 

3 

3 

10

Diameter 

(inches)

14

1.25 

1.25 

1.25 

1.25 

3

Altitude of 

measuring 

point 

(feet)

93.53 

93.27 

94.31 

91.53 

89.68

The hydraulic characteristics of the alluvial aquifer in the vicinity 

of Tallulah were determined by the Theis nonequilibrium method, 

using only data obtained during the early part of the test. In trial 

manipulations, logarithmic plots of drawdown versus time were compared with the leaky-aquifer type curve prepared by H. H. Cooper, 

Jr., of the Geological Survey (written communication, 1958). Even
ALLUVIAL AQUIFER, NORTHEASTERN LOUISIANA V13

though field conditions do not agree with Hantush's (1947, p. 19) 

assumption "that the head in the aquifer supplying leakage remains 

uniform," which was used in the derivation of the leaky-aquifer formula the calculated coefficient of transmissibility approximated that 

determined with the nonequilibrium method. Boulton's equation 

(1954a, p. 473) for delayed storage was not considered applicable because his assumption "that, above the coarse sand (aquifer), there is a 

bed of very fine sand and silt in which practically the whole of the 

depressed water-table is located" was not satisfied. After only a short 

period of pumping, the water level in the vicinity of the pumped well 

declined below the base of the fine sand and silt and into the aquifer.

In May 1957 a pumping test was made at well site Ma-25; but, 

because of a premature start, water levels in the observation wells were 

not measured until after about 100 minutes. After this time, the quantity of water from drainage significantly affected the water level, and 

it was not possible to determine the coefficients of transmissibility and 

storage.

A consistent coefficient of transmissibility of 240,000 gpd per ft 

was obtained by using data collected earlier, during the NovemberDecember 1956 test and by using the nonequilibrium method of analysis. The relation of the logarithmic plot of time and drawdown for 

well Ma-25-2 to the Theis-type curve is shown on figure 6. On the

10.0

i.o

o.i

Transmissibility (7)=240,000 gpd per ft 

^Yield (Q)= 3200 gpm

Distance (r) from observation well

to pumped well = 375 ft - 

Storage (S) coefficient=0.0016

10 100 1000 

TIME (0. IN MINUTES, SINCE PUMPING STARTED

10,000

FIGURE) 6, Logarithmic time-drawdown plot of water levels in observation well Ma-25~2,

November December 1956.

basis of the aquifer's thickness at the site of well Ma-25 and the coefficient of transmissibility, the average permeability of the sand and 

gravel is 1,700 gpd per square foot (meinzers), which is slightly higher 

than the average (1,500 meinzers) permeability of the alluvial de643873 62 3
V14 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

posits in East Carroll and West Carroll Parishes (Poole, 1961, table 

13). The average permeability of the alluvial aquifer was reported 

to be 1,700 meinzers in the Baton Rouge area (Meyer and Turcan, 

1955) and 1,900 meinzers in the Grand Prairie region of Arkansas 

(Engler and others, 1945, p. 43). Data collected during step-drawdown tests of short duration on wrells Ma-26 and -27 were analyzed, 

and the coefficients of permeability were 1,710 and 1,750 meinzers 

respectively. Thus, these comparative values indicate that computations made with early data and the nonequilibrium formula do provide 

a representative permeability value for the alluvial aquifer in the 

Tallulah area.

The coefficient of storage, which ranged from 0.0016 to 0.0027 and 

averaged 0.002, was computed by the Theis nonequilibrium formula 

from data collected in four wells during the early part of the test. Because the fine-grained sediments confine the water imperfectly, the 

amount of water released from storage is not constant within the cone 

of influence, and the calculated storage-coefficient values are considered 

representative only for the early part of the test. In 1958, TV. H. 

Walker, formerly with the Geological Survey, analyzed data collected 

during the pumping tests at Tallulah. He hypothesized (written communication) that a logarithmic plot of time against apparent storage 

coefficient formed a temporary straight line (fig. 7), which, with cono.i

o.oi i.o 10

TIME, IN DAYS

100

FIGURE 7. Graph showing logarithmic relation of apparent storage coefficient to time at 

a distance of 500 feet from the pumped well, November-December 1956.

tinuous pumping, would curve as the apparent storage coefficient 

approached the effective porosity of the aquifer. The plotted values 

of apparent storage coefficient on figure 7 were calculated mathematically by substituting into the nonequilibrium formula the corrected
ALLUVIAL AQUIFER, NORTHEASTERN LOUISIANA V15

observed drawdown for a given period of pumping time. This empirical analysis is applicable only for the geologic and hydrologic 

environments of the Tallulah area. Variance in the quantity of water 

released from storage or from the overlying fine materials was recognized by R. G. Kazmann (Engler and others, 1945, p. 42, fig. 10). 

The semilogarithmic plot (fig. 8) of drawdown in observation well

FEET CORRECTED DRAWDOWN (s), IN 

coo cr> who.p.vi u>- . 

Nonequilibr 

Water rel 

ously fro

D

Pf 

u 

ea 

m

lase 

m c< 

sed 

stor

T

jndition 

instant! 

age

>.

ne-

 K

O (pumping rate)=3200 gpm 

stance (r) from observation we 

to pumped well =375 ft

L 10

1111 Phaselll "'I 

ffects of dewatering 

upper part of aquifer 

and some drainage 

from semiconfining bee

II

r=

p=

26

A

4

s

3 =4^

III

L

Equi 

of

se

: V

N

^,000 II

T 445.000 , 

" 132||

i Him

ibn 

drc

TliC(

urr 

in 

jnl

PI 

\ <

38

in

lase 

:6nd 

e fr 

ing

AS per log

^ Ll ^_pkLLl 

gp<

30(

ip

g

1

er

N, tt' v

xl per

1 |

in

itions..E 

om ove 

beds

cycle =

X'S

sqft

II

ffec 

rlyi

1.9

X

ts 

ig

ft

X

100 1000 10.000 40,000

TIME (f), IN MINUTES, SINCE PUMPING STARTED

FIGURE 8. Semilogarithmic time-drawdown plot of water levels in observation well 

Ma-25-2 at test site Ma-25, November-December 1956.

Ma-25-2 against time forms a three-phase curve, which resembles that 

generally obtained for a water-table aquifer (WaJton, 1960b, p. 46). 

Some of the hydrologic factors, alone or in combination, that could 

affect the rate of water-level decline are a thickening or thinning of 

the aquifer; differences in permeability within the cone of influence; 

drainage from the overlying semiconfining beds; or intersection of the 

cone of influence with nearby streams, the Mississippi Kiver, or an 

impervious boundary. The aquifer's thickness (fig. 2) and permeability vary, but the pumping-test data were analyzed as if the aquifer 

were homogeneous and isotropic. Even though the cone of influence 

caused by pumping intersects the Mississippi River, the effect of the 

resultant image well on the cone of influence is not measurable because of the image well's relatively great distance from the test site. 

Available geohydrologic data indicate that Koundaway and Walnut 

Bayous have not cut into the aquifer at the sites of the irrigation wells.
V16 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

The beds of these streams are composed of silt or clay, which are relatively impermeable; therefore, the slope of the curve for the third 

phase (or latter part) of the pumping test on well Ma-25-2 (fig. 8) 

must be attributed to causes other than the connection with the Mississippi River and Walnut Bayou. Analysis of hydrologic and geologic conditions indicates that the rate of water-level decline is affected 

primarily by water that drains at a relatively uniform rate from the 

semiconfining beds down through the upper part of the aquifer, to the 

pumping piezometric surface. The effect of this drainage during the 

third phase (fig. 8), or the latter part of the test, obviates the use of 

data collected for calculating the hydraulic characteristics of the semiconfined aquifer at Tallulah by the equilibrium method of analysis 

(Cooper and Jacob, 1946). For example, the permeability determined 

by substituting the drawdown over 1 log cycle (fig. 8) and the yield 

(3,200 gpm) into the equilibrium formula is approximately twice the 

actual permeability of the alluvial aquifer at Tallulah.

THEORETICAL EFFECTS OF PUMPING

One of the principal uses of pumping-test results is in calculating 

the theoretical effect of pumping on water levels, generally by the 

Theis nonequilibrium method or by an analysis of time-drawdown and 

distance-drawdown straight-line plots. Except for a short time during the initial period of pumping, anomalous hydrologic conditions at 

Tallulah invalidate the use of the nonequilibrium formula for predicting the effect of pumping. However, when the cone of depression 

reaches equilibrium in form and the rate of drainage from the semiconfining materials is relatively uniform, plots of observed data can 

be used to approximate the effect of pumping in a pumping well and 

in a well field.

An indication of well efficiency (in percent) or the effectiveness of 

well development and construction is estimated by dividing the observed specific capacity of a well by the theoretical specific capacity 

and multiplying the results by 100. Specific capacity, which is defined as the yield per unit of drawdown for a given period of pumping, 

usually is expressed in gallons per minute per foot of drawdown. If 

the efficiency of a well screened in the shallow alluvial aquifer is less 

than 100 percent, the difference is due primarily to head loss resulting 

from turbulent flow around and through the well screen commonly 

called well-entrance loss. The specific capacity of wells in the alluvial 

valley of northeastern Louisiana and northwestern Mississippi is given 

in the section "Development."
ALLUVIAL AQUIFER, NORTHEASTERN LOUISIANA 

NONEQUrLIBKIUM METHOD

V17

During the initial period of pumping from well Ma-25, conditions 

conformed to the assumptions used in the development of the Theis 

nonequilibrium formula. This conformance made it possible to calculate the theoretical specific capacity by substituting into the nonequilibrium formula assumed values for time (40 min.) and welP 

radius (Y in.), and average values of transmissibility (240,000 gpd per 

ft) and storage (0.002) computed from early pumping-test data. 

After 40 minutes of pumping at a rate of 3,200 gpm, the calculated 

specific capacity is 145 gpm per foot of drawdown. Of particular 

interest is the fact that 88 percent of the total observed drawdown 

in well Ma-25 occurred during the first 40 minutes of pumping. (See 

fig. 9.) As shown in figure 9, the observed drawdown in well Ma-21

Jj Jj

±.

z 

^ 34

2

s

3

i<D

38

40 

1

Q = 3200 gpm

'

 

-

SL

-

i 

= 34 t~

'[

'1 

49

' \\"

-,/Yield declined 3088 toY\ valve adjusted gpm; 

/Yield 3160 'gpm; 

valve adjusted for 

3200 gpm

ft

Ave

j

'> > £ OB

raj- )i,qg rate Q) =

Sj=39.14

-.3'< 0() Bf i

j

0 100 1000 10,000 100,000

TIME (f). IN MINUTES, SINCE PUMPING STARTED

FIGURE 9. Semilogarithmic time-drawdown plot of water levels in pumping well Ma-25,

November-December 1956.

at the end of 40 minutes of continuous pumping was 34.49 feet; thus 

for a yield of 3,200 gpm, the observed specific capacity was 92.8 gpm 

per ft of drawdown. By dividing this observed specific capacity 

(92.8 gpm per foot of drawdown) by the theoretical specific capacity 

(145 gpm per foot of drawdown), the theoretical hydraulic efficiency 

for well Ma-25 at the end of 40 minutes of pumping is about 64 percent. The divergence of this well's efficiency from 100 percent is 

caused primarily by turbulent flow around and through the screen, 

which is the probable result of incomplete well development and 

increased velocity as the water passes through the screen openings.
V18 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES 

EQUILIBRIUM METHOD

The effect of pumping and the efficiency of the pumped well can be 

estimated by analyzing the shape of the cone of depression. This can 

be done by plotting the drawdown (s) in three or more observation 

wells against the logarithm of distance (r) from the pumped well. 

Theoretically the observation wells should be in only one direction 

from the pumping wells; however, provided that the cone of influence is symmetrical, a distance-drawdown plot for wells in different 

directions and at various distances from the pumped well is 

satisfactory.

Straight-line semilogarithmic plots of time (t) or radius (r) 

against drawdown (s) are legitimate only when the cone of depression 

reaches equilibrium in form when u is equal to or less than 0.02 

(Cooper and Jacob, 1946; Brown, 1953, p. 858). The following general equation for critical drawdown (where u is less than 0.02) may 

be obtained by solving for the constant values and substituting the 

corresponding W(u) value in the Theis nonequilibritim formula:

«- 

where Q (the yield) is in gallons per minute and T (the transmissibility) is in gallons per day per foot. On the basis of the coefficient 

of transmissibility (240,000 gpd per ft) for the alluvial aquifer and 

the average rate of pumping (3,200 gpm), the critical drawdown 

(sc ) at the end of about 13 days of pumping is calculated to be 5.1 

feet.

Even though the slope of the cone of depression is affected by a 

relatively uniform rate of drainage, which invalidates the use of the 

equilibrium method for calculating the correct coefficients of transmissibility and storage, the plot of drawdown against the logarithm 

of distance (fig. 10) forms a straight line and represents the cone of 

influence for the time and rate of pumping and the prevailing hydrologic conditions. The coefficient of transmissibility computed from 

the distance-drawdown plot (fig. 10) is 268,000 gpd per ft, which is 

about 10 percent greater than that considered to be correct 240,000 

gpd per ft. As the coefficient of transmissibility and the yield from 

the well are relatively constant, the variation of the theoretical slope 

of the cone of influence from the actual is caused by a relatively constant rate of vertical percolation, which amounts to about 320 gpm 

or 10 percent of the average rate of pumping.

The effect of pumping on water levels in wells within a radius of 

about TOO feet from well Ma-25 can be estimated from figure 10. Beyond a distance of about TOO feet, the line will curve slightly because
ALLUVIAL AQUIFER, NORTHEASTERN LOUISIANA V19

5 15

20

o 25

30

Criticale ra

.1

wi>v

m

CM

5

-1

O

f (Sc)

./^

c

b 

P

-

ftJ

^.s

ivergence from 

raight line caused 

y effects of partial 

enetration ftf^ 

&

per

I 1 X" n _

x-'

og cycle =6.3 ft 

, 528 Q 52

''<* 

in

CM

i 

ra

8x320

&s fi q

/

_ r m '_. 268.C

1^

^

Ma-25-] Well 

0

)00 

2-

JQ'

CM

in

CMi

i

"55

-">f

._.,

CO

CM 

1

i

<e

>8,OC

>i)l)0

/

Ogpd [

JI'd pe

 -

er

S£

^**

ft

t

0.1 , 1 10 100 1000 

DISTANCE (r), IN FEET FROM PUMPING WELL

10,000

FIGURE 10. Semilogiarithmic distance-drawdown relation for alluvial aquifer after 18,000 

minutes of continuous pumping, November-December 1&56.

of nonequilibrium conditions, and the effect of pumping can be approximated only. However, the distance-drawdown plot (fig. 10) can 

be extrapolated to the pumped well to determine the theoretical drawdown, the theoretical specific capacity, and the hydraulic efficiency 

of the pumped well. As shown on figure 10, the theoretical drawdown 

in well Ma-25 after 18,000 minutes (approximately 13 days) of continuous pumping is 25.1J!eet. Therefore, based upon a yield of 3,200 

gpm, the theoretical specific capacity is 128 gpm per foot of drawdown. The observed drawdown in well Ma-25 at the end of JiSjOOO 

minutes was 39.1 feet (fig. 9); thus, the observed specificfgravitv^ln 

well Ma-25 is computed to be 81.8 gpm per foot of drawdown. By 

dividing the observed specific capacity by the theoretical specific 

capacity, the hydraulic efficiency of well Ma-25 after 18,000 minutes is 

about 64 percent, which is the same as that computed for 40 minutes 

of continuous pumping.

Drawdown data for observation wells at well site Ma-25 obtained 

during a pumping test made in May 1957 were plotted against the logarithm of distance from the pumped well. The resultant straight 

line for a pumping period of 5,600 minutes was extrapolated to the 

pumped well (Ma-25). On the basis of a constant and measured yield 

of 3,400 gpm and a theoretical drawdown of 26.2 feet, the theoretical 

specific capacity for the indicated time and yield was 130 gpm per foot 

of drawdown. The observed drawdown of 41.98 feet in well Ma-25 

resulted in an observed specific capacity of 81.5 gpm per foot of drawdown. On the basis of analysis of these data, the efficiency of well
V20 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

Ma-25 after pumping 3,400 gpm continuously for 5,600 minutes was 

about 63 percent. As would be expected, the observed and theoretical 

specific capacities decrease with increased pumping time; however, the 

close comparison of the well efficiency for different tests, periods of 

pumping, and yields indicates the practicability and validity of estimating the effect of pumping by the equilibrium method of analysis.

WATER WELLS

The primary purpose of a water well is to provide an economical 

and efficient means of bringing ground water to the surface. Numerous methods exist for constructing wells; the selection of a particular 

method depends upon the use of the water, the quantity of water 

required, the depth to the aquifer, the hydrologic and geologic conditions, and the economic factors. In the Mississippi River alluvial 

valley, small-capacity shallow wells usually are dug, bored, or driven, 

and large-capacity deeper wells are drilled by the hydraulic-rotary or 

reverse-circulation methods. The installation of water wells can be 

divided into four major phases. The first phase is planning, which 

includes compilation and analyses of available hydrologic and geologic 

data; to obtain needed or supplemental data, it may be necessary to 

drill a test hole or holes. The second major phase is the drilling of a 

hole that will accommodate the specified casing and screen. The third 

phase is well development. After the casing and the screen are installed, a well should be developed for optimum yield and tested 

before selecting and installing a permanent pump. The fourth phase 

is installation of a pump of the required capacity and setting.

TEST DRILLING

Before drilling and constructing a supply well, especially in an 

area where hydrologic data are meager, it is common practice to drill a 

test hole or holes. In addition to determining the exact location of 

the aquifer containing fresh water, an important objective in test drilling is the collection of representative formation samples. As the 

depth of the alluvial aquifer at Tallulah was known approximately, 

the principal purpose of the test drilling was to collect sand samples 

for analysis. Representative formation samples are required for 

the proper selection of screen openings, and various sampling methods 

have been devised to obtain such samples from rotary-drilled holes.

The method used for collecting formation samples during the drilling of the holes near Tallulah was the bucket and decant method. 

This method generally requires patience, a knowledge of circulation 

time, a supply of clear water, and a specially designed pipe to channel 

the cuttings to the point of collection. The cuttings are placed in a
ALLUVIAL AQUIFER, NORTHEASTERN LOUISIANA V21

large vessel and washed slowly with clear water. After the finegrained sediments have been allowed to settle from the drilling fluid, 

the water may be decanted and a representative sample obtained 

from the vessel. The sample is then placed in a container, which is 

marked with the identifying well number and the depth interval.

When drilling with the rotary method in the Mississippi River alluvial valley, where the deposits usually increase in grain size from 

top to bottom, the mud viscosity should be kept constant to insure 

uniform and representative samples for the full depth of the test hole. 

The drilling fluid should be of a viscosity to assure that the coarser 

materials will be brought to the surface.

During the drilling of test holes a careful record, or a log, was kept 

of the various strata and their depths, the action of the drilling rig, 

and the time required to drill each interval. Formation samples 

were compared with the driller's log and examined in the laboratory 

to determine the extraneous effects of drilling muds and gel products. 

Commonly, when samples are improperly washed, the dried drilling 

mud may be erroneously logged as part of the sample. Sometimes 

clay, which may slump from the sides of the mud pit and ditch, may 

contaminate the formation sample, and extreme care was exercised 

during the collection and the examination of samples to avoid misinterpretations and improper screen selection.

In most areas it is necessary to make an electrical survey after the 

test hole is drilled to the desired depth. The importance of electrical 

logging for determining the exact location of fresh-water-bearing 

sands is discussed in detail by Rose, White, and Livingston (1944), 

and Jones and Buford (1951). Because of adequate information on 

the alluvial aquifer in the Tallulah area, it was not necessary to make 

an electrical survey at the site of each experimental well.

WELL CONSTRUCTION 

DRILLING PROBLEMS

The reverse-circulation rig used to drill the holes for the experimental irrigation wells, which were a few feet distant from the test 

holes, was satisfactory for drilling holes of the required diameters 

(16 and 22 inches) to the specified depths. However, the pit pump 

did not supply water at a rate adequate to overcome the loss of circulation to the permeable materials. A pump with a capacity of 1,000 

gpm was needed and eventually acquired and used to maintain the 

required constant head. Because of the inadequate water supply, one 

of the advantages of the re verse-circulation method that drilling 

muds are not needed was lost when drilling muds (aquagel and lime) 

had to be used during the drilling of the interval to be screened in
V22 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

well Ma-26. Even though the aquifer at the site of well Ma-26 is not 

as thick as it is at wells Ma-25 and -27, the results of development indicated that the drilling mud had not been flushed completely from 

the aquifer. The observed specific capacity (56 gpm per foot of 

drawdown) should have approximated that (about 90 gpm per foot 

of drawdown) observed in wells Ma-25 and -27. The relatively low 

specific capacity in well Ma-26 also may be attributed to well-entrance 

loss and to a small decrease in the aquifer's transmissibility. However, incomplete development is considered to be one of the principal 

causes of the relatively low hydraulic efficiency of well Ma-26.

To allow for proper alinement of the casing and screen, the hole 

must be drilled vertically. Perfect alinement of the hole and casing 

was necessary at Tallulah because the hole for the screen was drilled 

after the casing had been set and cemented. In well Ma-27 the alinement of the hole was slightly off vertical (about 4°), and the misalinement was not observed until an attempt was made to set the screen. 

During installation, the upper 7 feet of the screen was damaged by 

the bottom of the casing and required repair before use. It was determined that the casing was about 5° off vertical; therefore, it was 

necessary to drill the hole for the screen in the same plane as that for 

the casing. To produce a deflection in the same direction, casing 

guides were welded onto the drill stem.

Because of the relatively high permeability of the alluvial deposits, 

the large hole diameter, and the time required to weld and set casing, 

the hole for the casing should have been drilled below the proposed 

depth. This would have allowed for slumping or cave-ins and permitted the casing to be set to the desired depth. Because of failure 

to allow for slumping, the bottom of the casing was set at a depth 

above that specified.

SCREEN SELECTION

To reduce the head loss caused by turbulent flow around and through 

the screen, the open area of the screen should be at a maximum, and 

flow paths through the screen should be direct and not along a sinuous 

path. The selection of the openings of the screen, which is called "the 

heart of the well" by Schreurs (1959, p. 784), should be based upon distribution of grain size in the formation samples. This distribution 

may be determined by mechanical analyses, using sets of sieves that 

retain different grain sizes. The cumulative percentage retained by 

each sieve is determined and is plotted on grain-size graphs. From 

these graphs it is possible to determine what percentage of the finegrained material will pass through a selected opening. Some screen 

manufacturers indicate that the screen openings for an irrigation well 

should be selected to allow the passage of approximately 90 percent
ALLUVIAL AQUIFER, NORTHEASTERN LOUISIANA V23

of the finer grained material. The mechanical analyses of materials 

collected during test drilling at well sites Ma-25, -26, and -27 indicated that screen openings of 0.080 inch would allow retention of 10 

percent of the material. However, on the basis of drilling experience 

in the area, the water-well contractor decided to use a screen opening 

of 0.050 inch, which retained more than 10 percent of the finer grained 

materials.

Some irrigation wells in the Mississippi alluvial valley are gravel 

packed the annulus between the well screen and the bore hole is 

filled with selected coarse sand and gravel to allow for larger screen 

openings (Harvey, 1956; Poole, 1961). Theoretically, gravel packing decreases the head loss due to turbulent flow in the formation immediately adjacent to the screen. Gravel packing should not be 

confused with the stabilizing fill method, which is the placement, without special precautions, of ungraded material into the annulus between 

the screen and hole.

The gravel and coarse-grained sand in the intervals to be screened 

in the three experimental irrigation wells eliminated the need for 

gravel packing. The use of natural-packed wells in this area is congenial with suggestions made by Schreurs (1959, p. 787) who wrote:

In very fine and uniform sands it may be beneficial to place graded coarse sand 

or fine gravel around the well screen to form artifically a filter between the 

screen and the formation sand. This requires a larger casing or bore hole in 

order to provide an annulus for the placement. Its beneficial effect on the yield 

of the well is principally because of the increased size of slot openings that can 

be used in the well screen. Also, a slight increase in yield comes from the larger 

effective diameter.

The choice to gravel pack should be made on the basis of the conditions 

in each well. Satisfactory gravel-pack construction requires considerable skill and should be done only by thoroughly qualified men.

DEVELOPMENT

The completion of a well generally should not end with the placement of the screen. Well development is required to remove detrital 

materials, concentrate coarse-grained sand and gravel next to the 

screen, stabilize the aquifer in order to prevent sand pumping, and increase the well's efficiency.

Some of the development methods used in Louisiana are: surging 

with air or a surge block, cross washing, and overpumping. The experimental irrigation wells at Tallulah were developed by overpumping. When overpumping is used, the test pump should have a greater 

capacity than the desired well yield (Moss, 1958, p. 786). Sayre and 

Livingston (1945) suggested that the permanent pump capacity be not
V24 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

more than two-thirds the developed capacity. Even though the development of the experimental wells was considered to be satisfactory, 

they were not developed to optimum yield because of the relatively 

small capacity (about 3,600 gpm) of the test pump. The desired yield 

was 3,000 gpm; therefore, the wells should have been developed to a 

capacity of about 4,500 gpm.

Specific capacity generally is an indication of the productivity of a 

well and may indicate the success of well development. Before development, a 15- or 30-mimite specific-capacity test was made in each 

experimental well. After varying periods (8 to 10 hrs) of daily development, the pump was turned off until the following morning. A 

specific-capacity test was then made to determine the effects of previous development. As development was continued, the fine material in 

the immediate vicinity of the well screen was removed and the specific capacity increased. The specific capacity of well Ma-25 on August 

5,1956, was 88 gpm per foot of drawdown at a yield of 3,250 gpm. On 

the morning of August 6, after 1 day of continuous development, the 

specific capacity had increased to 93.5 gpm per foot of drawdown with 

a yield of 3,350 gpm. The specific capacity for well Ma-26 increased 

daily from a low of about 45 gpm per foot of drawdown with a yield of 

1,475 gpm on July 19, 1956, to 52 gpm per foot of drawdown with a 

yield of 2,700 gpm on July 31, 1956. The specific capacity in well 

Ma-27 after only 1 day of development increased from 100 gpm per 

foot of drawdown with a yield of 3,590 gpm to 103.5 gpm per foot of 

drawdown with a yield of 3,560 gpm.

Step-drawdown tests were made in each experimental well to determine if the critical discharge had been reached. Critical discharge 

is reached when the specific capacity decreases rather abruptly with 

increased yield. Because of possible errors in the measurements of 

yield and water level, a small variation from a straight line might 

be expected when specific capacity is plotted against increased yield. 

Plots of specific capacity against increased yield for wells Ma-25,

-26, and -27 indicate that the critical discharge had not been reached 

at their maximum yield.

The quality of the water high total iron and hardness content 

in the alluvial deposits combined with excessive head losses at the 

face of the screen may cause screen incrustation. Over a period of 

time, the incrustation tends to reduce the specific capacity of a well. 

Even though the experimental wells at Tallulah were not developed 

to their maximum efficiency, the specific capacity of wells Ma-25,

-26, and -27 has not decreased over a period of about 4 years 

(1956-60). (See table 1.)
ALLUVIAL AQUIFER, NORTHEASTERN LOUISIANA V25

TABLE 1. Measured operating yield and specific capacity of experimental 

irrigation wells in the Tallulah area, Madison Parish, La.

USQS well

Ma-25.. ........ ... .

26.. .....................

27.......................

Ma-25 

26-... ............ _.

27. .

Date of tests

July I960 

July I960.... _ - _

OptnHar iQf^fi

DuratioH of

tests (min.)

110

80

37

110

80

38

Static water 

leve. (feet)

20.45

10.45

26.74

17.00

17.70

Yield (gpm)

4,100

3,300

3,900

3,200

3,400

3,500

Specific 

capacity 

(gpm per 

foot)

89.3

56.4

99.6

90.8

56.6

102.0

SPECIFIC CAPACITY

Even though the specific capacity of wells Ma-25 and -27 is below 

the theoretical specific capacity, the yield and observed specific capacity are above the average measured and reported for wells in the alluvial valley in northeastern Louisiana and northwestern Mississippi. 

The data contained in table 2 were compiled from data presented by 

Poole (1961) and Harvey (1956). The specific capacity of the irrigation wells listed in table 2 ranges from 19 to 185 gpm per foot of 

drawdown and averages 66. The average yield for the 48 representative irrigation wells listed in table 2 is 1,900 gpm.

PUMPS

Proper pump installation involves a knowledge of the type of power, 

required pump capacity, casing diameter needed to accommodate the 

pump, and the required pump setting. Generally the type of power 

to be used is decided on the basis of availability and cost. For planning, the required pump capacity, size of casing, and pump setting 

are estimated from water requirement and hydrologic and geologic 

data. However, the pump and motor should not be selected until the 

well has been developed satisfactorily and the detailed hydrologic 

data necessary for pump and motor design have been obtained.

Preliminary information indicated that a yield of 3,000 gpm per 

well was obtainable. Therefore a 16-inch-diameter pump was required. On the basis of the expected dynamic head and yield, it was 

estimated that a 125-hp motor would be required. Because of the 

limited availability of large pumps and motors at the time the wells 

were installed, the final selection of the pump and motors was made 

on the basis of the preliminary data and not on the basis of final data. 

A 16-inch 1-stage deep-well turbine pump with a rated capacity of 

3,200 gpm was installed on each well, and each was powered by a 

125-hp 60-cycle 1,770-rpm 3-phase 440-volt electrical motor. If the 

final selection had been delayed, wells Ma-25 and -27 probably would
V26 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

TABLE 2. Specific capacity of irrigation wells in northeastern Louisiana and 

northwestern Mississippi

Parish or

County

Well

Diameter

(inches)

Yield

(gpm)

Specific

capacity

(gpm

per ft)

Parish or

County

Well

Diameter

(inches)

Yield

(gpm)

Specific

capacity

(gpm

per ft)

Northeastern Louisiana

East Carroll.... EC-19

33

39

41

42

44

52

60

61

62

64

65

72

80

14

16

16

12

12

18

12

12

8

12

12

16

12

12

1,235

1,725

1,470

1,475

1,880

1,900

2,000

800

400

2,300

2,450

2,100

700

1,100

39

64

49

42

37

47

80

40

20

92

100

70

25

48

East Carroll ....

West Carroll ...

EC-86

92

94

95

98

99

100

109

110

WC-19

20

21

32

16

12

16

16

16

12

16

10

12

8

12

16

8

2,200

810

2,000

490

1,000

1,800

2,300

2,800

2,500

460

600

2,550

1,600

60

45

60

29

36

40

50

70

71

77

19

75

40

Northwestern Mississippi

Humphrey _ ..

D-4 

F-20 

Q -3 

L-3 

15 

16 

D-l 

2 O-9 

P-5 

J-l

16 

16 

12 

16 

16 

16 

18 

12 

14 

12 

10

3,000 

2,390 

2,750 

2,490 

2,330 

2,050 

2,210 

2,750 

5,000 

1,850 

1,100

89 

75 

101 

78 

63 

52 

58 

80 

185 

62 

73

Tallahatrtiie...

Washington _ .

F-2 

C-2 

E-4 

13 

C-2 

H-l 

R-4 

C-3 

D-2 

L-9

6 

12 

1(0 

10 

16 

18 

12 

12 

16 

16

500 

3,160 

2,210 

2,090 

1,880 

2,390 

1,160 

3,200 

2, 650 

3,030

100 

112

74 

95 

47 

77 

58 

82 

72 

101

have been equipped with a pump with a rated capacity of 4,000-4,500 

gpm and a 175-hp motor.

POTENTIAL SUPPLY SUMMARIZED

The largest yield observed in the Tallulah area, about 4,000 gpm, 

is from well Ma-25. However, this yield is not considered the maximum that can be developed from a single well in the area. The 

potential yield of wells can be estimated on the basis of the hydrologic 

properties of the alluvial aquifer. The theoretical specific capacity of 

a properly developed and constructed well with an efficiency of 100 

percent has been shown to be about 130 gpm per foot of drawdown 

after pumping 13 days. Therefore, the yield of such an ideal well 

in the alluvial aquifer would be slightly more than 7,000 gpm, if the 

drawdown in the well was 55 feet. As the static water level is approximately 20 feet below the land surface in the area, the water level in 

the pumped well at the above pumping time and rate would be about 

75 feet below the land surface.

A group of 10 wells of this type, spaced so as to not interfere with 

each other, would yield about 100 mgd (million gallons a day) or 

155 cfs to supply irrigation requirements. Based on the profile of the
ALLUVIAL AQUIFER, NORTHEASTERN LOUISIANA V27

observed cone of depression at the end of about 13 days of pumping 

(fig. 10), the drawdown at a distance of 10,000 feet from a pumped 

well would be negligible. In addition, as the cone of influence expands in response to longer pumping periods, more and more water 

will be diverted from the Mississippi River. This diversion will result 

in a decrease in the rate of water-level decline, and it is estimated 

that 10 wells spaced along the Walnut-Roundaway Bayou system at 

3-mile intervals would supply 100 mgd without excessive mutual interference. In fact, at the end of a 13-day pumping period all the water 

now being discharged from the aquifer into the Mississippi River 

adjacent to the developed area would not be diverted toward the 

pumping wells. To salvage the natural discharge of water to the 

river and induce river water to recharge the aquifer, wells would 

have to be near the river and pumped at a high rate.

The large potential yield of the alluvial aquifer is assured by the 

proximity of the Mississippi River, which functions as a potential 

source of recharge. For example, Poole (1961) shows that in East 

and West Carroll Parishes, low stages of the Mississippi River cause 

greater water-level declines in the aquifer than those caused by the 

discharge from all the irrigation wells.

Disregarding quality-of-water requirements, the principal problem 

in obtaining a large supply of ground water in the Tallulah area is 

the construction and development of wells with a diameter and 

efficiency capable of yielding the quantity of water the aquifer will 

transmit.

SELECTED REFERENCES

Boulton, N. S., 1954a, Unsteady radial flow to a pumped well allowing for delayed 

yield from storage: Internat. Assoc. Sci. Hydrology, Assemblee Gen. Rome, 

tome 2. ,

 1945b, The drawdown of the water-table under non-steady conditions 

near a pumped well in an unconfined aquifier: Inst Civil Engineers Proc., 

v. 3, pt. 3, p. 564-597.

Brown, R. H., 1953, Selected procedures for analyzing aquifer test data: Am. 

Water Works Assoc. Jour., v. 45, no. 8, p. 844-866.

Cooper, H. H., and Jacob, C. E., 1946, A generalized graphical method of evaluating formation constants and summarizing well-field history: Am. Geophys. 

Union, v. 27, no. 4, p. 526-534.

Engler, Kyle, Thompson, D. G., and Kazmann, R. G., 1945, Ground water supplies for rice irrigation in the Grand Prairie Region, Arkansas: Arkansas 

Univ. Agr. Expt. Sta. Bull. 457, 56 p.

Fenneman, N. M., 1938, Physiography of eastern United States: New York and 

London, McGraw-Hill Book Co., 714 p.

Fisk, H. N., 1944, Geological investigation of the alluvial valley of the lower 

Mississippi River: U.S. Army Corps of Engineers, Mississippi River Comm., 

78 p.
V28 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

Hantush, M. S., 1957, Preliminary quantitative study of the Roswell groundwater reservoir, New Mexico: New Mexico Inst. Mining and Technology,

Socorro, 118 p.

Harvey, E. J., 1956, Records of wells in the alluvium in northwestern Mississippi: Mississippi Geol. Survey and Mississippi Board of Water Commissioners, Bull. 56-1,130 p. 

Hirsch, A. A., 1945, Manual for water plant operators: Brooklyn, Chemical

Publishing Co., 386 p. 

Johnston, C. N., 1951, Irrigation wells and well drilling: California Agr. Expt.

Sta. Circ. 404,32 p. 

Jones, P. H., and Buf ord, T. B., 1951, Electric logging applied to ground-water

exploration: Geophysics, v. 16, no. 1, p. 115-139.

Kristal, F. A., and Annett, F. A., 1953, Pumps: New York, McGraw-Hill, 373 p. 

Low, J. W., 1951, Examination of well cuttings: Colorado School of Mines

Quarterly, v. 46, no. 4,48 p. 

McEllheney, W. A., 1960, Application of rotary drilling to water wells: Am.

Water Works Assoc. Jour., v. 52, no. 3, p. 351-355. 

Meyer, R. R., and Turcan, A. N., Jr., 1955, Geology and ground-water resources

of the Baton Rouge area, Louisiana: U.S. Geol. Survey Water-Supply Paper

1296, table 4. 

Mogg, J. L., 1959, Effects of aquifer turbulence on well drawdown: Am. Soc.

Civil Eng. Proc., v. 85, no. Hy 11, p. 99-112. 

Moss, Roscoe, Jr., 1958, Water well construction in formations characteristic of

the southwest: Am. Water Works Assoc. Jour., v. 50, no. 6, p. 777-788. 

Mylander, H. A., 1953, Oil field techniques for water well drilling: Am. Water

Works Assoc. Jour., v. 45, no. 7, p. 764-772. 

Poole, J. L., 1961, Ground-water resources of Bast Carroll and West Carroll

Parishes, Louisiana: Louisiana Dept. Public Works, 174 p. 

Rorabaugh, A. M., 1953, Graphical and theoretical analysis of step-drawdown

test of artesian well: Am. Soc. Civil Eng. Proc., v. 79, Separate 362, 23 p. 

Rose, N. A., White, W. N., and Livingston, Penn, 1944, Exploratory water-well

drilling in the Houston district, Texas: U.S. Geol. Survey Water-Supply

Paper 889-D. 

Sayre, A. N., and Livingston, Penn, 1945, Ground-water resources of the El Paso

area, Texas: U.S. Geol. Survey Water-Supply Paper 919, 190 p. 

Schreurs, R. L., 1959, Elements of well construction: Am. Water Well Assoc.

Jour., v. 51, no. 6, p. 781-789. 

U.S. Army Corps of Engineers, Mississippi River Comm., 1950, Mississippi River

Hydrographic Survey, 1948-1949, Mouth of Arkansas River to Vicksburg,

Miss.

 1956, Investigation of underseepage Mississippi River levees: Waterways Expt. Sta. Tech. Memo. 3-430.

 1958, Stages and discharges of the Mississippi River and its outlets and

tributaries, 1958. 

Walton, W. C., 1960a, Leaky artesian aquifer conditions in Illinois: Illinois

Geol. Survey Rept. Inv. 39,27 p. 

 1960b, Application and limitation of methods used to analyze pumping

test data, pt 2: Natl. Water Well Jour., v. 14, no. 3, p. 20-52.

o