Evaluating the Variability of Sediment and Nutrient Loading 

from Riverine Systems into Texas Estuaries and Bays

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2011–3036

April 2011

In cooperation with the Texas Water Development Board

Evaluating the Variability of Sediment and Nutrient Loading 

from Riverine Systems into Texas Estuaries and Bays

Printed on recycled paper

The water quality in estuaries and bays and the health of 

these coastal ecosystems are affected by sediment and nutrient 

loads transported by streams. Large sediment loads delivered 

to an estuary or bay can degrade water quality. Concentrations 

of suspended sediment are affected by natural conditions (such 

as soil erosion and streambed resuspension) and can also be 

affected by human activities (such as development, timber 

harvesting, certain agricultural practices, and hydraulic alteration). An increased sediment load delivered to an estuary or bay 

can reduce water clarity and light penetration (Senus and others, 

2005) in the water column. Senus and others (2005, p. 1) also 

note that 

nutrients are needed to sustain life, but excess nutrient 

loads from human activities may cause unbalanced 

and unhealthy changes in water quality that are harmful to aquatic organisms. Nitrogen and phosphorus are 

two known nutrients of concern. Poor water quality 

caused by an abundance of these nutrients can stimulate the excessive growth of phytoplankton, promote 

algal blooms, reduce dissolved oxygen levels, and 

cause fish kills.

Approximately 60 percent of coastal rivers and bays in the 

United States have been moderately to severely degraded by 

excess nutrients (Howarth and others, 2002). 

Water quality in rivers constantly changes in response to 

rainfall in the watershed, and increased sediment and nutrient 

loads in rivers often occur during periods of high flow (Hubbard 

and others, 2011; Maryland Department of Natural Resources, 

2011). In Texas, periods of high flow in rivers flowing into 

coastal ecosystems are usually caused by local rainfall or by 

releases from upstream reservoirs made in response to rainfall 

farther upstream in the basin (Galveston Bay Estuary Program, 

2002). The increase in rain and resultant flooding can increase 

sediment erosion and nutrient runoff into coastal rivers and 

consequently increase sediment and nutrient input into estuaries 

and bays.

Flow, sediment, and nutrient data can be used for descriptive purposes as well as serving as input to hydrodynamic and 

water-quality models that aid the understanding of coastal 

ecosystems in Texas. At present (2011), these types of data 

are not widely available for many Texas estuaries, particularly 

during peak inflow periods, when large pulses of sediments and 

nutrients have the potential to substantially affect water quality 

and estuary and bay ecosystem health. 

Evaluating the Temporal Variability of Sediment 

and Nutrient Loads

In 2009, the U.S. Geological Survey (USGS), in cooperation with the Texas Water Development Board (TWDB), 

began evaluating the variability of sediment and nutrient loads 

in the lower reaches of the Trinity River during a variety of 

hydrologic conditions. Discharge, sediment concentration 

and sand/fine break, and nutrient concentration data (including nitrate and phosphate concentrations) were collected at 

USGS streamflow-gaging station 08067252 Trinity River at Trinity River near Wallisville, Texas flowing toward Galveston Bay. 

The Colorado River is surrounded by coastal marshes and 

wetlands as it enters Matagorda Bay. 
Wallisville, Tex. (fig. 1), to gain a better understanding of the 

hydrologic and water-quality characteristics for the Galveston 

Bay coastal ecosystem (Lee, 2010). This ongoing study is 

designed to help characterize the sediment and nutrient load 

transported into Galveston Bay as related to localized periods 

of high flow and releases of water from reservoirs upstream 

in the watershed. As an extension of the data collection that 

began in 2009 on the Trinity River, the collection of similar 

sediment and nutrient data by the USGS, in cooperation with 

the TWDB, in the lower reaches of the Colorado River and 

San Jacinto River in Texas began in 2010—USGS streamflowgaging stations 08162506 Colorado River Bypass Channel near 

Matagorda, Tex., and 08072050 San Jacinto River near Sheldon, 

Tex. (fig. 1). In addition to collecting suspended-sediment and 

nutrient samples to improve understanding of the amounts of 

sediment and nutrients entering into the Matagorda Bay and 

Galveston Bay estuary, periodic bedload samples are collected 

from the lower Colorado River site and the San Jacinto River 

site, respectively. The bedload data will help provide a better 

understanding of the contribution of bedload sediment to total 

sediment discharges. 

San Jacinto River viewed upstream from where it enters 

Galveston Bay near Sheldon, Texas. 

Figure 1. Location of data-collection sites on the Trinity River and San Jacinto River upstream from Galveston Bay and on the Colorado 

River upstream from Matagorda Bay, Texas.

#

#

#

08072050 San Jacinto River 

near Sheldon, Tex.

08067252 Trinity River at Wallisville, Tex.

08162506 Colorado River Bypass 

Channel near Matagorda, Tex.

£¤59

£¤90

£¤290 £¤59

£¤90 § ̈¦10 § ̈¦610

§ ̈¦45

§ ̈¦45

§ ̈¦10

Matagorda

Galveston Bay

Matagorda Bay

Gulf of Mexico

Houston Sheldon

Wallisville

Trinity River

River Colorado

Base modified from U.S. Geological Survey

digital data 1:24,000 quadrangles, Geographic

Coordinate system, North American Datum of 1983

0 12.5 25 50 MILES

0 12.5 25 50 KILOMETERS

LOCATION MAP

96°00' 95°20' 94°40'

30°00'

29°20'

28°40'

37.5

37.5

San Jacinto

River

08072050 San Jacinto River 

near Sheldon, Tex.

U.S. Geological Survey data-collection

site and number

EXPLANATION

#

TEXAS Colorado 

 River

 Basin

Trinity

River

Basin

San

Jacinto

River

Basin
Sample Collection

Criteria for the timing of sample collection are developed 

on the basis of historical streamflow in each basin. Particular 

emphasis is placed on high-flow events, but samples over the 

entire hydrograph range are collected to evaluate the temporal variability of sediment and nutrient loading to the coastal 

system.

Physical water-quality properties (water temperature, 

specific conductance, pH, dissolved oxygen concentration, 

and turbidity) are measured at the sampling site by using a 

water-quality multiprobe instrument at the time of sampling. 

Discharge measurements of the stream are made prior to the 

collection of each sample by using an acoustic Doppler velocity 

meter as described in Mueller and Wagner (2009). 

Discrete water-quality samples are routinely collected and 

analyzed for selected unfiltered and filtered constituents. These 

selected unfiltered constituents include suspended-sediment, 

total phosphorus, and total nitrogen concentrations. Filtered 

constituents include selected nutrients (filtered ammonia, filtered nitrate plus nitrite, filtered nitrite, and filtered orthophosphate concentrations).

Water-quality samples are collected and processed following standard USGS sampling methods as described in the 

“National Field Manual for the Collection of Water-Quality 

Data” (U.S. Geological Survey, variously dated). Depth integrated sampling is done along a river cross section to capture 

variability of constituent concentration within the river by 

using the equal discharge increment (EDI) approach (Edwards 

and Glysson, 1998). All nutrient samples are analyzed by 

the USGS National Water Quality Laboratory in Lakewood, 

Colo. Suspended-sediment samples are analyzed by the USGS 

Kentucky Water Science Center Sediment Laboratory in 

Louisville, Ky., for suspended-sediment concentration and 

particle-size distribution. Since 2010, the periodic bedload 

samples collected from the lower Colorado River and San 

Jacinto River sites have also been analyzed by the Kentucky 

Water Science Center Sediment Laboratory for particle-size 

distribution. 

Preliminary Results

Two periods of high flow on the Trinity River were initially 

evaluated in 2009 to assess the variability of sediment and 

nutrient data, and variations in loading caused by differences in 

flood-discharge magnitude and duration, origin of initial floodwater runoff, and timing of sample collection. The two periods 

of high flow had different flood and nutrient loading characteristics. Suspended-sediment, total nitrogen, and total phosphorus 

concentrations were compared to selected physical properties 

measured in place. These data indicate a relation exists between 

suspended-sediment concentrations measured in discrete waterquality samples and measured turbidity values (fig. 2). A similar 

relation exists between total nitrogen concentrations and turbidity and between total phosphorus concentrations and turbidity 

(fig. 3). 

Side-mounted ADCP and water-quality sampling equipment on a 

U.S. Geological Survey work boat used for coastal studies. 

Figure 2. Correlation between suspended-sediment 

concentration and turbidity during two periods of high flow, April 

20–23, 2009, and September 22–November 3, 2009, at 08067252 

Trinity River at Wallisville, Texas. 

TURBIDITY, IN FORMAZIN NEPHELOMETRIC UNITS 

0 50 100 150 200 250

SUSPENDED-SEDIMENT CONCENTRATION,

 IN MILLIGRAMS PER LITER

100

200

300

400

500

600

700

800

900

r

2

=0.9298

Figure 3. Correlation between total nitrogen or total 

phosphorus concentration and turbidity during two periods of 

high flow, April 20–23, 2009, and September 22–November 3, 

2009, at 08067252 Trinity River at Wallisville, Texas.

TURBIDITY, IN FORMAZIN NEPHELOMETRIC UNITS 

0 50 100 150 200 250

CONSTITUENT CONCENTRATION,

IN MILLIGRAMS PER LITER 

0

0.1

0.2

0.3

0.4

0.8

1.0

1.2

1.4

1.6

1.8

Total nitrogen

Total phosphorus

EXPLANATION

r

2

=0.8602

r

2

=0.8635
Publishing support provided by

Lafayette Publishing Service Center

For additional information, contact 

Director

USGS Texas Water Science Center

http://tx.usgs.gov/

gs-w-txpublic-info@usgs.gov 

USGS personnel collecting water-quality samples on the Trinity 

River near Wallisville, Texas. 

The initial sediment and nutrient loading estimates from 

the Trinity River to Galveston Bay indicate that discrete and 

continuous water-quality data can be used to make load estimates for sediment and nutrients. Additional data are needed 

to confirm the preliminary results. With a better understanding 

of the loads of these constituents, it might be possible to better 

understand the role sediment and nutrient loads have on the 

ecological health of other Texas estuaries and bays. 

References

Edwards, T.K., and Glysson, G.D., 1998, Field methods for 

measurement of fluvial sediment: U.S. Geological Survey 

Techniques of Water-Resources Investigations, book 3, 

chap. C2, 80 p.

Galveston Bay Estuary Program, 2002, The state of the bay—

A characterization of the Galveston Bay ecosystem (2d ed.): 

Galveston Bay Estuary Program GBEP–T7, chaps. 5–6.

Howarth, R.W., Sharpley, Andrew, and Walker, Dan, 2002, 

Sources of nutrient pollution to coastal waters in the United 

States—Implications for achieving coastal water quality 

goals: Estuaries, v. 25, no. 4b, p. 656–676. 

Hubbard, L., Kolpin, D.W., Kalkhoff, S.J., and Robertson, 

D.M., 2011, Nutrient and sediment concentrations and corresponding loads during the historic June 2008 flooding 

in eastern Iowa: Journal of Environmental Quality, v. 40, 

p. 166–175.

Lee, M.T., 2010, A preliminary evaluation of Trinity River sediment and nutrient loads into Galveston Bay, Texas, during 

two periods of high flow, in Second Joint Federal Interagency 

Conference (Ninth Federal Interagency Sedimentation 

Conference and Fourth Federal Interagency Hydrologic 

Modeling Conference), Las Vegas, Nevada, June 27–July 1, 

2010, Proceedings: 12 p.

Maryland Department of Natural Resources, 2011, Chesapeake 

Bay monitoring—Monitoring for management actions: 

accessed February 9, 2011, at http://www.dnr.state.md.us/bay/

monitoring/mon_mngmt_actions/chapter8.html.

Mueller, D.S., and Wagner, C.R., 2009, Measuring discharge 

with acoustic Doppler current profilers from a moving boat: 

U.S. Geological Survey Techniques and Methods 3A–22, 

72 p., accessed February 19, 2010, at http://pubs.water.usgs.

gov/tm3a22.

Senus, M.P., Langland, M.J., and Moyer, D.L., 2005, Nutrient 

and sediment concentrations, loads, and trends for four 

nontidal tributaries in the Chesapeake Bay watershed, 

1997–2001: U.S. Geological Survey Scientific Investigations 

Report 2004–5125, 33 p.

U.S. Geological Survey, variously dated, National field manual 

for the collection of water-quality data: U.S. Geological 

Survey Techniques of Water-Resources Investigations, 

book 9, chaps. A1–A9, accessed February 19, 2010, at 

http://pubs.water.usgs.gov/twri9A.

—Michael T. Lee

USGS personnel processing water-quality samples for sediment 

and nutrient data.