HYDROLOGY OF THE TEXAS GULF COAST 

AQUIFER SYSTEMS

^y Paul D. Ryder and Ann F. Ardis 

REGIONAL AQUIFER-SYSTEM ANALYSIS

U.S. GEOLOGICAL SURVEY 

OPEN-FILE REPORT 91-64

Austin, Texas 

1991
U.S. DEPARTMENT OF THE INTERIOR

MANUEL LUJAN, JR., Secretary

U.S. GEOLOGICAL SURVEY

Dallas L. Peck, Director

For sale by the Books and Open-File Reports Section, U.S. Geological Survey 

Federal Center, Box 25425 Denver, Colorado 80225
CONTENTS

Page

Abstract---------------------------------------------------------------- 1

Introduction------------------------------------------------------------ 2

Gulf Coast aquifer systems regional study-------------------------- 2

Texas Gulf Coast subregional study--------------------------------- 2

Purpose and scope--------------------------------------------- 3

Method of investigation--------------------------------------- 3

Description of the area--------------------------------------- 3

Previous investigations--------------------------------------- 3

Hydrogeology------------------------------------------------------------ 4

Hydrogeologic framework-------------------------------------------- 4

Hydraulic properties----------------------------------------------- 6

Horizontal hydraulic conductivity and transmissivity---------- 6

Vertical hydraulic conductivity------------------------------- 7

Storage coefficient------------------------------------------- 7

Dissolved-solids concentration and density of water---------------- 8

Regional flow system---------------------------------------------------- 9

Predevelopment steady-state flow system---------------------------- 9

Conceptual model of system------------------------------------ 9

Recharge and interaquifer leakage----------------------------- 9

Flow system, predevelopment to 1982-------------------------------- 10

Ground-water development-------------------------------------- 10

Recharge, discharge, and distribution of flow, 1982----------- 11

Subregional flow systems and hydrologic effects of development---------- 13

Houston-Calveston area--------------------------------------------- 13

Coastal rice-irrigation area--------------------------------------- 16

Evadale-Beaumont area---------------------------------------------- 17

Kingsvilie area---------------------------------------------------- 18

Winter Garden area------------------------------------------------- 19

Lufkin-Nacogdoches area-------------------------------------------- 20

Other areas-------------------------------------------------------- 21

Bryan-College Station area------------------------------------ 21

Orange County------------------------------------------------- 22

Potential for ground-water development---------------------------------- 22

Summary----------------------------------------------------------------- 25

Selected references----------------------------------------------------- 28

Appendix---------------------------------------------------------------- 33

Digital model of predevelopment steady-state flow system----------- 34

Digital model of transient flow system, predevelopment to 1982----- 34

Model grid and boundary conditions---------------------------- 35

Hydrologic input data----------------------------------------- 36

Calibration procedure and results----------------------------- 38

Sensitivity analysis------------------------------------------ 41

111
ILLUSTRATIONS

[Figures are at back of text]

Page

Figure 1-5. Maps showing:

1. Relation of the Texas Gulf Coast study area to the 

onshore part of the Gulf Coast Regional AquiferSystem Analysis study area------------------------- 46

2. Relation of the Texas subregional modeled area 

to other subregional modeled areas and to the 

regional modeled area-------------------------------- 47

3. Location of the Texas Gulf Coast study area--------- 48

4. Mean annual precipitation in the Texas

Gulf Coast study area-------------------------------- 49

5. Generalized outcrops of aquifers, permeable zones,

and confining units------------------------------- 50

6. Graph showing hydrogeologic section A-A'----------------- 51

7. Map showing field and simulated hydraulic conductivity 

of coastal uplands aquifers and coastal lowlands 

permeable zones---------------------------------------- 52

8-16. Maps showing simulated transmissivity of:

8. Permeable zone A------------------------------------ 53

9. Permeable zone B------------------------------------ 54

10. Permeable zone C------------------------------------ 55

11. Permeable zone D------------------------------------ 55

12. Permeable zone E------------------------------------ 57

13. The upper Claiborne aquifer------------------------- 58

14. The middle Claiborne aquifer------------------------ 59

15. The lower Claiborne-upper Wilcox aquifer------------ 60

16. The middle Wilcox aquifer--------------------------- 61

17-25. Maps showing estimated dissolved-solids concentration in 

water from:

17. Permeable zone A------------------------------------ 62

18. Permeable zone B------------------------------------ 63

19. Permeable zone C------------------------------------ 64

20. Permeable zone D------------------------------------ 65

21. Permeable zone E------------------------------------ 66

22. The upper Claiborne aquifer------------------------- 67

23. The middle Claiborne aquifer------------------------ 68

24. The lower Claiborne-upper Wilcox aquifer------------ 69

25. The middle Wilcox aquifer--------------------------- 70

26. Diagram showing conceptual model of aquifer

systems and generalized representation in the

digital model------------------------------------- 71

27. Map showing simulated predevelopment recharge

and discharge in the outcrop areas of aquifers,

permeable zones, and confining units------------------- 72

28. Diagram showing simulated predevelopment vertical flow

rates across hudrogeologic units in the study area----- 73

28a. Graph showing simulated pumpage, recharge, and depletion

of storage-------------------------------------------- 74

IV
ILLUSTRATIONS-Continued

Page

Figures 29-37. Maps showing estimated pumpage in 1980, by 25-squaremile grid block, for:

29. Permeable zone A----------------------------------- 75

30. Permeable zone B----------------------------------- 76

31. Permeable zone c----------------------------------- 77

32. Permeable zone D----------------------------------- 78

33. Permeable zone E----------------------------------- 79

34. The upper Claiborne aquifer------------------------ 80

35. The middle Claiborne aquifer----------------------- 81

36. The lower Claiborne-upper Wilcox aquifer----------- 82

37. The middle Wilcox aquifer-------------------------- 83

38. Map showing simulated recharge and discharge in the 

outcrop areas of aquifers, permeable zones, and 

confining units for 1982------------------------------ 84

39. Map showing change in simulated recharge and discharge

in the outcrop areas of aquifers, permeable zones, and 

confining units, predevelopment to 1982--------------- 85

40. Diagram showing simulated 1982 vertical flow rates

across hydrogeologic units in the study area---------- 86

41-46. Maps showing:

41. Locations of observation wells and precipitation 

stations in selected intensively pumped areas, 

and model subareas------------------------------- 87

42. Ground-water pumpage in selected counties in the

central part of the study area, 1960-85---------- 88

43. Location of subareas within the HoustonGalveston area (area 1) and average rates

of pumping for 1979------------------------------ 89

44. Decline of potentiometric surface of permeable

zone A, predevelopment to 1982, and simulated 

1982 horizontal flow vectors, HoustonCalves ton area----------------------------------- 90

45. Decline of potentiometric surface of permeable 

zone B, predevelopment to 1982, and simulated 

1982 horizontal flow vectors, HoustonGalveston area----------------------------------- 91

46. Decline of potentiometric surface of permeable 

zone C, predevelopment to 1982, and simulated 

1982 horizontal flow vectors, HoustonCalves ton area and Evadale-Beaumont area--------- 92

47. Graph showing ground-water levels in Harris County------ 93

48. Map showing land-surface subsidence in the HoustonGalveston area, predevelopment to 1973---------------- 94

49. Diagram showing simulated 1982 vertical flow rates across

hydrogeologic units in model subarea II (fig. 41)----- 95

50. Graph showing ground-water levels in Jackson County and

precipitation data in Wharton County------------------ 96

51. Diagram showing simulated 1982 vertical flow rates across

hydrogeologic units in model subarea III (fig. 41)---- 97
BLLUSTRATIONS-Continued

Page

52. Map showing ground-water pumpage in selected counties in

the eastern part of the study area, 1960-85----------- 98

53. Graph showing ground-water levels in Jasper and Hardin

Counties---------------------------------------------- 99

54. Diagram showing simulated 1982 vertical flow rates across

hydrogeologic units in model subarea I (fig. 41)------ 100

55-56. Maps showing:

55. Ground-water pumpage in selected counties in

the western part of the study area, 1960-85------ 101

56. Change of potentiometric surface of permeable

zone B, predevelopment to 1982, and simulated

1982 horizontal flow vectors, Kingsville area---- 102

57. Graph showing ground-water levels in Kleberg County----- 103

58. Diagram showing simulated 1982 vertical flow rates across

hydrogeologic units in model subarea IV (fig. 41)----- 104

59. Map showing change of potentiometric surface of the

lower Claiborne-upper Wilcox aquifer, predevelopment 

to 1982, and simulated 1982 horizontal flow vectors, 

Winter Garden area------------------------------------ 105

60-64. Graphs showing:

60. Ground-water levels and precipitation data

in Zavala County--------------------------------- 106

61. Ground-water levels in Nacogdoches Countiy--------- 107

62. Projected fresh ground-water use for selected

counties, 1985-2030------------------------------ 108

63. Measured and simulated water levels in the

Houston-Galveston area, projected to 2030-------- 109

64. Map showing projected land-surface subsidence in

the Houston-Galveston area, 1973 to 2030--------- 110

Figures 65-66. Graphs showing:

65. Simulated water levels in southeastern Harris

County, projected to 2030 with 1980 pumpage------ 111

66. Measured and simulated water levels in the Winter

Garden area, projected to 2030------------------- 112

67. Diagram showing simulated 2030 vertical flow rates

across hydrogeologic units in the study area---------- 113

68-76. Maps showing potential areas for development of large 

ground-water supplies from

68. Permeable zone A----------------------------------- 114

69. Permeable zone B----------------------------------- 115

70. Permeable zone c----------------------------------- 116

71. Permeable zone D----------------------------------- 117

72. Permeable zone E----------------------------------- 118

73. The upper Claiborne aquifer------------------------ 119

74. The middle Claiborne aquifer----------------------- 120

75. The lower Claiborne-upper Wilcox aquifer----------- 121

76. The middle Wilcox aquifer-------------------------- 122

VI
BLLUSTRATIONS-Continued

Page 

77-81. Maps showing:

77. Finite-difference grid superimposed on the modeled

area and study area------------------------------ 123

78. Estimated altitude of the water table for the

model constant-head boundary--------------------- 124

79. Measured and simulated altitude of the

potentiometric surface of permeable zone A

in the Houston-Galveston area, 1982-------------- 125

80. Measured and simulated altitude of the

potentiometric surface of permeable zone B

in the Houston-Galveston area, 1982-------------- 126

81. Measured and simulated altitude of the

potentiometric surface of permeable zone C in 

the Houston-Galveston and Evadale areas, 1982---- 127 

82-86. Graphs showing:

82. Measured and simulated water levels in wells

1, 2, 9, and 11 in the Houston-Galveston area---- 128

83. Measured and simulated water levels in wells

4, 7, 8, and 12 in the Houston-Galveston area---- 129

84. Measured and simulated water levels in wells

3, 5, 6, and 10 in the Houston-Galveston area---- 130

85. Measured and simulated water levels in wells

13, 14, and 15 in Jackson and Wharton Counties--- 131

86. Measured and simulated water levels in wells

16 and 17 in the Evadale-Beaumont area----------- 132

87. Map showing measured and simulated altitude of the 

potentiometric surface of permeable zone B in the 

Kingsville area, 1982--------------------------------- 133

88. Graph showing measured and simulated water levels in

wells 18, 19, 20, and 21 in the Kingsville area------- 134

89. Map showing measured and simulated altitude of the

potentiometric surface of the lower Claiborne-upper

Wilcox aquifer in the Winter Garden area, 1982-------- 135

90-94. Graphs showing:

90. Measured and simulated water levels in wells

22, 23, 24, and 26 in the Winter Garden area----- 136

91. Measured and simulated water levels in wells

27, 29, 30, and 31 in the Winter Garden area----- 137

92. Measured and simulated water levels in wells

25, 28, 32, and 34 in the Winter Garden area----- 138

93. Measured and simulated water levels in wells

33, 35, and 36 in the Winter Garden area--------- 139

94. Measured and simulated water levels in wells

37, 38, and 39 in the Lufkin-Nacogdoches area---- 140

95. Map showing measured and simulated land-surface 

subsidence in the Houston-Galveston area, 

predevelopment to 1973-------------------------------- 141

96-101. Graphs showing:

96. Sensitivity of simulated 1982 heads to change

in horizontal hydraulic conductivity (Kh)-------- 142

VI1
ILLUSTRATIONS-Continued

Page

96-101. Graphs showing--Continued:

97. Sensitivity of simulated 1982 heads to change

in vertical hydraulic conductivity (Kv)---------- 143

98. Sensitivity of simulated 1982 heads to changes

in water density--------------------------------- 144

99. Sensitivity of simulated 1982 heads to changes

in aquifer storage coefficient (s)--------------- 145

100. Sensitivity of simulated water levels, 1910-82,

to changes in storage coefficient (s)------------ 146

101. Sensitivity of simulated water levels, 1910-82,

to changes in storage coefficient (s)------------ 147

TABLES

Page

Table 1. Stratigraphic and hydrogeologic units for the

coastal lowlands aquifer system---------------------------- 5a

2. Stratigraphic and hydrogeologic units for the

coastal uplands aquifer S yS tem----------------------------- 5b

3. Horizontal hydraulic conductivity and transmissivity of

aquifers and permeable zones based on calibrated model----- 6a

4. Vertical hydraulic conductivity of aquifers, permeable

zones, and confining units based on calibrated model------- 7a

5. Calibrated storage coefficient for aquifers and

permeable zones, and inelastic specific storage for

compacting clays------------------------------------------- 7b

6. Estimated density of water in the hydrogeologic units-------- 8a

7. Summary of changes in simulated heads and recharge rates 

resulting from a hypothetical increase in pumping rate, 

1983 tp 2030----------------------------------------------- 24a

8. Summary of simulated and measured predevelopment altitudes

of potentiometric surfaces--------------------------------- 34a

9. Summary of simulated and measured 1982 altitudes of

potentiometric surfaces------------------------------------ 38a

10. Summary of simulated and measured water levels in wells

shown in figure 41----------------------------------------- 393

11. Summary of calibration residual errors for 1982 heads

and those resulting from changes in model variables-------- 42a

12. Summary of calibration residual errors for land-surface 

subsidence and those resulting from changes in model 

variables-------------------------------------------------- 42b

VI11
CONVERSION FACTORS

Multiply By To obtain

inch (in.) 25.4 millimeter

inch per year (in/yr) 25.4 millimeter per year

foot (ft) 0.3048 meter

foot per day (ft/d) 0.3048 meter per day

foot per year (ft/yr) 0.3048 meter per year

mile (mi) 1.609 kilometer

square mile (mi2 ) 2.590 square kilometer

million gallons per day 0.04381 cubic meter per second

(Mgal/d)

gallon per minute (gal/min) 0.06309 liter per second

cubic foot per day (ft 3/d) 0.02832 cubic meter per day

foot squared per day 0.0929 meter squared per day

(ft2/d)

Temperature can be converted from degrees Fahrenheit (*F) to degrees 

Celsius (*C) by the equation:

"C = 5/9 ("F-32)

Sea level: In this report, "sea level" refers to the National Geodetic 

Vertical Datum of 1929--a geodetic datum derived from a general 

adjustment of the first-order level nets of the United States and 

Canada, formerly called Sea Level Datum of 1929.

IX
HYDROLOGY OF THE TEXAS GULF COAST 

AQUIFER SYSTEMS

By 

Paul D. Ryder and Ann F. Ardis

ABSTRACT

A complex, multilayered ground-water flow system exists in the Coastal Plain sediments of Texas. The 

Tertiary and Quaternary clastic deposits have an areal extent of 114,000 square miles onshore and in the Gulf of 

Mexico. Two distinct aquifer systems are recognized within the sediments, which range in thickness from a few 

feet to more than 12,000 feet The older system--the Texas coastal uplands aquifer system-consists of four 

aquifers and two confining units in the Claiborne and Wilcox Groups. It is underlain by the practically 

impermeable Midway confining unit or by the top of the geopressured zone. It is overlain by the nearly 

impermeable Vicksburg-Jackson confining unit, which separates it from the younger coastal lowlands aquifer 

system. The coastal lowlands aquifer system consists of five permeable zones and two confining units that range 

in age from Oligocene to Holocene. The hydrogeologic units of both systems are exposed in bands that parallel 

the coastline. The units dip and thicken toward the Gulf. Quality of water in the aquifer systems is highly 

variable, with dissolved solids ranging from less than 500 to 150,000 milligrams per liter.

Substantial withdrawal from the aquifer systems began in the early 1900's and increased nearly 

continuously into the 1970's. The increase in withdrawal was relatively rapid from about 1940 to 1970. Adverse 

hydrologic effects, such as saltwater encroachment in coastal areas, land-surface subsidence in the HoustonGalveston area, and long-term dewatering in the Whiter Garden area, were among some of the factors that 

caused pumping increases to slow or to cease in the 1970's and 1980's.

Ground-water withdrawals in the study area in 1980 were about 1.7 billion gallons per day. Nearly all 

of the withdrawal was from four units: Permeable zones A, B, and C of Miocene age and younger, and the 

lower Claiborae-upper Wilcox aquifer. Ground-water levels have declined hundreds of feet in the intensively 

pumped areas of Houston-Galveston, Kingsville, Winter Garden, and Lufkin-Nacogdoches. Water-level 

declines have caused inelastic compaction of clays which, in turn, has resulted in land-surface subsidence of 

more than one foot in an area of about 2,000 square miles. Maximum subsidence of nearly 10 feet occurs in the 

Pasadena area east of Houston.

A three-dimensional, variable-density digital model was developed to simulate predevelopment and 

transient flow in the aquifer systems. The modeled area is larger than the study area, and includes adjacent 

parts of Louisiana and Mexico. The transient model calibration period was from 1910 (predevelopment) to 

1982. Model-generated head distributions, water-level hydrographs, and land-surface subsidence were matched 

to measured data in selected, intensively pumped areas.

For the study area, mean horizontal hydraulic conductivity in the calibrated model ranges from 10 feet 

per day for the middle Wilcox aquifer to 25 feet per day for permeable zone A. Mean transmissivity ranges 

from about 4,600 feet squared per day for the middle Claiborne aquifer to about 10,400 feet squared per day for 

permeable zone D. Mean vertical hydraulic conductivity ranges from 1.1 x 10"5 feet per day for the VicksburgJackson confining unit, to 3.8 x 10 feet per day for permeable zone A. Mean values of calibrated storage 

coefficient range from 52 x lO^for the middle Claiborne aquifer to 1.7 x 10"3 for the middle Wilcox aquifer and 

permeable zone C. Calibrated inelastic specific storage values for clay beds in permeable zones A, B, and C in 

the Houston-Galveston area are 83 x 10 , 8.0 x 10'5, and 8.0 x 10"6 feet'1, respectively. These values are 85, 80, 

and 8 times greater than the estimated elastic specific storage value for the clays in permeable zones A, B, and 

C, respectively.
Recharge rates were mapped for predevelopment conditions as determined from a steady-state model 

calibration. A maximum rate of 3 inches per year was simulated in small areas, and the average rate for the 

study area was 034 inch per year. Total simulated recharge was 85 million cubic feet per day in the outcrop 

area. Recharge was equal to discharge in outcrop areas (79 million cubic feet per day) plus net lateral flow out 

of the study area (6 million cubic feet per day).

Rates of inflow and outflow to the ground-water system have nearly tripled from predevelopment to 

1982 (85 to 276 million cubic feet per day) based on model simulation. Withdrawal of 231 million cubic feet per 

day was supplied principally by an increase in outcrop recharge and, to a lesser extent, from a decrease in 

natural discharge and release of water from storage in aquifers and compacting clay beds. The average 

simulated 1982 recharge rate for the study area was 0.52 inch per year, with a maximum simulated rate of 6 

inches per year in Jackson and Wharton Counties.

Because withdrawal has caused problems such as saltwater intrusion, land-surface subsidence, and 

aquifer dewatering, the Texas Department of Water Resources has projected that ground-water use will decline 

substantially in most of the study area by the year 2030. Some areas remain favorable for development of 

additional ground-water supplies. Pumping from older units that are farther inland and in areas where 

potential recharge is greater will minimize adverse hydrologic effects.

INTRODUCTION

Gulf Coast Aquifer Systems Regional Study

The Gulf Coast Regional Aquifer-System Analysis (GC RASA) study was begun in 1980 as part of a 

federally funded program of the UJS. Geological Survey to provide a regional understanding and assessment of 

major aquifer systems in the United States. The GC RASA study is focused on the Gulf Coastal Plain 

sediments of Tertiary and Quaternary age. The study area consists of about 230,000 mi2 onshore and about 

60,000 mi2 offshore (about 290,000 mi total) in parts of Alabama, Arkansas, Florida, Illinois, Kentucky, 

Mississippi, Missouri, Tennessee, Texas, and all of Louisiana (fig. 1). A complete discussion and description of 

the GC RASA study is given in Grubb (1984).

Many reports and abstracts resulting from the study have been published or are in press. These reports 

generally cover all or parts of the aquifer systems in the GC RASA study. They describe one or a combination 

of various aspects of the Gulf Coast aquifer systems such as geology and stratigraphy, geochemistry, groundwater hydraulics and flow, ground-water development and use, and digital model development

Final reports, regional and subregional in scope, that describe the hydrogeologic framework, hydrology, 

or geochemistry will be in a Professional Paper 1416 series that will consist of several chapters. This report is 

Chapter E in the series.

Texas Gulf Coast Subregional Study

The Texas Gulf Coast study is a part of the GC RASA study (fig. 1). Parts of the Texas Gulf Coast 

aquifer systems have sustained intensive ground-water development that has resulted in problems associated 

with large decreases of ground-water levels, land subsidence, and saltwater encroachment. Ground-water 

withdrawals were more than 600 Mgal/d in the Houston-Galveston area in 1980. Water levels in some wells 

declined from at or above land surface in the early 1900's to about 350 ft below land surface in the 1980's. The 

decreased artesian pressure head has caused land subsidence of almost 10 ft in the Pasadena area east of 

Houston during 1906-78 (Gabrysch, 1984b, p. 21). Extensive withdrawal has caused land subsidence in other 

areas, although less severe than in the Houston area.

Potential for saltwater encroachment is particularly great in the southwestern part of the study area. 

The city of Alice in Jim Wells County and the city of Brownsville in Cameron County have supplemented 

ground-water supplies with surface water because of saltwater encroachment (Texas Department of Water
Resources, 1984a, p. III-22-1). Because of saltwater encroachment, the cities of Agua Dulce, Banquette, 

Driscoll, and Bishop in Nueces County, and Kingsville in Kleberg County plan to supplement ground-water 

supplies with water from the Nueces River (Texas Department of Water Resources, 1984a, p. IH-22-1).

Other areas within the Texas part of the GC RASA study area have potential for significant additional 

ground-water development, but the effects of large increases in development are not known. Management of 

the regional ground-water resource will require quantitative evaluation of the geologic, hydrologic, and 

chemical-quality characteristics of the system in addition to definition of the hydrogeologic boundaries that 

affect development potential.

Purpose and Scope

The objectives of the Texas Gulf Coast study are to: (1) Define the hydrogeologic framework and 

hydraulic characteristics of the aquifer systems; (2) delineate the extent of fresh to slightly saline water in the 

various hydrogeologic units; (3) describe and quantify the ground-water flow system; (4) analyze the hydrologic 

effects of man's development on the flow system; and (5) assess the potential of the aquifer systems for further 

development A preliminary, or interim report (Ryder, 1988) describes in detail the hydrogeologic framework 

and the steady-state predevelopment flow system. Thus, a brief summary of these topics will be given in this 

report, and the emphasis of this report is on the effects of development and the potential for development

Method of Investigation

The basic approach to meet the study objectives is to collect and analyze hundreds of borehole 

geophysical logs, to review previously published interpretive reports, and to use data files from the Geological 

Survey and other Federal and State agencies and commercially available files from the petroleum industry. 

From these analyses a regionally consistent hydrogeologic framework is defined. Additionally, the analyses 

provide: (1) The hydrologic boundaries of the aquifer systems; (2) a definition of selected water-quality 

properties; (3) initial estimates of aquifer and confining-unit hydraulic characteristics; (4) estimates of 

withdrawal in each of the various aquifers; and (5) where sufficient data exist, potentiometric-surface maps for 

determining any long-term decline in water levels from predevelopment to modern-day conditions. All of these 

resulting data are incorporated into a multilayered, digital ground-water flow model Calibration of the model 

provides an improved estimate of aquifer and confining-unit hydraulic characteristics, a quantitative analysis of 

flow within and between each of the various aquifers, a better understanding of the total flow system, and a 

useful tool for assessing the potential of the aquifer systems for further development

The Texas Gulf Coast study is one of five subregions of the GC RASA study for which digital models 

have been developed. The five subregional models are nested within the GC RASA regional model. The 

relation of the regional modeled area, with a grid having 102 rows, 58 columns and 10-mi grid-block spacing, to 

the five subregional modeled areas, each with 5-mi grid-block spacing, is shown in figure 2. The model grid is 

explained in more detail in the Appendix.

Description of the Area

The study area is located within the coastal plain of Texas, and extends from Mexico in the west to 

Louisiana in the east It consists of about 90,000 mi2 onshore and an additional 24,000 mi2 in the Gulf for a total 

surface area of about 114,000 mi2 (fig. 3). The northern boundary is the updip limit of the Texas Gulf Coast 

aquifer systems-the practically impermeable, predominantly marine clays of the Midway Group. The southern 

boundary extends to the edge of the continental shelf in the Gulf of Mexico.

The study area encompasses all or parts of 109 counties. The principal physiographic province is the 

Gulf Coastal Plain, and the major structural features are the Rio Grande embayment, San Marcos arch, East 

Texas embayment, Sabine uplift, and the Gulf of Mexico geosyncline (fig. 1). Land surface is characterized by a 

smooth, low-lying coastal plain that gradually rises toward the north and northwest where the more dissected
and rolling terrain reaches altitudes of as much as 600 ft in the eastern and central areas, and to as much as 900 

ft in the west. The coastal uplands end at the contact with Cretaceous clay and limestone where the land 

surface generally rises steeply. Twelve major streams drain the area, flowing generally south-southeastward 

toward the Gulf. These are, from west to east, the Rio Grande, Nueces, Frio, San Antonio, Guadalupe, 

Colorado, Brazos, Navasota, Trinity, Neches, Angelina, and Sabine Rivers (fig. 4). Many large reservoirs that 

have been constructed on these and other streams supply substantial quantities of water for irrigation and 

municipal supply.

Average annual precipitation during 1951-80 varied greatly, ranging from about 21 in. in most of the 

Rio Grande valley in the southwest, to about 56 in. at the Texas-Louisiana boundary in the east (fig. 4). 

Average annual runoff for 1951-80 ranged from about 02 in. at the Rio Grande to more than 18 in. from the 

Houston area eastward into Louisiana (Gebert and others, 1987).

Previous Investigations

Numerous reports concerning the geology and hydrogeology of all or part of the study area have been 

written by personnel of the Geological Survey and other Federal and State agencies, consulting firms, and 

others. Several reports are regional in nature, including a report by the Texas Department of Water Resources 

(1984a) that describes the hydrology of the area and presents a comprehensive plan for future water 

development; a report by Baker and Wall (1976) that includes most of the study area and emphasizes the 

desirability of conjunctive use of ground water and surface water in any plans for future development; a report 

by Can* and others (1985) that includes much of the study area and applies digital modeling techniques to 

simulate flow in Miocene and younger deposits; a report by Baker (1979) that includes an area from Mexico to 

Louisiana and emphasizes the hydrogeologic framework of Miocene and younger units; a report by Baker 

(1986) that applies digital modeling to simulate predevelopment flow in Miocene deposits in a 25,000 mi2 area 

in the eastern part, and a report by Jones and others (1976) that describes the hydrogeology of the Wilcox 

Group. Some of the many reports dealing with more local ground-water problems are referenced throughout 

this report where the published data or conclusions are helpful for describing and analyzing the regional 

ground-water flow system.

Several recent reports have been generated by the GC RASA study. Grubb (1984,1987) presented an 

overview of the GC RASA. Hosman and Weiss (1988) described in detail the hydrogeologic framework for the 

Texas coastal uplands aquifer system. Weiss (1987) described methods for estimating dissolved-solids 

concentrations in water. Pettijohn and others (1988) presented maps of dissolved-solids concentrations. Ryder 

(1988) described the hydrogeology and predevelopment flow in the Texas Gulf Coast aquifer systems.

HYDROGEOLOGY

A detailed description of the hydrogeologic framework is given in Ryder (1988). A brief summary 

follows. Some model-derived values of transmissivity and horizontal and vertical hydraulic conductivity 

presented here are significantly different from those previously reported for the predevelopment model 

calibration. These properties are described in detail, as well as storage coefficient, which was estimated for the 

transient model calibration. Estimates of dissolved-solids concentrations and density of water are more 

accurate than reported previously.

Hydrogeologic Framework

Tertiary and Quaternary deposits of clay, silt, sand, and gravel as much as 12,000 ft thick underlie the 

Gulf Coastal Plain in Texas. The clastic sediments dip toward the Gulf of Mexico and thicken in that direction. 

The thick sequence of alternating fine- and coarse-grained sediments as subdivided into hydrogeologic units 

that can be represented as layers in a digital ground-water flow model. The number of model layers 

(hydrogeologic units) chosen is based on practical considerations for the scale of the system, objectives of the 

model study, and computer-cost limitations. Weiss and Williamson (1985) discussed the rationale and 

methodology for subdividing the Coastal Plain sediments into discrete hydrogeologic units for the GC RASA 

study.

4
Pre-Miocene sediments are distributed as relatively uniform sequences of predominantly fine- or 

coarse-grained material. Borehole geophysical data can be used to identify the intervals and to designate 

aquifers and confining units.

Miocene and younger deposits differ from pre-Miocene deposits. They exhibit more 

heterogeneity-the interfingering of many thin beds of differing texture and limited areal extent Where the 

system is heterogeneous, Weiss and Williamson (1985) stated that the subdivision into layers should include an 

evaluation of depths of producing zones and the resultant vertical distribution of hydraulic head. In addition, 

borehole geophysical data are used to suggest relative permeabilities and delineate model layers that are more 

likely to have uniform hydraulic properties. Thus, Miocene and younger deposits at large pumping centers in 

Houston, Texas, and Baton Rouge, Louisiana, were subdivided into discrete units (Weiss and Williamson, 

1985). These units are called "permeable zones" and confining units. The permeable zones typically contain 

discontinuous clay beds, in contrast to the pre-Miocene aquifers that are typically massive sand beds separated 

by regionally extensive clay beds.

The hydrogeologic units of the GC RASA study comprise three major aquifer systems (fig. 1). The 

Texas coastal uplands aquifer system occurs only in Texas; the coastal lowlands aquifer system occurs in Texas 

and several nearby states; the Mississippi embayment aquifer occurs in several states outside Texas. The two 

systems in Texas are separated by the poorly permeable Vicksburg-Jackson confining unit and are underlain by 

the practically impermeable Midway confining unit (tables 1 and 2). The Texas coastal uplands (hereafter 

simply the coastal uplands) and coasted lowlands aquifer systems consist of four aquifers, five permeable zones, 

and six confining units (including the Midway and Vicksburg-Jackson confining units). The definitions of the 

hydrogeologic units and the names assigned to them may not conform to conventional definitions and names as 

found in the published literature. The hydrogeologic units in the coastal uplands aquifer system are named for 

the group designation of the sediments that comprise the units (Hosman and Weiss, 1988). Grubb (1987) 

applied the designations "zone A" through "zone E" for the five permeable zones of the coastal lowlands aquifer 

system. Correlation of stratigraphic and hydrogeologic units is shown in table 1 for the coastal lowlands aquifer 

system and in table 2 for the coastal uplands aquifer system.

A note of explanation concerning the Trio" Formation (table 1) and the Frio Clay (table 2) is due here. 

The "Frio" Formation is from Texas oilfield nomenclature. It refers to a thick section of sand that begins to 

appear about 3,000 ft below land surface. The "Frio" Formation has no correlation with the Frio Clay which is 

the updip nonmarine, time-equivalent of the subsurface Vicksburg Group (Baker, 1979, p. 36).

The hydrogeologic units are, from youngest to oldest: Permeable zone A (Holocene-upper Pleistocene 

deposits); permeable zone B (lower Pleistocene-upper Pliocene deposits); permeable zone C (lower Plioceneupper Miocene deposits); zone D confining unit (middle Miocene deposits); permeable zone D (middle 

Miocene deposits); zone E confining unit (lower Miocene deposits); permeable zone E (lower Miocene-upper 

Oligocene deposits); Vicksburg-Jackson confining unit; upper Claiborne aquifer; middle Claiborne confining 

unit; middle Claiborne aquifer; lower Claiborne confining unit; lower Claiborne-upper Wilcox aquifer; middle 

Wilcox aquifer; Midway confining unit

All but two of the units (zone D and zone E confining units exist only in the subsurface) crop out in 

bands that are essentially parallel to the coastline (fig. 5). Generally, the units dip south-southeastward toward 

the Gulf of Mexico and thicken in that direction. An exception is in the Sabine uplift in the northeast, where 

older units are again exposed at the surface and dip in all directions away from the uplift center.

The arrangement and subsurface extent of the hydrogeologic units that comprise the aquifer systems 

are shown by the hydrogeologic section in figure 6. The hydrogeologic section is useful in that it presents a 

simple, two-dimensional view of the interrelationship of aquifers, confining units, and hydrologic boundaries. 

The section was drawn through about the center of the study area and along a row of a finite-difference grid 

(fig. 2) that was used for digital modeling (to be discussed in the Appendix). It was constructed by using mean 

layer thickness values for the 25-mi2 grid blocks. The line of section is nearly parallel to the dips of the units. 

The vertical scale is greatly exaggerated (more than 25 times); an absence of vertical exaggeration would show 

the attitude of the units as being more nearly horizontal.
Table j . Stratigraphic and hydrogeologic units for the coastal 

lowlands aquifer system.

SYSTEM

QUATERNARY

| TERTIARY

00in

DC 

LU 

00

1

OLU -iz 

OLU 

10

PLEISTOCENE

PLIOCENE

lOLIGOr MIOCENE 

CENEh iviiuociNt L

TEXAS COASTAL LOWLANDS

Modified from Baker (1979D

XHYDROGESTRATIGRAPHIC UNITS \ OLOGIC

\ UNITS

Alluvium

/ Beaumont Clay

Montgomery Formation 

Bentley Formation 

Willis Sand

Goliad Sand

Fleming Formation

Oakville Sandstone

Catahoula Sam 

or Tuff ^

Jstone

Anahuac 

Formation -^

Trio" 

Formation-^

CHICOT AQUIFER

EVANGEAQUIFER E 

^0 3

BURKEVIL CONFININ 

SYSTEM

CONFINING AHOULA 

(RESTRICTED] STEM aquifer Jaspe 

&.-rut>l>« /?&7

HYDROGEOLOGIC UNITS 

IN THIS REPORT

Permeable zone A

Permeable zone B

Permeable zone C

zone o

confining unit -I/

Permeable zone D

If 

zone E confining unit

Permeable zone E

HYDROGEOLOGIC 

UNIT NUMBERS

IN THIS 

REPORT

1

2

3

4

5

6

7

Present only in the subsurface 

Catahoula Tuff west of Lavaca County

0

oo

5a
Table 2.-Stratigraphic and hydrogeologic units for the coastal uplands aquifer system

SYSTEM

TERTIARY

SERIES

OLIGOCENE

EOCENE

PALEOCENE

TEXAS COASTAL UPLANDS

STRATIGRAPHIC UNITS 

Modified from Hosman and Weiss (1988)

SOUTHERN

VicksFrio burg 

Clay Group =/

Group Jackson 

Group Claiborne 

a, 

§

Vj

o

x 

o 

u f-l

 H

3

P.

9

o

Vj

o 

Js

sT>

 H

X

Whitsett 

Formation

Manning Clay

Wellborn 

Sandstone

Caddell Formation

Yegua Formation

Laredo 

Formation

El Pico Clay

Bigford Formation 

Carrizo Sand

Undif ferentiated

Wills Point 

Formation

Kincaid 

Formation

SOUTHEASTERN AND 

NORTHEASTERN

Frio VicksClay burg 

Group =/

Whitsett 

Formation

Manning Clay

Wellborn 

Sandstone

Caddell Formation

Yegua Formaton

Cook Mountain 

Formation

Sparta Sand 

Weches Formation 

Queen City Sand 

Reklaw Formation 

Carrizo Sand

Undif ferentiated

Wills Point 

Formation

Kincaid 

Formation

STATE OF TEXAS 

MAJOR AND MINOR 

AQUIFERS (Muller 

and Price, 1979)

Sparta i/ 

(Minor aquifer)

Queen City ^/ 

(Minor aquifer)

CarrizoWilcox 

(Major 

aquifer)

HYDROGIOlOGIC UNITS 

IN THIS REPORT 

(Hosman and 

Weiss, 1988)

Vicksburg- Jackson 

confining unit

-i

1

Upper Claiborne 

aquifer

Middle Claiborne 

confining unit

Middle Claiborne 

aquifer

Lower 

Claiborne 

confining 

unit

Lower C la i borne - 

upper Wilcox aquifer

Middle Wilcox aquifer

Midway confining unit

HYDROGEOLOGIC 

UNIT NUMBERS 

IN THIS 

REPORT

8

9

10

11

12

13

14

!/ Not recognized west of Frio County 

Present only in the subsurface

5b
The base of the combined systems is defined here as either the top of the Midway confining unit or the 

top of the geopressured zone. The geopressured zone occurs above the top of the Midway confining unit in 

downdip areas, where there is a transition from a predominantly sand facies to a predominantly clay facies. 

Very high pressures occur in this zone, which is evidence that hydraulic conductivities are very small with little 

or no upward migration of water. The top of the zone of geopressure is mapped by Wallace and others (1981). 

The irregular nature of the top of the geopressured zone is evident in the section. Also evident is the irregular 

nature of the units themselves. In some areas, they may be exposed but pinch out downdip, or they may not be 

exposed but exist only in the subsurface.

Hydraulic Properties

Initial estimates of aquifer properties were obtained from the literature or from analyses of field data. 

These estimates were tested in a digital ground-water flow model, and calibration of the model leads to refined 

estimates in some areas and for most hydrogeologic units. The hydraulic properties described below were 

obtained from the calibrated model.

Horizontal Hydraulic Conductivity and Transmissivity

Hydraulic conductivity for aquifers and permeable zones in the Gulf Coast aquifer systems was 

estimated by analyzing and averaging hundreds of aquifer tests and specific-capacity tests (Prudic, 1991). 

Statistical analyses of hydraulic conductivity showed that four subareas could be distinguished within the study 

area that contain significantly distinct geometric mean values (fig. 7). The mean values for the coastal uplands 

aquifers in subarea 1 are higher than for those in subarea 2, whereas the values for the coastal lowlands 

permeable zones in subarea 4 are higher than for those in subarea 3 and are the highest in the entire study area.

The initial estimates of hydraulic conductivity were refined during calibration of steady-state and transient 

ground-water flow models. A comparison of field determinations of hydraulic conductivity with those derived 

from model calibration is shown in figure 7 for the four subareas. Simulated values range from not greatly 

different from field values to about 1.5 times greater than field values in subarea 2.

Mean, minimum, and maximum grid-block values of hydraulic conductivity for each aquifer and 

permeable zone in the study area as derived from model calibration are shown in table 3. The values are 

designated as uniform in four of the units. This designation is made because the units are relatively 

undeveloped and field-test data are lacking, and further refinement of hydraulic conductivity with resulting areal 

variation among the grid blocks was not warranted. The hydraulic conductivity values range from 1 ft/d in the 

lower Claiborne-upper Wilcox aquifer (downdip in the Winter Garden area) to 102 ft/d in permeable zone A 

(in eastern Texas). Means range from 10 ft/d in the middle Wilcox aquifer to 25 ft/d in permeable zone A.

Tests to analyze sensitivity of the model to changes in selected model variables (discussed fully in the 

Appendix) show that the model is most sensitive to a decrease in horizontal hydraulic conductivity.

The thickness of each aquifer and permeable zone was described in detail by Ryder (1988). The 

transmissivity of each aquifer and permeable zone as derived through the calibration of the digital flow model is 

shown in figures 8-16. In general, the transmissivity is smallest in the extreme updip and downdip grid blocks, 

where thicknesses generally approach zero. Transmissivity within the study area reaches a maximum of more 

than 40,000 ftVd in three units: Permeable zone A (fig. 8), permeable zone D (fig. 11), and permeable zone E 

(fig. 12). In permeable zone A, the largest transmissivity is at the Texas-Louisiana boundary where the 

hydraulic conductivity of the zone is high. The largest transmissivity in permeable zones D and E is in downdip 

areas where the units have a large thickness.

Mean, minimum, and maximum grid-block values of transmissivity for each aquifer and permeable zone in 

the study area are shown in table 3. Values range from less than 500 ft*/d in each layer to about 50,000 f^/d in 

permeable zone A. Means range from about 4,600 frVd in the middle Claiborne aquifer to about 10,400 frVd 

in permeable zone D.
Table ^.-Horizontal hydraulic conductivity and transmissivity of aquifers and permeable

zones based on model calibration

[ < , less than ]

Aquifer Horizontal hydraulic 

or conductivity 

permeable (feet per dav)

zone Mean Minimum Maximum

Permeable 25 12 102 

zone A

Permeable 23 2 25 

zone B

Permeable 15 7 31 

zone C

Permeable 16 8 21 

zone D

Permeable 15 (uniform) 

zone E

Upper Claiborne 15 (uniform) 

aquifer

Middle Claiborne 15 (uniform) 

aquifer

Lower Claiborne- 23 1 72

Transmissivity 

(feet squared per dav)

Mean Minimum Maximum

6,956 <500 50,065

10,262 <500 27,534

9,298 <500 26,813

10,383 <500 49,258

7,766 <500 47,020

5,998 <500 23,101

4,602 <500 22,915

4,659 <500 30,922

upper Wilcox

Middle Wilcox 

aquifer

10 (uniform) 10,071 <500 34,688

6a
Vertical Hydraulic Conductivity

The vertical hydraulic conductivity values in table 4 were derived through the calibration of a digital 

ground-water flow model, wherein flow across a confining unit is the product of the vertical hydraulic-head 

gradient, the area of the grid block, and the effective leakance. The vertical hydraulic conductivity of a unit 

divided by the unit's thickness is defined as leakance. Effective leakance is the harmonic mean of the leakances 

of the confining unit, the underlying aquifer, and the overlying aquifer.

The grid-block means of the vertical hydraulic conductivity of the aquifers and permeable zones in table 4 

are generally a few orders of magnitude smaller than the horizontal hydraulic conductivity of the aquifers and 

permeable zones (table 3). Means of the vertical hydraulic conductivity of confining units are smaller than 

those of the aquifers and permeable zones, and the vertical conductivity of confining units below the VicksburgJackson is smaller than for the confining units above. Vertical hydraulic conductivity ranges from 1.0 x 10"6 to 

1.0 x 10'1 ft/d. Means range from 1.1 x 10'5 ft/d for the Vicksburg-Jackson confining unit to 3.8 x 10'3 ft/d for 

permeable zone A.

Tests to analyze sensitivity of the model to changes in selected model variables (discussed in the 

Appendix) show that the model is moderately sensitive to change in vertical hydraulic conductivity.

Storage Coefficient

The storage coefficient for the confined aquifers and permeable zones was estimated by applying a 

specific storage value of 1.0 x 10"6 ft*1 times the layer thickness. This specific storage value is an approximate 

value for most confined aquifers (Lohman, 1972, p. 8).

The storage coefficient of unconfined aquifers is virtually equal to the specific yield, which means that 

nearly all of the water is released from storage by gravity drainage (Lohman, 1972, p. 8). The lower Claiborneupper Wilcox aquifer has an exceptionally high percentage of sand relative to other aquifers and permeable 

zones in the study area (Ryder, 1988, table 3; Hosman and Weiss, 1988, fig. 33). The sand has been significantly 

de-watered in parts of the outcrop because of intense withdrawal in the agricultural Winter Garden area. An 

initial specific yield of 02 was assumed for this unit in its outcrop area; this is the average value between the 

general limits of 0.1 and 03 for unconfined aquifers (Lohman, 1972, p. 54). The value was reduced during 

model calibration to a maximum of 0.15.

Some of the shallow sands in the outcrop of units other than the lower Claiborne-upper Wilcox aquifer 

undoubtedly have storage coefficient values appropriate for unconfined aquifers. However, for modeling 

purposes, it is assumed that there is no significant change in the shallow water table because (1) the sands are 

recharged sufficiently by precipitation and return flow from applied irrigation water, or (2) there is no 

significant ground-water withdrawal in the proximity of the sands. Thus, in the digital model a confined storage 

coefficient is assigned to these units.

Values of storage coefficient in table 5 are as large as 0.15, which is the estimated specific yield in the 

unconfined part of the lower Claiborne-upper Wilcox aquifer. Means range from 5.2 x 10"4 for the middle 

Claiborne aquifer to 1.7 x 10"3for the middle Wilcox aquifer and permeable zone C.

Storage in confining units is considered negligible. However, significant amounts of water may be 

released from storage in younger clay beds in permeable zones A, B, and C when sufficient declines in head 

cause the beds to compact inelastically. The release of water by inelastic compaction of fine-grained deposits in 

these permeable zones causes land-surface subsidence. A digital model code incorporated from Leake and 

Prudic (1989) provides for the release of water by inelastic compaction of fine-grained deposits by converting 

from an elastic to an inelastic specific storage. This is done for the clay portion of a permeable zone when the 

head in a grid block declines below the critical head. The critical head is defined as the head that coincides with 

the maximum effective stress to which the deposits had previously been subjected.
Table 4.-- Vertical hydraulic conductivity of aquifers, permeable zones, and 

confining units based on calibrated model

Aquifer,

permeable zone, or 

confining unit

Vertical hydraulic conductivity 

_______(feet per day)______

Mean Minimum Maximum

Permeable 

zone A

Permeable 

zone B

Permeable 

zone C

Zone D confining unit

Permeable 

zone D

Zone E confining unit

Permeable 

zone E

Vicksburg-Jackson 

confining unit

Upper Claiborne aquifer

Middle Claiborne 

confining unit

Middle Claiborne aquifer

Lower Claiborne 

confining unit

Lower Claiborneupper Wilcox aquifer

Middle Wilcox aquifer

3.8 X 10"3 2.A X 10~6 1.0 X 10'1

1.3 X 10"3 1.0 X 10~6 5.0 X 10~2

8.0 X 10"4 5.3 X 10"6 5.0 X 10~2

1.1 X 10~4 1.0 X 10~4 1.7 X 10~4

1.3 X 10"4 1.0 X 10~5 8.3 X 10~4

1.1 X 10"4 1.0 X 10~4 1.3 X 10~4

2.1 X 10"4 1.0 X 10"4 1.0 X 10~2

1.1 X 10"5 1.0 X 10~5 1.5 X 10~5

2.3 X 10"3 1.0 X 10~3 5.0 X 10~2

A.I X 10"5 A.O X 10~5 5.A X 10~5

A.6 X 10"4 1.0 X 10~5 1.0 X 10~2

2.1 X 10"5 2.0 X 10~5 3.A X 10"5

2.0 X 10"3 2.0 X 10~6 1.0 X 10~2

1.0 X 10"4 1.2 X 10~6 1.2 X 10~3

7a
Table 5.-Calibrated storage coefficient for aquifers and permeable zones, and inelastic

specific storage for compacting clays

Aquifer or 

permeable zone

Permeable zone A

Permeable zone B

Permeable zone C

Permeable zone D

Permeable zone E

Upper Claiborne aquifer

Middle Claiborne aquifer

Lower Claiborne-upper 

Wilcox aquifer

Middle Wilcox aquifer

Storage coefficient inelastic specific 

(dimensionless) storage (ft"1 )

Mean

6.0 X 10"4

1.3 X 10"3

1.7 X 10"3

1.5 X 10~3

1.2 X 10"3

7.8 X 10"4

5.2 X 10"4

5.7 X 10"4

1.7 X 10~3

Maximum

9.4 X 10~4 8.5 X 10"5

4.4 X 10"3 8.0 X 10~5

4.9 X 10~3 8.0 X 10~6

5.1 X 10"3

4.4 X 10"3

2.5 X 10"3

2.5 X 10~3

0.15^

5.2 X 10~3

Specific yield assigned in outcrop area.

7b
When the critical head decline is reached in model simulation, the initial specific storage value of 1.0 x 

"1 is increased by factors of 85,80, and 8 for the clay portions of permeable zones A, B, and C, respectively, 

in the Houston-Galveston area (table 5). These factors were determined during model calibration and resulted 

from matching land subsidence in model simulations to measured values. The details of observed and 

simulated land-surface subsidence will be discussed in the Appendix.

Dissolved-Solids Concentration and Density of Water

The concentration of dissolved solids in water is commonly used as an indication of the water's 

suitability for use. The terms used to describe water salinity in this report are as follows (Hem, 1985, p. 157):

Dissolved solids concentration (mg/L)

Fresh ................ 0 - 1,000

Slightly saline ......... 1,000 - 3,000

Moderately saline ....... .3,000 - 10,000

Very saline .......... 10,000 - 35,000

Briny ............ .More than 35,000

Freshwater requires little or no treatment for most public and industrial use. Slightly saline water is marginal 

for many uses and often requires treatment or mixing with less mineralized water. The general term "saltwater" 

is used to describe water that is not fresh.

The area! distributions of dissolved-solids concentrations in water for the aquifers and permeable zones 

are shown in figures 17-25. The maps, modified from Pettijohn and others (1988), were generated from two 

types of data; (1) chemical analyses of water where dissolved-solids concentrations are less than 10,000 mg/L, 

and, (2) borehole geophysical log interpretations where concentrations are equal to or greater than 10,000 

mg/L. Because concentrations of dissolved solids vary with depth within a given aquifer or permeable zone, a 

depth-integrated average dissolved-solids concentration was calculated for each 100-mi2 grid block (regional 

grid, see fig. 2) in order to construct the maps (Pettijohn and others, 1988).

Dissolved-solids concentrations generally increase in a downdip, Gulfward direction. For most of the 

units, particularly the coastal lowlands permeable zones, dissolved-solids concentrations are higher in the west 

than in the east Dissolved-solids concentrations range from less than 500 mg/L for nearly all of the units to 

150,000 mg/L in a downdip area of permeable zone E (fig. 21). The areal extent of fresh to slightly saline water 

(dissolved-solids concentration less that 2,000 mg/L) is particularly small in permeable zone E (fig. 21) and in 

the upper Claiborne aquifer (fig. 22). This is apparently due, at least in part, to zone E confining unit and to the 

intervening, poorly permeable Vicksburg-Jackson confining unit, with a consequent restricted and sluggish flow 

system for these units.

When the dissolved-solids concentration of water approaches about 10,000 mg/L, the greater density of 

the water will begin to affect substantially its flow characteristics within the aquifer system. The technical 

aspects of variable density ground-water flow are explained by Kuiper (1985) whose model was used to simulate 

the flow system. Density of water in the aquifers and permeable zones was calculated by using a linear relation 

between density and dissolved-solids concentration (J.S. Weiss, U.S. Geological Survey, written commun., 

1985). Density was corrected for the effects of mean water temperature and hydrostatic pressure at each grid 

block (A.K. Williamson, U.S. Geological Survey, written commun., 1987) before inclusion into the variabledensity flow model Grid-block values of density estimated for aquifers and permeable zones were assigned to 

subjacent confining units for modeling purposes. A statistical summary of water density (corrected for 

temperature and pressure) is given in table 6. Mean values range from 1.001 gram per cubic centimeter 

(g/cm3) for the lower Claiborne-upper Wilcox aquifer to 1.027 g/cm3 for zone D confining unit.
Table 6.--Estimated density of water in the hydrogeologic units

Aquifer, 

permeable zone, or 

confining unit

Permeable

zone A

Permeable

zone B

Permeable

zone C

Zone D confining unit

Permeable

zone D

Zone E confining unit

Permeable

zone E

Vicksburg- Jackson 

confining unit

Upper Claiborne aquifer

Middle Claiborne confining

Water density at atmospheric pressure, 

20 degrees Celsius 

(grams Der cubic centimeter)

Mean

1.004

1.006

1.019

1.027

1.019

1.024

1.020

1.016

1.011

1.010

Minimum

0.995

.995

.994

.997

.994

.995

.990

.990

.988

.988

Maximum

1.029

1.048

1.069

1.068

1.087

1.087

1.072

1.072

1.047

1.047

unit

Middle Claiborne aquifer

Lower Claiborne confining 

unit

Lower Claiborne-upper 

Wilcox aquifer

1.003

1.003

1.001

990

994

988

1.046

1.046

1.020

Middle Wilcox aquifer 1.005 989 1.047

8a
REGIONAL FLOW SYSTEM

The predevelopment flow system was described in detail by Ryder (1988). He presented simulated 

predevelopment potentiometric-surface maps for each aquifer and permeable zone discussed herein. Further 

model calibration has resulted in considerably less flow in the predevelopment flow system than was previously 

reported but little change in potentiometric surfaces. The newer flow values are presented, including a map of 

recharge and discharge in the outcrop areas and a summary of vertical flow components for each layer. 

Changes in the flow system from predevelopment to 1982 are described, and a quantitative analysis of the 

simulated regional flow system for 1982 is presented.

Predevelopment Steady-State Flow System

The flow system prior to development is assumed to be a steady-state system in which inflow from the 

recharge areas is equal to outflow in the discharge areas. There is no net accretion to or release of water from 

storage in the aquifer systems. The assumption of steady state seems reasonable over long-term conditions. 

Climatic changes, sea-level changes, and tectonic movements that may have been occurring over the past 

hundreds or thousands of years have been neither rapid nor significant enough to preclude the establishment of 

steady-state conditions.

Conceptual Model of System

Water in the Texas Gulf Coast aquifer systems generally originates as precipitation that falls on the 

outcrops of the various hydrogeologic units. Most of the precipitation is returned to the atmosphere by 

evaporation and by plant transpiration. Much of the remaining precipitation runs into streams that drain into 

the Gulf of Mexico, while a small amount, on the order of a few inches per year, infiltrates to the water table in 

topographically high parts of the outcrops. After reaching the water table, most of the water moves 

downgradient for relatively short distances and is discharged in topographically low areas in the outcrop, in the 

form of evapotranspiration, seepage, and stream baseflow. A smaller, but significant part of the water enters a 

deeper confined part of the aquifer where vertical head gradients cause upward or downward leakage into 

adjacent units.

A variation of the above conceptual model occurs in the southwestern part of the study area. 

Westward from a line through Corpus Christ! and San Antonio, average annual precipitation ranges from about 

30 to about 21 in.. In this area of lesser precipitation, many of the streams are intermittent, and streamflow that 

does occur is often a source of recharge to the aquifers. Although springs and seeps generally are not visible, it 

is probable that a small, net ground-water discharge occurs in topographically low areas. Ground water is 

discharged principally by evapotranspiration in this part of the study area, with transpiration by phreatophytes, 

such as pecans, salt cedars, and mesquite, having a major role.

The conceptual model of the aquifer systems consists of four aquifers, five permeable zones, and six 

confining units as shown in figure 26. The water table in the uppermost 150 ft of the outcrop areas of the units 

is assumed to be at a constant altitude, thus providing recharge to and discharge from the deeper parts of the 

flow system. The relation between the conceptual model of the system and the digital model also is shown in 

figure 26. The construction of the digital model was discussed in detail by Ryder (1988) and is summarized in 

the Appendix.

Recharge and Interaquifer Leakage

Simulated values of recharge and discharge in the outcrop areas of the hydrogeologic units under 

predevelopment conditions are shown in figure 27. The pattern of recharge and discharge is a reflection of 

topography, with recharge occurring on topographically high areas, and discharge occurring in the stream 

valleys, low-lying coastal areas, and in the Gulf. The highest values of recharge, 1 to 3 in/yr, were simulated 

over relatively small areas. Generally, values of recharge and discharge are between 0 and 1 in/yr. The average 

recharge in the study area is 034 in/yr. Because the discharge area is larger, the average discharge rate is only 

0.18 in/yr. For those wanting a more detailed discussion of the technical aspects of recharge and interaquifer 

leakage, see Ryder (1988, p. 102-103).
A summary of the upward, downward, and net vertical flow rates for the outcrop and downdip parts of 

each aquifer and permeable zone is given in figure 28. The rates are for the study area only. The net leakage is 

always upward into the overlying unit Net leakage rates range from nearly 0 out of the lowermost unit to 24 

million fr/d into the uppermost unit

Simulation indicates a total recharge in the outcrop areas of 85 million ftVd. The middle Claiborne 

aquifer receives the largest share, 16 million ftVd, closely followed by permeable zones B, A, and C with 15,13, 

and 13 million frVd, respectively. Because steady-state conditions are assumed, the total recharge rate of 85 

million frVd is offset by an equal rate consisting of discharge in the outcrop (79 million ftVd) and net lateral 

flow out of the study area (6 million ftVd). Of the discharge in the outcrop areas, permeable zone A was 

simulated as discharging the most~37 million f^/d or nearly 50 percent of the total Factors that account for 

the large rates of recharge and discharge in permeable zone A are its relatively large outcrop area, and its 

relatively large values of vertical and horizontal hydraulic conductivity.

Flow System, Predevelopment to 1982

A digital ground-water flow model was calibrated for transient conditions, predevelopment to 1982, 

and is discussed in detail in the Appendix. Some model input data and results are presented here to quantify 

changes in the flow system from predevelopment to 1982, and to provide a quantitative description of the 

regional flow system in 1982.

Ground-Water Development

The estimated average pumping rates for selected time intervals for 1910-82 are shown below (for 

modeling purposes, it is assumed that there was no significant regional development prior to 1911):

Average Dumoine rate

Pumping 

period

1

2

3

4

5

6

7

8

9

10

Time 

interval

1910

1911-37

1938-47

1948-57

1958-62

1963-67

1968-72

1973-76

1977-81

1982

(Million 

ft3/d)

0

34

62

122

156

189

221

222

231

231

(Million 

gal/d)

0

254

464

913

1,167

1,414

1,653

1,661

1,728

1,728

The pumping rates were relatively small and constant from 1911 to the late 1930's; rates nearly doubled during 

the 1940's, and doubled again during the 1950's. Increases in pumping rates were smaller after 1957, and a 

leveling-off of rates is apparent after 1968.

Cumulative volumes of withdrawal, net recharge, and release of water from storage in the Texas Gulf 

Coast aquifer systems are shown in figure 28a. These values are simulated by the model for the period 1910-82. 

By 1982, an estimated 32 trillion ft3 of water had been withdrawn from the aquifer systems. Of this, 2.4 trillion 

ft3 or 75 percent had been derived from recharge, and 0.8 trillion ft3 or 25 percent had been derived from 

storage in aquifers and compacting clay beds.

10
The withdrawal distribution for 1980 was used for the simulation periods 1977-81 and 1982. Details of 

the withdrawal estimates are in the Appendix (see section "Hydrologic Input Data*1 ). In 1980, total withdrawal 

from the aquifer systems in the study area was 231 million fr/d (1.73 billion gal/d). About 90 percent of the 

withdrawal was from 4 units: Permeable zones A, B, and C, and die lower Claiborne-upper Wilcox aquifer. 

The remaining two permeable zones and three aquifers were relatively undeveloped. The area! distribution of 

1980 withdrawal for each aquifer and permeable zone is shown in figures 29-37. The withdrawal is shown by 25- 

mi2 grid block, where withdrawal for a block equals or exceeds 0.5 Mgal/d.

Withdrawal for permeable zone A is shown in figure 29. The largest withdrawal is centered in Jackson 

and Wharton Counties. Moderate to large withdrawal extends southward to the coast and eastward into Harris 

County. In 1980, permeable zone A was the most intensively pumped unit in the study area.

Intense withdrawal from permeable zone B is centered in Harris County, with moderate withdrawal 

extending into Galveston County (fig. 30). There is moderate withdrawal in updip areas in Colorado, Lavaca, 

Jackson, and Victoria Counties. Permeable zone B was the second most intensively pumped unit in 1980.

Intense withdrawal from deep wells in permeable zone C also is centered in Harris County (fig. 31). 

Withdrawal from permeable zones D and E, and from the upper and middle Claiborne aquifers is relatively 

small (figs. 32-35).

Withdrawal from the lower Claiborne-upper Wilcox aquifer is moderate to large in the western 

counties of Zavala, Dimmit, Frio, La Salle, Atascosa, and Wilson (fig. 36). Withdrawal is relatively small and 

scattered in the central and eastern areas. This was the third most intensively pumped unit in 1980. Scattered 

and relatively small withdrawal from the middle Wilcox aquifer occurs in the central and eastern areas (fig. 37).

Recharge, Discharge, and Distribution of Flow, 1982

The concept of a shallow water table that is replenished by precipitation and kept at an essentially 

constant altitude on an average annual basis is valid for undeveloped areas, and probably for developed areas 

receiving a large amount of precipitation such as in the east In some areas, however, such as in the west where 

withdrawal is large and precipitation is relatively small, dewatering has caused the water table to decline over 

the years.

The head for the water table is held constant through time, but the flow into or out of the boundary 

layer is the product of the vertical gradient between the constant head and the head in the aquifer, and the 

conductance to flow between the two layers. This conductance is the harmonic mean conductance of the 

bottom one-half of the constant-head grid block and the top one-half of the aquifer grid block. The amount of 

flow into or out of the constant-head layer can be reduced (to zero, if desired) by reducing the conductance in 

the desired grid blocks during model calibration.

For the permeable zones of the coastal lowlands system, the extremely large amount of vertical 

anisotropy, caused by the numerous interspersed clay layers, precludes the existence of water-table conditions 

except in the shallowest sands in the upper few feet or few tens of feet in the outcrop areas. It is assumed that 

these shallow sands are recharged sufficiently by precipitation and by return flow from applied irrigation water 

so that there is no increase or decrease in the shallow water table on a long-term basis.

There are suggestions by some investigators of a long-term rise in the shallow water table in 

agricultural areas because of return flow from applied irrigation water. Evidence to substantiate this is lacking. 

Long-term observation of the water level in a shallow well in an intensively pumped area of Jackson County 

shows a long-term decline (to be discussed in detail in the next section). It is not known whether the water-level 

change in this one well is representative of a regional water-level change in the shallow sands. In the absence of 

further evidence, it is assumed that there is no long-term change in the shallow water table that would 

significantly affect the rates of recharge, discharge, and storage changes as computed in the model simulations.

11
Simulated values of recharge and discharge in the outcrop areas of the hydrologic units for the final 

year of the model simulation, 1982, are shown in figure 38. Two features are apparent in figure 38 when 

compared to predevelopment recharge (fig. 27): The decrease in size of discharge areas compared to recharge 

areas, and the appearance of high rates of recharge in the central and western parts of the study area. Thus, 

ground-water development causes a decrease in natural discharge as well as an increase in recharge.

The average 1982 recharge in the study area is 0.52 in/yr, and the average discharge rate, excluding 

withdrawal, is 0.15 in/yr. As much as 6 in/yr of recharge occurs in Wharton and Jackson Counties. In this and 

adjacent areas, there is concentrated withdrawal for irrigation (mainly rice) from updip parts of permeable 

zones A and B. In these areas, the water withdrawn is supplied by local recharge. Where ground water is 

withdrawn for irrigation in outcrop areas, a considerable amount of applied irrigation water may reenter the 

aquifer by downward percolation. Jorgensen (1975, p. 55) estimated that as much as 30 percent of ground 

water pumped for irrigation in the Katy area returned to the Chicot aquifer (permeable zones A and B; table 

1). The Katy area is an area west of Houston that includes parts of Harris, Waller, and Fort Bend Counties; 

recharge in this area is as much as 5 in/yr (fig. 38). Thus, the recharge rates in figure 38, and as discussed 

generally in this report, may also include a considerable amount of return flow from irrigation in certain areas.

Another location of relatively high recharge, up to 4 in/yr, is in and near the outcrop of the lower 

Claiborne-upper Wilcox aquifer in northern Zavala and northern Frio Counties. This is also an area of 

intensive withdrawal for irrigation, and return flow from irrigation water probably makes up a substantial part 

of the recharge as shown in figure 38. Mackey (1987) estimated that as much as 54 percent of irrigation 

withdrawal from the sand and gravel High Plains aquifer is returned to the aquifer in part of the panhandle area 

of northwest Texas. The similar nature of the aquifer materials and hydrologic conditions suggest that this 

higher value of return flow could be applicable to Zavala and Frio Counties.

Concentrated withdrawal for municipal and industrial use in the Houston-Galveston area is mainly 

from deep wells in highly confined permeable zones. Excess water is generally discharged to surface drainage 

systems, with little opportunity for return to the ground-water system. Recharge in the immediate vicinity is 

restricted by intervening clay beds. Deep cones of depression are developed until the cones intercept sufficient 

recharge, or derive additional water from storage mainly from inelastic compaction of clays to satisy withdrawal. 

Recharge tends to be less in the Houston-Galveston area compared to the rice-irrigation areas in Wharton and 

Jackson Counties, as shown in figure 38.

The difference in simulated rates of recharge and discharge in the outcrop areas between 

predevelopment and 1982 is shown in figure 39. The area of greatest increase in recharge or decrease in 

discharge is in the updip areas of permeable zones A and B extending from the Guadalupe River in the south to 

the Trinity River in the east. Although the area south of Houston has changed from a discharging to a 

recharging area, the increased recharge is small when considering that there is large withdrawal in this area. 

Gabrysch (1977) reported that the presence of the Beaumont Clay overlying the permeable zones in this area 

restricts recharge.

A more moderate increase in recharge is in the coastal uplands units in western and northern Zavala 

County, and in the northern parts of Frio, Atascosa, and Wilson Counties. Another area of substantial increase 

in recharge, but of much less areal extent, is in the coastal uplands units along the Brazos River, near the 

junction of Milam, Robertson, Burleson, and Brazos Counties. Moderate to large withdrawal for irrigation and 

municipal supplies in this area is from several aquifers. Substantial but relatively smaller increases in recharge 

in other areas are scattered and of small areal extent

A summary of outcrop recharge, outcrop discharge, vertical leakage, withdrawal, and change in storage 

in each hydrogeologic unit in the study area for 1982 is shown in figure 40. For the combined units, net 

recharge in the outcrop areas supplied 76 percent of the total discharge (withdrawal plus a small amount of 

lateral outflow), while 24 percent of the discharge was derived from depletion of storage in aquifers and 

inelastic compaction of clay beds. Highest net recharge rates were in the outcrops of the four most intensively 

pumped units: permeable zones A, B, and C, and the lower Claiborne-upper Wilcox aquifer. Nearly 47 

percent, or 84 million ftVd, of the net recharge was into the most intensively pumped unit-permeable zone A.

12
Net downdip leakage tended to be from a unit with lesser withdrawal into an overlying or underlying 

unit with greater withdrawal. The highest rate of net vertical leakage was 6 million tf/d upward into permeable 

zone C from permeable zone D.

The change in the flow system between predevelopment and 1982 is dramatic. Flow through the 

system has more than tripled. Withdrawal in 1982 was almost three times the predevelopment recharge rate, as 

seen in the following summary:

RECHARGE AND STORAGE DISCHARGE:

(million tf/d) (million tf/d)

Predevelopment conditions

Total recharge 85 Outcrop discharge 79

Lateral outflow 6

1982 Conditions

Total recharge 219 Pumpage 231

Decrease in storage 57 Outcrop discharge 40

_ Lateral outflow 5

276 276

SUBREGIONAL FLOW SYSTEMS AND HYDROLOGIC 

EFFECTS OF DEVELOPMENT

For a more detailed analysis of the flow system, the study area was divided along model rows into four 

model subareas, labeled I through IV in figure 41. The lines separating the subareas were chosen to be nearly 

parallel to flow lines in the various hydrogeologic units, or to follow approximately the axes of ground-water 

divides located between cones of depression developed on the 1982 potentiometric surfaces of intensively 

pumped hydrologic units (model layers).

Six intensively pumped areas were selected for further description and model analysis; they are the 

circled areas in figure 41 and are labeled 1 through 6. The areas were selected on the basis of large withdrawal 

that has caused significant declines in heads over a substantial area, with present or potential adverse hydrologic 

effects. The six areas nearly coincide with six "critical areas" proposed for this part of the State by the Texas 

Water Commission (written commun., 1986). The Commission defined a critical area as an area that is 

experiencing or that is expected to experience critical ground-water problems. The six circled areas in figure 41 

are referred to in this report as the:

1. Houston-Galveston area.

2. Coastal rice-irrigation area.

3. Evadale-Beaumont area.

4. Kingsville area.

5. Winter Garden area.

6. Lufkin-Nacogdoches area.

Houston-Galveston Area

The Houston-Galveston area, area 1 in figure 41, comprises all or parts of eight counties: Chambers, 

Galveston, Brazoria, Fort Bend, Waller, Harris, Montgomery, and Liberty. Ground-water withdrawal data for 

1960-85 for counties with the most intense withdrawal within area 1 are shown in figure 42. Withdrawal in

13
Waller and Fort Bend Counties in the west is predominantly for irrigation use, and withdrawal hi Brazoria 

County hi the south is about evenly divided between irrigation use and nonirrigation use. Withdrawal in Harris 

and Galveston Counties hi the east is predominantly for municipal and industrial use. Withdrawal in Harris 

County is larger than the combined withdrawal from the other counties hi area 1, with a total pumping rate of 

380 Mgal/d hi 1985. The most apparent trends in withdrawal are the declines hi pumping rates hi Harris and 

Galveston Counties since 1970 (fig. 42).

In reports that describe this area, several local areas have been defined as shown hi figure 43. These 

are: Katy, Houston, Pasadena, Baytown-Laporte, Johnson Space Center, Alta Loma, and Texas City. Average 

rates of withdrawal hi each local area for 1979 are also shown hi figure 43. In the Katy area, recent municipal 

withdrawal has been added to the agricultural withdrawals that were used primarily for rice irrigation. The 

Houston area includes the city of Houston and the surrounding metropolitan area. Ground-water withdrawals 

are primarily for municipal use. Flowing wells (with depths ranging from about 700 to 1300 ft) were common 

hi the area hi the 1890's; heads were 15 to 30 ft above land surface. Historically, withdrawals hi the Houston 

area have steadily increased. In 1930, average private and public withdrawal hi the Houston area was 52 

Mgal/d. By 1932, water levels had lowered to 80 ft below land surface in downtown Houston (White and 

others, p. 10-11,1932). Vertical gradients are now downward from the water table hi most of the Houston area, 

which means there is a potential for deeper units to receive recharge from the water table. This is consistent 

with model simulation results.

The Pasadena area is east of Houston and includes a heavily industrialized zone along the Houston 

Ship Channel In 1937, a Pasadena paper mill added 19 Mgal/d of ground-water withdrawals to the area which 

accelerated water-level declines (White, 1938). This area has experienced large ground-water withdrawals since 

1937, with peak usage in 1968. Surface water has also been used throughout the history of development, but in 

1977 surface water became the primary source of water for the area. The adjoining areas of Baytown-Laporte 

and the Johnson Space Center also experienced drastic reductions in industrial ground-water withdrawal when 

surface-water use was increased hi the mid-1970's.

In the Alta Loma area, ground-water withdrawals are used for public supply for the town of Alta Loma 

and the city of Galveston. At the "old" Alta Loma well field in Galveston County, heads in wells ranging from 

726 to 868 ft deep were 28 feet above land surface hi 1893; by 1939 water levels were 45 to 50 feet below land 

surface (Petitt and Winslow, 1955, p24). Ground-water withdrawals gradually increased hi the County, mostly 

as a result of industrial expansion in the Texas City area. Since the early 1970's, ground-water use in the Alta 

Loma and Texas City areas has decreased substantially because of increased reliance on surface water.

Withdrawal in the Houston-Galveston area is from permeable zones A, B, and C. The 1980 withdrawal 

distribution by layer and by model grid block is shown in figures 29-31. Withdrawal has created large cones of 

depression hi the potentiometric surfaces of the three layers, with the centers located hi the general area of the 

city of Houston. Head declines for permeable zones A, B, and C are shown in figures 44, 45, and 46, 

respectively. The maps were constructed by subtracting 1982 measured heads (mean heads hi 25-mi2 grid 

blocks) from measured predevelopment heads for each permeable zone. Maximum head declines range from 

nearly 200 ft for permeable zone A to more than 400 ft for permeable zone C.

Hydrographs of wells 9,7, and 3 hi figure 47 were selected for analysis because of their long-term 

record and close proximity of the wells to the centers of the cones of depression developed in permeable zones 

A, B, and C, respectively. The hydrograph for well 9, located in southeastern Harris County hi the BaytownLaporte area (fig. 43), shows a continuous water-level decline until about 1976, when a substantial recovery of 

water levels began and continued into the 1980's. The hydrographs for wells 7 and 3 located hi the Houston 

area (fig. 43) show a more or less continuous decline hi water levels from the early 1940's to the middle 1980's.

Well 9 is hi an area of southeastern Harris County that has experienced severe land-surface subsidence. 

The large ground-water withdrawals have reduced the artesian pressure sufficiently to cause water from 

included and adjacent clay beds to flow into the sands. Water flows out of the compressible clays due to 

inelastic compaction which is largely irreversible. The loss of water from the clays results in a permanent loss of 

pore space. Land subsidence is approximately equivalent in volume to the reduction of pore space in the

14
compacted clays. As shown on figure 48, an area of about 2,000 mi2 around the cities of Galveston and Houston 

has undergone subsidence of more than 1 foot. From the beginning of man's development up to 1973, 

maximum land subsidence of nearly 9 ft has been recorded (fig. 48). Gabrysch (19845) noted that from 1906-78 

the Pasadena area east of Houston may have experienced as much as 10 ft of land subsidence.

Subsidence hi low-lying areas of Harris and Galveston Counties, combined with proximity to the Gulf 

of Mexico, has increased the risk of flood damage to residential and commercial properties. Subsidence has 

also caused activation of faults, and this has led to structural damage (Harris-Galveston Coastal Subsidence 

District, written commun., 1983). With the creation of the Houston-Galveston Coastal Subsidence District in 

1975, there has been a growing emphasis on reduction of ground-water withdrawal coupled with an increased 

reliance on surface-water supplies. Pumping rates hi the late 1970's and early and middle 1980's were 

substantially reduced in much of southeastern Harris County and hi Galveston County; this has caused a 

recovery of water levels and a cessation or sharp decrease hi the rate of land-surface subsidence in that area.

In addition to the head declines hi permeable zones A, B, and C, figures 44-46 show horizontal flow for 

these zones as simulated by the model for 1982. The ground-water flow directions and relative magnitudes are 

computed at the intersection of four adjacent grid blocks. A flow vector, as represented by an arrow on figures 

44-46, is the vector addition of the average of the two adjacent X-direction flows and the average of the two 

adjacent Y-direction flows. The size of the arrowhead indicates the order of magnitude (integer component of 

the logarithm, base 10 (Iog10)) of the flow, and the length of the arrow is proportional to the mantissa of the 

log1Q flow (Williamson and others, 1990, p. 76). The flow patterns are similar for the three zones, with the flow 

generally converging on areas that have the greatest amount of drawdown. The large withdrawals of ground 

water hi the Houston-Galveston area have reversed the coastward hydraulic gradients causing saltwater to move 

toward the centers of pumping.

An interesting circulating pattern of ground-water flow is shown hi offshore areas of permeable zone C 

(fig. 46). The circulation cells occur because of density forces resulting from heat and solute gradients as the 

denser, heavier water overturns to get under the fresher, lighter water (Williamson and others, 1990, p. 76).

The simulated average interstitial velocity of saltwater moving toward the pumping centers in 1982, 

assuming an effective porosity of 0.2 for the sands, is 22 ft/yr for permeable zone A, 41 ft/yr for permeable 

zone B, and 111 ft/yr for permeable zone C. These are average simulated velocities for water moving through 

the sands hi each permeable zone (zones A, B, and C); water in individual sand beds may actually have greater 

or smaller velocity, depending upon permeability.

Lateral migration of saltwater was evident hi 1954, when observation wells near the freshwatersaltwater interface hi Harris County had an increase hi chloride concentration of 122 mg/L since 1951 (Winslow 

and others, 1957). Saltwater contamination was also occurring in the shallower Chicot wells near the Houston 

Ship Channel (Baker and Wall, 1976). Changes in chloride concentrations with depth have been analyzed along 

the Ship Channel. The interpretations of the chemical data, along with head differences, indicate that saltwater 

is moving both vertically and laterally toward the Chicot aquifer (Jorgensen, 1977). The city of Galveston had 

to replace the Alta Loma well field northward because the "old" well field was contaminated by movement of 

saltwater from below and from downdip (Petit and Winslow, 1955).

A summary of 1982 withdrawal, change hi storage, and vertical flow rates (recharge and leakage) for 

each unit hi model subarea II is shown hi figure 49. The area encompasses the major cones of depression 

developed in permeable zones A, B, and C in the Houston-Galveston area. About 90 percent of the total 

withdrawal hi subarea II is from permeable zones A, B, and C. Small amounts of net lateral flow between 

model subareas are quantified by the NL" term hi the diagram (fig. 49). On the basis of simulation, net recharge 

hi the outcrop areas accounted for 68 percent of the total pumping rate of 102 million fr^/d (763 Mgal/d) for all 

units hi subarea II. Net recharge includes a decrease of natural discharge and an increase in induced recharge. 

Part of the induced recharge may include a return flow from applied irrigation water, as discussed earlier. 

Twenty-eight percent of the pumping rate was derived from depletion of ground water hi storage, and the 

remaining 4 percent was net lateral inflow from adjacent model subareas (I and HI). Nearly 61 percent of the 

net recharge was hi the outcrop of permeable zone A. The highest rate of net vertical leakage was 9 million 

downward into permeable zone B from permeable zone A.

15
In the Houston-Galveston area, model results indicate that about 21.9 million frVd or 76 percent of the 

29 million frVd of water released from storage from all model layers (fig. 49) during the 1982 simulation period 

was from inelastic compaction of clays in permeable zones A, B, and C. The following table summarizes the 

simulated rates of water released from storage from these permeable zones for 1982:

Total rate of

Hydrogeologic 

unit

Permeable

zone A

Permeable

zone B

Permeable

zone C

Pumping

rate 

in 1982 

(million 

ft 3 /d)

35

35

22

release

from

Amount 

(million 

ft 3 /d)

0.9

12.3

10.8

of water

storage

Percent 

of 

pumpage

2.6

35

49

Rate of release

of water resulting

from inelastic

compaction of clavs

Amount 

(million 

ft 3 /d)

0.8

11.9

9.2

Percent 

of 

pumpage

2.3

34

42

For the combined zones A, B, and C, about 26 percent of the pumping rate of 92 million frVd is supplied from 

storage releases; about 24 percent of the pumping rate is supplied from the component of storage that results 

from inelastic compaction of clays.

Coastal Rice-Irrigation Area

The coastal rice-irrigation area is shown as area 2 in figure 41. It consists of most of Jackson and 

Wharton Counties and parts of Colorado, Lavaca, Victoria, and Matagorda Counties. Withdrawal is mainly for 

irrigation, as shown in figure 42 for Wharton, Jackson, and Matagorda Counties. Rice is the major crop in the 

area, and the two-crop rice season requires large amounts of water for irrigation.

Withdrawal in area 2 is mostly from permeable zone A. A substantial amount of water is withdrawn 

from permeable zone B, mainly in the outcrop area, but other hydrologic units are essentially undeveloped. 

The 1980 withdrawal distribution by grid blocks is shown in figures 29 and 30 for permeable zone A and 

permeable zone B, respectively. As mentioned previously, model results indicate that the water withdrawn in 

this area is supplied by local recharge. Water derived from artesian storage in the units has been relatively 

small, and steep cones of depression, such as those in the Houston area, have not developed.

Ground-water withdrawal began in the early 1900's. Originally, artesian pressures were large enough 

to produce flowing wells from the Chicot and Evangeline aquifers (table 1). As pumping increased, most wells 

ceased to flow by the mid-1940's (Loskot and others, 1982, p. 33). In the early 1950's, there was a sharp 

increase in withdrawal because of a period of below-normal precipitation combined with the introduction of the 

two-crop rice season. The largest water-level declines from 1944 to 1964 were in the western section of 

Wharton County and in the southeastern section of Jackson County. In western Matagorda County from 1944 

to 1967, withdrawal for irrigation resulted in water-level declines of as much as 52 ft (Hammond, 1969, p. 32).

Hydrographs of wells 14a and 15 in Jackson County are shown in figure 50, as is a graph of mean 

annual precipitation in southwestern Wharton County. Well 14a is located in northwestern Jackson County 

near intense withdrawal in permeable zone A. However, the well is only 76 ft deep, and is open to the

16
Holocene alluvium above the intensively pumped zone. The water table in well 14a has declined at a rate of 

about 0.6 ft/yr since the late 1930's, with periods of partial recovery in 1958-61 and 1969-74 when precipitation 

was at or above normal (fig. 50). Baker and Follett (1973, p.18) used this well and other data to conclude that 

shallow sands in the area have been dewatered on a long-term basis (nearly 40 years), and that recharge from 

rainfall has been unable to stabilize the water table. They further concluded that the reduction in the gradient 

of the water table toward the Lavaca River has probably reduced stream baseflow. However, it is not known 

whether the water-level change in this one well is representative of a regional water-level change in the shallow 

sands. In the absence of further evidence, it is assumed that there is no long-term change in the shallow water 

table that would significantly affect the rates of recharge, discharge, and storage changes as computed in the 

model simulations. Well 15 is open to permeable zone A and is in the vicinity of moderate to large withdrawal 

from that zone. The water level in well 15 has been declining at an average rate of about 1.4 ft/yr since the 

middle 1950's (the beginning of record).

The large withdrawal in the coastal rice-irrigation area has resulted in compaction of clays present 

within the permeable zones. From 1900 to 1975, the land surface subsided less than a foot over most of the 

area, but Carr and others (1985, fig. 37) show as much as 15 ft of subsidence in eastern Jackson and western 

Matagorda Counties. Because the subsidence is fairly evenly distributed over large, mostly rural areas, the 

undesirable effects sometimes associated with subsidence are minimized.

Saltwater encroachment is a potential threat in this area, either by lateral migration updip or by vertical 

migration where freshwater sands are overlain by saltwater-bearing deposits. Saltwater encroachment is not 

currently a serious threat to the quality of ground water used in the coastal rice-irrigation area.

Simulated horizontal flow vectors for permeable zone A show a general zone of convergence near the 

intersection of Jackson, Wharton, and Matagorda Counties (fig. 44) resulting from intense withdrawal. A 

summary of 1982 flow components for units within model subarea III is shown in figure 51. The simulated net 

recharge in the outcrop areas was 98 percent of the total pumping rate of 58 million ffyd for all units. Nearly 

67 percent of the net recharge was in the outcrop of permeable zone A. About 4 million ftVd of water was 

released from storage in the simulations. A net lateral flow out of the model subarea amounted to about 3 

million ftVd. The highest rate of net vertical leakage was 5 million f^/d upward into permeable zone A from 

permeable zone B.

Evadale-Beaumont Area

The Evadale-Beaumont area is area 3 in figure 42. Included in this area are large ground-water 

withdrawals at the city of Evadale in southwest Jasper County, and moderate withdrawals at the city of 

Beaumont's well field in southeast Hardin County (fig. 52). Withdrawal in Jasper County has been fairly 

constant since 1970, but withdrawal in Hardin County, mainly for nonirrigation use, has risen since 1975.

Withdrawal at Evadale is about evenly divided between permeable zone B and permeable zone C. 

Withdrawal in the Beaumont well field is from permeable zone B. The 1980 withdrawal distribution by grid 

blocks is shown in figures 30 and 31 for permeable zone B and permeable zone C, respectively. Prior to 1955, 

ground-water resources in the Evadale area were relatively undeveloped. Predevelopment water levels in the 

lowest sands of permeable zone C that contained freshwater (locally called the Evangeline aquifer; table 1), 

were 20 to 30 ft above land surface (Wesselman, 1967). In 1955, a paper mill began withdrawals of nearly 18 

Mgal/d. Production increased to about 42 MgaJ/d by 1970 and remained at approximately that rate through 

1980. In Jefferson County, fresh ground-water supplies are limited. Prior to 1958, the city of Beaumont relied 

entirely on surface water. By 1965, Beaumont was pumping 6 Mgal/d from the well field in Hardin County. It 

was the approximate rate through 1980.

Sufficient data were available to map the head declines for permeable zone C at Evadale (fig. 46). The 

map was constructed by subtracting 1982 measured heads from measured predevelopment heads. The map 

shows between 150 and 200 ft of drawdown centered at Evadale, with the cone extending to surrounding 

counties.

17
Hydrographs of well 16 in Jasper County and well 17 in Hardin County are shown in figure 53. Well 16 

is located near the center of the drawdown cone at Evadale and is open to permeable zone C. Between 1955 

and 1967, the water level in well 16 declined about 190 ft. From 1968 to 1985, the water level declined only 

about 20 ft

Well 17 is located near the city of Beaumont's well field and is open to permeable zone B. From about 

1960 to 1968, the water level in well 17 declined 50 ft (about 55 ft/yr). During the next 6 years, the water level 

declined about 15 ft, and from 1974-82 was essentially stable (fig. 53).

In 1954, a network of bench marks was installed in and around the paper mill at Evadale to measure 

land-surface subsidence. The maximum differential subsidence from 1955 to 1963 was 0228 ft (Wesselman, 

1967, p. 58). This was at a point where the water-level difference, between the original reference point and the 

point of maximum subsidence, was about 25 ft. Recent measurements of subsidence are not available. 

However, if the ratio 0.228/25 is valid, the estimated maximum land-surface subsidence is nearly 2 ft at the 

center of the cone where the maximum drawdown is 210 ft

Simulated horizontal flow vectors in figure 45 show an area of convergence in permeable zone B at the 

Beaumont well field, and another zone of convergence at Evadale. A similar flow pattern at Evadale is seen for 

permeable zone C (fig. 46). A summary of 1982 flow components for model subarea I is shown in figure 54. 

Model simulations show a net recharge in the outcrop areas that was 84 percent of the total discharge rate 

(pumping plus a small lateral outflow) for all units in subarea I. Sixteen percent of the discharge was derived 

from ground-water storage. The withdrawal was fairly evenly distributed among permeable zones A and B, the 

lower Claiborae-upper Wilcox aquifer, and the middle Wilcox aquifer (fig. 54).

Kingsville Area

The Kingsville area is designated as area 4 in figure 41. It consists of parts of Kleberg, Nueces, and Jim 

Wells Counties. Ground-water withdrawals are largest in Kleberg County (fig. 55), and withdrawal is 

concentrated in the city of Kingsville's well field located near the Kleberg-Nueces County line. Withdrawal in 

area 4 is mainly from permeable zone B (see fig. 30 for the 1980 grid-block distribution). Flowing wells existed 

in the area in the early 1900's, one of which was at the railroad station in Kingsville. This well, open at a depth 

of about 600 to 700 ft, was reported to have had an artesian head of 20 ft above land surface (Livingston and 

Bridges, 1936). From 1901 to 1935, ground-water withdrawal in the Kingsville area was about 2 Mgal/d, which 

included supplies to small municipalities and small-scale irrigation (Groschen, 1985, p. 15). Since then, a steady 

increase of municipal and industrial withdrawal has lowered water levels. The aggregate withdrawal for 

Kleberg, Nueces, and Jim Wells Counties has been relatively constant since 1970 at about 16 Mgal/d (fig. 55). 

Concentrated withdrawal in and near the city of Kingsville, about 65 Mgal/d in 1980, has created a steep cone 

of depression in the potentiometric surface of permeable zone B, with the center of the cone near Kingsville.

A map of the head decline in permeable zone B is shown in figure 56. It represents the difference 

between measured predevelopment heads and measured 1982 heads. The 1982 head measurements are taken 

from Groschen (1985, fig. 9), who related the heads to the confined portion of the Evangeline aquifer (table 1). 

The heads also are applicable to the pumped interval of permeable zone B in this area, the upper part of the 

Goliad Sand (table 1). Drawdowns exceed 200 ft at the Kingsville well field, and the cone of depression extends 

to surrounding counties (fig. 56).

A hydrograph of well 19 in Kleberg County is shown in figure 57. Well 19 is open to permeable zone B 

and is located a short distance west of the center of the drawdown cone. From 1933 to 1972, the water level in 

well 19 declined 155 ft or at an average rate of about 4 ft/yr. From 1972-85, the water level was essentially 

stable.

The large water-level declines and proximity to saltwater in overlying and underlying deposits and 

downdip have created the potential for movement of saltwater into the freshwater. In the Kingsville area, 

Groschen (1985, p. 17) considered the upper limit of dissolved-solids concentration of freshwater to be 2,000

18
mg/L. The major source of potential contamination is saltwater in the overlying deposits, as opposed to 

saltwater encroachment from the Gulf of Mexico (Groschen, 1985, p. 59). Originally, the hydrostatic pressure 

in the producing zone B was higher than in the overlying deposits which contain saltwater. As well discharges 

increased and exceeded recharge, the hydraulic gradient was reversed, creating the potential for saltwater to 

flow into the pumped zone. The natural quality of water in the producing zone is marginal for drinking, and any 

deterioration due to saltwater encroachment is of serious concern (Groschen, 1985, p. 5).

Some municipalities reportedly have experienced water-quality problems and have taken, or plan to 

take, corrective measures. The city of Alice in Jim Wells County has supplemented its ground-water supplies 

with surface water because of saltwater encroachment Also because of saltwater encroachment, the cities of 

Agua Dulce, Banquette, Driscoll, and Bishop in Nueces County, and Kingsville in Kleberg County plan to 

supplement ground-water supplies with water from the Nueces River (Texas Department of Water Resources, 

1984a, p. III-22-1). Groschen (1985, p. 58) concluded that the pumping from zone B in the Kingsville area has 

most likely not created water-quality degradation on a regional scale.

Although there have been large water-level declines in deposits that are similar in age to those in the 

Houston area, subsidence in the Kingsville area for 1917 through 1976 has been estimated at less than 03 ft 

(Muller and Price, 1979, p. 42).

Simulated horizontal flow vectors in figure 56 are shown converging on the center of the drawdown 

cone near Kingsville. The large flows to the southwest in Jim Hogg, Brooks, Starr, and Hildago Counties are 

not the result of ground-water withdrawal. Land-surface gradients, and thus the estimated water-table 

gradients, are steeper here than elsewhere in the study area, and ground water is flowing naturally in greater 

volume downdip toward the Gulf.

A summary of 1982 flow components for model subarea IV is shown in figure 58. Most of the 

withdrawal in model subarea IV is from the lower Claiborne-upper Wilcox aquifer in the Winter Garden area.

Winter Garden Area

The Winter Garden area is intensively pumped area 5 in figure 41. It is defined as all or major parts of 

Zavala, Dimmit, Frio, La Salle, and Atascosa Counties, and minor parts of Bexar, Wilson, and McMullen 

Counties. The combination of infrequent killing frosts and fertile soils make the Winter Garden area ideal for 

garden vegetables and other food crops. Relatively little precipitation (about 21 to 29 in/yr from west to east) 

and a general lack of surface-water resources necessitate the withdrawal of large amounts of ground water for 

irrigation. Withdrawal is almost entirely from the lower Claiborne-upper Wilcox aquifer.

During the early development of irrigation, flowing wells were common in the Winter Garden area. 

The artesian head southeast of Carrizo Springs was estimated to be 18 to 40 ft above land surface (Turner and 

others, 1948). A few springs flowed into Carrizo Creek in Dimmit County, but by 1929, with continued 

withdrawal, springs on the creek no longer flowed. In Atascosa County, the first flowing well was drilled in 1904 

in the city of Poteet In 1929-30, intensive withdrawal for irrigation was predominantly within 5 mi of Poteet A 

drastic increase in withdrawal in the Winter Garden area beginning about 1950 was caused by widespread 

drought Increases in population, industry, and irrigated acreage have caused higher rates of ground-water 

withdrawal.

Largest withdrawals for most years are in Zavala, Frio, Atascosa, Dimmit, and La Salle Counties, in 

that order (fig. 55). Withdrawals for the three most intensively pumped counties in 1980~Zavala, Frio, and 

Atascosa-were spread fairly evenly (see figures 55 and 36). The intense withdrawal, which has exceeded 

recharge in this relatively dry area, has been mostly from the deep, confined parts of the lower Claiborne-upper 

Wilcox aquifer, and has caused a very large cone of depression. The drawdown map shown in figure 59 

represents the difference between measured predevelopment heads and measured 1982 heads in the lower 

Claiborne-upper Wilcox aquifer. The largest drawdowns, in excess of 250 ft, are in south-central Zavala County 

and at the boundary of southeastern Zavala and northeastern Dimmit Counties. Drawdowns exceed 100 ft in at 

least six counties (fig. 59).

19
Simulated horizontal flow vectors in figure 59 are shown converging in the vicinity of Zavala, Dimmit, 

Frio, and LaSalle Counties. Water is flowing toward the pumping center from a very large area, with the largest 

flows coming from the outcrop area.

Hydrographs of wells 23 and 24 and precipitation data in Zavala County are shown in figure 60. Well 

23 is more than 1,000 ft deep in the confined part of the aquifer; it is located near the center of the cone of 

depression in south-central Zavala County. From 1947-56, the water level in well 23 declined 270 ft or about 27 

ft/yr. The rapid decline resulted in large part from widespread drought conditions in the early and middle 

1950% when pumping demands were great and recharge rates minimal. Water levels recovered significantly in 

the late 1950's when precipitation returned to normal or above normal, but the trend continued downward in 

the 1960's until a decline of 355 ft below the 1947 level occurred in 1967 (fig. 60). A significant recovery 

occurred again beginning about 1968, and water levels appear to be relatively stable in the 1970's and 1980's.

Well 24 (fig. 60) is located in the outcrop of the lower Claiborne-upper Wilcox aquifer in the northeast 

corner of Zavala County. The well is relatively shallow (260 ft deep) and is in the proximity of moderate to 

large withdrawal in the downdip, confined parts of the aquifer. The water table in well 24 declined about 70 ft 

from 1953-67, or more than 4 ft/yr. From 1968-85, the water table declined about 25 ft, or about 1.5 ft/yr. 

Total decline for 1953-85 is about 95 ft, which means that a minimum of 95 ft of the aquifer has been dewatered 

in this area where the aquifer is unconfined.

Water-level declines in the Winter Garden area have produced undesirable effects, one of which is 

greater pumping lifts. In some cases, pump intakes have been lowered, wells deepened, or larger pumps 

installed. All of these factors result in increased pumping costs. In addition, saltwater is reported to be leaking 

downward from overlying deposits through old well bores and contaminating the aquifer. Muller and Price 

(1979, p. 18) noted that this problem is especially evident in Dimmit County, where saltwater from the overlying 

Bigford Formation is leaking downward through old well bores. The hydraulic gradient between the lower 

Caliborne confining unit and the lower Claiborne-upper Wilcox aquifer has been reversed as a result of the 

intense withdrawal. The old wells may have been poorly constructed initially or have been improperly plugged, 

and saltwater moves downward to mk with freshwater in the aquifer. Klemt and others (1976, p. 23) caution 

that continued increase in development of the aquifer could result in widespread contamination as a result of 

interformational leakage.

In model subarea IV (fig. 58), about 33 million frVd were pumped from the lower Claiborne-upper 

Wilcox aquifer during 1982 (nearly all in the Winter Garden area). Model results suggest that about 48.5 

percent of the withdrawal was derived from aquifer storage (including dewatering of the aquifer), and about 

39.4 percent was from net recharge in the outcrop area. The remaining 12 percent was from net upward 

leakage from the middle Wilcox aquifer (6 percent) and net downward leakage from the middle Claiborne 

aquifer (6 percent).

Lufkin-Nacogdoches Area

The Lufkin-Nacogdoches area, area 6 in figure 41, consists of most of Nacogdoches and Angelina 

Counties. There is concentrated withdrawal from industrial well fields located between the cities of Lufkin and 

Nacogdoches and straddling the Nacogdoches-Angelina County line (fig. 52). The two cities also maintain well 

fields for municipal supplies, and the combined withdrawal has created a steep cone of depression on the 

potentiometric surface of the lower Claiborne-upper Wilcox aquifer. Drawdowns of water levels near the 

pumping centers ranged to nearly 500 ft from the late 1930's to the late 1960's (William F. Guyton and 

Associates, 1970, p. 23). The major withdrawal is in Angelina County, and withdrawal from both counties has 

remained nearly constant during the 1970's and 1980's (fig. 52).

In 1907, hydraulic head in wells open to the Carrizo Sand (upper part of the lower Claiborne-upper 

Wilcox aquifer; table 2) in the city of Nacogdoches was as much as 40 ft above land surface (Deussen, 1914). 

The city of Nacogdoches began pumping from the Carrizo Sand in the early 1900's. After 30 yrs of pumping, 

water levels had declined about 39 ft A large paper mill and the city of Lufkin began pumping from the

20
Carrizo Sand in the late 1930's. Since then, water levels in the Carrizo have declined as much as 500 ft near the 

center of pumping. The water-level declines become less severe as distance increases northward away from the 

paper mill and towards the outcrop of the Carrizo Sand.

According to William F. Guyton and Associates (1970), the cone of depression is causing some 

brackish water to move toward the Lufkin and paper mill well fields. The movement is slow, and periodic 

observations may allow sufficient time to relocate wells when necessary.

Head data are insufficient to construct an accurate map of the potentiometric surface for development 

conditions, but a few observation wells with long-term record exist near the pumping centers. One such well is 

well 37 located in Nacogdoches County a short distance east of the major pumping center at the large paper 

mill A hydrograph of well 37 is shown in figure 61. The well is 900 ft deep and opens to the lower Claiborneupper Wilcox aquifer. The water level in well 37 has declined almost continuously since the beginning of record 

in 1947, with a total decline of 300 ft. The rate of decline mainly reflects pumping rates; it was rapid in the 

earlier years and becomes more gradual until the 1980's, when there appears to be no further decline (fig. 61).

The pumping rate from the lower Claiborne-upper Wilcox aquifer in model subarea I was estimated at 

8 million ftVd for 1982 (fig. 54). More than one-half of this withdrawal is in the Lufldn-Nacogdoches area. Of 

the 8 million ftVd of withdrawal, model results indicate that 25 percent is derived from decrease in aquifer 

storage, and the remainder is derived equally from recharge in outcrop areas and net downward leakage from 

the middle Claiborne aquifer.

Other Areas

Intense ground-water development has occurred in some areas without causing large, extensive cones 

of depression and without the threat of adverse effects, such as significant land-surface subsidence or aquifer 

dewatering. Two such areas are the Bryan-College Station area and most of Orange County.

Bryan-College Station Area

The Bryan-College Station area is located along the Brazos River, and includes parts of Brazos, 

Burleson, and Robertson Counties. Considerable amounts of ground water are pumped in this area for 

irrigation and municipal supplies (fig. 42). The water is being withdrawn from several aquifers, which has 

minimized drawdowns in any single unit The Yegua Formation (upper Claliborne aquifer; table 2) crops out in 

a belt that runs through the Bryan-College Station area, and the Sparta Sand (table 2) crops out just north of 

the Brazos County line. Texas Agricultural and Mechanical University (Texas A&M) at College Station has 

pumped water from the Yegua Formation since the institution's establishment in 1886. By the 1970's, Texas 

A&M, College Station, and Bryan were all using water from wells in the Sparta Sand and Wilcox Group (table 

2). In 1970, the city of Bryan was the largest user of ground water for public supply in Brazos and Burleson 

Counties (Follett, 1974).

In 1948, irrigation with water from the Brazos River alluvium began in Robertson County (Hughes and 

Magee, 1962, p.l). Little water was pumped from the alluvium prior to this date. But the drought of the early 

1950's led to the search for additional quantities of water for irrigation on the flood plain (Cronin and Wilson, 

1967 p. 1). From 1950-64, the number of irrigation wells pumping from the alluvium increased at a rapid rate. 

Withdrawal for irrigation decreased from 1964 to 1969, as Brazos County increased its surface-water use 

(Follett, 1974, p. 26). Approximately 98 percent of the ground water used for irrigation is pumped from the 

flood-plain alluvium, but no ground water is pumped from the alluvium for municipal uses.

By 1961, the water levels in the flood-plain alluvium had probably recovered from the intense pumping 

during 1950 to 1957 (Follett, 1974). Then, from 1961 to 1971, the water levels again declined in the flood-plain 

alluvium northwest of Bryan. According to Cronin and Wilson (1967, p. 32), the decline may have been the 

result of withdrawals from the underlying Sparta Sand (table 2), which is in direct hydraulic connection with the 

alluvium. Withdrawal from the Sparta Sand reduced the artesian pressure, which may have caused water from 

the alluvium to move downward in response to the change in head.

21
Orange County

The development of ground water in Orange County, located in southeast Texas, began relatively 

slowly. From 1910 to 1940, ground water was pumped for public supply, saw mills, railroads, and oil and gas 

production. By 1941, total ground-water withdrawal was only 2.6 Mgal/d (Wesselman, 1965, p.27). The 

principal source of water in this area is from the lower part of the Chicot aquifer (permeable zone B). In the 

early 1900's, prior to large-scale withdrawal, the deep wells had large artesian flows. In the city of Orange, the 

heads in the lower part of the Chicot aquifer were estimated to be about 25 to 30 feet above sea level 

(Wesselman, 1965, p. 28). The artesian pressure decreased as more wells were drilled and withdrawals 

increased. The demand for water increased during World War II, and by 1950 the declining heads caused all 

the deep wells to stop flowing (Wesselman, 1965, p28). Because of increased withdrawal and below-normal 

rainfall, the potentiometric surface in 1962 was below sea level throughout most of the County. The largest 

declines have been in the southeastern part of the County, an area of moderate to large industrial withdrawal. 

Water levels rose throughout most of the County between 1980 and 1985 because of a decrease in withdrawals. 

Ground-water levels in the the city of Orange recovered as much as 14 ft (Bonnett and Williams, 1987, p. 24).

In the coastal area of Orange County, there is the potential for vertical (upconing) and lateral 

encroachment of saltwater. Upconing is likely to occur when sand beds containing saltwater are not separated 

by clay beds from the freshwater sands. In some areas of Orange County, thin layers of clay separate the 

freshwater sands from sands containing saltwater. Increased withdrawal from 1963 to 1980 led to an increase in 

chloride concentrations in wells in an industrial area near the city of Orange. The upconing is directly related to 

pumping, and is evident when wells with high chloride concentrations are surrounded by wells with lower 

chloride concentrations (Bonnet and Williams, 1987, p. 16-22). Movement of saltwater updip, toward the center 

of pumping, has also been observed in the lower part of the Chicot aquifer (table 1) in southeastern Orange 

County (Gabrysch and McAdoo, 1972, p. 10). From 1980 to 1984, the decreases in withdrawals have caused 

chloride concentrations to stabilize throughout the county.

Land-surface subsidence, resulting from decreased artesian pressures, has been measured in the area. 

Some parts of eastern and western Orange County have experienced more than 0.5 ft of land-surface 

subsidence in the years 1900 to 1975 (Carr and others, 1985, fig. 25). This subsidence is much less than the 

amount measured in the Houston-Galveston area.

POTENTIAL FOR GROUND-WATER DEVELOPMENT

In the previous section, the history of development was described for the more intensively pumped 

areas along with some of the problems associated with that development There has been little development in 

a large part of the study area, and large quantities of ground water are available for various uses.

The availability of ground-water supplies will depend on the amount of withdrawal that can be 

sustained without exceeding acceptable limits of: (1) Water-level declines; (2) land-surface subsidence; (3) 

saltwater encroachment at the coast; (4) contamination from saltwater in adjacent beds or from downdip; and 

(5) reduced streamflow.

Reports that include a regional description of ground-water use and availability, projected groundwater requirements, and potential problems associated with future development include those by the Texas 

Department of Water Resources (1984a, 1984b, 1985), and Baker and Wall (1976). A common characteristic of 

problem areas is that large ground-water withdrawal is concentrated in small areas. Some general ways to 

reduce withdrawal and the potential or existing adverse effects of withdrawal are: (1) Water- conservation 

practices; (2) construction of reservoirs and more dependence on surface-water supplies; (3) relocation of well 

fields and spreading the withdrawal over a larger area; (4) importation of water from nonproblem areas; (5) 

artificial recharge; and (6) desalination of salty ground water.

Pumping from older units that are farther inland can minimize land-surface subsidence and saltwater 

encroachment If the withdrawal is in areas with more abundant precipitation, the potential for recharge is 

greater and aquifer dewatering is less likely to be a problem.

22
Fresh ground-water use for 1985 and projected use for 2000 and 2030 are shown for selected counties 

in the study area (fig. 62). The projections, made by the Texas Water Development Board, are tentative and 

undergo constant revision and updating depending on the many changing technical and socio-economic factors. 

Ground-water use in eight out of the nine most intensively pumped counties in 1985 is projected to decrease by 

2030 (fig. 62). Total decrease for the eight counties is expected to be from 872 Mgal/d in 1985 to 392 Mgal/d in 

2030, an average decrease of about 55 percent

The largest decrease, 143 Mgal/d, is projected for Harris County, closely followed by a projected 

decrease of 131 Mgal/d for Wharton County. Harris, Wharton, Jackson, Jasper, and Colorado Counties are 

part of a region designated by the State as the Southeast Texas and Upper Gulf Coast Region (Texas 

Department of Water Resources, 1984a, fig. 1). Although total water use is projected to increase in this region 

by about 20 percent from 1980 to 2030, ground-water use is projected to decrease by about 29 percent. 

According to the Texas Department of Water Resources (1984a, p. 53), an increasing dependence on surfacewater supplies will be necessary to prevent further land subsidence and saltwater encroachment

Zavala, Frio, and Atascosa Counties are within the Winter Garden area. In an area designated as the 

South Central Texas Region, the Texas Department of Water Resources (1984a, p. 51) projects shortages of 

water for irrigation, primarily in the Winter Garden area, to be about 151 Mgal/d by 2030.

It is apparent that the future development of ground water in the study area is a complex matter, with 

projected large decreases in withdrawal for some areas and projected increases for other areas. Such 

withdrawal projections could be simulated in the ground-water flow model, but such complex simulations are 

beyond the scope of this study. However, the model was used to simulate two simplified projected withdrawal 

scenarios. In the first, the calibration period from predevelopment to 1982 was extended to the year 2030 with 

the 1980 pumping rate remaining in effect for 1983-2030. In the second simulation, the calibration period from 

predevelopment to 1982 was again extended to the year 2030, but with an additional pumping rate of 0.5 Mgal/d 

assigned to each grid block (25 mi2 area) in all aquifers and permeable zones where the block contained mean 

dissolved solids concentrations of 2,000 mg/L or less and had a thickness greater than 25 ft An analysis of the 

two simulations provides a qualitative evaluation of the response of aquifer systems to additional large 

development

Representative water-level hydrographs for the 1910-2030 simulations are shown for permeable zones 

A, B, and C in Harris County (fig. 63). The well locations are shown in figure 41. In this section, simulated 

water levels will be discussed along with measured water levels in specific wells. Note that a simulated water 

level is the average water level for a large volume of aquifer sediments having the areal dimension of a model 

grid block (25 mi2) and an average aquifer thickness for that block.

Well 9 in figure 63 is open to permeable zone A in an area of southeastern Harris County where 

withdrawal from most zones has been substantially reduced starting in 1976 and continuing into the 1980's. 

Simulation of continual pumping at the 1980 rate resulted in little additional drawdown in well 9 after 1982.

Wells 7 and 3 in figure 63 are open to permeable zones B and C, respectively, in an area of southwest 

Harris County where pumping rates have generally continued to increase in the 1970's and through 1980. Wells 

7 and 3 had an additional simulated drawdown of 100 and 130 ft, respectively, between 1982 and 2030. Both 

drawdown curves are approaching horizontal near the end of the simulation period, signifying little further 

change in storage.

For the second simulation, involving increased withdrawal, about 50 ft of additional drawdown was 

simulated in well 9 after 1982. Simulated drawdowns in wells 7 and 3 after 1982 were 160 and 220 ft, 

respectively. The rates of decline of the water levels for wells 9,7, and 3 from 1983-2030 averaged 1.0,33, and 

4.6 ft/yr, respectively, compared to rates of 0.1,2.1, and 2.7 ft/yr for the first simulation with 1980 withdrawal.

Overall declines in heads in the Houston-Galveston area during the simulations caused additional landsurface subsidence as shown in figure 64. (As part of the model calibration, land-surface subsidence in the 

Houston-Galveston area from predevelopment to 1973 was simulated by the model. A comparison of measured

23
and simulated land subsidence is shown in figure 95 and is discussed in detail in the Appendix.) For the model 

simulation with 1980 withdrawal during 1983-2030, land subsidence in eastern Harris County and Galveston 

County increased by about 1 to 3 ft from 1973 to 2030 (fig. 64). For the same period, the land surface subsided 

by more than 4 ft in southwest Harris and northeast Fort Bend Counties.

Additional land-surface subsidence in southeastern Harris County beyond the 1980's may seem 

contradictory. Model results (fig. 63) indicate that a maximum water-level drawdown in the block containing 

well no. 9 occurred in 1976. The drawdown is from a block in permeable zone A. Projected drawdowns in this 

block to the year 2030 were never as large as in 1976. Thus, if water levels in the block containing well no. 9 are 

representative of ground-water levels in southeastern Harris County, additional land subsidence to the year 

2030 would not be expected. Because the model is projecting additional subsidence in southeastern Harris 

County, and specifically in the grid block containing well no. 9, the model output was further analyzed. 

Drawdowns for permeable zone B in this grid block (fig. 65) follow a pattern similar to that for permeable zone 

A (fig. 63). However, water levels in permeable zone C (fig. 65) show a continuous decline from 1910-2030, 

thus accounting for additional land-surface subsidence in the model simulations.

The additional land-surface subsidence in southeastern Harris County and adjacent areas, as projected 

from 1983 to 2030, results from 1980 pumping rates (the most recent withdrawal data available for the model 

simulations). Pumping rates in the southeastern Harris County area continued to decline substantially through 

1986. Land-surface subsidence data provided by the Houston-Galveston Coastal Subsidence District (written 

commun., 1987) show a continuing marked decrease or total cessation in the rate of subsidence at monitored 

sites in southeastern Harris County and in Galveston County through 1986.

For the simulation with increased withdrawal superimposed on the 1980 pumping rate, land-surface 

subsidence from 1973 to 2030 is more than 5 ft in eastern Harris County, and more than 7 ft in northeastern 

Fort Bend County (fig. 64).

Well 23 in figure 66 is located downdip in the lower Claiborne-upper Wilcox aquifer in southern Zavala 

County. With the 1980 pumping rate continuing for 1983-2030, simulated drawdown for this period was 45 ft 

Well 24 in figure 66 is located in the outcrop of the lower Claiborne-upper Wilcox aquifer in northeastern 

Zavala County. The depth of the well is reported as 260 ft. With the 1980 pumping rate continuing, simulated 

drawdown between 1982 and 2030 was 60 ft. Because the aquifer is under water-table conditions, an additional 

60 ft of the aquifer was dewatered at this location. By 2030, about 73 percent of the aquifer would be dewatered 

at this location.

For the simulation with additional withdrawal, drawdowns for 1983-2030 at wells 23 and 24 were 205 

and 130 ft, respectively (fig. 66). Average rates of decline of the water levels in wells 23 and 24 for 1983-2030 

were 43 and 2.7 ft/yr, respectively, compared to rates of 0.9 and 12 ft/yr for the first simulation. The aquifer at 

well 24 would be almost totally dewatered by the year 2030.

Major components of the ground-water budget are presented for the simulation with increased 

withdrawal superimposed on the 1980 pumping rate. A summary of withdrawal, change in storage, and vertical 

flow rates in the exposed and downdip parts of each hydrogeologic unit in the modeled area for the year 2030 is 

shown in figure 67. Net recharge in the outcrop areas of all units accounted for about 82 percent of the total 

pumping rate of 548 million ftVd, with about 16 percent of the pumping rate accounted for by water released 

from storage in aquifers and compacting clay beds, and about 2 percent contributed by net lateral flow into the 

study area. Highest recharge rates would occur in the outcrops of the most intensively pumped units, with 140 

million frVd or 31 percent of total net recharge entering the uppermost and most intensively pumped 

unit-permeable zone A (fig. 67).

The highest net leakage rate was 26 million ftVd downward into the lower Claiborne-upper Wilcox 

aquifer, followed by 23 million ftVd downward into permeable zone B (fig. 67).

A summary of changes in pumping rates, heads, and recharge rates for each aquifer and permeable 

zone is given in table 7 for the simulation with increased withdrawal. Increases in pumping rates range from 10

24
Table 1.-Summary of changes in simulated heads and recharge rates resulting from 

hypothetical increase in pumping rate, 19fS to 2030

Aquifer

or

permeable

zone

Permeable

zone A

Permeable

zone B

Permeable

zone C

Permeable

zone D

Permeable

zone E

Upper

Claiborne

aquifer

Middle

Claiborne

aquifer

1980

pumping

rate

(million

cubic feet

per day)

86

51

29

4

1

2

5

Lower Claiborne- 43

upper Wilcox

aquifer

Middle

Wilcox

aquifer

10

1983-2030

pumping

rate

(million

cubic feet

per day)

121

84

63

34

11

16

51

104

64

Increase

in

pumping

rate

(million

cubic feet

per day)

35

33

34

30

10

14

46

61

54

Mean

decrease

in head

from 1982

head

(feet)

13

28

45

98

76

48

120

276

160

Mean increase

in recharge

rate in outcrop

area from

1982 rate

(inches

per year)

0.2

.6

.5

.5

.4

.5

.8

1.1

.5

24a
million ftVd for permeable zone E to 61 million tf/d for the lower Claiborae-upper Wilcox aquifer. Mean 

head decreases between 1982 and 2030 range from 13 ft for permeable zone A to 276 ft for the lower Claiboraeupper Wilcox aquifer. Head declines for the latter aquifer are especially large downdip in the Winter Garden 

area, where freshwater is found at unusually great depths but aquifer transmissivity is small For the combined 

units, the mean increase in the recharge rate in the outcrops over the 1982 rate is 035 in/yr. The mean 

increases for the individual units range from 02 in/yr for permeable zone A to 1.1 in/yr for the lower 

Claiborae-upper Wilcox aquifer (table 7).

A final analysis of aquifer potential for development utilizes the difference between (1) 2030 water 

level simulated with additional withdrawal and (2) the 2030 water levels simulated with 1980 withdrawal 

continuing from 1982 to 2030. Because water levels in the simulations are the integrated result of all hydrologic 

properties and conditions, such as aquifer transmissivity, nearness to outcrop or recharge source, and vertical 

leakage, the head difference between the two simulations provides some measure of the capacity of the aquifer 

systems to accept additional large development. This water-level difference is shown for each aquifer and 

permeable zone in figures 68 through 76. Also shown on the maps are areas within each aquifer and permeable 

zone that are designated as having more or less potential for future ground-water development In addition to 

the difference in head as just described, other subjective criteria for rating the areas include:

1. Aquifer thickness: An area having a mean grid-block thickness of less than 25 ft is designated as having only 

some or limited potential for additional development;

2. Dissolved-solids concentration of water: An area having a mean dissolved-solids concentration greater than 

2,000 mg/L is designated as having limited potential for additional development;

3. Recharge potential: Precipitation, and thus recharge potential, is generally progressively smaller from east 

lowest

The rating of areas in each aquifer and permeable zone is subjective and is meant only to show areas 

within a given aquifer that have relatively more or less potential for additional large development The ratings 

do not necessarily indicate that a particular aquifer has more potential for development than another. For the 

development potential, it is generally assumed that the potential for saltwater intrusion at the coast and 

elsewhere is minimal and within acceptable limits. It is also assumed that additional land-surface subsidence, as 

discussed previously, is within acceptable limits. Examination of figures 68 through 76 shows that the potential 

for future development in each aquifer and permeable zone is generally rated more favorably from west to east 

across the study area.

For the middle Wilcox aquifer, the simulation with the superimposed withdrawal is significantly 

affected in the extreme northeast corner of the study area by nearness to the no-flow boundary (fig. 76). 

Testing of the effects of the no-flow lateral boundaries on the simulations (discussed in the Appendix) shows 

that this is the only area and the only aquifer so affected.

SUMMARY

Gulf Coastal Plain sediments as much as several thousand feet thick were represented as discrete 

aquifers, permeable zones, and confining units in a multilayered digital model. The bases for selecting the 

number of hydrogeologic units (model layers) include practical considerations of size of the area, objectives of 

the model study, and computer cost limitations. Electrical-log interpretations of lithology, and vertical head 

differences at major pumping centers in Texas and Louisiana were used to delineate hydrogeologic units.

Two aquifer systems are recognized for the Texas Gulf Coast: the Texas coastal uplands aquifer system 

and the coastal lowlands aquifer system. The coastal uplands aquifer system consists of four aquifers and two 

confining units in the Wilcox and Claiborae Groups. The system is bounded from below by the practically 

impermeable clays of the Midway Group, or by the top of the geopressured zone. The overlying VicksburgJackson confining unit separates the coastal uplands and the younger coastal lowlands aquifer systems. The 

coastal lowlands aquifer system consists of five permeable zones and two confining units that range in age from 

Holocene to Oligocene. Water quality in the aquifer systems varies from freshwater to brines, with dissolved 

solids concentrations ranging from a few hundred to as much as 150,000 mg/L.

25
In 1980, ground-water withdrawals in the study area, an area of about 114,000 mi2, were 1.7 billion 

gal/d. Withdrawal has caused large cones of depression in the potentiometric surfaces, particularly in the 

Houston-Galveston and Winter Garden areas, where water levels have declined hundreds of feet over large 

areas since the beginning of development Inelastic compaction of clays has resulted in land-surface subsidence 

of more than 1 ft in an area of about 2,000 mi2. As much as 10 ft of subsidence has occurred in the Pasadena 

area east of Houston. Movement of saltwater toward pumping centers by vertical migration or from downdip 

has caused water-quality problems. The potential for contamination is greatest along the coastal margins. 

Saltwater contamination and land-surface subsidence have prompted an increasing reliance on surface water for 

municipal and industrial supplies.

A three-dimensional, variable-density digital flow model was developed for simulation of 

predevelopment and transient flow conditions. The area simulated extends beyond die study area to include 

parts of Louisiana and Mexico. No-flow boundaries were used at the updip and downdip extent of the 

hydrologic units and at the eastern and western limits, A constant-head water-table boundary provides recharge 

to the units in their outcrop areas.

The model calibration period was from 1910 (predevelopment) to 1982. Simulated 1982 heads, longterm hydrographs, and land-surface subsidence were matched to measured data in selected, intensively pumped 

areas.

Mean horizontal hydraulic conductivity of hydrologic units in the calibrated model ranges from 10 ft/d 

for the middle Wilcox aquifer to 25 ft/d for permeable zone A. Mean transmissivity ranges from about 4,600 

tf/d for the middle Claiborne aquifer to about 10,400 ftVd for permeable zone D. Mean vertical hydraulic 

conductivity ranges from 1.1 x 10"5 ft/d for the Vicksburg-Jackson confining unit, to 3.8 x 10"3 ft/d for permeable 

zone A. Mean values of calibrated storage coefficient range from 52 x 10"4 for the middle Claiborne aquifer to 

1.7 x 10"3 for the middle Wilcox aquifer and permeable zone C. Calibrated inelastic specific storage values for 

clay beds in permeable zones A, B, and C in the Houston-Galveston area are 8^ x 10 ,8.0 x 10"5, and 8.0 x 10"6 

ft"1, respectively.

Model results indicate that recharge was the source of about 76 percent of the discharge in the study 

area (withdrawal plus a small net lateral outflow) for 1982; release of water from aquifer storage and 

compacting clay beds provided the remaining 24 percent The average 1982 recharge rate for the calibrated 

simulation was 0.52 in/yn the average discharge, not including ground-water withdrawal, was 0.15 in/yr. As 

much as 6 in/yr of recharge was simulated in the coastal rice-irrigation area; perhaps as much as 30 percent of 

this rate is return flow of ground water that has been pumped for irrigation.

A combination of intense withdrawal and low precipitation has caused long-term de-watering of the 

lower Claiborne-upper Wilcox aquifer in the Winter Garden area. Long-term de-watering of shallow sands was 

observed in a well in Jackson County, a part of the coastal rice-irrigation area where precipitation is more 

abundant than in the Winter Garden area. A regional assessment of dewatering in the coastal rice-irrigation 

area is precluded because of a lack of data.

Ground-water use is projected to decline substantially in most of the study area by the year 2030, as 

problems such as saltwater intrusion, land-surface subsidence, and aquifer dewatering become worse. The 

digital flow model developed for this study was used to simulate the flow system to 2030 assuming two pumping 

scenarios: (1) The 1980 pumping rate was applied to 1983-2030; and (2) an additional pumping stress of 0.5 

Mgal/d per 25 mi2 was superimposed on the 1980 pumping rate in those areas where water contains less than 

2,000 mg/L dissolved-solids concentration and the aquifer thickness is at least 25 ft; this rate was used for the 

period 1983-2030.

Additional water-level declines, several feet of additional land subsidence in the Houston-Galveston 

area, and increased recharge rates were projected for the year 2030 in both simulations. The difference 

between the 2030 heads generated by the two model simulations, along with other factors such as aquifer 

thickness, dissolved-solids concentration of water, and recharge potential provided the criteria for rating areas

26
within the aquifers and permeable zones as having relatively more or less potential for future development. The 

potential for future development in each aquifer and permeable zone becomes higher from west to east across 

the study area.

Permeable zone A has the highest potential for development of additional large ground-water supplies. 

Because it crops out over its entire landward extent, recharge is generally always nearby and water-level 

declines are not large. The potential for development is also high for large areas of permeable zones B and C. 

Areas for potential development are small for permeable zones D and E and for the upper Claiborne aquifer, 

largely because these units contain relatively little freshwater. The middle Claiborne, lower Claiborne-upper 

Wilcox and middle Wilcox aquifers have some potential for development, mostiy in the eastern areas.

Some general ways to reduce ground-water withdrawal or the adverse effects of withdrawal are: (1) 

Water conservation practices; (2) construction of reservoirs and more dependence on surface-water supplies; 

(3) relocation of well fields and spreading the withdrawal over a larger area; (4) importation of water from 

nonproblem areas; (5) artificial recharge; and (6) use of desalinated ground water.

27
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., 1989, Definition of geohydrologic framework and preliminary simulation of

ground-water flow in the Mississippi embayment aquifer system, south-central United States: U.S.

Geological Survey Water-Resources Investigations Report 86-4364,110 p. 

Baker, E.T., Jr., 1965, Ground-water resources of Jackson County, Texas Texas Water Development Board

Report 1,229 p.

 1979, Stratigraphic and hydrogeologic framework of part of the Coastal Plain of Texas: Texas Department 

of Water Resources Report 236,43 p.

 1985, Texas Ground-water resources, in National Water Summary 1984: UJS. Geological Survey WaterSupply Paper 2275, p. 397-402.

 1986, Hydrology of the Jasper aquifer in the southeast Texas Coastal Plain: Texas Water Development

Board Report 295,64 p. 

Baker, E.T., Jr., and Follett, C.R., 1973, Effects of ground-water development on the proposed Palmetto Bend

Dam and Reservoir in southeast Texas UJS. Geological Survey Water-Resources Investigations Report

18-73,70 p. 

Baker, E.T., Jr., and Wall, J.R^ 1976, Summary appraisals of the Nation's ground-water resources, Texas-Gulf

region: UJS. Geological Survey Professional Paper 813-F, 29 p. 

Baker, R.C., and Dale, O.C., 1961, Ground-water resources of the Lower Rio Grande Valley area, Texas Texas

Board of Water Engineers Bulletin 6014, vol. 1,81 p., vol. II, 336 p. 

Barnes, BA., Follett, C.R., and Sundstrom, R.W., 1944, Ground-water supply of Bryan, Texas: Texas State

Board of Water Engineers Report M025. 

Bonnett, C.W., and Williams, J.F., III, 1987, Development of ground-water resources in the Orange County

area, Texas and Louisiana, 1980-spring 1985: UJS. Geological Survey Water-Resources Investigations

Report 87-4158,50 p. 

Brahana, J.V., and Mesko, T.O., 1988, Hydrogeology and preliminary assessment of regional flow in the upper

Cretaceous and adjacent aquifers in the northern Mississippi embayment: UJS. Geological Survey WaterResources Investigations Report 87-4000,65 p.

Carr, JJL, Meyer, W.R^ Sandeen, W.M., and McLane, IJL, 1985, Digital models for simulation of groundwater hydrology of the Chicot and Evangeline aquifers along the Gulf Coast of Texas Texas Department

of Water Resources Report 289,101 p. 

Cronin, J.GM and Wilson, C A, 1967, Ground water in the flood-plain alluvium of the Brazos River, Whitney

Dam to vicinity of Richmond, Texas Texas Water Development Board Report 41,223 p. 

Deussen, A., 1914, Geology and underground waters of the southeastern part of the Texas Coastal Plain: UJS.

Geological Survey Water-Supply Paper 335,365 p. 

Duffin, G.L., and Elder, G.R., 1979, Variations in specific yield in the outcrop of the Carrizo Sand in South

Texas as estimated by seismic refraction: Texas Department of Water Resources Report 229,57 p. 

Elder, G.R., Duffin, G.L., and Rodriguez, Eulogio, Jr., 1980, Records of wells, water levels, pumpage, and

chemical analyses of water from the Carrizo aquifer in the Winter Garden area, Texas, 1970 through

1977: Texas Department of Water Resources Report 254,125 p. 

Ellisor, A.C., 1944, Anahuac Formation: American Association of Petroleum Geologists Bulletin, v. 28, no. 9, p.

1355-1375. 

Follett, C.R., 1974, Ground-water resources of Brazos and Burleson Counties, Texas: Texas Water

Development Board Report 185,1% p.

Freeze, RA^ and Cherry, J A., 1979, Groundwaten New Jersey, Prentice-Hall, Inc., 604 p. 

Gabrysch, R.K., 1977, Approximate areas of recharge to the Chicot and Evangeline aquifer systems in the

Houston-Galveston area, Texas UJS. Geological Survey Open-File Report 77-754,1 map.

 1984a, Ground-water withdrawals and changes in water levels in the Houston District, Texas 1975-79: Texas 

Department of Water Resources Report 286,42 p.

28
 19845, Ground-water withdrawals and land-surface subsidence in the Houston-Galveston region, Texas,

1906-80: Texas Department of Water Resources Report 287,64 p. 

Gabrysch, RJC, and Bonnett, C.W., 1975, Land-surface subsidence in the Houston-Galveston region, Texas:

Texas Water Development Board Report 188,19 p. 

Gabrysch, RJC, and McAdoo, GIX, 1972, Development of ground-water resources in the Orange County area,

Texas and Louisiana, 1963-71: Texas Water Development Board Report 156,47 p. 

Garza, Sergio, 1977, Artificial recharge for subsidence abatement at the NASA-Johnson Space Center, phase 1:

VS. Geological Survey Open-File Report 77-219,82 p. 

Garza, Sergio, Jones, B.D., and Baker, E.T., Jr., 1987, Approximate potentiometric surfaces for the aquifers of

the Texas coastal uplands aquifer system, 1980: VS. Geological Survey Hydrologic Investigations Atlas

704, scale 1:1,500,000. 

Gebert, W.A^ Graczyk, DJ., and Krug, W.R^ 1987, Average annual runoff in the United States, 1951-80: VS.

Geological Survey Hydrologic Investigations Adas HA-710,1 sheet, scale 1:7,500,000. 

Groschen, G.E., 1985, Simulated effects of projected pumping on the availability of freshwater in the

Evangeline aquifer in an area southwest of Corpus Christi, Texas: VS. Geological Survey WaterResources Investigations Report 85-4182,103 p. 

Grubb, HJP^ 1984, Planning report for the Gulf Coast Regional Aquifer-System Analysis in the Gulf of Mexico

Coastal Plain, United States: VS. Geological Survey Water-Resources Investigations Report 84-4219,

30 p.

 1986, Gulf Coastal Plain regional aquifer-system study, in Sun, Ren Jen, ed., Regional Aquifer-System 

Analysis Program of the VS. Geological Survey - Summary of Projects, 1978-84: VS. Geological Survey 

Circular 1002, p. 152-161.

 1987, Overview of the Gulf Coast Regional Aquifer-System Analysis, south-central United States: in,

Vecchioli, John, and Johnson, A.I., eds., Aquifers of the Atlantic and Gulf Coastal Plain: American

Water Resources Association, Monograph No. 9, p. 101-118. 

Hammond, W.W., Jr., 1969, Ground-water resources of Matagorda County, Texas: Texas Water Development

Board Report 91,180 p. 

Helm, D.C., 1975, One-dimensional simulation of aquifer system compaction near Pixley, California; 1,

Constant parameters: Water Resources Research, v. 11, no. 3, p. 465-478.

 1976, One-dimensional simulation of aquifer system compaction near Pixley, California; 2, Stress-dependent

parameters: Water Resources Research, v. 12, no. 3, p. 375-391. 

Hem, J.D., 1985, Study and interpretation of the chemical characteristics of natural water: VS. Geological

Survey Water-Supply Paper 2254,3rd Edition, 264 p. 

Hosman, R.L., and Weiss, JJS., in press, Geohydrologic units of the Mississippi embayment and Texas coastal

uplands aquifer systems, south-central United States: VS. Geological Survey Professional Paper 1416-B.

 1988, Geohydrologic units of the Mississippi embayment and Texas coastal uplands aquifer systems, southcentral United States: VS. Geological Survey Open-File Report 88-316,21 p.

Hubbert, MJC, 1940, The theory of ground-water motion: Journal of Geology, v. XLVIII, no. 8, p. 785-944.

Hughes, W.F., and Magee, A.C., 1962, An economic analysis of irrigated cotton production, Middle Brazos 

River Valley, 1955-58: Texas A&M University, MP-580,12 p.

Jones, P.H., Stevens, P.R., Wesselman, J.B., and Wallace, R.H., Jr., 1976, Regional appraisal of the Wilcox 

Group in Texas for subsurface storage of fluid wastes: VS. Geological Survey Open-File Report 76-394, 

107 p.

Jorgensen, D.G., 1975, Analog-model studies of ground-water hydrology in the Houston district, Texas: Texas 

Water Development Board report 190,84 p.

 1977, Salt-water encroachment in aquifers near the Houston Ship Channel, Texas: VS. Geological Survey

Open-File Report, 76-781,45 p. 

Jorgensen, D.G., and Gabrysch, RJK., 1974, Simulated water-level changes resulting from proposed changes in

ground-water pumping in the Houston, Texas, area: UJS. Geological Survey Open-File Report, 3 sheets. 

Klemt, W.B., Duffin, G.L., and Elder, GJ^, 1976, Ground-water resources of the Carrizo aquifer in the Winter

Garden area of Texas: Texas Water Development Board Report 210, v. 1,30 p. 

Kuiper, L.K., 1981, A comparison of the incomplete Cholesky-conjugate gradient method with the strongly

implicit method as applied to the solution of two-dimensional groundwater flow equations: Water

Resources Research, v. 17(4), p. 1082-1086.

29
 1983, A numerical procedure for the solution of the steady state variable density groundwater flow 

equation: Water Resources Research, v. 19(1), p. 234-240.

 1985, Documentation of a numerical code for the simulation of variable density ground-water flow in three 

dimensions: UJS. Geological Survey Water-Resources Investigations Report 84-4302,90 p.

 1986, A comparison of several methods for the solution of the inverse problem in two-dimensional steady 

state groundwater flow modeling: Water Resources Research, v. 22(5), p. 705-714.

Leake, SA., and Prudic, D.E., 1989, Documentation of a computer program to simulate aquifer-system 

compaction using the modular finite-difference ground-water flow model: UJS. Geological Survey OpenFile Report 88-482,80 p.

Livingston, Penn, and Bridges, T.W., 1936, Ground-water resources of Kleberg County, Texas: UJS. Geological 

Survey Water-Supply Paper 773-D, p. 197-232.

Lohman, S.W., 1972, Ground-water hydraulics: UJS. Geological Survey Professional Paper 708,70 p.

Lohman, S.W., Bennett, R.R., Brown, R.H., Cooper, H.H., Jr., Drescher, WJ., Ferris, J.G., Johnson, A.I., 

McGuinness, C.L., Piper, AM., Rorabaugh, MJ., StaUman, R.W., and Theis, C.V., 1972, Definitions of 

selected ground-water terms revisions and conceptual refinements: UJS. Geological Survey WaterSupply Paper 1988,21 p.

Loskot, C.L., Sandeen, W.M., and Follett, C.R., 1982, Ground-water resources of Colorado, Lavaca, and 

Wharton Counties, Texas: Texas Department of Water Resources Report 270,245 p.

Lusczynski, N J., 1961, Head and flow of ground water of variable density: Journal of Geophysical Research, v. 

66, no. 12, p. 4247-4256.

Mackey, G.W., 1987, Comparison of irrigation pumpage and change in water storage of the High Plains aquifer 

in Castro and Parmer Counties, Texas, 1975-83: UJS. Geological Survey Water-Resources Investigations 

Report 87-4032,48 p.

Martin, Angel, Jr., and Whiteman, C.D., Jr., 1989, Regional ground-water flow in the coastal lowlands aquifer 

system in parts of Alabama, Florida, Louisiana, and Mississippi--A preliminary analysis: UJS. Geological 

Survey Water-Resources Investigations Report 88-4100,88 p.

Mesko, T.O., Ackerman, D J., and Williamson, A.K., 1990, Ground-water pumpage from the Gulf Coast aquifer 

systems, 1960-85, south-central United States: UJS. Geological Survey Water-Resources Investigations 

Report 89-4180,177 p.

Meyer, W.R., and Carr, J.E., 1979, A digital model for simulation of ground-water hydrology in the Houston 

area, Texas: Texas Department of Water Resources Report LP-103,27 p., 3 app.

Muller, DA., and Price, R.D., 1979, Ground-water availability in Texas, estimates and projections through 

2030: Texas Department of Water Resources Report 238,77 p.

Payne, J.N., 1968, Hydrologic significance of the lithofacies of the Sparta Sand in Arkansas, Mississippi, and 

Texas: UJS. Geological Survey Professional Paper 569-A, 17 p.

 1970, Geohydrologic significance of lithofacies of the Cockfield Formation of Louisiana and Mississippi and 

of the Yegua Formation of Texas: UJS. Geological Survey Professional Paper 569-B, 14 p.

 1972, Hydrologic significance of lithofacies of the Cane River Formation or equivalents of Arkansas, 

Louisiana, Mississippi, and Texas: UJS. Geological Survey Professional Paper 569-C, 17 p.

 1975, Geohydrologic significance of lithofacies of the Carrizo Sand of Arkansas, Louisiana, and Texas and 

the Meridian Sand of Mississippi: UJS. Geological Survey Professional Paper 569-D, 11 p.

Petitt, B.M., and Winslow, A.G., 19515, Geology and ground-water resources of Galveston County, Texas: Texas 

Board of Water Engineers Bulletin 5502,219 p.

Pettijohn, RA^ 1986, Processing water-chemistry data, Gulf Coast aquifer systems, south-central United States, 

with summary of dissolved-solids concentrations and water types: UJS. Geological Survey WaterResources Investigations Report 86-4186,42 p.

Pettijohn, RA., Weiss, J.S., and Williamson, A.K., 1988, Dissolved-solids concentrations and water 

temperatures for aquifers in the Gulf Coast aquifer systems, south-central United States: UJS. Geological 

Survey Water-Resources Investigations Report 88-4082, map, scale 13,500,000,5 sheets.

Preston, R.D., 1983, Occurrence and quality of ground water in the vicinity of Brownsville, Texas: Texas 

Department of Water Resources Report 279,98 p.

Prudic, D.E., 1991, Estimates of hydraulic conductivity from aquifer-test analyses and specific-capacity data, gulf 

coast regional aquifer systems, south-central United States: U.S. Geological Survey Water Resources 

Investigations Report 90-4121,38 p.

30
Prudic, D.E., and Williamson, A.K., 1984, Evaluation of a technique for simulating a compacting aquifer system

in the Central Valley of California, U.SA: International Association of Hydrological Sciences

Publication no. 151, p. 53-63. 

Ratzlaff, K.W., 1982, Land-surface subsidence in the Texas coastal region: Texas Department of Water

Resources Report 272,26 p. 

Ryder, P.D., 1988, Hydrogeology and predevelopment flow in the Texas Gulf Coast aquifer systems: UJS.

Geological Survey Water-Resources Investigations Report 87-4248,109 p. 

Shafer, G.H., and Baker, E.T., Jr., 1973, Ground-water resources of Kleberg, Kenedy, and southern Jim Wells

Counties, Texas: Texas Water Development Board Report 173,162 p. 

Solley, W.B., Merk, C.F., and Pierce, R.R., 1988, Estimated use of water in the United States in 1985: UJS.

Geological Survey Circular 1004,82 p. 

Texas Department of Water Resources, 1984a, Water for Texas-A comprehensive plan for the future: Texas

Department of Water Resources GP-4-1, v. 1,72 p.

 1984b, Water for Texas-Technical appendix: Texas Department of Water Resources GP-4-1, v. 2.

 1985, Water use, projected water requirements, and related data and information for the metropolitan

statistical areas in Texas: Texas Department of Water Resources Report LP-201,226 p. 

Texas Water Development Board, 1986, Surveys of irrigation in Texas-1958,1964,1969,1974,1979, and 1984:

Texas Water Development Board Report 294,242 p. 

Turner, S.F., 1938, Ground water in the vicinity of Bryan and College Station, Texas: Texas State Board of

Water Engineers Miscellaneous Report, 44 p. 

Turner, S.F., Robinson, T.W., and White, W.N., 1948, Geology and ground-water resources of the Winter

Garden district, Texas, 1948: UJS. Geological Survey Water-Supply Paper 1481,248 p. 

UJS. Geological Survey, 1985, National water summary 1984-Hydrologic events, selected water-quality trends,

and ground-water resources: U.S. Geological Survey Water-Supply Paper 2275,467 p. 

Wallace, R.H., Jr., Wesselman, J.B., and Kramer, T.F., 1981, Map of the occurrence of geopressure in the

northern Gulf of Mexico basin, in Bebout, D.G., and Backman, A.L., eds., Proceedings of the 5th

geopressured-geothermal energy conference: Louisiana Geological Survey-Louisiana State UniversityUJS. Department of Energy, Baton Rouge, Louisiana, October 13-15,1981, map, scale 1:1,000,000,1

sheet 

Weiss, J.S., 1987, Determining dissolved-solids concentrations in mineralized ground water of the Gulf Coast

aquifer systems using electric logs, in Vecchioli, John, and Johnson, A.I., eds., Aquifers of the Atlantic

and Gulf Coastal Plain: American Water Resources Association, Monograph No. 9, p. 130-150. 

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. 

Wesselman, J.B., 1965, Geology and ground-water resources of Orange County, Texas: Texas Water

Commission Bulletin 6516,112 p.

 1967, Ground-water Resources of Jasper and Newton Counties, Texas: Texas Water Development Board 

Report 59,186 p.

 1971, Ground-water resources of Chambers and Jefferson Counties, Texas: Texas Water Development

Board Report 133,183 p. 

White, W.N., 1938, Progress report on the ground-water resources of the Houston district, Texas: Texas State

Board of Water Engineers Miscellaneous Report, 7 p. 

White, W.N., Livingston, Penn, and Turner, S.F., 1932, Ground-water resources of the Houston-Galveston area,

Texas, in Ground-water resources of the Houston-Galveston area and adjacent region, Texas, 1939:

Texas Board of Water Engineers Miscellaneous Report, p. 1-16. 

William F. Guyton and Associates, 1970, Ground-water conditions in Angelina and Nacogdoches Counties,

Texas: Texas Water Development Board Report 110,125 p. 

Williams, TA., and Williamson, A.K., 1989, Estimating water-table altitudes for regional ground-water flow

simulation, gulf coast aquifer systems, south-central United States: Ground Water v. 27, no. 3, p. 333-340. 

Williamson, AJC, 1987, Preliminary simulation of ground-water flow in the gulf coast aquifer systems, southcentral United States, in, Vecchioli, John, and Johnson, A.I., eds., Aquifers of the Atlantic and Gulf

Coastal Plain: American Water Resources Association, Monograph No. 9, p. 119 -137. 

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.

31
Wilson, TA., and Hosman, RL., 1988, Geophysical well-log database for the Gulf Coast aquifer systems, southcentral United States: US. Geological Survey Open-File Report 87-677,213 p.

Winslow, A.G., Doyel, W.W., and Wood, LA., 1957, Salt water and its relation to fresh ground water in Harris 

County, Texas: U JS. Geological Survey Water-Supply Paper 1360-F, p. 375-407.

Winslow, A.G., and Wood, LA., 1959, Relation of land subsidence to ground-water withdrawals in the upper 

Gulf Coast region, Texas: Mining Eng., p. 1030-1034.

Wood, LA., 1956, Availability of ground water in the Gulf Coast region of Texas: U.S. Geological Survey OpenFile Report, 55 p.

Wood, LA., Gabrysch, RX., and Marvin, Richard, 1963, Reconnaissance investigations of the ground-water 

resources of the Gulf Coast region, Texas: Texas Water Commission Bulletin 6305,114 p.

32
APPENDIX
The calibration of the digital model that was used to describe and quantify the regional and subregional 

flow systems in previous sections is detailed in this section. Because the details of the predevelopment digital 

flow model were presented in a previous report (Ryder, 1988), only a brief summary of the updated 

predevelopment model calibration will be presented. The transient model calibration includes additional data, 

such as pumping rates, development heads, and storage coefficients; thus a detailed discussion will follow.

A numerical model developed by Kuiper (1985) was used to simulate the ground-water flow system. 

The model simulates variable-density ground-water flow in three dimensions. The ground-water density is 

variable in space, but is assumed to be constant in time. Horizontal and vertical flow is computed for aquifers 

and permeable zones, and vertical flow is computed for confining units. The model utilizes an integrated finitedifference grid, wherein the six-sided grid blocks are rectangular when viewed from the vertical direction. The 

sides of the blocks are vertical planes, but their top and bottom surfaces follow the curvature of the 

hydrogeologic units (Kuiper, 1985). The strongly implicit procedure (SIP) was selected for solving the 

approximating flow equations. Kuiper (1985) presents a complete documentation of the model, including 

detailed instructions for the use of the computer program.

A numerical technique used to simulate land-surface subsidence and release of water from storage 

resulting from compacting fine-grained sediments was obtained from Leake and Prudic (1989). The technique 

for the simulation of compaction and land subsidence was incorporated into the model by L.K. Kuiper (UJS. 

Geological Survey, written commun., 1987).

Digital Model of Predevelopment Steady-State Flow System

As stated previously, further model calibration resulted in substantial differences in simulated aquifer 

and confining-unit properties, and consequently in simulated flow compared to the preliminary model results 

reported in Ryder (1988). However, statistical analyses of the residual errors (simulated aquifer heads minus 

measured aquifer heads) as shown in table 8 are similar to those previously reported in Ryder (1988, table 6). 

This similarity in simulated heads and difference in simulated flow rates results because the steady-state 

calibration does not provide a unique solution. When the distribution and amount of both recharge and 

discharge and the distribution of vertical and horizontal hydraulic conductivities are unknown, the calibration of 

a steady-state model to a set of water levels provides a solution, which may or may not be correct. 

Proportionately changing all values of hydraulic conductivities will result in the same set of simulated heads, but 

the flow through the system will be different because it is proportional to the assigned hydraulic conductivity 

values.

Residuals in table 8 range from a minimum value of -187 ft for permeable zone D to a maximum value 

of 184 ft for the lower Claiborne-upper Wilcox aquifer. Residuals are largest for the lower Clafoorne-upper 

Wilcox aquifer, with a standard deviation of 47 ft and an absolute mean of 53 ft. Permeable zone A has the 

smallest residuals, with a standard deviation of 12 ft and an absolute mean of 9 ft. For the combined aquifers 

and permeable zones, the standard deviation is 40 ft and the absolute mean is 30 ft.

The statistical analyses show that when the changed vertical and horizontal hydraulic conductivities, 

necessitated by the transient model calibration, are incorporated into the predevelopment, steady-state model, 

the predevelopment model calibration is statistically about the same as the original calibration.

Digital Model of Transient Flow System. Predevelopment to 1982

Transient model simulations allow for ground-water levels and flow to change with time in response to 

changes in the amount of recharge and discharge caused by man-induced stresses such as pumpage. Transient 

ground-water flow was simulated for the period 1910-82 to determine the effects caused by pumpage on water 

levels and flow in the aquifer systems. Initial water levels for 1910 were assumed equal to the predevelopment 

heads generated from the calibrated steady-state model Ground-water pumpage was added as a discharge and 

averaged over periods ranging from 1 to 27 years. Estimates of storage coefficients were added to the model 

and were adjusted during model calibration along with the values of vertical and horizontal hydraulic

34
Table ^.--Summary of simulated and measured predevelopment altitudes of

potentiometric surfaces

Aquifer or 

permeable 

zone

All

Permeable 

zone A

Permeable 

zone B

Permeable 

zone C

Permeable 

zone D

Permeable 

zone E

Total grid 

blocks with 

measured 

heads

4,588

621

906

495

259

68

Mean of 

residuals 

(feet)

12

2

9

6

-29

-18

Minimum 

residual 

(feet)

-187

-59

-69

-148

-187

-104

Maximum 

residual 

(feet)

184

37

54

115

103

77

Standard 

deviation 

(feet)

40

12

20

34

46

31

Absolute 

mean of 

residuals 

(feet)

30

9

17

25

43

27

Upper Claiborne 136 

aquifer

Middle Claiborne 544 

aquifer

Lower Claiborne- 596 

upper Wilcox 

aquifer

Middle Wilcox 

aquifer

963

29

13

47

16

-33

-59

-84

-97

149

129

184

172

39

41

47

44

34

34

53

37

34a
conductivity. Calibration was achieved when model-computed water levels reasonably matched selected 

hydrographs of wells and areally distributed water levels as measured in 1982. In areas of known land 

subsidence, the inelastic specific storage values of clays were adjusted until the amount and distribution of 

simulated land subsidence reasonably matched measured land subsidence.

Model Grid and Boundary Conditions

The model finite-difference grid superimposed on the modeled area and study area is shown in figure

77. The grid consists of 106 rows and 77 columns uniformly spaced 5 mi apart. The modeled area extends 

beyond the study area to include parts of Louisiana and Mexico, and has an area! extent of 149,000 mi2.

The general direction of ground-water flow prior to development was nearly parallel to the eastern and 

western boundaries of the study area; the flow paths followed the dips of the aquifers toward the Gulf. Little 

flow could be expected to enter or leave the study area under predevelopment conditions or where there has 

been little development, and the lateral boundaries of the model are designated as no-flow boundaries.

However, intense development in the Lake Charles area of southwestern Louisiana has caused a 

substantial amount of flow across the Texas-Louisiana border in the uppermost coastal lowlands permeable 

zones. Primarily for this reason, the eastern no-flow boundary was allowed to follow row 1 of the grid into 

southeastern Louisiana so that it increases to a maximum distance of about 195 mi from the Texas-Louisiana 

border (fig. 77).

The validity of retaining the lateral no-flow boundaries for the transient model calibration was tested 

by placing constant heads in the grid blocks just inside the no-flow boundaries. The constant heads were placed 

along the lateral edges in all layers, and the altitudes assigned to the constant heads were the starting heads 

(predevelopment) for the transient calibration. The transient predevelopment to 1982 simulation was run with 

the new boundaries, and the resulting simulated 1982 heads were compared to the 1982 heads simulated by the 

transient calibration. For all layers, the head changes at the boundaries of the study area were small in 

comparison to the residual errors (differences between simulated and measured heads) present in the model 

calibration. It is concluded that designation of the lateral boundaries as no-flow boundaries had no significant 

effect on the transient model calibration.

Another test of the no-flow lateral boundaries was made for the simulation involving the superposition 

of additional, hypothetical pumpage on 1980 pumping rates, and continuing the simulation to the year 2030. 

For this simulation, the constant-head lateral boundaries as described above were in effect for the entire 

simulation period-predevelopment to 2030. Differences in head caused by the changed boundary conditions 

were analyzed for all model layers. The heads in the middle Wilcox aquifer were significantly affected in the 

extreme northeastern comer of the study area (fig. 76). Head changes elsewhere for all other layers were small 

and of little consequence.

The base of the flow system is a no-flow boundary, which represents the top of the Midway confining 

unit, a thick deposit of nearly impermeable marine clays, or the top of the geopressured zone where it occurs 

above the top of the Midway confining unit It is assumed that abnormally high pressures in the geopressured 

zone are the result of greatly reduced permeability, which, in turn, precludes the possibility of significant flow 

out of this zone.

The updip limit of the flow system, where the aquifer system pinches out, is a no-flow boundary. The 

downdip limit of tile flow system is defined as the edge of the Continental Shelf. It is at a great distance from 

the coastline and is treated as a no-flow boundary.

The top of the simulated flow system is bounded by a layer of constant-head grid blocks that represent 

the water table in the uppermost 150 ft of the exposed portions of the units. The water table is shown in figure

78. Details of its construction are given in Ryder (1988) and in Williams and Williamson (1989). Altitude of 

the water table ranges from essentially sea level at the coast and in the Gulf to more than 800 ft above sea level 

in the west

35
The concept of a shallow water table that is replenished by precipitation and kept at an essentially 

constant altitude on an average annual basis is valid for undeveloped areas, and probably for developed areas 

receiving a large amount of precipitation such as in the east In some areas, however, such as the west where 

withdrawal is large and precipitation is relatively small, dewatering has caused the water table to decline over 

the years. The model grid blocks representing the outcrop of the lower Claiborne-upper Wilcox aquifer were 

assigned a specific yield rather than an artesian storage coefficient, as follows:

Row

2

2

3

3

4

6

7

8

9

11

12

13

14

14

15

15

16

16

17

17

18

18

18

19

19

19

21

Column

22

31-35

20

38

20

38

38

38

38

10

20

20

8

20

8

20

20

21

20-21

26-28

9

20-23

25-27

10

20

25

11

Specific 

yield

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

Row

23

25

31

33

34

35

39

40

47

48

52

55

58

61

62

64

65

68

69

70

71

72

73

74

75

76

77

Column

11

12

16

18

18

18

19

19

20

20

21

22

23

24

24

25

25

24

24

24

24

24

23

23

23

22

21-22

Specific 

yield

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

Row

78

79

80

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

94

95

96

97

98

99

100

101

Specific 

Column yield

21

19-21

19

20

18-19

18

17

16

15-16

14-15

13-14

13

12-13

12

12

11

11

11

17-18

13-18

16-18

17-18

17-19

18-20

19-20

20

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.15

0.10

0.10

0.10

0.10

0.10

0.10

0.10

0.10

0.10

0.10

The head for the water table is held constant through time, but the flow into or out of the boundary 

layer is the product of the vertical gradient between the constant head and the head in the aquifer, and the 

conductance to flow between the two layers. This conductance is the harmonic mean conductance of the bottom 

one-half of the constant-head grid block and the top one-half of the aquifer grid block. The amount of flow into 

or out of the constant-head layer can be reduced (to zero, if desired) by reducing the conductance in the desired 

grid blocks during the model calibration.

Hydrologic Input Data

Starting heads for the transient model are the calibrated predevelopment heads. Initial estimates of 

hydraulic conductivity were determined from the steady-state model. Water density was estimated as discussed 

earlier; it was not adjusted during model calibration. Thicknesses of the units were discussed hi detail hi Ryder 

(1988).

36
In general, pumping periods for the model were chosen on 5-yr intervals to coincide with irrigation 

pumpage surveys done by the State approximately every 5 yrs beginning in 1958 (Texas Water Development 

Board, 1986). Public and industrial pumpage data are more accurate than irrigation pumpage data and are 

generally available on an annual or more frequent basis from State and local files and from published reports. 

Average public and industrial pumping rates were calculated for the appropriate pumping periods.

Pumping rates prior to 1958 were estimated from historical pumpage data found in various published 

reports. These data were less comprehensive and sometimes less accurate than post-1958 rates, particularly in 

regard to irrigation pumpage. Longer pumping periods were selected for the pre-1958 simulations. For the 

Houston-Galveston area, detailed records of public and industrial pumpage showed a significant shift in 

pumpage distributions after 1976. Thus a 4-yr pumping period was selected for 1973-76. A single-year pumping 

period was chosen for 1982 to quantify the flow system for that year. The locations and depths of the pumping 

wells were used to assign pumpages to 5-mi grid blocks for the appropriate model layers. As an example, the 

1980 grid-block distributions of pumping rates that are applicable for the period 1977-82 are shown in figures 29- 

37. The pumping periods for the model and average pumping rates for the study area are summarized as 

follows:

Average PumDine Rate

Pumping

period

1

2

3

4

5

6

7

8

9

10

Time

interval

1910

1911-37

1938-47

1948-57

1958-62

1963-67

1968-72

1973-76

1977-81

1982

(Million

ft3/d)

0

34

62

122

156

189

221

222

231

231

(Million

gal/d)

0

254

464

913

1,167

1,414

1,653

1,661

1,728

1,728

A complete description and listing of pumpage data by State, county, model layer, and 5-mi grid block are given 

in Mesko and others (1990) for the GC RASA study.

During the calibration process, simulated heads are matched to measured heads. Two forms of 

measured head data were compiled for calibration purposes: (1) Potentiometric-surface maps in four intensively 

pumped areas (areas 1,3, 4, and 5 in fig. 41) for 1982, the final year of the calibration period, and (2) 

hydrographs from 39 wells in six intensively pumped areas (fig. 41) that show water-level changes with time. 

Water-level data were obtained from the files of the Texas Water Development Board and Texas Water 

Commission (formerly the Texas Department of Water Resources) and the US. Geological Survey, and from 

published reports and maps.

The water levels that were selected to construct the 1982 potentiometric-surface maps generally are 

averages of the measurements in the wells for the time period beginning in June 1981 and ending in June 1983. 

Only single measurements that were made in the spring of 1982 were used for many wells; these wells provided 

supplementary data in areas where more detailed measurements were sparse. The water-level data were 

plotted, and potentiometric contours were drawn only through areas where a sufficient number of measurements 

existed. From the potentiometric contour maps, average head values for each 25-mi2 grid block were determined 

for statistical comparison with simulated heads.

37
The wells for which hydrographs were constructed were selected on the following basis: (1) Even 

coverage of the major producing zones in the intensively pumped areas, (2) even distribution within the cones of 

depression, and (3) long-term record.

Initial estimates of storage coefficient values for aquifers and permeable zones were discussed in the 

earlier section "Storage Coefficient". The release of water by inelastic compaction of fine-grained deposits in 

permeable zones A, B, and C comprises a large percentage of total water released from storage during the 

transient simulations. This release of water also causes land-surface subsidence which was briefly discussed 

earlier. A digital model code incorporated from Leake and Prudic (1989) provides for the release of water by 

inelastic compaction of fine-grained deposits by converting from an elastic to an inelastic specific storage. This is 

done for the clay portion of a permeable zone when the head in a grid block declines below the critical head. 

The critical head is defined as the head that coincides with the maximum effective stress to which the deposits 

had previously been subjected.

If the computed head in a grid block recovers, the storage coefficient again becomes the elastic value, 

and the previous minimum head becomes the new critical head. If the head should decline below the new 

critical head, the storage coefficient again becomes the inelastic value, and so on. Simulated land-surface 

subsidence is the product of head decline below the critical head in each time step multiplied by the inelastic 

storage coefficient. See Leake and Prudic (1989) for a complete discussion and documentation of the landsubsidence simulation code, with qualifying assumptions and limitations.

Carr and others (1985, p. 45) concluded from a model calibration in the Houston area that a 

preconsolidation stress of 70 ft approximates the maximum effective stress to which deposits have been subjected 

prior to ground-water development This means that 70 ft of head decline (from predevelopment starting heads) 

must occur at a model grid block before the first model conversion to an inelastic storage coefficient occurs. A 

critical head of 70 ft was adopted for the Texas GC RASA model.

Carr and others (1985, p. 35) related subsidence of the land surface, clay thickness, and decrease in 

artesian pressure for 1943-73 to derive inelastic storage coefficient values of the clay beds in the Houston area. 

In their computations, specific unit-compaction values are derived. These are an approximation of specific 

storage if the resulting compaction approximates the ultimate compaction from an applied stress. Mean specific 

unit-compaction values were 1.0 x 10 ft"1 for the Chicot aquifer and 1.8 x 10"5 ft"1 for the Evangeline aquifer. In 

an earlier study in the Houston area, Meyer and Carr (1979, p. 13) calculated a mean specific unit-compaction 

value of 8.7 x 10"5 ft"1 for the Chicot aquifer and 15 x 10"5 ft-1 for the Evangeline aquifer. These values were used 

as guidelines for initial estimates of inelastic storage coefficient for the clay intervals of permeable zones A, B, 

and C. (See table 1 for the relationship between the Chicot and Evangeline aquifers and permeable zones A, B, 

andC.)

Calibration Procedure and Results

The transient model was calibrated by adjusting horizontal and vertical hydraulic conductivity and 

elastic and inelastic storage coefficients until: (1) measured potentiometric surfaces and hydrographs in 

intensively pumped areas were reasonably matched by simulated heads; and (2) the cumulative measured landsurface subsidence in the Houston-Galveston area from predevelopment to 1973 was reasonably matched by 

simulated land subsidence. Calibration was aided by applying the results of a parameter-estimation model (L.K. 

Kuiper, US. Geological Survey, written commun., 1987), which automatically adjusts values of model variables 

so that the residual errors are minimized.

The Houston-Galveston area is shown as area 1 in figure 41. Simulated and measured 1982 

potentiometric surfaces of permeable zones A, B, and C in the Houston-Galveston area are shown in figures 79, 

80, and 81, respectively. The best fit of the simulated to the measured surfaces is for permeable zone B. The 

simulated potentiometric surface of permeable zone A is generally higher than the measured surface, while the 

simulated surface of permeable zone C is lower than the measured surface in the center of the cone of 

depression. Statistically, the absolute means of the residuals are 34 ft for permeable zone A, 25 ft for permeable 

zone B (includes residuals in Kingsville area), and 35 ft for permeable zone C (includes residuals in the Evadale 

area) (table 9).

38
Table 9.-Summary of simulated and measured 1982 altitudes ofpotentiometric surfaces

Total grid Absolute

Aquifer or blocks with Mean of Minimum Maximum Standard mean of

permeable measured residuals residual residual deviation residuals

zone heads (feet) (feet) (feet) (feet) (feet)

Permeable 121 27 -26 108 35 34 

zone A

Permeable 192 9 -96 72 29 25 

zone B

Permeable 89 1 -117 91 42 35 

zone C

Lower 216 17 -75 82 30 30

Claiborne-upper

Wilcox aquifer

38a
Hydrographs of water levels in wells 1, 2, 9, and 11 (see fig. 41) open to permeable zone A in the 

Houston-Galveston area are shown in figure 82. Wells 1 and 2 are on the northwestern rim of the 1982 cone of 

depression, well 11 is on the southern rim, and well 9 is near the center of the cone. Residual errors for the 

water levels are computed as the difference between simulated and measured where both exist at the end of a 

pumping period. The absolute means of the water-level residuals for wells 1,2,9, and 11 are 7,9,36, and 40 ft, 

respectively (table 10).

Hydrographs of water levels in wells 4, 7, 8,12, and 10 (see fig. 41) open to permeable zone B in the 

Houston-Galveston area are shown in figures 83 and 84. Wells 4,7, and 8 are near the center of the 1982 cone 

of depression, well 10 is on the eastern rim, and well 12 is on the southeastern rim. The absolute means of the 

water-level residuals for wells 4,7,8,12, and 10 are 22,23,55,52, and 73 ft, respectively (table 10).

Hydrographs of water levels in wells 3,5, and 6 (see fig. 41) open to permeable zone C in the HoustonGalveston area are shown in figure 84. The wells are in the steep part of the 1982 cone of depression and are 

fairly well distributed about its center. The absolute means of the water-level residuals for wells 3,5, and 6 are 

49,36, and 63 ft, respectively (table 10).

Hydrographs of water levels in wells 13,14, and 15 open to permeable zone A in Jackson and Wharton 

Counties are shown in figure 85. All three wells are in the proximity of intense pumpage from permeable zone 

A for mainly rice irrigation; however, drawdowns are small in comparison to the Houston area. The absolute 

means of the water-level residuals for wells 13,14, and 15 are 6,9, and 6 ft, respectively (table 10).

The Evadale-Beaumont area is shown as area 3 in figure 41. Pumpage in the city of Evadale's well field 

(at the Jasper-Hardin County line) is from zones B and C. The simulated and measured 1982 potentiometric 

surfaces of permeable zone C in the well field area are shown in figure 81. The two surfaces are reasonably well 

matched. A water-level hydrograph of well 16 (see fig. 41) open to permeable zone C and located near the 

center of the 1982 cone of depression is shown in figure 86. The absolute mean of the water-level residuals for 

well 16 is 34 ft (table 10).

A water-level hydrograph of well 17 (see fig. 41), which is open to permeable zone B and located just 

north of the city of Beaumont's well field at the Jefferson-Hardin County line, is shown in figure 86. Pumpage in 

the well field is from permeable zone B. The absolute mean of the water-level residuals for well 17 is 13 ft (table 

10).

The Kingsville area is shown as area 4 in figure 41. Pumpage in the city of Kingsville's well field in 

Kleberg County is from permeable zone B. A distinctive feature of the simulated and measured 1982 

potentiometric surfaces shown in figure 87 is the shift of the simulated cone of depression toward the east This 

was the result of having to shift pumpage, which was located between grid blocks, to the bordering eastern grid 

block. Water-level hydrographs of wells 18,19, 20, and 21 open to permeable zone B are shown in figure 88. 

Wells 18 and 19 are on the western rim of the 1982 cone of depression and nearer to the center than wells 19 and 

20, which are on the eastern rim. The absolute means of the water-level residuals for wells 18,19,20, and 21 are 

55,42,17, and 22 ft, respectively (table 10).

The Winter Garden area is shown as area 5 in figure 41. Pumpage is mostly from the lower Claiborneupper Wilcox aquifer. The 1982 simulated and measured potentiometric surfaces of the lower Claiborne-upper 

Wilcox aquifer are shown in figure 89. The absolute mean of the water-level residuals for the aquifer in the 

Winter Garden area is 30 ft (table 9).

Water-level hydrographs of 15 wells open to the lower Claiborne-upper Wilcox aquifer in the Winter 

Garden area are shown in figures 90-93. Wells 23 and 26 (fig. 90), well 29 (fig. 91), and wells 25 and 32 (fig. 92) 

are nearest the center of the huge cone of depression. The remaining wells are located on the flanks of the cone 

in all directions from the center. Absolute means of the water-level residuals for the wells range from 8 ft for 

well 24 to 83 ft for well 34 (table 10).

39
Table W. Summary of simulated and measured water levels in

wells shown in figure 41

Well 

number

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

Absolute 

Aquifer or mean of 

permeable residuals 

zone (feet)

Permeable 7 

zone A

Permeable 9 

zone A

Permeable 49 

zone C

Permeable 22 

zone B

Permeable 36 

zone C

Permeable 63 

zone C

Permeable 23 

zone B

Permeable 55 

zone B

Permeable 36 

zone A

Permeable 73 

zone B

Permeable 40 

zone A

Permeable 52 

zone B

Permeable 6 

zone A

Permeable 9 

zone A

Permeable 6 

zone A

Permeable 34 

zone C

Permeable 13 

zone B

Permeable 55 

zone B

Permeable 42 

zone B

Permeable 17 

zone B

Absolute 

Aquifer or mean of 

Well permeable residuals 

number zone (feet)

21 Permeable 

zone B

22 Lower Claiborneupper Wilcox aquifer

23 Lower Claiborneupper Wilcox aquifer

24 Lower Claiborneupper Wilcox aquifer

25 Lower Claiborneupper Wilcox aquifer

26 Lower Claiborneupper Wilcox aquifer

27 Lower Claiborneupper Wilcox aquifer

28 Lower Claiborneupper Wilcox aquifer

29 Lower Claiborneupper Wilcox aquifer

30 Lower Claiborneupper Wilcox aquifer

31 Lower Claiborneupper Wilcox aquifer

32 Lower Claiborneupper Wilcox aquifer

33 Lower Claiborneupper Wilcox aquifer

34 Lower Claiborne 

upper Wilcox aquifer

35 Lower Claiborneupper Wilcox aquifer

36 Lower Claiborneupper Wilcox aquifer

37 Lower Claiborneupper Wilcox aquifer

38 Lower Claiborneupper Wilcox aquifer

39 Lower Claiborneupper Wilcox aquifer

22

57

53

8

61

54

10

26

65

30

9

79

36

83

37

37

53

91

87

39a
The Lufkin-Nacogdoches area is shown as area 6 in figure 41. A steep cone of depression has 

developed on the potentiometric surface of the lower Claiborne-upper Wilcox aquifer as a result of intense 

pumpage centered between Angelina and Nacogdoches Counties. Data do not exist to construct an accurate 

post-development potentiometric surface. Hydrographs of water-levels in wells 37,38, and 39 open to the lower 

Claiborne-upper Wilcox aquifer in the Lufkin-Nacogdoches area are shown in figure 94. Wells 37 and 38 are 

located east of and nearest the pumping center; well 39 is located southeast of the concentrated pumpage. The 

absolute means of the water-level residuals for wells 37,38, and 39 are 53,91, and 87 ft, respectively (table 10). 

Simulated heads are much higher then measured heads in the three wells near the center of withdrawal

Simulated and measured cumulative land-surface subsidence in the Houston-Galveston area from 

predevelopment to 1973 is shown in figure 95. The simulated subsidence tends to be somewhat less than 

measured values in the center of greatest subsidence, and somewhat greater in far western Harris and 

northeastern Fort Bend Counties. The absolute mean of the subsidence residuals for the 196 grid blocks is 0.6 

ft

Calibrated values of horizontal and vertical hydraulic conductivity and transmissivity are presented in 

figures 7 through 16 and in tables 3 and 4. A summary of calibrated elastic storage coefficient values is 

presented in table 5. Calibrated inelastic specific storage values for fine-grained deposits in permeable zones A, 

B, and C in the Houston-Galveston area are 85 x 10'5 ft'1,8.0 x 10'5 ft'1, and 8.0 x 10"6 ft'1, respectively.

The model calibration is sufficiently accurate for its intended purpose-to provide estimates of aquifer 

properties and to identify in a general way the sources and quantities of flow in the aquifer systems. Practical 

considerations of objectives of the model study, scale of the system, and computer-cost limitations have 

determined important factors such as the number of model layers and grid-block size. Some of the differences 

between simulated and measured heads that were just described may seem large, on the order of a few tens of 

feet A listing of some important sources of error in model calibration and resulting simulated heads and flow 

rates is as follows:

1. There is inherent difficulty in estimating values for a set of model variables that minimize residual errors in 

head and land subsidence in a complex, interrelated system of numerous aquifers, permeable zones, and 

confining units.

2. The physical system is overgeneralized by the restricted number of model layers, particularly for the coastal 

lowlands aquifer system where there is a large amount of heterogeneity. Additional layers would 

improve model accuracy in areas such as Houston, where the vertical distributions of numerous 

pumpage and head data are reasonably well known. A related source of error is that the model 

simulations assume that pumping and observation wells are open to the full length of the aquifer or 

model layer-generally, this is not true. Thus, simulated heads can only be approximations of measured 

heads.

3. In general, the accuracy of simulation models decreases with increasing grid-block size. The large grid-block 

size, 25 mi2, may lead to overgeneralization of the input data and poor resolution of model results in 

some areas. For example, in the Houston area pumpage and head data are of sufficient density to 

warrant smaller grid spacing. Another example is Khigsville, where significant error was introduced 

because the city's well field lies almost exactly between the centers of the large grid blocks.

4. The accuracy of simulated development heads and drawdowns is dependent upon correct predevelopment 

starting heads. Simulated starting heads are subject to considerable error in some areas.

5. The model must simulate average conditions over long time periods (generally of 5-yr duration after 1958). 

This is necessitated by long periods of unknown or poorly understood irrigation pumpage data, as well 

as variations in recharge.

6. A considerable portion of modeled recharge rates in some areas may consist of return flow from irrigation 

pumpage to the ground-water system. Such rates of return flow generally are unknown or poorly 

understood.

7. It is uncertain whether or not there is a long-term net dewatering of shallow sands in the eastern part of the 

study area, where precipitation is more abundant. Such knowledge may be important in evaluating 

modeled estimates of the amount of ground-water pumpage derived from recharge and from releases 

from storage.

40
8. Simulation of land-surface subsidence is subject to the following additional sources of error (Prudic and 

Williamson, 1984): (a) The critical head in the clay portion of a permeable zone is assumed to be equal 

to the head in the sand deposits. However, time is needed for a head change to propagate through the 

clay deposits. Ignoring the time lag affects the distribution and amount of the simulated subsidence, 

(b) Water is assumed to be released from the inelastic compaction of clays instantaneously with a head 

decline below the critical head. There may be a lag time of several years between observed subsidence 

and a head change in coarse-grained deposits as the head change gradually propagates through the finegrained deposits, (c) The inelastic specific storage is assumed to be constant. However, lab tests 

indicate that the amount of water released from inelastic compaction is a function of applied stress. In 

addition, the vertical hydraulic conductivity of the compacting deposits, treated as a constant in the 

model, should theoretically decrease with time. Most of the errors associated with item 8 tend to be 

minimized because of the large time periods for averaging pumpages in the model simulations.

Insight into the relative amount of error in simulated heads and land-surface subsidence resulting from 

incorrect estimates of aquifer and confining-unit properties can be gained by analyzing the sensitivity of the 

model calibration to changes in selected model variables.

Sensitivity Analysis

Ten transient model simulations were made in order to test the sensitivity of the model to changes in 

the calibrated values of horizontal and vertical hydraulic conductivity, water density, storage coefficient, and 

initial critical head (for land-surface subsidence). The changes for the 10 model simulations are summarized in 

the following table:

Model 

simulation Property change

1 Horizontal hydraulic conductivity (Kh) of all aquifers and permeable zones = calibrated 

Khxl5

2 Horizontal hydraulic conductivity (Kh) of all aquifers and permeable zones = calibrated 

Khx05

3 Vertical hydraulic conductivity (Kv) of all model layers = calibrated Kv x 15

4 Vertical hydraulic conductivity (Kv) of all model layers = calibrated Kv x 05

5 Water density (DEN) = 1.000 g/cm3 in all model layers

6 DEN = calibrated DEN + 0.010 g/cm3 for grid blocks in all model layers where DEN is 

greater than 1.002 g/cm3

7 Storage coefficient (S) of all aquifers and permeable zones = calibrated S x 15

8 Storage coefficient (S) of all aquifers and permeable zones = calibrated S x 05

9 Initial critical head (D) for conversion to inelastic storage coefficient = calibrated D x 15

10 Initial critical head (D) for conversion to inelastic storage coefficient = calibrated D x 05

Each change was uniform over the modeled area with the exceptions noted above. When the value of each 

property was changed for a model simulation, the values of all other properties remained unchanged from their 

calibrated values. Because recharge and discharge are simulated by a head-dependent flux boundary, these 

values are allowed to change with any change in head in the sensitivity simulations.

41
The sensitivity simulations are evaluated by: (1) Showing graphically the change from 1982 calibrated 

heads in permeable zones A, B, and C along row 43 of the model grid (fig. 77), and in the lower Claiborne-upper 

Wilcox aquifer along row 91; (2) statistically comparing the new residual errors for 1982 simulated and measured 

potentiometric surfaces with calibration residuals; (3) statistically comparing the new residual errors for 

simulated and measured predevelopment to 1973 land-surface subsidence with calibration residuals; and (4) 

comparing graphically and statistically simulated and measured hydrographs for selected wells in the Houston 

and Winter Garden areas.

Row 43 was selected because it goes approximately through the centers of the cones of depression in 

permeable zones A, B, and C in the Houston-Galveston area. Row 91 goes approximately through the center of 

the cone of depression in the lower Claiborne-upper Wilcox aquifer in the Winter Garden area.

The horizontal hydraulic conductivity of the aquifers and permeable zones was increased by 50 percent 

for the first sensitivity simulation. The changes in 1982 heads in intensively pumped units along the two model 

rows are shown in figure 96. Heads are greater than calibrated heads within the cones of depression developed 

in permeable zones A, B, and C in the Houston-Galveston area, and in the lower Claiborne-upper Wilcox 

aquifer in the Winter Garden area. For each unit, the peak departure from calibrated heads occurs where the 

cone of depression is steepest Peak departures range from 20 ft for permeable zone A to 150 ft for permeable 

zone C. For permeable zones A, B, and C, the departure of heads from calibrated heads is almost negligible 

beyond the coastline (beyond about column 50).

Statistical analyses of the residual errors for 1982 simulated and measured potentiometric surfaces 

resulting from the increased horizontal hydraulic conductivity are shown in table 11. Absolute means of the 

residuals increased from 34 ft (calibrated value) to 41 ft for permeable zone A, from 25 to 42 ft for permeable 

zone B, from 35 to 54 ft for permeable zone C, and from 30 to 56 ft for the lower Claiborne-upper Wilcox 

aquifer.

The effect of increased conductivity on land-surface subsidence in the Houston-Galveston area is shown 

statistically in table 12. The absolute mean of the residual errors for simulated and measured predevelopment to 

1973 land-surface subsidence increased from a calibrated value of 0.6 ft to 0.8 ft

A 50-percent decrease in horizontal hydraulic conductivity results in head departures that are nearly 

mirror images of those shown for the 50-percent increase (fig. 96). However, the departures are larger, with 

peak departures ranging from -37 ft for permeable zone A to -350 ft for permeable zone C. Absolute means of 

the 1982 head residuals are 28 ft for permeable zone A, 54 ft for permeable zone B, 87 ft for permeable zone C, 

and 74 ft for the lower Claiborne-upper Wilcox aquifer (table 11). The residuals for permeable zone A are an 

improvement over the calibration residuals. The reduced horizontal hydraulic conductivity causes additional 

drawdown that is generally needed in the Houston-Galveston area for an improved calibration. However, 

statistical data for the other units shown in table 11 indicate that the reduced hydraulic conductivity resulted in 

much poorer matches of simulated and measured heads. The absolute mean of the land-surface subsidence 

residuals is 0.9 ft (table 12).

For the third model sensitivity simulation, the vertical hydraulic conductivity of all model layers was 

increased by 50 percent. Generally, the increase had the same effect as the increase in horizontal hydraulic 

conductivity-to raise the heads above the calibrated heads (fig. 97). Peak departures from calibrated heads are 

much smaller, ranging from 11 ft for permeable zone A to 30 ft for the lower Claiborne-upper Wilcox aquifer. 

Absolute means of the 1982 head residuals are 37 ft for permeable zone A, 25 ft for permeable zone B, 35 ft for 

permeable zone C, and 39 ft for the lower Claiborne-upper Wilcox aquifer (table 11). The absolute mean of the 

land-surface subsidence residuals is 0.7 ft (table 12).

A 50-percent decrease in vertical hydraulic conductivity results in head departures that are nearly mirror 

images of those shown for the 50-percent increase (fig. 97). As for the case with horizontal conductivity, the 

departures are larger, with peak departures ranging from -25 ft for permeable zone A to -50 ft for the lower 

Claiborne-upper Wilcox aquifer. For permeable zone C, there is a rise in heads of about 10 to 15 ft extending 

from column 43 to the downdip limit

42
Table II. Summary of caubradon residual errors for 1982 heads and 

those resulting from changes in model variables

Grid 

blocks 

Aquifer with 

or mea- Change in Mean of Minimum 

permeable sured model residuals residual 

zone heads variable (feet) (feet)

Permeable 121

zone A

Permeable 192

zone B

Permeable 89

zone C

Lower 216

Claiborneupper

Vilcox

aquifer

CALIBRATION

1 /

1.5 X KH's ^

0.5 X KH's

1.5 X KV's *=/

0.5 X KV's

densities = 1.0

densities >1.002

= +0.01

1.5 X S ^

0.5 X S

CALIBRATION

1.5 X KH's

0.5 X KH's

1.5 X KV's

0.5 X KV's

densities = 1.0

densities >1.002

= +0.01

1.5 X S

0.5 X S

CALIBRATION

1.5 X KH's

0.5 X KH's

1.5 X KV's

0.5 X KV's

densities = 1.0

densities >1.002

= +0.01

1.5 X S

0.5 X S

CALIBRATION

1.5 X KH's

0.5 X KH's

1.5 X KV's

0.5 X KV's

densities = 1.0

densities >1.002

= +0.01

1.5 X S

0.5 X S

27

34

7

34

5

24

24

29

14

9

36

-48

12

-4

6

5

24

-24

1

40

-84

7

-14

-4

-1

20

-36

17

52

-66

36

-14

14

19

38

-20

-26

-32

-69

-25

-69

-39

-38

-35

-46

-96

-63

-405

-94

-125

-94

-96

-82

-147

-117

-68

-454

-109

-125

-124

-115

-68

-190

-75

-89

-235

-50

-116

-75

-74

-55

-114

Maximum 

residual 

(feet)

108

102

87

104

77

95

95

101

84

72

105

38

78

62

73

72

82

69

91

137

28

90

96

116

77

117

44

82

114

90

85

78

81

83

128

46

Standard 

deviation 

(feet)

35

39

35

35

39

36

35

37

34

29

33

64

29

38

32

31

32

39

42

54

108

41

46

44

41

45

51

30

38

61

29

35

28

31

33

30

Absolute 

mean of 

residuals 

(feet)

34

41

28

37

35

34

34

37

31

25

42

54

25

30

26

25

34

36

35

54

87

35

39

35

34

38

45

30

56

74

39

30

26

30

42

27

i/ 

3/

KH = horizontal hydraulic conductivity.

KV = vertical hydraulic conductivity.

S = storage coefficient or specific yield.

A2a
Table 12. Summary of calibration residual errors for land-surface subsidence and those

resultingfrom changes in model variables

Grid blocks

with

Change in model measured

variable subsidence

CALIBRATION 196

1.5 X KH i/

0.5 X KH

1.5 X KV ^/

0.5 X KV

density = 1.0

density >1.002 =

density + 0.01

1.5 X S 5/

0.5 X S

.5 X D 4/ = 105 feet

.5 X D =35 feet

-* KH = horizontal hydraulic conductivity.

21 

-1 KV = vertical hydraulic conductivity.

3/ 

-y S = storage coefficient.

4/

 ' H is hi»flH Hf*r1in»» that must nrrnr hRfnnp mr»H*»l

Mean of

residuals

(feet)

-0.2

-.6

.4

-.4

.2

-.2

-.2

-.02

-.5

-.5

.3

rnnvprts tn in*»1ncti

Minimum

residual

(feet)

-2.5

-3.7

-1.2

-2.8

-2.0

-2.5

-2.5

-1.9

-3.9

-3.2

-1.9

if stnrao«> vn1ii*»

Maximum

residual

(feet)

2.1

1.6

7.4

2.0

3.2

2.4

2.4

4.5

1.3

1.8

3.1

Standard

deviation

(feet)

0.7

.8

1.3

.7

.9

.8

.8

1.0

.8

.7

.9

Absolute

mean of

residuals

(feet)

0.6

.8

.9

.7

.7

.6

.6

.7

.7

.7

.7

42b
Absolute means of the potentiometric-surface residuals are 35 ft for permeable zone A, 30 ft for 

permeable zone B, 39 ft for permeable zone C, and 30 ft for the lower Claiborne-upper Wilcox aquifer (table 

11). The absolute mean of the land-surface subsidence residuals is 0.7 ft (table 12).

For the fifth model sensitivity simulation, the density of the water in all model layers was given a 

uniform value equal to 1.000 g/cm3. For permeable zones A, B, and C, the changed density produced essentially 

no change from the calibrated heads where the units originally contained fresh to slightly saline water (dissolvedsolids concentration less than about 3,000 mg/L) (fig. 98). Farther downdip in the three zones, the heads 

departed from the calibrated heads in an upward direction, with peak departures ranging from 15 ft for 

permeable zone A to 240 ft for permeable zone C. For the lower Claiborne-upper Wilcox aquifer along row 91, 

heads departed from calibrated heads in a downward direction, with a peak departure of -43 ft (fig. 98).

Absolute means of the 1982 potentiometric-surface residuals were nearly identical to the calibrated 

values for permeable zones A and B, and C (table 11). The absolute mean for the lower Claiborne-upper 

Wilcox residuals is 26 ft, an improvement over the calibrated value of 30 ft because of the additional drawdown 

downdip in the Winter Garden area. The statistical data for the land-surface subsidence residuals are nearly the 

same as for the calibrated values (table 12).

For the next model simulation, the water density in all model layers was increased by 0.010 g/cm3 for 

those grid blocks where the density was greater than 1.002 g/cm3. The changed density produced essentially no 

change from the calibrated heads where the units originally contained fresh to slightly saline water (fig. 98). For 

downdip blocks in zones A, B, and C, the heads were a few feet lower than calibrated heads. For the extreme 

downdip blocks in the lower Claiborne-upper Wilcox aquifer, the heads were a few feet higher. Statistical data 

for the potentiometric-surface and land-surface subsidence residuals were nearly identical to the calibrated 

values (tables 11 and 12).

The seventh model sensitivity simulation consisted of increasing the storage coefficient of all aquifers 

and permeable zones by 50 percent The increase tended to raise the heads above the 1982 calibrated heads for 

the inland parts of rows 43 and 91 (fig. 99). Peak departures from calibrated heads range from 7 ft for 

permeable zone A to 42 ft for permeable zone C.

Absolute means of the 1982 potentiometric-surface residuals are 37,34,38, and 42 ft for permeable 

zones A, B, C, and the lower Claiborne-upper Wilcox aquifer, respectively (table 11). The absolute mean of the 

land-surface subsidence residuals is 0.7 ft (table 12).

A 50-percent decrease in the storage coefficient had the opposite effect of the 50-percent increase. The 

heads are lower than the 1982 calibrated heads (fig. 99), with peak departures ranging from -17 ft for permeable 

zone A to -75 ft for permeable zone C. The departures are larger for the decrease in storage coefficient 

compared to the increase.

The effect of the decreased storage coefficient on 1982 potentiometric-surface residuals produced mixed 

results. For permeable zone A and the lower Claiborne-upper Wilcox aquifer, the statistical values of simulated 

to measured heads are slightly better than the calibration values, while the residuals for zones B and C are 

considerably worse than calibrated values (table 11). The absolute mean of the land-surface subsidence 

residuals is 0.7 ft (table 12).

An additional test of the sensitivity of the model to the change in storage coefficient consists of 

comparing the new drawdown distributions over time to calibrated values and to measured values. This was 

done at five observation wells located near the centers of large cones of depressions. Three wells in the Houston 

area are open to permeable zones A, B, and C (fig. 100). Two wells in the Winter Garden area are open to the 

lower Claiborne-upper Wilcox aquifer (fig. 101).

Simulated water levels for the three model simulations (calibration, 50-percent increase and 50-percent 

decrease in storage coefficient) are compared to measured water levels in the five wells at the end of each time 

step (where measured water levels exist). The results, in terms of absolute means of the residuals, are as 

follows:

43
Well no.

(see figs.

41, 100,

and 101)

9

7

3

23

29

Aquifer or

permeable

zone

Permeable zone A

Permeable zone B

Permeable zone C

Lower Claiborneupper Wilcox

Lower C la i borne -

upper Wilcox

Period

comparison

1957-82

1947-82

1947-82

1947-82

1957-82

Absolute

Calibration

36

23

49

53

65

mean of residuals (feet)

50-percent

increase

in storage

52

45

73

60

84

50-percent

decrease

in storage

19

28

23

40

33

For the five wells, the increase in storage coefficient produces residuals that are substantially larger than 

the calibration residuals. However, the decrease in storage coefficient produces residuals that are substantially 

better for four of the five wells. Only for well no. 7, open to permeable zone B in the Houston area, are the 

calibration residuals smaller. Although a smaller storage coefficient may seem indicated, at least for some areas 

in some layers, the following factors may suggest otherwise: (1) The specific storage estimate of 1.0 x 10"6 ft"1 is 

approaching a minimum value for confined clastic sediments; (2) the number of hydrographs (five) is a small 

sample considering the large areal extent of the major cones of depression in the study area; (3) the head as 

measured in a well may be an average over a smaller vertical thickness of aquifer than the thickness assigned to 

the model model block. Thus, to obtain a match of simulated and measured water levels, the storage coefficient 

may have to be adjusted downward to account for the lesser thickness open to the well; and (4) other factors that 

may contain considerable errors, such as estimates of starting heads and pumpage, exert a large influence on the 

configuration of the simulated hydrographs.

Final model sensitivity simulations were made to test the effect of raising and lowering the initial critical 

head on land-surface subsidence residuals. A 50-percent increase in initial critical head, from 70 to 105 ft, 

produces a rise in the absolute mean of the residuals from a calibrated value of 0.6 to 0.7 ft (table 12). A 50- 

percent reduction of the initial critical head, from 70 to 35 ft, produces the same absolute mean of the residuals 

as did the increase~0.7 ft Thus, the critical head does not seem sensitive to the simulation of land subsidence, 

but it may affect the simulation of drawdowns in the model.

To summarize the sensitivity analysis:

1. The sensitivity of the model calibration is tested by analyzing the impact of a changed model variable on 1982 

potentiometric-surface residuals, hydrograph residuals, and land-surface subsidence residuals.

2. The model is most sensitive and has the highest residuals when horizontal hydraulic conductivity is decreased 

by 50 percent. An exception is for permeable zone A, where a 50-percent decrease causes smaller 1982 

head residuals.

3. The model is moderately sensitive to 50-percent changes in vertical hydraulic conductivity and storage 

coefficient

4. The model is least sensitive to changes in water density.

44
ILLUSTRATIONS
EXPLANATION

MIDWAY CONFINING UNIT

TEXAS COASTAL UPLANDS AQUIFER SYSTEM «jjNK>a

MISSOURI'

MISSISSIPPI EMBAYMENT AQUIFER SYSTEM

VICKSBURG-JACKSON CONFINING UNIT 

COASTAL LOWLANDS AQUIFER SYSTEM

TEXAS GULF COAST STUDY 

AREA (ONSHORE PART) ARKANSAS

KENTUCKY

TENNESSEE

33° a

100 ZOO MILES

_J

100 200 KILOMETERS

Figure 1 . Relation of Texas Gulf Coast study area to onshore part of the Gulf 

Coast Regional Aquifer-System Analysis study area. (Modified from 

Grubb, 1984]

46
EXPLANATION 

REGIONAL 10-MILE AND SUBREGION 5-MiLE GRID BLOCKS

Texas

McNairy-Nacatoch

Mississippi 

embayment

Regional 10-mile 

grid

Mississippi River 

valley alluvium

^/r". Coastal lowlands o

^Sr ' Alabama. Florida.

r Louisiana, and

Bas» Iron U 3. Qeological Sur«»y \,A~ 

Scale 1:2.500.000 ' '"

Figure 2.--Relation of the Texas subregional modeled area to other subregional modeled areas and to the 

regional modeled area
EXPLANATION

__ OFFSHORE AREAS

systems 94

ARKANSAS

150 MILES 

J

150 KILOMETERS

Figure 3. Location of Texas Gulf Coast study area.

>48
-48-

EXPLANATION

LINE OF EQUAL MEAN ANNUAL 

PRECIPITATION-lnterval 2 and 4 inches

ISO MILES

100 150 KILOMETERS

Figure 4j. Mean annual precipitation in the Texas Gulf Coast study area. Based on National 

1 Oceanic and Atmospheric Administration records for the period 1951-80. (Modified 

from Texas Department of Water Resources, 1984, fig. 5).
EXPLANATION

MIDWAY CONFINING UNIT 

MIDDLE WILCOX AQUIFER

LOWER CLAIBORNE-UPPER WILCOX AQUIFER 

LOWER CLAIBORNE CONFINING UNIT 

MIDDLE CLAIBORNE AQUIFER 

MIDDLE CLAIBORNE CONFINING UNIT 

UPPER CLAIBORNE AQUIFER 

VICKSBURG-JACKSON CONFINING UNIT

LOWER MIOCENE-UPPER OLIGOCENE 

PERMEABLE ZONE

[ : | MIDDLE MIOCENE PERMEABLE ZONE

[N\j LOWER PLIOCENE-UPPER MIOCENE 

PERMEABLE ZONE

ARKANSAS

33*-

LOWER PLEISTOCENE-UPPER 

PLIOCENE PERMEABLE ZONE

HOLOCENE-UPPER PLEISTOCENE

OF

150 MILES

50 100 150 KILOMETERS

Figure 5 . Generalized outcrops of aquifers, permeable zones, and confining units.

50
\ ' 

I 4

10

EXPLANATIONHYDROGEOLOGIC UNITS 

! Permeable zone A

Permeable zone B

Permeable zone C

Zone D confining unit

Permeable zone D

Zone E confining unitPermeable zone E

Vicksburg- Jackson confining unit

Upper Claiborne aquifer

Middle Claiborne confining unitMiddle Claiborne aquifer

Lower Claiborne confining unitLower Claiborne-upper Wilcox aquifer

Middle Wilcox aquiferMidway confining unit

A'

VERTICAL SCALE GREATLY

8000

10,00012,000

Figure 6 .-Hydrogeologic section A-A'. Line of section shown on figure 5.
EXPLANATION

BOUNDARY OF SUBAREAS

MEAN HYDRAULIC CONDUCTIVITY, IN FEET 

PER DAY--From Prudic (1991). 

Number of values used in estimate 

shown in parentheses.

TEXAS COASTAL 

UPLANDS SUBA.REA 2

ARKANSAS

33*-

18 (23)

1 Q (99) Estimated from specific-capacity data

Estimated from aquifer-test analyses

MEAN HYYDRAULIC CONDUCTIVITY, IN FEET 

P -1 PER DAY, IN CALIBRATED DIGITAL MODEL

1 "" 

L --\J_ .--4

TEXAS COASTAL 

UPLANDS SUBAREA 1

TEXAS COASTAL 

LOWLANDS SUBAREA

TEXAS COASTAL 

LOWLANDS SUBAREA 3

150 MILES

100 150 KILOMETERS

Figure 7.--Field and simulated hydraulic conductivity of coastal 

uplands aquifers and coastal lowlands permeable zones.

52
systems

tec

stems j

5000

EXPLANATION

LINE OF EQUAL TRANSMISSIVITY Interval, 

In feet squared per day, Is variable

Hachures indicate closed areas 

of lesser transmissivity 3f_

,-^-J -"^ -,r, / -A

50 100 150 KILOMETERS

150 MILES 

J

Figure o .--Simulated transmissivity of permeable zone A.

53
5000

29*-

EXPLANATION

LINE OF EQUAL TRANSMISSIVITY Interval , 

1n feet squared per day, is variable

Hachures indicate closed areas 

of lesser transmissivity

-c'

T

' ) ? '

/ i i

/ V ' ^^V. ' '1 m"i?T\

~\i \ ^-^f i '

l V 1 '

i ^^v ' |J

^"-\1__ \

BUOWNSVILLE

ty 

O

0)

DO o

W

6^f F °

\

0

1 

0

\

J

50 100 15 

 , !__, H '

50 100 150 KILOMETERS

150 MILES

Figure . Simulated transmissivity of permeable zone B.

54
 . systems j

n

,-.J ARKANSAS

5000

EXPLANATION

LINE OF EQUAL TRANSMISSIVITY Interval, 

in feet squared per day, is variable

Hachures indicate closed areas 

of lesser transmissivity

150 MILES

I , L I H ' 

0 50 100 150 KILOMETERS

Figure \0 . Simulated transmissivity of permeable zone C.

55
systems j

I _ -%_ n»i i i. r^^ I

ARKANGA.

EXPLANATION

5000 LINE OF EQUAL TRANSMISSIVITY Interval, 

In foet squarrd DPr day.

Hachures indicate closed areas " 7 

of lesser transmissivity ,,-.

150 MILFS

50 100 150 KILOMETERS

Figure // .--Simulated transmlssivity of permeable zone D,

56
systems

ARKANSAS

5000

EXPLANATION

LINE OF EQUAL TRANSMISSIVITY Interval, 

1n feet squared per day, 1s variable

39'-

100 150 KILOMETERS

Figure 12. . Simulated transm1ss1v1ty of permeable zone E,

57
5000

ARKANSAS

EXPLANATION

LINE OF EQUAL TRANSMISSIVITY Interval, 

1n feet squared per day, 1s variable

50 100 150 KILOMETERS

Figure I 5 . Simulated transmisslvlty of the upper Claiborne aquifer.

58
» systems! \ ,~<-~ - ' "~

ARKANSAS

EXPLANATION

5000 LINE OF EQUAL TRANSMISSI VITY-- Interval , 

in feet squared per day, is variable

150 MILES

________________I

100 150 KILOMETERS

Figure /T Simulated transmissivity of the middle Claiborne aquifer,

59
5000

EXPLANATION

LINE OF EQUAL TRANSMISSIVITY Interval, £, 

1n feet squared per day, is variable g

ISO MILES

100 150 KILOMETERS

Figure / <J . Simulated transmissivity of the lower Claiborne-upper Wilcox aquifer.

60
systems I

5000

ARKANSAS

EXPLANATION

LINE OF EQUAL TRANSMISSIVITY Interval, . g 

in feet squared per day, is variable ^

c?

O ______ 

100 150 KILOMETERS

Figure /» . Simulated transmissivity of the middle Wilcox aquifer.

61
er. systems

; UK*"***'*'' 

NU ^_.^-| ARKANSAS

EXPLANATION

 500

less than 2 .000

-LINE OF EQUAL DISSOLVED-SOLIDS 

CONCENTRATION OF WATER IN 

PERMEABLE ZONE A, 1987-- 

Dissolved-solids concentration 

estimated from chemical analyses 

and depth-averaged geophysical 

well-log data. Interval, in 

milligrams per liter, is variable

150 MILES

____________ __________I

50 100 150 KILOMETERS

Figure IT. Estimated dlssolved-soUds concentration 1n water from permeable 

zone A. (Modified from Petti John and others, 1988.)

62
ARKANSAS

EXPLANATION

Dissolved-solids concentration less than 2,000 

milligrams per liter

500_ LINE OF EQUAL DISSOLVED-SOLIDS 

CONCENTRATION OF WATER IN 

PERMEABLE ZONE B, 1987 

Dissolved-solids concentration 

estimated from chemical analyses 

and depth-averaged geophysical 

well-log data. Interval, in 

milligrams per liter, is variable

I

150 MILES

____________ __________1

50 100 150 KILOMETERS

Figure 18 . Estimated dissolved-solids concentration in water from permeable 

zone B. (Modified from Petti John and others, 1988.)

63
EXPLANATION

Dissolved-solids concentration less than 2,000 

milligrams per liter

 LINE OF EQUAL DISSOLVED-SOLIDS 

CONCENTRATION OF WATER IN 

PERMEABLE ZONE C, 1987 

Dissolved-solids concentration 

estimated from chemical analyses 

and depth-averaged geophysical 

well-log data. Interval, in 

milligrams per liter, is variable O

ARKANSAS

1 J.,-.! -KT 

rr---J .^ ^<

0 50 100 If 

I , ^-n H ' 

0 50 100 150 KILOMETERS

I 50 MILES

Figure .--Estimated dissolved-solids concentration in water from permeable 

zone C. (Modified from Petti John and others, 1988.)
ARKANSAS

EXPLANATION

Dissolved-solids concentration less than 2 000 

milligrams per liter '

-500 OF EQUAL DISSOLVED-SOLIDS 

CONCENTRATION OF WATER IN 

PERMEABLE ZONE D, 1987-- 

Dissolved-solids concentration 

estimated from chemical analyses 

and depth-averaged geophysical 

well-log data. Interval, in 

milligrams per liter, is variable

-A- I

l"BROWNSVItLE

l l

1 

1 ,J 

1

ll

 I

Q) 

> DO 

TJ 

W

0

I .. ... 

'.1 

50 100 ISO MILES

I ... ....... ___! 1

50 100 150 KILOMETERS

Figure 20 . Estimated dissolved-solids concentration in water from permeable 

zone D. (Modified from Petti John and others, 1988.)

65
EXPLANATION

Dissolved-solids concentration less than 2,000 

milligrams per liter

500 LINE OF EQUAL DISSOLVED-SOLIDS 

CONCENTRATION OF WATER IN 

PERMEABLE ZONE E, 1987-- 

Dissolved-solids concentration 

estimated from chemical analyses 

and depth-averaged geophysical 

well-log data. Interval, in 

milligrams per liter, is variable

ITT.J' 

Shelf

-A

CO

I i

7/ /

-*c

,r3^O;/f-i/ ^

^/^/L Js.ooo-v

.s^ ^-^70.000 

r^ -^ w f ' .

xV'~l^T~J-^w» /

"~ |X

jt/^rr'-L/

IT7 r ,

.7. r si V\- y '! J -r ^

^ r\ , <y Vv) Vi -j «w

^\ :,

JJ^n-_a_ ____ I

1 BUOWMSVILLE

, \^'

of . 6*F

0 50 100 150 MILES

1 , « H '

0 50 100 150 KILOMETERS

Figure 11 . Estimated dissolved-solids concentration in water from permeable 

zone E. (Modified from Pettljohn and others, 1988.)

66
systems

ARKANSA

EXPLANATION

M Dissolved-solids concentration less than 2 000 

^ milligrams per liter

 LINE OF EQUAL DISSOLVED-SOLIDS 

CONCENTRATION OF WATER IN THE 

UPPER CLAIBORNE AQUIFER, 1987-- 

Dissolved-solids concentration 

estimated from chemical analyses 

and depth-averaged geophysical 

well-log data. Interval, in 

milligrams per liter, is variable

100

, I 

150 KILOMETERS

150 MILES

Figure 22. Estimated dissolved-solids concentration in water from the upper 

Claiborne aquifer. (Modified from Pettijohn and others, 1988.)

67
ARKANSAS

EXPLANATION

 6*

33TDissolved-solids concentration less than 2,000 

milligrams per liter

£00 LINE OF EQUAL DISSOLVED-SOLIDS 

CONCENTRATION OF WATER IN THE 

MIDDLE CLAIBORNE AQUIFER, 1987 

Dissolved-solids concentration 

estimated from chemical analyses 

and depth-averaged geophysical 

well-log data. Interval, in 

milligrams per liter, is variable

1SO MILES

100 150 KILOMETERS

Figure 23.--Estimated dissolved-solids concentration in water from the middle 

Claiborne aquifer. (Modified from Petti John and others, 1988.)

68
 systems

EXPLANATION

Dissolved-solids concentration less than 2,000 

milligrams per liter

 LINE OF EQUAL DISSOLVED-SOLIDS 

CONCENTRATION OF WATER IN THE 

LOWER CLAIBORNE-UPPER WILCOX 

AQUIFER, 1987--Dissolved-solids 

concentration estimated from 

chemical analysis and depthaveraged geophysical well-log 

data. Interval, in milligrams 

per liter, is variable

ARKANSAS

150 MILES

100 150 KILOMETERS

Figure 24---Estimated dlssolved-solids concentration 1n water from the lower 

Cla1borne-upper Wllcox aquifer. (Modified from Petti John and 

others, 1988.)

69
EXPLANATION

Dissolved-solids concentration less than 2,000 

milligrams per liter

500 LINE OF EQUAL DISSOLVED-SOLIDS 

CONCENTRATION OF WATER IN THE 

MIDDLE WILCOX AQUIFER, 1987-- 

Dissolved-solids concentration 

estimated from chemical analyses 

and depth-averaged geophysical 

well-log data. Interval, in V 

milligrams per liter, is variable

ARKANSAS

150 MILES

50 100 150 KILOMETERS

Figure 25 .--Estimated dissolved-solids concentration in water from the middle 

Wilcox aquifer. (Modified from Petti John and others, 1988.)

70
TEXAS GULF COAST 

AQUIFER SYSTEM

HYDROGEOLOGIC

Beaumont Clay Montgomery Fm. Bentley Fm. _, * 

Willis Sand

Lower Ptelstocene-upeer 

PSocsos depoettsl i;;

CONSTANT--HEAD LAYER 

CWATER TABLE)

Fleming __ _ Formation

Top of 

geopressured zone

Hortzontal aid 

vsrtcrf Sow"

Sandstone

"" Caddell Fm.

X

PREDOMINANTLY SAND 

PREDOMINANTLY CLAY MODEL LAYER NUMBER

Yegua Fm. ^ 

 > Cook Ml. Fm: 'No-Bow boundary I

SECTION OF CONCEPTUAL MODEL

IDEALIZED SECTION 

OF DIGITAL MODEL

Wills Point Fm. 

Kincaid Fm.

CORRELATION OF STRATIGRAPHIC 

AND HYDROGEOLOGIC UNITS

Figure2£.--Conceptual model of aquifer systems and generalized representation in the digital model
86*

EXPLANATION

SIMULATED RECHARGE AND 

DISCHARGE, ID INCHES PER YEAR

RECHARGE

ARKANSAS

1

2

&& 

*Z- £

4

5

2 to 3

I io 2

0 lo 1

0 to 1

f to Z

150 MILES 

J

0 50 100 150 KILOMETERS

Figure 2-7. Simulated predevelopment recharge and discharge In the outcrop areas of 

aquifers, permeable zones, and confining units.

72
EXPLANATION

AQUIFER OR PERMEABLE ZONE AND IDENTIFIER

j) Permeable zone Ay2} Permeable zone B(3) Permeable zone C(5) Permeable zone DQy Permeable zone E(^O Upper Claibome aquifer(M) Middle Claibome aquifer(M) Lower Claiborne-upper Wilcox aquifer($ Middle Wilcox aquiferZZ3 CONFINING UNIT

TOTAL RECHARGE OR DISCHARGE IN OUTCROP 

AREA~Includes flow Uirough superjaceni confining unii where ihe confining unil is exposed al the surface. Number 

i is flow rale, in million cubic feel per day

IS 

fr

1 '» Recharge 

Discharge

NET RECHARGE OR DISCHARGE IN OUTCROP AREAIncludes flow Uirough superjaceni confining unit where the 

. confinine unit is exposed at the.surface. Number | is flow 

L rale, in million cubic feel per day 

/4) Recliarge

A Discharge

TOTAL LEAKAGE THROUGH BOTTOM OP AQUIFERNumber is flow rale, in million cubic feel per day I (f

J Upward 

r Downward

NET LEAKAg^ THROUGH BOTrOM OP AQUIFER-- 

Number is flow rate, in million cubic feet per day

| Upward 

i Downward

-Z. NET LATERAL FLOW IN (+) OR OUT (-) OF STUDY 

AREA

U>

cor 1 MH

72. (30) ^

v|ST ANT-HEAD WATER-TABLE LAYER

2. 

l fr

",.t'[liv

| (14) 37

it 1 (2f f ' L=0

5 (1) - <f I '|- L=0 (

(?) i '^ ! \ =. -o (s) 

. r.. z. ..t....... L .... d-..,..... V

©

D

u

, lrr^^^ frf/ff rfrfrrmr

7 i T ° \_______l^o________^}\

3.

fO)

l c * '

3 i 1 1 i

f.f,/ f f3L-L

^ 1

L--i @

L=-l ©

Figure 28 . Simulated predevelopment vertical flow rates across hydrogeologic units In 

study area. 
WATER, OF VOLUME CUMULATIVE 

12 10 X FEET CUBIC IN 

to

-s

fD

CO

I

GO

->- o 

3 o 

c P» 

 > (f> 

pi <-t 

r+

n> o» 

a. ja 

3 O) 

T3 -S 

0>

(O CO 

fD << 

» CO 

cf

-s ro 

0) 3 

O CO 

o- i

0) CD 3 ro 

a. 

CL 

n> TJ

a>

o-s 

0) 

ta 

ro

n>

'2

 Pi

CO

O

c

MILLION IN RATE, PUMPING 

DAY PER FEET CUBIC 
EXPLANATION

Ground-water pumpage, in million 

gallons per day (Mgal/d) for blocks 

with 0.5 Mgal/d or more pumpage

ARKANSAS

o

D 

*

0

0.5 - 0.9 

1.0 - 4.9 

5.0 - 9.9 

10.0 - 24.9

150 MILES 

j

50 100 150 KILOMETERS

Figure 29. Estimated pumpage in 1980, by 25-square-raile grid block, for 

permeable zone A.

75
EXPLANATION

Ground-water pumpage, in million 

gallons per day (Mgal/d) for blocks 

with 0.5 Mgal/d or more pumpage

ARKANSAS

0 0.5 - 0.9

D 1.0 - 4.9

* 5.0 - 9.9

0 10.0 - 24.9

150 MILES

50 100 150 KILOMETERS

Figure 30. Estimated pumpage in 1980, by 25-square-mile grid block, for 

permeable zone B.

76
" : T systems 1

EXPLANATION

Ground-water pumpage, in million 

gallons per day (Mgal/d) for blocks 

with 0.5 Mgal/d or more pumpage

ARKANSAS

D

0.5 - 0.9 

1.0 - 4.9 

5.0 - 9.9 

10.0 - 24.9

150 MILES 

i

50 100 150 KILOMETERS

Figure 31. Estimated pumpage in 1980, by 25-square-mile grid block, for 

permeable zone C.

77
EXPLANATION

Ground-water pumpage, in million 

gallons per day (Mgal/d) for blocks 

with 0.5 Mgal/d or more pumpage

0 0.5 - 0.9 

n 1.0 - 4.9

ARKANSAS

100 150 KILOMETERS

Figure 32. Estimated pumpage in 1980, by 25-square-mile grid block, for 

permeable zone D.

78
EXPLANATION

Ground-water pumpage, in million *3 ~ 

gallons per day (Mgal/d) for blocks 

with 0.5 Mgal/d or more pumpage

0 0.5 - 0.9 

D 1.0 - 4.9

ARKANSAS

i -1 v --1

~~JF~T"

^T, ,-T^onO.ne*1

' X

\

-A

Shelf

r

J (

I

t

1

^riz~^

1 >

ft

\ I *\ IV^

-\T)(C\

Y\

X^o ^V^ '"_, I

^jBlJoWHSVILL

- ^

r 

>-,

r \

s

1

^J

S - i

E

f ^

° 6^uf

Q) W) o

W

0 50 100 1£

I i , i

0 50 100 150 KILOMETERS

150 MILES

Figure 33. Estimated pumpage in 1980, by 25-square-mile grid block, for 

permeable zone E.

79
EXPLANATION

Ground-water pumpage, in million 

gallons per day (Mgal/d) for blocks 

with 0.5 Mgal/d or more pumpage

0 0.5 - 0.9 

° 1.0 - 4.9

ARKANSAS

150 MILES

100 150 KILOMETERS

Figure 34. Estimated pumpage in 1980, by 25-square-mile grid block, for the 

upper Claiborne aquifer.

80
EXPLANATION

Ground-water pumpage, in million *'* 

gallons per day (Mgal/d) for blocks 

with 0.5 Mgal/d or more pumpage g

° 0.5 - 0.9

° 1.0 - 4.9

* 5.0 - 9.9

ARKANSAS

150 MILES

50 100 150 KILOMETERS

Figure 35.-Estimated pumpage in 1980, by 25-square-mile grid block, for the 

middle Claiborne aquifer.

81
EXPLANATION

Ground-water pumpage, in million 

gallons per day (Mgal/d) for blocks 

with 0.5 Mgal/d or more pumpage

0 0.5 - 0.9

° 1.0 - 4.9

* 5.0 - 9.9

0 10.0 - 24.9

ARKANSAS

150 MILES 

J

50 100 150 KILOMETERS

Figure 36. Estimated pumpage in 1980, by 25-square-mile grid block, for the 

lower Claiborne-upper Wilcox aquifer.

82
X

06* systems

EXPLANATION

Ground-water pumpage, in million 

gallons per day (Mgal/d) for blocks 

with 0.5 Mgal/d or more pumpage

° 0.5 - 0.9

° 1.0 - 4.9

* 5.0 - 9.9

a«*if®11

ARKANSAS

fo

\

\-y

Shelf

50 100 150 MILES

_I

50 100 150 KILOMETERS

Figure 37. Estimated pumpage in 1980, by 25-square-mile grid block, for the 

middle Wilcox aquifer.

83
EXPLANATION

SIMULATED RECHARGE 

IMSCIIAR6F, n-!

ARKANSAS

1

1

2

3

:. 4

5

6

7

8

5 to 6 

4 to S 

3 to A

2 fo 3 

1 10 ?_ 

0 to 1

0 lo | 1 

1 Jo ?. J

RECHAWG-E

DISCHARGE

50 100 |50 KILOMETERS

150 MILES 

J

Figure 3 o. Simulated recharge and discharge in the outcrop areas of aquifers, 

permeable zones, and confining units for 1982.

84
EXPLANATION

SIMULATED INCREASE IN RECHARGE OR 

bECREASE IN DISCHARGE, III UICIIEG l'C

,, , ItXAKKANAl

Hv ... ^ARKANSAS

93'-

1

2

3 .

4

5

6

7 ;

I.FSj THAN 0.5 

0.5 1o 1 

1 (o Z

2 to !> 

3 to 4 

4 to S 

5 lo 6

150 KILOMETERS

Figure 3 /. Change in simulated recharge and discharge in the outcrop areas of aquifers, 

permeable zones, and confining units, predevelopment to 1982.

85
IS

t

EXPLANATION

AQUIFER OR PERMEABLE ZONE AND IDENTIFIER 

Permeable zone A 

Permeable zone B Permeable zone C Permeable zone D 

Permeable zone E Upper Claibome aquifer 

Middle Claibome aquifer 

Lower Claibome-upper Wilcox aquifer 

Middle Wilcox aquifer

] CONFINING UNIT

TOTAL RECHARGE OR DISCHARGE IN OUTCROP 

AREA Includes flow llirough superjacent confining unit 

where the confining unit is exposed at the surface. Number 

i is flow rate, in million cubic feet per day

** Recharge 

Discharge

NET RECHARGE OR DISCHARGE IN OUTCROP AREAIncludes flow through superjacent confining unit where the 

. confining unit Is exposed at ihe.surface. Number is flow L rate, in million cubic feet per day 

/4) Recharge

X Discharge

TOTAL LEAKAGE THROUGH BOTTOM OP AQUIFERNumber is flow rate, in million cubic feet per day I U

| Upward 

V Downward

NET LEAKAGE THROUGH BOTTOM OP AQUIFERNumber is flow rate, in million cubic feet per day

* Upward 

« Downward ,,

L» -2. NET LATERAL FLOW IN (+) OR OUT (-) OP STUDY 

AREA

TOTAL WATER BALANCE Numbers are 

million cubic feet per day. Million gallons per day in 

parenthesis

Total pumpage (P) = 

Net lateral flow (L) = 

Total release of water fromstorage (S) = 

Net recharge from 

constant heads =

 231 (1,728) 

-5 (37)

57 (426) 

179 (1,339)

ooON

{'LTL

CONSTANT-I IEAD WAITER-TABLE LAYER

ft5) U , j.|.

1 1 1 * ' ,A it n W ( i .ill r.2 B ,.i. . . ,

t-

! f

1 f

do'

3 «

L=

13

0/5- L.= -I S= 1 V- - L= | 5=14 P*-£l (

-I S-13 P= -2.°! ©

^ ©

2)

t r / \ r~r

....... I l f I I l f ff

I 10 XQ '| -I i

P--IO

Figure . Simulated 1982 vertical flow rates across hydrogeo logic units in study area. 

iSum of flow rates may not exactly balance due to Independent round Ing.|
r\ »> I 4u?, pu

XPLANATION

Model subarea

.pumped area 

AjPrecipitation station 

Observation well

Figure4l .--Locations of observation wells and precipitation stations in selected 

pumped areas, and model subareas.
CO 

CO

EXPLANATION

PUBpage scale, in million gallons per day 

(Scale may vary according to county)

» Mean pumping rate (Hgal/day) 

Irrigation pumpage

Honirrigation punpage 

B» Year

KILOMETERS

WO B6S B70 WS 1980 BSS

Figure^2. .-Ground-water pumpage in selected counties in central part of study area, 1960-85.
CHAMBERS

JOHNSON SPACE

EXPLANATION

Observation well and number 

v_ _^ Area of intensive ground-water withdrawals _/

45 Public and industrial pumpage (in million gallons per day) 

83 Irrigation pumpage (in million gallons per day)

_/ From Gabrysch (1984a, p.4-6)

z&'oo'-r20 30 MILES

I I 1

I I I I I

0 10 2.0 30 40 RtlOMtTEKS

Figure43 . Location of subareas within the Houston-Galveston area (area 1) 

and average rates of pumping for 1979.

89
Decline in potentiometric surface, 

predevelopment to 1982, in feet 

decline

<50 (or insufficient data)

HORIZONTAL FLOW CUBIC FEET PER DAY 

I x\0 5 TO IX10*

n 10 20 30

Figure TT- Declineof potentiometric surface of permeable zone A, predevelopment to 1982, 

and simulated 1982 horizontal flow vectors, Houston-Galveston area.

90
Decline 1 " potentiomelric surface 

predevelopment to 198?, in feel 

decline

HORIZONTAL FLOW, IN CUBIC FEET PER 

Size of arrowhead Indicates range of flow, 

fenoth of shaft Indicates flow within stated range

0 \o 20 BO KILOMETERS

Figure4-S .- Declineof potentlometrlc surface of permeable zone B, predevelopment to 1982, 

and simulated 1982 horizontal flow direction and relative magnitude, 

Houston-Galveston area.

91
Decline in potentiometric surface 

predevelopment to 1982, in feet 

decline

HORIZONTAL FLOW, IN CUBIC FEET~PER DAY 

Size of arrowhead Indicates range of flow, 

length of shaft Indicates flow within stated range^

to 

1

I I

^o

\

30

vJ*'t -c^ ^- ?

&

Figure . --Decline of potentiometric surface of permeable zone C, predevelopment to 1982, 

and simulated 1982 horizontal flow direction and relative magnitude, 

Hoiistoh-Galveston area, and Evadale-Beaumont area.

92
Lu

a:

CO

Q

LU 

CO

LU

0

50

100

150

200

250

300

350

0

50

100

150

200

250

300

350

50

100

150

200

250

300

350

400

WELL NO. 9

-ii r t i i i i i i . , , , , r i

County:

State well number:uj-6s-24-2.0L 

Land surface datum: 

[ Well depth:

Aquifer: Permeable zone A

WETLL KJO. 7

 County: H/L/LJU-£

 State well number:U-i5-2.1-80S"

 Land surface datum: 67 UuL

Well depth: IjOlTfr^ 

Aquifer: Permeable zone B

WELL NO. 3

County:

State well number:Lj-6s-2.CH 1 o 

Land surface datum: BO 

Well depth: \,\BO

Aquifer: Permeable zone C

1930 36 40 46 60 66 60 66 70

Figure H7. Ground-water levels in Harris County. (See fig. 

location.)

76

for

80

-so

-o

--so

--100

--150

--200

- -250

-so

-o

--so

--loo

1-150 

1-200 

1-250 

1-300

1986

3

3

i i 

CO

CO

93
EXPLANATION

2.0~ LINE OF EQUAL LAND-SURFACE SUBSIDENCE 

Dashed where approximately located. Intervals 0.5 

and 1.0 foot _!/

From Can- anJ othai-S (1995", { ,'<3«t-e 30

0 1C 20 30 MILES

r . 1 t 1

0 10 ZO 10 40

Figure 48- Land-surface subsidence in the Houston-Gal veston area, predevelopment to 1973.
EXPLANATION

AQUIFER OR PERMEABLE ZONE AND IDENTIFIER

f^J Permeable zone A

(5) Permeable zone B

(3) Permeable zone C

(S) Perm eablc zone DQ) Permeable zone E

(*?) Upper Claibome aquifer

(u) Middle Claibome aquifer

(m Lower Claibome-upper Wilcox aquifer

(^ Middle Wilcox aquifer

v/;s > l CONFINING UNIT

TOTAL RECHARGE OR DISCHARGE IN OUTCROP 

AREA--Includes flow through superjacent confining unit 

where the confining unit is exp'osed at UK surface. Number 

i is flow rate, in million cubic feet per day

IS

t

Recharge 

Discharge

NET RECHARGE ORDISQIARGE IN OUTCROP AREAIncludes flow through superjacent confining unit where the 

. confining unit it exposed at thc.surfacc. Number is flow 

I rate, in million cubic feet per day 

14 ) Recharge

Discharge

TOTAL LEAKAGE THROUGH BOTTOM OP AQUIFERNumber is flow rale, in million cubic feet per day ( U

| Upward 

Downward

NET LEAKAGE THROUGH BOTTOM OP AQUIPER-- 

Number is flow rate, in million cubic feet per day

*

Upward 

Downward

- 2. NET LATERAL FLOW IN (+) OR OUT (-) OP STUD Y 

AREA

TOTAL WATER BALANCE Numbers are million cubic feet per day. Million gallons per day in parenthesisTotal pumpage (P) Net lateral flow (L) 

Total release of water from 

storage (S) 

Net recharge from 

constant heads

 102 

4

(763) 

(30)

29 (217) 

69 (516)

VO

CO

30 C«)

NSTANT-HEAD-WAtER-TABLE LAYER

0

^ , ll

0

^ ,cU, ? L=I s* i P=-3r©

A 1 I 1 41,1 s-\

 i 4 Li 05") <f 2U) (_= | 5=12. PS- 35" © rt (5) (|J ^^?i4- L= 1 S=- " P= -22. C?) 

, , , , ll r ^

.l

. i

I t I

I I I I r~r~l r ry i * f r r t J jy z f f r i f 7 j r i / r / j f t r. r for^r*^ L=O &f i >v-i

\~i r * r r i~& r j]s 7 V~f r * f J J * f J r rriij'riiiriei/ff 7~i ' ' ' ''

o P

I I i .1. !,

Figure 4? . Simulated 1902 vertical flow rates across hytlrogeo"logic units 1n moti^l sub&rea JE 

(f1g.4/ ) [Sum of flow rates may not exactly balance due to independent roundlng.]
WATER-LEVEL ALTITUDE,' DATUM IS SEA LEVEL

QN\n 133 j NI '13A31 HBJLVM S3HDNI NI 'NOIIViIdI03bd
EXPLANATION

AQUIFER OR PERMEABLE ZONE AND IDENTIFIER

f^ Permeable zone A^) Permeable zone B

(5) Permeable zone C

(S) Permeable zone D

(?) Pcrmeabl e zone E

(2) Upper Claibome aquifer

Qi) Middle Claibome aquifer

(Jf) Lower Claibome-upper Wilcox aquifer(§) Middle Wilcox aquifer

T7-\ CONFINING UNIT

TOTAL RECHARGE OR DISCHARGE IN OUTCROP 

AREA--Includes flow through supt-rjacent confining unit where the confining unit is exposed ai the surface. Number 

'i is flow rate, in million cubic feel per day

v * Recharge 

f Discharge

NOT RECHARGE OR DISCHARGE IN OUTCROP AREAIncludes flow through superjaccnt confining unit where the TOTAL WATER BALANCE--NumberS are

. confining upit is exposed at the.surface. Number is flow , i i , « ~,,w,-~ r««4. «« /-i-nr ! rate, in million cubic feet per day - million CUblC feet per day.

- "-- ---- ' pillion gallons per day in

parenthesis

£4) Recharge

i>[. Discharge

TOTAL LEAKAGE THROUGH BOTTOM OP AQUIFER- Total PUmpase (P)

XTuw\Kj»r if flrvtu rol«» in millirtn /*iiKi/* f^^l riAr stau * ^J * ' Number is flow rate, in million cubic feel per day I U

\ Upward

Downward

NET LEAKAGE THROUGH BOTTOM OP AQUIFER-- 

Number is flow rate, in million cubic feet per day

T Upward

« Downweid.

L« -Z. NET LATERAL FLOW IN (+) OR OUT (-) OP STUDY 

AREA

= -58

Net lateral flow (L) = -3 

Total release of 

water from

storage (S) = 4 

Net recharge from 

constant heads = 57

(434) 

(22)

(30) 

(426)

vo

CONSTANT-HEAD WATER-TABLE LAYER 

1

* , * 1 ? i C ^) 3 : ,|

M h 

3? ,iVf t L= 0 S*0 P=-

;i | |/, 00 ^ i ^ L= 0 5=0 P=-IO (

,°» il^ fP o ?. L J_| c_ | p_^2. (3) .1 h . .1. ...... . . . . h . . . .^. .. " . . d ^

43 ©

D

L«0 S=l P»-|

f i f f r

= 0 = 0

u_l i t * f~"| I t \j[^[_7_^_ ~ f, f \ 7, JY ? * ^ * f \~2- ^^-JfI^l^^£.s£r/F 7 f_£^f ^ T TJ f^ ^y^} f^?

I 1 w ', ^pl *\~ L° 0 S - 0 P- oQ

0 I ,\ ' 1 1 1 1 1 1 1 1 ° 11 11

t^ o (o)

1 o

1L--I

r 

!_= (

5=1

> ;: 5=l p=-| @

P=-l ®

Figure 51 . Simulated 1982 vertical flow rates across hydrogeologlc units 1n mo<la| jubareai III

4'l ) [Sum of flow rates may not exactly balance due to independent roundlng.]
CO

RKANSAS

EXPLANATION

Pumpage scale, in million gallons per day 

(Scale may vary according to county)

Mean pumping rate (Mgal/day) 

Irrigation pumpage 

I Nonirr igat ion pumpage

Well field

50

_____I_____

50 100

100 MILES

I

KILOMETERS

Figure SZ .--Ground-water pumpage in selected counties in eastern part of study area, 1960-85.
<c 

u_ 

on

CO

z

3

3

o

LU

OQ

1 

LU 

LU 

U_

2: 

t i

 > 

_l 

LU

> 

LU

_J

LU

1 

3

^ WELL NO. \7

0 

50 

100 

150 

200 

250

-50 

0 

50 

100 

150 

200 

250 

300

1 County: 1I|A^^_ j- ~~-~ ~^__ _ - :i1 State well number :LH-£, 1-5 5"-2 04 

1 Land surface datum: 2.5 Liai - 

1 Well depth: ^oOxJUfljt - 

l Aquifer: Permeable zone B :

WELL Mo. 16 -r-T-r-T-T-p-r-T-T- r^1 ' ' '' 1 '

- County: 

- State well number: 

- Land surface datum: 

1 We'll depth: 

1 Aquifer:

-T-T-T- r-T-r-r-T T r r-r r T i i i i | i i i i ( i i i i | i i i i | I ' ' ' .

PR-6T4feo9 ~~~~N\ " 

1,2. ^5" ^-^ ^v^- . * 

Permeable zone C :

/D

- 25

1C

'- -75 

L -125 

--175 

--225

- *J/D

1-50

--150 

--200 

L-2W1

1930 1935 1940 1945 1950 1955 1960 1965 1970 . 1975 1980 1985

o

>

00

Figure 53- Ground-water levels in Jasper and Hardin Counties. (See fiq -41 

for locations.) 

99
IS

t

EXPLANATION

AQUIFER OR PERMEABLE ZONE AND IDENTIFIER

Permeable zone APermeable zone B

Permeable zone C 

i Permeable zone D 1 Permeable zone E I Upper Claibome aquifer i Middle Claibome aquifer i Lower Claibome-upper Wilcox aqu ifer i Middle Wilcox aquifer3 CONFINING UNIT

TOTAL RECHARGE OR DISCHARGE IN OUTCROP 

AREA-Includes flow through superjacent confining unit 

where the confining unit is exposed at the surface. Number 

i is flow rate, in million cubic feet per day

u Recharge 

Discharge

l

NET RECHARGE OR DISCHARGE IN OUTCROP AREAIncludes flow through superjacent confining unit where the 

confining unit is expos.ed at the.surface. Number is flow rate, in million cubic feet per day

) Recharge f

Discharge

TOTAL LEAKAGE THROUGH BOTTOM OF AQUIFERNumber is flow rate, in million cubic feel per day I U>

| Upward 

Downward

NET LEAKAGE THROUGH BOTTOM OP AQUIFER-- 

Number is flow rate, in million cubic feet per day

, | Upward 

« Downward _ ,

L» -2. NET LATERAL FLOW IN (+) OR OUT (-) OF STUDY 

AREA

TOTAL WATER BALANCE--Numbers are 

million cubic feet per day. Million gallons per day in 

parenthesisTotal pumpage (P) = -29 (217)Net lateral flow (L) = -3 (22)

Total release of

water from

storage (S) = 5 (37)

Net recharge from

constant heads = 27 (202)

oo

'-' ' CONSTANT-HEAD WATER-TABLE LAYER

| l 

3 T 0&) l& ill i °i ri^

,-i-Ll U ^i^Jl

0

\ ,cl) , ? L 1 S-0 p=-

I ix 1 f ($ 3 K$ L = 0 5=0 p=-5" (

1 1 L S-Q P=-3 ©

r

5- ©

2)

« co'

 .

I * f-f f~f f A

I roi *

, 

l-y l J' x KiyJ'-y ^^ x -? '/r K^

( °^^ L-0 ©

P=-| (9

L=0 5 =

-J 1-2-H4

LFigure S"4. Simulated 1982 vertical flow rates across hydrogeologic units 1n model 5

(fig.4'. ) [Sum of flow rates may not exactly balance due to Independent roundlng.j
EXPLANATION

Pumpage scale, in million gallons per day 

(Scale may vary according to county)

Mean pumping rate (Mgal/day) 

Irrigation pumpage

NonirrIgation pumpage

SS3 Year

1965 and 1970 punpage modified from 

Klem t and others (1976, fig. 7)

Well field £

GO 10 0

Figure 55". Ground-water pumpage in selected counties in western part of study area, 1960-85.
Decline in potentiometrlc surface, 

predevelopment to 1982, In feet 

decline

<50 (or Insufficient data)

HORIZONTAL FLOW, IN CUBIC FEET PER DAY 

Size of arrowhead Indicates range of flow, 

length of shaft Indicates flow within stated range

0.0 TO I X\0

* \ 4 /

Figure Jo . Decline of potentiometrlc surface of permeable zone B, predevelopment to 1982,

and simulated 1982 horizontal flow direction and relative magnitude 

Kingsville area. °

102
o:

ID

oo

o

CO

0

50

100

150

200

250

300

350

V1ELL NO. 19

County:

State well number:RK&Vis-Sol 

"Land surface datum: 106 \^ 

Well depth: 4ft? )***£

Aquifer: Permeable zone B

-100

-so

-o

--50

--100

--ISO

--200

00

m

1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985

Figure 57. Ground-water levels in Kleberg County. (See fig. 41 for 

location.)

103
Decline in potent iome Irk surface, 

predevelopment to 198?, in feet 

decline

 | I <50 (or insufficient data)

HORIZONTAL FLOW. IN CUBIC FEET PER DAY 

Size of arrowhead indicates range of flow, 

length of shaft Indicates flow within stated range

Figure 5~9- Decline O f potent iome trie surface of the lower Claiborne-upper Wilcox aquifer, 

predevelopment to 1982, and simulated 1982 horizontal flow direction and 

relative magnitude, Winter Garden area.

105
WELL Mo. Z3

UJ

o

o

LU 

U.

Z 0

~ 50

_; loo

£ 150

^ 200

Q, 250

£ 300

< 350

I ' ' ' ' I

State well number:zx-i7-ia-voi 

Land-surface datum: SG& 

Well depth: 1,054- 

Aquifer:

VJE.LL M

PRLC»PVTAT\oM i) f\

r 550 d

: 500 >

-450 -1

-400 <

-350 °°

-300 |2

-250 2;

-200 fE

L 150 g

-100 

UJ

o

~ ' X.

. State well number :zx-£9-6i-so2. ~ ^~^~ ____^ 

LLand-surface datum: 750 U*Jt - ^^^^

L Well depth: 2.60 (jJwX 

1 Aquifer: Lcv^Ci*-*Anrx*xj_-ju^^

- - ~

-700 

-650 

-600

-550 

-500 

- 450 

-Ann

LU

>

LU 

_4 

1

o:

LU

** 

1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985

Figure 60. Ground-water levels and precipitation data In Zavala County

41 -for locations.)

106
EXPLANATION

IS 

f

AQUIFER OR PERMEABLE ZONE AND IDENTIFIER 

Permeable zone A Permeable zone B Permeable zone C Permeable zone D 

Permeable zone E 

Upper Claibome aquifer 

Middle Claibome aquifer 

Lower Claibome-upper Wilcox aquifer 

Middle Wilcox aquifer

1 CONFINING UNIT

TOTAL RECHARGE OR DISCHARGE IN OUTCROP 

AREA Includes flow through superjacent confining unit 

where the confining unit is exposed at UK surface. Number is flow rate, in million cubic feet per day

i* Recharge

Discharge

NET RECHARGE OR DISCHARGE IN OUTCROP AREAIncludcs flow through superjacent confining unit where the 

. confining unit is exposed at ihc.surface. Number is flow L rate, in million cubic feet per day 

/4) Recharge '

A Discharge

TOTAL LEAKAGE THROUGH BOTTOM OP AQUIPERNumber is flow rate, in million cubic feet per day

| Upward 

v Downward

NET LEAKAGE THROUGH BOTTOM OP AQUIFERNumber is flow rate, in million cubic feet per day

J Upward

\.

l» -2, NET LATERAL FLOW IN (+) OR OUT (-) OP STUDY 

AREA

TOTAL WATER BALANCE Numbers are 

million cubic feet per day. Million gallons per day "in 

parenthesis

Total pumpage (P) = -41 (307)

Net lateral flow (L) = -3 (22)

Total release of

water fromstorage (S) = 18 (135)Net recharge from

constant heads « 26 (194)

I

CONSTANT-HEAD WATER-TABLE LAYER

-M L=

o 1=0 5=0 P'- Z (

Figure S8 .--Simulated 1982 vertical flow rates across hydrogeologic units in mo-J^I jub^rca TV 

(fig. 4"! ) [Sum of flow rates may not exactly balance due to Independent roundlng.]
Iuu

UJ UJ

UJ C3

UJ <.

 1 I

ce 3

UJ O

rf Li-l -i CQ

50

100

150

200

250

300

350

400

450

500

WELL Mo. "57

State well number: 

Land surface datum: 7.00 

Well depth: 900 

Aquifer:

1030 36 40 45 60 66 60 66 70 75 80 1986

 200

 150

 100

 SO

 0

 50

 100

 150

 200

 250 

300

UJ

a

I- 

<

-J

UJ

>

UJ-J I

UJ 

H00

00

Figure > . Ground-water levels 1n Nacogdoches County, 

location.)

(See fig. ^/ for

107
 i 1985 

E2 2000 

CD 2030

0 100 200 300 400 500

FRESH GROUND-WATER USE, IN MILLION GALLONS PER DAY

Figure .--Projected fresh ground-water use for selected counties, 1985 

2030. (Data from Texas Water Development Board.)

108
A. Permeable zone A. Well No. 9. Harris County.

UJ

CO

UJ 

>

Oi 

UJ

B. Permeable zone B. Well No. 7. Harris County.

-25

75

125

175

225

275

325

375

425

475

-50 

0

50

100

150

200

250

300

350

400

450

500

530

C. Permeable zone C. Well No. 3. Harris County.

191Q915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1900 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030

EXPLANATION

MEASURED WATER LEVEL

O -O SIMULATED WATER LEVEL (WITH INCREASED PUMPAGE FOR 1983-2030) 

 --- SIMULATED WATER LEVEL (WITH 1980 PUMPAGE FOR 1983-2030)

Figure 6B . Measured and simulated water levels in the Houston-Galveston 

area, projected to year 2030. {$**. -T/. ^/

109
GRIMES 

WALLER

EXPLANATION

LINE OF EQUAL SIMULATED LAND-SURFACE 

SUBSIDENCE Interval 1.0 foot. With 

1980 pumpage for 1983-2030

3 LINE OF EQUAL SIMULATED LAND-SURFACE 

SUBSIDENCE Interval 1.0 foot. With 

increased pumpage for 1983-2030

0 10 2.0 ID 40 KlLOMtTERS

Figure6!T . Projected land-surface subsidence in the Houston-Galveston area, 

1973 to 2030.

110
A. Permeable zone B. In vicinity of well no. v 9, Harris County

-100 

-50

0

LU 

< 50

£ 100 

S 150

a 200

<j 250

 -£ 300

3 350

LU

03 400

fLU 

LU

( *~------_

.i .... i. .i ... .1 .... .... .

B. Permeable zone C. In vicinity of well no. 9, Harris County

LU 

LU

a: 

LU

0

50

100

150

200

250

300

350

400

1910.915 1920 1925 1930 1935 1940 1945 1950 1955 I960 1965 1970 1975 I960 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030

Figure^5".. Simulated water levels in southeastern Harris County, projected to

2030 with 1980 pumpage.

Ill
A. Lower Claiborne-upper Wilcox aquifer. Well No. 23. Zavala County

y~'^L'l'll<|llllllll>|IIIIIITIt|tt<l|llll|lllllllll|T»lllllll|1lll|l»l t '""'""' l "" t " l""l'" ' I" " I " "I

QC

=3 

00

o

50

100

150

200

250

300

350

400

450

500

550 , I . . . . I . . I . f . . I . . . I . . . I . . . . I . . . . I . . . . I . . . . I . . . I . . . I . . . I . . I . I I 1 . 1

CO

hLU 

LU

LU 

> 

LiJ

B. Lower Claiborne-upper Wilcox aquifer. Well No. 24. Zavala County.

50

100

150

200

250

300

'-~0 ,.

H)

191Q91S 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1960 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030

EXPLANATION

MEASURED WATER LEVEL

0---0 SIMULATED WATER LEVEL (WITH INCREASED PUMPAGE FOR 1983-2030) 

 -- SIMULATED WATER LEVEL (WITH 1980 PUMPAGE FOR 1983-2030)

Figure Measured and simulated water levels in the Winter Garden area, 

projected to 2030. Cs *e 4->V/ -W

112
EXPLANATION

AQUIFER OR PERMEABLE ZONE AND IDENTIFIER

Q) Permeable zone A

(2) Permeable zone B

(3) Permeable zone C

(S) Permeable zone D

(T) Permeable zone E

(^) Upper Claiborne aquifer

Qj) Middle Claiborne aquifer

Q|) Lower aaiborne-upper Wilcox aquifer

@l Middle Wilcox aquifer

-7-T\ CONFINING UNIT

TOTAL RECHARGE OR DISCHARGE IN OUTCROP 

AREA Includes flow through superjaccnt confining unit 

where the confining unit is exposed at the surface. Number 

i is flow rate, in million cubic feet per day

v u Recharge

S

t Discharge

NET RECHARGE OR DISCHARGE IN OUTCROP AREAIncludes flow through superjaccnt confining unit where the 

. confinin* upit is exposed at the.surface. Number , is flow 

L rate, in million cubic feet per day 

4) Recharge '

($> A Discharge

TOTAL LEAKAGE THROUGH BOTTOM OF AQU1FERNumber is flow rate, in million cubic feet per day

| Upward 

* Downward

NET LEAKAGE THROUGH BOTTOM OF AQUIFER-- 

. -. Number is flow rate, in million cubic feet per day

, | Upward

I.

L1 -£. NET LATERAL FLOW IN (+) OR OUT (-) OP STUDY 

AREA

TOTAL WATER BALANCE Numbers are 

million cubic feet per day. 

Million gallons per day in 

parenthesis

Total pumpage (P) 

Net lateral flow (L) 

Total release of 

water from 

storage (S) 

Net recharge from 

constant heads

 548 (4,099) 

13 (97)

86 (643) 

449 (3,359)

CC

, 00.)

)NT ANT-HE AD WATER-TABLE LAYER

7 ,'

10 1 I t I ^ 

'i ] \L^ i * «K*iS=!2. P--8.Y ©

it hi 00 i ^5 (f4?r- L-5" S- II P = -^3 © ill 1 . fc 1 Vfl/xr i- J \_/

i

f l . fj\' tf } j j f~ r \ f f \jjjjf jf

Figure &7 . Simulated 2.030 vertical flow rates across hydrogeologic units In study area 

[Sum of flow rates may not exactly balance due to Independent rounding.j
EXPLANATION

POTENTIAL FOR ADDITIONAL GROUND-WATER DEVELOPMENT

Q Additional development possible

Some additional development possible. Development may be 

limited by water-level declines, aquifer thickness, or 

lack of potential recharge

Limited potential for development because dlssolved-solIds 

concentration in water is greater than 2,000 milligrams 

per 11ter

50 LINE OF EQUAL DIFFERENCE IN 2030 POTENTIOMETRIC SURFACE-- 

Shows amount of difference between simulations with 1980 

withdrawals and with 1980 plus additional withdrawals. 

Interval 25 feet

33f150 MILES i

100 150 KILOMETERS

Figure (c&. Potential areas for development of large ground-water supplies 

from permeable zone A.
EXPLANATION

POTENTIAL FOR ADDITIONAL GROUND-HATER DEVELOPMENT 

Additional development possible

Some additional development possible. Development may be 

limited by water-level declines, aquifer thickness, or 

lack of potential recharge

Limited potential for development because dissolved-solids 

concentration in water is greater than 2,000 milligrams 

per liter

Limited potential for development because of water-level 

declines, saturated thickness of aquifer less than 25 feet, 

or lack of potential recharge

50 LINE OF EQUAL DIFFERENCE IN 2030 POTENTIOMETRIC SURFACE-- 

Shows amount of difference between simulations with 1980 

withdrawals and with 1980 plus additional withdrawals. e 

Interval 50 and 100 feet 31*-

150 M

100 150 KILOMETERS

Figure£9---Potential areas for development of large ground-water supplies 

from permeable zone B.

115
EXPLANATION

POTENTIAL FOR ADDITIONAL GROUND-WATER DEVELOPMENT

r**1 i

IDI Additional development possible

Some additional development possible. Development may be 

limited by water-level declines, aquifer thickness, or 

lack of potential recharge

Limited potential for development because dissolved-solIds 

concentration in water is greater than 2,000 milligrams 

per liter

Limited potential for development because of water-level 

declines, saturated thickness of aquifer less than 25 feet, 

or lack of potential recharge

50 LINE OF EQUAL DIFFERENCE IN 2030 POTENTIOMETRIC SURFACE--, 

Shows amount of difference between simulations with 1980' 

withdrawals and with 1980 plus additional withdrawals. QT«. 

Interval 50 and 100 feet

ARKANSAS

150 MILf

100 150 KILOMETERS

Figure 70 -PjtentU^rees fo^deve^nt of large grounds supp,1es

116
EXPLANATION

POTENTIAL FOR ADDITIONAL GROUND-WATER DEVELOPMENT 

Additional development possible

ARKANSAS

Some additional development possible. Development may be 

limited by water-level declines, aquifer thickness, or 

lack of potential recharge

Limited potential for development because dissolved-so1ids 

concentration in water is greater than 2,000 milligrams 

per liter

Limited potential for development because of water-level 

declines, saturated thickness of aquifer less than 25 feet, 

or lack of potential recharge

 |00 LINE OF EQUAL DIFFERENCE IN Z030 POTENTIOHETRIC SURFACE--' 

.Shows amount of difference between simulations with 1980 , 

withdrawals and with 1980 plus additional withdrawals 

Interval 50 feet

33'-

100 150 MILES 

150 KILOMETERS

Figure 7/. Potential areas for development of large ground-water supplies 

from permeable zone D.

117
EXPLANATION

POTENTIAL FOR ADDITIONAL GROUND-WATER DEVELOPMENT 

Additional development possible

06*

Some additional development possible. Development may be 

limited by water-level declines, aquifer thickness, or 

lack of potential recharge

Limited potential for development because dissolved-sol1ds 

concentration in water is greater than 2,000 milligrams 

per liter

Limited potential for development because of water-level 

declines, saturated thickness of aquifer less than 25 feet, 

or lack of potential recharge

-LINE OF EQUAL DIFFERENCE IN 2030 POTENTIOMETRIC SURFACE-- 

Shows amount of difference between simulations with 1980 

withdrawals and with 1980 plus additional withdrawals or' 

Interval 50 feet

150 MILES

100 150 KILOMETERS

Figure 72 . Potential areas for development of large ground-water supplies 

from permeable zone E.

118
EXPLANATION

POTENTIAL FOR ADDITIONAL GROUND-WATER DEVELOPMENT

Additional development possible

Some additional development possible. Development may be 

limited by water-level declines, aquifer thickness, or 

lack of potential recharge

Limited potential for development because d1ssolved-so1ids 

concentration in water is greater than 2,000 milligrams 

per liter

Limited potential for development because of water-level 

declines, saturated thickness of aquifer less than 25 feet, 

or lack of potential recharge

50 LINE OF EQUAL DIFFERENCE IN 2030 POTENTIOMETRIC SURFACE-- 

Shows amount of difference between simulations with 1980 

withdrawals and with 1980 plus additional withdrawals.

Interval 50 and 100 feet

31

a^vi}.£er

e:- - « 

-^* I TEX*«K*N*P

^J- W-__-~] A R K A N S A S 

I i !

[2

-Sr-L,' 

Shelf

/-A

! DO J-D

w

1J 

0

1 

0

50 100 150 MILES

 , ' , H '

50 100 150 KILOMETERS

Figure ~JS~ Potential areas for development of large ground-water supplies 

from the upper Claiborne aquifer.

119
EXPLANATION

POTENTIAL FOR ADDITIONAL GROUND-WATER DEVELOPMENT 

Q Additional development possible

IMj Some additional development possible. Development may be 

limited by water-level declines, aquifer thickness, or 

lack of potential recharge

08*

ARKANSAS

Limited potential for development because dissolved-sol1ds 

concentration in water is greater than 2,000 milligrams 

per liter

Limited potential for development because of water-level 

declines, saturated thickness of aquifer less than 25 feet, 

or lack of potential recharge

J LINE OF EQUAL DIFFERENCE IN 2030 POTENT IOHETRIC SURFACE-- .. 

Shows amount of difference between simulations with 1980 

withdrawals and with 1980 plus additional withdrawals 

Interval 50 feet 31'

/00

\

\

\ 

\

\

\

\

Shelf

100 150 MILES

_J

100 150 KILOMETERS

Figure 74.--Potential areas for development of large ground-water supplies 

from the middle Claiborne aquifer.

120
EXPLANATION

POTENTIAL FOR ADDITIONAL GROUND-HATER DEVELOPMENT 

JQIAdditional development possible

gjij Some additional development possible. Development may be 

^ ""^ limited by water-level declines, aquifer thickness, or 

lack of potential recharge

JOlLimited potential for development because di ssol ved-sol1 ds 

concentration in water is greater than 2,000 milligrams 

per liter

JOlLimited potential for development because of water-level 3f. 

*^ ' declines, saturated thickness of aquifer less than 25 feet, 

or lack of potential recharge

 -200 LINE OF EQUAL DIFFERENCE IN 2030 POTENTIOMETRIC SURFACE-- 

Shows amount of difference between simulations with 1980 

withdrawals and with 1980 plus additional withdrawals. 8r* 

Interval, In feet, 1s variable

50

ARKANSAS 

100

33P50

150 MILES

100 150 KILOMETERS

Figure75~. Potential areas for development of large ground-water supplies 

from the lower Clalborne-upper Wilcox aquifer.

121
EXPLANATION

POTENTIAL FOR ADDITIONAL GROUND-WATER DEVELOPMENT 

IQI Addi t tonal development possible

Llal Some additional development possible. Development may be 

limited by water-level declines, aquifer thickness, or 

lack of potential recharge

|2|Limited potential for development because di ssol ved-sol ids 

concentration in water is greater than 2,000 milligrams 

per 11ter

50

ARKANSAS

Limited potential for development because of water-level 

declines, saturated thickness of aquifer less than 25 feet 

or lack of potential recharge

Results unreliable because of 

lateral boundary effects

-200-..L1NE DF EQUAL DIFFERENCE IN 2030 POTENTIOMETRIC SURFACE-- 

Shows amount of difference between simulations with 1980 

withdrawals and with 1980 plus additional withdrawals 

Interval, in feet, is variable

Updip limit of the 

middle Wilcox

100

100 150 KILOMETERS

Figure 76 . Potential areas for development of large ground-water supplies 

from the middle Wilcox aquifer.

122
..EXPLANATION

' ROW USED FOR HYDROGEOLOGIC 

SECTION --Shown in figure £

BOUNDARY OF MODELED AREA

ARKANSAS 

\

150 MILES

50 lo ° ISO KILOMETERS

n*i ' Figure f (.-Finite-difference grid superimposed on modeled area and study area.

123
 4OOEXPLANATION

-WATER-TABLE CONTOUR Shows altitude 

of water table in outcrop area of the 

Texas Gulf Coast aquifer system. 

Contour intervals 25 feet (near coast) 

and 50 feet. Datum is sea level

UPDIP LIMIT of

DOWNDIP LIMIT o

JA8KANSAS

19'

150 MILES 

J

50 100 150 KILOMETERS

Figure 7&~Estimated altitude of the water table for the model constant-head boundary.

124
-50 POTENTIOMETRIC CONTOUR-Shows altitude at 

which water levels would have_stood in tightly 

_ wells. Contour interval 50 feet. Datum is 

sea level

SIMULATED POTENTIOMETRIC CONTOUR-Shows 

altitude at which water levels would have stood 

in tightly cased wells. _ 

Hachures indicate depression. Contour 

interval 50 feet. Datum is sea level

10

1

1 I I f 

0 10 2.0 30

20 }0 MILES

I 1 1

KILOMETERS

Figure 7 /.--Measured and simulated altitude of the potentiometric surface of permeable 

zone A in the Houston-Galveston area, 1982.

125
POTENTIOMETRIC CONTOUR-Shows altitude at 

which water levels would have stood in tightly 

jiased wells. Contour interval 50 feet. Datum is 

sea level

O

 SIMULATED POTENTIOMETRIC CONTOUR-Shows 

altitude at which watar levels would have stood 

in tightly cased wells. _ _ _ 

Hachures indicate depression. Contour 

interval 50 ieet. Datum is sea level

ouTCRoP AREA

o

V

fc" oo'

20 30 MILES I 1 1

I I IT I

0- 10 2.0 30 40 RiLOMtTERS

Figure 8<9 . Measured and simulated altitude of the potentiometric surface of permeable 

zone B in the Houston-Galveston area, 1982.

126
EXPLANATION

POTENTIOMETRIC CONTOUR-Shows altitude at 

which water levels would have stood in tightly 

£ased wells. Contour interval 50 feet. Datum is 

sea level

SIMULATED POTENTIOMETRIC CONTOUR Shows 

altitude at which water levels would have stood 

in tightly cased wells. _____ 

Hachures indicate depression. Contour 

interval 50 feet. Datum is sea level

OUTCROP AREfl

I i^r

10 2.0 30

30 MILES

I 1

kiLOMtTERS

Figure 8 I . Measured and simulated altitude of the potentiometric surface of permeable 

zone C in the Houston-Galveston and Evadale areas, 1982.

127
WELL

-103 

-93

°(

im

ISO 

200

300 

393 

400 

490

-193

-103

-93

a * c

2 103

9| ISO

oo 200

0 293

lr S00 

-J 393

2: 400

3 «

"-1-1 500

co

1 

^ -ISO

LU " 

u_ -100 

z -«0 

0<

_; GO

uj 100

uj I® 

-l 200

cy ga} 

UJ ___ 

( 300

< 390

)---

State well number: 

Land-surface datum: 

Well depth: 

Aquifer:

WELL MO. 2.

-

State well number: 

Land-surface datum: 

Well depth: 

Aquifer:

\A/£LL NO. 9

I __

 State well number: 

: Land-surface datum:

l.l^l 1 ,r4 <".!-. 4- ll«

J '(- (o S-l 0-7 o 2. 

Permeable zone A

LJ-G5-H-405"

35^ }j CA^-~ 

Permeable zone A

 ~-Q ........

^ *** ^^ 

*~ ^.

LJ -G 5-2 4-2.02. 

33 Ujr

C" A r\ 0| 4^

j"

^o=-= -©^^-xrr^-p^-e Q -

. . i . . . . i . . . . i . , . , i . . . . i , , . .

-

^^lp=^^D^r^rF^a^--o_-

. . 1 .... 1 .... 1 ... 1 1 ....

..l....l....^....,....,...l^

»-- ^ '

WELL No. I/

-ISO

-100

-50

0<

SO

100

190

200

290

300

350

400

453

-

'.

'-

'-

'

State

1 ' ' ' '

well

1 1 1 1 1 1 1 1 1 ' i » » > » i » i ' » * i ' ' i ' *

_

 1 " ' i J J ' i ' l ' " ' ' ' ' ' ' " ' ' .

*

-

-

i -G----O. _ -o o ' 

 -~ -* -- .""*. ~

number :Kv\-65"-4o-bol :

'- Land-surface datum:

-

'-

-

'

Wel 1 depth:

Aquifer:

i . .... .1 i.^j

1910 1915 1920 1925 1930

2.O \stsuC

4-&0 IM£

Permeable zone A

.. i .... 1 .... 1 .... 1 ... .T. .

1935 1940 1945 1950 1955

-

-

*

**

, . | . . . . 1 . . . . t r T . . T . . . . T . . . .-

l

1990 1965 1970 1975 1990 1995

EXPLANATION

MEASURED WATER LEVEL

_e & SIMULATED WATER LEVEL

Figure 8 2-. -Measured and simulated water levels In welle I, 2, 9, and 11 In the Houston-8alve«ton area.

128
WELL No. 4

UJ

u_ 

o:

oo

Q

3 

O

UJ 

CO

hUJ 

UJ

u_

z t i

_i

UJ

>

UJ

_l 

o:

UJh-

<

3

-wu

-too

-50 

0<

50

too

ISO 

200

250 

300

350 

400 

450

-150

-100

-50 

0<

SO 

100 

150 

200

250 

300 

350 

400 

450 

500

-150

-100 

 50 

0<

SO 

100 

150 

200 

250 

300 

350 

400 

450

DUU

-150

-100 *<

so

100

150 

200

250 

300 

350 

400 

450

500

^ . . . . 1 i i . . , . . . . t j j i i 4 . . . . j j i . . , . . . . , . . . . j . . . j 1 ; j . . j . . - - , . . . . I i . i . , i . , . . i 

I _____

J. State well number :LJ-6S-/3-4o 8 ^^^^T^- 

'- Land-surface datum: 80 )^jjJ: *" e 

: Well depth: $fe2 |«A£ 

r Aquifer: Permeable zone B

WELL NO. 7

; . > -^^^^^^

j State well number :LJ-feS-2.1-fio£T ^^HSks,, 

 Land-surface datum: ^7 y&t ^^**t*& 

: Well depth: \p\~i jjviJ' 

: Aquifer: Permeable zone B

WELL MO. 8

l..l|....|...l|.i..|....,..l.|..!.|l..J,ll.,|....,...J|.... | .J.J|II..J.J

^ ^^~^^^^ " State well number :LJ-^ 5-2 z-6i 8 ^^^^^ >>"'-O---vc& 

[ Land-surface datum: 38 \pa£ ^ ^_ /^^**

: Well depth: ST6 Y^~ 

'. Aquifer: Permeable zone B

WELL NO. IZ

^ °" ""«-- « « " 0 -0.-.Q. ____ ^

"^^ " ~*^*^-_ /"^

^ State well number :KH-G 4-^3-5 02 

 Land-surface datum: s l**£ 

: Well depth: fesfe ^*-»^ 

: Aquifer: Permeable zone B

1910 1915 1920 1925 1930 1935 1940 194B 1950 1955 1980 1965 1970 1975 1980

EXPLANATION 

MEASURED WATER LEVEL

_3 e SIMULATED WATER LEVEL

-t

\

**+ 

 j

 j

-

u 

 j

 j

' 

191

Figure g 3 . Measured and simulated water levels In wells 4, 7, 8, and 12 In the Hou«ton~6alveeton area,

129
-ISO

-100

WELL NO. 3

0 

GO 

100 

ISO 

200 

250 

300 

350 

400 

450 

900

State we 11 nurnoer:LJ-^ 5-2. o-i \ o 

Land-surface datum: go 

Well depth: ij a 8

Aquifer: Permeable zone C

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

WELL NO. 5

UJ 

CJ

Cd 

Z3 

IS)

a

UJ

ca

UJ

>

UJ

UJI 

<

~*aw

-100

-50( 

0

GO

100

150

200

250 

300

350 

400 

450 

BOO

.' ' ' ' I ' ' ' ' 1 ' ' ' ' 1 ' ' ' ' 1 ' ' ' ' 1 ' ' ' ' 1 ' ' ' ' 1 ' ' ' ' I ' ' ' ' I ' ' ' ' I '

^ ___

r >0 -- ^^

- ""*"* -..

 ^"*1Q-^

 Vx\* ^^.^ *"

 State well number :Lj-65-/*H0 7 ^^^ 

r Land-surface datum: 7^ A^-^ 

r Well depth: l,i?>lo ^f 

[ Aquifer: Permeable zone C

1 ' * . » « * ' i » * i * * » i » » » v

-

J

s».^ 

 ' '' ' '' '

-150

-100 

-50<>- 

0 

GO 

100 

150 

200 

250 

300 

350 

400 

450

UUELL NO. 6

State well number:LJ-£5-£l-3o2_ 

Land-surface datum: 4G (y^ 

Well depth: 1^10 ^sjjt

Aquifer: Permeable zone C

WELL NO. 1O

-150

-100

-50

0<

GO

100

150

200

250

300

350

400 

450

am

 >-ri . | r t I i [ I i I l-f t rrfT Tt

L

i _ ______

1.'.

'.

 State well number

: Land-surface datum

: Well depth

[ Aquifer

 -O _ _

"~ "^ "" "" "®" " -o.

_ - ^ i _ ^^ *** * **j

*"~~**>1^>^_

:u- 6>5-l f>-°lo7

: 27 Wt

: ;/7?.7 L&i>x~

: Permeable zone B

. . i . . . . i . . . ^ t . . . . i . . . . i . .. . ._ i . . i . 1 1

' ' ''1 ' ' ' ' 1 ' ' ' '.

-

 j

>-^Q o :

^x " 

"" ^^ "

-

"

1

1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 I960 1985 1970 1975 1980 1985

EXPLANATION

_______ MEASURED WATER LEVEL 

__e 9 SIMULATED WATER LEVEL

Figure 84~ .--Meaeured and simulated water level. In well* 3, 5, 6, and 10 In the Hou«ton-6alve«ton area.

130
VJELL NO. /3

~15U 

-100

-a

BO f- "° «»*« "*« . -e e Q. 

100

150

200

250 '- State well number :zA-ktr4 5^03

SOD - Land-surface datum: 12%

350 : Well depth: 108

2 '- Aquifer: Permeable zone A

ct. 500

" WELL MO. 14

O -ISO 

rf -100

-1 -so 

o »* -i SO

1-lJ .«*.

co 100

h- I50 

uj 200

290 - State well number:pp-6S-5"2-8oI 

SOD '- Land-surface datum: 9o 

3S> Wel 1 depth:

Aquifer: Permeable zone A

45u 

BOO i-i~i - -

^ VJELL NO, /f __________

^ -150 pt t t r | i i i t i' i i i i | t r t i | i i i t | t i i i | i i i i | T i » r-| i i > i | i i i i | i i i i | i i i i | i i i * | i r i r f 

< -100

2 -aoO>- 

so 

100

ISO 

200

2so 1 State well number:pp-$t)-o6-7o3

soo - Land-surface datum: 38

350 : Well depth: 59<

400 : Aquifer: Permeable zone A

490 -

egg ' i ' r « ' i T ' ' ' ' ' ' ' ' ' ' ' » ' ' ' ' * ' ' ' ' ' * ' * * * ' ' ' ' ' * ' ' ' ' I ' ' ' *

1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1990 1965 1970 1975 1980 1905

EXPLANATION

MEASURED WATER LEVEL

8 5*

-0 -o SIMULATED WATER LEVEL 

 Measured and simulated water levels In wells 13, 14, and 15 In

*v<sf 7c 

Jac&son/Whorton County

131
WELL

O

C£

Q z.

5

2 

O

UJ 

CO

a:

UJ

 100 *<

0

50 

100 

150

200

250 

300

350 

400 

490 

*nt

F~ -_ _ _

: °---W^

' « 

[ State well number:pR-fcKg-eo9 

m Land-surface datum: 45 Joot 

 ' Well depth: \,2- cf5'jf*.vt 

 Aquifer: Permeable zone C j

VJilELL MO. IT -wu

-100

-50

0<

60

100

150

0JU 9fYl

250

300

350

400

490 

em

1 f 1 1 i i i i i i i i

.

^-^ ^tty^J- «- -<^CW

-

-

L State well number:LH-£>i-55;2.o4

L Land-surface datum: 2.5 Lut 

- Well depth: QoO Jjudt

: Aquifer: permeable zone B

, . . . 1 . . . . 1 . . . . t . . . . L . . . . 1 . . . . 1 L . L ^ 1 . . . t t . .. ^ L > .^ ^ 1 . . . . t . . . . 1 t LJ

r' 1 ' ' 1 ' ' ' '.

-

 

-

-

.

J

-

 ;

-

1910 1915 1990 192S 1930 1935 1940 1945 1950 1955 I960 1965 1970 197S 1980 1905

EXPLANATION

MEASURED WATER LEVEL

_e e SIMULATED WATER LEVEL

Figure 2 6. Measured and simulated water levels In well* 16 and 17 In the Evadale-Beaumont area.

132
-50

-So

.POTENTIOMETRIC CONTOUR-Shows altitude at 

which water levels would have_stpod in tightly 

jjased wells. Contour interval 50 feet. Datum is 

sea level _!/

-SIMULATED POTENTIOMETRIC CONTOUR-Shows 

altitude at which water levels would have stood 

in tightly cased wells. _ _ 

Hachures indicate depression. Contour 

interval 50 feet. Datum is sea level

OUTCR.QP

J/ Mod;f;eJ from £i-oS 

0 10 10 \. I.I.I ,1 I 1 1 I I 

0 10 T-Q *°

0985, 4 .'jure 9)

MVLCS

FigureS? .--Measured and simulated altitude of the potentiometric surface of permeable 

zone B in the Kingsville area, 1982.

133
WELL MO. 18

LU 

CO

*au 

-100 *<

0 

GO 

100 

150 

200

250 

300 

350 

400 

450 

GOO

-r-f ri , ri-T l-r-r-t-r-rr i ' r T 'T t |'i . r . p r ... r ... ,,>,,,,.,, t ,,,,.,,. r 

J _______

L * « x/""*"16

1 i. ^Xs" 

1 State well number :RR-gvzS-7c*l 

. Land-surface datum: /i^JuL^f 

- Well depth: 49BjtJ^ 

 Aquifer: Permeable zone B

>- -^__ __ 0 :

 j

WhLL

 »au 

-100

-so(

0

GO

100

150

200

250

900

350

400

JBfi 4MJ

500

i i i i 1 i i * i i i i

» ______ *~-~-O---.--__

 -* - --^

- ^"~~~~~~'~~- - 

^ 

"""^---G.

^. - "^~

- ~ ~ ' ^^ p "^~J4

1 State well number :RR-# 3-2 5^-50!

- Land-surface datum: |o6 Uja^T

 Well depth: 435 Vati"

 Aquifer: Permeable zone B *

1" i . i . > . . n,i.L^. i. > t i > i t > 1 1 r-rrr-rrrJ.vi-i rm-rrt,-i :rrn rr n rrri r i rt i;,t t.ri

1 r

-

^

-

-

J

^, , _JIL> ,, *if3' ""

J

-

 ^

-

rvri ^ f i ii i i i r

VJELL MO. 2.0

-100 

-50 (

0 

50

100 

150 

200 

25Q 

300 

350 

400 

450 

500

t ____

^tilJa-©*^WXQ

- State well numoer:RR- 83-2. 7-8 oH 

 Land-surface datum: 39 -J^^t 

; Well depth: 948 j^o^ 

Aquifer: Permeable zone B

1 1 1 1 1 1 1 1 . . i . ^

J

ISO I

 100 

- D<

0

50

100

150

200

250

300

350

400

450

Km

WELL

 IT T i 1 y r FT r-|

^~_ _

c.

-

-

1

[ State

MO. 2.1

i i i » 1 i i i i | i « i i | i i » I ' ' ' 1 ' ' ' 1 '' ' ' 1 ' * 1 ' '' '' ' M

 -o -..Q._ :__

_.. .. -

, well number :Rp.-g i-35-2. ol

-

V7*~-©~ -{J

* 

-

J

: Land-surface datum: 41 '^jjc 

.

-

.

«, 1 1 1 1 1, . i * i

Well depth: ^^^ /JOJP/

Aquifer: Permeable zone B

.^ J.».t.. 1 .i.tf ....i^.^.f« T ^«i.«--i--'«i««««t.»««.«i«

-

~

1 L 1 i II ' t ' -t 1 ' ^ ' ' ' ' * ' 

1810 1915 1920 1825 1830 1835 1»« 1»4S 1850 1855 I960 1866 1970 1875 1890 188S

" EXPLANATION

________ MEASURED WATER LEVEL 

__Q ^3 SIMULATED WATER LEVEL

Flgur* 8£- ««»ured and sUuLated watw UeveU In w«lU 18, 19, 20, and 21 In the Ktngavllle

134
EXPLANATION

POTENTIOMETRIC CONTOUR-Shows altitude at 

which water levels would have_stopd in tightly 

_cased wells. Contour interval 50 feet. Datum is 

sea level

4OO-*-SIMULATED POTENTIOMETRIC CONTOUR-Shows 

altitude at which water levels would have stood 

in tightly cased wells. 

Hachures indicate depression. Contour 

interval 50 feet. Datum is sea level

OUTCROP AREA

FigureS/. Measured and simulated altitude of the potentiometric surface of the lower 

Claiborne-upper Wilcox aquifer in the Winter Garden area, 1982.

135
WELL NO. 2.2

-100 

-50 

0

SD <

uxr

ISO

aoo

250 

300

350 

400 

450 

500

i i i | t i r | r i t-i-T T-i-r-i-[ t i r r | i r i . [ , i i i | r , ,- r r, , , , , , , , ,,,,,,,,,,,,,,

> __ _

- State well number : 2x-77_o 1-50! ^lV^vv^v%\""""0"'"" 

 Land-surface datum: 775- j^ ^-^V4^^

Well depth: 483 VZu!"

» i ' » » i » ' ' ' .

"«*-*- <;

-150

-100

WELL wo. 13

o

i

CO

0

50

100

150

250

300

350

400

450

500

State well number :zx-l>i 8-4-ot 

Land-surface datum: 568 

Well depth: 

Aquifer:

VIELL MO. ^4

<

3 WE.LL Mo.

-leu 

-100

-so

0

(

150

300

250 

300 

350 

400

450 

cm

* -. ___________ _,

i State well number :zx-69-£ |-soz 

 Land-surface datum: 7/^0 V18^" 

; Well depth: 2.60 V^jt ./j 

; Aquifer: L0u^n_TlAUrtr^^-/u^m6A VJJU*X

'^ L.L »-J- ^ »-^»-L ^_»_^.-i_L-»,j_m_»-l^-^ . I 1 ! . . I 1 1 >. t. . 1 1 1 . t 1 . . 1 i. i. ,«..!.. .ll.lttllllil.t.llttlllll

 j

-m

 ISO

-100 

-KD< ou ^ 

0

50

100

150

aoo

250

300

350 

400

450

cm

' i i ' 1 ' ' ' T" ' \ ' ' » " 

i ,__ ___ __

-

-

.

'. State well number:

- Land-surface datum:

 Well depth: 

; Aquifer:

.

1 1 ... ^ , ... i .... i ....(..

1 1 1 1 1 1 1 1 1 n i i i » i 1 1 1 1 1 1 1 1 1 1 1 r *'

 >- - -&-,.._

""" O O

"^

*"

KB-7T-I4-60I

sio ^^ 

1,450 JjuU .

( '

.. 1 .... 1 .... 1 .... 1 .... 1 .... L . ^

» i I i i i » M i i i I i i i i I i i ' i.

 j

"

^ ^**""8- """""" 0-^^ _ ^ -

V\^_ X r~«^^A, y ^\

^^ \J " 

\

*

. . 1 . . . . I . . . . t ^ . . . 1 . t ^

Figure CJO

1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1985 1970 1975 I860 1985

EXPLANATION

______ .._ MEASURED WATER LEVEL 

_© © SIMULATED WATER LEVEL '

24 26 

Measured and simulated water levels In wells 22, 23, ,f, and . In the Winter Garden area.

136
WELL 2.7

-100

-50 

0

,S< 100 

150 

200

250 

300

350 

400

450 

SOD

. State well number: w-68-57-4 02. 

: Land-surface datum: 667 Uud 

'. Well depth: 2.60 Sit

\

^ _ :

LI-I.J.I.I L.I.J.I.:

lA/ELL NO. 29

UJ 

CO

UJ 

> 

UJ

o:

LU

-100 "<

0

so

100 

150 

200 

293 

300 

350 

400 

450

SUJ

"100 

-50

°<

50 

100 

150 

200

250 

300

350 

400 

450 

am

, ..,....,.,,., i-r-r r T i-r-r-r T f ri i v , ,, T f ti 

\ ___________

1 ^

^ State well number:KB-77_2. 3-70! 

[ Land-surface datum: 56 0 i^

 Aquifer: L^ JfVj^

WELL NO- ^>0

i . r i t r r r . pr r r-r T r r r t t r i r r f i r . i | r i r f i

: State well number:KB-77-;6-8o\ 

L Land-surface datum: 520 Uajt 

- Well depth: l % ^»2.& UaX 

7 Aquifer: LXIVU^L CJUVi/

1 1 1 | 1 1 . 1 | 1 1 1 1 | 1 1 1 1 | 1 , . . , 1 1 1 1 [ 1 1 . 1 J 1 1 1 J ^

111-litllll.li.l.llillllllilli.ilifctlt.itI.lb.iA/0. "51 150

 100

-50 MrI

0

50

100

150

200

293

300

350

400

450

GOO

-

F-

-

-

-

-

'.

-

; 

"

19

ii»|'iiir|iiii|itir|iiii|iiii|itii'|rrrrfirirfii»i|"rr

 O- "°-----._

--O--.si^

State well number:K&-78rOi-80l

Land-surface datum: sos \JvJt

Well depth: \ ) ^-\3> "ij^:

Aquifer: Lirwfi ciiuirtr^M,-- jAjppJLnvvAjL^fT£

...l....l.^..l....t.tt^LLt t ^Ltt^^Lii-^i.lii- 1 i.liiiilti.

10 1915 1920 1925 1930 1935 1940 1945 1950 1955 I960

' ' 1 ' ' T r 1 ' ' ' ' 1 ' ' ' ' 1 ' ' ' '.

-

-

'r*-*. ' "

^SX^^^-xj.Q.^^-^ "

v^ ^J^v

_

 ;

-

1965 1970 1975 1960 1985

EXPLANATION

MEASURED WATER LEVEL

__e__ &- SIMULATED WATER LEVEL

2_7, 31 

Figure cjf I .-Measured and simulated water levels In vells^, 30, 3& and T52 In the Winter Garden area

137
WELL MO.

-*3U

-100 - <

0

50

100

150

200

250

300

350

400

450

BOO

. ' ' ' 1 ' ' ' ' 1 ' ' '"''I ' r t i pi i i i | i i i i [ i ri r | i i t i | i i r i r rt ' ' » ' ' ' ' 1 ' ' r 1 ' ' ' « 1 "' "' ' ' f '

i _______

 '° -

"O.^

- *"-^

1 ' ».

: County: Dx/m^/J "° : >-,. a

: State well number:Hz-77-2k3o| ^,J\^^Q""'' ^^

 Land-surf ace datum: 52.si^ \ ^ S^X*"

; Well depth: 1,0(0 L&jJt ^

~ Aquifer: L^uj^(H<vJlrui^u-M^jaJwUJ>iJU*/. ' /

 III! 1 1 1 1 1 1 .III 1 till t 1- . 1 t . . . . 1 . . . . i . . . . 1 ...... j L f f . 1 .... 1 .... j , , . . 1 .... 1 .

1 t I 1 f

 ;

-

1

*

£ft »

-

-

. . ^

WELL - 2.8

o z.

o

LU

03

 WU

-100

-SO

0

50<

100

150

200

290

300

350

400

450

an

-

-

f _..._ y-««.Bl<Jl- Q..

L ^ ;*^^5

County: D^m^rU/

: State well number:HZ-7742_-8ol

: Land-surface datum: &|2> ijui± -

" Well depth: i,374L»J»i"

[ Aquifer: L<pjj^&^<ri^jt-wja^VUJ^

,1 i t. t. t i 1 1 In 1 t 1.1 i 1 1 1 1. t L 1. 1 t-L. L 1 t 1 ll 1 1. 1.. 1. . 1 t » 1 1 1 t t 1 1 1 1 1 1 1 . 1 1 ( . 1

-

-

.

_

> -©--:Qi_ -o -

-

-

-

-

m

. . i . . . . f . . . . i . , . . '

WELL L3U

-100 <

-SO

0

so

100

150

200

250

300

ffn

400

450

500

^-~-----__.-

- ^5 ^^

*"~-«..^

v®~~- 

 >SN

County: \_^ ^/ALu

' State well number :R*-7 7.3 8-2.0 \

r Land-surface datum: 475 -LsjeJ:

[ Well depth: Z.ZooMjj^

* Anui f P Y* * \ r\w/l 'l \ \ * 1 J

(Til

-r^-fi-TT-t-r^-f r T T r r-t-i | --. , 

-

-

^ -

"to "©>- "

\^^ " ^-^>_ ___ ~ -

^^'^^^V V^""^^-^. y ^V "-

<rf. -

-

j..iJ. ui-i-x-L i t > i 1 1 1 i i 1 > i i. ..

VJELL MO. 34 -200

-100

-BO

0

so

100 

ISO

200

250

300

350

400

Aon

"rtrrrr'r*'lril 't''' l f l

^_ __ ____ ___

-

'-

'-

: County

: State well number

' Land-surface datum

: Well depth

: Aquifer

-

.... i .... i .... i .... i .

» > ' i i » » » i ' ' » i ' » * i ' ' ' ' i ' ' ' ' i ' '

 -0 0--^

""-- o .- o.^ ~\I

:RX-77-40-303

: 42.0 VrR-ft-^

: 3,000 Lsjit . .»

 Ltruj^-a ClL-Jrcara- i^p^vOJuux

v U

i i. t t.i i i 1 . i i 1 < i i *l i i i i > I . . i 1 i i i i » i i

' ' 1 ' ' ' ' 1 ' ' ' ' 1 ' ' ' '.

 j

>%* Ot ^8 e 0 :

"^^ ^ ^~ ^~-^^- <

-

*

1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1980 1985 1970 1975 I960

EXPLANATION

________ MEASURED WATER LEVEL 

__e ©._ SIMULATED WATER LEVEL

1985

Figure . Measured and simulated water levels In wells . / ~ iAand 34 In the Winter Garden area

138
WELL MO. 33

UJ 

CO

-100 

-50f

0 

GO

190

200

250

900

950

400

450

-100 

-»<

0

60

100

190

200 

290

900

950 

400

450 

mn

i f i . , r i r . , rp i | rt-j r i i i |TTI-TJ t-t-t-f r-r-r r r r r r I i | t I I i f i . t I y i I

 ~ i^^ ^*^""""""*Q

_ ^""vv^Vi

r e>-

l State well number :AL-ta-6o^-o|

1 Land-surface datum: SI5 Loct*

: Well depth: fcfc6 -jLud"

^ Aquifer: L,6^r?A (L^uXrirlxrU -M&bJVi \\}JL<*jt

WELL No. 35"

 *-. """"-Q

"^~\

-

1 State well number: AL-7&-I i-3o I

: Land- surf ace datum: 47^ Landt

; Well depth: 2,122. Lui 

: Aquifer: Ltf^^i^l^ifi^

'

^*yvX^v^;'n"' o 

-

~

-

-

-

j

>--.~

 -^^~^v>***Ph "

-

"

J

no. -isg

 100 » « 1 ^

-50

0

100

190

200

290

900

950

400

450

Dm

i . . t | . . . r r i t i i f i . . . t rr i

^_-^__^ _.__ __ _«^

.

-

L

'. State well number: P

l Land-surface datum:

 Well depth:

: Aquifer:

:. .. ... .,.... .... ,,.

V O ~-^^

 - ^-^^S^^^

-"_

U.-6 8-6 0-9/3

430 iJW-i'

/ lt>0 Loji^

L ovoen. (LjLwJlni Or\ J - A^a*^ WjJcX^T:

' * .

-

 

"

 j

-

-

 j

-

1910 1915 WX 1825 1930 1935 1940 1945 1950 1955 1980 1965 1970 1875 I960 1965

EXPLANATION

MEASURED WATER LEVEL

 o- - SIMULATED WATER LEVEL

Figure^) 3 . heosured and simulated water levels In wells _, 33, 35, and 36 In the Winter Garden area,

139
No.

UJ 

0

u_

Qi 

00

0

2 

O 

_J

LU 

CO

1 

LU 

UJ 

U_

i i

_J 

LU

LU

_J

LU 

1 

2

-*w» 

-100 < 

-50 

0 

SO 

100 

150 

200 

290 

300 

350 

400 

450 

GOO

-ISO 

-100 <

0 

60 

100 

ISO 

200 

290 

300 

350 

400 

450 

500

-100 ( 

-50 

0 

50 

100 

153 

200 

290 

300 

350 

400 

450 

500

 i i . . i . . 1 i i j i 1 i i i 1 i i i . 1 i i j . 1 j . . i 4 i i . i , . j i i 1 i j . i 1 . . 

1 __ _ _

: \^^-«.

; State well number:TX-y?-36-/o2. ^^^X *""" x * 

: Land-surface datum: ^oo LW~ - 

r Well depth: 900 ^^t * 

Aquifer: Le\wt/i(!iJU-iJj1^^~>i/'/|^-^

lA/£LL HO. 38

j..i|ii..|iiir[iiii|iii.|ji,i|jii.^.ij.|iiii^ii.. | .jji^j.ji|.. 

>___________ __ _ _ f->

: vl'*""^^ State well number : AD-37-3 £4-0 3 ^ ^ 

: Land-surface datum: 2.04- \*aJt ' ^"""~~~~"" 

' Well depth: £4-7 fcjf .A

WELL M& 39

: ^^^^^ ~"^^^- 

: ^^^^~^--^.

State well number^D-^T-^-Sol 

 Land-surface datum: 2.2^8 AJLJ^ 

- Well depth: l,os^ fr8^ 

r Aquifer: \_(ryk^vv.Q-X*^trx^-/>ji>^L^ w/xc^i^x

1910 1915 1990 1925 1930 1935 1940 1945 1950 1955 1980 1965 1970

EXPLANATION 

MEASURED WATER LEVEL

rifiifiji,..^

. . i . . . . i . . . . 

t 'i* jii r r ' trJ-^ ___ :

 j

1975 19BO 19

_e e__ SIMULATED WATER LEVEL

Figure ^4. Measured and simulated water levels In veils 37, 38, and 39 In the Lufkln

140
EXPLANATION

2.0- LINE OF EQUAL LAND-SURFACE SUBSIDENCE-- 

Dashed where approximately located. Intervals 0.5 

and 1.0 foot _!/

LINE OF EQUAL SIMULATED LAND-SURFACE 

SUBSIDENCE Intervals 0.5 and 1.0 foot

_!/ from Ca.-r- and

20 30 MILES

i i i

0 10 10 30 KILOMETERS

Figure Measured and simulated land-surface subsidence in the Houston-Galveston area, 

predevelopment to 1973.

141
A. Permeable zone A

hHl 

HI 

U_

Q 

< 

HI

I

Q 

HI

h- 

< 

CC 

CD

-J 

< 

O

2 

o

cc 

u_

Q 

< 

HI

I

Q 

HI

CO

>

HI 

CC

U_ 

O

HI 

CC 

D 

H 

CC 

< 

Q. 

HI 

Q

25

0 

-25

-50

100 

50 

0 

-50 

-100 

-150

100 

50 

0 

-50 

-100 

-150 

-200 

-250 

1

1 ' ' \Js^^_ _!__

 r '

\ y'- 1-5 x CALIBRATED (Kh). 

. ROW 43 *^ - 0.5 x CALIBRATED CKh) -

L_ L j. 1 i 1 i ' --1 - * ' ' 

B. Permeable zone B

-.^.. ... T _» _r. .,-, ,..,. ., . ,. . , . r,. .,..,.. ,, . ,

 ' V .~.r'

^ 

v f ^.. -l^vPAIIRR \ .O X OMLIDn

- ROW 43 'X^ f - 0.5 x CALIBR

I 1 L 1 , L t L ' ' 1 1 ? '

C. Permeable zone C

: '^^x/rXv^^' '

-

ATED (Kh)-; 

ATED (Kh)-

1111 r 11 ' ' __

: \ x"'*' " -

r K / 1.5 x CALIBRATED (Kh)l

[ ROW 43 \ J -^ 0.5 x CALIBRATED CKh^ 

" i ' iLt_i L 'k1 i_ f L! t- 1 » "

D. Lower Claiborne-upper Wilcox aquifer

._ 7 , -i_ -__^__ ^ .-.-,-

1 t «- 

 V ^"" 1 5 x CALIBRATED CKW : 

[ ROW 91 \S*~ - 0.5 x CALIBRATED CKW ". 

: i , i L__ __i i . i t L L ' "

3 10 20 30 40 50 60 

COLUMN

70 81

*, Figure^6.-Sensitivity of simulated^yheads to change in horizontal hydraulic 

conductivity (Kh).

142
A. Permeable zone A

FEE CALIBRATED HEAD, FROM INHEADREVISED DEPARTURE OF

2b 

0 

-25 

-50

25 

0 

-25

-50

25 

0 

-25 

-50

50 

25 

0 

-25

-50 

I

 - r r "-r T i 1 

V,

. ROW 43 

i . i , . i

B. Permeable zone B

 , ! , , , ! -T----

. ROW 43 ~»x^

 1 i | i T 

"*"~ - _ __ _. .

-i -T - ?- 

*~" -15 x CALIBRATED CKv) - 

-»-05 x CALIBRATED CKv) 

1 . 1 . 1 L ^L , 

r ' i ! i

. r ,, . ,

S

/' 1 .5 x CALIBRATED CKv] - 

- -05 x CALIBRATED CKv) . 

i i i i . i i

C. Permeable zone C

'-^-^

" ROW 43 jr--'

.1 1 1 1 , ,L. .,,.-. L-.-,.,-l ___

D. Lower Claiborne-upper Wilcox

 i i i i 

- - vf

- ROW 91 ___. -./

L i_V, ^ i ' *_

] 10 20 30

i i i 

^N^^^- -~ *

>_^_ JM , -._ 0 

 15 x CALIBRATED CKv) -

 «-05 x CALIBRATED CKv) ' l i l i l i 

aquifer

r i i

-

 1 5 x CALIBRATED CKv) "

- 05 x CALIBRATED CKv) . i i i I . i .

40 50 60 70 81

COLUMN

Figure c)T. Sensitivity of simulatedAheads to change in vertical 

hydraulic conductivity CKv).

143
A. Permeable zone A

FEET HEAD, IN CALIBRATED SEDFROM HEAD 

DEPARTURE OFREV

ou 

25 

0 

-25

50 

25 

0 

-25 

-50

250 

200 

150 

100 

50 

0 

-50

50 

25 

0 

-25 

-en

1 ADDED 0.01 TO DENSITIES>1.002

* -* ALL DENSITIES = 1.000 ^ _,. - """ ~~- ~. 

; ROW 43

 i 1 j 1 t. ~.J .1 ...L., .. . i . 1 i .1 ,i 1 i

B. Permeable zone B

1 ADDED 0.01 TO DENSITIES>1.002 . 

. _^ ALL DENSITIES = 1.000 ^^^^- ^

" *~ " ' \, ~^-,

" ROW 43

 1 , L L L . ... . 1 . 1 . 1 . 1

C. Permeable zone C

 ADDED 0.01 TO DENSITIES>1.002 , -~x /

: -* ALL DENSITIES = 1.000 / X_X

 ROW 43 / " ^~'

-

-

-

-

-

D. Lower Claiborne-upper Wilcox aquifer

; ___ ^ ':

 ADDED 0.01 TO DENSITIES>1.002 

: ROW 91 \ *-ALL DENSITIES = 1.000

..,, , L. ,.,.,, i i .-j.... ...i.. ,.,....,.,i, , , i ; i i , !...., ..*., , ..i ,. i.., .,,..L ...... ...i ,.

-

10 20 30 40

COLUMN

50 60 70 60

Figure^8 . Sensitivity of simulated 1982 heads to changes in water density,

144
A. Permeable zone A

tLLJ 

UJ 

U_

~7

FROM CALIBRATED REVISED HEAD, 1DEPARTURE OF

50 

25 

0 

-25

-50

50 

25 

0 

-25 

-50 

-75 

-100

50 

25 

0

-25 

-50 

-75 

-100

50 

25 

0 

-25 

-50 

-75 

-100

- 1.5 X CALIBRATED (S) - 

b 0.5 X CALIBRATED (S) 

~ ROW 43 '

i t i > i I i i < I , L 

B. Permeable zone B

..,.,,, ^^~^^_

- '^ ^^' 1.5 X CALIBRATED 

1 ROW 43 ""' - 0.5 X CALIBRATED

« n ' 1 ' \ f 4 1 v ] I

C. Permeable zone C

.->.,. '^jx^^<^_ '

1 nniAi A* \ j*^ 1 ' 5 X CALIBRATED 

- HUW 4d 

1.1.1,1.1,1 

\ ^^ -*-'0.5 X CALIBRATED

, _.!._.

D. Lower Claiborne-upper Wilcox aquifer

i i i i i i ' i

- " " "^x^

L -^-^. __^ ,.'^ ^1.5 X CALIBRATED

1 ROW 91 -* -0.5 X CALIBRATED

, 1 . 1 . 1 . 1 . 1 ,.!.... 1 

n in on trt Aft en en Tr\

-

(S) : 

(S) :

-

 

(S): (S):

-

(S) : 

(S) :

R

COLUMN

Figure -Sensitivity of simulated 1982 heads to changes in aquifer storage 

coefficient (S).

145
A. Permeable zone A. Well No. 9. Harris County.

UJ

<c 

u. 

a:

-50 

0

50 

100 

150 

200 

250 

300 

350 

400

B. Permeable zone B. Well No. 7. Harris County.

o

3 50

UJ 150

CO

, 200

UJ 

UJ 250 

U_

z 300

350

H 400

a: -50

UJ

so

100

150

200

250

300

350

400

C. Permeable zone C. Well No. 3. Harris County.

1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1965

EXPLANATION

MEASURED WATER LEVEL

--- e SIMULATED WATER LEVEL, CALIBRATED

'- ©SIMULATED WATER LEVEL, 1.5 X CALIBRATED (S)

>-~- SIMULATED WATER LEVEL, 0.5 X CALIBRATED (S)

Figure |00 . Sensitivity of simulated* 

storage coefficient (S).

levels

, 1910-82, to changes in aquifer

146
A. Lower Claiborne-upper Wilcox aquifer. Well No. 23. Zavala County.

o

00

o

UJ 

CO

UJ

-50 

0 

50 

100 

150 

200 

250 

300 

350 

400 

450

QL

UJ

0 

SO 

100 

150 

2GO 

250 

300 

550

B. 

<FLower Claiborne-upper Wilcox aquifer. Well No. 29. Frio County

r-f-r-r-i-r-j"r-r-r-r | r-r-r-r-ff t t »;»»«< j~r~r~i » | » » r-r-|~i-T

_l_«..*.j.-k.-i.*-»-ju^-L.>_*..*_*. U-> > i i t i.«- *_»_.L-»-».-*-t_l_j.a-4_«~ 1

1910 1S!5 1S20 1925 IS30 1S5S 134D ISiS 19SO 1S5S 1960 1965 1S70 1S7S 1980 1965

EXPLANATION

 MEASURED WATER LEVEL 

G----0 SIMULATED WATER LEVEL, CALIBRATED 

«*--« SIMULATED WATER LEVEL, 1.5 X CALIBRATED (S)

 ---- SIMULATED WATER LEVEL, 0.5 X CALIBRATED (S)

_ i lA/a

Figure |01 . Sensitivity of simulated 

storage coefficient (S).

, 1910-82, to changes in aquifer

147