WEBB

COUNTY

DUVAL

COUNTY

FRIO

COUNTY

EDWARDS

COUNTY

KERR

COUNTY

UVALDE

COUNTY

STARR

COUNTY

BEXAR

COUNTY

KENEDY

COUNTY

KINNEY

COUNTY

VAL VERDE

COUNTY

DIMMIT

COUNTY

HIDALGO

COUNTY

ZAVALA

COUNTY

MEDINA

COUNTY

LA SALLE

COUNTY

ZAPATA

COUNTY

REAL

COUNTY

LAVACA

COUNTY

MAVERICK

COUNTY

ATASCOSA

COUNTY

JIM HOGG

COUNTY

BROOKS

COUNTY

LIVE OAK

COUNTY

GOLIAD

 COUNTY

DE WITT

COUNTY

WHARTON

WILSON COUNTY

COUNTY

NUECES

 COUNTY

GONZALES

COUNTY

MCMULLEN

COUNTY

JACKSON

COUNTY

KARNES

COUNTY

VICTORIA

COUNTY

KLEBERG

COUNTY

BANDERA

COUNTY

COMAL

COUNTY

KENDALL

COUNTY

WILLACY

COUNTY

GUADALUPE

COUNTY

HAYS

COUNTY

CAMERON

 COUNTY

REFUGIO

COUNTY

BEE COUNTY

JIM WELLS

COUNTY

MATAGORDA

COUNTY

ARANSAS

COUNTY

COLORADO

COUNTY

FAYETTE

COUNTY

SAN PATRICIO COUNTY

CALDWELL

COUNTY

CALHOUN

COUNTY

Rio Grande

Arroyo

Nueces

Atascosa River

River

Medina

River

Rio Bravo

Colorado

River

Guadalupe

Nueces River

Hondo

Creek

San

 Geronimo

 Creek

Verde

Creek

Cibolo

Creek

Salado Leon Creek Creek

San Geronimo

Creek

Miguel San

Falcon

Reservoir

Lake

Corpus

Christi

Choke Canyon Reservoir

Lake Coleto Creek Texana Reservoir

Medina 

Lake

Canyon

Lake

Laguna 

Madre

Creek

Nueces Estuary

Seco Creek

San Anto nio River

Navidad River

Sabinal River

Leo n a River

Frio River

Arans as River

Lavaca River

G

ULF

OF MEXICO

UNITED STATES

MEXICO

! !

!

! !

!

! ! ! ! !

!

! !

! ! !

!

!

!

!

!

!

! !

!

! !

!

George 

West

Brownsville

Hondo

Corpus 

Christi

Floresville

Goliad

Ingram

Karnes 

 City

Kenedy

Robstown

Sabinal

San 

Antonio

Taft

Yorktown

Beeville

Harlingen

Victoria

Comfort

Kerrville

Laredo

Mission

New 

Braunfels

Nixon

Pleasanton Runge

Three Rivers

Uvalde

Castroville

Bandera

TEXAS

South Texas

60 KILOMETERS

0 15 30 45 60 MILES

0 3015 45

Base modified from U.S. Geological Survey

1:100,000-scale digital data

Universal Transverse Mercator projection, zone 14

North American Datum of 1983

Aquifers from Ashworth and Hopkins, 1995 

30°

29°

28°

27°

26°

101°

97°

98° 99° 100°

96°

Trinity aquifer outcrop

Carrizo-Wilcox aquifer

 outcrop

Watershed

 Arroyo Colorado

 Hondo Creek

 Leon Creek

 Lower Nueces River

 Lower San Antonio River

 San Geronimo Creek

 Upper Cibolo Creek

 Verde Creek

Edwards aquifer (recharge

 zone) outcrop boundary

EXPLANATION

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3005

January 2012 Printed on recycled paper

Watershed Modeling Applications in South Texas

Introduction

Watershed models can be used to simulate natural and 

human-altered processes including the flow of water and 

associated transport of sediment, chemicals, nutrients, and 

microbial organisms within a watershed. Simulation of these 

processes is useful for addressing a wide range of waterresource challenges, such as quantifying changes in water 

availability over time, understanding the effects of development and land-use changes on water resources, quantifying 

changes in constituent loads and yields over time, and 

quantifying aquifer recharge temporally and spatially 

throughout a watershed.

The U.S. Geological Survey (USGS), 

in cooperation with State and Federal 

agency partners, developed simulation 

models for several watersheds 

in south Texas (fig. 1). These 

models provide the capability 

to simulate scenarios of 

possible future conditions 

and management alternatives 

to help water-resource 

professionals with planning 

decisions. The program used for 

creating these Texas watershed 

models is the Hydrological 

Simulation Program—FORTRAN 

(HSPF) (Bicknell and others, 2001). 

HSPF is one of the most comprehensive 

watershed modeling programs because it 

can simulate a variety of stream and watershed 

conditions with reasonable accuracy and enables 

flexibility in adjusting the model to simulate 

alternative conditions or scenarios (Donigian and 

others, 1995). The HSPF model provides time-series 

data simulating water movement (runoff from land 

surfaces, infiltration of water through soil layers, flow in 

stream channels) and water-quality parameter values and 

constituent concentrations associated with the water 

movement at any selected location in the watershed. Timeseries outputs from an HSPF simulation are continuous 

(for example, hourly or daily). Continuous models provide 

the advantage of simulating watershed processes for a full 

range of streamflow conditions. Continuous models can 

illustrate how processes that appreciably affect waterquality conditions during low flows might have relatively 

minor effects on water-quality conditions during high 

flows.

This fact sheet presents an overview of six selected watershed modeling studies by the USGS and partners that address 

a variety of water-resource issues in south Texas. These studies 

provide examples of modeling applications and demonstrate 

the usefulness and versatility of watershed models in aiding the 

understanding of hydrologic systems.

Figure 1. Locations of Hydrological Simulation Program—FORTRAN (HSPF) models in south Texas.
An HSPF watershed model was developed, calibrated, and tested by the 

USGS—in cooperation with the U.S. Army Corps of Engineers, San Antonio 

River Authority, San Antonio Water System, and Guadalupe–Blanco River 

Authority—to simulate streamflow and estimate groundwater recharge for 

the approximately 274-square-mile upper Cibolo Creek watershed (fig. 1) 

(Ockerman, 2007). Rainfall, evapotranspiration, and streamflow data were 

collected during 1992–2004 for model calibrations and simulations. Estimates 

of average groundwater recharge during 1992–2004 from the simulation were 

79,800 acre-feet (5.47 inches) per year or about 15 percent of the area rainfall. 

Simulation of flood-control/recharge-enhancement structures in Cibolo Creek 

showed that certain structures might decrease flood peaks and increase recharge. 

Simulation of individual structures on tributaries showed relatively little 

effect. Larger structures on the main stem of Cibolo Creek were more effective 

than were structures on tributaries, in terms of both flood-peak reduction and 

recharge enhancement. One simulated scenario that incorporated two main-stem 

structures resulted in a 37-percent reduction of peak flow at the watershed outlet 

and increases in stream-channel recharge of 6.6 percent in the Trinity aquifer 

outcrop and 12.6 percent in the Edwards aquifer (recharge zone) outcrop.

• 2007 USGS Scientific Investigations Report 2007–5202: 

http://pubs.usgs.gov/sir/2007/5202

Simulating the Effects of Recharge-Enhancement Structures—Cibolo Creek 

 A River System Water-Budget Analysis—Lower San Antonio River

The USGS—in cooperation with the San Antonio River Authority, the 

Evergreen Underground Water Conservation District, and the Goliad County 

Groundwater Conservation District—configured, calibrated, and tested a watershed model for a study area consisting of about 2,150 square miles of the lower 

San Antonio River watershed (fig. 1) (Lizarraga and Ockerman, 2010). The 

model simulated streamflow, evapotranspiration, and groundwater recharge to 

the Carrizo–Wilcox aquifer outcrop in the lower San Antonio River watershed. 

The mean annual rainfall on the outcrop during 1961–2008 was 26.5 inches. Of 

this rainfall, it was determined that about 92 percent evapotranspires, less than 

7 percent becomes groundwater recharge, and less than 2 percent becomes runoff. Mean annual recharge varied spatially throughout the watershed, ranging 

from 1.0 to 2.7 inches per year and generally increasing from west to east.

• 2010 USGS Scientific Investigations Report 2010–5027: 

http://pubs.usgs.gov/sir/2010/5027

In cooperation with the U.S. Army Corps of Engineers, Fort Worth District; San Antonio River 

Authority; San Antonio Water System; and Guadalupe-Blanco River Authority 

Simulation of Streamflow and Estimation

of Ground-Water Recharge in the

Upper Cibolo Creek Watershed,

South-Central Texas, 1992–2004

Scientific Investigations Report 2007–5202

U.S. Department of the Interior

U.S. Geological Survey

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2010–5027

In cooperation with the San Antonio River Authority, the Evergreen Underground Water 

Conservation District, and the Goliad County Groundwater Conservation District

Simulation of Streamflow, Evapotranspiration, and 

Groundwater Recharge in the Lower San Antonio River 

Watershed, South-Central Texas, 2000–2007
The USGS—in cooperation with the U.S. Army Corps of Engineers and 

the San Antonio River Authority—configured, calibrated, and tested an HSPF 

watershed model for the approximately 238-square-mile Leon Creek watershed 

in Bexar County, Texas, and used the model to simulate streamflow and water 

quality (focusing on loads and yields of selected constituents) (fig. 1) (Ockerman and Roussel, 2009). Streamflow in the model was calibrated and tested with 

available data from five USGS stream-gaging stations.

Water-quality properties and constituents (water temperature, dissolved 

oxygen, suspended sediment, and dissolved and total lead and zinc) in the model 

were calibrated by using available data from 13 sites in and near the Leon Creek 

watershed for varying periods of record during 1992–2005.

The Leon Creek watershed model was used to simulate streamflow constituent loads and yields for suspended sediment, dissolved nitrate nitrogen, and 

total lead at the mouth of Leon Creek (outlet of the watershed) for 1997–2004. 

The average suspended-sediment yield was 0.34 ton per acre per year. The average load of dissolved nitrate at the outlet of the watershed was 802 tons per year; 

the corresponding yield was 10.5 pounds per acre per year. The average load of 

lead at the outlet was 3,900 pounds per year; the average lead yield was 0.026 

pound per acre per year.

• 2009 USGS Scientific Investigations Report 2009–5191: 

http://pubs.usgs.gov/sir/2009/5191

The USGS—in cooperation with the U.S. Army Corps of Engineers, City 

of Corpus Christi, Guadalupe–Blanco River Authority, San Antonio River 

Authority, and the San Antonio Water System—compiled and assessed available data on suspended-sediment loads in the lower Nueces River and developed, calibrated, and tested an HSPF watershed model for the approximately 

216-square-mile lower Nueces River watershed to simulate streamflow and to 

estimate suspended-sediment loads to the lower Nueces River and Nueces 

Estuary (fig. 1) (Ockerman and Heitmuller, 2010).

The watershed model also was designed to account for sources of suspended sediment delivered to the Nueces River and Nueces Estuary. On average, during 1958–2008, about 31.6 percent of the suspended-sediment load 

that entered the lower Nueces River was carried by releases from Lake Corpus 

Christi. Erosion and washoff of suspended sediment from cropland (in the watershed downstream from Lake Corpus Christi) accounted for 37.7 percent of the 

total sediment load. Erosion and washoff from all other land types downstream 

from Lake Corpus Christi accounted for 11.9 percent of the total sediment load. 

Channel erosion accounted for 18.7 percent of the total sediment load.

• 2010 USGS Scientific Investigations Report 2010–5194: 

http://pubs.usgs.gov/sir/2010/5194

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2009–5191

In cooperation with the U.S. Army Corps of Engineers and the San Antonio River Authority

Simulation of Streamflow and Water Quality in the Leon 

Creek Watershed, Bexar County, Texas, 1997–2004

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2010–5194

In cooperation with the U.S. Army Corps of Engineers, Fort Worth District; City of Corpus Christi; 

Guadalupe-Blanco River Authority; San Antonio River Authority; and San Antonio Water System

Simulation of Streamflow and Suspended-Sediment 

Concentrations and Loads in the Lower Nueces River 

Watershed, Downstream from Lake Corpus Christi to the 

Nueces Estuary, South Texas, 1958–2008

A Contaminant-Loading Model for an Urban Stream—Leon Creek 

Modeling Suspended-Sediment Loads to Bays and Estuaries—Lower Nueces River 
A Total Maximum Daily Load (TMDL) Model—Arroyo Colorado

Modeling Recharge to the Edwards Aquifer—Hondo Creek, Verde Creek, San Geronimo Creek

The USGS—in cooperation with the Texas Commission on Environmental Quality (TCEQ) and 

the Nueces River Authority—developed an HSPF watershed model to simulate flow and water quality 

for selected properties and constituents for the Arroyo Colorado from the city of Mission to the Laguna 

Madre, Texas (fig. 1) (Raines and Miranda, 2002). The model was used to estimate a total maximum 

daily load (TMDL) for selected properties and constituents in the Arroyo Colorado. Specific objectives 

of the study were (1) to set up a model of the Arroyo Colorado Basin that would allow for simulation 

of different best management practices in order to estimate the TMDL for selected constituents to meet 

dissolved oxygen water-quality standards and (2) to calibrate and test a set of process-related model 

parameters with available streamflow and water-quality data for the Arroyo Colorado.

• 2002 USGS Water-Resources Investigations Report 02–4110: http://pubs.usgs.gov/wri/wri02-4110/

The USGS—in cooperation with the San Antonio Water System—constructed three HSPF 

watershed models to simulate streamflow and estimate recharge to the Edwards aquifer in the 

Hondo Creek, Verde Creek, and San Geronimo Creek watersheds (fig. 1) (Ockerman, 2005). 

The three models were calibrated and tested with available data collected during 1992–2003. 

Streamflow and recharge were simulated for 1951–2003. Estimated average annual Edwards 

aquifer recharge for the Hondo Creek, Verde Creek, and San Geronimo Creek watersheds for 

1951–2003 was 37,900 acre-feet (5.04 inches); 26,000 acre-feet (3.36 inches); and 5,940 acre-feet 

(1.97 inches), respectively. Most of the estimated recharge (about 77 percent for the three watersheds together) occurred as streamflow channel infiltration. Estimated diffuse recharge (direct 

infiltration of rainfall to the aquifer) accounted for the remaining 23 percent of recharge. For the 

Hondo Creek watershed, the HSPF recharge estimates for 1992–2003 averaged about 22 percent 

less than those estimated by the Puente method (Puente, 1978), a method the USGS has used to 

compute annual recharge to the Edwards aquifer since 1978. HSPF recharge estimates for the 

Verde Creek watershed averaged about 40 percent less than those estimated by the Puente method.

• 2005 USGS Scientific Investigations Report 2005–5252: http://pubs.usgs.gov/sir/2005/5252/

References Cited

Ashworth, J.B., and Hopkins, J., 1995, Major and minor aquifers of Texas: 

Texas Water Development Board Report 345, 69 p. 

Bicknell, B.R., Imhoff, J.U.C., Kittle, J.L., Jr., Donigian, A.S., and Johanson, 

R.C., 2001, Hydrological Simulation Program—FORTRAN, user’s manual 

for version 12: Research Triangle Park, N.C., U.S. Environmental Protection 

Agency, National Exposure Research Laboratory, Office of Research and 

Development, 843 p.

Donigian, A.S., Jr., Bicknell, B.R., and Imhoff, J.C., 1995, Hydrological Simulation Program—FORTRAN (HSPF), in Sing, V.P., ed., Computer models of 

watershed hydrology: Highlands Ranch, Colo., Water Resources Publications, p. 395–442.

Lizarraga, J.S., and Ockerman, D.J., 2010, Simulation of streamflow, evapotranspiration, and ground-water recharge in the lower San Antonio River 

watershed, south-central Texas, 2000–2007: U.S. Geological Survey Scientific Investigations Report 2010–5027, 41 p.

Ockerman, D.J., 2005, Simulation of streamflow and estimation of recharge to 

the Edwards aquifer in the Hondo Creek, Verde Creek, and San Geronimo 

Creek watersheds, south-central Texas, 1951–2003: U.S. Geological Survey 

Scientific Investigations Report 2005–5252, 37 p.

Ockerman, D.J., 2007, Simulation of streamflow and estimation of groundwater recharge in the upper Cibolo Creek watershed, south-central Texas, 

1992–2001: U.S. Geological Survey Scientific Investigations Report 

2007–5202, 37 p.

Ockerman, D.J., and Heitmuller, F.T., 2010, Simulation of streamflow and 

suspended-sediment concentrations and loads in the lower Nueces River 

watershed, downstream from Lake Corpus Christi to the Nueces Estuary, 

South Texas, 1958–2008: U.S. Geological Scientific Investigations Report 

2010–5194, 50 p.

Ockerman, D.J., and Roussel, M.C., 2009, Simulation of streamflow and water 

quality in the Leon Creek watershed, Bexar County, Texas, 1997–2004: U.S. 

Geological Survey Scientific Investigations Report 2009–5191, 50 p.

Puente, Celso, 1978, Method of estimating natural recharge to the Edwards 

aquifer in the San Antonio area, Texas: U.S. Geological Survey WaterResources Investigations Report 78–10, 34 p.

Raines, T.H., and Miranda, R.M., 2002, Simulation of flow and water quality 

of the Arroyo Colorado, Texas, 1989–99: U.S. Geological Survey Water 

Resources Investigations Report 02–4110, 56 p.

For additional information, contact 

Director, USGS Texas Water Science Center

http://tx.usgs.gov/

gs-w-txpublic-info@usgs.gov 

Publishing support provided by

Lafayette Publishing Service Center

—Diana E. Pedraza and Darwin J. Ockerman 

Contacts: J. Mark Null Loren L. Wehmeyer

U.S. Geological Survey U.S. Geological Survey

Texas Water Science Center Texas Water Science Center

Chief, South Texas Program Office Chief, Hydrologic Studies Section

5563 De Zavala Rd., Ste. 290 5563 De Zavala Rd., Ste. 290

San Antonio, TX 78249 San Antonio, TX 78249

jmnull@usgs.gov llwehmey@usgs.gov