U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2015–3043

June 2015

Sediment Conditions in the San Antonio River Basin 

Downstream From San Antonio, Texas, 2000–13

Introduction

Sediment plays an important role in the ecological health 

of rivers and estuaries and consequently is an important issue 

for water-resource managers. To better understand sediment 

characteristics in the San Antonio River Basin, the U.S. 

Geological Survey (USGS), in cooperation with the San Antonio 

River Authority (SARA), completed a two-part study in the 

San Antonio River Basin downstream from San Antonio, Texas 

(fig. 1), to (1) collect and analyze sediment data to characterize 

sediment conditions and (2) develop and calibrate a watershed 

model to simulate hydrologic conditions and suspendedsediment loads during 2000–12. 

Sediment Data Collection and Analysis

During January 2011 through May 2013, the USGS 

collected data on suspended sediment, bedload sediment, 

sediment particle-size distribution, and turbidity for a range 

of hydrologic conditions at selected sampling sites in the San 

Antonio River Basin. These data were combined with available 

historical (1966–2004) sediment data collected at the same 

sampling sites for analysis. The results of the sampling and analysis 

are described in USGS Scientific Investigations Report 2014–5048 

(Crow and others, 2014). 

Hydrologic and Sediment Modeling

USGS streamflow and sediment data were used to help 

calibrate a watershed model to simulate hydrologic conditions and 

suspended-sediment loads during 2000–12. The model was used 

to estimate sources of suspended-sediment loads and can be used 

to estimate suspended-sediment conditions at the outlet of any 

selected model segments in the study area. The model development, 

calibration, and simulation results are described in USGS Scientific 

Investigations Report 2014–5182 (Banta and Ockerman, 2014).

Sediment Data Collection Methods 

Sediment transport in streams generally can be categorized 

as suspended-sediment transport (sediment transported within 

the water column) and bedload-sediment transport (sediment 

transported along the bottom of the streambed). During 2011–13, 

sediment samples were collected at 10 sites for the analysis of 

suspended-sediment concentration and particle-size distribution.

C

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08185000

 08181800

08185065

08185100

08185500

08186000

08186500

08188500

08188570

08183200

08183500

97°00'

97°30'

29°30' 98°00'

29°00'

28°30'

BEE COUNTY

LIVE OAK

COUNTY

BEXAR COUNTY

ATASCOSA COUNTY

VICTORIA 

COUNTY

DEWITT

COUNTY

WILSON COUNTY

KARNES COUNTY

GONZALES

COUNTY

GUADALUPE COUNTY

COMAL

COUNTY

GOLIAD

COUNTY

REFUGIO

COUNTY

Poth

Falls City

Floresville

Sutherland

Springs

Stockdale

Nixon

Cibolo

San

Antonio

Goliad

McFaddin

Kenedy

Runge

Karnes

City

Yorktown

Saint 

Hedwig

Elmendorf

Selma

La Vernia

Manahuilla Ecleto Creek

San Antonio

Martinez

Calaveras Lake

Guadalupe River

Medina

Cibolo Creek

San Antonio River

Cabeza Creek

 River

Guadalupe Bay

Hynes Bay San Antonio Bay

Cibolo Creek

San Antonio River

San Antonio River

Creek

Creek

Rive r

EXPLANATION

Study area

U.S. Geological Survey streamflow-gaging

 station and station number

C 08181800

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

Universal Transverse Mercator, zone 14

North American Datum of 1983

Modified from Banta and Ockerman, 2014

0 10 15 20 MILES 5

0 10 15 20 KILOMETERS 5

TEXAS

San Antonio

River Basin GULF OF 

MEXICO

Study area

Figure 1. The study area, the San Antonio River Basin downstream from San Antonio, Texas, consists of 2,150 square miles and 

encompasses parts of Bexar, Comal, Guadalupe, Wilson, Karnes, DeWitt, Goliad, Victoria, and Refugio Counties. In addition to the San Antonio 

River, major streams in the study area include Cibolo and Ecleto Creeks. The San Antonio River in the study area extends about 190 river miles 

(mi) from Elmendorf, Tex., to the downstream boundary. From the upstream boundary of the study area near Selma, Tex., Cibolo Creek extends 

about 75 river mi downstream to its confluence with the San Antonio River in Karnes County. Ecleto Creek extends about 55 river mi from 

northern Wilson County to its confluence with the San Antonio River in Karnes County. 

ISSN 2327-6916 (print) ISSN 2327-6932 (online)

http://dx.doi.org/10.3133/fs20153043
In addition, samples of bedload sediment were collected at 

six sites for the analysis of bedload mass and particle-size 

distribution (Crow and others, 2014). Figures 2, 3, and 4 show 

sediment samplers used in the study. A combination of 67 

suspended-sediment samples and 22 bedload-sediment samples 

were collected over a variety of hydrologic conditions with 

stream discharge rates ranging from 1.9 to 10,600 cubic feet per 

second. Collecting stream discharge data at the same time as 

suspended-sediment concentration data allowed for calculations 

of suspended-sediment discharge, or load, in tons per day. 

The suspended-sediment samples were collected by following 

standard USGS methods (Edwards and Glysson, 1999). 

Sediment Load Characterization

Results from the data that were collected indicated that 

bedload sediment is a small percentage of total sediment load 

because most of the sediment in the study area is fine-grain 

material (silt and clay-size particles) that tends to remain in 

suspension. For example, at the sampling site at the San Antonio 

River near Elmendorf, Tex. (station 08181800, fig. 1), bedload 

sediment accounted for only about 0.2 percent of the total 

sediment (by weight) in the samples collected during 2011–12.

Figure 2. At each sampling site, suspended-sediment samples 

were collected at a minimum of 10 equal-width increments 

across the stream by using samplers designed to allow water 

to enter the sampler with no change in velocity or direction, 

a method referred to as “isokinetic sampling.” When stream 

depths were shallow enough to be waded, samples were 

collected by using a US DH–81 1-liter bottle sampler (Davis, 

2005) attached to a wading rod.

Figure 3. When stream depths were too deep to be waded, 

suspended-sediment samples were collected from a bridge or a 

boat by using a US DH–2 1-liter collapsible bag sampler (Davis, 

2005) attached to a reel and crane system. 

One of the goals of collecting the suspended-sediment 

data was to characterize suspended-sediment concentrations 

and loads for a range of streamflow conditions at selected 

locations in the study area. Suspended-sediment loads estimated 

from regression equations that relate measured suspendedsediment concentrations to daily streamflow provided a means 

to estimate continuous (daily) values of suspended-sediment 

loads at selected locations in the study area. All available data 

(historical and 2011–12 data) were included in the regression 

analyses (fig. 5). For five sampling locations where sufficient 

suspended-sediment sample data were available to develop these 

relations (San Antonio River near Elmendorf, Tex.; San Antonio 

River near Falls City, Tex.; Cibolo Creek near Falls City, 

Tex.; Ecleto Creek near Runge, Tex.; and San Antonio River 

Figure 4. Bedload-sediment samples were collected with a 

sampler such as the BL–84 (Davis, 2005), which is designed to 

collect bedload sediment as it rests on the streambed. Bedload 

samplers were deployed by a wading rod, a bridge crane, or a boatdeployed reel.

Streamflow, in cubic feet per second

1 10 100 1,000 10,000 100,000

1

10

100

1,000

10,000

100,000

Suspended-sediment concentration, in milligrams per liter

R2 = 0.42

SSC = 0.46 x Q0.949

EXPLANATION

Relation between suspended-sediment concentration

 (SSC) and streamflow (Q)—Dotted where suspended

 sediment no longer increases with increasing streamflow

1974–94 historical sample data

2011–12 sample data

Coefficient of determination for the log-transformed

 regression equation, where suspended sediment 

 increases with increasing streamflow

R2

Figure 5. Relation between suspended-sediment concentration 

and streamflow at U.S. Geological Survey streamflow-gaging station 

at the San Antonio River at Goliad, Texas (modified from Crow and 

others, 2014, fig. 5E).
at Goliad, Tex.), daily time series of suspended-sediment loads 

were estimated to compare with model-simulated loads at the 

same locations. Crow and others (2014) and Banta and Ockerman 

(2014) give additional information on the development of the 

regression equations and use of the equations and estimated timeseries data for model calibration.

Simulation Modeling Approach

Hydrologic conditions (streamflow, evapotranspiration, and 

groundwater recharge) and suspended-sediment concentrations 

and loads were simulated by using the Hydrological Simulation 

Program—FORTRAN (HSPF) model (Bicknell and others, 2001). 

The HSPF model 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 sediment concentrations and loads 

associated with the water movement at any selected location in 

the watershed. Time-series outputs (figs. 6 and 7) from HSPF 

Year

2006 2007 2008 2009 2010 2011 2012 2013

10

100

1,000

10,000

100,000

Daily mean streamflow,

in cubic feet per second 

Measured

Simulated

EXPLANATION

Figure 6. Measured and simulated daily mean streamflow at U.S. Geological Survey 

streamflow-gaging station at the San Antonio River at Goliad, Texas, 2006–12 (modified 

from Banta and Ockerman, 2014, fig. 12A). 

Year

2006 2007 2008 2009 2010 2011 2012 2013

1

10

100

1,000

10,000

100,000

1,000,000

Daily mean suspended-sediment load,

in tons per day

Estimated

Simulated

EXPLANATION

Figure 7. Estimated and simulated daily mean suspended-sediment load at U.S. 

Geological Survey streamflow-gaging station at the San Antonio River at Goliad, Texas, 

2006–12 (modified from Banta and Ockerman, 2014, fig. 12D). 

simulations represent continuous daily mean values of streamflow 

and suspended-sediment loads. Previous HSPF models of the 

lower San Antonio River (Lizárraga and Ockerman, 2010; 

URS Corporation, 2012) were modified to simulate hydrologic 

conditions and sediment transport for this study. 

By using the regression equation in figure 5, daily time 

series of suspended-sediment loads were estimated to compare 

with model-simulated loads at the same location. Figure 7 

shows a comparison of estimated and model-simulated loads at 

San Antonio River at Goliad, Tex. Crow and others (2014) and 

Banta and Ockerman (2014) give additional information on the 

development of the regression equations and use of the equations 

and estimated time-series data for model calibration. 

Model-Simulated Suspended-Sediment Loads 

Estimated suspended-sediment loads upstream from the 

study area and model-simulated contributions of suspended 

sediment from the four major watersheds within the study area 

are shown in figure 8. The estimated daily mean suspendedsediment loads entering the study area were 737 tons per day 

(tons/d) and 22 tons/d at the San Antonio River near Elmendorf, 

Tex., and Cibolo Creek near Selma, Tex., respectively, during 

2006–12. At the outlet of the study area, the confluence of the 

San Antonio River with the Guadalupe 

River, the simulated daily mean suspendedsediment load during 2006–12 was 1,230 

tons/d, indicating that, for the years evaluated, 

the study area watershed delivered a load 

of 471 tons/d of suspended sediment to the 

Guadalupe River in excess of the 759 tons/d 

that enter the San Antonio River from 

upstream from the study area. For periods 

other than the years evaluated, the suspendedsediment loads will likely be different.

Model results also provide an indication 

of the sources of sediment within the study 

area. Model simulations indicate that, among 

the four major watersheds, the Cibolo Creek 

watershed was the largest contributor of 

suspended sediment, generating an average 

sediment yield of 230 tons/d, or 145 tons per 

square mile per year ([tons/mi2]/yr). Steeper 

topography and more developed and cropland 

land cover in the Cibolo Creek watershed are 

likely factors that contributed to more runoff 

and sediment yield compared to the other 

watersheds in the study area. The simulated 

daily mean suspended-sediment load from 

the San Antonio River watershed upstream 

from the confluence with Cibolo Creek (not 

including the 757 tons/d of sediment load 

entering from upstream from the study area, 

near Elmendorf, Tex.) was 94 tons/d, or 

62 (tons/mi2)/yr. The simulated daily mean 

suspended-sediment load from the Ecleto 

Creek watershed was 43 tons/d, or 59 (tons/

mi2)/yr. The simulated daily mean suspendedsediment load from the San Antonio River 

watershed downstream from the confluence 

with Cibolo Creek was 104 tons/d, or 

51 (tons/mi2

)/yr, not including upstream 

contributions of sediment. 
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08185000

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08185065

08185100

08185500

08186000

08186500

08188500

08188570

08183200

08183500

97°00'

97°30'

29°30' 98°00'

29°00'

28°30'

BEE COUNTY

LIVE OAK

COUNTY

BEXAR COUNTY

ATASCOSA COUNTY

VICTORIA 

COUNTY

DEWITT

COUNTY

WILSON COUNTY

KARNES COUNTY

GONZALES

COUNTY

GUADALUPE COUNTY

COMAL

COUNTY

GOLIAD

COUNTY

REFUGIO

COUNTY

Poth

Falls City

Floresville

Sutherland

Springs

Stockdale

Nixon

Cibolo

San

Antonio

Goliad

McFaddin

Kenedy

Runge

Karnes

City

Yorktown

Saint 

Hedwig

Elmendorf

Selma

Manahuilla Ecleto Creek

San Antonio

Martinez

Calaveras Lake

Guadalupe River

Medina

Cibolo Creek

San Antonio River

Cabeza Creek

 River

Guadalupe Bay

Hynes Bay San Antonio

Bay

Cibolo Creek

San Antonio River

San Antonio River

Creek

Creek

Rive r

EXPLANATION

Model watershed of San Antonio 

 River Basin downstream from

 San Antonio, Texas

 San Antonio River upstream 

 from Cibolo Creek

 Cibolo Creek

 Ecleto Creek

 San Antonio River downstream 

 from Cibolo Creek

Suspended-sediment load entering

 or exiting the study area

Study area boundary

U.S. Geological Survey 

 streamflow-gaging station

 and station number

C

08181800

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

Universal Transverse Mercator, zone 14

North American Datum of 1983

Modified from Banta and Ockerman, 2014

0 10 15 20 MILES 5

0 10 15 20 KILOMETERS 5

Estimated suspended sediment

entering study area from

upstream at Cibolo Creek at

Selma, Texas, 22 tons per day

Estimated suspended sediment

entering study area from

upstream at San Antonio River

near Elmendorf, Texas,

737 tons per day

Simulated suspended sediment generated

in San Antonio River watershed upstream

from Cibolo Creek, 94 tons per day,

or 62 tons per square mile per year

Simulated suspended sediment generated

in San Antonio River watershed downstream

from Cibolo Creek, 104 tons per day,

or 51 tons per square mile per year

Simulated suspended sediment generated

in Cibolo Creek watershed, 230 tons per day, 

or 145 tons per square mile per year

Simulated suspended sediment generated

in Ecleto Creek watershed, 43 tons per day,

or 59 tons per square mile per year

Estimated suspended sediment exiting

San Antonio River at confluence with

Guadalupe River, 1,230 tons per day

Figure 8. Average daily suspended-sediment loads entering, exiting, and generated within the San Antonio River Basin downstream from San 

Antonio, Texas, 2006–12. 

References

Banta, J.R., and Ockerman, D.J., 2014, Simulation of hydrologic 

conditions and suspended-sediment loads in the San Antonio 

River Basin downstream from San Antonio, Texas, 2000–12: U.S. 

Geological Survey Scientific Investigations Report 2014–5182, 46 p., 

accessed May 18, 2015, at http://dx.doi.org/10.3133/sir20145182.

Bicknell, B.R., Imhoff, J.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.

Crow, C.L., Banta, J.R., and Opsahl, S.P., 2014, Sediment 

characteristics in the San Antonio River Basin downstream from San 

Antonio, Texas, and at a site on the Guadalupe River downstream 

from the San Antonio River Basin, 1966–2013: U.S. Geological 

Survey Scientific Investigations Report 2014–5048, 33 p., accessed 

May 18, 2015, at http://dx.doi.org/10.3133/sir20145048.

Davis, B.E., 2005, A guide to the proper selection and use of federally 

approved sediment and water-quality samplers: Vicksburg, Miss., 

U.S. Geological Survey Open File Report 2005–1087, 20 p.

Donigian, A.S., Jr., Bicknell, B.R., and Imhoff, J.C., 1995, Hydrological 

Simulation Program—FORTRAN (HSPF), in Singh, V.P., ed., 

Computer models of watershed hydrology: Highlands Ranch, Colo., 

Water Resources Publications, p. 395–442.

Edwards, T.K., and Glysson, G.D., 1999, Field methods for 

measurement of fluvial sediment: U.S. Geological Survey Techniques 

of Water-Resource Investigations, book 3, chap. C2 (rev.), 89 p. 

[Also available at http://pubs.usgs.gov/twri/twri3-c2/.]

Lizárraga, J.S., and Ockerman, D.J., 2010, Simulation of streamflow, 

evapotranspiration, and groundwater recharge in the lower San 

Antonio River watershed, south-central Texas, 2000–2007: U.S. 

Geological Survey Scientific Investigations Report 2010–5027, 

41 p.

URS Corporation, 2012, Lower San Antonio River watershed HSPF 

model calibration: URS Corporation, 54 p.

—Darwin J. Ockerman, J. Ryan Banta, Cassi L. Crow, and 

Stephen P. Opsahl

For additional information contact: 

Director, Texas Water Science Center 

U.S. Geological Survey 

1505 Ferguson Lane 

Austin, Texas 78754–4501 

http://tx.usgs.gov/

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