Withdrawals in the Northern Part of the 

Gulf Coast Aquifer System, Texas 

Scientific Investigations Report 2005–5024 

U.S. Department of the Interior 

U.S. Geological Survey 
Back of Cover 
Evaluation of Ground-Water Flow and LandSurface Subsidence Caused by Hypothetical 

Withdrawals in the Northern Part of the 

Gulf Coast Aquifer System, Texas 

By Mark C. Kasmarek, Brian D. Reece, and Natalie A. Houston 

In cooperation with the Texas Water Development Board and 

the Harris-Galveston Coastal Subsidence District 

Scientific Investigations Report 2005–5024 

U.S. Department of the Interior 

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

Gale A. Norton, Secretary 

U.S. Geological Survey 

Charles G. Groat, Director 

U.S. Geological Survey, Reston, Virginia: 2005 

For sale by U.S. Geological Survey, Information Services


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Suggested citation:


Kasmarek, M.C., Reece, B.D., and Houston, N.A., 2005, Evaluation of ground-water flow and land-surface 

subsidence caused by hypothetical withdrawals in the northern part of the Gulf Coast aquifer system, 

Texas: U.S. Geological Survey Scientific Investigations Report 2005–5024, 70 p. 
 iii 

Contents 

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


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


Description of the Northern Gulf Coast Ground-Water Availability Modeling Model . . . . . . . . . . . . . . . . . . . 2


Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4


Hypothetical Withdrawals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4


Description of Texas Water Development Board Scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . 4


Description of Harris-Galveston Coastal Subsidence District Scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4


Evaluation of Ground-Water Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6


Results Using Texas Water Development Board Scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6


Results Using Harris-Galveston Coastal Subsidence District Scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13


Evaluation of Land-Surface Subsidence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34


Results Using Texas Water Development Board Scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34


Results Using Harris-Galveston Coastal Subsidence District Scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53


Limitations on Use of Model Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53


Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58


References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59


Appendix 1—Modifications to Northern Gulf Coast Ground-Water Availability Modeling Model Based 


on Simulations of Hypothetical Withdrawals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61


Appendix 2—Description of Methods for Distributing Withdrawals to Model Cells . . . . . . . . . . . . . . . . . . . . . . . . . . 65


Figures 

1.	 Map showing location of Northern Gulf Coast Ground-Water Availability Modeling (NGC 


GAM) model area and the Harris-Galveston Coastal Subsidence District (HGCSD) subarea,


Texas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3


2–3. Graphs showing:


2.	 Withdrawals in the Chicot, Evangeline, and Jasper aquifers in the NGC GAM model 


area from 2000 to 2050, TWDB withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5


3.	 Withdrawals in the Chicot, Evangeline, and Jasper aquifers in the NGC GAM model 


area from 1995 to 2030, HGCSD withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6


4–21. Maps showing:


4.	 Simulated 2000 potentiometric surface of the Chicot aquifer in the NGC GAM model


area resulting from TWDB withdrawal scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7


5.	 Simulated 2010 potentiometric surface of the Chicot aquifer in the NGC GAM model


area resulting from TWDB withdrawal scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8


6.	 Simulated 2020 potentiometric surface of the Chicot aquifer in the NGC GAM model


area resulting from TWDB withdrawal scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9


7.	 Simulated 2030 potentiometric surface of the Chicot aquifer in the NGC GAM model


area resulting from TWDB withdrawal scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10


8.	 Simulated 2040 potentiometric surface of the Chicot aquifer in the NGC GAM model


area resulting from TWDB withdrawal scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

iv 

9.	 Simulated 2050 potentiometric surface of the Chicot aquifer in the NGC GAM model


area resulting from TWDB withdrawal scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12


10.	 Simulated 2000 potentiometric surface of the Evangeline aquifer in the NGC GAM 


model area resulting from TWDB withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14


11.	 Simulated 2010 potentiometric surface of the Evangeline aquifer in the NGC GAM 


model area resulting from TWDB withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15


12.	 Simulated 2020 potentiometric surface of the Evangeline aquifer in the NGC GAM 


model area resulting from TWDB withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16


13.	 Simulated 2030 potentiometric surface of the Evangeline aquifer in the NGC GAM 


model area resulting from TWDB withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17


14.	 Simulated 2040 potentiometric surface of the Evangeline aquifer in the NGC GAM 


model area resulting from TWDB withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18


15.	 Simulated 2050 potentiometric surface of the Evangeline aquifer in the NGC GAM 


model area resulting from TWDB withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19


16.	 Simulated 2000 potentiometric surface of the Jasper aquifer in the NGC GAM model 


area resulting from TWDB withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20


17.	 Simulated 2010 potentiometric surface of the Jasper aquifer in the NGC GAM model 


area resulting from TWDB withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21


18.	 Simulated 2020 potentiometric surface of the Jasper aquifer in the NGC GAM model 


area resulting from TWDB withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22


19.	 Simulated 2030 potentiometric surface of the Jasper aquifer in the NGC GAM model 


area resulting from TWDB withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23


20.	 Simulated 2040 potentiometric surface of the Jasper aquifer in the NGC GAM model 


area resulting from TWDB withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24


21.	 Simulated 2050 potentiometric surface of the Jasper aquifer in the NGC GAM model 

area resulting from TWDB withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25


22–25. Diagrams showing:


22.	 Simulated 2000 water-budget components of the hydrogeologic units of the NGC 


GAM model resulting from TWDB withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26


23.	 Simulated 2010 water-budget components of the hydrogeologic units of the NGC 


GAM model resulting from TWDB withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27


24.	 Simulated 2030 water-budget components of the hydrogeologic units of the NGC 


GAM model resulting from TWDB withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28


25.	 Simulated 2050 water-budget components of the hydrogeologic units of the NGC 

GAM model resulting from TWDB withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29


26–37. Maps showing:


26.	 Simulated 1995 potentiometric surface of the Chicot aquifer in the NGC GAM model


area resulting from HGCSD withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30


27.	 Simulated 2010 potentiometric surface of the Chicot aquifer in the NGC GAM model


area resulting from HGCSD withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31


28.	 Simulated 2020 potentiometric surface of the Chicot aquifer in the NGC GAM model


area resulting from HGCSD withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32


29.	 Simulated 2030 potentiometric surface of the Chicot aquifer in the NGC GAM model


area resulting from HGCSD withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33


30.	 Simulated 1995 potentiometric surface of the Evangeline aquifer in the NGC GAM 


model area resulting from HGCSD withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35


31.	 Simulated 2010 potentiometric surface of the Evangeline aquifer in the NGC GAM 


model area resulting from HGCSD withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

 v 

32.	 Simulated 2020 potentiometric surface of the Evangeline aquifer in the NGC GAM 


model area resulting from HGCSD withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37


33.	 Simulated 2030 potentiometric surface of the Evangeline aquifer in the NGC GAM 


model area resulting from HGCSD withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38


34.	 Simulated 1995 potentiometric surface of the Jasper aquifer in the NGC GAM model 


area resulting from HGCSD withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39


35.	 Simulated 2010 potentiometric surface of the Jasper aquifer in the NGC GAM model 


area resulting from HGCSD withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40


36.	 Simulated 2020 potentiometric surface of the Jasper aquifer in the NGC GAM model 


area resulting from HGCSD withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41


37.	 Simulated 2030 potentiometric surface of the Jasper aquifer in the NGC GAM model 

area resulting from HGCSD withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42


38–41. Diagrams showing:


38.	 Simulated 1995 water-budget components of the hydrogeologic units of the NGC GAM 


model resulting from HGCSD withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43


39.	 Simulated 2010 water-budget components of the hydrogeologic units of the NGC GAM 


model resulting from HGCSD withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44


40.	 Simulated 2020 water-budget components of the hydrogeologic units of the NGC GAM 


model resulting from HGCSD withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45


41.	 Simulated 2030 water-budget components of the hydrogeologic units of the NGC GAM 

model resulting from HGCSD withdrawal scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46


42–51. Maps showing: 


42.	 Simulated 2000 land-surface subsidence in the NGC GAM model area resulting from


TWDB withdrawal scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47


43.	 Simulated 2010 land-surface subsidence in the NGC GAM model area resulting from


TWDB withdrawal scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48


44.	 Simulated 2020 land-surface subsidence in the NGC GAM model area resulting from


TWDB withdrawal scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49


45.	 Simulated 2030 land-surface subsidence in the NGC GAM model area resulting from


TWDB withdrawal scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50


46.	 Simulated 2040 land-surface subsidence in the NGC GAM model area resulting from


TWDB withdrawal scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51


47.	 Simulated 2050 land-surface subsidence in the NGC GAM model area resulting from


TWDB withdrawal scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52


48.	 Simulated 1995 land-surface subsidence in the NGC GAM model area resulting from


HGCSD withdrawal scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54


49.	 Simulated 2010 land-surface subsidence in the NGC GAM model area resulting from


HGCSD withdrawal scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55


50.	 Simulated 2020 land-surface subsidence in the NGC GAM model area resulting from


HGCSD withdrawal scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56


51.	 Simulated 2030 land-surface subsidence in the NGC GAM model area resulting from


HGCSD withdrawal scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57


Datums 

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 


(NGVD 29).


Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). 
vi

Blank Page 
Evaluation of Ground-Water Flow and LandSurface Subsidence Caused by Hypothetical 

Withdrawals in the Northern Part of the 

Gulf Coast Aquifer System, Texas 

By Mark C. Kasmarek, Brian D. Reece, and Natalie A. Houston 

Abstract 

During 2003–04 the U.S. Geological Survey, in cooperation with the Texas Water Development Board (TWDB) and the 

Harris-Galveston Coastal Subsidence District (HGCSD), used 

the previously developed Northern Gulf Coast Ground-Water 

Availability Modeling (NGC GAM) model to evaluate the 

effects of hypothetical projected withdrawals on ground-water 

flow in the northern part of the Gulf Coast aquifer system and 

land-surface subsidence in the NGC GAM model area of Texas. 

The Gulf Coast aquifer system comprises, from the surface, the 

Chicot and Evangeline aquifers, the Burkeville confining unit, 

the Jasper aquifer, and the Catahoula confining unit. Two withdrawal scenarios were simulated. The first scenario comprises 

historical withdrawals from the aquifer system for 1891–2000 

and hypothetical projected withdrawals for 2001–50 compiled 

by the TWDB (TWDB scenario). The projected withdrawals 

compiled by the TWDB are based on ground-water demands 

estimated by regional water planning groups. The second 

scenario is a “merge” of the TWDB scenario with an alternate 

set of projected withdrawals from the Chicot and Evangeline 

aquifers in the Houston metropolitan area for 1995–2030 provided by the HGCSD (HGCSD scenario). 

Under the TWDB scenario withdrawals from the entire 

system are projected to be about the same in 2050 as in 2000. 

The simulated potentiometric surfaces of the Chicot aquifer for 

2010, 2020, 2030, 2040, and 2050 show relatively little change 

in configuration from the simulated 2000 potentiometric surface (maximum water-level depths in southern Harris County 

150–200 feet below NGVD 29). The simulated decadal potentiometric surfaces of the Evangeline aquifer show the most 

change between 2000 and 2010. The area of water levels 250– 

400 feet below NGVD 29 in western Harris County in 2000 

shifts southeastward to southern Harris County, and water levels recover to 200–250 feet below NGVD 29 by 2010. Water 

levels in southern Harris County recover to 150–200 feet below 

NGVD 29 by 2020 and remain in that range through 2050. A 

relatively small cone of depression in southern Montgomery 

County that did not appear in the 2000 surface develops and 

enlarges during the projected period, with a maximum depth of 

250–300 feet below NGVD 29 in 2030, 2040, and 2050. The 

simulated decadal potentiometric surfaces of the Jasper aquifer 

each have a major cone of depression centered in southern 

Montgomery County that was minimally developed in 2000 but 

reaches depths of 550–650 feet below NGVD 29 in the 2020, 

2030, 2040, and 2050 surfaces. Under the TWDB scenario the 

percentage of withdrawals supplied by net recharge increases 

from 75 percent in 2000 to 87 percent in 2050, and the percentage of withdrawals supplied by storage decreases from 25 percent in 2000 to 13 percent in 2050. 

Under the HGCSD scenario, withdrawals from the Chicot 

and Evangeline aquifers increase about 74 percent during 

1995–2030; Jasper aquifer withdrawals are unchanged from 

those of the TWDB scenario. For the 2010, 2020, and 2030 

potentiometric surfaces of the Chicot and Evangeline aquifers, 

the substantially greater withdrawals of the HGCSD scenario 

relative to those of the TWDB scenario result in progressively 

deeper cones of depression than those in the potentiometric surfaces associated with the TWDB scenario—for the Chicot aquifer in southern Harris County, 400–450 feet below NGVD 29 in 

2030; for the Evangeline aquifer in southern Montgomery 

County, 700–750 feet below NGVD 29 in 2030. Although 

Jasper aquifer withdrawals are the same for both scenarios, the 

major cone of depression centered in southern Montgomery 

County in the 2030 potentiometric surface is 50 feet deeper at 

its center (600–700 feet below NGVD 29) than the cone in the 

2030 surface under the TWDB scenario. Under the HGCSD 

scenario, the percentage of withdrawals supplied by net 

recharge decreases from 72 percent in 1995 to 57 percent in 

2030, and the percentage of withdrawals supplied by storage 

increases from 28 percent in 2000 to 43 percent in 2030. About 

85 percent of the increase supplied by storage is from the compaction of clay. 
2 Ground-Water Flow and Land-Surface Subsidence in the Northern Part of the Gulf Coast Aquifer System, Texas 

Land-surface subsidence in the major area of subsidence 

centered in Harris and Galveston Counties during 2000–50 

that results from simulating the TWDB withdrawal scenario 

expands slightly to the west and increases in places. The 

maximum change occurs in the Conroe area where subsidence 

increases from about 4 to about 13 feet during the projected 

period. Land-surface subsidence in the major area of subsidence 

during 1995–2030 that results from simulating the HGCSD 

withdrawal scenario increases substantially. For example, in 

east-central Harris County maximum subsidence increases 

from about 10–11 feet in 1995 to 22 feet in 2030. 

The hypothetical projected withdrawal scenarios are estimates of future withdrawals and might not represent actual 

future withdrawals. The simplifying assumptions that the 

downdip limit of freshwater flow in each hydrogeologic unit is 

a stable, sharp interface across which no flow occurs and that 

the base of the system is a no-flow boundary become less realistic and thus increase the uncertainty in results as drawdowns 

increase. The presence of uncertainty dictates that the results of 

the predictive simulations described in this report be used with 

caution in any decision-making process. 

Introduction 

The northern part of the Gulf Coast aquifer system in 

Texas supplies most of the water for municipal, industrial, and 

agricultural uses in an approximately 25,000-square-mile (mi

2) 

area that includes the Houston metropolitan area. From land 

surface downward, the aquifer system comprises the Chicot and 

Evangeline aquifers, the Burkeville confining unit, the Jasper 

aquifer, and the Catahoula confining unit. These hydrogeologic 

units are composed of interbedded sand, clay, and silt. Withdrawals of large quantities of ground water that began around 

1900 have resulted in declines in the potentiometric surfaces 

of the aquifers of tens to hundreds of feet and subsequent landsurface subsidence of as much as about 10 feet (ft), primarily in 

the Houston metropolitan area. 

During 1999–2004, the U.S. Geological Survey (USGS), 

in cooperation with the Texas Water Development Board 

(TWDB) and the Harris-Galveston Coastal Subsidence District 

(HGCSD), conducted a study as a part of the TWDB GroundWater Availability Modeling (GAM) program to develop a 

computer model to simulate ground-water flow and landsurface subsidence in the northern part of the Gulf Coast aquifer 

system in Texas (Kasmarek and Robinson, 2004) (fig. 1). The 

objective of the GAM program is to provide reliable, timely 

data on ground-water availability to the citizens of Texas to 

ensure adequacy of water supplies or recognition of inadequacy 

of supplies throughout the 50-year planning (or projected) 

period 2001–50 (Texas Water Development Board, 2004). The 

ground-water-flow model of Kasmarek and Robinson (2004) 

(hereinafter, the Northern Gulf Coast [NGC] GAM model) was 

calibrated in a series of transient simulations using distributed, 

historical withdrawals from 1891 through 2000. Hypothetical 

withdrawals to represent potential future water demand during 

the GAM 50-year projected period 2001–50 were not simulated 

as a part of the Kasmarek and Robinson (2004) study. 

During 2003–04 the USGS, again in cooperation with the 

TWDB and the HGCSD, conducted a second-phase, or followup, study using the NGC GAM model to evaluate the effects of 

hypothetical projected withdrawals on ground-water flow and 

land-surface subsidence in the NGC GAM model area. Two 

withdrawal scenarios were simulated in this NGC GAM study. 

The first scenario comprises historical withdrawals for 1891– 

2000 (Kasmarek and Robinson, 2004) and hypothetical projected withdrawals for 2001–50 compiled by the TWDB (Cindy 

Ridgeway, Texas Water Development Board, written commun., 

2004) from the Chicot, Evangeline, and Jasper aquifers (and 

nominally, the Burkeville confining unit) throughout the NGC 

GAM model area. This scenario is referred to hereinafter as the 

TWDB scenario (or TWDB dataset). The second scenario is a 

“merge” of the TWDB scenario with an alternate set of hypothetical projected withdrawals from the Chicot and Evangeline 

aquifers in the Houston metropolitan area for 1995–2030 provided by the HGCSD (Tom Michel, Harris-Galveston Coastal 

Subsidence District, written commun., 2004). This scenario is 

referred to hereinafter as the HGCSD scenario (or HGCSD 

dataset). 

The purpose of this report is to describe the results of NGC 

GAM model simulations of the TWDB and the HGCSD withdrawal scenarios. The report briefly describes the two scenarios 

and then describes the simulated effects of the two scenarios on 

potentiometric surfaces (water levels), selected water-budget 

components, and land-surface subsidence. Limitations on the 

use of the NGC GAM model results also are discussed. 

Description of the Northern Gulf Coast Ground-Water 

Availability Modeling Model 

The USGS MODFLOW finite-difference model 

(Harbaugh and McDonald, 1996; Leake and Prudic, 1991) 

was used to simulate ground-water flow and land-surface 

subsidence. The NGC GAM model comprises four layers, one 

for each of the three aquifers and the Burkeville confining unit. 

The base of the Jasper aquifer/top of the Catahoula confining 

unit is simulated as a no-flow boundary. Each layer consists of 

137 rows and 245 columns of uniformly spaced grid cells, each 

cell representing 1 mi2

. The northwestern no-flow boundaries 

of the hydrogeologic units are the northwestern extent of the 

updip outcrop sediments. The estimated downdip limit of freshwater (dissolved solids concentration of 10,000 milligrams per 

liter) in each hydrogeologic unit is the southeastern no-flow 

boundary of each. The southwestern and northeastern no-flow 

boundaries of the hydrogeologic units coincide with groundwater-flow divides associated with major streams—the Lavaca 

River to the southwest and the Sabine River to the northeast. 

The NGC GAM model was calibrated in a series of transient 

simulations using distributed, historical withdrawals from 1891 

through 2000 with 68 stress periods of variable, but mostly 
W

T F

AN 

JACI

IVER 

COLORADO 

TRIN TY RI

RIVER 

I ER 

A I E R VE

MA

S

A

 SAN

CALHOUN 

ES

HES NACOGDOC

AUGUSTINE 

SABINE 

ANGELINA

TRINITY 

VERNON 

BRAZOS

BURLESON

HINGTON 

WA

BASTROP 

YETTE

LEE 

GONZALES

CALDWELL 

GAL

ON 

o 93 ALLEN 

ORK S

NTO R

 B

A

VER

AZ S 

O 

OR

R

GALVEST

Y

ON

BR

O

TAG

GULF OF MEXIC

DA

Y

B

A

VEST

30o 

F

NECHES R V

S B N

I R 

I

RIVE

TOLEDO

SOMERVILLE LAKE 

GRIMES 

FORT BEND 

CONROE 

94o 

SHELBY

 BEND
 RESERVOIR


95o SAM RAYBURN

 RESERVOIR 

SABINE 

NEWTON 

JASPER 31o 

POLK TYLER B.A. STEINHAGEN

 LAKE 

HUNTSVILLE LAKE BEAUREGARD

WALKER LIVINGSTON 96o 

SAN JACINTO 

LAKE CONROE 

LOUISIANA MONTGOMER EVADALE Y JEFF CALCASIEU DAVIS CALCASIEU LAKE HARDIN 

TEXAS BEAUMONT ORANGE 

WALLER 

LIBERTY CAMERON 97o 

LAKE HOUSTON JEFFERSON SABINE AUSTIN ADDICKS RESERVOIR LAKE 0 10 20 

HARRIS PORT ARTHUR KATY HOUSTON BAYTOWN 

BARKER CHAMBERS 

 RESERVOIR 

COLORADO 

LAVACA 

WHAR NGC GAM area TON 

BRAZORIA 

LAKE
 TEXANA
 29o JACKSON MA HGCSD subarea TAGORDA 

TEXAS 

Base modified from U.S. Geological Survey digital data 

Scale 1:250,000 

Albers equal-area projection, Datum NAD 83 

Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊ 

Figure 1. Location of Northern Gulf Coast Ground-Water Availability Modeling (NGC GAM) model area and the Harris-Galveston Coastal Subsidence 

Texas. 
4 Ground-Water Flow and Land-Surface Subsidence in the Northern Part of the Gulf Coast Aquifer System, Texas 

annual, length until simulated potentiometric surfaces, landsurface subsidence, and selected water-budget components 

reasonably reproduced field measured (or estimated) aquifer 

responses. 

More information about the hydrogeology of the aquifer 

system, the NGC GAM model design and input datasets, calibration procedure, and simulation results are in Kasmarek and 

Robinson (2004). Simulations of hypothetical withdrawals indicated the need for modifications to the NGC GAM model input 

data of Kasmarek and Robinson (2004). Those modifications, 

and their effects on the NGC GAM model calibration, are documented in appendix 1 of this report. 

Acknowledgments 

The authors thank the Texas Water Development Board, 

the Harris-Galveston Coastal Subsidence District, and the Fort 

Bend Subsidence District for their assistance in compiling pertinent hydrogeologic and withdrawal data. The authors also 

thank Robert K. Gabrysch, U.S. Geological Survey (retired) for 

his advice and insight on land-surface subsidence and the 

hydrogeology of the Houston area. 

Hypothetical Withdrawals 

The hypothetical withdrawals consist of the projected parts 

of the TWDB and HGCSD withdrawal scenarios described 

below. Hypothetical projected withdrawals for the two scenarios were developed to provide representation of possible future 

withdrawal rates. 

Description of Texas Water Development Board 

Scenario 

The TWDB scenario comprises historical withdrawals 

for 1891–2000 and hypothetical projected withdrawals for 

2001–50 from the Chicot, Evangeline, and Jasper aquifers (and 

nominally, the Burkeville confining unit) throughout the NGC 

GAM model area. The hypothetical projected withdrawals were 

compiled by the TWDB (Cindy Ridgeway, Texas Water Development Board, written commun., 2004). They are based on 

ground-water demands estimated by regional water planning 

groups in the NGC GAM model area (Texas Water Development Board, 2002). The hypothetical projected withdrawals, in 

units of acre-feet per year, were contained in spreadsheets subdivided by aquifer (Gulf Coast aquifer [system] or Brazos River 

alluvium only), county, stream basin, water-user group (aggregation of similar users/suppliers in an area), water-use category 

(municipal [major cities], manufacturing, mining, power generation, livestock, irrigation, and county-other [rural domestic]), 

and year. 

The USGS distributed the hypothetical projected withdrawals vertically among the hydrogeologic units and spatially 

to the individual model cells of each unit using the methods 

described in appendix 2 of this report, converted the withdrawals to NGC GAM model units of cubic feet per day, and 

appended the projected withdrawals (50 annual stress periods) 

onto the historical withdrawals for simulation. 

Figure 2 shows the withdrawals from the three aquifers for 

the NGC GAM model area from 2000 to 2050 for the TWDB 

scenario. For the three aquifers combined, hypothetical projected withdrawals increase about 8 percent during 2000–10 

from about 850 to about 920 million gallons per day (Mgal/d), 

decrease to about 830 Mgal/d in 2030, and gradually increase to 

nearly 850 Mgal/d, the rate at the beginning of the projected 

period, by 2050. For the Chicot aquifer, projected withdrawals 

increase 20 percent during the first decade of the period from 

about 400 to about 480 Mgal/d, then stabilize to rates within 4 

percent of that rate through 2050. For the Evangeline aquifer, 

projected withdrawals decrease about 7 percent during the first 

decade of the period from about 420 to about 390 Mgal/d in 

2010. Withdrawals continue to decrease during the next decade 

so that by 2020 the rate is about 315 Mgal/d, a decrease of 25 

percent from the rate in 2000. From 2020 through 2050, rates 

stabilize to levels within 4 percent of the 2020 rate. Current 

(2004) and projected withdrawals from the Jasper aquifer are 

much less than those from the other two aquifers. For the Jasper 

aquifer, projected withdrawals during the first decade of the 

period increase about 42 percent from about 36 to about 51 

Mgal/d in 2010, then stabilize to rates within 6 percent of that 

rate through 2050. Negligible withdrawals compared to those of 

the aquifers (maximum about 2 Mgal/d) are projected for the 

Burkeville confining unit during 2001–50. 

Description of Harris-Galveston Coastal Subsidence 

District Scenario 

The HGCSD scenario consists of the TWDB scenario with 

an alternate set of projected withdrawals from the Chicot and 

Evangeline aquifers in the Houston metropolitan area (HGCSD 

subarea) for 1995 through 2030. The HGCSD subarea (fig. 1) 

encompasses the jurisdictional area of the HGCSD and immediately adjacent areas. The withdrawals for the HGCSD subarea 

were merged into the TWDB dataset—that is, HGCSD Chicot 

and Evangeline aquifer withdrawals replaced historical (1995– 

2000) and TWDB projected (2001–30) Chicot and Evangeline 

aquifer withdrawals in the subarea. 

These data reflect different estimation and distribution 

processes than those of the TWDB data. The HGCSD projected 

withdrawals were developed by Turner Collie & Braden (1996) 

on the basis of projected water demand in Harris, Galveston, 

and Fort Bend Counties and adjacent parts of Austin, Brazoria, 

Chambers, Grimes, Liberty, Matagorda, Montgomery, Waller, 

and Wharton Counties for 1995–2030. Projected water demand 

during the period was based on projected population. Population projections, associated water demand, and withdrawals 

were developed for the cells of a MODFLOW model grid 

encompassing the HGCSD subarea (LBG-Guyton Associates, 
5 

Chicot aquifer 

Total 

Hypothetical Withdrawals 

Jasper aquifer 

Evangeline aquifer 

1,600 1,000

WITHDRAWALS, IN MILLION GALLONS PER DAY


WITHDRAWALS, IN CUBIC FEET PER SECOND


900
 1,400


800
 1,200


700 

1,000 

600 

800
 500


400
 600 

300 

400 

200 

200 100 

0 0 

2000 2010 2020 2030 2040 2050 

YEAR 

Figure 2. Withdrawals in the Chicot, Evangeline, and Jasper aquifers in the NGC GAM model area from 2000 to 2050, TWDB withdrawal 

scenario. 

1997). The grid orientation is that of USGS 7.5-minute 

topographic quadrangles encompassing the HGCSD subarea, 

and each cell represents a 2.5-minute quadrangle area (about 

7 mi2) within the applicable 7.5-minute quadrangle. The projected withdrawals, in units of cubic feet per day, were thus contained in a MODFLOW-readable file composed of rows and 

columns representing Chicot and Evangeline aquifer withdrawals distributed among the cells of a model grid. 

The USGS redistributed the HGCSD withdrawals from 

their original grid cells to grid cells of the NGC GAM model 

using the methods described in appendix 2 of this report and 

formatted the withdrawals into annual stress periods for input to 

the NGC GAM model. To summarize the results of this merge 

of TWDB and HGCSD datasets in the context of NGC GAM 

model layers: 

Layers 1 and 2 (Chicot and Evangeline aquifers)— 

•	 Within HGCSD subarea—1995–2030, HGCSD 

dataset 

•	 Outside HGCSD subarea—1891–2030, TWDB 

dataset 

Layers 3 and 4 (Burkeville confining unit and Jasper aquifer)— 

•	 Within HGCSD subarea—1891–2030, TWDB 

dataset 

•	 Outside HGCSD subarea—1891–2030, TWDB 

dataset 

Figure 3 shows withdrawals from the three aquifers for 

the NGC GAM model area from 1995 to 2030 for the HGCSD 

scenario. As described above, Jasper aquifer withdrawals are 

the same as for the TWDB scenario. Unlike in the TWDB 

scenario, projected withdrawals from the Chicot and Evangeline aquifers for the HGCSD scenario increase continuously 

during 1995–2030. Also, projected withdrawals from both the 

Chicot and Evangeline aquifers for the period are substantially 

larger than those of the TWDB scenario. Total withdrawals 

from all three aquifers increase about 74 percent from about 

875 Mgal/d in 1995 to about 1,520 Mgal/d in 2030. For the 

Chicot aquifer, projected withdrawals increase continuously 

from about 420 Mgal/d in 1995 to about 520, 590, and 670 

Mgal/d in 2010, 2020, and 2030, respectively, an approximately 

60-percent increase during the period. For the Evangeline aquifer, projected withdrawals increase continuously at a greater 

rate from about 420 Mgal/d in 1995 to about 580, 670, and 

nearly 800 Mgal/d in 2010, 2020, and 2030, respectively, an 

approximately 90-percent increase during the period. 
6 

 aquifer 

Ground-Water Flow and Land-Surface Subsidence in the Northern Part of the Gulf Coast Aquifer System, Texas 

Evangeline 

Chicot aquifer

Jasper aquifer 

Total 

1,600 2,500

1,400


WITHDRAWALS, IN MILLION GALLONS PER DAY


2,000 

1,200 

1,000 1,500 

WITHDRAWALS, IN CUBIC FEET PER SECOND


800 

600 

400 

1,000


500 

200 

0 0

1995 2010 2020 2030 

YEAR 

Figure 3. Withdrawals in the Chicot, Evangeline, and Jasper aquifers in the NGC GAM model area from 1995 to 2030, HGCSD withdrawal 

scenario. 

Evaluation of Ground-Water Flow 

The evaluation of ground-water flow comprises descriptions of potentiometric-surface maps (water levels) of the aquifers and selected water-budget components resulting from 

simulation of the TWDB and HGCSD withdrawal scenarios. 

HGCSD and TWDB results are compared. 

Results Using Texas Water Development Board 

Scenario 

The simulated potentiometric surfaces of the Chicot aquifer for 2000, 2010, 2020, 2030, 2040, and 2050 (figs. 4–9) that 

result from the TWDB withdrawal scenario show relatively 

little change in configuration over time. The broad area 150– 

200 ft below NGVD 29 at the center of the major cone of 

depression in southern Harris County in the simulated 2000 surface (fig. 4) remains similarly configured in the 2010 surface 

(fig. 5). In the 2020 surface (fig. 6), this area is smaller than in 

the 2000 and 2010 surfaces and becomes smaller still in the 

2030 and 2040 surfaces (figs. 7, 8). A small cone of depression 

150–200 ft below NGVD 29 in northern Brazoria County 

appears in the 2020, 2030, and 2040 surfaces. In the 2050 surface (fig. 9), the area 150–200 ft below NGVD 29 is similarly 

configured to that in the 2030 surface and has coalesced with 

the small cone of depression in northern Brazoria County. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

95o 

96o 

30

97o 

o 

29o 

31o 

-50

50

150

150

200

200

250

250

300 300

300

350

200

100

-50

-150

100

100

150

200

250

200

200

0

100

0

50

-100

150

LOUISIANA

300

N 

WALLER 

HARRIS 

COLORADO 

WASHINGTON 

CAL

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

Updip limit of the Chicot aquifer LAKE	 RA

CONROE 250 POLK R

AUSTIN 

LAKE 

MONTGOMERY LIVINGSTON 

LAVACA SAN 250

 JACINTO 

TYLER 

JAS

B.A. STE

ADDICKS RESER

VOIR LAKE 

LAKE 150

BARKER HOUSTON 

 RESER

VOIR 

WHARTON FORT BEND 

LAKE

 TEXANA 

50

HARDIN 

LIBERTY EVADALE 

JACKSON 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

Estimated downdip limit of freshwater SABINEin the Chicot aquifer LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contou

which water would have stood in tig50 feet. Datum is NGVD 29 

Figure 4. Simulated 2000 potentiometric surface of the Chicot aquifer in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE LAKE 

BRAZOS 

LEE 

TEXAS

95o 

96o 

30

97o 

o 

29o 

31o 

-100

-50

150

50

150

150

200

200

250 250

300

300

350

100

-50

50

100

100

150

200

250

200

200

100

0

-50

-50

0

50

-150

350

150 150

-100

LOUISIANA

300

N 

WALLER 

HARRIS 

WASHINGTON 

CAL

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

Updip limit of the Chicot aquifer LAKE	 RA

CONROE POLK R

AUSTIN 250

LAKE 

COLORADO MONTGOMERY	 LIVINGSTON 

LAVACA SAN 250 

JACINTO 

TYLER 

JAS

B.A. STE

ADDICKS RESER

VOIR LAKE 

LAKE 150

BARKER HOUSTON 

 RESER

VOIR 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON 

CALHOUN BEAUMONT MATAGORDA -50 ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

Estimated downdip limit of freshwater SABINEin the Chicot aquifer LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contou

which water would have stood in tig50 feet. Datum is NGVD 29 

Figure 5. Simulated 2010 potentiometric surface of the Chicot aquifer in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

95o 

96o 

30

97o 

o 

29o 

31o 

-50

0

0

50

50

100

100

100

150

150

200

 JACINTO 

250 200

250 250

300

300

350

350

200

200

150

100

200

250

-50

150

50

-50

-150

-100

-50

200 250

0

-150

LOUISIANA

300

250

N 

SAN

WALLER 

WASHINGTON 

CAL

300

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

350 Updip limit of the Chicot aquifer LAKE	 RA

CONROE POLK R

AUSTIN 

LAKE 

COLORADO MONTGOMERY LIVINGSTON 

LAVACA 

TYLER 

JAS

B.A. STE

ADDICKS RESER

VOIR LAKE 

LAKE

BARKER HOUSTON HARRIS 150 RESER

VOIR 100

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON	 -100 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

Estimated downdip limit of freshwater SABINEin the Chicot aquifer LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contou

which water would have stood in tig50 feet. Datum is NGVD 29 

Figure 6. Simulated 2020 potentiometric surface of the Chicot aquifer in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE LAKE 

BRAZOS 

LEE 

TEXAS

95o 

96o 

30

97o 

o 

29o 

31o 

-50

-50

0

0

50

100

100

100

150

150

200

 JACINTO 

250 200

250 250

300 300

350

200

200

150

200

250

-50

150

50

-50

-100

100

250

-150

-150

LOUISIANA

300

50

N 

WASHINGTON 

CAL

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

Updip limit of the Chicot aquifer LAKE	 RA

CONROE POLK R

AUSTIN 200

WALLER LAKE 

COLORADO MONTGOMERY LIVINGSTON 

LAVACA SAN 

TYLER 

JAS

B.A. STE

ADDICKS RESER

VOIR LAKE 

LAKE

BARKER 150 HOUST ON RESER

VOIR HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

-100 JACKSON 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

Estimated downdip limit of freshwater SABINEin the Chicot aquifer LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contou

which water would have stood in tig50 feet. Datum is NGVD 29 

Figure 7. Simulated 2030 potentiometric surface of the Chicot aquifer in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

95o 

96o 

30

97o 

o 

29o 

31o 

-150

-50-100

0

50

150

150

250

COLORADO 250 300 300

350

350

100

-50

50

-100

100

100

150

200

250

200 200

100

0

-50

-50

0

50

150

150

-150

200

300

LOUISIANA

300

N 

CONROE 

EVADALE 

WASHINGTON 

CAL

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

Updip limit of the Chicot aquifer 350 LAKE	 RA

250 POLK R

AUSTIN 200

WALLER LAKE 

MONTGOMERY 

250 LIVINGSTON 

LAVACA SAN 200 

250 JACINTO 

TYLER 

JAS

B.A. STE

ADDICKS RESER

VOIR LAKE 

LAKE

BARKER 150 HOUSTON 

 RESER

VOIR HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY 

JACKSON 

CALHOUN -100 BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

Estimated downdip limit of freshwater SABINEin the Chicot aquifer LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contou

which water would have stood in tig50 feet. Datum is NGVD 29 

Figure 8. Simulated 2040 potentiometric surface of the Chicot aquifer in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE LAKE 

BRAZOS 

LEE 

TEXAS

95o 

96o 

30

97o 

o 

29o 

31o 

-150

-100

-50-100

50

150

150

200

 JACINTO 200

250

COLORADO 250 300 300

350

100

-50

50

-100

100

100

150

200

250

200 200

100

0

-50

0

50

150

150

100

LOUISIANA

300

N 

EVADALE 

WASHINGTON 

CAL

Updip limit of the Chicot aquifer 

250

250

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

LAKE	 RA

CONROE POLK R

AUSTIN 

WALLER LAKE 

MONTGOMERY LIVINGSTON 

LAVACA SAN 

TYLER 

JAS

B.A. STE

ADDICKS RESER

VOIR LAKE 

LAKE

BARKER 150 HOUSTON 

 RESER

VOIR HARRIS 

WHARTON FORT BEND 

LAKE 0

 TEXANA HARDIN 

LIBERTY 

JACKSON 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

Estimated downdip limit of freshwater SABINEin the Chicot aquifer LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contou

which water would have stood in tig50 feet. Datum is NGVD 29 

Figure 9. Simulated 2050 potentiometric surface of the Chicot aquifer in the NGC GAM model area resulting from TWDB withdrawal scenario. 
Evaluation of Ground-Water Flow 13 

In the second of three principal areas of withdrawals, the 

coastal irrigation area centered in Wharton and Jackson Counties, an area of water levels 50–100 ft below NGVD 29 first 

appears in southeastern Jackson and southwestern Matagorda 

Counties in the 2010 surface and expands eastward in Matagorda County over time. In the third principal area of withdrawals, the Evadale-Beaumont area (southern Jasper and 

Hardin Counties), little or no change in Chicot aquifer water 

levels over the TWDB projected period is evident. 

The simulated potentiometric surfaces of the Evangeline 

aquifer for 2000, 2010, 2020, 2030, 2040, and 2050 (figs. 10– 

15) show the most change between 2000 (fig. 10) and 2010 (fig. 

11). Water levels 250–400 ft below NGVD 29 in the major cone 

of depression in the simulated 2000 Evangeline aquifer potentiometric surface in western Harris County do not appear in the 

2010 surface; for 2010, the area of deepest water levels shifts 

southeastward to southern Harris County and recovers to 200– 

250 ft below NGVD 29. However, another, smaller cone of 

depression 200–250 ft below NGVD 29 appears in the 2010 

surface in southern Montgomery County, a feature that did not 

appear in the 2000 surface. The 2020 Evangeline aquifer potentiometric surface (fig. 12) indicates continued water-level 

recovery in southern Harris County, with an area of water levels 

150–200 ft below NGVD 29 the deepest there. The relatively 

small cone of depression 200–250 ft below NGVD 29 in the 

2010 surface in southern Montgomery County is slightly larger 

in the 2020 surface. For 2030, 2040, and 2050 (figs. 13–15) the 

Evangeline aquifer surfaces are essentially stable at levels comparable to those of 2020 in southern Harris County; but the cone 

of depression in southern Montgomery County becomes 

slightly larger each decade, with maximum depths of 250–300 

ft below NGVD 29 in 2030, 2040, and 2050. 

In the coastal irrigation area, negligible change in Evangeline aquifer water levels is evident throughout the projected 

period, except for the appearance of an area 50–100 ft below 

NGVD 29 in southeastern Jackson and southwestern Matagorda 

Counties in 2010 and slight expansion of that area in Matagorda 

County over time. In the Evadale-Beaumont area, the simulated 

cone of depression in the Evangeline aquifer recovers from a 

maximum of 250–300 ft below NGVD 29 in 2000 to 150–200 ft 

below NGVD 29 in 2010. For the remainder of the projected 

period, negligible change appears in the simulated EvadaleBeaumont cone of depression. 

The simulated potentiometric surfaces of the Jasper aquifer for 2000, 2010, 2020, 2030, 2040, and 2050 (figs. 16–21) 

each have a major cone of depression centered in southern 

Montgomery County. This feature is minimally developed in 

the simulated 2000 surface (fig. 16) but reaches a depth of 500– 

600 ft below NGVD 29 in the 2010 surface (fig. 17). Essentially 

all of the approximately 42-percent increase in simulated Jasper 

aquifer withdrawals between 2000 and 2010 (fig. 2) is concentrated in southern Montgomery County. The maximum depth of 

the cone increases to 550–650 ft below NGVD 29 in the 2020, 

2030, 2040, and 2050 surfaces (figs. 18–21). Lateral expansion 

of the cone is minimal between 2030 and 2050. No noticeable 

change in Jasper aquifer water levels appears in the coastal irrigation area or the Evadale-Beaumont area during the projected 

period. 

Water-budget components for 2000, 2010, 2030, and 2050 

that result from simulating the TWDB withdrawal scenario are 

shown in figures 22–25. Projected withdrawals from the aquifer 

system increase about 8 percent during 2000–10, then decrease 

to rates close to those of 2000 for the remainder of the projected 

period (fig. 2). In response, net recharge (recharge minus natural discharge, simulated using the MODFLOW general-head 

boundary package [Kasmarek and Robinson, 2004]) increases 

from 995 cubic feet per second (ft3

/s) in 2000 to 1,067 ft3/s 

in 2010, 1,105 ft3

/s in 2030, and 1,144 ft3/s in 2050. In units of 

inches per year (in/yr) over the NGC GAM model area (25,121 

mi2

), net recharge increases from 0.54 in/yr in 2000 to 0.62 in/yr 

in 2050. Although simulated net recharge increases about 15 

percent over the projected period, the amount of water supplied 

by storage (sum of sand storage and storage from inelastic compaction of clay) over the projected period decreases about 48 

percent. Simulated storage increases about 11 percent during 

2000–10 from 326 to 363 ft3

/s, then decreases about 52 percent 

to about 173 ft3/s in 2030, and then decreases slightly to 168 

ft3

/s in 2050. The major fraction of the 158-ft

3/s decrease in 

storage (about 80 percent) from 2000 to 2050 is in sand storage. 

Although under the TWDB scenario withdrawals from the 

entire system are projected to be about the same in 2050 as in 

2000, the percentage of withdrawals supplied by net recharge 

increases from 75 percent in 2000 to 87 percent in 2050, and the 

percentage of withdrawals supplied by storage decreases from 

25 percent in 2000 to 13 percent in 2050. 

Results Using Harris-Galveston Coastal Subsidence 

District Scenario 

The simulated 1995 potentiometric surface of the Chicot 

aquifer resulting from the HGCSD withdrawal scenario 

(fig. 26) shows a cone of depression in southern Harris County 

about the same as that in the simulated 2000 potentiometric surface resulting from the TWDB withdrawal scenario (fig. 4). For 

the 2010, 2020, and 2030 Chicot aquifer potentiometric surfaces associated with the HGCSD scenario (figs. 27–29), the 

substantially greater Chicot aquifer withdrawals of the HGCSD 

scenario relative to those of the TWDB scenario (figs. 2, 3) 

result in progressively deeper cones of depression in southern 

Harris County than those in the potentiometric surfaces associated with the TWDB scenario (figs. 5–7). Projected water levels 

near the Harris-Fort Bend County line reach depths of 250–300 

ft below NGVD 29 in 2010 (fig. 27), 300–350 ft below NGVD 

29 in 2020 (fig. 28), and 400–450 ft below NGVD 29 in 2030 

(fig. 29). Also notable in the HGCSD Chicot aquifer potentiometric surfaces is a developing cone of depression in northern 

Galveston County that reaches depths of 200–250 ft below 

NGVD 29 in 2020 and 250–300 ft below NGVD 29 in 2030; 

and a small cone of depression in northeastern Brazoria County 

300–350 ft below NGVD 29 in 2030. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

-250

-200

-150

-200

-50

-50

0

0

150

200

200

250

250 250

250

250

300

300

300 300

300SAN

300

350

-150

-100

-50

100

200

250

50

100

150

100

200

150

250

200

300

250

50

0

100

150

150

300

-300

-350

-100

-250

100

300

N

BARKER

CONROE 

MONTGOMERY 

AUSTIN 

COLORADO 

WASHINGTON 

CAL

LAVACA 

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

Updip limit of the Evangeline aquifer	 SAM 

350

LAKE 300 RA

350 POLK R

350

WALLER LAKE 

LIVINGSTON 

JACINTO 250 TYLER 

JAS

B.A. STE

ADDICKS RESER

VOIR LAKE 

LAKE

 HOUSTON

 RESER

VOIR HARRIS

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

Estimated downdip limit of freshwater LAKE CAMERON in the Evangeline aquifer 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION


Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contour—

which water would have stood in tightly 50 feet. Datum is NGVD 29 

Figure 10. Simulated 2000 potentiometric surface of the Evangeline aquifer in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

-200

-200

-150

-150

-100

-50

-50

-50

0

0

100

150

200

200

300

250

250

250

250

300

250

300

300

300 300

300SAN

350

-150

-100

-50

100

200

250

50

100

150

100

200

150

200

300

50

0

100

150

150

-50

250 250

N 

CONROE 

COLORADO MONTGOMERY 

WASHINGTON 

CAL

LAVACA 300

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

Updip limit of the Evangeline aquifer	 SAM 

350

LAKE 300 RA

350 POLK R

350 350 AUSTIN 

WALLER LAKE 

LIVINGSTON 

JACINTO 250 300 TYLER 

JAS

B.A. STE

ADDICKS RESER

VOIR LAKE 

LAKE 

BARKER HOUSTON 

 RESER

VOIR HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

Estimated downdip limit of freshwater LAKE CAMERON in the Evangeline aquifer 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION


Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contour—

which water would have stood in tightly 50 feet. Datum is NGVD 29 

Figure 11. Simulated 2010 potentiometric surface of the Evangeline aquifer in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

-150

-200

-150

-150

-100

-50

0

0

100

150

200

200

250

250 250

250

250

300

300 300

300SAN

300

350

350

-150

-100

-50

100

200

250

50

100

150

100

200

150

250

200

300

250

-50

50

0

100

150

300

-150

-50

-100

-100

-50

300

300

N 

CONROE 

MONTGOMERY 

AUSTIN 

COLORADO 

WASHINGTON 

CAL

LAVACA 

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

Updip limit of the Evangeline aquifer	 SAM 

350

LAKE	 300 RA

350 POLK R

350 350

WALLER LAKE 

LIVINGSTON 

JACINTO 150 250 TYLER 

JAS

B.A. STE

ADDICKS RESER

VOIR LAKE 

LAKE

BARKER HOUSTON 

 RESER

VOIR HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

Estimated downdip limit of freshwater LAKE CAMERON in the Evangeline aquifer 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION


Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contour—

which water would have stood in tightly 50 feet. Datum is NGVD 29 

Figure 12. Simulated 2020 potentiometric surface of the Evangeline aquifer in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

-150

-100

-100

0

0

100

150

200

200

200

250

250

250

250

300

300

300 CONROE 300

300SAN

300

350

-150

-100

 HOUST -50

100

250

50

100

150

100

200

150

250

200

300

300

250

-50

50

0

100

150

150

300

250

-200

-100

RESER

VOIR -50

-150

-50

300

N 

ON 

MONTGOMERY 

WASHINGTON 

CAL

LAVACA 

-250

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

Updip limit of the Evangeline aquifer	 

350 SAM 300 LAKE	 RA

350 POLK R

350 AUSTIN 

WALLER LAKE 

COLORADO LIVINGSTON 

JACINTO 250 TYLER 

JAS

B.A. STE

ADDICKS -150-200 LAKE 

LAKE

BARKER

 RESER

VOIR HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON	 -50 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

Estimated downdip limit of freshwater LAKE CAMERON in the Evangeline aquifer 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION


Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contour—

which water would have stood in tightly 50 feet. Datum is NGVD 29 

Figure 13. Simulated 2030 potentiometric surface of the Evangeline aquifer in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

-200

-100

-150

-150

-100

-50

-50

0

100

150

200

200

250

250

250

 JACINTO 250

300

300

300 300

300

350

350

-150

-50

200

50

100

150

100

200

150

250

200

300

-50

50

BARKER0

100

150

150

150

250

300

-100

-150

-250

250

N 

HOUST ON 

CONROE 

SAN

MONTGOMERY 

AUSTIN 

WASHINGTON 

CAL

LAVACA 

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

Updip limit of the Evangeline aquifer SAM 

350

300 LAKE RA

350 POLK R

300 350

WALLER LAKE 

COLORADO 

250 LIVINGSTON 

250

TYLER 

JAS

B.A. STE

ADDICKS RESER

VOIR LAKE 

LAKE 

 RESER

VOIR HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

Estimated downdip limit of freshwater LAKE CAMERON in the Evangeline aquifer 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION


Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contour—

which water would have stood in tightly 50 feet. Datum is NGVD 29 

Figure 14. Simulated 2040 potentiometric surface of the Evangeline aquifer in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

-150

-200

-150

-100

-150

-250

-50

-50

0

100

150

200

200

250

250

250

250

250

300

300

300 CONROE 300

300SAN

350

-150

-100

-50

100

200

250

50

100

150

100

200

150

200

300

250

-50

50

0

100

150

150

300

-100

250

300

N 

HOUST ON 

EVADALE 

MONTGOMERY 

AUSTIN 

COLORADO 

WASHINGTON 

CAL

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

Updip limit of the Evangeline aquifer SAM 

350

LAKE 300 RA

350 POLK R

350 350

WALLER LAKE 

LIVINGSTON 

LAVACA 300 

JACINTO 250 300 TYLER 

JAS

B.A. STE

ADDICKS RESER

VOIR LAKE 

LAKE 20

BARKER

 RESER

VOIR HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY 

JACKSON 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

Estimated downdip limit of freshwater LAKE CAMERON in the Evangeline aquifer 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION


Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contour—

which water would have stood in tightly 50 feet. Datum is NGVD 29 

Figure 15. Simulated 2050 potentiometric surface of the Evangeline aquifer in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

100

100

150

150

200

200

250

250

TYLER 250

B.A. STE

250

 LAKE 200

300

300

300

POLK 

300

350

350

350 400 400

400

300

50

250

200

200

250

150

150

450 400

450

150

200

250

400

450

N 

WASHINGTON 

FAYETTE 

WALKER 

JAS

CAL

350

400

400

200

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

GRIMES TRINITY ANGELINA 350 Updip limit of the Jasper aquif

SAM LAKE 250 RA 

CONROE R

AUSTIN 

WALLER LAKE 

COLORADO MONTGOMERY LIVINGSTON 

LAVACA SAN

JACINT O 

ADDICKS 

RESER

VOIR 

LAKE 

BARKER HOUSTON 

RESER

VOIR HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON	 Estimated downdip limit of freshwater 

CALHOUN in the Jasper aquifer BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83


Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


EXPLANATION 

-150

Potentiometric contour—Showwater would have stood in tightly Interval 50 feet. Datum is NGVD 

Figure 16. Simulated 2000 potentiometric surface of the Jasper aquifer in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

0

50

100

100

150

150

150

200

250

CONROE 250

250

250

 LAKE 200

300

300

300

300

300

LIVINGSTON300

350

350

GONZALES 

350

400

400

400

300

50

150

250

200

200

250

150

B.A. STE

-50

-100

-150

-200

-300

-500

-400

0

150

200

400

450

N 

POLK 

SAN

MONTGOMERY 

WASHINGTON 

FAYETTE 

WALKER 

TYLER 

CAL

350

400

400

250

CALDWELL BASTROP BURLESON NACOGDO

TRINITY ANGELINA 

Updip limit of the Jasper aquif

SAM 

GRIMES 350

LAKE RA 

250 R

AUSTIN 

WALLER LAKE 

COLORADO 

LAVACA 

JACINT O 

JAS

ADDICKS RESER

VOIR 

LAKE 

BARKER HOUSTON 

RESER

VOIR HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON	 Estimated downdip limit of freshwater 

CALHOUN in the Jasper aquifer BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data 

Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES 

Albers equal-area projection, Datum NAD 83 

Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊ 

EXPLANATION 

-150

Potentiometric contour—Showwater would have stood in tightly Intervals 50 and 100 feet. Datum 

Figure 17. Simulated 2010 potentiometric surface of the Jasper aquifer in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

0

100

100

150

200

250

250

250

250

B.A. STE

250

 LAKE 200

300

300

300

300

LIVINGSTON300

350

350

350

400 400

400

450

200

300

350

50

150

250

CONROE 200

200

250

150

-50

-100

-150

-200

-350 -550

-450

0

150

-250

300

50

150

150

150

450

400

450

N 

POLK 

WASHINGTON 

FAYETTE 

WALKER 

JAS

TYLER 

CAL

400

200

200

CALDWELL BASTROP BURLESON NACOGDO

GRIMES TRINITY ANGELINA

GONZALES 350 Updip limit of the Jasper aquif

SAM 

LAKE RA 

250 R

AUSTIN 

WALLER LAKE 

COLORADO MONTGOMERY LAVACA SAN

JACINT O 

ADDICKS 

RESER

VOIR 

LAKE 

BARKER HOUSTON 

RESER

VOIR HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON	 Estimated downdip limit of freshwater 

CALHOUN in the Jasper aquifer BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83


Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


EXPLANATION 

-150

Potentiometric contour—Showwater would have stood in tightly Intervals 50 and 100 feet. Datum 

Figure 18. Simulated 2020 potentiometric surface of the Jasper aquifer in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

0

100

150

150

200

200

WASHINGTON 250

250

CONROE 250

300

250

250

250

 LAKE 200

300

300

300

LIVINGSTON 300

350

GRIMES 350

350

400 400

400

200

300

50

150

250

200

200

250

B.A. STE

-50

-100

-150

-200 -350

-550

-450

0

150

150

400

150

100

-250

300

450400

450

250

400

350

N 

MONTGOMERY 

FAYETTE 

WALKER 

JAS

TYLER 

CAL

350

400

350

CALDWELL BASTROP BURLESON NACOGDO

450

GONZALES 

TRINITY ANGELINA Updip limit of the Jasper aquif

SAM LAKE RA 

POLK R

250 AUSTIN 

WALLER LAKE 

COLORADO 

LAVACA SAN

JACINT O 

ADDICKS 

RESER

VOIR 

LAKE 

BARKER HOUSTON 

RESER

VOIR HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON	 Estimated downdip limit of freshwater 

CALHOUN in the Jasper aquifer BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data 

Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES 

Albers equal-area projection, Datum NAD 83 

Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊ 

EXPLANATION 

-150

Potentiometric contour—Showwater would have stood in tightly Intervals 50 and 100 feet. Datum 

Figure 19. Simulated 2030 potentiometric surface of the Jasper aquifer in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

0

100

100

150

150

200

200

250

250

250

300

250

TYLER 250

 LAKE 200

300

300

300

350

350

400

400

400

300

350

50

250

200

200

250

150

B.A. STE

-50

-100

-150

-200

-350 -550

-450

0

150

-250

300

150

50

450

450

400

200

350

450

N 

CONROE 

WASHINGTON 

FAYETTE 

WALKER 

JAS

CAL

400

400

200

350

CALDWELL BASTROP BURLESON NACOGDO

GRIMES TRINITY ANGELINA

GONZALES Updip limit of the Jasper aquif

SAM LAKE RA 

POLK R

250 AUSTIN 

WALLER	 LAKE 300

COLORADO MONTGOMERY LIVINGSTON 

LAVACA SAN

JACINT O 

ADDICKS RESER

VOIR 

LAKE 

BARKER HOUSTON 

RESER

VOIR HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON	 Estimated downdip limit of freshwater 

CALHOUN in the Jasper aquifer BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83


Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


EXPLANATION 

-150

Potentiometric contour—Showwater would have stood in tightly Intervals 50 and 100 feet. Datum 

Figure 20. Simulated 2040 potentiometric surface of the Jasper aquifer in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

100

100

150

150

200

250

W250ASHINGTON 

250

250

250

250

250

 LAKE 20

300

300

300

350

350

400

400

450

200

350

50

150

250

200

200

250

150

-50

-100

-150

-200

-550 -450

0

150

150

150

50

B.A. STE

450

-250

-350

400

350

N 

WALKER 

JAS

TYLER 

CAL

400

300

200

200

CALDWELL BASTROP BURLESON NACOGDO

300 300

GONZALES 

FAYETTE 350 TRINITY ANGELINA Updip limit of the Jasper aquif

SAM 

GRIMES 

LAKE 250 RA 

CONROE POLK R

AUSTIN 

WALLER	 LAKE 

COLORADO MONTGOMERY 

SAN LIVINGSTON300 

LAVACA 

JACINT O 

ADDICKS RESER

VOIR 

LAKE 

BARKER HOUSTON 

RESER

VOIR HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON	 Estimated downdip limit of freshwater 

CALHOUN in the Jasper aquifer BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data 

Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES 

Albers equal-area projection, Datum NAD 83 

Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊ 

EXPLANATION 

-150

Potentiometric contour—Showwater would have stood in tightly Intervals 50 and 100 feet. Datum 

Figure 21. Simulated 2050 potentiometric surface of the Jasper aquifer in the NGC GAM model area resulting from TWDB withdrawal scenario. 
OUTCROP AREAS, OUTCROP AREA, All units except Chicot aquifer Chicot aquifer 

EXPLANATION 

Jasper aquifer 

Burkeville confining unit 

Evangeline aquifer 

50 (17) 33 16 (4) 12

NEGLIGIBLE 

78 (18) 60 627 (582) 45

11 (3) 14

1,032 (960) 72

SS=35 

SC=0 

W=56 

SS=8 

SC=0 

W=1 

SS=4 

SC=47 

W=654 

SS=195 

SC=37 

W=610 

No-flow boundary 

(Catahoula confining unit) 

WATER BALANCE RECHARGE + SC = NATURAL DISCHARGE + W 

1,160 + 242 + 84 = 165 + 1,321


1,486 = 1,486


SS +

Recharge or discharge in outcrop in cubic feet per second 

1,032 (960) 7

RECHARGE NET 

Leakage through bottom of hydroflow rate in cubic feet per second 

627 (582) 4

DOWNWARD NET 

SS Net rate of release of wate

cubic feet per second 

SC Net rate of release of wate

compaction, in cubic feet p

W Withdrawal rate, in cubic fe

Figure 22. Simulated 2000 water-budget components of the hydrogeologic units of the NGC GAM model resulting from TWDB withdrawal scenario. 
OUTCROP AREAS, OUTCROP AREA, All units except Chicot aquifer Chicot aquifer 

EXPLANATION 

Jasper aquifer 

Burkeville confining unit 

Evangeline aquifer 

52 (21) 31 17 (6) 11

NEGLIGIBLE 

82 (25) 57 593 (532) 61

13 (1) 12

1,091 (1,021) 70

SS=52 

SC=0 

W=79 

SS=7 

SC=0 

W=2 

SS=8 

SC=41 

W=605 

SS=192 

SC=63 

W=744 

No-flow boundary 

(Catahoula confining unit) 

WATER BALANCE RECHARGE + SC = NATURAL DISCHARGE + W 

1,225 + 259 + 104 = 158 + 1,430


1,588 = 1,588


SS +

Recharge or discharge in outcrop in cubic feet per second 

1,091 (1,021) 7

RECHARGE NET 

Leakage through bottom of hydroflow rate in cubic feet per second 

593 (532) 6

DOWNWARD NET 

SS Net rate of release of wate

cubic feet per second 

SC Net rate of release of wate

compaction, in cubic feet p

W Withdrawal rate, in cubic fe

Figure 23. Simulated 2010 water-budget components of the hydrogeologic units of the NGC GAM model resulting from TWDB withdrawal scenario. 
OUTCROP AREAS, OUTCROP AREA, All units except Chicot aquifer Chicot aquifer 

EXPLANATION 

Jasper aquifer 

Burkeville confining unit 

Evangeline aquifer 

55 (25) 30 19 (11) 8

NEGLIGIBLE 

85 (30) 55 481 (417) 64

15 (6) 9

1,118 (1,050) 68

SS=45 

SC=0 

W=81 

SS=7 

SC=0 

W=2 

SS=5 

SC=27 

W=473 

SS=64 

SC=25 

W=722 

No-flow boundary 

(Catahoula confining unit) 

WATER BALANCE RECHARGE + SC = NATURAL DISCHARGE + W 

1,258 + 121 + 52 = 153 + 1,278


1,431 = 1,431


SS +

Recharge or discharge in outcrop in cubic feet per second 

1,118 (1,050) 6

RECHARGE NET 

Leakage through bottom of hydroflow rate in cubic feet per second 

481 (417) 6

DOWNWARD NET 

SS Net rate of release of wate

cubic feet per second 

SC Net rate of release of wate

compaction, in cubic feet p

W Withdrawal rate, in cubic fe

Figure 24. Simulated 2030 water-budget components of the hydrogeologic units of the NGC GAM model resulting from TWDB withdrawal scenario. 
OUTCROP AREAS, OUTCROP AREA, All units except Chicot aquifer Chicot aquifer 

EXPLANATION 

Jasper aquifer 

Burkeville confining unit 

Evangeline aquifer 

58 (29) 29 20 (12) 8

NEGLIGIBLE 

87 (34) 53 487 (420) 67

16 (7) 9

1,147 (1,081) 66

SS=43 

SC=0 

W=84 

SS=7 

SC=0 

W=2 

SS=4 

SC=27 

W=478 

SS=62 

SC=25 

W=748 

No-flow boundary 

(Catahoula confining unit) 

WATER BALANCE RECHARGE + SC = NATURAL DISCHARGE + W 

1,292 + 116 + 52 = 148 + 1,312


1,460 = 1,460


SS +

Recharge or discharge in outcrop in cubic feet per second 

1,147 (1,081) 6

RECHARGE NET 

Leakage through bottom of hydroflow rate in cubic feet per second 

487 (420) 6

DOWNWARD NET 

SS Net rate of release of wate

cubic feet per second 

SC Net rate of release of wate

compaction, in cubic feet p

W Withdrawal rate, in cubic fe

Figure 25. Simulated 2050 water-budget components of the hydrogeologic units of the NGC GAM model resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE LAKE 

BRAZOS 

LEE 

TEXAS

95o 

96o 

30

97o 

o 

29o 

31o 

-150

-50

-50

50

150

150

200

200

250

COLORADO 250

250

300 300 300

350

350

100

50

-100

100

100

150

200

250

200

200

100

0

-50

0

50

-50

150

LOUISIANA

300

N 

WASHINGTON 

CAL

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

Updip limit of the Chicot aquifer 350 LAKE	 RA

CONROE	 POLK R

AUSTIN 

WALLER LAKE 

MONTGOMERY LIVINGSTON 

LAVACA SAN 250

 JACINTO 

TYLER 

JAS

B.A. STE

ADDICKS RESER

VOIR LAKE 

LAKE 150

BARKER HOUSTON

 RESER

VOIR HARRIS

WHARTON FORT BEND 

LAKE

 TEXANA 

-200

HARDIN 

LIBERTY EVADALE 

JACKSON 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

Estimated downdip limit of freshwater SABINEin the Chicot aquifer LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contou

which water would have stood in tig50 feet. Datum is NGVD 29 

Figure 26. Simulated 1995 potentiometric surface of the Chicot aquifer in the NGC GAM model area resulting from HGCSD withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

95o 

96o 

30

97o 

o 

29o 

31o 

-250

-200 -100

-50

150

50

150

150

200

200

250 250

300

300

350

100

-50

50

100

100

150

200

250

200

200

0

100

-50

-50

0

50

-100-150

-200

-50

LOUISIANA

300

N 

HOUST ON HARRIS 

WASHINGTON 

CAL

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

Updip limit of the Chicot aquifer LAKE	 RA

CONROE POLK R

AUSTIN 250

WALLER LAKE 

COLORADO MONTGOMERY	 LIVINGSTON 

LAVACA SAN 250 

JACINTO 

TYLER 

JAS

B.A. STE

ADDICKS RESER

VOIR LAKE 

LAKE 150

BARKER

 RESER

VOIR 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

Estimated downdip limit of freshwater SABINEin the Chicot aquifer LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contou

which water would have stood in tig50 feet. Datum is NGVD 29 

Figure 27. Simulated 2010 potentiometric surface of the Chicot aquifer in the NGC GAM model area resulting from HGCSD withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE LAKE 

BRAZOS 

LEE 

TEXAS

95o 

96o 

30

97o 

o 

29o 

31o 

-200

-150

-100

-100

-50

50

150

150

200

 JACINTO 200

250

COLORADO 250

250

300

300

350

100

-50

50

-150

100

100

150

200

250

200 200

0

100

-50

-50

0

-300

-250

150

LOUISIANA

300

50

N 

HOUST ON 

WALLER 

HARRIS 

WASHINGTON 

CAL

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

Updip limit of the Chicot aquifer LAKE	 RA

200 CONROE	 POLK R

250 AUSTIN 

LAKE 

300 MONTGOMERY LIVINGSTON 

LAVACA SAN 250 

TYLER 

JAS

B.A. STE

ADDICKS RESER

VOIR LAKE 

LAKE

BARKER 150

 RESER

VOIR 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON -250 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA -200 CHAMBERS GALVESTON 

JEFFERSON 

Estimated downdip limit of freshwater SABINEin the Chicot aquifer LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contou

which water would have stood in tig50 feet. Datum is NGVD 29 

Figure 28. Simulated 2020 potentiometric surface of the Chicot aquifer in the NGC GAM model area resulting from HGCSD withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

-400

-50

-50

0

0

BARKER 50

50

100

100

100

150

150

200

 JACINTO 

250 200

250 250

300 300

350

200

200

150

200

250

-50

150

50

-50

-150

-100

250

-200

-250

-300

-350

-300

-250

-100 -200

300

100

N 

WASHINGTON 

CAL

-100

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

Updip limit of the Chicot aquifer LAKE	 RA

CONROE POLK R

AUSTIN 200

WALLER LAKE 

COLORADO MONTGOMERY LIVINGSTON 

LAVACA SAN 

TYLER 

JAS

B.A. STE

ADDICKS RESER

VOIR LAKE 

LAKE

150

HARRIS HOUST ON RESER

VOIR 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

Estimated downdip limit of freshwater SABINEin the Chicot aquifer LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contou

which water would have stood in tig50 feet. Datum is NGVD 29 

Figure 29. Simulated 2030 potentiometric surface of the Chicot aquifer in the NGC GAM model area resulting from HGCSD withdrawal scenario. 
34 Ground-Water Flow and Land-Surface Subsidence in the Northern Part of the Gulf Coast Aquifer System, Texas 

For the Evangeline aquifer, comparable simulated 1995 

HGCSD and 2000 TWDB withdrawals result in similar potentiometric surfaces for the HGCSD scenario (fig. 30) and the 

TWDB scenario (fig. 10). But unlike the decreasing or stable 

Evangeline aquifer withdrawals of the TWDB scenario for 

2010, 2020, and 2030, progressively larger increases in withdrawals in the HGCSD scenario for 2010, 2020, and 2030 result 

in substantially deeper cones of depression in the simulated 

HGCSD potentiometric surfaces (figs. 31–33) than in the simulated TWDB potentiometric surfaces (figs. 11–13) for those 

years. For 2010, simulated water levels in western Harris 

County (major cone of depression associated with HGCSD scenario has shifted westward relative to that of the TWDB scenario) reach depths of 350–400 ft below NGVD 29; and in 

southern Montgomery County, 300–350 ft below NGVD 29 

(fig. 31). For 2020, simulated water levels in western Harris 

County reach depths of 450–500 ft below NGVD 29; and in 

southern Montgomery County, 500–550 ft below NGVD 29 

(fig. 32). For 2030, simulated water levels in western Harris 

County reach depths of 500–550 ft below NGVD 29; and in 

southern Montgomery County, depths of 700–750 ft below 

NGVD 29 (fig. 33). 

Jasper aquifer withdrawals for 1995 and 2000 are within 

6 percent, which accounts for similar 1995 and 2000 potentiometric surfaces for the HGCSD scenario (fig. 34) and the 

TWDB scenario (fig. 16). Although Jasper aquifer withdrawals 

are the same for both scenarios, the major cone of depression 

centered in southern Montgomery County in the HGCSD 

potentiometric surfaces for 2010, 2020, and 2030 (figs. 35–37) 

is slightly different from that feature in the TWDB potentiometric surfaces for those years (figs. 17–19). The differences likely 

are attributable to differences in projected Chicot and Evangeline aquifer withdrawals. For 2010 the differences in the surfaces are minimal and deepest water levels are 500–600 ft 

below NGVD 29. For 2020, the cone expands slightly farther to 

the south under the HGCSD scenario; deepest water levels are 

550–650 ft below NGVD 29. For 2030, the cone expands still 

farther south and is 50 ft deeper at its center (600–700 ft below 

NGVD 29) than the cone in the comparable surface under the 

TWDB scenario. 

Water-budget components for 1995, 2010, 2020, and 2030 

that result from simulating the HGCSD withdrawal scenario are 

shown in figures 38–41. Not surprisingly, projected withdrawals of the HGCSD scenario greater than those of the TWDB scenario cause greater changes in the sources of water that supply 

withdrawals than the changes that result from the TWDB scenario. In response to projected withdrawals from the aquifer 

system that increase about 32 percent during 1995–2010 and 

about 15 percent during each of the following two decades 

(fig. 3), simulated net recharge increases from 974 ft3/s in 1995 

to 1,094 ft3/s in 2010, 1,204 ft3

/s in 2020, and 1,329 ft3/s in 

2030. In units of inches per year over the NGC GAM model 

area, net recharge increases from 0.53 in/yr in 1995 to 0.72 in/yr 

in 2030. Rather than a long-term decrease in the amount of 

water supplied by storage as with the relatively unchanging 

TWDB scenario, the amount of water supplied by storage 

increases substantially over time with the HGCSD scenario— 

and the increase primarily is from the compaction of clay, 

which has implications for subsidence as described in the section “Evaluation of Land-Surface Subsidence/Results Using 

HGCSD Scenario.” Between 1995 and 2030, the amount of 

water supplied by storage increases about 168 percent (from 

382 to 1,022 ft3/s), and about 85 percent of that increase (543 

ft3/s) is from compaction of clay. Under the HGCSD scenario, 

a projected increase in withdrawals from the entire system of 

about 74 percent during 1995–2030 causes the percentage of 

withdrawals supplied by net recharge to decrease from 72 percent in 1995 to 57 percent in 2030, and the percentage of withdrawals supplied by storage to increase from 28 percent in 2000 

to 43 percent in 2030. 

Evaluation of Land-Surface Subsidence 

The evaluation of land-surface subsidence comprises 

descriptions of subsidence maps resulting from simulation of 

the TWDB and HGCSD withdrawal scenarios. Not surprisingly, larger withdrawals of the HGCSD scenario cause greater 

subsidence than those of the TWDB scenario during the projected period to 2030. 

Results Using Texas Water Development Board 

Scenario 

Land-surface subsidence in the NGC GAM model area for 

2000, 2010, 2020, 2030, 2040, and 2050 that results from simulating the TWDB withdrawal scenario is shown in figures 42– 

47. In the major area of subsidence centered in Harris and 

Galveston Counties, little difference in the configuration or 

maximum depths of subsidence is seen between 2000 (fig. 42) 

and 2010 (fig. 43). For 2020 (fig. 44), the area within the closed 

1-ft contour that encompasses the major area of subsidence 

expands slightly to the west from its 2010 location in Fort Bend 

and Brazoria Counties, and the area of subsidence in central 

Montgomery County (Conroe area) deepens from about 6 ft in 

2010 to about 9 ft in 2020. For 2030 (fig. 45), the westward 

expansion of subsidence in Fort Bend and Brazoria Counties 

and the deepening of the area of subsidence in central Montgomery County noted for 2020 continues; about 9 ft of subsidence in 2020 increases to about 10 ft in central Montgomery 

County by 2030. For 2040 (fig. 46), the only notable change 

from 2030 within the closed 1-ft contour that encompasses the 

major area of subsidence is an increase in the depth of the area 

of subsidence in central Montgomery County from 10 to 13 ft. 

For 2050 (fig. 47), the area within the closed 1-ft contour 

changes little from that of 2040. Maximum depths appear to 

have stabilized at 2040 levels, except in central Montgomery 

County where an increase from 13 to 14 ft is seen. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

-250

-200

-150

-100

-50

50

-50

-50

-250 0

100

150

200

200

250

250 250

250

250

300

300

300 300

300

350

-150

-100

-50

100

200

250

50

100

150

100

200

150

250

200

300

250

50

0

100

150

150

-300

300

0

-200

N 

CONROE 

HARRIS 

AUSTIN 

WASHINGTON 

CAL

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

Updip limit of the Evangeline aquifer	 

350 SAM

LAKE 300 RA

350

300 350 POLK R

WALLER LAKE 

COLORADO MONTGOMERY	 LIVINGSTON 

LAVACA SAN 

JACINTO 250 TYLER 

JAS

B.A. STE

ADDICKS RESER

VOIR LAKE 

LAKE

BARKER HOUSTON 

 RESER

VOIR 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

Estimated downdip limit of freshwater LAKE CAMERON in the Evangeline aquifer 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION


Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contour—

which water would have stood in tightly 50 feet. Datum is NGVD 29 

Figure 30. Simulated 1995 potentiometric surface of the Evangeline aquifer in the NGC GAM model area resulting from HGCSD withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

-350

-200

-250 -150

-100

-50

-50

0

0

100

150

200

200

250

250

250

250

250

300

300 300

300SAN

300

350

-150

-100

-50

100

200

50

100

150

100

200

150

250

200

300

250

-50

50

0

100

150

150

-300

-50

300

250

300

300

N 

HOUST ON 

CONROE 

MONTGOMERY 

HARRIS 

AUSTIN 

WASHINGTON 

CAL

JACKSON 

350

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

Updip limit of the Evangeline aquifer	 SAM 

350 300 LAKE RA

350 POLK R

WALLER LAKE 

COLORADO LIVINGSTON 

LAVACA 300 

JACINTO 250 TYLER 

JAS

B.A. STE

ADDICKS RESER

VOIR LAKE 

LAKE 

BARKER

 RESER

VOIR 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

Estimated downdip limit of freshwater LAKE CAMERON in the Evangeline aquifer 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION


Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contour—

which water would have stood in tightly 50 feet. Datum is NGVD 29 

Figure 31. Simulated 2010 potentiometric surface of the Evangeline aquifer in the NGC GAM model area resulting from HGCSD withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

-150

-100

-50

0

0

100

150

200

200

250

250 250

250

250

300

300 300

300SAN

300

350

-150

-100

 HOUST-50ON 

100

200

250

50

100

150

100

200

150

250

200

300

250

-50

50

0

100

150

300

-50

-100

RESER

V-150 OIR 

-250

-500

-300

HARRIS -450

-450

-350

-400

-300

-400 -450

-50

300

300

N 

ADDICKS 

 RESER

VOIR 

CONROE 

COLORADO MONTGOMERY 

WASHINGTON 

CAL

LAVACA 

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

Updip limit of the Evangeline aquifer	 SAM 

350

300 LAKE 300 RA

350 POLK R

350 AUSTIN 

WALLER LAKE 

LIVINGSTON 

JACINTO 250 TYLER 

150 JAS

B.A. STE

 LAKE 

LAKE

BARKER

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON 

CALHOUN -200 BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

Estimated downdip limit of freshwater LAKE CAMERON in the Evangeline aquifer 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION


Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contour—

which water would have stood in tightly 50 feet. Datum is NGVD 29 

Figure 32. Simulated 2020 potentiometric surface of the Evangeline aquifer in the NGC GAM model area resulting from HGCSD withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

-150

-100

-100

0

0

100

150

200

200

200

250

SAN 250

250

250

300

300

300 CONROE 300

300

300

350

-150

-100

-50

100

250

50

100

150

100

200

150

250

200

300

300

250

-50

50

0

100

150

150

300

250

-200

-200

 ADDICKS -150

-50

-250

-700

-250

-650

-600

-350

-450

-500

-400

-450

-300

-500

-50

300

N 

HOUST ON RESER

VOIR 

MONTGOMERY 

WASHINGTON 

CAL

LAVACA 

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

Updip limit of the Evangeline aquifer	 

350 SAM 300 LAKE	 RA

350 POLK R

350 AUSTIN 

WALLER LAKE 

COLORADO LIVINGSTON 

JACINTO 250 TYLER 

JAS

B.A. STE

RESER

VOIR LAKE 

LAKE

BARKER

HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON -50 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

Estimated downdip limit of freshwater LAKE CAMERON in the Evangeline aquifer 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION


Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


-150 Simulated potentiometric contour—

which water would have stood in tightly 50 feet. Datum is NGVD 29 

Figure 33. Simulated 2030 potentiometric surface of the Evangeline aquifer in the NGC GAM model area resulting from HGCSD withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

100

100

150

150

200

250

TYLER 250

 LAKE 200

300

300

300

350

350

350

350

400

400

400

300

150

250

200

200

250

150

B.A. STE

50

150

450 400

450

300

200

250

300

450

N 

POLK 

WASHINGTON 

FAYETTE 

WALKER 

CAL

GONZALES

350

400

200

CALDWELL BASTROP BURLESON NACOGDO

TRINITY ANGELINA 

Updip limit of the Jasper aquif

SAM 

GRIMES 350

LAKE RA 

CONROE 250 R

AUSTIN 

WALLER LAKE 

COLORADO MONTGOMERY LIVINGSTON 

LAVACA SAN

JACINT O 

JAS

ADDICKS RESER

VOIR 

LAKE

BARKER 

 HOUSTON 

RESER

VOIR HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON	 Estimated downdip limit of freshwater 

CALHOUN in the Jasper aquifer BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data 

Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES 

Albers equal-area projection, Datum NAD 83 

Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊ 

EXPLANATION 

150

Potentiometric contour—Showwater would have stood in tightly Interval 50 feet. Datum is NGVD 

Figure 34. Simulated 1995 potentiometric surface of the Jasper aquifer in the NGC GAM model area resulting from HGCSD withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

100

100

200

150

150

200

200

250

250

250

 LAKE 200

300

300

300

LIVINGSTON 300

350

350

400 400

400

300

50

150

250

200

250

150

B.A. STE

3

-50

-100

-150

-200

-300

-500

-400

0

150

400450

450

200

300

450

N 

SAN

WASHINGTON 

FAYETTE 

WALKER 

JAS

TYLER 

CAL

350

400

250

200

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

GRIMES TRINITY ANGELINA 350 Updip limit of the Jasper aquif

SAM 

LAKE 250 RA 

CONROE POLK R

AUSTIN 

WALLER LAKE 

COLORADO MONTGOMERY 

LAVACA 

JACINT O 

ADDICKS RESER

VOIR 

LAKE 

BARKER HOUSTON 

RESER

VOIR HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON	 Estimated downdip limit of freshwater 

CALHOUN in the Jasper aquifer BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83


Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


EXPLANATION 

-150

Potentiometric contour—Showwater would have stood in tightly Intervals 50 and 100 feet. Datum 

Figure 35. Simulated 2010 potentiometric surface of the Jasper aquifer in the NGC GAM model area resulting from HGCSD withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

0

100

100

150

150

200

200

CONROE 250

250

250

300

300

300

350

350

350

GRIMES 350

350

400 400

400

400

300

350

50

150

250

200

200

250

150

B.A. STE

-50

-100

-150

-200

-350

-550

-450

0

150

-250

150

300

200

450400

450

200

250

300

450

N 

LAKE 

MONTGOMERY 

WASHINGTON 

FAYETTE 

WALKER 

TYLER 

CAL

200

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

TRINITY ANGELINA Updip limit of the Jasper aquif

SAM 

350 LAKE 250 RA 

POLK R

AUSTIN 

WALLER 

COLORADO LIVINGSTON 

LAVACA SAN

 JACINT O 

JAS

ADDICKS RESER

VOIR LAKE

LAKE

BARKER HOUSTON 

RESER

VOIR HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON	 Estimated downdip limit of freshwater 

CALHOUN in the Jasper aquifer BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data 

Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES 

Albers equal-area projection, Datum NAD 83 

Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊ 

EXPLANATION 

-150

Potentiometric contour—Showwater would have stood in tightly Intervals 50 and 100 feet. Datum 

Figure 36. Simulated 2020 potentiometric surface of the Jasper aquifer in the NGC GAM model area resulting from HGCSD withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

0

100

100

150

1

200

200

450

CONROE 250

250

250

 LAKE 200

300

300

GRIMES 

300

350

350

400

400

400

400

400

200

300

50

150

250

200

200

250

150

B.A. STE

-50

-100

-300

-200

-400

-600

-500

0

150

150

450 400

450

-150

300

-250

250

150

350

N 

MONTGOMERY 

WASHINGTON 

FAYETTE 

WALKER 

TYLER 

CAL

350

350

200

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

TRINITY ANGELINA 

350 Updip limit of the Jasper aquif

SAM LAKE 250 RA 

POLK 200 R

AUSTIN 

WALLER LAKE 

300 LIVINGSTON COLORADO 

LAVACA SAN

 JACINT O 

JAS

ADDICKS RESER

VOIR 

LAKE 

BARKER HOUSTON 

RESER

VOIR HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

JACKSON	 Estimated downdip limit of freshwater 

CALHOUN in the Jasper aquifer BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS GALVESTON 

JEFFERSON 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83


Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


EXPLANATION 

-150

Potentiometric contour—Showwater would have stood in tightly Intervals 50 and 100 feet. Datum 

Figure 37. Simulated 2030 potentiometric surface of the Jasper aquifer in the NGC GAM model area resulting from HGCSD withdrawal scenario. 
OUTCROP AREAS, OUTCROP AREA, All units except Chicot aquifer Chicot aquifer 

EXPLANATION 

Jasper aquifer 

Burkeville confining unit 

Evangeline aquifer 

50 (17) 33 15 (3) 12

NEGLIGIBLE 

78 (18) 60 604 (557) 47

11 (3) 14

1,011 (939) 72

SS=39 

SC=0 

W=59 

SS=8 

SC=0 

W=2 

SS=5 

SC=63 

W=646 

SS=225 

SC=42 

W=649 

No-flow boundary 

(Catahoula confining unit) 

WATER BALANCE RECHARGE + SC = NATURAL DISCHARGE + W 

1,139 + 277 + 105 = 165 + 1,356


1,521 = 1,521


SS +

Recharge or discharge in outcrop in cubic feet per second 

1,011 (939) 7

RECHARGE NET 

Leakage through bottom of hydroflow rate in cubic feet per second 

604 (557) 4

DOWNWARD NET 

SS Net rate of release of wate

cubic feet per second 

SC Net rate of release of wate

compaction, in cubic feet p

W Withdrawal rate, in cubic fe

Figure 38. Simulated 1995 water-budget components of the hydrogeologic units of the NGC GAM model resulting from HGCSD withdrawal scenario. 
OUTCROP AREAS, OUTCROP AREA, All units except Chicot aquifer Chicot aquifer 

EXPLANATION 

Jasper aquifer 

Burkeville confining unit 

Evangeline aquifer 

52 (20) 32 17 (6) 11

NEGLIGIBLE 

82 (24) 58 779 (720) 59

13 (1) 14

1,121 (1,050) 71

SS=53 

SC=0 

W=79 

SS=9 

SC=0 

W=2 

SS=11 

SC=136 

W=892 

SS=267 

SC=213 

W=810 

No-flow boundary 

(Catahoula confining unit) 

WATER BALANCE RECHARGE + SC = NATURAL DISCHARGE + W 

1,255 + 340 + 349 = 161 + 1,783


1,944 = 1,944


SS +

Recharge or discharge in outcrop in cubic feet per second 

1,121 (1,050) 7

RECHARGE NET 

Leakage through bottom of hydroflow rate in cubic feet per second 

779 (720) 5

DOWNWARD NET 

SS Net rate of release of wate

cubic feet per second 

SC Net rate of release of wate

compaction, in cubic feet p

W Withdrawal rate, in cubic fe

Figure 39. Simulated 2010 water-budget components of the hydrogeologic units of the NGC GAM model resulting from HGCSD withdrawal scenario. 
OUTCROP AREAS, OUTCROP AREA, All units except Chicot aquifer Chicot aquifer 

EXPLANATION 

Jasper aquifer 

Burkeville confining unit 

Evangeline aquifer 

54 (23) 31 18 (8) 10

NEGLIGIBLE 

83 (26) 57 881 (817) 64

14 (1) 13

1,225 (1,155) 70

SS=48 

SC=0 

W=79 

SS=9 

SC=0 

W=2 

SS=12 

SC=183 

W=1,037 

SS=278 

SC=294 

W=910 

No-flow boundary 

(Catahoula confining unit) 

WATER BALANCE RECHARGE + SC = NATURAL DISCHARGE + W 

1,362 + 347 + 477 = 158 + 2,028


2,186 = 2,186


SS +

Recharge or discharge in outcrop in cubic feet per second 

1,225 (1,155) 7

RECHARGE NET 

Leakage through bottom of hydroflow rate in cubic feet per second 

881 (817) 6

DOWNWARD NET 

SS Net rate of release of wate

cubic feet per second 

SC Net rate of release of wate

compaction, in cubic feet p

W Withdrawal rate, in cubic fe

Figure 40. Simulated 2020 water-budget components of the hydrogeologic units of the NGC GAM model resulting from HGCSD withdrawal scenario. 
OUTCROP AREAS, OUTCROP AREA, All units except Chicot aquifer Chicot aquifer 

EXPLANATION 

Jasper aquifer 

Burkeville confining unit 

Evangeline aquifer 

55 (25) 30 19 (9) 10

NEGLIGIBLE 

84 (28) 56 1,002 (931) 71

15 (1) 14

1,344 (1,276) 68

SS=47 

SC=0 

W=81 

SS=10 

SC=0 

W=2 

SS=14 

SC=256 

W=1,228 

SS=303 

SC=392 

W=1,040 

No-flow boundary 

(Catahoula confining unit) 

WATER BALANCE RECHARGE + SC = NATURAL DISCHARGE + W 

1,483 + 374 + 648 = 154 + 2,351


2,505 = 2,505


SS +

Recharge or discharge in outcrop in cubic feet per second 

1,344 (1,276) 6

RECHARGE NET 

Leakage through bottom of hydroflow rate in cubic feet per second 

1,002 (931) 7

DOWNWARD NET 

SS Net rate of release of wate

cubic feet per second 

SC Net rate of release of wate

compaction, in cubic feet p

W Withdrawal rate, in cubic fe

Figure 41. Simulated 2030 water-budget components of the hydrogeologic units of the NGC GAM model resulting from HGCSD withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

1

23

1

1

1

1

1

2

2

2

2

 RESER

VOIR 3

3

 ADDICKS 3

3

3 3

3

3

OIR 

4 4

4

4

GALVEST 4

4

RESER5

V

5

5

5

N 5 6

6

6

6

6

6

6

6

6 6

8

7

8

8

9

9

10

1

2 2 3

3

4

4

4

4

4

5

5

5

5

6 6 6

6

6

7

7

8

8

8

6

2

1

1

KATY 

BARKER2

4

4

7

6

8

1

1 BAYT

OWN 

ON 

WASHINGTON 

CAL

JACKSON 

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

LAKE	 RA

CONROE POLK R

AUSTIN 

WALLER	 LAKE 

COLORADO MONTGOMERY CONROE LIVINGSTON 

LAVACA SAN 

JACINTO 

TYLER 

JAS

B.A. STE

 LAKE 

LAKE

 HOUSTON HARRIS 

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS 

JEFFERSON 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


5 Simulated land-surface subsiden

variable, in feet 

Figure 42. Simulated 2000 land-surface subsidence in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

1

1 1

1

1

1

3

2

4

5

5 6

4

3

7

8

10

9

7

HARRIS 6

4

5

4 4

5

4

2 3

 ADDICKS 3

1

RESER5

V

7

1

3 4

4

4

4

4

8

8

5

6

8 6 7

1

1

1

2 3

N 4

1

3

4

5

3

6

4

2

8

6

6

1

1

OIR 

 RESER

VOIR 

 TEXANA 

EVADALE 

GALVESTON 

WASHINGTON 

CAL

6

5

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

LAKE	 RA

CONROE POLK R

AUSTIN 

WALLER	 LAKE 

COLORADO MONTGOMERY	 CONROE LIVINGSTON 

LAVACA 3 SAN 

JACINTO 

TYLER 

JAS

B.A. STE

5 LAKE 

KATY LAKE

BARKER 2 HOUST ON 

WHARTON FORT BEND 

LAKE

HARDIN 

LIBERTY 

JACKSON 

BAYT

OWN 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS 

JEFFERSON 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


5 Simulated land-surface subsiden

variable, in feet 

Figure 43. Simulated 2010 land-surface subsidence in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

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CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

LAKE	 RA

CONROE POLK R

AUSTIN 

WALLER	 LAKE 

COLORADO MONTGOMERY CONROE LIVINGSTON 

LAVACA SAN 

JACINTO 

TYLER 

JAS

B.A. STE

 LAKE 

5

BARKER 3 HOUST ON HARRIS 

WHARTON FORT BEND 

LAKE 2

 TEXANA 3 HARDIN 

LIBERTY EVADALE 

5 JACKSON 

4 BAYT

OWN 

CALHOUN BEAUMONT MATAGORDA 5 ORANGE BRAZORIA CHAMBERS 

JEFFERSON 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


5 Simulated land-surface subsiden

variable, in feet 

Figure 44. Simulated 2020 land-surface subsidence in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

95o 

96o 

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97o 

o 

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LOUISIANA

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V

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4

1

ADDICKS OIR 

 RESER

VOIR 

EVADALE 

HARRIS 

GALVESTON 

WASHINGTON 

CAL

5

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

LAKE	 RA

CONROE POLK R

AUSTIN 

WALLER	 LAKE 

COLORADO MONTGOMERY	 LIVINGSTON CONROE 

LAVACA SAN 

6 JACINTO TYLER 2 

10

JAS

B.A. STE

 LAKE 

KATY LAKE

BARKER 2 HOUST ON 

WHARTON FORT BEND 

LAKE 2 3 TEXANA HARDIN 

LIBERTY 

JACKSON 

BAYT

OWN 

CALHOUN BEAUMONT MATAGORDA ORANGE BRAZORIA CHAMBERS 

JEFFERSON 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


5 Simulated land-surface subsiden

variable, in feet 

Figure 45. Simulated 2030 land-surface subsidence in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

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1 1

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GALVEST

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HARRIS 6

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RESER

V

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N 4

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1

1

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OIR 

 RESER

VOIR 

EVADALE 

BAYT

OWN 

KATY 

ON 

WASHINGTON 

CAL

2

6

4 6

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

LAKE	 RA

CONROE POLK R

AUSTIN 

WALLER	 LAKE 

COLORADO MONTGOMERY	 LIVINGSTON CONROE 

LAVACA SAN 

JACINTO 10 TYLER 13 

1

JAS

B.A. STE

5 LAKE 

LAKE

BARKER 2 HOUST ON 

WHARTON FORT BEND 

LAKE	 2 3 TEXANA HARDIN 

LIBERTY 

JACKSON 

CALHOUN

3 BEAUMONT 

MATAGORDA ORANGE BRAZORIA 

CHAMBERS 

JEFFERSON 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


5 Simulated land-surface subsiden

variable, in feet 

Figure 46. Simulated 2040 land-surface subsidence in the NGC GAM model area resulting from TWDB withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

30

97o 

o 

29o 

31o 

JACKSON 1

1

1

1

1

1 1

1

1

1

1

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2

2

2

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2

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V

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3 ADDICKS 3

3

3 3

3

3

3

44

 RESER

VOIR 4 44

4

4

4

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4

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5 5

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GALVESTON 

5

5

5

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6HARRIS 

6

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N 

BAYT

OWN 

CONROE 

WASHINGTON 

BRAZORIA 

CAL

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

LAKE	 RA

CONROE POLK R

AUSTIN 

WALLER	 LAKE 

COLORADO MONTGOMERY LIVINGSTON 

LAVACA SAN 

13 JACINTO TYLER 

JAS

B.A. STE

 LAKE 

KATY LAKE

BARKER HOUSTON 

WHARTON 

LAKE 3

 TEXANA HARDIN 

LIBERTY 5 EVADALE 

CALHOUN BEAUMONT MATAGORDA ORANGE CHAMBERS 

JEFFERSON 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


5 Simulated land-surface subsiden

variable, in feet 

Figure 47. Simulated 2050 land-surface subsidence in the NGC GAM model area resulting from TWDB withdrawal scenario. 
Limitations on Use of Model Results 53 

Some relatively small areas of land-surface subsidence are 

indicated outside the closed 1-ft contour that encompasses the 

major area of subsidence during the projected period. In the 

coastal irrigation area centered in Wharton and Jackson Counties, subsidence of about 1 ft appears in parts of each of those 

counties in each of the decadal maps. The only noticeable 

change during the projected period is an enlargement of the area 

of subsidence in Jackson County between 2000 and 2010 and a 

slightly greater enlargement between 2010 and 2020 (figs. 42– 

44). In the Evadale-Beaumont area, the relatively small area of 

subsidence about 3 ft deep on the 2000 map increases to 4 ft in 

the 2010 and subsequent maps through 2050. A small area of 

about 1 ft of subsidence in southern Brazoria County is stable 

on each of the 2000–50 maps. In Liberty and Chambers Counties, small areas of about 1 ft of subsidence that do not appear in 

2000 are indicated in each of those counties for 2010. These two 

areas expand throughout the simulation, coalesce in 2030, and 

nearly coalesce with the major area of subsidence centered in 

the Harris-Galveston County area in 2040 and 2050. The subsidence deepens in a small area in Chambers County to about 

3 ft in 2030, 2040, and 2050. 

Results Using Harris-Galveston Coastal Subsidence 

District Scenario 

Land-surface subsidence in the NGC GAM model area 

for 1995, 2010, 2020, and 2030 that results from simulating 

the HGCSD withdrawal scenario is shown in figures 48–51. In 

the major area of subsidence centered in Harris and Galveston 

Counties, the configuration and maximum depths of subsidence 

for 1995 (HGCSD scenario, fig. 48) are nearly the same as those 

for 2000 (TWDB scenario, fig. 42). Throughout the HGCSD 

projected period, the area within the closed 1-ft contour that 

encompasses the major area of subsidence expands, primarily in 

Fort Bend County, and the depths of subsidence increase substantially. For example, in east-central Harris County, maximum subsidence of about 10–11 ft in 1995 (fig. 48) increases to 

about 13 ft in 2010 (fig. 49), 17 ft in 2020 (fig. 50), and 22 ft in 

2030 (fig. 51). In central Montgomery County (Conroe area), 

maximum subsidence of about 4 ft in 1995 increases to about 

7 ft in 2010, 12 ft in 2020, and 17 ft in 2030. In west-central 

Harris County (Katy area), maximum subsidence of about 7 ft 

in 1995 increases to about 9 ft in 2010, 11 ft in 2020, and 14 ft 

in 2030. These or similar results would be expected as simulated withdrawals increase with time, given the simulated 

increases with time in the amount of water supplied by storage 

derived from the compaction of clay. 

Limitations on Use of Model Results 

In the documentation of the NGC GAM model (Kasmarek 

and Robinson, 2004), factors that limit the ability of the NGC 

GAM model to reliably predict aquifer-system responses to 

future conditions were described. Some of the factors pertain to 

assumptions, or simplifications, about the aquifer system necessary to reduce the complexity of the system so that its functions 

can be described mathematically and simulated numerically. 

Some pertain to the model input data and the uncertainty, bias, 

and non-uniqueness associated with the different datasets of 

aquifer-system properties and conditions. And some pertain to 

the scale of application of the NGC GAM model, which necessarily is regional rather than local because of the size of the 

model grid cells (1 mi

2). Site-specific analysis is precluded 

because aquifer properties and conditions are averaged over the 

area of each cell. These factors contribute a cumulative uncertainty to the results of predictive aquifer-system simulations. 

In addition to the factors described that cause uncertainty 

in simulation results, there is uncertainty associated with each 

of the two projected withdrawal scenarios. The hypothetical 

projected withdrawal scenarios are estimates of future withdrawals and might not represent actual future withdrawals. 

The effects that variations in rainfall might have on future 

withdrawals, and thus on aquifer-system responses, are 

unknown and add uncertainty. The simplifying assumptions 

that the downdip limit of freshwater flow in each hydrogeologic 

unit is a stable, sharp interface across which no flow occurs, 

and that the base of the system at the Jasper aquifer/Catahoula 

confining-unit boundary is no-flow, become less realistic and 

thus contribute greater uncertainty in results as drawdowns 

increase. In other words, the potential for lateral and vertical 

saline-water encroachment into freshwater zones, which the 

NGC GAM model does not simulate, increases as drawdowns 

increase. 

The presence of uncertainty dictates that the results of the 

NGC GAM predictive simulations described in this report be 

used with caution in any decision-making process. The information on the potentiometric-surface maps, water-budget 

diagrams, and subsidence maps is meant to be more of a guide 

or indicator of issues or areas of potential concern than a predictor of specific future conditions in all areas. For example, 

whether water levels in the Jasper aquifer in southern Montgomery County would decline to 500–600 ft below NGVD 29 

by 2010 under the TWDB withdrawal scenario as indicated (fig. 

17), or whether the actual decline would be 300 –400 ft below 

NGVD 29, is less of the message than the fact that deep water 

levels in the Jasper aquifer in southern Montgomery County 

likely would be an issue of concern. Similarly, whether subsidence in east-central Harris County would increase 9 ft between 

2010 and 2030 under the HGCSD scenario (figs. 49, 51) is less 

of the message than the fact that a relatively large fraction of the 

water necessary to supply projected withdrawals likely would 

come from compaction of clay, which in turn would increase 

subsidence in east-central Harris County enough that subsidence might be an issue of concern. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

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CAL

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6

4

CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

LAKE	 RA

CONROE POLK R

AUSTIN 

WALLER	 LAKE 

COLORADO MONTGOMERY CONROE SAN LIVINGSTON 

LAVACA 

JACINTO 

TYLER 

JAS

B.A. STE

 LAKE 

KATY LAKE

BARKER

WHARTON FORT BEND 

LAKE

 TEXANA HARDIN 

LIBERTY EVADALE 4

CALHOUN BEAUMONT 3 1 MATAGORDA ORANGE BRAZORIA CHAMBERS 

JEFFERSON 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


5 Simulated land-surface subsiden

variable, in feet 

Figure 48. Simulated 1995 land-surface subsidence in the NGC GAM model area resulting from HGCSD withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

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CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

LAKE	 RA

CONROE POLK R

AUSTIN 

WALLER	 LAKE 

COLORADO MONTGOMERY	 LIVINGSTON CONROE 

LAVACA SAN 

JACINTO 

TYLER 

7

5 JAS

B.A. STE

 LAKE 

8 LAKE2 8 4

 RESER

VOIR 7 7 2 WHARTON FORT BEND 2 LAKE

 TEXANA 9 10 4 HARDIN 13 8 5 7 LIBERTY EVADALE 4 3

9 

CALHOUN BEAUMONT MA 7 TAGORDA ORANGE BRAZORIA 5 CHAMBERS 1

JEFFERSON 2

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


5 Simulated land-surface subsiden

variable, in feet 

Figure 49. Simulated 2010 land-surface subsidence in the NGC GAM model area resulting from HGCSD withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE

 LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

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ON 

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9 

10 

4 

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CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

LAKE	 RA

CONROE POLK R

AUSTIN 

WALLER	 LAKE 

COLORADO MONTGOMERY	 LIVINGSTON CONROE 

LAVACA SAN 

JACINTO 8 6 TYLER 4 

7 

2 6 JAS

5 B.A. STE

ADDICKS 6 9 12 LAKE 

LAKE

BARKER 11 9 10 8 HOUST ON RESER

VOIR 6 HARRIS 9 8 10

WHARTON FORT BEND 9 10 6 4 3 10 8 LAKE

 TEXANA 

9 9 6 

HARDIN 3 9 4 1 10 LIBERTY 15 3 17 5 2 12 8 JACKSON 

14 BAYT

OWN 

CALHOUN BEAUMONT 3 MATAGORDA ORANGE BRAZORIA 5 CHAMBERS 

2 JEFFERSON 

2 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


5 Simulated land-surface subsiden

variable, in feet 

Figure 50. Simulated 2020 land-surface subsidence in the NGC GAM model area resulting from HGCSD withdrawal scenario. 
WEST FORK SA

JACINTO RIVER 

COLORADO RIVER

GULF OF MEXICO 

GALVESTON

 BAY 

TRINITY RIVER

BRAZOS RIVER 

NECHES RIVER 

SA

MATAGORDA

 BAY 

SOMERVILLE LAKE 

BRAZOS 

LEE 

TEXAS

LOUISIANA

95o 

96o 

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97o 

o 

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RESER

V

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N 

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ON 

WASHINGTON 

BRAZORIA 

CAL

5 

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CALDWELL BASTROP BURLESON NACOGDO

GONZALES 

FAYETTE GRIMES 

WALKER TRINITY ANGELINA 

SAM 

LAKE	 RA

CONROE POLK R

AUSTIN 

WALLER	 LAKE 

COLORADO MONTGOMERY	 LIVINGSTON CONROE 

LAVACA SAN 1 

JACINTO 13 

17	 TYLER 2 

8 3 

1 9 5	 JAS

B.A. STE

 LAKE 

BARKER HOUSTON 

WHARTON FORT BEND 

LAKE

HARDIN 

LIBERTY EVADALE 

JACKSON 

BAYT

OWN 

CALHOUN BEAUMONT MATAGORDA ORANGE CHAMBERS 

JEFFERSON 

SABINE

 LAKE CAMERON 

Base modified from U.S. Geological Survey digital data


Scale 1:24,000 (except Louisiana hydrography 1:100,000) 0 10 20 30 40 MILES


Albers equal-area projection, Datum NAD 83 EXPLANATION
 Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊


5 Simulated land-surface subsiden

variable, in feet 

Figure 51. Simulated 2030 land-surface subsidence in the NGC GAM model area resulting from HGCSD withdrawal scenario. 
58 Ground-Water Flow and Land-Surface Subsidence in the Northern Part of the Gulf Coast Aquifer System, Texas 

Summary 

From land surface downward, the Gulf Coast aquifer 

system comprises the Chicot and Evangeline aquifers, the 

Burkeville confining unit, the Jasper aquifer, and the Catahoula 

confining unit. During 1999–2004, the U.S. Geological Survey 

(USGS), in cooperation with the Texas Water Development 

Board (TWDB) and the Harris-Galveston Coastal Subsidence 

District (HGCSD), conducted a study as a part of the TWDB 

Ground-Water Availability Modeling (GAM) program to 

develop a northern Gulf Coast (NGC) GAM model to simulate 

ground-water flow and land-surface subsidence. The NGC 

GAM model, which is a USGS MODFLOW finite-difference 

model, comprises four layers, one for each of the three aquifers 

and the Burkeville confining unit. The base of the Jasper aquifer/top of the Catahoula confining unit is simulated as a no-flow 

boundary. Each layer consists of 137 rows and 245 columns of 

uniformly spaced grid cells, each cell representing 1 mi2. 

During 2003–04 the USGS, again in cooperation with the 

TWDB and the HGCSD, conducted a follow-up study (this 

report) using the NGC GAM model to evaluate the effects of 

hypothetical projected withdrawals on ground-water flow and 

land-surface subsidence in the approximately 25,000-mi2 NGC 

GAM model area. Two withdrawal scenarios were simulated. 

The first scenario comprises historical withdrawals from the 

aquifer system for 1891–2000 and hypothetical projected withdrawals for 2001–50 compiled by the TWDB (TWDB scenario, 

or dataset). The projected withdrawals compiled by the TWDB 

are based on ground-water demands estimated by regional 

water planning groups. In the TWDB scenario, withdrawals 

increase about 8 percent during 2000–10 from about 850 to 

about 920 Mgal/d, decrease to about 830 Mgal/d in 2030, and 

gradually increase to nearly 850 Mgal/d, the rate at the beginning of the projected period, by 2050. The second scenario is a 

“merge” of the TWDB scenario with an alternate set of projected withdrawals from the Chicot and Evangeline aquifers in 

the Houston metropolitan area for 1995–2030 provided by the 

HGCSD (HGCSD scenario, or dataset). In the HGCSD scenario, withdrawals from the Chicot and Evangeline aquifers 

(Jasper aquifer withdrawals are the same as those in the TWDB 

scenario) increase continuously during 1995–2030 so that total 

withdrawals from the system increase about 74 percent from 

about 875 Mgal/d in 1995 to about 1,520 Mgal/d in 2030. 

The simulated potentiometric surfaces of the Chicot 

aquifer for 2010, 2020, 2030, 2040, and 2050 that result from 

the TWDB withdrawal scenario show relatively little change in 

configuration from the simulated 2000 potentiometric surface 

of the Chicot aquifer and relatively little change in configuration over time. In the Harris-Galveston County area, a broad 

area of water levels 150–200 ft below NGVD 29 at the center of 

the major cone of depression in southern Harris County 

decreases in size during the projected period. In the coastal irrigation area centered in Wharton and Jackson Counties, an area 

of water levels 50–100 ft below NGVD 29 first appears in 

southeastern Jackson and southwestern Matagorda Counties in 

the 2010 surface and expands eastward in Matagorda County 

over time. In the Evadale-Beaumont area (southern Jasper and 

Hardin Counties), little or no change in Chicot aquifer water 

levels over the TWDB projected period is evident. 

The simulated potentiometric surfaces of the Evangeline 

aquifer for 2000, 2010, 2020, 2030, 2040, and 2050 show the 

the most change between 2000 and 2010. The area of water 

levels 250–400 ft below NGVD 29 in the major cone of depression in the simulated 2000 surface in western Harris County 

shifts southeastward to southern Harris County, and water 

levels recover to 200–250 ft below NGVD 29 by 2010. Water 

levels in southern Harris County recover to 150–200 ft below 

NGVD 29 by 2020 and remain in that range through 2050. A 

relatively small cone of depression in southern Montgomery 

County that did not appear in the 2000 surface develops and 

enlarges during the projected period, with a maximum depth of 

250–300 ft below NGVD 29 in 2030, 2040, and 2050. In the 

coastal irrigation area, negligible change in Evangeline aquifer 

water levels is evident throughout the projected period, except 

for the appearance of an area 50–100 ft below NGVD 29 in 

southeastern Jackson and southwestern Matagorda Counties in 

2010 and slight expansion of that area in Matagorda County 

over time. In the Evadale-Beaumont area, 100 ft of recovery in 

the simulated cone of depression occurs by 2010, and for the 

remainder of the projected period, there is negligible change. 

The simulated potentiometric surfaces of the Jasper aquifer for 2000, 2010, 2020, 2030, 2040, and 2050 each have a 

major cone of depression centered in southern Montgomery 

County. This minimally developed feature in the 2000 simulated Jasper aquifer potentiometric surface has a maximum 

depth of 550–650 ft below NGVD 29 in the 2020, 2030, 2040, 

and 2050 surfaces. No noticeable change in Jasper aquifer water 

levels appears in the coastal irrigation area or the EvadaleBeaumont area during the projected period. 

Simulated net recharge (recharge minus natural discharge) 

under the TWDB scenario increases from 995 ft3/s (0.54 in/yr) 

in 2000 to 1,144 (0.62 in/yr) in 2050, and the amount of water 

supplied by storage (sum of sand storage and storage from 

inelastic compaction of clay) decreases from 326 ft3/s in 2000 

to 168 ft3/s in 2050. Although withdrawals from the entire system are projected to be about the same in 2050 as in 2000, the 

percentage of withdrawals supplied by net recharge increases 

from 75 percent in 2000 to 87 percent in 2050, and the percentage of withdrawals supplied by storage decreases from 25 percent in 2000 to 13 percent in 2050. 

For the 2010, 2020, and 2030 Chicot aquifer potentiometric surfaces associated with the HGCSD scenario, the substantially greater Chicot aquifer withdrawals of the HGCSD 

scenario relative to those of the TWDB scenario result in progressively deeper cones of depression in southern Harris 

County (400–450 ft below NGVD 29 in 2030) than those in the 

potentiometric surfaces associated with the TWDB scenario. 

Unlike the decreasing or stable Evangeline aquifer withdrawals 

of the TWDB scenario, progressively larger increases in 

withdrawals in the HGCSD scenario for 2010, 2020, and 

2030 result in substantially deeper cones of depression in the 
simulated HGCSD potentiometric surfaces than in the simulated TWDB potentiometric surfaces for those years. For 2030, 

simulated water levels in western Harris County reach depths 

of 500–550 ft below NGVD 29; and in southern Montgomery 

County, depths of 700–750 ft below NGVD 29. Although 

Jasper aquifer withdrawals are the same for both scenarios, the 

major cone of depression in the Jasper aquifer centered in southern Montgomery County in the 2030 potentiometric surface is 

50 ft deeper at its center (600–700 ft below NGVD 29) than the 

cone in the 2030 surface under the TWDB scenario. 

Simulated net recharge under the HGCSD scenario 

increases from 974 ft3/s (0.53 in/yr) in 1995 to 1,329 ft3/s 

(0.72 in/yr) in 2030. The amount of water supplied by storage 

increases about 168 percent (from 382 to 1,022 ft3/s) under 

the HGCSD scenario, and about 85 percent of that increase 

(543 ft3

/s) is from the compaction of clay. During 1995–2030 

the percentage of withdrawals supplied by net recharge 

decreases from 72 percent in 1995 to 57 percent in 2030, and the 

percentage of withdrawals supplied by storage increases from 

28 percent in 2000 to 43 percent in 2030. 

Land-surface subsidence in the major area of subsidence 

centered in Harris and Galveston Counties during 2000–50 

that results from simulating the TWDB withdrawal scenario 

expands slightly to the west and increases in places. The maximum change occurs in the Conroe area where subsidence 

increases from about 4 to about 13 ft during the projected 

period. Land-surface subsidence in the major area of subsidence 

during 1995–2030 that results from simulating the HGCSD 

withdrawal scenario increases substantially. For example, in 

east-central Harris County maximum subsidence increases 

from about 10–11 ft in 1995 to 22 ft in 2030. These or similar 

results would be expected under the HGCSD scenario as simulated withdrawals increase with time, given the simulated 

increases with time in the amount of water supplied by storage 

derived from the compaction of clay. 

In addition to factors involving model assumptions, input 

data, and scale of application that give rise to uncertainty in simulation results, additional uncertainty in simulation results is 

associated with each of the two projected withdrawal scenarios. 

The hypothetical projected withdrawal scenarios are estimates 

of future withdrawals and might not represent actual future 

withdrawals. The simplifying assumptions that the downdip 

limit of freshwater flow in each hydrogeologic unit is a stable, 

sharp interface across which no flow occurs, and that the base 

of the system at the Jasper aquifer/Catahoula confining-unit 

boundary is no-flow, become less realistic and thus increase the 

uncertainty in results as drawdowns increase. The presence of 

uncertainty dictates that the results of the predictive simulations 

References 59 

described in this report be used with caution in any decisionmaking process. 

References 

Harbaugh, A.W., and McDonald, M.G., 1996, User’s documentation for MODFLOW–96, an update to the U.S. Geological 

Survey modular finite-difference ground-water flow model: 

U.S. Geological Survey Open-File Report 96–485, 56 p. 

Kasmarek, M.C., and Robinson, J.L., 2004, Hydrology and 

simulation of ground-water flow and land-surface subsidence 

in the northern part of the Gulf Coast aquifer system, Texas: 

U.S. Geological Survey Scientific Investigations Report 

2004–5102, 111 p. 

LBG-Guyton Associates, 1997, Ground-water model review 

and conversion: Prepared for Harris-Galveston Coastal 

Subsidence District, Friendswood, Tex., 18 p. 

Leake, S.A., and Prudic, D.E., 1991, Documentation of a computer program to simulate aquifer-system compaction using 

the modular finite-difference ground-water flow model: 

U.S. Geological Survey Techniques of Water-Resources 

Investigations, book 6, chap. A2, 68 p. 

Texas Commission on Environmental Quality, 2004, Search the 

water utility database (WUD): accessed August–October 

2004 at URL http://www3.tnrcc.state.tx.us/iwud 

Texas Water Development Board, 2002, Water for Texas - 

2002—Volumes I–III: Texas Water Development Board, 

Document No. GP–7–1, 155 p. 

Texas Water Development Board, 2003, Groundwater database 

reports: accessed March 2003 at URL 

http://www.twdb.state.tx.us/publications/reports/ 

GroundWaterReports/GWDatabaseReports/ 

GWdatabaserpt.htm 

Texas Water Development Board, 2004, GAM groundwater 

availability modeling: accessed March 10, 2004, at URL 

http://www.twdb.state.tx.us/gam/ 

Turner Collie & Braden, Inc., 1996, Update of population and 

water demand forecasts for the Harris-Galveston Coastal 

Subsidence District: Turner Collie & Braden, Inc., project 

number 11–00246–005, 36 p. 

U.S. Environmental Protection Agency, 2004, Facility registry 

system—Search the Envirofacts facility tables: accessed 

November 2004 at URL http://www.epa.gov/enviro/html/ 

fii/fii_query_java.html 

U.S. Geological Survey, 2004, Land Cover Characterization 

Program—National land cover/MRLC: Earth Resources 

Observation Systems (EROS) Data Center, accessed May 27, 

2004, at URL http://landcover.usgs.gov/index.asp 
60 Ground-Water Flow and Land-Surface Subsidence in the Northern Part of the Gulf Coast Aquifer System, Texas 

Blank Page 
Appendix 1 61

Appendix 1

Appendix 1—Modifications to Northern Gulf 

Coast Ground-Water Availability Modeling 

Model Based on Simulations of Hypothetical 

Withdrawals
62 Ground-Water Flow and Land-Surface Subsidence in the Northern Part of the Gulf Coast Aquifer System, Texas 

Blank Page 
Appendix 1 63

Appendix 1

Appendix 1—Modifications to Northern Gulf Coast Ground-Water Availability 

Modeling Model Based on Simulations of Hypothetical Withdrawals 

In the process of simulating TWDB and HGCSD hypothetical projected withdrawals, interim results indicated a 

need for reassessment of selected input data for the model of 

Kasmarek and Robinson (2004). Accordingly, input data 

changes were made, and the NGC GAM model was recalibrated 

in a series of trial-and-error simulations, each beginning with 

the steady-state model and proceeding to the transient model 

of historical and hypothetical projected withdrawals. The 

changes are summarized below by area. The root mean square 

errors between simulated and measured 2000 potentiometric 

surfaces resulting from the TWDB scenario before and after 

model modifications are shown in table a1.1. The simulated 

2000 water-budget components resulting from the TWDB 

scenario before and after model modifications are shown in 

table a1.2.

Area Near Harris-Montgomery County Line Between 

Houston and Conroe

Simulated head declines in the Jasper aquifer in an area of 

about 200 mi2

 that were considered excessive prompted review 

of input values of transmissivity (and component hydraulic conductivity) and historical withdrawals in the area. Hydraulic conductivity values assigned to model cells of the Evangeline and 

Jasper aquifers in the area appeared anomalously low relative to 

those of cells in surrounding areas. No hydrogeologic evidence 

for the low values could be established. A comparison of late 

1990s simulated withdrawals in the area with the distribution of 

known wells in the area indicated that some late 1990s withdrawals from the Jasper aquifer might not be accounted for in 

the NGC GAM model dataset of historical withdrawals. The 

anomalously low hydraulic conductivity values arrived at during the original calibration could have resulted from attempts to 

match measured head declines created by withdrawals unaccounted for in the NGC GAM model. Despite the possibility of 

missing late 1990s Jasper aquifer withdrawals, no changes were 

made to the dataset of historical withdrawals before recalibration in the area. Input data were changed in the recalibration 

process as follows:

• Evangeline aquifer hydraulic conductivity in 388 

cells was increased from an average of 2.64 to an 

average of 2.86 feet/day (ft/d).

• Jasper aquifer hydraulic conductivity in 208 cells 

was decreased from an average of 1.42 to an average 

of 0.63 ft/d.

Table a1.1. Root mean square (RMS) errors between simulated 

and measured 2000 Chicot, Evangeline, and Jasper aquifer 

potentiometric surfaces resulting from the TWDB scenario before 

and after model modifications described in appendix 1. 

Table a1.2. Simulated 2000 water-budget components resulting 

from the TWDB scenario before and after model modifications 

described in appendix 1. 

Coastal Irrigation Area Centered in Wharton and 

Jackson Counties

In parts of Wharton, Jackson, and Matagorda Counties, a 

sudden decrease in the number of Evangeline aquifer model 

cells containing withdrawals was noted as simulation progressed from the last historical stress period (2000) to the first 

projected stress period (2001). So many more Evangeline aquifer model cells contained withdrawals for 2000 than for 2001 

that the transition appeared unrealistic. Upon investigation, it 

was discovered that some late 1990s withdrawals in those counties that should have been assigned to the Chicot aquifer had 

been inadvertently assigned to the Evangeline aquifer. Because 

the NGC GAM model had been calibrated with those incorrectly assigned withdrawals, some recalibration was done after 

Aquifer

RMS error

(feet)

Before

(Kasmarek and Robinson, 2004) After

Chicot 30.7 31.0

Evangeline 40.1 45.0

Jasper 33.8 37.9

Component

(cubic feet per second)

Before

(Kasmarek and

Robinson, 2004,

fig. 73)

After

(fig. 22)

Sources

Recharge 965 1,160

Net release from sand storage 410 242

Net release from clay compaction 106 84

Discharges

Natural discharge 161 165

Withdrawals 1,322 1,321
64 Ground-Water Flow and Land-Surface Subsidence in the Northern Part of the Gulf Coast Aquifer System, Texas 

correctly assigning withdrawals. Input data were changed in the 

recalibration process as follows: 

•	 Vertical hydraulic conductance between the water 

table and the immediately adjacent deeper zone 

(general head boundary [GHB] conductance) of the 

Chicot aquifer in 1,395 cells was increased from an 

average of 74.7 to an average of 344.6 feet squared 

per day (ft2

/d). 

•	 Chicot aquifer storativity in 730 cells was decreased 

from an average of 0.14 to an average of 0.017. 

•	 Chicot aquifer hydraulic conductivity in 792 cells 

was decreased from an average of 96.6 to an average 

of 48.3 ft/d. 

Area Between Conroe and Updip Limit of Chicot 

Aquifer 

Several dry cells (water-level decline to altitude below 

altitude of base of aquifer) in an area of about 80 mi

2

 persisted 

throughout simulations of both the historical and projected periods. Unrealistically small GHB conductances of the Chicot 

aquifer in dry cells were identified as the primary cause. Some 

recalibration was done to maintain simulated water levels above 

the altitudes of the base of the aquifer. Input data were changed 

in the recalibration process as follows: 

•	 Chicot aquifer GHB conductance in 115 cells was 

increased from an average of 0.17 to an average of 

1,950 ft2/d. 

•	 Chicot aquifer hydraulic conductivity in 213 cells 

was increased from an average of 0.03 to an average 

of 0.10 ft/d. 

•	 Evangeline aquifer hydraulic conductivity in 709 

cells was increased from an average of 0.51 to an 

average of 0.60 ft/d. 

Area in NortheasternFortBend County 

Unrealistically large water-level gradients in simulations 

of the HGCSD scenario in an area of about 160 mi2 in Fort Bend 

County near the confluence of the Fort Bend-Harris-Brazoria 

County lines prompted re-evaluation of selected input data 

there. Consequently, some recalibration was done to lessen the 

gradients. Input data were changed in the recalibration process 

as follows: 

•	 Chicot aquifer GHB conductance in 156 cells was 

increased from an average of 81 to an average of 

449 ft2

/d. 

•	 Chicot aquifer hydraulic conductivity in 53 cells 

was increased from an average of 3.28 to an average 

of 10.4 ft/d. 

Area in Central HarrisCounty 

Unrealistically large water-level gradients in simulations 

of the TWDB scenario in an area of about 20 mi2 in central 

Harris County prompted re-evaluation of selected input data 

there, and some recalibration was done to lessen the gradients. 

Input data were changed in the recalibration process as follows: 

•	 Chicot aquifer storativity in 11 cells was increased 

from an average of 0.0004 to an average of 0.005. 

•	 Evangeline aquifer hydrauilic conductivity in 19 

cells was increased from an average of 0.12 to an 

average of 0.20 ft

2

/d. 
Appendix 2 65

Appendix 2

Appendix 2—Description of Methods for 

Distributing Withdrawals to Model Cells
66 Ground-Water Flow and Land-Surface Subsidence in the Northern Part of the Gulf Coast Aquifer System, Texas 

Blank Page 
Appendix 2—Description of Methods for Distributing Withdrawals to Model Cells 67 

Appendix 2—Description of Methods for Distributing Withdrawals to Model Cells


Texas Water Development Board Scenario 

All withdrawals for the NGC GAM model area were 

assigned to either the Gulf Coast aquifer [system] or the Brazos 

River alluvium in the TWDB spreadsheets. Subdividing Gulf 

Coast aquifer [system] withdrawals into the four hydrogeologic 

units of the NGC GAM model is addressed among methods 

described below. All Brazos River alluvium withdrawals were 

reassigned as Chicot withdrawals. 

Point-Source Withdrawals 

The spatial (lateral) distribution of point-source withdrawals among NGC GAM model cells remained constant from 

stress period to stress period during simulations unless, for a 

particular stress period, point-source withdrawals for one or 

more cells became zero and no nonpoint-source withdrawals 

were assigned to those cells; in that case, those cells became 

non-withdrawal cells. The assumption was made that the water 

users in a particular water-user group during the projected 

period would be the same as the water users during the historical period, unless additional point-source water users in that 

group were identified in the spreadsheets. 

Municipal 

Hypothetical projected withdrawals for municipalities for 

the NGC GAM model area for the period 2001–50 were based 

on estimated ground-water demands provided by regional water 

planning groups (RWPG) and compiled by the TWDB. Municipalities were identified by water-user information provided by 

the TWDB (Cindy Ridgeway, Texas Water Development 

Board, written commun., 2004). 

Point-source (well) locations were obtained from the 

Texas Commission on Environmental Quality (2004) Public 

Water System database, and the Texas Water Development 

Board (2003) State well database. If no point sources could be 

located for a municipality, an artificial point source was placed 

(using geographic information system [GIS] technology) at one 

of the following points, as applicable: centroid of city, centroid 

of zip code area, or centroid of basin/county/hydrogeologic-unit 

intersect area. 

Point-source withdrawals were assigned to a hydrogeologic unit or units (vertically distributed) through an automated 

process1

 using the location and the screened interval(s) or 

well depth, or both, before the spatial distribution of withdrawals. Withdrawals also were assigned to a point source in an automated process on the basis of the water-user group, water user, 

water-use category, county, and source basin. 

Withdrawals within each unique assemblage (group of 

wells) were divided (laterally distributed) evenly among the 

wells in that assemblage. For example, if an assemblage comprised 20 wells, each well was assigned 1/20th of the withdrawal (Q/20) for that assemblage. If one of the 20 wells in the 

assemblage was screened 60 percent in the Chicot aquifer and 

40 percent in the Evangeline aquifer, then the withdrawal rate 

for that well would have been allocated accordingly, 0.6 times 

Q/20 to the Chicot aquifer and 0.4 times Q/20 to the Evangeline 

aquifer. 

Manufacturing, Mining, and Power Generation 

Hypothetical projected withdrawals for manufacturing, 

mining, and power generation (industrial uses) for the NGC 

GAM model area for the period 2001–50 were based on 

estimated ground-water demands provided by RWPGs and 

compiled by the TWDB. Industrial users were identified by 

water-user information provided by the TWDB (Cindy 

Ridgeway, Texas Water Development Board, written commun., 

2004). 

As for municipal point-source locations, industrial pointsource locations were obtained from the Texas Commission on 

Environmental Quality (2004) Public Water System database 

and the Texas Water Development Board (2003) State well 

database; and additionally from the U.S. Environmental Protection Agency (2004) Envirofacts facilities database. If no point 

sources could be located for an industrial user, an artificial point 

source was placed (using GIS technology) at one of the following points, as applicable: centroid of city, centroid of zip code 

area, or centroid of basin/county/hydrogeologic-unit intersect 

area. 

Point-source withdrawals were assigned to a hydrogeologic unit by an automated process1

 using the spatial location 

and the screened interval(s) or well depth, or both. Withdrawals 

also were assigned to a point source in an automated process on 

the basis of water-user group, water user, water-use category, 

county, and source basin. Withdrawals within each unique 

assemblage were divided evenly among the point sources in that 

assemblage, per the example in the “Municipal” section. 

1 An automated GIS-based hydrogeologic-unit identification program was developed to associate point sources with hydrogeologic units (model layers). The 

program identifies all the units that exist at the latitude and longitude of a point source. The program then assigns a unit to the point source on the basis of its 

screened interval(s) or well depth, or both. This program identified 1,435 point sources automatically. One-hundred and forty-five point sources were assigned to 

one or more units manually, which was necessary for point sources lacking sufficient descriptive information for automated assignment. 
68 Ground-Water Flow and Land-Surface Subsidence in the Northern Part of the Gulf Coast Aquifer System, Texas 

Nonpoint-Source Withdrawals 

The spatial (lateral) distribution of nonpoint-source withdrawals among NGC GAM model cells remained constant from 

stress period to stress period during simulations unless, for a 

particular stress period, nonpoint-source withdrawals for one or 

more cells became zero and no point-source withdrawals were 

assigned to those cells; in that case, those cells became nonwithdrawal cells. The nonpoint-source distributions for the 

projected period were coincident with those of the historical 

period (Kasmarek and Robinson, 2004). 

Nonpoint-source withdrawals were simulated as artificial 

point sources, one per model cell per category (livestock [per 

rangeland category], irrigation [per crop category], and countyother), on the basis of information in the Texas Water Development Board (2003) State well database. Withdrawals were 

assigned to hydrogeologic units (vertically distributed) by joining attributes from the database to the artificial points using 

GIS techniques. If information in the database was not available 

to assign hydrogeologic units, nonpoint-source withdrawals 

were assigned to the respective outcropping hydrogeologic 

unit. 

Livestock 

Hypothetical projected withdrawals for livestock for the 

NGC GAM model area for the period 2001–50 were based on 

estimated ground-water demands provided by RWPGs and 

compiled by the TWDB by county and basin. Within each 

county/basin area, livestock areas were laterally distributed 

over rangeland on the basis of land-use maps, using the categories “herbaceous rangeland,” “shrub and brush rangeland,” and 

“mixed rangeland” from the U.S. Geological Survey (2004) 

national land cover. Withdrawals were assigned to these 

livestock areas through an automated process on the basis of 

water-use category, county, and basin. Withdrawals within 

each unique livestock assemblage (group of artificial point 

sources) were divided evenly among the model grid cells in that 

assemblage. 

Irrigation 

Hypothetical projected withdrawals for irrigation for the 

NGC GAM model area for the period 2001–50 were based on 

estimated ground-water demands provided by RWPGs and 

compiled by the TWDB by county and basin. Within each 

county/basin area, irrigated areas were laterally distributed for 

the land-use categories “row crops,” “orchards/vineyards,” and 

“small grains” obtained from the U.S. Geological Survey 

(2004) national land cover. Withdrawals were assigned to these 

irrigated areasin an automated process on the basis of water-use 

category, county, and basin. Withdrawals within each unique 

irrigation assemblage were divided evenly among the model 

grid cells in that assemblage. 

County-Other 

Hypothetical projected withdrawals for county-other 

(primarily rural domestic) for the NGC GAM model area for 

the period 2001–50 were based on estimated ground-water 

demands provided by RWPGs and compiled by the TWDB by 

county and basin. The county-other areas of withdrawal were 

distributed within each county/basin excluding urban areas and 

using a 1-mile buffer around surficial water bodies. Withdrawals were assigned to county-other areas of withdrawal in an 

automated process on the basis of water-use category, county, 

and basin. Withdrawals within each unique county-other 

assemblage were divided evenly among the model grid cells in 

that assemblage. 

Harris-Galveston Coastal Subsidence District 

Scenario (Merge of HGCSD Dataset into TWDB 

Dataset) 

The merge of the HGCSD subarea dataset with the TWDB 

dataset was done using raster (cell-based) data analysis. This 

process provided accurate transfer of withdrawal values from 

the coarse (about 7 mi2) HGCSD model grid cells to the finer 

(1 mi2

) NGC GAM model grid cells (fig. a2.1). Raster data 

analysis also preserved HGCSD model grid cell values that 

might otherwise be affected by the approximately 36-degree 

difference in orientation between the NGC GAM and HGCSD 

model grids. The merge was done only for layers 1 and 2 (Chicot and Evangeline aquifers) in the coincident NGC GAM and 

HGCSD model areas for the period 1995–2030. All raster data 

analysis described below was done using a 100- by 100-ft raster 

cell size. 

Vector NGC GAM model grid cells in the coincident 

model areas were identified and converted to a raster grid. All 

raster cells (about 2,800) within an NGC GAM model grid cell 

were grouped into a raster zone (NGC GAM zone) identified by 

its corresponding NGC GAM sequence number. 

For each of the 72 simulated layer/year combinations (two 

layers, 36 years), vector HGCSD model grid cells were converted to a raster grid, vertically integrated to match cell-for-cell 

to the raster NGC GAM zones. All raster cells (about 20,000) 

within an HGCSD model grid cell were assigned a withdrawal 

value according to the following equation: 

raster cell withdrawal = (HGCSD model grid cell withdrawal, 

in cubic feet per day / HGCSD model grid cell area, in square 

feet) X area of raster cell, in square feet 

This normalization process allowed for the summation of 

raster-cell withdrawals within an NGC GAM model grid cell 

regardless of which HGCSD model grid cell(s) contained the 

initial source of withdrawal. The withdrawal assigned to an 

NGC GAM model grid cell for the HGCSD scenario was then 

replaced with this summed value of raster-cell withdrawals. 
Appendix 2—Description of Methods for Distributing Withdrawals to Model Cells 69 

NGC GAM model grid cells at the boundary of the coinci- NGC GAM model grid cell withdrawal was retained. Otherwise 

dent areas of the NGC GAM and HGCSD model grids were the NGC GAM model grid cell withdrawal was computed as the 

assigned withdrawals on the basis of the percentage of the sum of (1) the original NGC GAM model grid cell withdrawal 

model grid cell area that is coincident with an HGCSD model times the fraction of noncoincident NGC GAM model grid 

grid cell(s). If more than 95 percent of the area of an NGC GAM cell area plus (2) the raster-cell withdrawals in the coincident 

model grid cell was outside the coincident area, the original area. 
70 

WEST FORK SAN JACINTO RIVER 

COLORADO RIVE R

GULF OF MEXICO 

GALVESTON

 BAY

TRINITY RIVER

BRAZOS 

RIVER 

NECHES RIVER 

SABINE RIVER 

MATAGORDA BAY 

GALVESTON 

WASHINGTON 

TRINITY 

FAYETTE 

VERNON 

ALLEN 

ANGELINA 

NACOGDOCHES 

 SAN

 AUGUSTINE 

CALHOUN 

GONZALES 

BURLESONBRAZOS 

BASTROP 

LEE 

CALDWELL 

SABINE 

30o 

93o 

TOLEDO

SOMERVILLE

GRIMES 

FORT BEND 

Ground-Water Flow and Land-Surface Subsidence in the Northern Part of the Gulf Coast Aquifer System, Texas 

Approximately 2,800 100-foot raster cells per NGC GAM model grid cell 

Approximately 20,000 100-foot raster cells per HGCSD model grid cell 

EXPLANATION


Cell (ignores relative scale)


NGC GAM model grid


HGCSD model grid


Raster


Scenario of normalized 100-foot raster cells per NGC GAM model grid cell 

Entirely in NGC GAM model grid cell overlapping single HGCSD model grid cell 

Entirely in NGC GAM model grid cell overlapping different HGCSD model grid cells 

Entirely in NGC GAM model grid cell partially overlapping HGCSD model grid cell 

94o 

SHELBY

 BEND

 RESERVOIR 

95o SAM SABINE RAYBURN RESERVOIR 

NEWTON 

JASPER 31o 

POLK TYLER B.A. STEINHAGEN LAKE 

HUNTSVILLE LAKE BEAUREGARD 96o WALKER LIVINGSTON

SAN

 JACINTO LAKE 

CONROE 

LOUISIANA

MONTGOMER EVADALE Y JEFF

CALCASIEU DAVIS 

CALCASIEU

 LAKE 

HARDIN 

TEXAS

BEAUMONT ORANGE 

LAKE WALLER 

97o LIBERTY CAMERON 

LAKE 

HOUSTON JEFFERSON SABINE AUSTIN ADDICKS LAKE RESERVOIR HARRIS PORT ARTHUR 

HOUSTON BAYTOWN 

BARKER CHAMBERS 

 RESERVOIR 

COLORADO 

LAVACA 0 10 20 30 40 MILES

WHARTON 

BRAZORIA 

LAKE

29o TEXANA 

JACKSON MATAGORDA 

Base modified from U.S. Geological Survey digital data 

Scale 1:250,000 

Albers equal-area projection, Datum NAD 83 

Standard parallels 34 ̊55’ and 27 ̊25’, central meridian -100 ̊ 

EXPLANATION TEXAS LOUISIANA

Boundary of area of withdrawal dataset 

Texas Water Development Board NGC GAM area 

Harris-Galveston Coastal Subsidence District 

Figure a2.1. Relations between NGC GAM model grid cells, HGCSD model grid cells, and raster cells associated with merge of HGCSD

dataset into TWDB dataset.
Prepared by the USGS Texas Water Science Center: 

U.S. Geological Survey


8027 Exchange Drive


Austin, TX 78754–4733


Information regarding water resources in Texas is available at URL 

http: //tx.usgs.gov/