![](media/image1.png){width="1.75in" height="0.6416666666666667in"}

In cooperation with the Texas Water Development Board

Geologic and Hydrogeologic Information for a Geodatabase for the Brazos
River Alluvium Aquifer, Bosque County to Fort Bend County, Texas

By Sachin D. Shah and Natalie A. Houston

Open-File Report 2007--1031, version 3

U.S. Department of the Interior

U.S. Geological Survey

U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

For product and ordering information:\
World Wide Web: http://www.usgs.gov/pubprod\
Telephone: 1-888-ASK-USGS

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the Earth\
its natural and living resources, natural hazards, and the environment:\
World Wide Web: http://www.usgs.gov\
Telephone: 1-888-ASK-USGS

Suggested citation:\
Shah, S.D., and Houston, N.A., 2007, Geologic and hydrogeologic
information for a geodatabase for the Brazos River alluvium aquifer,
Bosque County to Fort Bend County, Texas: U.S. Geological Survey
Open-File Report 2007--1031 \[version 3\], 10 p.

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

Although this report is in the public domain, permission must be secured
from the individual\
copyright owners to reproduce any copyrighted material contained within
this report.

# Contents {#contents .TOCHeading1}

Abstract [1](#abstract)

Introduction [1](#introduction)

Purpose and Scope [3](#purpose-and-scope)

Acknowledgments [3](#acknowledgments)

Geologic and Hydrogeologic Setting
[3](#geologic-and-hydrogeologic-setting)

Geodatabase [3](#geodatabase)

Methodology [5](#methodology)

Data Compilation [5](#data-compilation)

Data Input [6](#data-input)

Data Quality [9](#data-quality)

Metadata [9](#metadata)

References [9](#references)

# Figures {#figures .TOCHeading1}

1\. Brazos River alluvium aquifer study area, Bosque County to Fort Bend
County, Texas, showing\
1/2- by 1/2-mile grid used to facilitate uniform data distribution
[2](#__RefHeading___Toc158008895)

2\. Well-numbering system for the Texas Water Development Board Ground
Water Data System [8](#__RefHeading___Toc158008896)

# Tables {#tables .TOCHeading1}

1\. Lithology and water-yielding characteristics of the major geologic
units of the Brazos River alluvium aquifer study area, Bosque County to
Fort Bend County, Texas. [4](#__RefHeading___Toc158437747)

2\. Sources of data compiled and entered into the geodatabase of
geologic and hydrogeologic\
information, Bosque County to Fort Bend County, Texas .
[6](#__RefHeading___Toc158437749)

3\. Description and definition of data compiled and entered into the
geodatabase of geologic and hydrogeologic information, Bosque County to
Fort Bend County, Texas . [7](#__RefHeading___Toc158437750)

# Datums {#datums .TOCHeading1}

Vertical coordinate information is referenced to North American Vertical
Datum of 1988 (NAVD 88).

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

Geologic and Hydrogeologic Information for a Geodatabase of the Brazos
River Alluvium Aquifer, Bosque County to Fort Bend County, Texas

By Sachin D. Shah and Natalie A. Houston

# Abstract 

During July--October 2006, the U.S. Geological Survey (USGS), in
cooperation with the Texas Water Development Board (TWDB), developed
geologic and hydrogeologic information for a geodatabase for use in
development of a Groundwater Availability Model (GAM) of the Brazos
River alluvium aquifer along the Brazos River from Bosque County to Fort
Bend County, Texas. The report provides geologic and hydrogeologic
information for a study area that encompasses the Brazos River alluvium
aquifer, a 1/2-mile-wide lateral buffer surrounding the aquifer, and the
rocks immediately underlying the aquifer. The geodatabase involves use
of a thematic approach to create layers of feature data using a
geographic information system. Feature classes represent the various
types of data that are keyed to spatial location and related to one
another within the geodatabase. The 1/2-mile-wide buffer surrounding the
aquifer was applied to include data from wells constructed primarily in
alluvium but outside the boundary of the Brazos River alluvium aquifer.
A 1/2- by 1/2-mile grid was generated on the study area to facilitate
uniform distribution of data for eventual input into the GAM. Data were
compiled primarily from drillers' and borehole geophysical logs from
government agencies and universities, hydrogeologic sections and maps
from published reports, and agency files. The geodatabase contains 525
points with geologic data and 280 points with hydrogeologic data.

# Introduction 

During July--October 2006, the U.S. Geological Survey (USGS), in
cooperation with the Texas Water Development Board (TWDB), developed
geologic and hydrogeologic information for a geodatabase for use in
development of a Groundwater Availability Model (GAM) (Texas Water
Development Board, 2006a) for the Brazos River alluvium aquifer. The
geologic and hydrogeologic information pertains to a study area (fig. 1)
that encompasses the Brazos River alluvium aquifer (the area of
occurrence of which comprises parts of Bosque, Hill, McLennan, Falls,
Grimes, Brazos, Burleson, Robertson, Milam, Washington, Waller, Austin,
and Fort Bend Counties), a 1/2-mile-wide lateral buffer surrounding the
aquifer, and the rocks immediately underlying the aquifer. The
information, in geodatabase format (Zeiler, 1999), includes altitudes of
the top and base of the aquifer and hydrogeologic properties such as
hydraulic conductivity, specific capacity, and transmissivity. The
geodatabase does not include data for every part of the study area; it
is limited to selected digital and hard-copy data from published
reports, the TWDB, Texas Commission on Environmental Quality (TCEQ),
various universities, and ground-water conservation districts (table 2).

![](media/image2.png){width="6.418055555555555in" height="8.03125in"}

[]{#__RefHeading___Toc158008895 .anchor}**Figure 1.** Brazos River
alluvium aquifer study area, Bosque County to Fort Bend County, Texas,
showing 1/2- by 1/2-mile grid used to facilitate uniform data
distribution.

## Purpose and Scope

The purpose of this report is to provide information for a geodatabase
for use in development of a Brazos River alluvium aquifer GAM. The
information is in the GAM Source Data Geodatabase format (Texas Water
Development Board, 2006b). After a brief description of the geology and
hydrogeology of the study area, the characteristics and function of the
geodatabase are described and then the methodology used to create the
geologic and hydrogeologic components of the geodatabase.

## Acknowledgments

The authors thank Dr. Joe Yelderman, Baylor University Department of
Geology, for providing valuable data on the Brazos River alluvium for
McLennan County. The authors also thank Dr. Clyde Munster, Department of
Biological and Agricultural Engineering, Texas A&M University, for site
access and Brazos River alluvium information for Burleson County.

# Geologic and Hydrogeologic Setting

The Brazos River alluvium aquifer is defined by the TWDB as a minor
aquifer (Ashworth and Hopkins, 1995). The aquifer comprises
Quaternary-age, unconsolidated clay, silt, sand, and gravel deposited by
flooding of the Brazos River, and Pleistocene-age fluvial terrace
deposits. The 1/2-mile-wide buffer surrounding the aquifer primarily
comprises Pleistocene-age fluvial terrace deposits. The rocks
immediately underlying the aquifer compose numerous sedimentary geologic
units of Tertiary and Cretaceous age. The thickness of the Brazos River
alluvium aquifer exceeds 80 feet in some isolated, downstream areas but
averages about 45 to 50 feet throughout its extent (Cronin and Wilson,
1967). The geologic units immediately beneath the aquifer primarily are
composed of sand and clay and the thickness of the units varies
substantially (table 1).

According to HDR Engineering, Inc. (2001), water in the alluvial aquifer
occurs under water-table conditions and primarily is used for
irrigation. The water table slopes toward the Brazos River, indicating
that the Brazos is gaining water from the aquifer. Recharge to the
aquifer occurs primarily through direct rainfall on the aquifer and
subsequent downward leakage to the saturated zone. Discharge from the
aquifer primarily occurs through evapotranspiration and withdrawals from
wells.

# Geodatabase

A geodatabase is a spatially enabled database that contains spatial
information; it is an extension of tabular data that allows users to
correlate tabular data with physical and spatial components. With a
geodatabase, geographically referenced data can be manipulated using a
geographic information system (GIS) to produce maps, interactive
queries, and various types of spatial analyses. A geodatabase provides a
framework and an interactive tool to aid in understanding subsurface
structure. The geodatabase developed for the GAM is an Environmental
Systems Research Institute (ESRI) ArcGIS personal geodatabase. ArcGIS
personal geodatabases are stored as Microsoft Access files (Zeiler,
1999). The geodatabase can be used to interpret the thickness of the
Brazos River alluvium aquifer on the basis of aquifer top and base
altitudes and to associate hydrogeologic properties such as hydraulic
conductivity and specific capacity with point locations in the study
area.

[]{#__RefHeading___Toc158437747 .anchor}[**Table 1.** Lithology and
water-yielding characteristics of the major geologic units of the Brazos
River alluvium aquifer study area, Bosque County to Fort Bend County,
Texas (modified from Cronin and Wilson, 1967).]{.mark}

  -------------------- ------------- ---------------- ------------ ---------------- --------------------
  System               Series        Geologic\        Maximum\     Lithology        Water-yielding\
                                     unit             thickness\                    characteristics
                                                      (feet)                        

  Quaternary           Holocene      Alluvium         82           Fine to coarse   Yields small to
                                                                   sand, gravel,    large quantities of
                                                                   silt, and clay   fresh water mostly
                                                                                    to irrigation wells
                                                                                    along the Brazos
                                                                                    River.

                       Pleistocene   Fluvial terrace  70           Fine to coarse   Yields small to
                                     deposits                      sand, gravel,    large quantities of
                                                                   silt, and clay   fresh water mostly
                                                                                    to wells for
                                                                                    rural-domestic and
                                                                                    livestock use and
                                                                                    some irrigation
                                                                                    wells.

  Tertiary             Miocene       Catahoula        460          Clay and sand    Yields small
                                     Sandstone                                      quantities of water
                                                                                    to wells in the
                                                                                    outcrop for
                                                                                    rural-domestic and
                                                                                    livestock use.

                       Eocene        Jackson Group    1,480        Shale, volcanic  Yields small
                                                                   ash, sand, and   quantities of water
                                                                   clay             to wells in the
                                                                                    outcrop for
                                                                                    rural-domestic and
                                                                                    livestock use.

                                     Yegua Formation  1,150        Fine to medium   Yields small
                                                                   sand, silt,      quantities of water
                                                                   clay, and gypsum to wells for public
                                                                   and lignite      supply, domestic,
                                                                                    livestock, and
                                                                                    irrigation use

                                     Cook Mountain    550          Clay, small      Yields small
                                     Formation                     amount of sand,  quantities of water
                                                                   sandstone,       to wells that tap
                                                                   limestone,       the Spiller Sand
                                                                   glauconite, and  Member
                                                                   gypsum           

                                     Sparta Sand      290          Fine to medium   Yields small to
                                                                   sand with some   large quantities of
                                                                   clay, and sandy  water to wells in
                                                                   clay             and downdip from the
                                                                                    outcrop

                                     Weches Formation 130          Iron-bearing     Yields small
                                                                   glauconitic clay quantities of water
                                                                   and sand         to wells in the
                                                                                    outcrop for
                                                                                    rural-domestic and
                                                                                    livestock use.

                                     Queen City Sand  540          Massive to       Yields small
                                                                   thin-bedded,     quantities of water
                                                                   fine to medium   to wells in and
                                                                   sand, clay, and  several miles
                                                                   some lenses of   downdip from the
                                                                   conglomerate     outcrop
                                                                   containing iron  

                                     Reklaw Formation 430          Glauconitic sand Capable of yielding
                                                                   and silt in the  small quantities of
                                                                   lower part of    water to wells.
                                                                   the formation;   
                                                                   clay and thin    
                                                                   beds of          
                                                                   sandstone in the 
                                                                   upper part       

                                     Carrizo Sand     250          Fine to coarse,  Yields small
                                                                   cross-bedded     quantities of water
                                                                   sand and some    mostly to
                                                                   thin beds of     public-supply wells.
                                                                   sandstone and    
                                                                   clay             

                                     Wilcox Group     3,900        Fine to coarse   Yields water to
                                                                   sand and         public-supply,
                                                                   sandstone, sandy irrigation,
                                                                   clay, clay, and  domestic, and
                                                                   shale, with some livestock wells.
                                                                   lenses of        Most water is
                                                                   limestone and    produced from the
                                                                   lignite          Simsboro Formation.

                       Paleocene     Midway Group     900          Glaucontic sand, Yields small to
                                                                   silt, calcareous moderate quantities
                                                                   clay, and        of water chiefly
                                                                   limestone        from limestone
                                                                                    lentils.

  **Table 1.**                                                                      
  Lithology and                                                                     
  water-yielding                                                                    
  characteristics of                                                                
  the major geologic                                                                
  units of the Brazos                                                               
  River alluvium                                                                    
  aquifer study area,                                                               
  Bosque County to                                                                  
  Fort Bend County,                                                                 
  Texas (modified from                                                              
  Cronin and Wilson,                                                                
  1967)---Continued.                                                                

  Cretaceous           Gulfian       Navarro Group    200          Sandy marl and   Locally yields small
                                                                   clay,            quantities of fresh
                                                                   glauconitic;     to moderately saline
                                                                   fine sand in     water to wells.
                                                                   places lime      
                                                                   cemented         

                                     Taylor Marl      1,110        Marl, sandy      Locally yields small
                                                                   marl, chalky     quantities of fresh
                                                                   limestone, and   to moderately saline
                                                                   calcareous       water to wells.
                                                                   sandstone.       

                                     Austin Chalk     600          Chalky and marly Locally yields small
                                                                   limestone and    quantities of fresh
                                                                   limey shale.     to moderately saline
                                                                                    water to wells.

                                     Eagle Ford Shale 200          Shale, thinly    Locally yields small
                                                                   bedded sandstone quantities of fresh
                                                                   and limestone.   to moderately saline
                                                                                    water to wells.

                                     Woodbine         185          Cross-bedded     Locally yields small
                                     Formation                     ferruginous      quantities of fresh
                                                                   sandstone,       to moderately saline
                                                                   shale, clay,     water to wells.
                                                                   sandy clay,      
                                                                   lignite, and     
                                                                   gypsiferous      
                                                                   clay.            

                       Comanchean    Washita Group    580          Fossiliferrous   Yields small to
                                                                   limestone and    large quantities of
                                                                   marl; some       water to
                                                                   shale, clay,     public-supply,
                                                                   sand, and        domestic, and
                                                                   shells.          livestock wells and
                                                                                    springs.

                                     Fredericksburg   580          Fossiliferrous   Yields small to
                                     Group                         limestone and    large quantities of
                                                                   marl; some       water to
                                                                   shale, clay,     public-supply,
                                                                   sand, and        domestic, and
                                                                   shells.          livestock wells.
  -------------------- ------------- ---------------- ------------ ---------------- --------------------

A geodatabase involves use of a thematic approach to create spatial
layers of data called feature classes in a GIS. Feature classes
represent the various types of data that are keyed to spatial location
and related to one another within the geodatabase. Point feature classes
typically represent wells in the study area. The various types of data
are separated into relational tables in the geodatabase on the basis of
how they interact and correspond with the spatial feature class. These
relational tables represent a collection of features and the relations
between them. The goal is to provide accurate representations of the
spatial extent and properties of the Brazos River alluvium aquifer using
the geologic and hydrogeologic data that have been compiled in the GAM
geodatabase format.

## Methodology

A ground-water model requires a large amount of information about the
aquifer. Initial steps in developing a ground-water model are obtaining
and preparing for use detailed information on the structure and
properties of the hydrogeologic units, specifically geologic and
hydrogeologic data. The Brazos River alluvium aquifer is the single
hydrogeologic unit that is the focus of the Brazos River alluvium
aquifer GAM. Compiling data, entering data into the geodatabase,
ensuring data quality, and documenting the associated metadata are the
primary steps involved.

### Data Compilation

Geologic and hydrogeologic data were organized and incorporated into the
geodatabase. The 1/2-mile-wide buffer surrounding the aquifer (fig. 1)
was applied to include data from wells constructed primarily in alluvium
but outside the boundary of the Brazos River alluvium aquifer delineated
by Ashworth and Hopkins (1995). A 1/2- by 1/2-mile grid was generated on
the study area to facilitate uniform distribution of data for eventual
input into the GAM. Data were compiled primarily from drillers' and
borehole geophysical logs from government agencies and universities,
hydrogeologic sections and maps from published reports, and agency files
(table 2). Drillers' and geophysical logs were used to obtain lithology
and altitudes of the top and base of the Brazos River alluvium aquifer.
Data gaps exist in parts of the study area; for example, at some sites,
drillers did not describe the lithology and thickness of the alluvium as
separate and distinct from the underlying unit where the two showed
similar lithologic characteristics, thus precluding identification of
the base of the aquifer at those sites. Data gaps also exist in areas
where the alluvium is too thin to yield adequate amounts of water and
therefore contains no wells.

[]{#__RefHeading___Toc158437749 .anchor}**Table 2.** Sources of data
compiled and entered into the geodatabase of geologic and hydrogeologic
information, Bosque County to Fort Bend County, Texas.

  -------------------- --------------------------------------------------
  Data source          Supplying entity or report

  Drillers\' logs      Texas Commission on Environmental Quality - Public
                       Drinking Water Division

                       Texas Water Development Board - Water Information
                       Integration Dissemination System

                       Texas A&M University Department of Geology

                       Baylor University Department of Geology

                       U.S. Geological Survey Brazos River alluvium
                       archives

                       Fort Bend Subsidence District

                       Post Oak Savannah Groundwater Conservation
                       District

                       

  Geophysical logs     University of Texas Bureau of Economic Geology

                       Texas Commission on Environmental Quality Surface
                       Casing Division

                       

  Hydrogeologic        Cronin and Wilson (1967)
  sections and maps    

                       Cronin and Follet (1963)

                       Baker and others (1974)

                       Follet (1974)

                       Naftel and others (1976)

                       Sandeen (1972)

                       Turner (1950)

                       Wesselman (1972)

                       Wilson (1967)

                       

  Files                U.S. Geological Survey Brazos River alluvium
                       archives
  -------------------- --------------------------------------------------

### Data Input

Digital data were imported and hard-copy data were entered manually into
the geodatabase according to the TWDB GAM geodatabase scheme. Because
the scope of geodatabase development was limited to geologic and
hydrogeologic data, only feature classes and tables containing geologic
and hydrogeologic attributes were populated. Spatial and lithologic data
from drillers' and geophysical logs were input into the GeoLocations and
WellLogs feature classes, respectively. Related data were populated in
corresponding tables. The feature classes and tables that were populated
in the geodatabase are listed in table 3. Drillers' logs of wells are
recorded at the time of drilling and are subsequently assigned a State
well number by the Texas Water Development Board. The well-numbering
system of this report (fig. 2) is that of the TWDB Ground Water Data
System (GWDS) (Nordstrom and Quincy, 1999). Wells not in the GWDS were
numbered using a modified State well number called the key well number,
as described in TWDB GAM technical memo 06--01
*(*[Texas](http://www.twdb.state.tx.us/gam/GAM_documents) Water
Development Board, 2006b). The key well number retains the locational
aspect of a State well number---that is, wells sited in increasingly
smaller quadrangles.

[]{#__RefHeading___Toc158437750 .anchor}**Table 3.** Description and
definition of data compiled and entered into the geodatabase of geologic
and hydrogeologic information, Bosque County to Fort Bend County, Texas.

  ----------------- ------------- ------------------------- -------------------------
  Dataset           Data type     Feature class\            Definition
                                  or table name             

  Geology           Point feature GeoLocations              Spatial locations of
                    class                                   points with elevations of
                                                            the top and bottom of the
                                                            Brazos River alluvium.

                    Table         GEOL_CrossSections        Non-spatial lithologic
                                                            information collected
                                                            from cross-sections used
                                                            in Cronin and Wilson
                                                            (1967). Data includes
                                                            well ID, top and base
                                                            elevations of the
                                                            alluvium.

                    Table         GEOL_Data                 Non-spatial lithologic
                                                            information collected
                                                            from drillers\' logs.
                                                            Data includes well ID,
                                                            top and base elevation of
                                                            the alluvium.

  Geophysics        Point feature WellLogs                  Spatial locations of
                    class                                   wells with borehole
                                                            geophysical logs in which
                                                            the base of the Brazos
                                                            River alluvium can be
                                                            determined.

                    Table         GEOL_WellLogData          Non-spatial location
                                                            information from the
                                                            geophysical logs used to
                                                            obtain the base of the
                                                            Brazos River alluvium.
                                                            The types of geophysical
                                                            logs collected are
                                                            included for each well.

  SubSurfaceHydro   Point feature Wells                     Spatial locations of
                    class                                   wells with hydrologic
                                                            property information in
                                                            the Brazos River alluvium
                                                            such as hydraulic
                                                            conductivity, specific
                                                            capacity, and
                                                            transmissivity

                    Table         SUBHYD_Conductivity       Non-spatial data that
                                                            have hydraulic
                                                            conductivity information.

                    Table         SUBHYD_SpecificCapacity   Non-spatial data that
                                                            have specific capacity
                                                            information.

                    Table         SUBHYD_Transmissivity     Non-spatial data that
                                                            have transmissivity
                                                            information.
  ----------------- ------------- ------------------------- -------------------------

[]{#__RefHeading___Toc158008896 .anchor}

![](media/image3.wmf){width="6.625in" height="8.03125in"}

**Figure 2.** Well-numbering system for the Texas Water Development
Board Ground Water Data System (Nordstrom and Quincy, 1999).

### Data Quality

Quality-assurance techniques were applied to ensure the quality of the
data entered into the geodatabase. Digital elevation models (DEM) were
used to improve the accuracy of land-surface altitudes. To remove
duplicate data sites, database queries and GIS proximity analyses were
used to match duplicate records. After removal of duplicate sites, 525
points with geologic data and 280 points with hydrogeologic data
populated the final geodatabase.

### Metadata

Metadata that comply with Federal Geographic Data Committee standards
were created for each spatial component. The metadata record documents
the basic characteristics of the data or information resource in the
study area. Metadata components include information such as the title,
abstract, and publication date of source documents; geographic elements
such as geographic extent and projection information; and database
elements such as attribute label definitions and attribute domain
values.

# References

Ashworth, J.B., and Hopkins, Jamie, 1995, Aquifers of Texas: Texas Water
Development Board Report 345, 69 p.

Baker, E.T., Jr., Follet, C.R., McAdoo, G.D., and Bonnet, C.W., 1974,
Ground-water resources of Grimes County, Texas: Texas Water Development
Board Report 186, 109 p.

Cronin, J.G., and Follett, C.R., 1963, Reconnaissance investigation of
the ground-water resources of the Brazos River Basin, Texas: Texas Water
Commission Bulletin 6310, 152 p.

Cronin J.G., and Wilson, C.A., 1967, Ground water in the floodplain
alluvium of the Brazos River, Whitney Dam to vicinity of Richmond,
Texas: Texas Water Development Board Report 41,\
206 p.

Follett, C.R., 1974, Ground-water resources of Brazos and Burleson
Counties, Texas: Texas Water Development Board Report 185, 194 p.

HDR Engineering, Inc., 2001, Brazos River alluvium groundwater model and
conjunctive use analysis: HDR Engineering, Inc., File Copy 2002--0152,
27 p.

Naftel, W.L., Vaught, Kenneth, and Flemming Bobbie, 1976, Records of
wells, drillers' logs, water-level measurements, and chemical analyses
of ground water in Brazoria, Fort Bend, and Waller Counties, Texas,
1966--74: Texas Water Development Board Report 201, 90 p.

Nordstrom, P.L., and Quincy, Roger, 1999, UM-50 ground-water data system
data dictionary: Texas Water Development Board, 99 p.

Sandeen, W.L., 1972, Ground-water resources of Washington County, Texas:
Texas Water Development Board Report 162, 103 p.

Texas Water Development Board, 2006a, Groundwater availability modeling
(GAM): Accessed November 1, 2006, at http://www.twdb.state.tx.us/gam/

Texas Water Development Board, 2006b, Groundwater availability modeling
(GAM), GAM documents, technical memos, GAM technical memo 06--01:
Accessed November 1, 2006, at
http://www.twdb.state.tx.us/gam/GAM_documents/GAM_Memo_06-01.pdf

Turner, S.F., 1950, Milam County, Texas: Texas Board of Water Engineers
Report, 50 p.

Wesselman, J.B., 1972, Ground-water resources of Fort Bend County,
Texas: Texas Water Development Board Report 155, 179 p.

Wilson, C.A., 1967, Ground-water resources of Austin and Waller
Counties, Texas: Texas Water Development Board Report 68, 201 p.

Zeiler, Michael, 1999, Modeling our world---The ESRI guide to
geodatabase design: Redlands, Calif., Environmental Systems Research
Institute Press, 10 p.