610

45

10

10

610

290

90

59

LJ–65–32–625

Seabrook

LJ–65–23–322

Pasadena

LJ–65–16–930 (Shallow)

LJ–65–32–401

Johnson Space Center

LJ–65–32–424 (Shallow)

LJ–65–22–622

East End LJ–65–21–226

 Southwest

LJ–65–12–726

Addicks

LJ–65–14–746

Northeast

LJ–65–07–909

Lake Houston

LJ–65–32–428 (Deep)

Clear Lake

LJ–65–16–931 (Deep)

Baytown

7

5

4

3

22

11

6

6

6

55

10

9

8

7

7

8

9 8

8 99

Addicks Reservoir

Barker Reservoir

Galveston Bay

Lake Houston

HARRIS

 COUNTY

29o45'

30o00'

29o30'

29o45'

30o00'

29o30'

95o30' 95o15'

95o45'

95o00'

95o15'

95o30'

45 249

59

95o00'

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2013–5034

Prepared in cooperation with the Harris-Galveston Subsidence District

Groundwater Withdrawals 1976, 1990, and 2000–10 and LandSurface-Elevation Changes 2000–10 in Harris, Galveston, 

Fort Bend, Montgomery, and Brazoria Counties, Texas
Cover:

Top right, Typical turbine public-supply production well in the study area, southeastern Texas (2011).

Center, U.S. Geological Survey borehole extensometer located at the Addicks extensometer site in 

Harris County, Texas (2010).

Bottom right, Typical Port-A-Measure trailer and associated equipment operated by the HarrisGalveston Subsidence District (2001; photograph used with permission from the Harris-Galveston 

Subsidence District).

Left, Estimated land-surface subsidence in Harris County, Texas (from sheet 2 of Kasmarek and others, 

2009).
Groundwater Withdrawals 1976, 1990, 

and 2000–10 and Land-Surface-Elevation 

Changes 2000–10 in Harris, Galveston, Fort 

Bend, Montgomery, and Brazoria Counties, 

Texas

By Mark C. Kasmarek and Michaela R. Johnson

Prepared in cooperation with the Harris-Galveston Subsidence District

Scientific Investigations Report 2013–5034

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013

This and other USGS information products are available at http://store.usgs.gov/

U.S. Geological Survey

Box 25286, Denver Federal Center

Denver, CO 80225

To learn about the USGS and its information products visit http://www.usgs.gov/

1-888-ASK-USGS

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Kasmarek, M.C., and Johnson, M.R., 2013, Groundwater withdrawals 1976, 1990, and 2000–10 and land-surfaceelevation changes 2000–10 in Harris, Galveston, Fort Bend, Montgomery, and Brazoria Counties, Texas: U.S. 

Geological Survey Scientific Investigations Report 2013–5034, 17 p.
iii

Contents

Abstract ..........................................................................................................................................................1

Introduction ....................................................................................................................................................2

Purpose and Scope .............................................................................................................................2

Land-Surface-Elevation Loss and Compaction Processes ..........................................................4

Description of Study Area ...........................................................................................................................5

Hydrogeology ........................................................................................................................................6

Groundwater Withdrawals ..........................................................................................................................6

Methods for Determining Land-Surface-Elevation Changes ................................................................8

Land-Surface-Elevation Changes ............................................................................................................11

Data Limitations ...........................................................................................................................................15

Summary .......................................................................................................................................................15

References Cited .........................................................................................................................................16

Figures

1. Map showing locations of the study area and groundwater-regulatory districts 

in Harris, Galveston, Fort Bend, Montgomery, and Brazoria Counties, Texas ...................3

2. Photograph showing damaged water well with the lower section of slab and 

well casing protruding above land surface because of a decrease in land-surface 

elevation in Baytown, Texas, September 2004 .......................................................................4

3. Diagram depicting the mechanism of aquifer compaction and resultant decrease 

in land-surface elevation in an aquifer composed of sand, clay, and silt ..........................5

4. Hydrogeologic section of the Gulf Coast aquifer system in Grimes, Montgomery, 

Harris, and Galveston Counties, Texas ....................................................................................7

5. Graph showing total groundwater withdrawals in order from highest to lowest 

in Harris, Fort Bend, Montgomery, Brazoria, and Galveston Counties, Texas, 

2000–10 ..........................................................................................................................................9

6. Map showing locations of the U.S. Geological Survey borehole-extensometer 

sites, National Geodetic Survey Continuously Operating Reference Station, and 

Global Positioning System Port-A-Measure sites in Harris, Galveston, Fort Bend, 

Montgomery, and Brazoria Counties, Texas .........................................................................10

7. Map showing approximate land-surface-elevation changes caused by 

groundwater withdrawals and subsequent compaction of subsurface sediments 

in Harris, Galveston, Fort Bend, and Brazoria Counties, Texas, 2000–10 .........................12

8. Map showing approximate land-surface-elevation changes caused by 

groundwater withdrawals and subsequent compaction of subsurface sediments 

in Harris, Galveston, Fort Bend, Brazoria, and Montgomery Counties, Texas, 

2005–10 ........................................................................................................................................14

Tables

1. Total groundwater withdrawals in Harris, Galveston, Fort Bend, Montgomery, 

and Brazoria Counties, Texas, 1976, 1990, and 2000–10 ........................................................8

2. Land-surface-elevation-change data from monitoring sites in Harris, Galveston, 

Fort Bend, Montgomery, and Brazoria Counties, Texas ......................................................13
iv

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2)

Volume

gallon (gal) 3.785 liter (L)

Flow Rate

gallon per day (gal/d) 0.003785 cubic meter per day (m3/d)

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27).
Groundwater Withdrawals 1976, 1990, and 2000–10 and 

Land-Surface-Elevation Changes 2000–10 in Harris, 

Galveston, Fort Bend, Montgomery, and Brazoria 

Counties, Texas

By Mark C. Kasmarek and Michaela R. Johnson

Abstract

The study area comprising Harris County and parts of 

Galveston, Fort Bend, Montgomery, and Brazoria Counties 

in southeastern Texas forms part of one of the largest areas 

of land-surface-elevation change in the United States. Landsurface-elevation change in the study area primarily is caused 

by the withdrawal of groundwater. Groundwater withdrawn 

from the Chicot and Evangeline aquifers has been the 

primary source of water for municipal supply, industrial and 

commercial use, and irrigation in the study area. Groundwater 

withdrawals cause compaction of clay and silt layers abundant 

in the aquifers, which has in turn resulted in the widespread, 

substantial land-surface-elevation changes in the region 

with increased flooding. To estimate land-surface-elevation 

changes, the U.S. Geological Survey (USGS), in cooperation 

with the Harris-Galveston Subsidence District (HGSD), 

documented land-surface-elevation changes in the study area 

that occurred during 2000–10 and 2005–10 based on elevation 

data measured by 11 USGS borehole-extensometer sites, a 

National Geodetic Survey Continuously Operating Reference 

Station, and Global Positioning System Port-A-Measure 

(PAM) sites operated by the HGSD and the Fort Bend 

Subsidence District. Groundwater withdrawals in the study 

area also were documented for 1976, 1990, and 2000–10.

In 1976, about 428.9 million gallons per day (Mgal/d) 

were withdrawn from the aquifer system in Harris County, 

but by 2000, because of HGSD regulation, withdrawals 

had decreased to about 337.8 Mgal/d, or about a 21-percent 

reduction since 1976. By 2010, withdrawals had decreased 

to about 227.1 Mgal/d, or about a 47-percent reduction 

since 1976. Among the counties in the study area, the 

largest decrease in groundwater withdrawals has occurred in 

Galveston County since 1976. In 1976, about 27.4 Mgal/d 

were withdrawn from the aquifer system, and by 2000, 

withdrawals had decreased to about 4.12 Mgal/d, or about 

an 85-percent reduction since 1976. By 2010, withdrawals 

had decreased to about 0.626 Mgal/d, or about a 98-percent 

decrease since 1976.

Since the mid-1970s, Fort Bend and Montgomery 

Counties have undergone extensive urban development and 

corresponding large increases in groundwater withdrawals. 

Total groundwater withdrawal for Fort Bend County in 

1976 was about 16.0 Mgal/d, and by 2000, withdrawals 

had increased to about 86.5 Mgal/d, or about a 441-percent 

increase since 1976. By 2010, withdrawals in Fort Bend 

County had increased to about 99.8 Mgal/d, or about 

a 524-percent increase since 1976. Total groundwater 

withdrawal for Montgomery County in 1976 was about 7.84 

Mgal/d, and by 2000, withdrawals had increased to about 

43.6 Mgal/d, or about a 456-percent increase since 1976. By 

2010, withdrawals in Montgomery County had increased to 

about 64.2 Mgal/d, or about a 719-percent increase since 

1976. Total groundwater withdrawal in Brazoria County in 

1976 was about 18.0 Mgal/d, and by 2000, withdrawals 

had increased to about 26.0 Mgal/d, or about a 44-percent 

increase. By 2010, withdrawals in Brazoria County had 

increased to about 24.7 Mgal/d, or about a 37-percent increase 

since 1976.

Measured land-surface-elevation changes from December 

31, 2000, to December 31, 2010, ranged from an elevation 

increase of 0.06 feet (ft), or an average increase in elevation 

of 0.006 ft per year, at the Seabrook borehole extensometer 

located near Seabrook, Tex., to an elevation decrease of 1.28 

ft, or an average decrease in elevation of 0.128 ft per year, at a 

PAM station north of Jersey Village, Tex. (PAM 07). Measured 

land-surface-elevation changes from December 31, 2005, to 

December 31, 2010, ranged from an elevation increase of 0.07 

ft, or an average increase in elevation of 0.014 ft per year, 

at PAM 09 in far northeastern Harris County to an elevation 

decrease of 0.51 ft, or an average decrease in elevation of 

0.102 ft per year, at PAM 07.
2 Groundwater Withdrawals 1976, 1990, and 2000–10 and Land-Surface-Elevation Changes 2000–10

Introduction

The study area comprising Harris County and parts of 

Galveston, Fort Bend, Montgomery, and Brazoria Counties 

in southeastern Texas forms part of one of the largest areas 

of land-surface-elevation change in the United States (fig. 1) 

(Coplin and Galloway, 1999). Land-surface subsidence, 

which causes a decrease in land-surface elevation, was first 

documented in the study area in 1906 in Galveston County 

(Coplin and Galloway, 1999). Allen (1969) described groundsurface displacement (land-surface-elevation change) as the 

result of a variety of subsurface displacement mechanisms 

that included (among others) compaction of sediments by 

loading, drainage, vibration, and hydrocompaction. Landsurface-elevation change in the study area primarily is 

caused by the withdrawal of groundwater (Kasmarek, 2012, 

p. 13). Groundwater withdrawn from the Chicot, Evangeline, 

and Jasper aquifers has been the primary source of water 

for municipal supply, industrial and commercial use, and 

irrigation in the study area. Groundwater withdrawals cause 

compaction of clay and silt layers abundant in the aquifers, 

which has in turn resulted in the widespread, substantial 

land-surface-elevation changes in the region with increased 

flooding. Groundwater withdrawals in the area began as early 

as the 1890s (Kasmarek, 2012). By 1979, as much as 10 feet 

(ft) of subsidence had occurred in the study area, and about 

one-third of the study area had subsided more than 1 ft (Coplin 

and Galloway, 1999, p. 40). Comparison of the earliest 

measured land-surface elevations for 1915–17 to the Tropical 

Storm Allison Recovery Project (Harris County Flood Control 

District, 2012) elevations of 2001indicated that as much as 

13 ft of subsidence has occurred in southeastern Harris County 

(Kasmarek and others, 2009). This decrease in land-surface 

elevation has allowed saltwater inundation of coastal areas 

(Coplin and Galloway, 1999) and has increased the frequency 

and extent of flooding, such as the widespread, devastating 

flooding in the study area that resulted from Tropical Storm 

Allison in 2001 (Federal Emergency Management Agency 

and Harris County Flood Control District, 2002). Another 

effect of land-surface-elevation change is protrusion above 

land surface of wells and other fixed infrastructure (fig. 2), 

which is common in the study area. When the water well 

shown in figure 2 was initially constructed, the lower section 

of the slab and well casing were below land surface. As landsurface elevation decreased, the bottom section of the slab and 

casing protruded above the land surface, and by 2004, it was 

protruding more than 1ft.

The effects of groundwater withdrawals on landsurface-elevation changes and subsequent increased flooding 

prompted the Texas State Legislature in 1975 to authorize the 

establishment of the Harris-Galveston Subsidence District 

(HGSD) (Harris-Galveston Subsidence District, 2013) to 

regulate and reduce groundwater withdrawals in Harris and 

Galveston Counties. After the HGSD adopted a regulatory 

plan (Harris-Galveston Subsidence District, 2013), Harris and 

Galveston Counties were subdivided into Regulatory Areas 

1, 2, and 3 (fig. 1). In 1976, the first groundwater regulations 

were implemented in the study area in Harris and Galveston 

Counties. Later, in 1989, the Texas State Legislature 

established the Fort Bend Subsidence District (FBSD) to 

regulate groundwater withdrawals in Fort Bend County. After 

the FBSD adopted a regulatory plan (Fort Bend Subsidence 

District, 2009), Fort Bend County was subdivided into Area 

A, Area B, and the Richmond-Rosenberg Subarea (fig. 1). In 

1990, the first groundwater regulations were implemented 

in Fort Bend County. In 2001, the Lone Star Groundwater 

Conservation District (LSGCD) was established by the Texas 

State Legislature to regulate groundwater withdrawals in 

Montgomery County (Lone Star Groundwater Conservation 

District, 2011). In 2003, the Brazoria County Groundwater 

Conservation District (BCGCD) was established by the 

Texas State Legislature with the purpose to maintain the 

quality and availability of the county’s groundwater resource 

for current users and future generations (Brazoria County 

Groundwater Conservation District, 2008). Currently (2013), 

a transition to surface water as the primary source of supply 

in Harris and Galveston Counties is in effect as stipulated by 

the groundwater-regulatory plan developed by the HGSD in 

2001. This regulatory plan gradually decreases groundwater 

withdrawals while increasing usage of surface-water supplies.

To estimate the spatial distribution of land-surfaceelevation changes in the study area, the U.S. Geological 

Survey (USGS), in cooperation with the HGSD, documented 

land-surface-elevation changes in the study area that occurred 

during 2000–10 and 2005–10 based on elevation data 

measured by 11 USGS borehole-extensometer sites, a National 

Geodetic Survey (NGS) Continuously Operating Reference 

Station (CORS), and Global Positioning System (GPS) 

Port-A-Measure (PAM) sites operated by the HGSD and the 

FBSD. Groundwater withdrawals in the study area also were 

documented for 1976, 1990, and 2000–10 based on written 

communication in 2012 of withdrawal data from the HGSD, 

the Texas Water Development Board, and the LSGCD.

Purpose and Scope

This report describes total groundwater withdrawals 

in the study area for 1976, 1990, and 2000–10 and depicts 

land-surface-elevation changes during 2005–10 and 2000–10 

in parts of Harris, Galveston, Fort Bend, Montgomery, and 

Brazoria Counties. Changes in land-surface elevation were 

determined from land-surface-elevation data measured by 

the USGS borehole-extensometer network, an NGS CORS, 

and PAM sites operated by the HGSD and the FBSD in the 

study area. The hydrogeology of the study area is described, 

along with an overview of the mechanism of compaction. 

This report is intended to provide water-district managers and 

regional resource planners a means of evaluating the effect of 

changes in groundwater use on the occurrence of land-surfaceelevation change in the study area.
Introduction 3

Figure 1. Locations of the study area and groundwater-regulatory districts in Harris, Galveston, Fort Bend, Montgomery, and Brazoria 

Counties, Texas.

FORT BEND COUNTY

BRAZORIA 

COUNTY

GALVESTON 

COUNTY

WHARTON 

 COUNTY MATAGORDA

 COUNTY

HARRIS COUNTY

LIBERTY COUNTY

MONTGOMERY COUNTY

CHAMBERS 

COUNTY

WALLER COUNTY

Katy

Spring

Humble

Waller

Baytown

Houston

Tomball

Richmond

Galveston

Rosenberg

Sugar

Land

The Woodlands

Jersey

 Village

Seabrook

£¤90A

£¤90A

¦§ ̈610

¦§ ̈45

¦§ ̈10

146

£¤90

£¤59

¦§ ̈45

£¤ ¦§ ̈10

90

8

35

6

8

288

36

249

£¤90

146

146

Study area

TEXAS

29°58'

29°27'30"

95°37' 95°06'30"

Base from U.S. Geological Survey digital data, 1:100,000

Universal Transverse Mercator projection, zone 15

North American Datum of 1927

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Groundwater regulatory district

 Harris-Galveston Subsidence District

 Fort Bend Subsidence District

 Lone Star Groundwater Conservation District

 Brazoria County Groundwater Conservation District

Groundwater regulatory district area or subarea

 boundary

Fort Bend Subsidence

District Area A

Fort Bend

Subsidence

District Area B

Harris-Galveston 

Subsidence District 

Area 1

Harris-Galveston 

Subsidence District 

Area 3

Harris-Galveston 

Subsidence District 

Area 2

RichmondRosenberg 

Subarea

Spring Creek

Buffalo Bayou

Greens Bayou

Brays Bayou

Whiteoak Bayou

Sims Bayou

Chocolate Bayou

Little C

Cypress Creek

ypress Creek

Carpenters B ayou

Armand Bayou

San Jacinto River

West Fork

San Jacinto River

Barker 

Reservoir

Addicks 

Reservoir

Sheldon 

Reservoir

Lake 

Houston 

East Fork San Jacinto River

Trinity River

West Bay

Trinity Bay

GULF OF

MEXICO

Clear Creek

Galveston Bay

Brazos River

MONTGOMERY

COUNTY

BRAZORIA

 COUNTY

GALVESTON

 COUNTY

HARRIS

COUNTY

FORT BEND

COUNTY

Area enlarged
4 Groundwater Withdrawals 1976, 1990, and 2000–10 and Land-Surface-Elevation Changes 2000–10

Land-Surface-Elevation Loss and Compaction 

Processes

Land-surface subsidence, a decrease in land-surface 

elevation, can occur because of potentiometric-surface 

declines in the affected sections of the unconsolidated 

confined aquifers (Galloway and others, 1999). From the 

1890s to 1979, as much as 10 ft of land-surface-elevation 

loss had occurred in the study area, and approximately 

3,200 square miles (mi2) of the 11,000-mi2 geographic area 

had subsided more than 1 ft (Coplin and Galloway, 1999). 

Potentiometric-surface declines related to groundwater 

withdrawal cause a decrease in hydraulic pressure 

(depressuring) that creates a load on the skeletal matrix of 

the sediments in the aquifer and adjacent confining units 

(fig. 3). Because sand layers are more transmissive and 

less compressible compared to clay and silt layers (referred 

to hereinafter as “clay layers”), sand layers depressure 

more rapidly compared to clay layers. In addition, when 

groundwater withdrawals decrease, pressure equilibrium 

is reestablished more rapidly in the sand layers compared 

to the clay layers, with the amount of compaction of the 

sand layers usually being minor compared to the amount of 

compaction of the clay layers (Trahan, 1982; Galloway and 

others, 1999). The clay layers are often interbedded within 

the sand layers, and when depressuring occurs, the clay layers 

dewater more slowly compared to the sand layers. Some of the 

factors controlling land-surface-elevation change are (1) the 

percentage and age of clay composing the affected aquifer 

sediment, (2) the rate that withdrawal changes (decreases or 

increases), (3) the thicknesses of the individual clay layers 

controlling the time required for equilibrium of excessresidual-pore pressure, (4) the historical preconsolidation 

head, (5) the vertical stress of the saturated and unsaturated 

sediment overburden, and (6) the heterogeneity of the affected 

aquifer sediments (Coplin and Galloway, 1999; Kasmarek, 

2012; Kasmarek and others, 2012). As depressuring caused 

by groundwater withdrawals progresses, slow drainage of the 

clay layers continues to occur until the excess-residual-pore 

pressure in the clay layers equilibrates with the pore pressure 

of the adjacent sand layers. Adjacent sand layers undergo a 

similar loading process but are more transmissive and less 

compressible and therefore are more resistant to compaction 

than are clay layers (Kasmarek, 2012, p. 13). Clay layers 

compact more for a given water-level decline because, when 

the aquifer sediments are initially deposited, the individual flat 

and platy clay grains composing the clay layers are randomly 

oriented. After the clay layers depressurize, the orientation 

of the clay grains realigns, becoming perpendicular to the 

applied vertical overburden load (Galloway and others, 1999). 

Figure 2. Damaged water well with the lower section of slab and well casing protruding above land surface because of a decrease in 

land-surface elevation in Baytown, Texas, September 2004. 

Original land-surface 

elevation of slab when 

well was installed

Protruding well casing

 above land surface

Protruding well casing

 above land surface

Elevation of land

surface in 2004

Decrease in landsurface elevation

Decrease in landsurface elevation
Description of Study Area 5

Essentially, the water stored in the sand and clay layers prior 

to depressuring provides interstitial pore-space support for the 

sand- and clay-skeleton matrixes but provides more structural 

support to the clay-layer matrix compared to the sand-layer 

matrix. Additionally, compaction of the clay layers reduces 

the porosity and groundwater-storage capacity of the clay 

layers (fig. 3). Because most compaction of the clay layers 

is inelastic, about 90 percent of the compaction is permanent 

(Gabrysch and Bonnet, 1975). In areas where groundwater 

withdrawals decrease, the water level in the aquifers rises 

and repressures the compacted clay layers, but only a small 

amount of rebound of the land-surface elevation occurs 

(Gabrysch and Bonnet, 1975) (fig. 3). The compaction of one 

thin clay layer generally will not cause a measureable decrease 

in the land-surface elevation, but when thousands of feet of 

stacked clay- and sand-layer sequences (characteristic of the 

aquifer system in the study area) depressure and compact, a 

decrease in land-surface elevation often occurs (Gabrysch and 

Bonnet, 1975).

Description of Study Area

The study area (fig. 1) includes all of Harris County and 

parts of Galveston, Fort Bend, Montgomery, and Brazoria 

Counties. The study area is a gently sloping coastal plain, 

and land-surface elevations are topographically highest along 

the northwestern boundary. The vegetation in the northern 

parts of the study area generally is composed of hardwood 

and pine forests, but as land-surface elevation decreases 

toward the coast, the vegetation becomes increasingly 

dominated by shrubs and grasses. Surficial water bodies in 

the study area include Sheldon, Addicks, and Barker 

Reservoirs and Lake Houston; parts of the Brazos and 

San Jacinto River Basins; Trinity and Galveston Bays; 

and the Gulf of Mexico. The Gulf of Mexico, Trinity Bay, 

and Galveston Bay have a large effect on the downdip 

groundwater-flow system and climate of the area. Winters in 

the area generally have few days of freezing temperatures. 

During winter, moisture-laden Pacific and Canadian air masses 

produce regionally extensive bands of moderate rainfall. In 

contrast, summers generally have high relative humidity, and 

prevailing winds are from the southwest. During summer, 

atmospheric convective cells can produce low to high rates of 

localized rainfall, and infrequently, moisture-laden tropical air 

masses produce moderate to extremely high rates of rainfall 

(Kasmarek and Robinson, 2004). The average annual rainfall 

over the area is about 48 inches, and the average annual 

temperature is about 68 degrees Fahrenheit (Larkin and 

Bomar, 1983).

Figure 3. Diagram depicting the mechanism of aquifer compaction and resultant decrease in land-surface elevation in an aquifer 

composed of sand, clay, and silt (modified from Galloway and others, 1999, p. 9).

Permanent decrease in landsurface elevation caused by 

irreversible-inelastic 

deformation 

Compaction of the aquifer system is

concentrated in the fine-grained 

clay and silt layers 

When long-term withdrawals

lower groundwater levels

and raise pressure on the

clay and silt layers beyond a 

threshold amount, the clay 

and silt layers compact, and 

the land-surface elevation

decreases permanently

Depth

to water

Long-term water-level decline

modulated by the seasonal cycles

of groundwater withdrawals

Clay and silt

Sand and gravel

Original land surface

Resultant

land surface

Time Granular clay and silt

skeleton defining fluidfilled interstitial pore 

spaces that store 

groundwater 

Rearranged and compacted

granular clay and silt 

skeleton with reduced 

porosity and groundwaterstorage capacity

Sand and gravel

Clay and silt

Initial aquifer 

sediment 

thickness

before 

groundwater 

withdrawals

began

Recoverable land-surface 

elevation caused by reversible 

elastic deformation
6 Groundwater Withdrawals 1976, 1990, and 2000–10 and Land-Surface-Elevation Changes 2000–10

Hydrogeology

The three primary aquifers in the Gulf Coast aquifer 

system are the Chicot, Evangeline, and Jasper (fig. 4), 

which are composed of laterally discontinuous deposits of 

gravel, sand, silt, and clay. The Chicot aquifer, the youngest 

and uppermost, consists of Holocene- and Pleistocene-age 

sediments; the Evangeline aquifer, which underlies the Chicot 

aquifer, consists of Pliocene- and Miocene-age sediments; and 

the Jasper aquifer, the oldest and most deeply buried, consists 

of Miocene-age sediments. Additionally, the Burkeville 

confining unit and Catahoula confining system consist of 

Miocene-age sediments (fig. 4) (Baker, 1979, 1986). Through 

time, geologic and hydrologic processes created accretionarysediment wedges (stacked sequences of sediments) more 

than 7,600 ft thick at the coast (fig. 4) (Chowdhury and 

Turco, 2006). The sediments composing the Gulf Coast 

aquifer system were deposited by fluvial-deltaic processes 

and subsequently were eroded and redeposited (reworked) by 

reoccurring eustatic changes in sea level that occurred as a 

result of oscillations between glacial and interglacial climate 

conditions (Lambeck and others, 2002). The hydrogeologic 

units that dip and thicken from northwest to southeast 

compose the Gulf Coast aquifer system (fig. 4); the aquifers 

thus crop out in bands inland from and approximately 

parallel to the coast of the Gulf of Mexico (hereinafter the 

coast) and become progressively more deeply buried and 

confined toward the coast. Because of the paleodepositional 

environment, the highest percentage of clay in the sediments 

in the Chicot, Evangeline, and Jasper aquifers is adjacent 

to the coast; the percentage of clay progressively decreases 

towards the outcrop areas (Kasmarek and Robinson, 2004). 

The Burkeville confining unit separates the Evangeline and 

Jasper aquifers and restricts groundwater flow between the 

two aquifers. The Chicot aquifer can be differentiated from 

the geologically similar Evangeline aquifer based on hydraulic 

conductivity differences (Carr and others, 1985, p. 10) and 

where each aquifer outcrops—the Chicot aquifer outcrops 

closer to the coast compared to the Evangeline aquifer. The 

Chicot and Evangeline aquifers are hydraulically connected, 

which allows groundwater flow between the aquifers (fig. 4) 

allowing water-level changes in one of the aquifers to affect 

water levels in the adjacent aquifer (Kasmarek and Robinson, 

2004). Evidence of this exchange of flow between the aquifers 

is substantiated by two long-term (1977–2012) water-levelchange maps (Kasmarek and others, 2012, sheets 5 and 10) 

that show that the geographic areas where water levels have 

declined or risen in the Chicot and the Evangeline aquifers are 

approximately coincident.

The hydrogeologic cross section A–A ́ (fig. 4) extends 

from Grimes County through Montgomery and Harris 

Counties, terminates at the coast in Galveston County, and 

shows the three aquifers thickening and dipping toward the 

coast. Each aquifer becomes progressively thinner in the updip 

outcrop areas, and even though the aquifers exist in these 

areas, the saturated thickness of the sediments composing 

the aquifers is effectively insufficient to supply substantial 

quantities of groundwater. Most groundwater withdrawn in 

the updip outcrop areas is pumped from individual wells for 

domestic purposes.

Groundwater Withdrawals

Since the 1890s, groundwater withdrawals from the 

Chicot and Evangeline aquifers have been the primary source 

of water for development in Harris, Galveston, Fort Bend, 

Montgomery, and Brazoria Counties (Kasmarek, 2012). 

Groundwater withdrawals from the Jasper aquifer also are 

an important source of water in northern Harris County and 

in Montgomery County. Because of and coinciding with 

the establishment of the HGSD in 1975 and its subsequent 

regulatory plan, reductions in groundwater withdrawals began 

in 1976 because water levels of the Chicot and Evangeline 

aquifers had declined as much as 250 and 350 below sea 

level, respectively, (Gabrysch, 1979) and the relation between 

water-level declines and land-surface-elevation loss had been 

established and documented (Coplin and Galloway, 1999). 

Similarly, the FBSD, the LSGCD, and the BCGCD were 

established in 1990, 2000, and 2003, respectively, and have 

groundwater regulatory plans in effect. Hence, temporal and 

spatial changes in water use, use of surface-water sources, 

or conservation have resulted in appreciable changes in the 

volume and location of groundwater withdrawn in the study 

area. Additionally, the spatial distribution and amount of 

precipitation for any given year or period have an important 

effect on the volume of water withdrawn from the aquifer 

system. Even though withdrawals are regulated in the study 

area, an appreciable increase or decrease in withdrawals can 

occur for any given year or period when precipitation is below 

average or above average, respectively. For example, during 

2011, the total precipitation in the study area was below 

average, causing increased groundwater withdrawals and a 

subsequent decrease in water levels in the Chicot, Evangeline, 

Jasper aquifers (Kasmarek and others, 2012) compared to 

water levels in 2010 (Johnson and others, 2011).

Because of the establishment of the HGSD in 1975, 

groundwater withdrawals have been restricted in Harris and 

Galveston Counties. In 1976, a total of about 428.9 million 

gallons per day (Mgal/d) were withdrawn from the aquifer 

system in Harris County (Greg Lackey, Harris-Galveston 

Subsidence District, written commun., 2012) (table 1). 

By 1990, because of HGSD regulation, withdrawals had 

decreased to about 363.4 Mgal/d, or about a 15-percent 

reduction since 1976, and by 2000, withdrawals had 

decreased to about 337.8 Mgal/d (fig. 5), or about a 21-percent 

reduction since 1976. By 2010, withdrawals had decreased 

to about 227.1 Mgal/d, or about a 47-percent reduction since 

1976. For 2000–10, withdrawals ranged from a maximum 

of about 337.8 Mgal/d in 2000 to a minimum of about 213.8 

Mgal/d in 2007. The average withdrawal for 2000–10 was 

263.7 Mgal/d, or about a 38-percent reduction compared to 

withdrawals in 1976.
Figure 4. Hydrogeologic section of the Gulf Coast aquifer system in Grimes, Montgomery, Harris, and Galveston Counties, Texas (modified from Bake

Jasperoutcrop

Catahoula

 outcrop

Tertiary outcrop Quaternary outcrop

Evangeline

 outcrop

Burkevilleconfining unit outcrop

A

A'

10

1

2

3 4 5

6

7

8 9

11

WALLER COUNTY

GRIMES COUNTY

GALVESTON COUNTY

HARRIS COUNTY

MONTGOMERY COUNTY

HUMBLE

No. 1 Sealy

EXETER

No. 1 Bradley

KURDICK

No. 1 Stoneham

LONE STAR

No. 1 Goforth

SUPERIOR

No. B-1 McWhorter

NEWMAN & GEOTEK

No. 1 Ziegenhain

SPARTA

No. 1 Suttles et al.

TENNESSEE GAS

No. 1 Martin Unit

HUGHES

No. 1 Goar Est.

PHILLIPS

No. 5 Guaranty

Well number on location map

A 

NORTHWEST 

MONTGOMERY

COUNTY HARRIS COUNTY GALVESTON CO

GRIMES COUNTY

NAVD 88, North American Vertica

1 2 3 4 5 6 7 8 9 10 

Anahuac

Formation

Formation

Frio

Upper part of 

Catahoula

Sandstone

Base of 

Catahoula 

Sandstone 

Catahoula 

confining 

system (restricted) 

Jasper

aquifer

Base of 

Fleming 

Formation

Chicot aquifer

Evangeline aquifer

Burkeville

confining

unit

Approximate land surface

(Holocene- and Pleistocene-age sedimen

(Pliocene- and Miocene-age sediments)

(Miocene-age 

(Miocene-age 

(Miocene-age sediments)

Undifferentiated pre-Miocene deposits

+400

-400

-800

-1,200

-1,600

-2,000

-4,400

-4,800

-4,000

-3,600

-3,200

-2,800

-2,400

-5,200

-7,600

-7,200

-6,800

-6,400

-6,000

-5,600

NAVD 88

FEET 

VERTICAL SCALE GREATLY EXAGGERATED

0 4 8 12 16 MILES

0 4 8 12 16 KILOMETERS
8 Groundwater Withdrawals 1976, 1990, and 2000–10 and Land-Surface-Elevation Changes 2000–10

Groundwater withdrawals have decreased more in 

Galveston County since 1976 compared to all of the other 

counties in the study area. In 1976, about 27.4 Mgal/d were 

withdrawn from the aquifer system in Galveston County 

(Greg Lackey, Harris-Galveston Subsidence District, written 

commun., 2013) (table 1). By 1990, withdrawals had 

decreased to 4.56 Mgal/d, or about an 83-percent reduction 

since 1976, and by 2000, withdrawals had decreased to about 

4.12 Mgal/d (fig. 5), or about an 85-percent reduction since 

1976. By 2010, withdrawals had decreased to about 0.626 

Mgal/d, or about a 98-percent decrease since 1976. For 

2000–10, withdrawals ranged from a maximum of about 4.12 

Mgal/d in 2000 to a minimum of about 0.626 Mgal/d in 2010. 

The average withdrawal for 2000–10 was about 1.21 Mgal/d, 

or about a 96-percent reduction compared to withdrawals in 

1976.

Since the mid-1970s, Fort Bend and Montgomery 

Counties have undergone extensive urban development and 

corresponding large increases in groundwater withdrawals. 

Total groundwater withdrawal for Fort Bend County in 

1976 was about 16.0 Mgal/d (Bill Billingsley, Texas Water 

Development Board, written commun., 2012) (table 1). By 

1990, as development and groundwater use in the county 

continued to increase, withdrawals had increased to about 

62.6 Mgal/d, or about a 291-percent increase since 1976, and 

by 2000, withdrawals had increased to about 86.5 Mgal/d 

(fig. 5), or about a 441-percent increase since 1976. By 2010, 

withdrawals had further increased to about 99.8 Mgal/d, or 

about a 524-percent increase. For 2000–10, withdrawals 

ranged from a maximum of about 111.3 Mgal/d in 2009 

to a minimum of about 74.6 Mgal/d in 2001. The average 

withdrawal for 2000–10 was about 89.8 Mgal/d or about a 

461-percent increase compared to withdrawals in 1976.

Total groundwater withdrawal for Montgomery County 

in 1976 was about 7.84 Mgal/d (Bill Billingsley, Texas Water 

Development Board, written commun., 2012) (table 1). By 

1990, as development and groundwater use in the county 

continued to increase, withdrawals had increased to about 

24.9 Mgal/d, or about 218-percent increase since 1976, and by 

2000, withdrawals had increased to about 43.6 Mgal/d (fig. 5) 

(Samantha Reiter, Lone Star Groundwater Conservation 

District, written commun., 2012) (table 1), or about a 

456-percent increase since 1976. By 2010, withdrawals 

had increased to about 64.2 Mgal/d, or about a 719-percent 

increase since 1976. For 2000–10, withdrawals ranged from 

a maximum of about 64.7 Mgal/d in 2008 to a minimum of 

about 40.3 Mgal/d in 2001. The average withdrawal for 2000–

10 was about 53.3 Mgal/d, or about a 580-percent increase 

compared to withdrawals in 1976.

Total groundwater withdrawals in Brazoria County 

exceeded withdrawals in Fort Bend and Montgomery 

Counties in 1976, with a withdrawal of about 18.0 Mgal/d 

(Bill Billingsley, Texas Water Development Board, written 

commun., 2012) (table 1). By 1990, withdrawals had 

decreased to 15.4 Mgal/d, or about a 14-percent decrease since 

1976, but by 2000, withdrawals had increased to about 26.0 

Mgal/d, or about a 44-percent increase since 1976. By 2010, 

withdrawals had decreased to about 24.7 Mgal/d (fig. 5), or 

about a 37-percent increase since 1976 (table 1). For 2000–10, 

withdrawals ranged from a maximum of about 49.2 Mgal/d in 

2008 to a minimum of about 21.5 Mgal/d in 2002. The average 

withdrawal for 2000–10 was about 29.4 Mgal/d, or about a 

63-percent increase compared to withdrawals in 1976.

Methods for Determining LandSurface-Elevation Changes

Since mid-1973, the USGS has been collecting landsurface-elevation data (subsurface clay compaction) at 

borehole-extensometer sites in Harris and Galveston Counties. 

The HGSD has been monitoring land-surface elevation with 

the NGS by periodically conducting first-order leveling 

surveys and by using land-based GPS methods; one NGS 

CORS was used in this report. In 2000, the HGSD in 

cooperation with the FBSD began to establish a network of 

PAM sites in the study area based on land-surface-based GPS 

technology. Subsequently, in 2011 the LSGCD initiated PAM 

site installations in Montgomery County. The PAM network 

Table 1. Total groundwater withdrawals in Harris, Galveston, 

Fort Bend, Montgomery, and Brazoria Counties, Texas, 1976, 1990, 

and 2000–10.

[Groundwater withdrawal values are in million gallons per day]

Year Harris 

County1

Galveston 

County1

Fort Bend 

County2

Montgomery 

County2, 3

Brazoria 

County2

1976 428.9 27.4 16.0 7.84 18.0

1990 363.4 4.56 62.6 24.9 15.4

2000 337.8 4.12 86.5 43.6 26.0

2001 289.6 1.63 74.6 40.3 21.7

2002 276.9 1.03 78.7 42.7 21.5

2003 276.5 1.01 80.5 47.0 21.7

2004 233.6 0.692 82.0 47.0 24.1

2005 295.8 0.820 100.5 58.8 24.8

2006 246.6 0.751 94.2 59.6 31.5

2007 213.8 0.630 79.1 54.0 34.6

2008 256.4 0.783 101.1 64.7 49.2

2009 246.9 1.21 111.3 64.1 43.2

2010 227.1 0.626 99.8 64.2 24.7

1

Greg Lakey, Harris-Galveston Subsidence District, written commun., 2012.

2

Bill Billingsley, Texas Water Development Board, written commun., 2012.

3

Samantha Reiter, Lone Star Groundwater Conservation District, written 

commun., 2012.
Methods for Determining Land-Surface-Elevation Changes 9

continues to be expanded into other areas of interest as time 

and resources become available.

To define the geographic areas subject to land-surfaceelevation change and to quantify land-surface-elevation 

changes, data obtained from a combined monitoring network 

of 11 USGS borehole-extensometer sites, 1 NGS CORS, 

and 25 PAM sites were analyzed. The extensometer sites are 

located in Harris and Galveston Counties, the CORS is located 

in south-central Harris County, and the PAM sites are located 

in Harris, Galveston, Fort Bend, Brazoria, and Montgomery 

Counties (fig. 6). The USGS borehole-extensometer network 

was installed between 1973 and 1980 and continues to provide 

site-specific continuous land-surface-elevation-change data 

at 11 sites with an accuracy of 0.001 ft. At each extensometer 

site, an analog recorder is mounted to a steel table that is 

attached to the borehole-extensometer slab. A calibrated steel 

tape connects the recorder to the top of the 2.5-inch diameter 

inner pipe that is installed within the 4.5-inch-diameter outer 

casing. The outer casing is effectively a sleeve that isolates the 

inner casing from the adjacent borehole sediments. Because 

the steel table is anchored to the slab, land-surface-elevation 

changes can be accurately measured and recorded. These 

recorded values represent land-surface-elevation changes 

caused by compaction of subsurface sediment from the base of 

the slab (land surface) to the total depth of the extensometer. 

Detailed information on the scientific theory, operation, 

and construction of a borehole extensometer is presented in 

Gabrysch (1984) and Kasmarek and others (2012).

Figure 5. Total groundwater withdrawals in order from highest to lowest in Harris, Fort Bend, Montgomery, Brazoria, and Galveston 

Counties, Texas, 2000–10 (Harris-Galveston Subsidence District, written commun., 2012; Texas Water Development Board, written 

commun., 2012; Lone Star Groundwater Conservation District, written commun., 2012).

Year

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Total groundwater withdrawals, in million gallons per day

0

50

100

150

200

250

300

350

Total groundwater withdrawals, in million gallons

 per day, by county in order of highest to lowest 

 withdrawals (Harris-Galveston Subsidence

 District, written commun., 2012; Texas Water

 Development Board, written commun., 2012)

 Harris County

 Fort Bend County

 Montgomery County

 Brazoria County

 Galveston County

EXPLANATION
10 Groundwater Withdrawals 1976, 1990, and 2000–10 and Land-Surface-Elevation Changes 2000–10

Figure 6. Locations of the U.S. Geological Survey borehole-extensometer sites, National Geodetic Survey Continuously Operating 

Reference Station, and Global Positioning System Port-A-Measure sites in Harris, Galveston, Fort Bend, Montgomery, and Brazoria 

Counties, Texas.

FORT BEND COUNTY

BRAZORIA 

COUNTY

GALVESTON 

COUNTY

WHARTON 

 COUNTY MATAGORDA

 COUNTY

HARRIS COUNTY

LIBERTY COUNTY

WALLER COUNTY MONTGOMERY COUNTY

CHAMBERS 

COUNTY

£¤90A

£¤90A

¦§ ̈610

¦§ ̈45

¦§ ̈10

146

£¤90

£¤59

¦§ ̈45

£¤ ¦§ ̈10

90

8

35

6

8

288

36

249

£¤90

146

146

Katy

Spring

Humble

Waller

Baytown

Houston

Tomball

Richmond

Galveston

Rosenberg

Sugar

Land

The Woodlands

Jersey

 Village

Seabrook

Study area

TEXAS

ADDICKS

SEABROOK

EAST END

PASADENA

TEXAS CITY

SOUTHWEST

LAKE HOUSTON

CLEAR LAKE

DEEP

BAYTOWN

 SHALLOW

CLEAR LAKE 

SHALLOW

NORTHEAST 

TMCC

PAM 28

PAM 27

PAM 26

PAM 24

PAM 22 PAM 23

PAM 21 PAM 20

PAM 18

PAM 17

PAM 16

PAM 14

PAM 13

PAM 12

PAM 11

PAM 10

PAM 09

PAM 08

PAM 07

PAM 06

PAM 05

PAM 04

PAM 03

PAM 02

PAM 00 Johnson

 Space

 Center

29°58'

29°27'30"

95°37' 95°06'30"

Base from U.S. Geological Survey digital data, 1:100,000

Universal Transverse Mercator projection, zone 15

North American Datum of 1927

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Groundwater regulatory district boundary

Groundwater regulatory district area or subarea

 boundary

Measurement site, by type, and station name (table 1)

 Borehole-extensometer site

 Continuously Operating Reference Station (CORS)

PAM 05 Port-A-Measure (PAM) site

EAST END

TMCC

Spring Creek

Buffalo Bayou

Greens Bayou

Brays Bayou

Whiteoak Bayou

Sims Bayou

Chocolate Bayou

Little C

Cypress Creek

ypress Creek

Carpenters B ayou

Armand Bayou

San Jacinto River

West Fork

San Jacinto River

Barker 

Reservoir

Addicks 

Reservoir

Sheldon 

Reservoir

Lake 

Houston 

East Fork San Jacinto River

Trinity River

West Bay

Trinity Bay

Galveston Bay

GULF OF

MEXICO

Clear Creek

Brazos River
Land-Surface-Elevation Changes 11

Because the installation of additional borehole 

extensometers is cost prohibitive, in late 1993, the HGSD and 

the NGS cooperatively pioneered an improved, less expensive 

method of monitoring land-surface-elevation changes in 

the study area with the installation of PAM sites. The PAM 

sites measure land-surface-elevation changes by using 

GPS technology with dual-frequency, full-wavelength GPS 

receivers and geodetic fixed-height antennas. These data are 

collected at 30-second intervals and averaged over a 24-hour 

period. Subsequently, these data are post processed and 

analyzed and have a differential vertical accuracy of less than 

1 centimeter (Zilkowski and others, 2012). The CORS uses 

the same technology and has the same accuracy as do the 

PAM sites. Unlike the permanently located boreholeextensometer network, each PAM is mounted on a portable 

trailer and continually relocated among its four predetermined 

reference sites, each PAM occupying each of its reference 

sites for 1 week. This continuous and repetitive process allows 

one PAM trailer to provide measurements of land-surfaceelevation changes at each of its four reference sites on a 

monthly basis.

Land-Surface-Elevation Changes

To define the geographic areas that were undergoing 

land-surface-elevation changes and to quantify the rates of 

land-surface-elevation changes, data were obtained from the 

combined monitoring network from the 11 USGS borehole 

extensometers, 1 CORS, and 25 PAM sites (fig. 6) and 

contours of land-surface elevation were created. The contoured 

depictions of land-surface-elevation change were created 

by converting the point values of land-surface-elevation 

change to digital-elevation models (DEMs) for 2000–10 and 

2005–10. These DEMs were then used to generate contours 

within a geographic information system (GIS) for the two 

periods of interest. Subsequently, all contours were evaluated 

for accuracy and spatial location and manually modified as 

needed to ensure that they honored the point values of landsurface-elevation change. 

The contour creation technique used the Topo to Raster 

tool in the Environmental Systems Research Institute, 

Inc. (Redlands, Calif.), software package ArcGIS 9.3.1. 

(Environmental Systems Research Institute, Inc., 2012). Topo 

to Raster is based on the ANUDEM program that uses iterative 

finite-difference interpolation (Hutchinson, 1988, 1989). Topo 

to Raster is the same method in ArcGIS 9.x that was migrated 

from TopoGrid from ArcInfo Workstation 7.x (Environmental 

Systems Research Institute, Inc., 2012).

To estimate the spatial distribution of land-surfaceelevation changes in the study area, measured changes in landsurface elevation from 2000 to 2010 were calculated as the 

difference between the land-surface elevations on December 

31, 2000, and December 31, 2010. For the 10-year period, 

land-surface-elevation changes ranged from an increase of 

0.06 ft, or an average increase in elevation of 0.006 ft per 

year, at the Seabrook borehole extensometer located near 

Seabrook, Tex., to a decrease of 1.28 ft, or an average decrease 

in elevation of 0.128 ft per year, at PAM 07 located north of 

Jersey Village, Tex. (fig. 7) (table 2). Measured land-surfaceelevation changes during 2005–10 (December 31, 2005, to 

December 31, 2010) ranged from an increase of 0.07 ft, or 

an average increase in elevation of 0.014 ft per year, at PAM 

09 located in far northeastern Harris County to a decrease 

of 0.51 ft, or an average decrease in elevation of 0.102 ft 

per year, at PAM 07 located north of Jersey Village (fig. 8) 

(table 2). The spatial distribution of the land-surface-elevation 

changes (figs. 7 and 8) are either related to areas affected by 

increases in groundwater withdrawals such as HGSD Area 3 

and Fort Bend, Montgomery, and Brazoria Counties (areas 

where decreases in land-surface elevation occurred) or related 

to areas affected by decreases in withdrawals such as HGSD 

Area 1 and the extreme northeastern part of HGSD Area 3 

adjacent to Liberty County (areas undergoing no change in 

elevation or increases in land-surface elevation). These landsurface-elevation changes occur slowly and nonuniformly 

across the study area because of a variety of reasons. Some 

of the reasons for differences in land-surface-elevation 

changes include (1) the heterogeneity of the aquifer system; 

(2) inconsistent distribution and variable rates of precipitation 

that cause more groundwater to be withdrawn during below 

average periods or, conversely, less water withdrawn during 

above average periods; and most importantly (3) the spatial 

and temporal patterns of groundwater withdrawals stipulated 

by the regulatory policies of the HGSD, FBSD, BCGCD, 

and LSGCD. Therefore, in areas where withdrawals were 

restricted or areas where withdrawals were unrestricted, 

decreases and increases (respectively) in land-surface 

elevation can occur.

Groundwater withdrawals in Harris and Galveston 

Counties have been restricted in HGSD Area 1 since the mid1970s with a mandate by the HGSD that withdrawals were not 

to exceed more than 10 percent of total water demand (HarrisGalveston Subsidence District, 2013). Consequently, during 

2000–10, at the sites in HGSD Area 1 where water levels in 

the Chicot and Evangeline aquifers had been restricted and 

water levels rose, the affected numerous clay and silt layers 

responded elastically (fig. 3). This water-level rise caused a 

slight rise in land-surface elevation ranging from 0.01 ft to 

0.06 ft at the Northeast, Pasadena, Seabrook, and Johnson 

Space Center extensometer sites in the eastern part of the 

study area (fig. 7). Similarly, for 2005–10, a slight rise in 

land-surface elevation of as much as 0.05 ft at PAM 24 and 

PAM 28 and as much as 0.07 ft at PAM 09 was measured 

(fig. 8). Conversely, during 2000–10 in HGSD Area 3, where 

groundwater withdrawals were not restricted until 2010 

(Harris-Galveston Subsidence District, 2013), water levels in 

the aquifers declined, and a general decrease in land-surface 

elevation occurred (figs. 7 and 8) as the clay and silt layers 

responded inelastically (fig. 3).
12 Groundwater Withdrawals 1976, 1990, and 2000–10 and Land-Surface-Elevation Changes 2000–10

Figure 7. Approximate land-surface-elevation changes caused by groundwater withdrawals and subsequent compaction of 

subsurface sediments in Harris, Galveston, Fort Bend, and Brazoria Counties, Texas, 2000–10.

FORT BEND COUNTY

BRAZORIA 

COUNTY

GALVESTON 

COUNTY

WHARTON 

 COUNTY MATAGORDA

 COUNTY

HARRIS COUNTY

LIBERTY COUNTY

WALLER COUNTY MONTGOMERY COUNTY

CHAMBERS 

COUNTY

£¤90A

£¤90A

¦§ ̈610

¦§ ̈45

¦§ ̈10

146

£¤90

£¤59

¦§ ̈45

£¤ ¦§ ̈10

90

8

35

6

8

288

36

249

£¤90

146

146

0

-0.3

-0.1

-0.5

-0.6

-1.1

-1.2

-0.2

-0.4

-0.9

-1.0

-0.8

-0.3

-0.4

-0.5

-1.1

-1.0

-0.8

-0.3

-0.2

0

0.05

-0.2

-0.7

-0.6

-0.5

-0.4

-0.1

-0.7

-0.9

-0.1

Katy

Spring

Humble

Waller

Baytown

Houston

Tomball

Richmond

Galveston

Rosenberg

Sugar

Land

The Woodlands

Jersey

 Village

Seabrook

Study area

TEXAS

0.01

-0.1

0.01

-0.2

-0.02

-0.01

-0.02

-0.53

-0.92

-0.05

-0.14

0.06

-0.02

-0.19

-0.47

-0.95

-1.28

29°58'

29°27'30"

95°37' 95°06'30"

Base from U.S. Geological Survey digital data, 1:100,000

Universal Transverse Mercator projection, zone 15

North American Datum of 1927

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Approximate contour of land-surface-elevation 

 change—Interval 0.1 foot

Groundwater regulatory district boundary

Groundwater regulatory district area or subarea

 boundary

Monitoring site location—Value is land-surface-

 elevation change, in feet

-0.2

-0.05

Spring Creek

Buffalo Bayou

Brazos River

Greens Bayou

Brays Bayou

Whiteoak Bayou

Sims Bayou

Chocolate Bayou

Little C

Cypress Creek

ypress Creek

Carpenters B ayou

Armand Bayou

San Jacinto River

West Fork

San Jacinto River

Barker 

Reservoir

Addicks 

Reservoir

Sheldon 

Reservoir

Lake 

Houston 

East Fork San Jacinto River

Trinity River

West Bay

Trinity Bay

GULF OF

MEXICO

Clear Creek

Galveston Bay
Land-Surface-Elevation Changes 13

Table 2. Land-surface-elevation-change data from monitoring sites in Harris, Galveston, Fort Bend, Montgomery, and Brazoria 

Counties, Texas. 

[----, no change value determined because measurement(s) not available in date range; PAM, Harris-Galveston Subsidence District Port-A-Measure station; 

****, no January measurements were available at the beginning or ending of the year; CORS, National Geodetic Survey Continuously Operating Reference 

Station. Sites with site type “extensometer” represent data measured by the U.S. Geological Survey by using borehole extensometers. PAM and CORS 

station names and site types are from National Geodetic Survey CORS site search (http://www.ngs.noaa.gov/CORS/) or Harris-Galveston Subsidence District 

subsidence charts (http://mapper.subsidence.org/Chartindex.htm)]

Station name Site type Latitude Longitude

Beginning 

year of 

measurements

Land-surfaceelevation 

change, 2000–10

(feet)

Land-surfaceelevation 

change, 2005–10

(feet)

Addicks Extensometer 29° 47′ 27.47′′ N 95° 35′ 11.04′′ W 1974 -0.47 -0.14

Baytown C–1 Extensometer 29° 45′ 28.28′′ N 95° 1′ 50.38′′ W 1973 -0.14 -0.15

Clear Lake (shallow) Extensometer 29° 33′ 50.21′′ N 95° 7′ 10.16′′ W 1976 -0.01 ----

Clear Lake (deep) Extensometer 29° 33′ 49.14′′ N 95° 7′ 9.03′′ W 1976 -0.02 -0.02

East End Extensometer 29° 42′ 7.32′′ N 95° 16′ 27.43′′ W 1973 -0.02 -0.02

Lake Houston Extensometer 29° 54′ 48.44′′ N 95° 8′ 44.69′′ W 1980 -0.02 -0.01

Johnson Space Center Extensometer 29° 33′ 7.01′′ N 95° 5′ 46.44′′ W 1973 0.01 -0.03

Northeast Extensometer 29° 47′ 28.14′′ N 95° 20′ 3.17′′ W 1980 0.01 -0.02

Pasadena Extensometer 29° 42′ 36.63′′ N 95° 9′ 33.40′′ W 1975 0.05 -0.01

Seabrook Extensometer 29° 33′ 53.24′′ N 95° 1′ 17.27′′ W 1973 0.06 -0.01

Southwest Extensometer 29° 43′ 38.00′′ N 95° 27′ 3.00′′ W 1980 -0.10 -0.10

Texas City Extensometer 29° 24′ 58.80′′ N 94° 53′ 42.01′′ W 1973 0.00 0.00

PAM 00 PAM 29° 32′ 19.01′′ N 95° 9′ 8.02′′ W 1999 -0.05 0.00

PAM 02 PAM 30° 0′ 2.34′′ N 95° 24′ 57.09′′ W 1996 -0.92 -0.39

PAM 03 PAM 29° 49′ 14.91′′ N 95° 36′ 48.15′′ W 1999   -0.29

PAM 04 PAM 29° 37′ 49.40′′ N 95° 35′ 48.68′′ W 1996 -0.53 -0.26

PAM 05 PAM 29° 47′ 28.33′′ N 95° 35′ 9.24′′ W 1996 ** ** -0.21

PAM 06 PAM 29° 48′ 58.92′′ N 95° 40′ 40.00′′ W 1997   -0.31

PAM 07 PAM 29° 56′ 10.65′′ N 95° 34′ 35.91′′ W 1999 -1.28 -0.51

PAM 08 PAM 29° 58′ 46.82′′ N 95° 28′ 34.54′′ W 1999 -0.95 -0.39

PAM 09 PAM 30° 2′ 17.23′′ N 95° 4′ 17.24′′ W 1999 ** ** 0.07

PAM 10 PAM 29° 33′ 58.97′′ N 95° 47′ 57.01′′ W 1999 -0.20 -0.10

PAM 11 PAM 30° 1′ 55.77′′ N 95° 51′ 54.78′′ W 1999 -0.19 -0.10

PAM 12 PAM 30° 3′ 34.89′′ N 95° 15′ 47.04′′ W 2000   -0.44

PAM 13 PAM 30° 11′ 41.29′′ N 95° 29′ 23.94′′ W 2000 ** ** -0.27

PAM 14 PAM 29° 28′ 25.14′′ N 95° 38′ 38.75′′ W 2001 ---- -0.15

PAM 16 PAM 29° 32′ 40.05′′ N 95° 31′ 38.05′′ W 2000   -0.17

PAM 17 PAM 30° 5′ 28.17′′ N 95° 36′ 55.03′′ W 2000 ** ** -0.26

PAM 18 PAM 29° 57′ 53.75′′ N 95° 40′ 41.59′′ W 2000 **** -0.39

PAM 20 PAM 29° 31′ 58.44′′ N 95° 0′ 47.64′′ W 2002 ---- 0.02

PAM 21 PAM 29° 32′ 43.66′′ N 95° 18′ 43.44′′ W 2002 ---- -0.06

PAM 22 PAM 29° 20′ 4.26′′ N 95° 1′ 14.53′′ W 2002 ---- -0.05

PAM 23 PAM 29° 20′ 6.27′′ N 94° 55′ 3.97′′ W 2002 ---- 0.04

PAM 24 PAM 29° 40′ 7.65′′ N 95° 2′ 26.78′′ W 2002 ---- 0.05

PAM 26 PAM 29° 12′ 37.12′′ N 94° 56′ 17.94′′ W 2002 ---- 0.00

PAM 27 PAM 29° 34′ 59.28′′ N 95° 0′ 55.95′′ W 2002 ---- -0.06

PAM 28 PAM 29° 45′ 4.37′′ N 94° 55′ 3.44′′ W 2002 ---- 0.05

TMCC CORS 29° 42′ 8.42′′ N 95° 23′ 42.82′′ W 2003 ---- -0.05
14 Groundwater Withdrawals 1976, 1990, and 2000–10 and Land-Surface-Elevation Changes 2000–10

Figure 8. Approximate land-surface-elevation changes caused by groundwater withdrawals and subsequent compaction of 

subsurface sediments in Harris, Galveston, Fort Bend, Brazoria, and Montgomery Counties, Texas, 2005–10.

FORT BEND COUNTY

BRAZORIA 

COUNTY

GALVESTON 

COUNTY

WHARTON 

 COUNTY MATAGORDA

 COUNTY

HARRIS COUNTY

LIBERTY COUNTY

WALLER COUNTY MONTGOMERY COUNTY

CHAMBERS 

COUNTY

£¤90A

£¤90A

¦§ ̈610

¦§ ̈45

¦§ ̈10

146

£¤90

£¤59

¦§ ̈45

£¤ ¦§ ̈10

90

8

35

6

8

288

36

249

£¤90

146

146

0

-0.10

-0.20

-0.05

-0.15

-0.25

-0.30

-0.40

-0.35

0.05

-0.45

-0.50

-0.15

-0.10

0.05

-0.15

-0.25

-0.20

-0.05

-0.25

-0.05

0.05

0.05

0

0

0 0.02

0.07

-0.10

0.04

-0.10

-0.10

-0.06

-0.31

-0.21

-0.29

-0.03

-0.01

-0.02

-0.02

-0.15

-0.01

-0.02

-0.01

-0.14

-0.05

-0.05

-0.06

-0.39

-0.26

-0.17

-0.15

-0.27

-0.44

-0.39

-0.51

-0.26

-0.39

0.05

-0.10

0

-0.10 Katy

Spring

Humble

Waller

Baytown

Houston

Tomball

Richmond

Galveston

Rosenberg

Sugar

Land

The Woodlands

Jersey

 Village

Seabrook

Study area

TEXAS

29°58'

29°27'30"

95°37' 95°06'30"

Base from U.S. Geological Survey digital data, 1:100,000

Universal Transverse Mercator projection, zone 15

North American Datum of 1927

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

Approximate contour of land-surface-elevation 

 change—Interval 0.05 foot

Groundwater regulatory district boundary

Groundwater regulatory district area or subarea

 boundary

Monitoring site location—Value is land-surface-

 elevation change, in feet

0.05

-0.17

Spring Creek

Buffalo Bayou

Greens Bayou

Brays Bayou

Whiteoak Bayou

Sims Bayou

Chocolate Bayou

Little C

Cypress Creek

ypress Creek

Carpenters B ayou

Armand Bayou

San Jacinto River

West Fork

San Jacinto River

Barker 

Reservoir

Addicks 

Reservoir

Sheldon 

Reservoir

Lake 

Houston 

East Fork San Jacinto River

Trinity River

West Bay

Trinity Bay

GULF OF

MEXICO

Clear Creek

Galveston Bay

Brazos River
Summary 15

Data Limitations

The contour depictions of land-surface-elevation changes 

at any specific location are approximate. As such, these 

depictions are not intended for use in site-specific engineering 

or other design applications. Because the locations of the 

land-surface-elevation-monitoring sites are widely spaced in 

the study area, all contours are considered approximate. In 

addition to the different rates of groundwater withdrawals in 

the areas adjacent to each monitoring site, there is a difference 

in the clay-to-sand ratio at each site, and thus the rate of 

land-surface-elevation change varies from one monitoring 

site to another. Therefore, it is not possible to extrapolate or 

infer a rate of land-surface-elevation change between two 

adjacent monitoring sites. Users need to exercise discretion 

when drawing conclusions or making policy decisions based 

on these contoured depictions, with full awareness of the data 

limitations.

Summary

The study area comprising Harris County and parts of 

Galveston, Fort Bend, Montgomery, and Brazoria Counties 

in southeastern Texas forms part of one of the largest areas 

of land-surface-elevation change in the United States. Landsurface subsidence, which causes a decrease in land-surface 

elevation, was first documented in the study area in 1906 in 

Galveston County. Groundwater withdrawn from the Chicot 

and Evangeline aquifers has been the primary source of water 

for municipal supply, industrial and commercial use, and 

irrigation in the study area. Groundwater withdrawals cause 

compaction of clay and silt layers abundant in the aquifers, 

which has resulted in the widespread, substantial land-surfaceelevation changes in the region. Groundwater withdrawals in 

the area began as early as the 1890s. By 1979, as much as 10 

ft of subsidence had occurred in the study area, and about onethird of the study area had subsided more than 1 ft.

The effects of groundwater withdrawals on land-surfaceelevation change and the subsequent increased flooding 

prompted the Texas State Legislature in 1975 to authorize the 

establishment of the Harris-Galveston Subsidence District 

(HGSD) to regulate and reduce groundwater withdrawals in 

Harris and Galveston Counties. Subsequently, the Texas State 

Legislature established the Fort Bend Subsidence District 

(FBSD) in 1989, the Lone Star Groundwater Conservation 

District (LSGCD) in 2001, and the Brazoria County 

Groundwater Conservation District (BCGCD) in 2003 to 

regulate groundwater withdrawals.

The three primary aquifers in the Gulf Coast aquifer 

system are the Chicot, Evangeline, and Jasper, which are 

composed of laterally discontinuous deposits of gravel, sand, 

silt, and clay. The Chicot aquifer, the youngest and uppermost, 

consists of Holocene- and Pleistocene-age sediments; the 

Evangeline aquifer, which underlies the Chicot aquifer, 

consists of Pliocene- and Miocene-age sediments; and the 

Jasper aquifer, the oldest and most deeply buried, consists 

of Miocene-age sediments. Through time, geologic and 

hydrologic processes created accretionary-sediment wedges 

(stacked sequences of sediments) more than 7,600 ft thick at 

the coast.

Since the 1890s, groundwater withdrawals from the 

Chicot and Evangeline aquifers have been the primary 

source of water for development in Harris, Galveston, Fort 

Bend, Montgomery, and Brazoria Counties. Groundwater 

withdrawals from the Jasper aquifer also are an important 

source of water in northern Harris County, and in Montgomery 

County. Temporal and spatial changes in water use, through 

regulation, use of surface-water sources, or conservation, have 

resulted in appreciable changes in the volume and location of 

groundwater withdrawn in the study area.

Because of and coinciding with the establishment of the 

HGSD in 1975, groundwater withdrawals have been restricted 

in Harris and Galveston Counties. In 1976, a total of about 

428.9 million gallons per day (Mgal/d) were withdrawn in 

Harris County. By 2000, withdrawals had decreased to about 

337.8 Mgal/d, or about a 21-percent reduction since 1976. 

The average withdrawal for 2000–10 was 263.7 Mgal/d, or 

about a 38-percent reduction compared to withdrawals in 

1976. Galveston County has had the greatest decrease in 

groundwater withdrawal of all the counties in the study area. 

In 1976, about 27.4 Mgal/d were withdrawn in Galveston 

County from the aquifer system. By 2000, withdrawals had 

decreased to about 4.12 Mgal/d, or about an 85-percent 

reduction since 1976. The average withdrawal for 2000–10 

was about 1.21 Mgal/d, or about a 96-percent reduction 

compared to withdrawals in 1976.

Since the mid-1970s, Fort Bend and Montgomery 

Counties have undergone extensive urban development and 

corresponding large increases in groundwater withdrawals. 

Total groundwater withdrawal for Fort Bend County in 1976 

was about 16.0 Mgal/d. By 2000, withdrawals had increased to 

about 86.5 Mgal/d, or about a 441-percent increase since 1976. 

The average withdrawal for 2000–10 was about 89.8 Mgal/d, 

or about a 461-percent increase compared to withdrawals 

in 1976. Total groundwater withdrawal for Montgomery 

County in 1976 was about 7.84 Mgal/d. By 2000, withdrawals 

had increased to about 43.6 Mgal/d, or about a 456-percent 

increase since 1976. The average withdrawal for 2000–10 was 

about 53.3 Mgal/d, or about a 580-percent increase compared 

to withdrawals in 1976. Total groundwater withdrawal in 

Brazoria County in 1976 was about 18.0 Mgal/d. By 2000, 

withdrawals had increased to about 26.0 Mgal/d, or about a 

44-percent increase. The average withdrawal for 2000–10 was 

about 29.4 Mgal/d, or about a 63-percent increase compared to 

withdrawals in 1976.

To define the geographic areas that were undergoing 

land-surface-elevation changes and to quantify the rates of 

land-surface-elevation changes, data were obtained from the 

combined monitoring network of 11 U.S. Geological Survey 

(USGS) borehole-extensometer sites, 1 National Geodetic 
16 Groundwater Withdrawals 1976, 1990, and 2000–10 and Land-Surface-Elevation Changes 2000–10

Survey (NGS) Continuously Operating Reference Station 

(CORS), and 25 Global Positioning System Port-A-Measure 

(PAM) sites. Measured changes in land-surface elevation from 

2000 to 2010 were calculated as the difference between the 

land-surface elevations on December 31, 2000, and December 

31, 2010. For the 10-year period, land-surface-elevation 

changes ranged from an increase of 0.06 ft, or an average 

increase in elevation of 0.006 ft per year, at the Seabrook 

borehole extensometer located near Seabrook, Tex., to a 

decrease of 1.28 ft, or an average decrease in elevation of 

0.128 ft per year, at PAM 07 located north of Jersey Village, 

Tex.

Measured land-surface-elevation changes during 2005–10 

(December 31, 2005, to December 31, 2010) ranged from 

an increase of 0.07 ft, or an average increase in elevation 

of 0.014 ft per year, at PAM 09 located in far northeastern 

Harris County to a decrease of 0.51 ft, or an average decrease 

in elevation of 0.102 ft per year, at PAM 07 located north of 

Jersey Village. The spatial distribution of the land-surfaceelevation changes are related to areas affected by increases 

in groundwater withdrawals such as HGSD Regulatory Area 

3 and Fort Bend, Montgomery, and Brazoria Counties (areas 

undergoing decreases in land-surface elevation) or areas 

affected by decreases in withdrawals such as HGSD Area 1 

(areas undergoing increases in land-surface elevation or no 

change in elevation).

These land-surface-elevation changes occur slowly 

and nonuniformly across the study area because of a variety 

of reasons. Some of the reasons for differences in landsurface-elevation changes include (1) the heterogeneity of 

the aquifer system; (2) inconsistent distribution and variable 

rates of precipitation that cause more groundwater to be 

withdrawn during below average periods or, conversely, 

less water withdrawn during above average periods; and 

most importantly (3) the spatial and temporal patterns of 

groundwater withdrawals stipulated by the regulatory policies 

of the HGSD, FBSD, LSGCD, and BCGCD. Therefore, 

in areas where withdrawals were restricted or areas where 

withdrawals were unrestricted, decreases and increases 

(respectively) in land-surface elevation can occur.

References Cited

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D.J., and Kiersch, George, eds., Reviews in engineering 

geology: Geological Society of America, v. 2, p. 305–342.

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http://tx.usgs.gov/
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