HYDROLOGY OF THE COASTAL LOWLANDS 

AQUIFER SYSTEM IN PARTS OF ALABAMA, 

1 FLORIDA, LOUISIANA, AND MISSISSIPPI

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Hydrology of the Coastal 

Lowlands Aquifer System in Parts of 

Alabama, Florida, Louisiana, and 

Mississippi

By ANGEL MARTIN, JR., andC.D. WHITEMAN.JR.

REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1416-H
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Charles G. Groat, Director

Any use of trade, product, or firm names in this publication 

is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Reston, Virginia 1999

Library of Congress Cataloging in Publication Data

Martin, Angel.

Hydrology of the coastal lowlands aquifer system in parts of Alabama, Florida, Louisiana, and Mississippi / by Angel Martin, Jr., and 

C.D. Whiteman, Jr.

p. cm. (Regional aquifer-system analysis Gulf Coastal Plain) ( U.S. Geological Survey professional paper ; 1416-H)

Includes bibliographical references.

Supt.ofDocsno.: 119.16: 1416-H

I. Aquifers Southern States. I. Whiteman, Charles D. (Charles Decker), 1931-. II. Title. Ill Series IV. Series: U.S. 

Geological Survey professional paper ; 1416-H. 

GB1199.3.S68M37 1994.

551.49'0976-dc20 93-16286

CIP

For sale by the U.S. Geological Survey, Information Services, Box 25286, 

Federal Center, Denver, CO 80225.
FOREWORD

THE REGIONAL AQUIFER-SYSTEM ANALYSIS PROGRAM

The RASA Program represents a systematic effort to study a number of the Nation's 

most important aquifer systems, which, in aggregate, underlie much of the country and 

which represent an important component of the Nation's total water supply. In general, 

the boundaries of these studies are identified by the hydrologic extent of each system 

and, accordingly, transcend the political subdivisions to which investigations have 

often arbitrarily been limited in the past. The broad objective for each study is to 

assemble geologic, hydrologic, and geochemical information, to analyze and develop 

an understanding of the system, and to develop predictive capabilities that will 

contribute to the effective management of the system. The use of computer simulation 

is an important element of the RASA studies to develop an understanding of the natural, 

undisturbed hydrologic system and the changes brought about in it by human activities 

and to provide a means of predicting the regional effects of future pumping or other 

stresses.

The final interpretive results of the RASA Program are presented in a series of U.S. 

Geological Survey Professional Papers that describe the geology, hydrology, and 

geochemistry of each regional aquifer system. Each study within the RASA Program 

is assigned a single Professional Paper number beginning with Professional Paper 

1400.

Charles G. Groat 

Director

CONTENTS

	Page

Foreword............................................................................................................................................................ Ill

Abstract .............................................................................................,.....................'......................................... HI

Introduction....................................................................................................................................................... 1

Purpose and scope .................................................................................................................................... 2

Previous studies........................................................................................................................................ 2

Physical setting......................................................................................................................................... 2

Physiography............................................................................................................................................. 2

Climate ..................................................................................................................................................... 5

Hydrogeologic setting....................................................................................................................................... 5

Regional permeable zones ................................................................................................................................ 9

Hydraulic properties of the regional permeable zones............................................................................ 9

Ground-water pumpage............................................................................................................................ 13

Regional ground-water flow.............................................................................................................................. 13

Model development and boundaries ....................................................................................................... 13

Model calibration and sensitivity analysis............................................................................................... 17

Predevelopment flow system.................................................................................................................... 19

Subdivision of the flow system ................................................................................................................ 24

1987 flow system...................................................................................................................................... 28

Potential of the aquifer system for development.............................................................................................. 33

Summary .......................................................................................................................................................... 40

Selected references............................................................................................................................................ 50

ILLUSTRATIONS

I Plates arc in pocket]

PLATE 1. Hydrogeologic sections B-B' and C-C of the coastal lowlands aquifer system showing the permeable zones and limits of the flow system in

Louisiana, Mississippi, and Alabama. 

2-8. Maps of the coastal lowlands aquifer system in Alabama, Florida, Louisiana, and Mississippi showing:

2. Simulated water levels under predevelopment conditions and simulated flow within and between areas and across boundaries.

3. Changes from predevelopment water levels caused by pumpage through 1987.

4. Simulated water levels under 1987 conditions and flow within and between areas and across boundaries.

5. Changes from 1987 water levels resulting from an additional 50 years of pumpage at the 1983-87 rate.

6. Projected changes from 1987 water levels resulting from an additional 50 years of pumpage at 150 percent of the 1983-87 rate.

7. Recovery from 1987 water levels resulting from an additional 50 years of pumpage at 50 percent of the 1983-87 rate.

8. Suitability for future ground-water development based on sand thickness and projected drawdown in each permeable zone.

Page

FIGURE 1. Map showing regional and subregional model area.......................................................................................................................................... H3

2. Map showing location of the study area and major structural features in and near the study area................................................................... 4

3. Graphs showing monthly mean temperature, precipitation, and potential evapotranspiration at selected sites in and near the

study area for the period 1951-80............................................................................................................................................................. 6
VI CONTENTS

4-7. Maps showing:

4. Annual mean precipitation in and near the study area for the period 1951-80............................................................................... 7

5. Thickness of the freshwater-bearing part of the coastal lowlands aquifer system........................................................................... 8

6. Total thickness of sand and gravel in the freshwater-bearing part of the coastal lowlands aquifer system..................................... 10

7. Percentage of sand and gravel in the freshwater-bearing part of the coastal lowlands aquifer system ........................................... 11

8. Generalized hydrogeologic section showing zonation of the coastal lowlands aquifer system and direction of regional

ground-water flow.......................................................................................................................................................................... 12

9. Diagram showing variation of water levels with depth and the zonation of the coastal lowlands aquifer system at

Baton Rouge, Louisiana................................................................................................................................................................. 13

10. Map showing the areal extent of the coastal lowlands aquifer system and the outcrop areas of the permeable zones......................... 15

11. Histogram showing pumpage from the coastal lowlands aquifer system by major category of use, 1960-85 ..................................... 17

12. Map showing areal distribution of pumpage from the coastal lowlands aquifer system, 1985............................................................. 18

13. Map showing the finite-difference grid, boundary conditions, the active area of the model, and location of observation wells.......... 20

14. North-south and east-west schematic sections through the coastal lowlands aquifer system showing vertical structure of the

model including model layers and the simulated boundary conditions......................................................................................... 21

15. Hydrographs showing comparisons between simulated and measured water levels for the period 1958-87....................................... 23

16. Profiles showing water levels in each permeable zone under predevelopment conditions.................................................................... 24

17. Map showing simulated ground-water flow in the aquifer system under predevelopment conditions.................................................. 25

18. Map showing the areal distribution of simulated rates of recharge to and discharge from the aquifer system under

predevelopment conditions............................................................................................................................................................ 26

19. Schematic section showing simulated flow between permeable zones and across boundaries of the coastal lowlands aquifer

system under predevelopment conditions..................................................................................................................................... 27

20. Profiles showing water levels in each permeable zone under 1987 conditions..................................................................................... 29

21. Map showing simulated ground-water flow in the aquifer system under 1987 conditions ................................................................... 30

22. Map showing areal distribution of simulated recharge to and discharge from the aquifer system under 1987 conditions.................. 31

23. Schematic section showing simulated flow between permeable zones and across boundaries of the coastal lowlands aquifer system

under 1987 conditions.................................................................................................................................................................... 32

24. Graph showing cumulative pumpage and the sources of water for the coastal lowlands aquifer system for the period 1958-87........ 33

25. Graph showing pumpage and cumulative flow of water to or from storage and adjacent aquifers for the period 1958-87 ................. 33

26. Hydrographs showing the projected effects of an additional 50 years of pumpage at the 1983-87 rate and at increased and

decreased rates.......................................................................................................................................................................^ 35

27. Schematic section showing simulated flow between permeable zones and across boundaries of the coastal lowlands aquifer system

after an additional 50 years of pumpage at the 1983-87 rate........................................................................................................ 36

28. Profiles along north-south and east-west lines showing projected water levels in each permeable zone after an additional 50 years

of pumpage at 150 percent of the 1983-87 rate............................................................................................................................. 38

29. Schematic section showing simulated flow between permeable zones and across boundaries of the coastal lowlands aquifer system

after an additional 50 years of pumpage at 150 percent of the 1983-87 rate............................................................................... 39

30. Graph showing cumulative pumpage and the sources of water for the coastal lowlands aquifer system for an additional 50 years

of pumpage at 150 percent of the 1983-87 rate............................................................................................................................. 40

31. Graph showing pumpage and the cumulative flow of water to or from storage and adjacent aquifers for an additional 50 years of

pumpage at 150 percent of the 1983-87 rate................................................................................................................................. 40

32. Map showing simulated ground-water flow in the aquifer system after an additional 50 years of pumpage at 150 percent of the

1983-87 rate...:............................................................................................................................................................................... 41

33. Map showing the areal distribution of simulated rates of recharge to and discharge from the aquifer system after an additional

50 years of pumpage at 150 percent of the 1983-87 rate.............................................................................................................. 42

34. Profiles along north-south and east-west lines showing projected water levels in each permeable zone after an additional 50 years

of pumpage at 50 percent of the 1983-87 rate .............................................................................................................................. 43

35. Schematic section showing simulated flow between permeable zones and across boundaries of the coastal lowlands aquifer system

after an additional 50 years of pumpage at 50 percent of the 1983-87 rate................................................................ .^................ 44

36. Graph showing cumulative pumpage and the sources of water for the coastal lowlands aquifer system for an additional 50 years

of pumpage at 50 percent of the 1983-87 rate............................................................................................................................... 45

37. Graph showing pumpage and the cumulative flow of water to or from storage and adjacent aquifers for an additional 50 years

of pumpage at 50 percent of the 1983-87 rate............................................................................................................................... 45

38. Map showing simulated ground-water flow in the aquifer system after an additional 50 years of pumpage at 50 percent of the

1983-87 rate.................................................................................................................................................................................... 46

39. Map showing areal distribution of simulated rates of recharge to and discharge from the aquifer system after an additional

50 years of pumpage at 50 percent of the 1983-87 rate................................................................................................................ 47
CONTENTS VII

40. Profiles along north-south and east-west lines showing projected steady-state water levels in each permeable zone resulting

from pumpage of 10,000 cubic feet per day (75,000 gallons per day) per square mile uniformly distributed across the extent

of the aquifer system ..................................................................................................................................................................... 48

41. Map showing simulated ground-water flow in the aquifer system resulting from pumpage of 10,000 cubic feet per day

(75,000 gallons per day) per square mile uniformly distributed across the extent of the aquifer system..................................... 49

TABLES

TABLE I. Relation of the regional permeable zones to model layers and to previously named principal aquifers ...............

2. Lateral hydraulic conductivities of sand beds within the permeable zones based on aquifer-test results..............

3. Pumpage of water from the coastal lowlands aquifer system in the study area for the period 1960-85...............

4. Results of statistical analysis of water-level residuals of the transient calibrated model for the period 1957-82.

Page

H14 

... 16 

... 19

...22

CONVERSION FACTORS

Multiply By To obtain

foot (ft)

foot per day (ft/d)

foot per mile (ft/mi)

inch (in.)

inch per year (in./yr)

mile (mi)

million cubic feet per

day (MftVd)

million gallons per day

(Mgal/d)

square mile (mi 2 )

0.3048

0.3048

0.1894

25.4

25.4

1.609

0.3278

0.04381

2.590

meter

meter per day

meter per kilometer

millimeter

millimeter per year

kilometer

cubic meter per second

cubic meter per second

square kilometer

To convert million cubic feet per day to million gallons per day: multiply by 7.48.

Temperature in degrees Celsius (°C) can be converted to degrees Fahrenheit (°F) as follows: °F= (1.8 x°C)+32.

Sea level: In this report "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929) a geodetic datum 

derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level. 

Datum of 1929.
REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER

SYSTEM IN PARTS OF ALABAMA, FLORIDA,

LOUISIANA, AND MISSISSIPPI

By ANGEL MARTIN, JR., and C.D. WHITEMAN, JR.

ABSTRACT

The coastal lowlands aquifer system of Louisiana, Mississippi, Alabama, 

and Florida consists of alternating beds of sand, gravel, silt, and clay of late 

Oligocene age and younger in off-lapping, coastward-thickening wedges of 

sediment deposited under fluvial, deltaic, and marine conditions. The sediments are highly heterogeneous. Individual sand beds generally are not traceable for more than a few miles.

This study is limited to that part of the aquifer system containing water 

with 10,000 milligrams per liter or less dissolved solids. Thickness of the 

studied part of the aquifer system ranges from a featheredge along the updip 

edges of the system to more than 4,000 feet in southeastern Louisiana. Sand 

content of the aquifer system ranges from less than 10 to greater than 80 

percent, and total sand thickness exceeds 2,000 feet in southeastern Louisiana 

and southern Mississippi.

The coastal lowlands aquifer system was divided into five overlapping regional permeable zones, A through E, to quantify flow in the aquifer system. 

The permeable zones were defined on the basis of water-level data from heavily 

pumped areas. From youngest to oldest the zones are the Holocene-upper 

Pleistocene deposits (zone A), lower Pleistocene-upper Pliocene deposits (zone 

B), lower Pliocene-upper Miocene deposits (zone C), middle Miocene deposits 

(zone D), and the lower Miocene-upper Oligocene deposits (zone E).

Prior to development, flow in the aquifer system was primarily from upland 

outcrop areas in southwestern Mississippi and central and southeastern Louisiana toward lowlands along the coast and in the major river valleys. Results of 

simulations of flow in the aquifer system using a six-layer finite-difference flow 

model indicate that pumpage has significantly altered the natural ground-water 

flow system. Pumpage from the aquifer system for all uses peaked in 1980 at 

about 251 million cubic feet per day (1,874 million gallons per day), then declined to about 211 million cubic feet per day (1,579 million gallons per day) 

by 1985. The total flow circulating within the aquifer system in 1987, about 

354 million cubic feet per day, is about 62 percent greater than the predevelopment flow of 222 million cubic feet per day. A large part of the low-lying coastal area has been transformed from areas of natural discharge to areas of 

recharge. Throughout much of the Coastal Plain, flow directions have been altered and flow converges toward pumping centers.

Simulations of ground-water flow indicate that the aquifer system was near 

steady state in 1987, so pumpage could be continued indefinitely at the 1983-87 

rate of about 1,600 million gallons per day. Results of modeling experiments 

conducted to evaluate the effects of future ground-water pumpage from the 

coastal lowlands aquifer system show that pumping at a rate 50 percent greater 

than the 1983-87 rate would be feasible. The upper permeable zones and the

outcrop areas of the lower zones, in general, would be most favorable for intensive development based on projected drawdowns of water levels. Development 

of a major pumping center near the downdip limit of a permeable zone would 

entail risk of saltwater encroachment.

INTRODUCTION

The study described in this report was done as part of the 

Gulf Coast Regional Aquifer System Analysis begun in 1980 

(Grubb, 1984). The study was designed to describe and 

quantify regional ground-water flow in the eastern part of the 

coastal lowlands aquifer system to understand the effects of 

the present level of development and the probable effects of 

future development.

The Gulf Coast Regional Aquifer-System Analysis is one 

of about 30 similar studies in the Regional Aquifer-System 

Analysis program conducted by the U.S. Geological Survey 

in support of Federal and State needs for information to 

improve ground-water management (Sun, 1986, p. 4). The 

total area of the Gulf Coast regional study is about 290,000 

mi2 and consists of all of Louisiana, and parts of Alabama, 

Arkansas, Florida, Illinois, Kentucky, Mississippi, Missouri, 

Tennessee, and Texas.

Three regional aquifer systems are delineated in the 

regional study: the coastal lowlands aquifer system, the Mississippi embayment aquifer system, and the Texas coastal 

uplands aquifer system (Grubb, 1984). The three aquifer systems were delineated based on differences in geologic framework, distribution of fine-grained sediments, and regional 

ground-water-flow patterns.

Five subregional studies were conducted to study in detail 

different parts of these aquifer systems. The regional and 

subregional model areas are shown in figure 1. This report 

describes the hydrology of the coastal lowlands aquifer

HI
H2 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

system of Alabama, Florida, Louisiana, and Mississippi. The 

subregional studies include three aquifer systems the 

coastal lowlands aquifer system of Alabama, Florida, Louisiana, and Mississippi; the Mississippi embayment aquifer system; and the Texas coastal uplands and lowlands aquifer 

systems; and two regional aquifers the Mississippi River 

valley alluvial aquifer and the McNairy-Nacatoch aquifer. 

Preliminary results of the regional study and the subregional 

studies have been published in numerous reports (Weeks and 

Sun, 1987, p. 49; Williamson and others, 1990). Final 

reports of both regional and subregional scope that describe 

the geohydrologic framework, ground-water flow, and 

geochemistry of the aquifers and aquifer systems are planned 

for release in U.S. Geological Survey Professional Paper 

1416 as parallel chapters to this report.

Massive clays of minimal permeability comprising the 

Vicksburg-Jackson confining unit underlie the coastal lowlands aquifer system and separate it from the underlying 

Texas coastal uplands aquifer system in Texas and the underlying Mississippi embayment aquifer system to the east. The 

upper 200 ft of the coastal lowlands aquifer system is equivalent to the Mississippi River valley alluvial aquifer in 

east-central Louisiana. The coastal lowlands aquifer system 

is equivalent to the Chickasawhay River aquifer of the 

Southeastern Coastal Plain to the east in Alabama and Florida (Miller and Renken, 1988, p. 7).

The eastern part of the coastal lowlands aquifer system 

includes aquifers in deposits of late Oligocene age and 

younger in central and southern Louisiana, southern Mississippi, southern Alabama, and western Florida (fig. 2). This 

study is restricted to that part of the aquifer system containing water with dissolved-solids concentrations of 10,000 

mg/L or less.

PURPOSE AND SCOPE

This report presents the results and conclusions of a study 

of the eastern part of the coastal lowlands aquifer system. 

Existing data on water levels, water use, water quality, and 

aquifer properties were used to construct a multilayer digital 

model to simulate flow in the aquifer system. The report 

briefly describes the geohydrologic framework of the aquifer 

system and the development, calibration, and sensitivity analysis of a ground-water-flow model, but it is primarily 

focused on the results of the simulations that show the natural flow of ground water throughout the regional aquifer system and the changes from the natural flow caused by 

development of ground-water supplies.

PREVIOUS STUDIES

Previous regional studies of the Mississippi embayment 

and the Gulf Coastal Plain were used to establish the broad

geologic and hydrologic framework of the study area. 

Statewide, multicounty, and multiparish reports were used to 

define the framework. Where necessary, and particularly in 

heavily stressed areas, local and single county or parish studies were used to complete the definition of the hydrologic 

framework. Previous model studies of parts of the study 

area were used as guides in the development of the digital 

ground-water flow model used in this study. (See "Selected 

References.")

An interim report by Martin and Whiteman (1989) 

describes the geohydrologic framework of the aquifer system 

and the development of the digital ground-water-flow model 

used to quantify flow in the aquifer system. Calibration and 

sensitivity analysis of the model under both steady-state and 

transient flow conditions are described by Martin and Whiteman. (1990).

Other reports prepared as part of this study include a 

series of maps of the potentiometric surfaces of major aquifers in deposits of late Oligocene age and younger in Louisiana (Martin and Whiteman, 1985a; 1985b; 1986; Martin, 

Whiteman, and Becnel, 1988), a statistical summary of aquifer-test results for aquifers in Louisiana (Martin and Early, 

1987), and a report showing two geohydrologic sections in 

northern Louisiana (Whiteman and Martin, 1984).

PHYSICAL SETTING

The study area is in the eastern part of the Gulf of Mexico 

Coastal Plain in the Southeastern United States and covers 

72,700 mi2 of which about 58,500 mi2 is land area and 

inland water bodies and the rest is offshore in the Gulf of 

Mexico. It extends from the Sabine River, the boundary 

between Louisiana and Texas, on the west to the Escambia 

River in the Florida Panhandle on the east (fig. 2). The 

study area extends from about 50 mi offshore to 100 mi 

inland at its western end, from near the coastline to 220 mi 

inland in the central part, and from about 25 mi offshore to 

75 mi inland near its eastern end.

PHYSIOGRAPHY

Land-surface altitude in the study area ranges from more 

than 500 ft above sea level in southwestern Mississippi to 

sea level along the coast. Much of the marsh area along the 

Louisiana coast is at or only slightly above sea level. Several large agricultural areas in the coastal marshes and parts 

of the city of New Orleans lie several feet below sea level. 

The land surface in the study area originally consisted of a 

sequence of terraces sloping gently toward the coast. The 

older, higher terraces have been heavily dissected in the 

northern and eastern parts of the study area, resulting in a 

terrain of gently rolling to steep hills and valleys with local 

relief of 100 to 200 ft common. Large areas of the younger,
EXPLANATION

REGIONAL 10-MILE AND SUBREGION 5-MILE GRID BLOCKS

Texas coastal uplands 

and lowlands aquifer system

McNairy-Nacatoch 

aquifer

Mississippi embayment 

aquifer system

Regional 10-mile grid

Mississippi River valley 

alluvial aquifer

Coastal lowlands aquifer 

system of Alabama, 

Florida, Louisiana, and

Missippi

o ^(f^vVP^^Jf^V^?8*?*1^^^^

96» %^£^S^^

,^5^^;^^ :^ A. §^$^^?®§% ':^^^<^^^c^

\.$$&$$&$8^

* V^' m^m^m >'X '^'VA" Jx^A'V*''v\ xVA

Modified from Williamson and others (1989, fig. 2)

3 50 100I 150 MILES

1 ' 1 1

0 50 100 150 KILOMETERS

Ro o~<

o-d

H 

I W 

O O

O

cs

Base from U. S. Geological 

Survey 1:2 500 000

FIGURE 1. Regional and subregional model areas.

ffi

UJ
H4 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

EXPLANATION

 ------ BOUNDARY OF THE REGIONAL STUDY AREA

 BOUNDARY OF THE EASTERN COASTAL LOWLANDS STUDY AREA

 | AXIS OF SYNCLINE

 | AXIS OF ANTICLINE

i i i r FAULT Hachures on downthrown side

FIGURE 2. Location of the study area and major structural features in and near the study area.

lower terraces remain nearly undissected in the central part 

of the study area.

The Mississippi River and its alluvial valley are dominant 

features. The river and its broad, low-lying, poorly drained 

valley have, from the time of the earliest travelers, hindered 

east-west movement of people and goods while providing 

relatively easy and economical north-south travel by boat and 

barge. From the northern edge of the study area to a few 

miles south of Baton Rouge, La., the altitude of the alluvial

valley floor is lower than the surrounding area, so the valley 

forms a drain for both the surface-water and the 

ground-water flow systems. The Mississippi River is presently flowing along the eastern side of the valley, which 

ranges from about 25 to 50 mi wide. This area was designated the Mississippi Alluvial Plain by Fenneman (1938).

In coastal southeastern Louisiana natural levees along the 

present and ancestral courses of the Mississippi River and its 

distributaries form the highest land. No tributaries enter the
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H5

Mississippi River below Baton Rouge. The natural levees 

slope gently downward from crests near the stream banks to 

merge into surrounding backswamps and marshes. The 

bands of high ground formed by the natural levees range 

from less than 1 mi wide along smaller distributaries and 

near the coast to more than 20 mi wide where the modern 

channel of the Mississippi River emerges from the youngest 

of the terrace surfaces south of Baton Rouge. Almost all 

residential, commercial, and industrial development along the 

Mississippi River and its distributaries south of Baton Rouge 

has been along the crests of the natural levees.

Several major rivers in addition to the Mississippi River 

drain parts of the study area. The Sabine River forms the 

western boundary of the area. The Red and Homochitto Rivers drain into the Mississippi River in the north-central part. 

The Pearl, Leaf, and Tombigbee Rivers drain the eastern part 

of the area. The Alabama and Escambia Rivers form the 

eastern boundary. Numerous smaller rivers, streams, and 

bayous drain intervening parts of the area.

CLIMATE

The study area is characterized by long, hot, humid summers and relatively short, mild winters. Throughout the area, 

monthly mean temperatures are lowest in January and highest in July (fig. 3). Mean temperatures generally increase 

from north to south, but temperature extremes are moderated 

in the coastal part of the area by the effects of the Gulf of 

Mexico and the water surfaces exposed in lakes, streams, and 

marshes.

Precipitation, almost all in the form of rain, increases from 

northwest to southeast across the area, with the greatest 

amount, over 64 in., occurring a short distance inland from 

the coasts of Mississippi, Alabama, and Florida and inland 

northeast of Baton Rouge, La. (fig. 4). Although there are 

no pronounced wet or dry seasons, October is generally the 

driest month. Potential evapotranspiration, estimated by the 

Thornthwaite technique (Thornthwaite, 1948; Thornthwaite 

and Mather, 1955), generally exceeds precipitation from June 

through August (fig. 3). Precipitation exceeds potential 

evapotranspiration from November through April. Precipitation and potential evapotranspiration are generally about 

equal during May, September, and October.

HYDROGEOLOGIC SETTING

The coastal lowlands aquifer system consists of alternating 

beds of sand, gravel, silt, and clay in off-lapping, coastward-thickening wedges of sediment deposited under fluvial, 

deltaic, and marine conditions. The aquifer system 

comprises sediments of late Oligocene age and younger in

the study area (Grubb, 1984) and has been described in 

detail by Weiss (1990).

Sediments of the coastal lowlands aquifer system are 

extremely heterogeneous. Changes in lithology occur over 

short distances laterally and vertically. Sand or gravel beds 

are not traceable for more than a few miles. Coarse sand 

and gravel are common in the northern part of the study area 

but become finer and less common southward, grading to 

sandy silt or clay and finally to clay. Lime and marl occur in 

the lower and eastern parts of the aquifer system. Dip of 

individual beds is southward, ranging from about 10 to 50 

ft/mi in the outcrop and subcrop areas. Dip increases in a 

southerly direction and with increasing depth. Maximum dip 

is well over 100 ft/mi in the southern parts of the study area 

(Martin and Whiteman, 1989, p. 3). Total thickness of the 

coastal lowlands aquifer system ranges from a featheredge 

along the northern edge of the outcrop of the aquifers to 

more than 16,000 ft in southeastern Louisiana near New 

Orleans (Grubb, 1987, fig. 7).

The coastal lowlands aquifer system is underlain by the 

Jackson and Vicksburg Groups, designated the Vicksburg-Jackson confining unit (Grubb, 1986, p. 6). The Jackson and Vicksburg Groups consist of extensive beds of clay, 

silt, and lime deposited during the last major transgression of 

the sea across the area in late Eocene and Oligocene time. 

Sands in the upper part of the Jackson and Vicksburg 

Groups, where thick and extensive enough to form aquifers, 

have been included in the coastal lowlands aquifer system.

Two major structural features, the north-south-trending 

Mississippi structural trough and the east-west-trending Gulf 

Coast geosyncline, intersect near the southern boundary of 

the study area (fig. 2). These two structural troughs, by controlling the location and thickness of sediment deposition, 

have been the dominant factors shaping the aquifer system in 

the study area. '

Large systems of growth faults and numerous salt domes 

occur in the southern part of the study area. The faults displace sediments downward to the south and may act as barriers to ground-water movement in the aquifer system (Rollo, 

1969). Salt domes displace sediments of the aquifer system 

and distort the sediments immediately around them. For this 

study, the collective effect of the growth fault systems has 

been considered as a reduction in the transmissivity of the 

aquifers within the system. The effects of the salt domes are 

thought to be too localized to have a significant effect on 

regional ground-water flow and were not considered in this 

investigation.

The geometry of the aquifer system was defined using a 

network of 279 electrical logs spaced 10 to 20 mi apart. 

Sand and gravel beds were identified on the logs and the 

depth, thickness, spontaneous potential, and resistivity of 

each bed over 20 ft thick were recorded and analyzed. 

Similarly, silt and clay beds were identified and their 

thickness and resistivity were recorded and analyzed.
H6 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

35 

^ 30

u3 25 

V) 20

LU 

LU

§ 15

LU

Q 10

5

8

VICKSBURG, MS

LU m~

LAKE CHARLES, LA

E -J - 

o<zf

| | POTENTIAL EVAPOTRANSPIRATION 

| | PRECIPITATION

z £

o <

2 >

O 2 -

n

M O N D M

35 

Z ?« 30

5 D Lu 25 

j < w 20

I- LU HI _

Z Q- oc 15 

O 2 CD

 5 LU LU

^ I- Q 10

5

8

UF 5 6

u $z 5

H O 2 

§ £

MOBILE, AL NEW ORLEANS, LA

1 -

0

JFMAMJJASOND JFMAMJJASOND 

FIGURE 3. Monthly mean temperature, precipitation, and potential evapotranspiration at selected sites in and near the study area for the period 1951-80.

These data were summarized by Wilson and Hosman 

(1987).

A zone of abnormally high lluid pressure, the geopressured 

zone, occurs in the southern part of the study area within the 

sediments comprising the coastal lowlands aquifer system.

Movement of fluids between the geopressured zone and the 

normally pressured overlying sediments is probably small 

compared to movement of fluid within the normally pressured zone (Grubb, 1986, p. 4). Where the geopressured 

zone occurs within the sediments of the coastal lowlands
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H7

60 80 100 MILES 

I____I_____I

I I I I I I

0 20 40 60 80 100 KILOMETERS

EXPLANATION

. 60 __ LINE OF EQUAL NORMAL ANNUAL 

PRECIPITATION Hachures indicate 

closed areas of lesser precipitation. 

Interval 2 inches

 CONTROL POINT

FIGURE 4. Annual mean precipitation in and near the study area for the period 1951-80.

aquifer system, the top of the geopressured zone is considered to be the base of the aquifer system. (See pi. 1.) 

This study is restricted to the freshwater-bearing part of 

the coastal lowlands aquifer system, defined as that part of 

the system containing water with dissolved solids

concentration of 10,000 mg/L or less. Water with dissolved 

solids concentration greater than 10,000 mg/L is not considered part of the flow system. Thus, the thickness of the part 

of the coastal lowlands aquifer system considered in this 

study is much less than that of the total aquifer system. The
H8 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

40 60 80 100 MILES

I I I I I I

0 20 40 60 80 100 KILOMETERS

EXPLANATION

_7/000 _ LINE OF EQUAL THICKNESS - 

Hachures indicate closed areas of 

lesser thickness. 

Interval 1,000 feet; 

supplemental Interval 500 feet

FIGURE 5. Thickness of the freshwater-bearing part of the coastal lowlands aquifer system.

thickness of the freshwater-bearing part ranges from 0 ft 

along the northern edge of the aquifer system to more than 

4,000 ft in southeastern Louisiana and southern Mississippi 

(fig. 5). Total sand-and-gravel thickness within this part of 

the aquifer system ranges from 0 ft along the northern edge 

of the aquifer system to more than 2,000 ft in southeastern

Louisiana and southern Mississippi (fig. 6). The percentage 

of sand and gravel, and, thus, the transmissivity of a given 

thickness of the aquifer system, varies from less than 10 to 

over 80 percent (fig. 7).

Ground-water flow in the coastal lowlands aquifer system 

prior to development was primarily in a southerly direction
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H9

from the upland terrace areas of south-central and southeastern Louisiana and southwestern Mississippi (fig. 8). Some 

water was discharged locally in these areas to streams or by 

evapotranspiration. Water not locally discharged moved 

downward and merged with the regional flow system to be 

discharged at lower altitudes along the major river valleys 

and near the coast. Under natural conditions water levels 

decreased with depth in the recharge areas and increased 

with depth in the discharge areas.

Saltwater occurs in the downdip marine and deltaic parts 

of the aquifer system. Freshwater moving downdip from the 

recharge areas tends to flush the saltwater ahead of it until 

pressures are in balance or unless movement is blocked by 

pinchout of the sand beds or by faulting. The sand beds 

offshore dip at steeper angles than the slope of the sea floor 

and are covered by a blanket of hundreds of feet of unconsolidated clay so there is no direct hydraulic connection 

between sands of the aquifer system and the Gulf of Mexico. 

Saltwater in the downdip part of the aquifer system may 

leave the system by moving vertically upward through overlying sediments.

The present position of the freshwater-saltwater interface 

is the result of the interactions of the driving hydraulic head, 

the density of the saltwater, the permeability and porosity of 

the sands, and the vertical hydraulic conductivity of the sediments overlying the saltwater (Martin and Whiteman, 1989, 

p. 4).

REGIONAL PERMEABLE ZONES

The coastal lowlands aquifer system was subdivided into 

five regional permeable zones to quantify the distribution of 

flow within the system (Grubb, 1987, p. 110-113). The 

permeable zones were defined in areas of intense pumpage, 

such as Baton Rouge, La., and Houston, Tex., by delineating 

zones of similar water levels (Weiss and Williamson, 1985). 

Measured water levels in the zones near Baton Rouge in 

1980 are shown in figure 9. After the zones were defined in 

the areas of heavy pumpage, they were extended along the 

strike of the beds by maintaining the thickness of each zone 

as a constant percentage of the aquifer system thickness. 

The zones pinch out in the updip direction, approximating 

the outcrop pattern in which progressively older bands of 

sediment are exposed in the updip direction (fig. 8). The 

zones were terminated downdip along the line where water 

in all sand beds over 20 ft thick within the zone had dissolved solids concentrations of more than 10,000 mg/L. The 

dissolved solids concentration was estimated from spontaneous potential and resistivity data from electric logs (Weiss, 

1987).

The permeable zones represent deposits that from youngest to oldest are Holocene-upper Pleistocene deposits (zone

A), lower Pleistocene-upper Pliocene deposits (zone B), 

lower Pliocene-upper Miocene deposits (zone C), middle 

Miocene deposits (zone D), and the lower Miocene-upper 

Oligocene deposits (zone E). Table 1 shows the relation 

between the permeable zones and local aquifer names. The 

ages designated for the regional permeable zones are relative. 

The zones may contain beds that are younger or older than 

the indicated age. Plate 1 shows the regional zones on 

east-west and north-south hydrogeologic sections, respectively. The areal extent of permeable zone A, the uppermost 

zone, and the outcrop areas of underlying zones B through E 

are shown in figure 10.

HYDRAULIC PROPERTIES OF THE 

REGIONAL PERMEABLE ZONES

Lateral hydraulic conductivities of sand beds within the 

regional permeable zones were determined by examining 

3,077 aquifer tests from the coastal lowlands aquifer system 

within the study area (A.K. Williamson, U.S. Geological 

Survey, written commun., 1988). The aquifer tests are 

clustered in areas of heavy ground-water pumpage rather 

than uniformly distributed. Martin and Early (1987) 

described the compilation, summarization, and statistical 

analysis of 1,001 aquifer-test results in Louisiana which 

include tests of aquifers in the coastal lowlands aquifer 

system.

The "effective" lateral hydraulic conductivity of the permeable zones is lower than the arithmetic mean of values 

from aquifer tests. Clay beds separating the discontinuous 

sand beds within each zone disrupt the continuity of lateral 

flow within the zone. In addition, wells generally are completed in the most permeable, highest yielding sand beds 

available at a given site, so aquifer test results typically will 

be biased toward the sand beds with the highest hydraulic 

conductivities.

The results of statistical analysis of lateral hydraulic conductivity values from all of the aquifer tests are shown in 

table 2. Arithmetic, geometric, and harmonic means were 

calculated for each permeable zone. The arithmetic mean is 

most affected by extreme high values, whereas the harmonic 

mean is most affected by extreme low values. The average 

of the arithmetic and harmonic means of lateral hydraulic 

conductivity for each zone was used as a representative value 

for that zone in estimating transmissivities during initial 

model simulations. The average of the arithmetic and harmonic means is slightly higher than the geometric mean for 

each zone.

Lateral hydraulic conductivity decreases from the upper to 

the lower permeable zones. On average, zone A, of 

Holocene-upper Pleistocene age, has the highest hydraulic 

conductivity, whereas zone E, of lower Miocene-upper Oligocene age, has the lowest. The large standard deviation
H10 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

0 20 40 60 80 100 MILES

I_____|_____II I I 

I I \ T I I

0 20 40 60 80 100 KILOMETERS 

EXPLANATION

-500- LINE OF EQUAL THICKNESS - 

Hachures indicate closed areas 

of lesser thickness. 

Interval 500 feet

FIGURE 6. Total thickness of sand and gravel in the freshwater-bearing part of the coastal lowlands aquifer system.

about the arithmetic mean indicates the large variability of 

lateral hydraulic conductivity within the permeable zones.

Extensive confining clay beds do not occur within the 

coastal lowlands aquifer system, but large water-level differences do occur vertically within the flow system. To provide 

the restriction to vertical flow needed to produce these

water-level differences, all the clay beds (including silt and 

sandy clay) between the centers of adjacent permeable zones 

were treated as being equivalent to a single clay layer (Bredehoeft and Finder, 1970).

Few data exist to define the vertical hydraulic conductivity 

of the aquifer system. None of the aquifer tests were
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM Hll

0 20 40 60 80 100 MILES

I . I . I . I. I I

I I \ I I 1

0 20 40 60 80 100 KILOMETERS

EXPLANATION

SAND PERCENTAGE

80 to 90 

70 to 80 

60 to 70

50 to 60 

40 to 50 

30 to 40

20 to 30 

10 to 20 

OtolO

FIGURE 7. Percentage of sand and gravel in the freshwater-bearing part of the coastal lowlands aquifer system.

suitable for calculation of vertical leakage across interbedded 

clays. Laboratory measurements of two core samples under 

in-situ confining pressures from test wells at Baton Rouge,

La. (Whiteman, 1980, table 4), gave values of vertical 

hydraulic conductivity of l.lxlfJ6 fl/d for a core from a 

depth of 450 ft (zone A) and 1.7xlO~5 ft/d for a core from a
H12 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

Gulf of Mexico

A i DISCHARGE

Not to scale

EXPLANATION

FRESHWATER 

SALTWATER

BASE OF THE FLOW 

SYSTEM STUDIED

GENERAL DIRECTION 

OF REGIONAL 

GROUND-WATER FLOW

FIGURE 8. Generalized hydrogeologic section showing zonation of the coastal lowlands aquifer system and direction of regional ground-water

flow.

depth of 2,1(5 ft (zone C). Laboratory measurements of 

clay cores from the Lake Charles industrial area (F.S. Riley, 

U.S. Geological Survey, written commun., 1973) gave aver-

-6

age values of vertical hydraulic conductivity of 7.6x10 ft/d

under a confining pressure equivalent to a 400 ft depth of 

burial and 3.8x10 ft/d under a confining pressure equivalent 

to a 600 ft depth of burial. The mixtures of clay, silt, and 

sandy clay that form the beds that account for most of the
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H13

500

1,000

1,500

2,000

2,500

3,000

3,500

MEASURED WATER 

LEVEL, 1980

Permeable zone A , *

Permeable zone B

Permeable zone C

Permeable zone D

Permeable zone E (No measurements at Baton 

i Rouge-contains saltwater) ,

100 0 -100 -200 -300 

WATER LEVEL ABOVE OR BELOW SEA LEVEL, IN FEET

FIGURE 9. Variation of water levels with depth and the zonation of the 

coastal lowlands aquifer system at Baton Rouge, Louisiana.

restriction of vertical flow within the coastal lowlands aquifer system would be expected to have larger vertical hydraulic conductivities than the relatively pure clays used for the 

laboratory tests. For initial simulations of the aquifer system, a uniform value of 2.0x10"5 ft/d was used for the vertical hydraulic conductivity of the clays within and between 

permeable zones.

Initial transient simulations specified a uniform storage 

coefficient of l.OxlO"4 for all permeable zones throughout 

the model. Too few values of storage coefficient were available from aquifer-test results to permit statistically valid 

determinations of areal or vertical variations. The uniform 

value of storage coefficient was later refined by calculating 

values for each model block. The thicknesses of sand and 

clay (including silt and sandy clay) in each block were multiplied by values of specific storage of l.OxlO'6 for sand 

(Lohman, 1972, p. 12) and 4.0x10'6 for clay (Ireland and 

others, 1984, table 4). This provides an areal variability in 

storage coefficient that reflects the areal variations in the 

thickness and the sand and clay content of each permeable 

zone.

GROUND-WATER PUMPAGE

Ground water is pumped for municipal, industrial, agricultural, and domestic use throughout most of the study 

area. The division of pumpage, between point-type withdrawals (as defined by Mesko and others, 1990, p. 25), primarily for public supply and industrial use, and areal-type 

withdrawals, primarily for irrigation, is shown in figure 11. 

Martin and Whiteman (1989, figs. 24-28) gave the areal

distribution of the pumpage for 1980 from each zone. The 

areal distribution of pumpage in 1985 from all permeable 

zones combined is shown in figure 12.

Table 3 summarizes pumpage from each of the permeable 

zones of the coastal lowlands aquifer system at 5-year intervals for the period 1960-85. Throughout the period 

1960-85, pumpage from permeable zone A, the youngest 

deposits, has ranged from 59 to 67 percent of the total pumpage from the aquifer system. Most of the water from zone A 

is used for rice irrigation in southwest Louisiana, but significant amounts are pumped for industrial and municipal use at 

Lake Charles, La., industrial use at Baton Rouge, La., and 

industrial and commercial use at New Orleans, La., and 

Natchez, Miss. Pumpage from permeable zones B through E 

is less concentrated than that from zone A, but significant 

amounts of water are withdrawn at Baton Rouge (zones B 

through D), Beaumont, Tex. (zones B and C), Alexandria, 

La. (zone D), Bogalusa, La. (zone D), and in the Pensacola, 

Fla., area (zones D and E).

Total pumpage from the coastal lowlands aquifer system 

generally increased from 1960 to 1980, when it peaked at 

about 1,874 Mgal/d (251 Mft3/d). Pumpage then declined by 

more than 15 percent to about 1,579 Mgal/d (211 Mft3/d) by 

1985 (table 3). Pumpage for industry and public supply 

peaked in 1975 (fig. 11). After 1975, declines in industrial 

pumpage in response to economic and environmental factors

were greater than increases in pumpage for municipal use. 

Changes in pumpage for agriculture were primarily a result 

of changes in pumpage for rice irrigation in southwestern 

Louisiana.

REGIONAL GROUND-WATER FLOW

The primary tool used to analyze regional ground-water 

flow in the coastal lowlands aquifer system was a six-layer 

finite-difference ground-water-flow model. Conceptualization, construction, calibration, and sensitivity analysis of this 

model are described in detail by Martin and Whiteman 

(1989; 1990). A brief description of the model and of modifications made to the model since completion of the earlier 

reports is given in this report.

MODEL DEVELOPMENT AND BOUNDARIES

Each permeable zone of the aquifer system is represented 

by a model layer (table 1) with an additional layer used as 

the upper boundary of the model. Model layer 1, consisting 

of constant-head nodes, forms an upper boundary covering 

all of the active area of the model. The heads of the constant-head nodes are set at the altitude of the water table. 

The constant-head layer represents the effects of all surficial 

sources of natural recharge to and discharge from the aquifer 

system, such as precipitation, evapotranspiration, and
TABLE 1. Relation of the regional permeable zones to model layers and to previously named principal aquifers

Gulf Coast RASA 

regional 

permeable zone

Zone A 

(Holocene-upper 

Pleistocene 

deposits) 1

Zone B 

(Lower 

Pleistocene-upper 

Miocene deposits)

ZoneC 

(Lower Plioceneupper Miocene 

deposits)

ZoneD

(Middle Miocene 

deposits)

Zone E 

(Lower Mioceneupper Oligocene 

deposits)

Model 

layer 

number

2

3

4

5

6

Aquifers in Louisiana

Upland terraces Alluvial "400-foot" sand 

"Shallow sands" Plaquemine of Baton Rouge 

Chicot Gramercy ("200-foot" "600-foot" sand 

"200-foot" sand sand of New Orleans) of Baton Rouge 

of Lake Charles Norco ("400-foot" Atchafalaya 

"500-foot" sand sand of New Orleans)

of Lake Charles Gonzales-New Orleans 

"700-foot" sand ("700-foot" sand 

of Lake Charles of New Orleans) Ponchatoula (upper)

"1 ,200-foot" sand of New Orleans Ponchatoula (lower) 

"800-foot" sand of Baton Rouge Big Branch 

"1,000-foot" sand of Baton Rouge Kentwood 

"1,200-foot" sand of Baton Rouge Abita 

"1,500-foot" sand of Baton Rouge Covington 

"1 ,700-foot" sand of Baton Rouge Slidell 

Blounts Creek 

Evangeline (upper)

"2,000-foot" sand of Baton Rouge Evangeline (lower) 

"2,400-foot" sand of Baton Rouge 

Tchefuncta 

Hammond 

Zone 2 of Florida parishes and Williamson Creek 

Pointe Coupee (upper) Jasper (upper)

Zone 2 of Florida parishes and Jasper (lower) 

Pointe Coupee (lower) Carnahan Bayou 

Zone 3 of Florida parishes and 

Pointe Coupee 

"2,800-foot" sand of Baton Rouge 

Amite 

Ramsay 

Franklinton

Catahoula

Aquifers in Mississippi

Undifferentiated alluvial and 

terrace

Mississippi River alluvial

Terrace 

Citronelle

Miocene (upper)

Miocene (middle)

Miocene (lower)

Aquifer

Alabam

Absen

Absen

Alluvial 

Terrace 

Citronelle (

Citronelle (

Miocene (u

Miocene (lo

'Grubb, 1987, p. 110-113. RASA, Regional Aquifer-System Analysis. Because of regional structure and the way the regional permeable zones were d

chronostratigraphic lines in places; the greatest discrepancies occur in western Florida and southwestern Alabama, where zones D and E consist of sedime

Miocene age.
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H15

0 20 40 60 80 100 MILES

I . I . I . I. I I I i i ri i

0 20 40 60 80 100 KILOMETERS

EXPLANATION

OUTCROPS OF THE PERMEABLE ZONES

Zone D, middle Miocene deposits Zone A, Holocene upper 

Pleistocene deposits

Zone B, lower Pleistocene upper 

Pliocene deposits 

Zone C, lower Pliocene upper 

Miocene deposits

Zone E, lower Miocene upper 

Oligocene deposits

FIGURE JO. Area) extent of the coastal lowlands aquifer system and the outcrop areas of the permeable zones.
H16 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

TABLE 2. Lateral hydraulic conductivities of sand beds within the permeable zones based on aquifer-test results

Ifi/d, I'ccl per day]

Permeable 

zone

A

B

C

D

E

Number of 

aquifer tests

1,126

515

487

521

428

Arithmetic 

mean (ft/d)

163

97

96

78

72

Standard 

deviation 

(ft/d)

152

110

99

71

55

Harmonic 

mean (ft/d)

49

19

19

18

11

Average of harmonic and 

arithmetic mean (ft/d)

106

58

58

48

42

Geometric 

mean (ft/d)

101

51

51

42

36

seepage to or from streams, lakes, and the Gulf. Use of a 

constant-head upper boundary for modeling is justified 

because there has been no significant decline in the water 

table as a result of ground-water pumpage through 1987. 

The constant-head boundary has the potential of supplying 

unlimited recharge from layer 1 to underlying layers. Flow 

downward from layer 1 was monitored during model simulation to ensure that recharge does not reach unreasonable 

levels at any point (Martin and Whiteman, 1990, p. 7). 

Model layer 2 represents the youngest part of the aquifer 

system, the Holocene-upper Pleistocene deposits (permeable 

zone A). Progressively older deposits are represented by 

lower model layers, with model layer 6 representing the 

lower Miocene-upper Oligocene deposits (permeable zone 

E).

The finite-difference grid and the active area of the model 

are shown in figure 13. A uniform grid-block (node) spacing of 5 mi was used (fig. 1). The vertical structure of the 

model and boundaries is shown in figure 14. Lateral boundaries in the model are predominantly no-flow. Along the 

northern side of the model, no-flow boundaries in each 

model layer simulate the updip limit of the permeable zone 

represented by that layer. Along the eastern side of the 

model, permeable beds within the aquifer extend beyond the 

study area but are thin and are not extensively used as a 

source of ground water. The potential flow across the eastern boundary is sufficiently small to permit use of a no-flow 

boundary without introducing significant errors at the scale

of this model. Alluvial deposits of the Mississippi River, 

included in zone A, extend northward beyond the boundary 

of this model. A line of specified-flux nodes across the river 

valley in layer 2 at the northern edge of the model (fig. 13). 

simulates ground-water inflow to the model area in the alluvial deposits. The amount of flow specified for each node 

was determined from a model of the alluvial aquifer covering this area (fig. 1), which is described by Ackerman 

(1989).

The southern boundary for each model layer represents 

the downdip extent of water with a dissolved solids concentration of 10,000 mg/L or less in any sand bed within the 

layer. This is a modification of the southern boundary of the

steady-state model described in Martin and Whiteman 

(1989, p. 9). The downdip boundary used in the 

steady-state model described in that report was determined 

by estimating the average dissolved solids concentration of 

water in all sands greater than 20 ft thick within each permeable zone. Where the average dissolved solids concentration was greater than 10,000 mg/L, the entire thickness of 

the zone was considered saline and not part of the active 

flow system. This procedure produced a boundary with 

abrupt cutoffs of permeable zones that did not realistically 

approximate the observed freshwater-saltwater interface 

(Martin and Whiteman, 1989, pi. 2). The modified southern 

boundary used in the model described in this report 

represents actual conditions more realistically, better simulating ground-water flow near the interface.

Assuming that no flow occurs in that part of the aquifer 

system with water containing more than 10,000 mg/L dissolved solids introduces some distortion to the analysis of 

regional ground-water flow because such water may move 

into the part of the aquifer system simulated in this study in 

response to pumpage. But on a regional scale, the distortion 

is not significant. On a local scale, intense pumpage near 

the southern boundary of a permeable zone could induce 

saltwater encroachment. Prediction of the rate of encroachment would be adversely affected by the flow distortion, but 

such local effects were not addressed in this study. Flow in 

the entire aquifer system, including the saltwater-bearing 

part, is discussed in Williamson and others (1989).

No natural hydrologic boundaries are present in the 

coastal lowlands aquifer system on the western edge of the 

study area. To minimize boundary effects within the study 

area, the model was extended into Texas to a line between 

pumping centers at Lake Charles, La., and Houston, Tex. 

The area west of the Sabine River is included in a study of 

the coastal lowlands aquifer system of Texas (Ryder, 1988). 

In the steady-state model described in Martin and Whiteman 

(1989), the western boundary was treated as a no-flow 

boundary lying along a ground-water divide between the 

pumping centers. Further analysis of water-level data indicated that there was the potential for significant flow across 

this divide under both predevelopment (inflow to the model)
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H17

250 -

2,000

1,500

1,000

- 500

1960 1965 1970 1975 1980 1985

YEAR

EXPLANATION

PUMPAGE

!: : I Agricultural and

rural domestic 

^^ Industrial and

public supply

FIGURE 11. Purnpage from the coastal lowlands aquifer 

system by major category of use, 1960-8.5.

and 1987 (outflow from the model) conditions. To simulate 

these flows, the no-flow nodes along the western boundary 

of the steady-state model were changed to general-head 

nodes (McDonald and Harbaugh, 1988, chap. 11) in model 

layers 2-6. Heads at the general-head boundary were determined from simulations of the coastal lowlands aquifer system in Texas (Ryder, 1988). These heads were updated at 

the start of each pumping period to reflect changes in water 

levels along the boundary through time. General-head 

nodes pcnnit flow across the model boundary based on the 

gradient between simulated water levels at the boundary and 

specified water levels outside of the boundary.

The base of the model was initially treated as a no-flow 

boundary (Martin and Whiteman, 1989, p. 9). During the 

conceptualization and development of the model, flow 

across the thick and areally extensive clays of the Vicksburg-Jackson confining unit were assumed to be negligible. 

Modeling results from a parallel study of the Mississippi 

cmbayment aquifer system of Eocene age underlying the 

Vicksburg-Jackson confining unit indicated relatively small 

flows across the confining unit under conditions existing 

from predcvelopment to 1987 (Arthur and Taylor, 1990). 

These flows, on the order of 0.1 to 0.7 MiVVd, were

incorporated during calibration of the model of the coastal 

lowlands aquifer system (Martin and Whiteman, 1990, p. 

21) by specifying flows into or out of parts of model layer 6 

representing permeable zone E (fig. 14).

MODEL CALIBRATION AND SENSITIVITY 

ANALYSIS

The flow model was initially calibrated to 1980 conditions 

treated as steady state. Although the entire model area was 

not at steady state in 1980, the rate at which water levels 

and storage were changing was not considered significant in 

relation to the scale of the aquifer system (Martin and 

Whiteman, 1989, p. 14). Calibration consisted of adjusting 

transmissivities of the permeable zones represented by 

model layers and the vertical leakances between layers that 

control vertical flow. Other parameters required for simulation, such as water-table altitudes for the constant-head 

upper layer, ground-water pumpage, and specified flows 

across the boundaries of the model, were assumed to be correct; therefore, they were not adjusted during calibration. 

Calibration was based on minimizing root-mean-square error 

(RMSE) values of the residuals between simulated and measured water levels for all permeable zones throughout the 

model area. Flow rates and volumetric budgets of the 

coastal lowlands aquifer system could not be measured independently with enough accuracy to use quantitatively in calibrating the model because errors in measurement of 

surface-water flow in the study area may be greater than 

total flow in the aquifer system. Model-computed flow rates 

and volumetric budgets, however, provided essential qualitative checks on model results. The model cannot be considered to be adequately calibrated if simulated flows are not 

within a range of expected values defined by previous studies in similar areas even though simulated and measured 

water levels may closely match. After steady-state calibration using 1980 pumpage (table 3), ground-water pumpage 

was removed from the model to simulate predevelopment 

conditions.

Storage coefficients were calibrated using a transient version of the model for the period from 1898 to 1987. Nine 

pumping periods were simulated: 1898-1917, 1918-37, 

1938-57, 1958-62, 1963-67, 1968-72, 1973-77, 1978-82, 

and 1983-87. Although pumpage and water-level data prior 

to 1958 were too sparse to use statistically in calibration of 

the model, the first three pumping periods produce transient 

conditions in the simulated flow system similar to the transient conditions present in the aquifer system in 1958 at the 

start of the calibration period. The distribution of the water 

levels used for calibration to 1980 conditions is shown in 

Martin and Whiteman (1989, figs. 34-38). Similar distributions of water levels were used for each of the other
HIS REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

0 20 40 60 80 100 MILES

I_____\_____II I I

I I I I I I

0 20 40 60 80 100 KILOMETERS

EXPLANATION

PUMPAGE RATE, IN MILLION GALLONS

PER DAY (MILLION CUBIC FEET PER DAY)

Less than 0.05 (0.007) not shown.

E) 0.05-1(0.007-0.13) 10-15(1.34-2.00)

 1-5(0.13-0.87) 15-20(2.00-2.67)

 5-10(0.87-1.34) Greater than 20 (2.67)

FIGURE 12. Area! distribution of pumpage from the coastal lowlands aquifer system, 1985.

pumping periods. The pumpages shown in table 3 were 

used for calibration.

The model was calibrated by matching simulated and 

measured water levels at the ends of pumping periods 3

through 9, from 1957 to 1987, which coincide with periods 

of significant changes of ground-water development and 

with periods of intensive collection of pumpage and 

water-level data. Complete water-level data for 1987 (the
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H19

TABLE 3. Pumpa^e of water from the coastal lowlands aquifer system in the study area for the period 1960-85

|Mgal/d, million gallons per day|

Perm- I960 1965 1970 1975 1980 1985

eable Rate Percent Rate Percent Rate Percent Rate Percent Rate Percent Rate Percent

zone (Mgal/d)______(Mgal/d)______(Mgal/d)______(Mgal/d)______Mgal/d)______(Mgal/d)

A

B

C

D

E

800.2

70.3

100.1

164.6

59.7

67

6

8

14

5

901.9

87.9

112.7

191.5

65.8

66

7

8

14

5

1,140.0

116.4

150.8

232.5

79.1

66

7

9

13

5

1,059.4

114.1

165.8

290.0

89.4

61

7

10

17

5

1 ,244.8

114.3

165.3

268.6

81.1

67

6

9

14

4

930.7

103.7

153.1

299.7

91.4

59

6

10

19

6

Total 1,194.9 100 1,359.8 100 1,725.8 100 1,718.7 100 1,874.1 100 1,578.6 100

end of pumping period 9) were not available when the 

model was calibrated, so this period was not included in the 

statistical evaluation of calibration results. However, pumping period 9 was included in the analysis of water-level 

trends in heavily pumped areas.

Initial values of storage coefficients for the transient simulation were based on the thicknesses of sand and clay 

present in each model block. The final values of storage 

coefficients resulting from the transient calibration were 

one half of the initial values. Initial values of transmissivity and vertical leakance derived from steady-state calibration were not significantly changed during transient

calibration.

Mean error, RMSE, and standard deviation values of 

water-level residuals for each permeable zone and for the 

entire aquifer system for pumping periods 3 through 8 are 

shown in table 4. Values for the end of pumping period 3 

(1957) are included because these water levels are the starting values for pumping period 4 (1958-62). Zone A, 

because of the relatively low topographic relief of its outcrop area, consistently shows the best match between simulated and measured values, whereas zones D and E show the 

poorest matches. The largest differences between simulated 

and measured water levels occur in areas of high topographic relief in the outcrops of the lower zones and near 

major pumping centers (Martin and Whiteman, 1990, fig. 5). 

These results are similar to those produced in the preliminary version of the model (Martin and Whiteman, 1989, 

figs. 39^43). In the outcrop areas and in areas of intense 

pumpage, ground-water gradients may be steep and large 

water-level differences may exist within a single model 

block making it difficult or impossible to accurately simulate measured water levels.

Hydrographs (fig. 15) show changes in measured water 

levels during the calibration period (1958-87) in each permeable zone and the simulated water levels at the same sites 

in the corresponding model layers. These show that the 

general water-level trends are simulated by the model.

Sensitivity analysis using both the steady-state and transient versions of the model determined the effects of varying 

the values of transmissivity, vertical leakance, and storage

coefficient on the output of the model. These are the same 

properties adjusted during calibration. A detailed description of the methods and results of the sensitivity analysis is 

given in Martin and Whiteman (1990). Model sensitivity to 

changes in these values was calculated in terms of RMSE of 

the residuals between simulated and measured water levels. 

The model is generally most sensitive to changes in transmissivity and least sensitive to changes in storage coefficient. When transmissivity or vertical leakance is changed 

for one zone at a time, the upper part of the aquifer system, 

represented by permeable zone A, is most sensitive. When 

transmissivities or vertical leakances are changed in all 

zones at once, however, the deeper permeable zones (B-E) 

become more sensitive because flow between the constant-head upper boundary and the deeper zones is affected 

by the transmissivities and vertical leakances of all intervening zones. Generally, simulated water levels are more sensitive to decreases than to increases in transmissivities and 

vertical leakances. Though relatively insensitive to changes 

in storage coefficient, the model is more sensitive to 

increases than to decreases.

PREDEVELOPMENT FLOW SYSTEM

Simulated results for predevelopment conditions indicate 

that flow in the coastal lowlands aquifer system was generally from the upland outcrop areas of southern Mississippi 

and central Louisiana toward the Gulf of Mexico and the 

major river valleys. Predevelopment water-level profiles 

along north-south and east-west sections are shown in figure 

16. In the upland outcrop areas, water levels decrease with 

depth, producing relatively steep downward vertical gradients. Upward vertical gradients in discharge areas near the 

coast and along the major river valleys are generally smaller 

than the downward vertical gradients in the recharge areas 

because the upward flow is distributed over a larger area. 

Simulated predevelopment potentiometric surfaces of each 

zone and the vertical average water levels of all zones 

present in the aquifer system are shown on plate 2. Average 

water levels are given here and in connection with later
H20 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

EXPLANATION

B ACTIVE AREA OF THE MODEL 

GENERAL-HEAD BOUNDARY 

SPECIFIED-FLUX BOUNDARY 

OBSERVATION WELL AND NUMBER

20 40 60 80 100 MILES

0 20 40 60 80 100 KILOMETERS

FIGURE 13. Finite-difference grid, boundary conditions, the active area of the model, and location of observation wells.

discussions of water levels to emphasize the unity of the 

aquifer system and to provide a convenient way of assessing 

the overall effects that changes in pumpage have on the 

aquifer system. The water levels in each zone used in computing the average values were weighted by the thickness of 

their respective zones.

The rate and direction of simulated ground-water flow in 

the aquifer system are shown in figure 17. Each of the 

major streams received ground-water discharge under predevelopment conditions. Drainage of water toward the 

Mississippi Alluvial Plain during predevelopmenl time was 

more toward the western and central parts of the valley 

than toward the present course of the river along the eastern side of the valley. Also shown in figure 17 are the

areas where the aquifer system received recharge from 

(downward flow) or discharged to (upward flow) the water 

(able. Large flows radiated from the topographically high 

outcrop areas.

On the basis of simulation, rates of recharge to and discharge from the aquifer system are shown in figure 18. 

Positive flow represents recharge to the aquifer system, and 

negative flow represents discharge from the aquifer system. 

The recharge and discharge rates and flows shown in this 

and following figures and discussed in the text include only 

water that remains in the aquifer system sufficiently long to 

cross at least one grid-block boundary and become part of 

the regional flow system. Large flows occur locally in the 

surficial part of the aquifer system that travel short
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H21

OKLA.

Cul

gl 

g"

UJ|

PERMEABLE ZONE A I 

xxxxxxxxxxxxxxxxxxxxxxxxx> 

PERMEABLE ZONE B

PERMEABLE ZONE C

frxxxxxxxxxxxxxxxxxxxxxxxKxxxxxx?i 

PERMEABLE ZONE D

<xxxxxxxxxxxxx> 

PERMEABLE ZONE E

tl^e<

xxxx: tt

PERMEABLE ZONE A

<xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

PERMEABLE ZONE B

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX*XXXXXXXXXXXXXXX> Axxxxxxx:

PERMEABLE ZONE C

MODEL 

D' LAYER

<XXXXXXXXXXXXXXXXXX i 

<xxxxxxxxxxx> innnnnnnnnnnnifrJ

rf(XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX)

I PERMEABLE ZONE D

xxxx

PERMEABLE ZONE E

MODEL 

E' LAYER

Not to scale

EXPLANATION

CONSTANT-HEAD BOUNDARY 

(SOURCE-SINK)

NO-FLOW BOUNDARY 

SPECIFIED-FLUX BOUNDARY

GENERAL-HEAD BOUNDARY

RESTRICTION OF VERTICAL 

FLOW BETWEEN LAYERS

DIRECT FLOW TO OR FROM 

THE WATER TABLE

FIGURE 14. North-south and east-west schematic sections through the coastal lowlands aquifer system showing vertical structure of the model

including model layers and the simulated boundary conditions.

distances and have little or no effect on the regional flow 

system. Such local flows are not included in the totals 

given in this report. An example of such a flow would be 

water that recharges the aquifer system on a hilltop and 

leaves the aquifer system by evapotranspiration or by discharge to a stream at the foot of the hill. Relatively large 

downward vertical flows occurred in and near the upland 

outcrop areas. More than 4 in./yr of recharge occurred in a 

high area in south-central Mississippi, east of the Pearl 

River. Recharge rates of 1 in./yr or greater occurred in the 

outcrop areas in the northern part of the study area.

Discharge rates of up to 2 in./yr occurred along major river 

valleys, whereas discharge rates are less than 1 in./yr along 

the coast.

The total simulated flow of water circulating through the 

aquifer system under predevelopment conditions was about 

222 MfVVd. The distribution of recharge to and discharge 

from the outcrops of the permeable zones and the distribution of flow within the aquifer system are shown in figure 

19. The flows shown are for the areal extent of the aquifer 

system within the model area. About 207 Mft3/d (94 percent of the total simulated flow) entered the aquifer system
H22 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

TABLE 4. Results of statistical analysis of water-level residuals of the transient calibrated model for the period 1957-82

Permeable 

zone

A 

B 

C 

D 

E 

All

A 

B 

C 

D 

E 

All

A 

B 

C 

D 

E 

All

A 

B 

C 

D 

E 

All

A 

B 

C 

D 

E 

All

A 

B 

C 

D 

E 

All

A

B . 

C 

D 

E 

All

N

i 2

Mean error =

"I/

Root-mean- I/ 

square error = I/

Number 

of 

observations

301 

55 

62 

70 

20 

508

344 

96 

167 

180 

74 

861

283 

121 

252 

222 

116 

994

348 

151 

301 

365 

150 

1,315

348 

43 

71 

64 

29 

555

349 

73 

164 

278 

132 

996

Overall

1,973

539 

1,017 

1,179 

521 

5,229

/hs - nm\ 

I i V

N = h

2 /hs - hm ' 

i=l V i

N

Mean ^ 

error 

(feet)

End of Stress Period 3 -

-0.82 

-17.22 

-18.00 

-.23 

-6.00 

-4.81

End of Stress Period 4 -

3.18 

7.06 

-3.49 

16.92 

29.45 

7.45

End of Stress Period 5 -

3.87 

6.94 

.39 

12.45 

21.09 

7.29

End of Stress Period 6 -

-1.36 

3.56 

6.80 

18.01 

18.16 

8.68

End of Stress Period 7 -

2.24 

4.97 

3.65 

9.16 

27.30 

4.74

End of Stress Period 8 -

-0.18 

7.09 

6.74 

2.64 

19.70 

4.92

Model, Stress Periods 3

1.11

3.41 

1.78 

11.61 

20.39 

5.77

Root-mean- 2 Standard 3 

square error deviation 

(feet) (feet)

1957

18.27 

33.17 

32.42 

44.57 

38.05 

27.86

1962

18.35 

30.52 

32.70 

46.54 

57.30 

34.36

1967

15.25 

27.86 

34.52 

48.08 

48.26 

35.37

1972

19.57 

31.31 

38.06 

53.82 

46.86 

40.00

1977

17.70 

25.38 

39.55 

37.15 

54.47 

27.58

1982

14.75 

33.40 

40.31 

55.84 

46.82 

39.83

through 8 - 1957-82

17.45

30.49 

36.54 

50.90 

48.92 

35.96

3 "1 / 1 f ( h? - h!j) -

Standard I/ i=l I \ x 1 7

18.25 

28.36 

26.96 

44.57 

37.57 

27.44

18.08 

29.69 

32.51 

43.35 

49.16 

33.54

14.75 

26.98 

34.51 

46.44 

43.41 

34.61

19.52 

31.10 

37.45 

50.71 

43.20 

39.04

17.56 

24.89 

39.38 

36.00 

47.13 

27.17

14.75 

32.64 

39.74 

55.77 

42.48 

39.52

17.30 

29.45 

35.93 

49.10 

43.99 

34.50

K]2

deviation I/ N

\ 2 Where hs 

/ hm

N

= simulated water level 

= measured water level 

= number of water-level pairs compared.
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H23

WELL Cu-635 

PERMEABLE ZONE A

I I I I I I I I I I I i i i i i I I I i I I I I I I I I I I 

WELL Or-42 

PERMEABLE ZONE A

I I I I I I I I I ]! I I I I I 1 I I I I I I I I I I I I I

WELL EB-301 

PERMEABLE ZONE B

I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I

00 O CM *COCOOCN-*lDOOOCSI-*eDOO 

G) G) CJ) O)O>O)O)O)O)O)0)OOO)OO)

YEAR

EXPLANATION

______ MODEL - SIMULATED

WATER LEVEL

MEASURED WATER 

LEVEL

WELL EB-90 

PERMEABLE ZONE C

ijj m 

> -J I- 

"j < uJ S UJ

CE ^ LJ.

HI 00

 , LJ_I

< >

£ o

CO

<

100

80

60

40

20

0

20

40

160

HO 

120 

100

I i I I i I I I I I I I I I I I I I I I I I I I I I i i i i 

WELL EB-468 

PERMEABLE ZONE D

i i i i i i rr i i i f i i i i i i i i i i i i i r i i r 

WELLM011 

PERMEABLE ZONE E

i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i

YEAR

FIGURE 15. Comparisons between simulated and measured water levels for the period 1958-87.

as recharge from the surface, of which about 94.6 MiV/d 

entered the outcrop of permeable zone D. About 14.1 

Mft-Vd (6 percent) enters the aquifer system laterally from 

adjacent aquifers in Texas and in the Mississippi River alluvial valley in northern Louisiana and vertically from the

underlying Mississippi embayment aquifer system. On the 

basis of a more detailed breakdown of flows within the aquifer system than that shown in figure 19, approximately 41 

percent (85 MfVVd) of the recharge entering the aquifer system moves downward to a lower permeable zone or
H24 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

450

400

350

300

250

200

150

u- 100

z

50

50

100

150

 ------- LAND SURFACE

PREDEVELOPMENT WATER LEVELS

 ZONE A

 ZONE B

 ZONE C

 ZONE D

 ZONE E

GAPS INDICATE 

INACTIVE NODES

VERTICAL SCALE 

GREATLY EXAGGERATED

50 100 150 200 250 0 

MILES FROM SOUTH EDGE OF MODEL

50 100 150 200 250 300 

MILES FROM WEST EDGE OF MODEL

350 400 450

FIGURE 16. Profiles showing water levels in each permeable zone under predevelopment conditions.

downdip beneath an overlying permeable zone. About 59 

percent (122 Mft3/d) of the recharge returns to the surface as 

discharge without having moved beyond the outcrop area of 

the permeable zone it entered.

SUBDIVISION OF THE FLOW SYSTEM

The model was divided into seven areas to investigate 

flow patterns and distributions in the coastal lowlands aquifer system in detail (pi. 2). The areas were chosen on the 

basis of factors affecting flow in the aquifer system, such as 

topography, the outcrop pattern of the permeable zones, and 

drainage boundaries. Area 1, designated the southeastern 

Texas area, is the area west of the Sabine River in Texas. 

The central Louisiana area (area 2), is an area of relatively

high relief where permeable zones B through E crop out and 

are recharged. The southwestern Louisiana area (area 3) to 

the south of the central Louisiana area is an area of comparatively low relief and nearly flat natural hydraulic gradients. 

The Mississippi Alluvial Plain (area 4) in central and southern Louisiana is an area of low relief and generally low 

hydraulic gradients. The Mississippi Alluvial Plain separates the upland terraces of central Louisiana (area 1} and 

the low-lying coastal plain of southwestern Louisiana (area 

3) from hydrogeologically comparable areas to the cast. 

The southern Mississippi area (area 5) that is east of the 

Mississippi Alluvial Plain consists predominantly of upland 

terraces in Mississippi and Alabama where permeable zones 

B through E crop out and are recharged. As in the central 

Louisiana area, high topographic relief greatly influences 

hydraulic gradients. The southeastern Louisiana area (area
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H25

0 20 40 60 80 100 MILES 

I I I I I

I I I I I 

0 20 40 60 80 100 KILOMETERS

"O,

EXPLANATION

VERTICAL FLOW THROUGH 

TOP OF AQUIFER SYSTEM

[...... j Recharge area j____ Discharge area

RATE AND DIRECTION OF LATERAL 

FLOW, IN CUBIC FEET PER DAY

- 0 to 100,000

*- 100,000 to 500,000

!« 500, 000 to 1,000,000

|*~ 1,000,000 to 5,000,000

^~ Greater than 5,000,000

FIGURE 17. Simulated ground-water flow in the aquifer system under predevelopment conditions.
H26 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

< *>. -%k

0 20 40 60 80 100 MILES 

I_____I I I I

I I I I I 

0 20 40 60 80 100 KILOMETERS

EXPLANATION

RECHARGE AREA 

DISCHARGE AREA

LINE OF EQUAL FLOW RATE Interval 

1 inch per year. Positive flow is recharge 

to aquifer system. Negative flow is discharge 

from aquifer system

FIGURE 18. Areal distribution of simulated rates of recharge to and discharge from the aquifer system under predevelopment conditions.
OUTCROP OF PERMEABLE ZONE A IN THE MISSISSIPPI RIVER VALLEY

OUTCROP-SUBCROP OUTCROP-SUBCROP OUTCROP-SUBCROP OUTCROP-SUBCROP 

AREA OF PERMEABLE ZONE E AREA OF PERMEABLE ZONE D AREA OF PERMEABLE ZONE C AREA OF PERMEABLE ZONE B

OUTCROP OF PERMEABLE ZONE A OUTSIDE 

OF THE MISSISSIPPI RIVER VALLEY

FLOW ACROSS NORTHERN 

BOUNDARY OF PERMEABLE 

ZONE A IN THE MISSISSIPPI

RIVER VALLEY (SPECIFIEDFLUX BOUNDARY)

FLOW SUMMARY Negative

values denote flow out

of the coastal lowlands

aquifer system

MILLION MILLION

CUBIC FEET GALLONS

PER DAY PER DAY

NET DISCHARGE -4.0 -30NET LATERAL FLOW FROM:

ADJACENT PERMEABLE 3.4 25 ZONES IN TEXAS

MISSISSIPPI RIVER 0.3 2

VALLEY ALLUVIALAQUIFER

VERTICAL FLOW FROM 0.3 2 

UNDERLYING AQUIFER 

SYSTEM

Figures may not add to total because of independent rounding

FLOW ACROSS WESTERN \ °'47 ' 

BOUNDARY OF PERMEABLE J 0 .32 

ZONE (GENERAL-HEAD ) 

BOUNDARY) (

UPDIP LIMIT OF PERMEABLE ZONE 

(NO-FLOW BOUNDARY)

1.86 2.62 3.04 3.80 H-t H^t-H

0.76 0.47*- °- 76 0.12*- 

+ 0.32 0.41 41 o 06 4.-^ 0.33 » 0.06 

1.14 1.15 3.40 3.48 ^44 ^ 

0.01

FLOW BETWEEN SUBCROP 

OF LOWER PERMEABLE 

ZONE AND PERMEABLE 

ZONE A IN THE MISSISSIPPI 

RIVER VALLEY

FLOW ACROSS THE WATER 

TABLE IN THE OUTCROP OF 

THE PERMEABLE ZONE 

\ 0.02 *^

8.55

lit - - - - * * , 

+ 1 1

0.08

0.39*- 

"I

87.94

1 i it

2.09 3.02 i it! , : °'93 :::;

-* 0' 07 2.142.14 - 

1 t t i~F

0.00

1.08 *- 

0.80 *-

29.2*

2 -<> 4 2.19 WATER TABLE 

i4- f (CONSTANT-HEAD UPPER BOUNDARY MODEL LAYER 1)

26.9761.47 t t

II III 

- 

°' 15 1.26* 34 ' 50 

_ 0.80 4 I PERMEABLE ZONE A (HOLOCEME-UPPER PLEISTOCENE _w 012 ___ ^ 046 DEPOSITS-MODEL LAYER 2) 

1.24 1.24 H-t 

' ^

°-°° 12^09 0.69 4p Q7i 28.46 34.86

1 t t L i ^ T iii

26.68 14.58 6.40 

PERMEABLE ZONE B (LOWER PLEISTOCENE-UPPER 

PLIOCENE DEPOSITS MODEL LAYER 3)

L. Ut ------ I 39.14 99.90 

> 2.12 PERMEABLE ZONE C (LOWER PLIOCENE-UPPER 

MIOCENE DEPOSITS MODEL LAYER 4)

6.03 16.45

I + t

94.58 6.64 10.42 

"^ 3 ° 4 PERMEABLE ZONE D (MIDDLE MIOCENE DEPOSITS MODEL LAYER 5)

18.24

I 1 t

_ 9.45 0.90 18.50 0.26 _ 

PERMEABLE ZONE E (UPPER OLIGOCENE-LOWER MIOCENE DEPOSITS MODEL LAYER 6)

-* 0.15 

0.31 8.07

1 t t

15.9422.75

6- 81 ^^- DOWNDIP LIMIT OF 

 ^"^ PERMEABLE ZONE 

(NO-FLOW BOUNDARY)

EXPLANATION

I 8 I5 FLOW INTO OR OUT OF PERMEABLE 

^ ZONE Number is flow, in million

FLOW ACROSS LOWER BOUNDARY OF AQUIFER 

SYSTEM (SPECIFIED-FLUX BOUNDARY)

cubic feet per day

8.0? | NET FLOW TO OR FROM PERMEABLE

ZONE Number is flow, in million 

0-9" cubic feet per day

o

r > zO 

oo

I

8.07 I 

I 0.90

FIGURE 19. Schematic section showing simulated flow between permeable zones and across boundaries of the coastal lowlands aquifer system under predevelopment conditions.
H28 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

6) consists predominantly of low coastal plain in southeastern Louisiana and in small areas of southern Mississippi and 

Alabama. The area has nearly flat topographic relief and 

nearly flat natural hydraulic gradients. The southwestern 

Alabama area (area 7) is at the eastern edge of the model 

area, east of Mobile Bay and the Tombigbee River. The 

area includes sections of upland terraces and low-lying 

coastal plain in southwestern Alabama and western Florida.

A schematic representation of simulated flow between and 

within the seven areas under predevelopment conditions is 

shown on plate 2. Of the total of about 207 Mft3/d of

o

recharge, 114 Mft /d (55 percent) entered the aquifer system 

in southern Mississippi (area 5). About 39 percent (80.8 

Mft3/d) of the total discharge from the aquifer system also 

occurred in the southern Mississippi area. The upland terraces east and west of the Mississippi River valley (areas 2 

and 5) had the greatest net recharge to the aquifer system, 

5.5 Mff/d in central Louisiana (area 2) and 32.6 Mft3/d in 

southern Mississippi (area 5). The lower altitude coastal 

plain had net discharge from the aquifer system, 8.0 Mft/Vd 

in southwestern Louisiana (area 3) and 15.9 Mft/Vd in southeastern Louisiana (area 6). Net flow of about 21.5 Mft/Vd of 

water entered the Mississippi Alluvial Plain (area 4) laterally 

from the adjoining areas (areas 2, 3, 5, and 6, pi. 2). Most 

of the lateral flow, about 17.3 Mft /d (80 percent), was westward from the southern Mississippi and southeastern Louisiana areas. Net vertical flow within the Mississippi Alluvial 

Plain (area 4) was upward in all permeable zones because 

the valley drained a large part of the aquifer system during 

predevelopment time. Three of the areas had net discharge, 

southwestern and southeastern Louisiana (areas 3 and 6) and 

the Mississippi Alluvial Plain (area 4). Nearly half of the 

total discharge from the three areas (22.2 Mft3/d) was discharged in the Mississippi Alluvial Plain area. Southeastern 

Texas (area 1) and southwestern Alabama (area 7) had relatively small rates of net recharge, 3.2 Mft3/d and 0.6 Mft3/d. 

In addition to recharge, the aquifer system received rela-

'j

tively small net inflows from the west (3.4 Mft /d to the 

southeastern Texas area), from the north (0.3 Mft3/d to the 

Mississippi Alluvial Plain area from the Mississippi River 

valley alluvial aquifer), and from below (0.3 Mft /d as 

upward leakage through the Vicksburg-Jackson confining 

unit).

1987 FLOW SYSTEM

Ground-water pumpage has significantly altered the natural ground-water flow system. Comparison of simulated 

results for 1987 conditions (figs. 20-23 and pis. 3-4) with 

results for predevelopment conditions (figs. 16-19, and pi. 

2) indicates that major changes in water-level altitudes and 

flow rates have occurred. Changes from predevelopment 

water levels caused by pumpage through 1987 are shown on

plate 3. Figure 20 shows water-level profiles for 1987 along 

the same north-south and east-west lines shown for predevelopment conditions in figure 16. Comparisons show that, 

in general, lateral and vertical hydraulic gradients have 

steepened since predevelopment time in all permeable zones 

and that vertical hydraulic gradients have reversed in some 

areas.

Intensive pumpage has produced areally extensive cones 

of depression in the aquifer system (pi. 4). Major pumping 

centers in southern Louisiana, in permeable zone A, and at 

Baton Rouge, La., in permeable zone C, have had the greatest effect on the aquifer system. Comparison with the predevelopment maps (pi. 2) indicates that hydraulic gradients 

between the pumping centers and recharge areas have significantly increased while gradients toward discharge areas 

have been reduced or reversed. Flow in the northern part of 

the coastal lowlands aquifer system in 1987 remains primarily southerly and toward the major river valleys from the 

recharge areas in the upland terraces (fig. 21). Throughout 

most of the coastal plain of southern Louisiana, 

ground-water pumpage has altered or reversed flow directions and caused flow to converge toward the major pumping centers.

The rate of simulated recharge to the aquifer system 

under 1987 conditions is shown in figure 22. Comparison to 

the map of predevelopment flows (fig. 18) indicates that 

large parts of the Gulf Coastal Plain have been transformed 

from areas of natural discharge to areas of recharge. A large 

area in southwestern Louisiana that had been discharging up 

to 1 in./yr under predevelopment conditions receives 

recharge up to 3 in./yr under 1987 conditions in response to 

pumpage from permeable zone A. Smaller areas near major 

pumping centers, such as Baton Rouge, La., and Pensacola, 

Fla., show rates of induced recharge of 3 to 6 in./yr. The 

distribution of flow throughout the aquifer system in 1987 is 

shown in figure 23. The total flow entering the regional 

aquifer system under 1987 conditions was about 354 Mft3/d 

(about 62 percent more than the predevelopment rate of 222 

Mft3/d) and natural discharge was reduced to 143 Mft3/d 

(about 65 percent of the predevelopment rate). Pumpage of 

211 Mft-Vd (1,578 Mgal/d) accounts for about 60 percent of 

the total discharge from the aquifer system. The pumpage 

from permeable zone A of 124 Mft3/d (928 Mgal/d) 

amounts to about 35 percent of the total discharge. Pumpage of 86.6 Mft3/d (647.8 Mgal/d) from permeable zones B 

through E makes up about 25 percent of the total discharge.

Less than 1 percent of the total flow into or out of the 

aquifer system under 1987 conditions is caused by water 

moving into or out of storage. Pumping rates decreased in 

permeable zones A through C after 1980 causing water levels to recover and the amount of water in storage to increase 

in these zones (fig. 23). Pumping rates increased in permeable zones D and E. Of the increased pumpage from permeable zone E, about 1.3 Mft3/d is derived from storage.
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H29

D' E

LAND SURFACE 

1987 WATER LEVELS 

ZONE A 

ZONEB 

ZONEC 

ZONED 

ZONEE

150

50 100 150 200 250 0 

MILES FROM SOUTH EDGE OF MODEL

150 200 250 300 

MILES FROM WEST EDGE OF MODEL

FIGURE 20. Profiles showing water levels in each permeable zone under 1987 conditions.

The relation between cumulative pumpage since the 

beginning of development and the cumulative tlows derived 

from recharge from the water table, lateral flow from adjacent aquifers, flow from the underlying Mississippi embayment aquifer system, and flow from storage within the 

aquifer system for the period 1958-87 is shown in figure 24. 

About 6 percent of the water pumped from the aquifer system prior to 1958 was derived from a decrease in storage, 

lateral flow from adjacent aquifers and permeable zones, and 

vertical flow from the underlying aquifer system. By 1987, 

the cumulative decrease in storage plus lateral and vertical 

flow from beyond the study area was less than 4 percent of 

the total amount of water pumped. Figure 25 shows separately the amounts of water derived from storage, lateral 

flow from adjacent aquifers, and vertical flow from the 

underlying aquifer system in the period 1958-87. The 

cumulative volume of water derived from storage increased 

through the first 8 pumping periods (1898-1982). In pumping period 9 (1983-87), water goes into storage as water 

levels rise due to a decrease in overall pumpage. The

natural flow of water into the western parts of the model 

area in Texas had been reversed to a net outflow by pumping 

period 4 (1958-62). Increasing outflow from 1973 through 

1987 (pumping periods 7 through 9) coincided with relatively large increases in pumpage outside of the study area 

in southeastern Texas and decreases in industrial pumpage 

within the study area at Lake Charles, La. The cumulative 

flow of water into the aquifer system from the north in the 

Mississippi River valley alluvial aquifer and upward through 

the underlying Vicksburg-Jackson confining unit reached a 

maximum in 1967. The cumulative total held relatively 

steady through 1977 and then declined from 1978 to 1987 

as flow from the north decreased and inflow through the 

Vicksburg-Jackson confining unit reversed to a net outflow.

The distribution of flow under 1987 conditions between 

and within the seven areas is shown on plate 4. Comparison 

with the flow distribution under predevelopment conditions 

(pi. 2) indicates that recharge has increased into all areas. 

The greatest change occurred in southwestern Louisiana 

(area 3) where simulated recharge increased from 6.7 Mfr/d
H30 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

0 20 40 60 80 100 MILES 

I I I

I I I I I 

0 20 40 60 80 100 KILOMETERS

EXPLANATION

VERTICAL FLOW THROUGH 

TOP OF AQUIFER SYSTEM

|____I Recharge area j____ Discharge area

RATE AND DIRECTION OF LATERAL 

FLOW, IN CUBIC FEET PER DAY

- 0 to 100,000

^ 100,000 to 500,000

^ 500,000 to 1,000,000

^ 1,000,000 to 5,000,000

^- Greater than 5,000,000

FIGURE. 21. Simulated ground-water flow in the aquifer system under 1987 conditions.
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H31

0 20 40 60 80 100 MILES

I . I . I . I. I I

I I n r I i

0 20 40 60 80 100 KILOMETERS

EXPLANATION

RECHARGE AREA 

DISCHARGE AREA

LINE OF EQUAL FLOW RATE Interval 

1 inch per year. Positive flow is recharge 

to aquifer system. Negative flow is discharge 

from aquifer system

FIGURE 22. Areal distribution of simulated recharge to and discharge from the aquifer system under 1987 conditions.
OUTCROP OF PERMEABLE ZONE A IN THE MISSISSIPPI RIVER VALLEY

M OUTCROP-SUBCROP OUTCROP-SUBCROP OUTCROP-SUBCROP OUTCROP-SUBCROP IN AREA OF PERMEABLE ZONE E AREA OF PERMEABLE ZONE D AREA OF PERMEABLE ZONE C AREA OF PERMEABLE ZONE B

FLOW ACROSS NORTHERN (^ 0 12 ^_ 

BOUNDARY OF PERMEABLE \ 

ZONE A IN THE MISSISSIPPI < 

RIVER VALLEY (SPECIFIED- ) 

FLUX BOUNDARY) C^

values denote flow out 

of the coastal lowlands 

aquifer system

MILLION MILLION 

CUBIC FEET GALLONS 

PER DAY PER DAY

NET RECHARGE 215.2 1,610NET LATERAL FLOW FROM:

ADJACENT PERMEABLE -3.6 -27 

ZONES IN TEXAS

MISSISSIPPI RIVER 0.06 0.4 

VALLEY ALLUVIAL AQUIFER

VERTICAL FLOW FROM -0.3 -2 

UNDERLYING AQUIFER SYSTEM

TOTAL PUMPAGE -211.0 -1,578

NET CHANGE IN -0.4 -3 

STORAGE

Figures may not add to total because of independent founding

FLOW ACROSS WESTERN C °-*2 <- 

BOUNDARY OF PERMEABLE J n.21 4" 

ZONE (GENERAL-HEAD ) 

BOUNDARY) (^ 

^

0.60 0.58 1.57

lit ' * f '

- 3 - 08 2' 48 0.49 «-

 ^ 0.06 P = 3.63 0.46 41 

S = 0.00 

^-0.18 

0.63 0.66

it!

0.03

FLOW BETWEEN SUBCROP 

OF LOWER PERMEABLE 

ZONE AND PERMEABLE 

ZONE A IN THE MISSISSIPPI 

RIVER VALLEY

FLOW ACROSS THE WATER 

TABLE IN THE OUTCROP OF 

THE PERMEABLE ZONE 

\ 0.27 *-

6.49

III 1 

°- 98 0.02 <-p 4' 65 

_ 

P=1.42 L+ 0.03 P 

S = 0.00 I S 

-> 0.04 L> 0.06 

2.49 2.59

Iff i

III 1 

0.10 0.00

I

1.29 ^- 46^3 

t* 1.0^ 

-^2.36 R 

75.13 s

OUTCROP OF PERMEABLE ZONE A OUTSIDE 

OF THE MISSISSIPPI RIVER VALLEY 

____ 

-^- 

______ 

0.80 0.921.43 WATER TABLE 15. 

| A | ^ A (CONSTANT-HEAD UPPER BOUNDARY MODEL LAYER 1) | '

1.05 0.17 ^-p °'51 1.27 ^-p- 128.38113.29= 5.83 0.074^ P=0.58 0.804!- PERMEABLE ZONE A (HOLOCENE-UPPER PLEISTOCENE 

= 0.00 1 S=0.00 1 DEPOSITS MODEL LAYER 2) I fr 0.10 1-> 0.47 1.67 1.67 0.78 0.79

t t i t t

'' ^ ' ' 3.97^

001 0 Q-7 ^ ' » 3 - 97 *p 0.o

P= 112.96 

S = -0.41 

4.8424.16

_L t 5

1 1 i T III

2 - 17 ^-J 35.9528.76 19.32 2.01 + I PERMEABLE ZONE B (LOWER PLEISTOCENE-UPPER 

' PLIOCENE DEPOSITS MODEL LAYER 3)

P= 13.86 

24.13 S = -041 -H - -i * r - - 9.83 I 1 t

22.20 16.696.86 DOWNDIP LIMIT OF 

PERMEABLE ZONE C (LOWER PLIOCENE-UPPER -^^ PERMEABLE ZONE 

MIOCENE DEPOSITS-MODEL LAYER 4) (NO-FLOW BOUNDARY* 

= 20.47 

= -0.53 1°- 41 

1 1 t

117.2042.07 17.86 7. 4E 

"^ 1 ' 54 PERMEABLE ZONE D (MIDDLE MIOCENE DEPOSITS -MODEL LAYER 5)

P = 40.06 

S = -0.32 16.53

I I t

i i T 4 *

_ 10.39 3.90 24.73 8.20 _ 

PERMEABLE ZONE E (UPPER OLIGOCENE-LOWER MIOCENE DEPOSITS MODEL LAYERS)

-> 0.21 P= 12.22 

S=1.27 1-03

I I t

1

S

^

09 

L

REGION;*iL AQUIFER-SYSTEM ANALYSIS GULF

EXPLANATION O

O

I 1 03

1 A FLOW INTO OR OUT OF PERMEABLE ^ 

1 1 ZONE Number is flow, in million > 

cubic feet per day ^

f

UPDIP LIMIT OF PERMEABLE ZONE 

(MO-FLOW BOUNDARY)

FLOW ACROSS LOWER BOUNDARY OF AQUIFER 

SYSTEM (SPECIFIED-FLUX BOUNDARY)

5.54 | NET FLOW TO OR FROM PERMEABLE 

ZONE Number is flow, in million 

cubic feet per day

5.54 I

tot

20.47 PUMPAGE FROM UNIT In million 

cubic feet per day

= -o.4i WATERINTO(-)OROUTOF

STORAGE In million cubic feet 

per day

FIGURE 23. Schematic section showing simulated flow between permeable zones and across boundaries of the coastal lowlands aquifer system under 1987 conditions.
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H33

500

° 450

m 400 - O RECHARGE FROM THE WATER TABLE

PUMPAGE

(j O

0

500

400

300

200

100

0

A LATERAL FLOW FROM THE MISSISSIPPI RIVER 

VALLEY ALLUVIAL AQUIFER, VERTICAL FLOW 

FROM THE UNDERLYING AQUIFER SYSTEM, 

LATERAL FLOW FROM ADJACENT AQUIFERS 

IN TEXAS, AND STORAGE

159.7

1,195

- 159.7 

1,195

PUMPING

PERIOD 4

I I

MILLION CUBIC FEET PER DAY 

MILLION GALLONS PER DAY

181.8 230,7 r 229.8 ^^

1,360

PUMPING 

PERIOD 5

1 1 1

1,726 

PUMPING

PERIOD 6

1 1

PUMPING 

PERIOD 7

1 1 1

PUMPING 

PERIOD 8

1 1 1

211.0 "

1,578

PUMPING 

PERIOD 9

Ml

00 O CM in co co <o

3,000

2,000

1,000

0

O Q.

FIGURE 24. Cumulative pumpage and the sources of water for the coastal 

lowlands aquifer system for the period 1958-87.

under predevelopment conditions to 68.7 MftVd in 1987 and

o

a net discharge of 8.0 Mft /d to the water table under predevelopment conditions has been converted to a net recharge 

of 68.2 Mft3/d from the water table in 1987. Net recharge 

in the Mississippi Alluvial Plain (area 4) and southeastern 

Louisiana (area 6) has replaced the net discharge that 

occurred under predevelopment conditions. Southward flows 

from the central Louisiana and southern Mississippi areas to 

the southwestern and southeastern Louisiana areas increased 

significantly. The Mississippi Alluvial Plain (area 4) continues to act as a drain for much of the central part of the study 

area, receiving net inflows from central Louisiana, southern 

Mississippi, and southeastern Louisiana. However, southwestern Louisiana (area 3) receives about 1.0 Mff/d net 

inflow from the Mississippi Alluvial Plain area instead of 

the predevelopment outflow of about 1.7 Mft'/d. Pumpage 

in southwestern Louisiana (area 3) has altered gradients 

along the western side of the Mississippi Alluvial Plain (area 

4) by capturing much of the flow that formerly drained to 

the Alluvial Plain and by inducing flow from the Alluvial 

Plain toward the pumping centers. East-west flows between 

other areas have not been greatly altered by pumpage.

Under 1987 conditions, a relatively small amount of water 

was derived from storage in southeastern Texas (area 1), 

central Louisiana (area 2), and southern Mississippi (area 5),

3 * 

o o

> m

ill )

> u

- m <

Uj D Q

' =! UJ

 gu.

uo

130

120

110

100

90

80

70

60

50

40

30

20

10

0

500

400

300

200

100

0

A LATERAL FLOW FROM THE MISSISSIPPI RIVER 

VALLEY ALLUVIAL AQUIFER AND VERTICAL 

FLOW FROM THE UNDERLYING AQUIFER SYSTEM -

 LATERAL FLOW TO ADJACENT 

AQUIFER IN TEXAS

STORAGE

_ 159.7

1,195

1,195 

PUMPING 

PERIOD 4

I I I I

MILLION CUBIC FEET PER DAY 

MILLION GALLONS PER DAY 

230.7 229 R 250- 5

1,360

PUMPING 

PERIOD S

I I I I

PUMPING 

PERIOD 6

111!

1,719

PUMPING 

PERIOD 7

MM

PUMPING 

PERIOD 8

MM

1 1 1 1

211.0 ~

1,578 

PUMPING

PERIOD 9

Mil

3,000

2,000

1,000

-

_

 5 r^ 2i O

YEAR

FIGURE 25. Pumpage and cumulative flow of water to or from storage and 

adjacent aquifers for the period 1958-87.

indicating that water levels in parts of these areas were still 

declining slightly. Ground water in storage increased in 

southwestern Louisiana (area 3), the Mississippi Alluvial 

Plain (area 4), and southeastern Louisiana (area 6) as water 

levels generally rose slightly in response to reduced pumpage during the period 1983-87. There was no change in 

storage in southwestern Alabama (area 7) in 1987, 

indicating that the area as a whole was at steady state.

POTENTIAL OF THE AQUIFER SYSTEM 

FOR DEVELOPMENT

Four experiments were conducted utilizing the 

steady-state and transient models to evaluate the effects of 

possible future ground-water pumpage from the coastal lowlands aquifer system. The effects on water levels and flows 

of continuing the 1983-87 pumping rates and increasing or 

decreasing pumping rates were evaluated in three of the 

experiments. The fourth experiment was designed to determine which parts of the study area are hydrogeologically 

most favorable or least favorable for the development of 

large ground-water supplies without regard to the present 

pattern of development.

In the first model experiment, the 1983-87 pumping rate 

was extended for an additional 50 years (1988 to 2037). At 

the beginning of this experiment, water levels throughout 

most of the aquifer system were still changing in response 

to earlier changes in pumping rates and distribution. From 

1980 to 1985 pumpage decreased more than 25 percent in
H34 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

permeable zone A, 9 percent in permeable zone B, and 7 

percent in permeable zone C; pumpage increased more than 

11 percent in permeable zone D and 12 percent in permeable zone E. At the end of 1987, water levels were, on 

average, rising in permeable zones A through D, and falling 

in permeable zone E. By the end of the experiment in 2037, 

water levels were near steady state throughout the aquifer 

system with only permeable zones D and E showing slight 

declines, on average.

Simulated water-level changes, 1987-2037 with 1983-87 

pumpage continued, for each permeable zone and the average change in the entire aquifer system are shown on plate 

5. Water levels would rise throughout permeable zones A 

and B and in most of permeable zone C with maximum 

rises of more than 2 ft in each zone. Water levels in permeable zone D would rise in southeastern Louisiana, ranging 

up to more than 3 ft near Baton Rouge, but would fall by 

less than 1 ft north of Lake Charles and by more than 1 ft in 

southern Mississippi. Water levels would decline throughout 

permeable zone E except in the outcrop area in Alabama 

and Florida. Maximum declines would exceed 6 ft in 

south-central Louisiana and 11 ft in southwestern Mississippi. The relatively large water-level declines in permeable 

zone E are largely the result of the low transmissivity of the 

zone, which slows its adjustment to changes in pumpage. 

At the beginning of this simulation, water levels had not yet 

adjusted throughout a large part of permeable zone E to the 

increase in pumpage that occurred between 1980-1985.

Considering the entire aquifer system, average water levels would rise throughout the southern part of the study 

area, with rises of more than 2 ft near New Orleans and 

Baton Rouge, La. Average water levels would decline 

throughout the northern part of the study area, with maximum declines of more than 7 ft in southwestern Mississippi. 

Hydrographs in figure 26 show water-level changes resulting 

from this experiment at selected sites.

Because of the relatively small changes in water levels 

throughout the aquifer system, little difference would occur 

in the rate and direction of flow as a result of the additional

50 years of pumpage. The distribution of flow within the 

aquifer system at the end of the 50-year period is shown in 

figure 27. Comparison with 1987 conditions shows little 

difference in the total flow and the distribution of flow 

within the aquifer system. At the end of 1987; there was a

o

net 0.4 Mft /d increase in aquifer system storage (fig. 23). 

The total gain in storage of 1.7 Mft3/d in permeable zones A 

through D was greater than the loss in storage of 1.3 Mft /d 

in permeable zone E. By 2037 there would be a net inflow 

from storage of 0.05 Mft3/d to permeable zones D and E 

(fig. 27). Net recharge to permeable zones C through E 

would increase slightly while net recharge to permeable 

zones A and B would decrease by 1.3 MfrVd. Net outflow

across the western boundary would decrease by about 0.2 

Mft3/d.

In the second model experiment, the 1983-87 pumping 

rate was increased by 50 percent for a period of 50 years 

(1988 to 2037). Water-level changes for each permeable 

zone and the average change in the aquifer system resulting 

from this additional pumping period are shown on plate 6. 

Because the rate of pumping was increased without changing the distribution of pumpage, water levels would be lower 

throughout the aquifer system, but the general patterns of 

water levels and flows in the aquifer system would be 

almost unchanged. Additional drawdown would range from 

less than 1 ft in parts of the outcrop areas to more than 80 ft 

in the Baton Rouge area in permeable zone C. More than 

50 ft of decline from 1987 levels would occur in the Lake 

Charles area and more than 40 ft in the New Orleans area of 

Louisiana in permeable zone A. Declines of more than 70 ft 

in permeable zone E and more than 50 ft in permeable zone 

D would occur in a small area near Alexandria, La. The 

average drawdown in the aquifer system would be more 

than 20 ft in a broad area of southeastern Louisiana and 

southwestern Mississippi. Average drawdown would exceed 

30 ft in the Alexandria, New Orleans, and Bogalusa, La., 

areas, and 40 ft near Lake Charles and Baton Rouge, La. 

Water-level changes resulting from this experiment at 

selected well sites are shown in figure 26. Profiles along 

north-south and east-west lines (fig. 28) show that 

water-level gradients would increase throughout the aquifer 

system from 1987 conditions (fig. 20), with the largest gradient increases in the lower permeable zones where transmissivity is generally less than the transmissivity of the 

upper permeable zones.

The distribution of flow at the end of the 50-year period 

with a 50-percent increase in pumpage is shown in figure 

29. The relation between pumpage, recharge, change in 

storage, and net flows from adjacent aquifers and the underlying aquifer system is shown in figures 30 and 31. More 

than 95 percent of the flow would be derived from recharge. 

Increasing the pumpage in permeable zone A by 50 percent,

from about 124 to about 187 Mft3/d (928 to about 1,399

Mgal/d), would increase the net recharge to permeable zone 

A by 61 percent, from 118 to 190 Mft3/d (figs. 23 and 29). 

More than 93 percent of the additional water derived from 

storage would be withdrawn during the first 20 years of the 

period (fig. 31). Less than 0.3 Mft3/d would be derived 

from storage at the end of the period, indicating that the 

aquifer system would be approaching steady state.

The simulated rate and direction of flow in the aquifer 

system at the end of the 50-year period are shown in figure 

32. Comparison with flow vectors showing 1987 conditions 

(fig. 21) indicates that the increased pumpage would induce 

more lateral flow toward the major pumping centers. A 

larger area of the aquifer system would receive recharge
LU 

LU 

LL

z 

_r

LU

LU 

CO

o

CD

O

o

LU

LU

CC 

LU

1

Q

LU

<

2

CO

0

20 

40

60

OU

100 

120 

140

20

0 

20

40

60

on

40

20

0

20 

40

60

a

IS

a

i i i I i i i I i i i i i i i i i i i I i i i I i i i I i i i I i i i i i i i i i i i 1 1 i i i i . i i i . i i i i i I i i i I i i i i i i i i i i . i . i i 

WELL Or-42 

PERMEABLE ZONE A ._ _ .-

: A.......... . ;

WELLCu-635 .____. _____________

PERMEABLE ZONE A '

, , , i , , , i , , , i , , , i , , , i , , , i , , , i , , , i , , , i , , , i , , , i , , , i , , , 1 1 , 1 1 , , , i , , , i , , , i , , , i , , , i , , i

WELL EB-301

PERMEABLE ZONE B y. ~" "~

^ """^V^

i<ocor-r-.r-oocoa>a>o>oo«-«-f-cNCMoocor 

>cn<ncncn<T>o>cno>a>o>oooooooooc

YEAR 

YEAR

EXPLANATION

MODEL - SIMULATED WATER LEVEL

-. 1983-87 RATE

- - 50-PERCENT DECREASE

----- 50-PERCENT INCREASE

FIGURE 26. Projected effects of an additional 50 years of pumpage at the 1983-87 rate and at increased and decreased rates.
OUTCROP OF PERMEABLE ZONE A IN THE MISSISSIPPI RIVER VALLEY

I OUTCROP-SUBCROP OUTCROP-SUBCROP OUTCROP-SUBCROP OUTCROP-SUBCROP 

AREA OF PERMEABLE ZONE E AREA OF PERMEABLE ZONE D AREA OF PERMEABLE ZONE C AREA OF PERMEABLE ZONE B

OUTCROP OF PERMEABLE ZONE A OUTSIDE 

OF THE MISSISSIPPI RIVER VALLEY

FLOW ACROSS NORTHERN C « , ^ 

BOUNDARY OF PERMEABLE \ ' 

ZONE A IN THE MISSISSIPPI < 

RIVER VALLEY (SPECIFIED- / 

FLUX BOUNDARY) C^ ~

values denote flow out 

of the coastal lowlands 

aquifer system

MILLION MILLION 

CUBIC FEET GALLONS 

PER DAY PER DAY

NET RECHARGE 214.6 1,605NET LATERAL FLOW 

FROM:

ADJACENT PERMEABLE -3.4 -25 ZONES IN TEXAS

MISSISSIPPI RIVER 0.06 0.4 

VALLEY ALLUVIAL AQUIFER

VERTICAL FLOW FROM -0.3 -2 

UNDERLYING AQUIFER 

SYSTEM

TOTAL PUMPAGE -211.0 -1,578

NET CHANGE IN -0.05 0.4 

STORAGE

Figures may not add to total because of independent rounding

FLOW ACROSS WESTERN C 0.39 <- 

BOUNDARY OF PERMEABLE } 0 15 * 

ZONE (GENERAL-HEAD ) 

BOUNDARY) (^ 

^

0.58 0.57 1.56 +44 ^^

- 313 2 ' 55 0.50 ++ 0.06 P = 3.63 0.46 4 

S = 0.00 

>-0.18 

0.57 0.60

it!

0.03

FLOW BETWEEN SUBCROP 

OF LOWER PERMEABLE 

ZONE AND PERMEABLE 

ZONE A IN THE MISSISSIPPI 

RIVER VALLEY

FLOW ACROSS THE WATER 

TABLE IN THE OUTCROP OF 

THE PERMEABLE ZONE

\ 0.25 <-

6.49 +44 - ^ 

0.60

I I f

4 1 1 4 + I

°-9 9 0.02 «-j- 4' 64 4 ' 04 0.17-4- 

_ 

P=1.42 1^0.04 P = 5.83 0.07 > 

S = 0.00 1 S = 0.00 

-+0.04 \-+ 0.06 

2.49 2.59 1.69 1.69 H-4 - ^*-

4 I i

0.10

1.27 <- 

74.97

4 I I

0.00

,16 *J 

1.99 « 

24.09 

I I t

0.94 1.44 WATER TABLE 

i* A (CONSTANT-HEAD UPPER BOUNDARY MODEL LAYER 1)

15.46 

I t

I I i + I 

0.30 1 27 ^ 127.62112.16

P=0.58 0.80 ^L- PERMEABLE ZONE A (HOLOCENE-UPPER PLEISTOCENE 

S - 0.00 I DEPOSITS MODEL LAYER 2) -^ 0.10 1 » 0.47

XII 1 P = 112.96

oJi 723 !:IJfc i i T ~+>0-°° 5.54 24.50 1 4 t L i i T j-i 

35.81 28.58 18.96 

_ 

PERMEABLE ZONE B (LOWER PLEISTOCENE-UPPER 

PLIOCENE DEPOSITS MODEL LAYER 3) 

rO.17 

P = 13.86 

S = 0.00 10.03 

1 1 t i I * T ; + 46.38 22.29 16.43 6.40 

F^ 1.10 PERMEABLE ZONE C (LOWER PLIOCENE-UPPER 

MIOCENE DEPOSITS MODEL LAYER 4) 

-^ 2.37 

P = 20.47 

S = 0.00 TO-S4 

1 t 1 I it - ^ 

117.42 42.45 17.98 7.64 

"^ 1 ' 63 PERMEABLE ZONED (MIDDLE MIOCENE DEPOSITS MODEL LAYER 5)

P = 40.06 

S = 0.01 16.11 

I I t

_ 10.52 4.03 25.29 9.18 

_ 

PERMEABLE ZONE E (UPPER OLIGOCENE-LOWER MIOCENE DEPOSITS MODEL LAYER 6)

-> 0.24 P = 12.22 1 7s 

S = °-°4 ! , ^3 134 I

1

^^- DOWNDIP LIMIT OF 

-""^ PERMEABLE ZONE 

INO-FLOW BOUNDARY)

EXPLANATION

FLOW INTO OR OUT OF PERMEABLE 

ZONE Number is flow, in million cubic feet per day

FLOW ACROSS LOWER BOUNDARY OF AQUIFER 

SYSTEM (SPECIFIED-FLUX BOUNDARY)

5.54 I 

I 0.32

UPDIP LIMIT OF PERMEABLE ZONE 

(NO-FLOW BOUNDARY) NET FLOW TO OR FROM PERMEABLE 

ZONE Number is flow, in million cubic feet per day

p = 20.47 PUMPAGE FROM UNIT In million 

cubic feet per day

s = 0.04 WATE R INTO (-) OR OUT OF

STORAGE In million cubic feet 

per day

FIGURE 27. Schematic section showing simulated flow between permeable zones and across boundaries of the coastal lowlands aquifer system after an additional 50 years of pumpage at the

1983-87 rate.

O

ci73
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H37

(downward flow) at higher rates at the end of the period 

than in 1987. Simulation suggests that from 4 to 9 in./yr of 

recharge would occur near major pumping centers (fig. 33). 

This is about 1 to 3 in./yr more than under 1987 conditions 

(fig. 22).

Results from this experiment indicate that pumping at a 

rate 50 percent greater than the 1983-87 rate would be feasible based on the effects on water levels. Even though 

additional water-level declines of more than 80 ft would 

occur, this would not seriously affect the regional aquifer 

system because of the large available drawdowns and relatively high water levels in the aquifer system. Although 

recharge and lateral flow rates are high enough to maintain a 

50-percent increase in pumpage from present pumping sites, 

there would be some adverse effects on water quality 

through increased saltwater encroachment or infiltration near 

the downdip limit of each permeable zone. Increased 

land-surface subsidence would accompany the greater 

water-level declines.

In the third model experiment, the 1983-87 pumping rate 

was decreased by 50 percent for a period of 50 years (1988 

to 2037). The water-level changes for each permeable zone 

and the average change in all permeable zones are shown on 

plate 7. As in the experiment with increased pumping rates, 

the areas of greatest change are in and near the major pumping centers. Average water levels would rise by more than 

10 ft across much of the central part of the study area and 

by more than 20 ft throughout much of the northern part of 

southeast Louisiana extending a short distance into southwestern Mississippi. Recoveries of more than 50 ft would 

occur at Baton Rouge, La., more than 40 ft at Lake Charles, 

La., more than 30 ft at New Orleans, La., and more than 20 

ft at Alexandria, La. Water-level profiles along north-south 

and east-west lines for each permeable zone in this experiment are shown in figure 34. Hydraulic gradients would 

decrease throughout the aquifer system, most notably 

between the outcrop of each permeable zone and the pumping centers downdip in that zone.

The maximum water-level recovery of more than 80 ft 

would occur at Baton Rouge, La., in permeable zone C. 

Permeable zone A would have more than 50 ft of recovery 

at Lake Charles and more than 40 ft at New Orleans, La. 

Recoveries of more than 30 ft would occur at Lake Charles 

and Baton Rouge, La., in permeable zone B. Small areas of 

southeastern Texas and coastal Mississippi would experience 

recoveries of more than 30 and 40 ft in permeable zone C. 

Water-level recovery in permeable zone D would be more 

than 70 ft near Baton Rouge, La., while small areas near 

Alexandria and Bogalusa, La., would recover more than 50 

ft. More than 60 ft of recovery would occur at Alexandria, 

La., and more than 40 ft in southern Mississippi in permeable zone E. Water-level changes resulting from this experiment at selected sites are shown in figure 26.

The distribution of flow within the aquifer system and 

between the aquifer system and the water table and 

adjoining aquifer systems at the end of the 50-year recovery period with reduced pumpage is shown in figure 35. 

Decreasing the pumpage in permeable zone A from about 

124 to 62.2 Mft3/d (928 to 465 Mgal/d) would reduce the 

net recharge to permeable zone A by 62 percent, from 

118 to 44.3 Mft3/d. (See figs. 23 and 35.) The relation 

between pumpage, recharge, change in storage, and flows 

to and from adjacent aquifers and the underlying aquifer 

system is shown in figures 36 and 37. As in the second 

experiment where pumpage was increased by 50 percent, 

more than 95 percent of the flow would be derived from 

recharge. The cumulative amount of water derived from 

storage would decrease with the reduced pumpage as 

water would go into storage and water levels would rise 

(fig. 37). Most of the water going into storage would do 

so during the first 20 years after the pumpage reduction. A relatively small amount of water (0.2 Mff/d) 

would be going into storage at the end of the period, 

indicating that the aquifer system would be approaching 

steady state.

The rate and direction of flow in the aquifer system at the 

end of the 50-year period of reduced pumpage are shown in 

figure 38. Comparison with the map illustrating 1987 conditions (fig. 21) indicates that flow patterns generally would 

be similar but that flow rates around the major pumping centers would be less. Less water would move northward from 

coastal Louisiana toward pumping centers at Lake Charles, 

in the rice-growing area east of Lake Charles, and at New 

Orleans. Reducing the pumpage would decrease the amount 

of induced recharge from the surface. The reduction in 

pumpage would cause some areas that received recharge 

under 1987 conditions to become discharge areas by the end 

of the 50-year period. Recharge to and discharge from the 

aquifer system at the end of the period are shown in figure 

39. Comparison with the map simulating 1987 conditions 

(fig. 22) shows that much of the Mississippi Alluvial Plain 

would revert to a discharge area as during predevelopment 

time (fig. 18) and that recharge rates in the central part of 

the rice-growing area would be decreased by 1 in./yr or 

more. No negative effects on the aquifer system would be 

expected due to a 50-percent decrease in pumpage.

In the fourth model experiment, designed to determine 

favorable and less favorable areas for development, 10,000 

ff/d (75,000 gal/d) of pumpage was simulated from each 

square mile of the aquifer system in lieu of any other 

pumpage. The pumpage was distributed among the permeable zones beneath each grid block in proportion to the 

transmissivity of the zones. Total pumpage of 450 Mff/d 

(3,370 Mgal/d) was slightly more than double the 1985 

pumpage. The steady-state model was used for this experiment to insure that the results would represent the full 

effects of the simulated pumpage. Drawdowns from
H38 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

D' E

450

LAND SURFACE 

PROJECTED WATER LEVELS 

ZONE A 

ZONEB 

ZONEC 

ZONE D 

ZONEE

150

FIGURE 28,

GAPS INDICATE 

INACTIVE NODES

VERTICAL SCALE 

GREATLY EXAGGERATED

50 100 150 200 

MILES FROM SOUTH EDGE OF MODEL

50 100 150 200 250 300 

MILES FROM WEST EDGE OF MODEL

350 400 450

-Profiles along north-south and east-west lines showing projected water levels in each permeable zone after an additional 50 years of pumpage

at 150 percent of the 1983-87 rate.

predevelopment levels for each permeable zone are shown 

on plate 8. These maps show that, in general, the most 

favorable conditions for development occur in the upper 

permeable zones. Using arbitrary criteria of a minimum 

thickness of 100 ft of sand and a maximum of 200 ft of 

projected drawdown in a zone, large parts of permeable 

zones A and B would be favorable for additional development. A small area near the Mississippi River southeast of 

New Orleans would be less favorable for development 

because relatively thick and nearly impermeable surficial 

clays impede recharge and more than 200 ft of drawdown 

occurs in each permeable zone. Some outcrop areas would 

be less favorable because the zones contain less than 100 ft 

of sand. Most of permeable zone C would be favorable 

except for part of the outcrop area in southern Mississippi 

and Alabama, where sand thickness is less than 100 ft, and 

a relatively small area north and east of New Orleans where 

more than 200 ft of drawdown occurs. Most of the outcrop 

area and shallow subsurface extent of permeable zone D

would be favorable for development, but the deeper 

subsurface extent across southern Mississippi and in southeast Louisiana would be less favorable because of drawdown greater than 200 ft. Maximum drawdown in 

permeable zone D of more than 300 ft occurs near the 

downdip limit of the zone north of New Orleans. Permeable zone E would be favorable for development throughout 

most of its extent in western Florida, southern Alabama, 

and in the eastern part of southern Mississippi. Permeable 

zone E would be less favorable for development throughout 

most of southwestern Mississippi and central and southeastern Louisiana. Drawdowns of more than 400 ft were projected throughout most of southwestern Mississippi, all of 

southeastern Louisiana, and in central Louisiana in the 

Alexandria area.

Projected water-level profiles along north-south and 

east-west lines (fig. 40) show that water-level gradients 

are steeper and water levels are lower than under 1987 

conditions throughout the area (fig. 20). Water-level
OUTCROP OF PERMEABLE ZONE A IN THE MISSISSIPPI RIVER VALLEY

l OUTCROP-SUBCROP OUTCROP-SUBCROP OUTCROP-SUBCROP OUTCROP-SUBCROP 

AREA OF PERMEABLE ZONE E AREA OF PERMEABLE ZONE D AREA OF PERMEABLE ZONE C AREA OF PERMEABLE ZONE B

OUTCROP OF PERMEABLE ZONE A OUTSIDE 

OF THE MISSISSIPPI RIVER VALLEY

FLOW ACROSS NORTHERN (^" 0 18 ^_ 

BOUNDARY OF PERMEABLE \ 

ZONE A IN THE MISSISSIPPI < 

RIVER VALLEY (SPECIFIED- /

FLUX BOUNDARY) k^

FLOW SUMMARY Negative 

values denote flow out

of the coastal lowlands

aquifer system

MILLION MILLION 

CUBIC FEET GALLONS

PER DAY PER DAY

NET RECHARGE 318.4 2,382

NET LATERAL FLOWFROM: 

ADJACENT PERMEABLE -1.8 -13.5ZONES IN TEXAS

MISSISSIPPI RIVER 0.09 0.7

VALLEY ALLUVIALAQUIFER

VERTICAL FLOW FROM -0.5 -3.7 

UNDERLYING AQUIFER 

SYSTEM

TOTAL PUMPAGE -316.6 -2.368

NET CHANGE IN 0.3 2.2

STORAGE

Figures may not add to total

because of independent rounding

(^ r^ FLOW ACROSS WESTERN \ °-33-«-

BOUNDARY OF PERMEABLE </ 0.034 

ZONE (GENERAL-HEAD ) 

BOUNDARY) ( 

^^

/" ~"~~~~- ~"~" ~~\ /" ~~~~~

0.33

H4 ^

"~~~~~ ~\ f ~" ~^~ ~\ /' ~~~~ ^" ~\^"

1.03 0.22 0.39 1.26

^

WATER TABLE 1 ° 23

| ^ It ft (CONSTANT-HEAD UPPER BOUNDARY MODEL LAYER 1) | ^

V 1 T ^ ^11

_ 4.844.51 Q 53 « 1.680.65 0.01 «-| 7.307.08 0 . 20 « 0.87 1 2g ^ __ -^ 0.09 P=5.45 0.49 4 I P = 2.13 1 fr 0.07 P = 8.74 0.10 4 I P = 0.88 0.80 < i

1 * 1

188.57 178.34 

PERMEABLE ZONE A (HOLOCENE-UPPER PLEISTOCENE

S = 0.00 I S = 0.00 I S = 0.00 I S = 0.00 I DEPOSITS MODEL LAYER 2) ->027 | fc. 0.04 Ufcnna l-fc- 0.10 I k 0.48

0.36 0.42

±44 i0.06 0.11

FLOW BETWEEN SUBCROP 

OF LOWER PERMEABLE 

ZONE AND PERMEABLE ZONE

A IN THE MISSISSIPPI

RIVER VALLEY

2.04 2.15 1.49 1.49 0.57 0.59 +4 H-4 K4^

o.oo 0.02 6 Q2 3 : 61 4X1 1 1 ~^

1 1^1

1.62 +-> 40.9834.96

P= 169.43 

S = 0.00

27.89 H^4 

32.40 4.51

=

DOO O

1.37 44 PERMEABLE ZONES (LOWER PLEISTOCENE-UPPER <

' PLIOCENE DEPOSITS MODEL LAYER 3) I > 0.25

P = 20.79

22.00 S = 0.01 ,.*r-H^ 

1 -u/ ^ 1 50.21 28.21

8.07

i *1

24.8216.75 DOWNDIP LIMIT OF

o-d

HI mno

-^ ^ 1.37 PERMEABLE ZONE C (LOWER PLIOCENE-UPPER -"" PERMEABLE ZONE >

FLOW ACROSS THE WATER 

TABLE IN THE OUTCROP OF 1 THE PERMEABLE ZONE +-

I 4 MIOCENE DEPOSITS-MODEL LAYER 4) (NO-FLOW BOUNDARY) ^

P = 30.70

70 - 44 S = 0.01 +4 H

\ n 90 ^ 1 v T u "" ^1 129.86 59.42 22.89 14.1 ^__^^ i ftfl ^^ ^^ i .00

/ "- ^/\ --" N W ^.10

5.97 s

1 1 A1 1 I

T *

_ 11.62 5.65

PERMEABLE ZONE D (MIDDLE MIOCENE DEPOSITS MODEL LAYER 5)

= 60.10 

n nK 1 5 -°' = U.UD .

| | T

r ^ '

29.02 13.35

_ 

PERMEABLE ZONE E (UPPER OLIGOCENE-LOWER MIOCENE DEPOSITS-MODEL LAYER 6) 

-> 0.30 p= 18.33

S = 0.20

UPDIP LIMIT OF PERMEABLE ZONE 

(NO-FLOW BOUNDARY)

1.54 H^4 

2.01 0.48

FLOW ACROSS LOWER BOUN DARY OF AQUIFER

SYSTEM (SPECIFIE&FLUX BOUNDARY)

8.74

|

5

EXPLANATION

I 1 I4 FLOW INTO OR OUT OF PERMEABLE 

^ ZONE Number is flow, in million 2.01 1 . . , cubic feet per day

r t~ 

O

r~zoC/3

O

C 71 c*nPC onH

m ? 

°- 57 1 NET FLOW TO OR FROM PERMEABLE ^ 

T -T ZONE Number is flow, in million

' ° 48 cubic feet per day

p = 18.33 PUMPAGE FROM UNIT In million

cubic feet per day

s = 0.20 WATER INTO (-) OR OUT OF

STORAGE In million cubic feet

per day

FIGURE 29. Schematic section showing simulated flow between permeable zones and across boundaries of the coastal lowlands aquifer system after an additional 50 years of pumpage at 150

percent of the 1983-87 rate.

K

\D
H40 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

1,200

cd 1,100

S3

2 1,000 -

900 -

A LATERAL FLOW FROM THE MISSISSIPPI RIVER 

VALLEY ALLUVIAL AQUIFER. VERTICAL FLOW 

FROM THE UNDERLYING AQUIFER SYSTEM. 

LATERAL FLOW FROM ADJACENT AQUIFERS 

IN TEXAS, AND STORAGE

200 -

iS 100 ; u_

0

2,368 MILLION GALLONS PER DAY 

PUMPING PERIOD 10

3,000

2,000

1,000

o "- -

YEAR

FIGURE 30. Cumulative purnpage and the sources of water for the coastal 

lowlands aquifer system for an additional 50 years of pumpage at 150 

percent of the 1983-87 rate.

declines are greatest in the downdip section of each 

permeable zone and become progressively greater in the 

lower zones.

The rate and direction of simulated ground-water flow in 

the aquifer system resulting from this experiment are shown 

in figure 41. Almost all natural discharge has been 

eliminated. The uniformly distributed pumpage across the 

area has created a pattern of ground-water flow in the northern part of the area similar to the pattern under predevelopment conditions (fig. 17), though the rate of flow is greater 

with pumpage.

The pattern of ground-water flow in two areas of 

coastal Louisiana differs from the predevelopment pattern. 

The areas, one south of Lake Charles and the other 

southeast of New Orleans, both show converging radial 

flow. Both areas are characterized by thick surficial clays 

of minimal permeability that impede recharge from land 

surface. To meet the pumpage demand, water must flow 

laterally through the aquifer system from surrounding 

areas.

The preceding discussion of the fourth pumping experiment to determine favorable and less favorable areas for 

future development is based on minimum sand thicknesses 

and projected maximum drawdowns. Salty water is 

present downdip from and below the aquifer system as 

defined for this study. Development of a major pumping 

center near the downdip limit of freshwater (less than 

10,000 mg/L dissolved solids) in a permeable zone would 

entail risk of saltwater encroachment. In addition, 

because water in the active area of the flow system may 

contain up to 10,000 mg/L dissolved solids, water in

U u cc

180 

170 

160 

150 

HO 

130 

120 

110 

100

90

80

70

60

50

40

30

20

10 

0

500 p 

400 - 

300 

200 - 

100 - 

0

A LATERAL FLOW FROM THE MISSISSIPPI

RIVER VALLEY ALLUVIAL AQUIFER AND

VERTICAL FLOW FROM THE UNDERLYING 

AQUIFER SYSTEM

 LATERAL FLOW TO ADJACENT AQUIFERS

IN TEXAS

 STORAGE

316.5 MILLION CUBIC FEET PER DAY

2,368 MILLION GALLONS PER DAY 

PUMPING PERIOD 10

co

Z

3,000 5 O

2,000 ^ (3 Q

1,000 ^o£

oo

CO «

8 S

VEAR

FIGURE 31. Pumpage and the cumulative flow of water to or from storage 

and adjacent aquifers for an additional 50 years of pumpage at 150 percent of the 1983-87 rate.

some areas shown as favorable for development on a 

quantitative basis may be too highly mineralized for public supply and many industrial and agricultural uses. A 

potential exists for significant land subsidence in areas 

where thick clay sections occur and projected drawdowns 

are greatest.

SUMMARY

The coastal lowlands aquifer system of Louisiana, Mississippi, Alabama, and Florida consists of alternating beds of 

sand, gravel, silt, and clay deposited under fluvial, deltaic, 

and marine conditions. The aquifer system comprises sediments of late Oligocene age and younger that thicken and 

dip toward the Gulf Coast. The sediments are highly heterogeneous with sand beds that are not traceable for more than 

a few miles.

This study was limited to the part of the aquifer system 

containing water with dissolved solids concentration of 

10,000 mg/L or less. Thickness of that part of the aquifer 

system ranges from a featheredge along the northern edge 

of its outcrop area to more than 4,000 ft, with maximum 

sand thickness of over 2,000 ft in southeastern Louisiana 

and southern Mississippi. Sand content (including gravel) 

ranges from less than 10 percent to greater than 80 

percent.
  i.jtpfw 

HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H41

0 20 40 60 80 100 MILES

I I I I I

I I I I I 

0 20 40 60 80 100 KILOMETERS

EXPLANATION

VERTICAL FLOW THROUGH 

TOP OF AQUIFER SYSTEM

[ . | Recharge area j____] Discharge area

RATE AND DIRECTION OF LATERAL 

FLOW, IN CUBIC FEET PER DAY

- 0 to 100,000

*- 100,000 to 500,000

^ 500,000 to 1,000,000

|p». 1,000,000 to 5,000,000

^ Greater than 5,000,000

FIGURE 32. Simulated ground-water flow in the aquifer system after an additional 50 years of pumpage at 150 percent of the 1983-87 rate.
H42 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

0 20 40 60 80 100 MILES

I I I I I I

I I I I I 1

0 20 40 60 80 100 KILOMETERS

EXPLANATION

RECHARGE AREA 

DISCHARGE AREA

LINE OF EQUAL FLOW RATE Interval 

1 inch per year. Positive flow is recharge 

to aquifer system. Negative flow is discharge 

from aquifer system

FIGURE 33. Areal distribution of simulated rates of recharge to and discharge from the aquifer system after an additional 50 years of pumpage at

150 percent of the 1983-87 rate.
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H43

D' E

450

LAND SURFACE 

PROJECTED WATER LEVELS 

ZONE A 

ZONEB 

ZONEC 

ZONED 

ZONEE

100 -

150

FIGURE 34.

GAPS INDICATE 

INACTIVE NODES

VERTICAL SCALE 

GREATLY EXAGGERATED

50 100 150 200 250 0 

MILES FROM SOUTH EDGE OF MODEL

50 100 150 200 250 300 

MILES FROM WEST EDGE OF MODEL

350 400 450

-Profiles along north-south and east-west lines showing projected water levels in each permeable zone after an additional 50 years of purnpage

at 50 percent of the 1983-87 rate.

The coastal lowlands aquifer system was divided into five 

regional permeable zones to quantify the distribution of flow 

in the system. The permeable zones were defined on the 

basis of purnpage and water-level data from heavily pumped 

areas, and zone divisions were extrapolated into lesser 

developed areas. The permeable zones represent deposits 

that from youngest to oldest are referred to as: 

Holocene-upper Pleistocene deposits (zone A), lower 

Pleistocene-upper Pliocene deposits (zone B), lower 

Pliocene-upper Miocene deposits (zone C), middle Miocene 

deposits (zone D), and the lower Miocene-upper Oligocene 

deposits (zone E).

Flow in the aquifer system prior to development was primarily from the upland terrace areas of southwestern Mississippi and south-central and southeastern Louisiana toward 

the Gulf Coast and major river valleys. Water-level altitudes decreased with depth in the recharge areas and

increased with depth in the discharge areas. Freshwater 

moving from the recharge areas tends to flush saltwater 

occurring in the downdip parts of the aquifer system unless 

movement is blocked by pinchout of the sand beds or by 

faulting.

Lateral hydraulic conductivities of sand beds within the 

permeable zones were determined from aquifer-test results. 

Lateral hydraulic conductivity decreases from the upper to 

the lower permeable zones. On average, permeable zone A 

has the highest lateral hydraulic conductivity and zone E has 

the lowest.

Ground water is pumped for municipal, industrial, agricultural, and domestic use throughout most of the study 

area. Total purnpage increased during 1960-80 and peaked 

in 1980 at 251 MtVVd (1,874 Mgal/d). Purnpage then 

declined by more than 15 percent to 211 Mff/d (1,579 

Mgal/d) in 1985. Purnpage from permeable zone A has
OUTCROP OF PERMEABLE ZONE A IN THE MISSISSIPPI RIVER VALLEY

i OUTCROP-SUBCROP OUTCROP-SUBCROP OUTCROP-SUBCROP OUTCROP-SUBCROP

1 AREA OF PERMEABLE ZONE E AREA OF PERMEABLE ZONE D AREA OF PERMEABLE ZONE C AREA OF PERMEABLE ZONE B

OUTCROP OF PERMEABLE ZONE A OUTSIDE 

OF THE MISSISSIPPI RIVER VALLEY

FLOW ACROSS NORTHERN (^" 0 064- 

BOUNDARY OF PERMEABLE \ ' 

ZONE A IN THE MISSISSIPPI < 

RIVER VALLEY (SPECIFIED- / 

FLUX BOUNDARY) (^

values denote flow out 

of the coastal lowlands 

aquifer system

MILLION MILLION 

CUBIC FEET GALLONS 

PER DAY PER DAY

NET RECHARGE 110.8 829

NET LATERAL FLOW FROM:

ADJACENT PERMEABLE -4.9 -37 

ZONES IN TEXAS

MISSISSIPPI RIVER 0.03 0.2 

VALLEY ALLUVIAL 

AQUIFER

VERTICAL FLOW FROM -0.2 -1.5 

UNDERLYING AQUIFER SYSTEM

TOTAL PUMPAGE -105.5 -789NET CHANGE IN -0.2 -1.5 STORAGE

Figures may not add to total because of independent rounding

FLOW ACROSS WESTERN \ °-*5 4- 

BOUNDARY OF PERMEABLE / 0264- 

ZONE (GENERAL-HEAD ) 

BOUNDARY) (^ 

^

r~ ~~ """" 

A

1.08 4-W-n

1.66 0.58 4? 

^

-^ 0.03 P= 1.82 0.43 4 

S = 0.00 

-> 0.09 - 

0.78 0.79 H-r-J

0.02

FLOW BETWEEN SUBCROP 

OF LOWER PERMEABLE 

ZONE AND PERMEABLE 

ZONE A IN THE MISSISSIPPI 

RIVER VALLEY

FLOW ACROSS THE WATER 

TABLE IN THE OUTCROP OF 

THE PERMEABLE ZONE

\ 0.28 4H

7.26

/" ~~~~~ """ 

A

1.80 2.62

f A -^

1.48 

1 1 t

r ~~~ ^- " "\ /^~ -^~ - 1.48 1.69 WATER TABLE 26. 

I + 4 (CONSTANT-HEAD UPPER BOUNDARY MODEL LAYER 1) 1 ' ITT i ^ i iii i +

r °' 81 0.074 2 ' 47 °'" 0.144 °'21 1.264-- 72.6445.98 

P = 0.71 0.01 4r P = 2.91 0.04 4-I P = 0.29 0.804!- PERMEABLE ZONE A (HOLOCENE-UPPER PLEISTOCENE 

S = 0.00 I S = 0.00 I S = 0.00 I DEPOSITS MODEL LAYER 2) * 0.04 » 0.06 ^0.11 L^. 0.47 

2.94 3.03 1.90 1.90 1.02 1.02 L^H LJt^ 1^^ 1

0.09 

1.504-

^M

80,49

1 1 1 

0.00

2.73 4-2.61 4^

26.41 

1 1 t

.r^ts^ i i T ' ^°'c P = 56.48 S = 0.00

I i ^ 1 1 ' 11 31.3422.20 10.11 h PERMEABLE ZONES (LOWER PLEISTOCENE-UPPER 

PLIOCENE DEPOSITS MODEL LAYER 3) 

ro.12 

P = 6.93 

S = 000 3.94 14.18 

1 4 t

, \ i T ; i i1 42.81 16.40 10.24 DOWNDIP LIMIT OF PERMEA F>- 0.82 PERMEABLE ZONE C (LOWER PLIOCENE-UPPER -^"^ (NO-FLOW BOUNDAF 

MIOCENE DEPOSITS MODEL LAYER 4) -fr 2.32 

P = 10.23 

S = -0.03 T2.77 

1 t

106.00 25.51 13.39 1.1 

^^ 1 W ^ PERMEABLE ZONE D (MIDDLE MIOCENE DEPOSITS MODEL LAYER 5)

P = 20.03 

S = -0.03 16.78 

I 1 t

__ 9.85 2.39 21.79 5.01 

_ 

PERMEABLE ZONE E (UPPER OLIGOCENE-LOWER MIOCENE DEPOSITS MODEL LAYER 6)

-> 0.19 P = 6.11 

S = -0.11 0.52

I I. t

1 2

EXPLANATION

1 °i2 FLOW INTO OR OUT OF P

0.67 1 34* 1 NET FLOW T0 OR FROM F 

T ^ Number is flow, in million

1 0.15

P = 6.ii PUMPAGE FROM UNIT,

~^\

66 

L

<

(

C C]

BLEZONE : 1Y) I

C 

C

(.C 

E C 

ERMEABLE ZONE 3 

cubic feet per day ^ 

3

'ERMEABLE ZONE ^ 

cubic feet per day |~

UPDIP LIMIT OF PERMEABLE ZONE 

(NO-FLOW BOUNDARY)

FLOW ACROSS LOWER BOUNDARY OF AQUIFER 

SYSTEM (SPECIFIED-FLUX BOUNDARY)

s=-o.ii WATER INTO (-) OR OUT OF STORAGE, 

in million cubic feet per day

FIGURE 35. Schematic section showing simulated flow between permeable zones and across boundaries of the coastal lowlands aquifer system after an additional 50 years of pumpage at 50 percent

of the 1983-87 rate.
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H45

O O

> 5

£3

z^ >

- 5 <

400

300

200

A LATERAL FLOW FROM THE MISSISSIPPI RIVER 

VALLEY ALLUVIAL AQUIFER, VERTICAL FLOW 

FROM THE UNDERLYING AQUIFER SYSTEM, 

LATERAL FLOW FROM ADJACENT AQUIFERS 

IN TEXAS, AND STORAGE

O RECHARGE FROM THE WATER TABLE 

 PUMPAGE

300

O <-> cc 200 

^O?- 100

n n n n r i 1 1 1 1 1 1 1 1 n

PUMPING PERIOD 10 

105.5 MILLION CUBIC FEET PER DAY

789 MILLION GALLO

i i l l l l l i i i l n l

MS PER DAY

2,000 ,,rzj

1,000

o o_

YEAR

FIGURE 36. Cumulative pumpagc and the sources of water for the coastal 

lowlands aquifer system for an additional 50 years of pumpage at 50 

percent of the 1983-87 rate.

ranged from 59 to 67 percent of the total pumpage from 

the aquifer system during the period 1960-85.

A six-layer, finite-difference ground-water-flow model was 

used to investigate and quantify regional flow in the coastal 

lowlands aquifer system and to evaluate the effects of possible future ground-water pumpage. The model was calibrated to steady-state and transient conditions by adjusting 

transmissivities of the model layers that represent the five 

permeable zones, vertical leakances between layers, and 

storage coefficients of the permeable zones. Calibration was 

based on minimizing the RMSE of the residuals between 

simulated and measured water levels throughout the modeled 

area.

The model is generally most sensitive to changes in transmissivity and least sensitive to changes in storage coefficient. 

Generally, the model is more sensitive, in terms of 

water-level changes, to decreases than to increases in transmissivities and vertical leakances. The model is relatively 

insensitive to changes in storage coefficients.

The model was divided into seven areas to investigate in 

detail the flow patterns and distributions in the aquifer system. The areas were chosen based on factors affecting 

flow in the aquifer system, such as topography, the outcrop 

pattern of the zones, and drainage boundaries.

Simulation results indicate that pumping has significantly 

altered the natural ground-water flow system. Under 1987 

conditions, about 60 percent of the water entering the 

regional flow system is discharged by pumping. The total 

flow circulating through the regional aquifer system in 1987 

was about 354 Mft3/d, which is about 62 percent greater 

than the predevelopment flow of 222 Mft /d. Less than 1 

percent of the flow in the aquifer system under 1987

-

 CD <

uj =3 Q

U CJ ffi

A LATERAL FLOW FROM THE

MISSISSIPPI RIVER VALLEY

ALLUVIAL AQUIFER AND VERTICAL 

FLOW FROM THE UNDERLYING 

AQUIFER SYSTEM

LATERAL FLOW TO ADJACENT 

AQUIFERS IN TEXAS

300

200

100

0

PUMPING PERIOD 10

105.5 MILLION CUBIC FEET PER DAY

789 MILLION GALLONS PER DAV

2,000

1,000

0

YEAR

FIGURE 37. Pumpage and the cumulative flow of water to or from storage and adjacent aquifers for an additional 50 years of pumpage at 50 

percent of the 1983-87 rate.

conditions is derived from water moving into or out of storage. Throughout most of the Coastal Plain of southern Louisiana, flow directions have been altered or reversed due to 

pumping so that flow now converges toward the major 

pumping centers. A large part of the Gulf Coastal Plain has 

been transformed from areas of natural discharge to areas of 

induced recharge. Major pumping centers in southern Louisiana, in permeable zone A, and at Baton Rouge, La., in permeable zone C, have had the greatest effect on the 

ground-water-flow system.

Four model experiments were conducted to evaluate the 

effects of possible future ground-water pumpage from the 

aquifer system. Results of the first experiment show that 

relatively small changes in water levels occurred throughout the aquifer system when the 1983-87 pumping rate 

was continued for an additional 50 years (1988 to 

2037). In the second experiment, results indicate that 

pumping from existing pumping centers at a rate 50 percent greater than the 1983-87 rate would be feasible 

based on the effects on water levels. Because of the 

large available drawdowns and relatively high water levels, 

there would be no serious impact on the regional aquifer 

system even though additional water-level declines of 

more than 80 ft would occur in places. There would be 

some adverse effects on water quality through increased 

saltwater encroachment or infiltration and on the rate of 

land-surface subsidence. Results of the third model
H46 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

0 20 40 60 80 100 MILES 

I I

I I I I I 

0 20 40 60 80 100 KILOMETERS

EXPLANATION

VERTICAL FLOW THROUGH 

TOP OF AQUIFER SYSTEM

_J Recharge area |____| Discharge area

RATE AND DIRECTION OF LATERAL 

FLOW, IN CUBIC FEET PER DAY

" 0 to 100,000

* 100,000 to 500,000

+» 500,000 to 1,000,000

* 1,000,000 to 5,000,000

^ Greater than 5,000,000

FIGURE 38. Simulated ground-water flow in the aquifer system after an additional 50 years of pumpage at 50 percent of the 1983-87 rate.
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H47

0 20 40 60 80 100 MILES

I I I.I. I____I 

I I I T I I

0 20 40 60 80 100 KILOMETERS 

EXPLANATION

RECHARGE AREA 

DISCHARGE AREA

 1 LINE OF EQUAL FLOW RATE - Interval 

1 inch per year. Positive flow is recharge 

to aquifer system. Negative flow is discharge 

from aquifer system

FIGURE 39. Areal distribution of simulated rates of recharge to and discharge from the aquifer system after an additional 50 years of pumpage at 50

percent of the 1983-87 rate.
H48

450

400

350

300

250

200

150

100

100

150

200

250

300

350

400

REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

D 1 E

 ---- LAND SURFACE 

PROJECTED 

WATER LEVELS

 ZONE A

 ZONE B

 ZONEC

 ZONE D 

____ ZONE E

n r

\T i GAPS INDICATE 

INACTIVE NODES

VERTICAL SCALE 

GREATLY EXAGGERATED

0 50 100 150 200 250 0 

MILES FROM SOUTH EDGE OF MODEL

OK

50 100 150 200 250 300 350 

MILES FROM WEST EDGE OF MODEL

400 450

FIGURE 40. Profiles along north-south and east-west lines showing projected steady-state water levels in each permeable zone resulting from 

pumpage of 10,000 cubic feet per day (75,000 gallons per day) per square mile uniformly distributed across the extent of the aquifer system.
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H49

0 20 40 60 80 100 MILES 

I I I I I

I I I I I 

0 20 40 60 80 100 KILOMETERS

EXPLANATION

VERTICAL FLOW THROUGH 

TOP OF AQUIFER SYSTEM

Recharge area Discharge area

RATE AND DIRECTION OF LATERAL 

FLOW, IN CUBIC FEET PER DAY

- 0 to 100,000

*- 100,000 to 500,000

^ 500,000 to 1,000,000

^ 1,000,000 to 5,000,000

^- Greater than 5,000,000

FIGURE 41. Simulated ground-water flow in the aquifer system resulting from pumpage of 10,000 cubic feet per day (75,000 gallons per day) per

square mile uniformly distributed across the extent of the aquifer system.
H50 REGIONAL AQUIFER-SYSTEM ANALYSIS GULF COASTAL PLAIN

experiment, involving a 50-percent pumpage reduction 

from the 1983-87 rate, show that water levels would 

recover rapidly throughout the aquifer system in response 

to the reduced pumpage. Results of the fourth experiment show that the most favorable conditions for development occur in the upper permeable zones. Favorable 

and less favorable areas are described in qualitative terms 

based on maximum drawdowns and minimum sand thicknesses within each permeable zone. Development of a 

major pumping center near the downdip limit of a permeable zone would entail risk of saltwater encroachment and 

the potential for land subsidence.

SELECTED REFERENCES

Ackerman, D.J., 1989, Hydrology of the Mississippi River valley alluvial 

aquifer, south-central United States A preliminary assessment of the 

regional flow system: U.S. Geological Survey Water-Resources Investigations Report 88-4028, 74 p.

Arthur, J.K., and Taylor, R.E., 1990, Definition of the geohydrologic framework and preliminary simulation of ground-water flow in the Mississippi embayment aquifer system, Gulf Coastal Plain, United States: 

U.S. Geological Survey Water-Resources Investigations Report 

86-4364, 97 p.

Brahana, J.V., and Mesko, TO., 1988, Hydrogeology and preliminary 

assessment of regional flow in the upper Cretaceous and adjacent 

aquifers in the northern Mississippi embayment: U.S. Geological Survey Water-Resources Investigations Report 87-4000, 65 p.

Bredehoeft, J.D., and Pinder, G.F., 1970, Digital analysis of areal flow in 

multiaquifer groundwater systems A quasi three-dimensional model: 

Water Resources Research Journal, v. 6, no. 3, p. 883-888.

Cushman-Roisin, Mary, and Franks, B.J., 1982, Sand and gravel aquifer, in 

Franks, B.J., ed., Principal aquifers in Florida: U.S. Geological Survey Water-Resources Investigations Open-File Report 82-0255, maps 

(4 sheets).

Dial, D.C., and Sumner, D.M., 1989, Geohydrology and simulated effects 

of pumpage on the New Orleans aquifer system at New Orleans, Louisiana: Louisiana Department of Transportation and Development 

Water Resources Technical Report 46, 54 p.

Fenneman, N.M., 1938, Physiography of the Eastern United States: New 

York and London, McGraw Hill Book Co., 714 p.

Franks, B.J., 1988, Hydrogeology and flow of water in a sand and gravel 

aquifer contaminated by wood-preserving compounds, Pensacola, 

Florida: U.S. Geological Survey Water-Resources Investigations

Report 87-4260, 72 p.

Grubb, H.F., 1984, Planning report for the Gulf Coast Regional Aquifer-System Analysis in the Gulf of Mexico Coastal Plain, United 

States: U.S. Geological Survey Water-Resources Investigations Report 

84-4219, 30 p.

 1986, Gulf Coast Regional Aquifer-System Analysis A Mississippi 

perspective: U.S. Geological Survey Water-Resources Investigations 

Report 86-4162, 22 p.

 1987, Overview of the Gulf Coast Regional Aquifer-System Analysis, South-Central United States, in Vecchioli, John, and Johnson, A.I., 

eds., Regional Aquifer Systems of the United States: Aquifers of the 

Atlantic and Gulf Coastal Plain, American Water Resources Association Monograph Series 9, p. 101-118.

Huntzinger, T.L., Whiteman, C.D., Jr., and Knochenmus, D.D., 1985 

[1986], Simulation of ground-water movement in the "1,500- and 

1,700-foot" aquifer of the Baton Rouge area, Louisiana: Louisiana

Department of Transportation and Development, Office of Public 

Works Water Resources Technical Report 34, 52 p.

Ireland, R.L., Poland, J.F., and Riley, F.S., 1984, Land subsidence in the 

San Joaquin Valley, California, as of 1980: U.S. Geological Survey 

Professional Paper 437-1, 93 p.

Lohman, S.W., 1972, Ground-water hydraulics: U.S. Geological Survey 

Professional Paper 708, 70 p.

McDonald, M.G., and Harbaugh, A.W., 1988, A modular three-dimensional 

finite-difference ground-water flow model: U.S. Geological Survey 

Techniques of Water Resource Investigations, book 6, chap. A1, 576 p.

Martin, Angel, Jr., and Early, D.A., 1987, Statistical analysis of aquifer-test 

results for nine regional aquifers in Louisiana: U.S. Geological Survey Water-Resources Investigations Report 87-4001, 26 p.

Martin, Angel, Jr., and Whiteman, C.D., Jr., 1985a, Map showing generalized potentiometric surface of aquifers of Pleistocene age, southern 

Louisiana, 1980: U.S. Geological Survey Water-Resources Investigations Report 84-4331, map (I sheet).

 1985b, Map showing generalized potentiometric surface of the 

Evangeline and equivalent aquifers in Louisiana, 1980: U.S. Geological Survey Water-Resources Investigations Report 84-4359, map (I 

sheet).

 1986, Generalized potentiometric surface of the Catahoula aquifer 

in central Louisiana, 1980: U.S. Geological Survey Water-Resources 

Investigations Report 86-4059, map (1 sheet).

 1989, Geohydrology and regional ground-water flow of the coastal 

lowlands aquifer system in parts of Louisiana, Mississippi, Alabama, 

and Florida A preliminary analysis: U.S. Geological Survey 

Water-Resources Investigations Report 88-4100, 88 p.

 1990, Calibration and sensitivity analysis of a ground-water flow

model of the coastal lowlands aquifer system in parts of Louisiana, 

Mississippi, Alabama, and Florida: U.S. Geological Survey 

Water-Resources Investigations Report 89-4189, 54 p.

Martin, Angel, Jr., Whiteman, C.D., Jr., and Becnel, M.J., 1988, Generalized potentiometric surfaces of the upper and lower Jasper and equivalent aquifers in Louisiana, 1984: U.S. Geological Survey 

Water-Resources Investigations Report 87-4139, maps (2 sheets).

Mesko, TO., Williams, T.A., Ackerman, D.J., and Williamson, A.K., 1990, 

Ground-water pumpage from the Gulf Coast aquifer systems, 

south-central United States: U.S. Geological Survey Water-Resources 

Investigations Report 89-4180, 177 p.

Meyer, William, Reussow, J.P., and Gillies, D.C., 1975, Availability of 

ground water in Marion County, Indiana, with a section on Water 

quality by W.J. Shampine: U.S. Geological Survey Open-File Report 

75-312, 87 p.

Miller, J.A., and Renken, R.A., 1988, Nomenclature of regional hydrogeologic units of the Southeastern Coastal Plain aquifer system: U.S. 

Geological Survey Water-Resources Investigations Report 87-4202, 21

PNyman, D.J., Halford, K.J., and Martin, Angel, Jr., 1990, Geohydrology

and simulation of flow in the Chicot aquifer system of southwestern

Louisiana: Louisiana Department of Transportation and Development

Water Resources Technical Report 50, 58 p. 

Rollo, J.R., 1969, Saltwater encroachment in aquifers of the Baton Rouge

area, Louisiana: Department of Conservation, Louisiana Geological

Survey, and Louisiana Department of Public Works Water Resources

Bulletin 13, 45 p. 

Ryder, P.O., 1988, Hydrogeology and predevelopment flow in the Texas

Gulf Coast aquifer systems: U.S. Geological Survey Water-Resources

Investigations Report 87-4248, 109 p. 

Smoot, C.W., 1989, Louisiana hydrologic atlas map no. 4 Geohydrologic

sections of Louisiana: U.S. Geological Survey Water-Resources

Investigations Report 87-4288, map (1 sheet). 

Sumner, D.M., Wasson, B.E., and Kalkhoff, S.J., 1987, Geohydrology and

simulated effects of withdrawals on the Miocene aquifer system in the
HYDROLOGY OF THE COASTAL LOWLANDS AQUIFER SYSTEM H51

Mississippi Gulf Coast area: U.S. Geological Survey Water-Resources 

Investigations Report 87-4172, 203 p.

Sun, R.J., ed., 1986, Regional Aquifer-System Analysis program of the U.S. 

Geological Survey Summary of projects, 1978-84: U.S. Geological 

Survey Circular 1002, 264 p.

Thornthwaite, C.W., 1948, An approach toward a rational classification of 

climate: Geographic Review 38, p. 55-94.

Thornthwaite, C.W., and Mather, J.R., 1955, The water balance: Laboratory of Climatology, Drexel Institute Publications in Climatology, v. 8, 

no. I, 104 p.

Torak, L.J., and Whiteman, C.D., Jr., 1982, Applications of digital modeling for evaluating the ground-water resources of the "2,000-foot" sand 

of the Baton Rouge area, Louisiana: Louisiana Department of Transportation and Development, Office of Public Works Water Resources 

Technical Report 27, 87 p.

Wasson, B.E., 1986, Sources for water supplies in Mississippi, Revised 

1986: Jackson, Mississippi, Cooperative study by U.S. Geological 

Survey and the Mississippi Research and Development Center, 113 p.

Weeks, J.B., and Sun, R.J., 1987, Regional Aquifer-System Analysis program of the U.S. Geological Survey Bibliography, 1978-86: U.S. 

Geological Survey Water-Resources Investigations Report 87-4138, 81

P

Weiss, J.S., 1987, Determining dissolved-solids concentrations in mineralized ground water of the Gulf Coast aquifer system using electric

logs, in Vecchioli, John, and Johnson, A.I., eds., Regional Aquifer 

Systems of the United States: Aquifers of the Atlantic and Gulf 

Coastal Plain, American Water Resources Association Monograph 

Series 9, p. 139-150.

 1992, Geohydrologic units of the coastal lowlands aquifer system, 

south-central United States: U.S. Geological Survey Professional 

Paper 1416-C, 32 p.

Weiss, J.S., and Williamson, A.K., 1985, Subdivision of thick sedimentary 

units into layers for simulation of ground-water flow: Ground Water, 

v. 23, no. 6, p. 767-774.

Whiteman, C.D., Jr., 1980, Measuring local subsidence with extensometers 

in the Baton Rouge area, Louisiana, 1975-79: Louisiana Department 

of Transportation and Development, Office of Public Works Water 

Resources Technical Report 20, 18 p.

Whiteman, C.D., Jr., and Martin, Angel, Jr., 1984, Geohydrologic sections, 

northern Louisiana: U.S. Geological Survey Water-Resources Investigations Report 84-4211, map (I sheet).

Williamson, A.K., Grubb, H.F., and Weiss, J.S., 1990, Ground-water flow in 

the Gulf Coast aquifer systems, south-central United States A preliminary analysis: U.S. Geological Survey Water-Resources Investigations Report 89-4071, 124 p.

Wilson, T.A., and Hosman, R.L., 1987, Geophysical well-log database for 

the Gulf Coast aquifer systems, south-central United States: U.S. 

Geological Survey Open-File Report 87-0677, 213 p
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