In cooperation with the Texas Water Development Board 

Base Flow (1966–2005) and Streamflow 

Gain and Loss (2006) of the Brazos 

River, McLennan County to Fort 

Bend County, Texas, 2006 

Scientific Investigations Report 2007–5286


U.S. Department of the Interior 

U.S. Geological Survey 
Cover:  U.S. Geological Survey field technician deploying discharge measurement equipment at Hidalgo

Falls on the Brazos River near Navasota, Texas, March 8, 2006 (photograph by Jimmy Hopkins, U.S.

Geological Survey).
Base Flow (1966–2005) and Streamflow 

Gain and Loss (2006) of the Brazos 

River, McLennan County to Fort 

Bend County, Texas

By Michael J. Turco, Jeffery W. East, and Matthew S. Milburn

In cooperation with the Texas Water Development Board

Scientific Investigations Report 2007–5286

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

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Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Turco, M.J., East, J.W., and Milburn, M.S., 2007, Base flow (1966–2005) and streamflow gain and loss (2006) of the 

Brazos River, McLennan County to Fort Bend County, Texas: U.S. Geological Survey Scientific Investigations Report 

2007–5286, 27 p.
iii

Contents

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

Introduction ....................................................................................................................................................1

Purpose and Scope .............................................................................................................................3

Description of Study Area ..................................................................................................................3

Acknowledgments ...............................................................................................................................5

Methods ..........................................................................................................................................................5

Hydrograph Separation ......................................................................................................................5

Streamflow Data Collection ...............................................................................................................5

Streamflow Gain and Loss Computation ..........................................................................................7

Base Flow .......................................................................................................................................................7

Streamflow Gain and Loss .........................................................................................................................10

Summary .......................................................................................................................................................25

References ...................................................................................................................................................26

Figures

1–2. Maps showing: 

1. Study area, Brazos River, and extent of Brazos River alluvium aquifer, 

McLennan County to Fort Bend County, Texas ..............................................................2

2. Brazos River alluvium aquifer, McLennan County to Fort Bend County, 

Texas; outcrops of underlying aquifers; and data-collection sites ............................4

3–9. Graphs showing: 

3. Base flow and runoff components of streamflow, 1966–2005, from hydrograph 

separation for (A) 08098290 Brazos River near Highbank, Texas; (B) 08111500 

Brazos River near Hempstead, Texas; and (C) 08114000 Brazos River at 

Richmond, Texas .................................................................................................................8

4. (A) Relation between annual base-flow index for 08098290 Brazos River 

near Highbank, Texas, and for 08111500 Brazos River near Hempstead, 

Texas; (B) relation between annual base-flow index for 08098290 Brazos 

River near Highbank, Texas, plus six inflow tributary sites, and for 08111500 

Brazos River near Hempstead, Texas; (C) time series of annual base-flow 

index for 08111500 Brazos River near Hempstead, Texas, 1966–2005; and 

(D) time series of annual base-flow index for 08098290 Brazos River near 

Highbank, Texas, 1966–2005, and for 08098290 Brazos River near Highbank, 

Texas, plus six inflow tributary sites, 1966–2005 .........................................................11

5. (A) Relation between annual base-flow index for 08111500 Brazos River 

near Hempstead, Texas, and for 08114000 Brazos River at Richmond, Texas; 

(B) relation between annual base-flow index for 08111500 Brazos River near 

Hempstead, Texas, plus one inflow tributary site, and for 08114000 Brazos 

River at Richmond, Texas; (C) time series of annual base-flow index for 

08114000 Brazos River at Richmond, Texas, 1966–2005; and (D) time series of 

annual base-flow index for 08111500 Brazos River near Hempstead, Texas, 

1966–2005, and for 08111500 Brazos River near Hempstead, Texas, plus one 

inflow tributary site, 1966–2005 ......................................................................................12
iv

6. Daily mean streamflow for March 1–15, 2006, at (A) 08096500 Brazos River 

at Waco, Texas; (B) 08108700 Brazos River at State Highway 21 near Bryan, 

Texas; and (C) 08111500 Brazos River near Hempstead, Texas ................................14

7. Daily mean streamflow for August 5–20, 2006, at (A) 08096500 Brazos River 

at Waco, Texas; (B) 08108700 Brazos River at State Highway 21 near Bryan, 

Texas; and (C) 08111500 Brazos River near Hempstead, Texas ................................15

8. Instantaneous streamflow at 36 sites on the Brazos River, McLennan County 

to Fort Bend County, Texas, March 6–10, 2006 ............................................................16

9. Instantaneous streamflow at 28 sites on the Brazos River, McLennan County 

to Fort Bend County, Texas, August 10–18, 2006 ..........................................................16

10–11. Maps showing: 

10. Reaches of the Brazos River, McLennan County to Fort Bend County, Texas, 

identified as gaining or losing streamflow, March 6–10, 2006 ..................................17

11. Reaches of the Brazos River, McLennan County to Fort Bend County, Texas, 

identified as gaining or losing streamflow, August 10–18, 2006 ................................18

Tables

1. U.S. Geological Survey streamflow-gaging stations on the Brazos River and 

selected tributaries, McLennan County to Fort Bend County, Texas, that provided 

data for hydrograph separation, water years 1966–2005 (October 1965 through 

September 2005) ..........................................................................................................................5

2. Sites on the Brazos River and selected tributaries, McLennan County to Fort 

Bend County, Texas, at which measurements for streamflow gain and loss 

computation were made, March and August 2006 ................................................................6

3. Results of hydrograph separation for 08098290 Brazos River near Highbank, Texas, 

08111500 Brazos River near Hempstead, Texas, and 08114000 Brazos River at 

Richmond, Texas, 1966–2005 ......................................................................................................9

4. Results of hydrograph separation for 08098290 Brazos River near Highbank, 

Texas, plus six inflow tributary sites, 1966–2005; and 08111500 Brazos River near Hempstead, Texas, plus one inflow tributary site, 1966–2005 .......................................................13

5. Instantaneous streamflow, water temperature, and specific conductance for 

sites on the Brazos River and selected tributaries, McLennan County to Fort Bend 

County, Texas, March 6–10, 2006 ............................................................................................19

6. Instantaneous streamflow for sites on the Brazos River and selected tributaries, 

McLennan County to Fort Bend County, Texas, August 10–18, 2006 .................................21

7. Streamflow gains and losses computed for 35 reaches on the Brazos River, 

McLennan County to Fort Bend County, Texas, March 6–10, 2006 ....................................22

8. Streamflow gains and losses computed for 27 reaches on the Brazos River, 

McLennan County to Fort Bend County, Texas, August 10–18, 2006 .................................24
v

Conversion Factors and Datum

Inch/Pound to SI

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

inch (in.) 25.4 millimeter (mm)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2) 

Flow

cubic feet per second (ft3/s) 0.02832 cubic meters per second (m3/s)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm).

Water year is defined as the 12-month period October 1 through September 30 and is designated 

by the calendar year in which it ends.

Datum

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). 
Blank Page
Base Flow (1966–2005) and Streamflow 

Gain and Loss (2006) of the Brazos 

River, McLennan County to Fort 

Bend County, Texas, 2006

By Michael J. Turco, Jeffery W. East, and Matthew S. Milburn

Abstract

During 2006–07, the U.S. Geological Survey (USGS), in 

cooperation with the Texas Water Development Board, did a 

study to quantify historical (water years 1966–2005) base 

flow and streamflow gains and losses from two streamflowmeasuring surveys (March and August 2006) in the Brazos 

River from McLennan County to Fort Bend County, Texas. 

The Brazos River is hydraulically connected to the Brazos 

River alluvium aquifer, which in turn is hydraulically connected to several underlying aquifers, the outcrops of which 

occur in laterally adjacent layers generally parallel to the coast 

(major aquifers, Carrizo-Wilcox and Gulf Coast, and minor 

aquifers, Queen City, Sparta, and Yegua-Jackson). Hydrograph separation was done using the USGS computer program 

Hydrograph Separation and Analysis with historical streamflow from 10 USGS gaging stations, three on the Brazos River 

and seven on selected tributaries to the Brazos River. Streamflow data for computation of gains and losses were collected 

in March 2006 from 36 sites on the Brazos River and 19 sites 

on 19 tributaries to the Brazos River; and in August 2006 

from 28 sites on the Brazos River and 16 sites on tributaries. 

Hydrograph separation and associated analyses indicate an 

appreciable increase in base flow as a percentage of streamflow in the reach of the Brazos River that crosses the outcrops 

of the Carrizo-Wilcox, Queen City, Sparta, and Yegua-Jackson aquifers compared to that in the adjacent upstream reach 

(on average from about 43 percent to about 60 percent). No 

increase in base flow as a percentage of streamflow in the 

reach of the Brazos River crossing the Gulf Coast aquifer 

compared to that in the adjacent upstream reach was indicated. Streamflow gains and losses computed for March 2006 

for 35 reaches defined by pairs of sites on the Brazos River 

indicated that five reaches were verifiably gaining streamflow 

(computed gain exceeded potential flow measurement error) 

and none were verifiably losing streamflow. Four of the five 

gaining reaches are in the outcrop areas of the Carrizo-Wilcox 

and Yegua-Jackson aquifers. The results of the synoptic gain 

and loss surveys are consistent with the results of the baseflow analysis of historical streamflow. Appreciable increases 

in streamflow, apparently the result of increases in base flow, 

occur in the reach of the Brazos River that crosses the outcrops 

of the Carrizo-Wilcox, Queen City, Sparta, and Yegua-Jackson 

aquifers. 

Introduction

The Brazos River alluvium aquifer is an important 

resource to water users in the Brazos River Basin from 

McLennan County to Fort Bend County, Texas (fig. 1). As 

demands on the resource increase in the future, the Brazos 

River alluvium aquifer likely will become more important. 

Quantification of base flow in the Brazos River and the 

exchange of water between the Brazos River and the underlying Brazos River alluvium aquifer could assist water managers 

and planners responsible for the long-term sustainability of 

surface- and ground-water resources in the area.

Slade and others (2002) identified 31 previous studies in 

which streamflow gain and loss data were collected in the Brazos River, which extends across Texas from southeastern New 

Mexico to the Gulf of Mexico (fig. 1). However, none of those 

studies were done in the reach of the river that flows through 

the area of the Brazos River alluvium aquifer (the reach that 

defines the area of this study). General qualitative descriptions 

of base flow in segments of the study area were reported by 

the Texas Board of Water Engineers (1960):

Area between Waco and the northern Falls County 

line—Geologic formations can be expected to make 

extremely small contributions to base flow of the 

Brazos River. 

Area between the northern Falls County line and 

Bryan—Geologic formations can be expected to make 

large contributions to base flow of the Brazos River. 

Area between Bryan and Hempstead—Geologic formations can be expected to make small contributions to 

base flow of the Brazos River. 

•

•

•
Figure 1. Study area, Brazos River, and extent of Brazos River alluvium aquifer, McLennan County to Fort Bend County, Texas. 

   Base Flow and Streamflow Gain and Loss of the Brazos River, McLennan County to Fort Bend County, Texas, 2006

Little

River

Navasota

River

Davidson

Creek

Little Pond

Creek

Middle Yegua Creek

East

Yegua

Creek

Mill

Creek

Yegua Creek

Little Brazos River

Colorado

River

Trinity

River

San

Jacinto

River Neches

River

Brazos

River

BOSQUE

MC LENNAN

FALLS

MILAM

ROBERTSON

BURLESON

BRAZOS

WASHINGTON WALLER

AUSTIN

FORT BEND

HARRIS

Study area Waco

Bryan

Richmond

Hempstead

Austin

College

Station

Houston

97° 96° 95°

32°

31°

30°

Albers Equal Area Projection

North American Datum 1983 0 25 50 MILES

0 25 50 KILOMETERS EXPLANATION

Brazos River alluvium aquifer TEXAS

Study area

NEW 

MEXICO

Brazos 

River 

Basin

Gulf of Mexico
Area between Hempstead and Richmond—Geologic 

formations can be expected to make moderate contributions to base flow of the Brazos River. 

During 2006–07, the U.S. Geological Survey (USGS), 

in cooperation with the Texas Water Development Board 

(TWDB), did a study to quantify base flow and streamflow 

gains and losses in the Brazos River from McLennan County 

to Fort Bend County. Of particular interest were potential 

gains and losses in the river where it flows across the outcrop areas of the Carrizo-Wilcox aquifer, the Queen City 

aquifer, the Sparta aquifer, and the Yegua-Jackson aquifer 

(fig. 2). These outcrop areas are essentially coincident with 

the area between the southern Falls County line and Bryan 

that, according to the Texas Board of Water Engineers (1960), 

is expected to make large contributions to base flow of the 

Brazos River.

Purpose and Scope

The purpose of this report is to document the results 

of base-flow analysis (hydrograph separation) of historical 

(water years 1966–2005 [October 1965 through September 

2005]) streamflow and two synoptic streamflow gain and loss 

surveys of the Brazos River from McLennan County to Fort 

Bend County, Texas, in March and August 2006. Methods of 

data collection and analysis are described. Results of hydrograph separation based on available historical data for three 

sites on the Brazos River and seven sites on tributaries to 

the Brazos River are presented. Streamflow gains and losses 

based on flow data collected from 55 sites on the Brazos River 

and selected tributaries during the two synoptic surveys are 

presented, and the respective gaining and losing reaches are 

identified. Water-quality properties (temperature and specific 

conductance) were collected as a part of the March 2006 

survey and are included in the report, but those data were not 

used in the analysis of gains and losses.

Description of Study Area

The study area encompasses a 310-mile reach of the 

Brazos River from Waco in McLennan County to Richmond 

in Fort Bend County (fig. 1) and includes selected inflow 

tributaries along the reach. The major tributaries are the Little 

River, Little Brazos River, Yegua Creek, Navasota River, and 

Mill Creek. Average annual rainfall (1971–2000) at College 

Station is 39.67 inches (National Weather Service, 2007). Five 

real-time USGS streamflow-gaging stations are on the Brazos 

River in the study area (fig. 2): 

1. 08096500 Brazos River at Waco, Tex. (site B1, fig. 2)

2. 08098290 Brazos River near Highbank, Tex. (site B6, 

fig. 2)

3. 08108700 Brazos River at State Highway 21 near Bryan, 

Tex. (site B14, fig. 2)

• 4. 08111500 Brazos River near Hempstead, Tex. (site B26, 

fig. 2)

5. 08114000 Brazos River at Richmond, Tex. (site B36, 

fig. 2)

Daily mean streamflow (1941–2006) ranged from 2,147 cubic 

feet per second at the Brazos River at Waco to 7,532 cubic feet 

per second at the Brazos River at Richmond (U.S. Geological 

Survey, 2007).

The Brazos River is hydraulically connected to the Brazos River alluvium aquifer. The alluvium aquifer is composed 

of fine to coarse sand, gravel, silt, and clay, the distribution of 

which varies from place to place (Cronin and others, 1963). 

Beds or lenses of sand and gravel grade laterally into vertically 

finer or coarser material. In general, the finer material is in the 

upper part of the aquifer. The thickness of the aquifer throughout most of its extent is less than 100 feet (Shah and others, 

2007, sheet 4). 

Underlying the Brazos River alluvium aquifer in laterally 

adjacent layers generally parallel to the coast are two major 

aquifers, Carrizo-Wilcox and Gulf Coast, and three minor 

aquifers, Queen City, Sparta, and Yegua-Jackson (Texas Water 

Development Board, 2007) (fig. 2). The Gulf Coast aquifer 

is actually an aquifer system, the principal aquifers of which 

are the Chicot, Evangeline, and Jasper (not differentiated in 

this report). Upstream from the outcrop of the Carrizo-Wilcox 

aquifer, the Brazos River alluvium aquifer is underlain by 

rocks not characterized as part of a major or minor aquifer by 

the TWDB. Like the Brazos River alluvium aquifer, each of 

the underlying aquifers is composed of interbedded sand, clay, 

gravel, and silt in varying amounts (Ashworth and Hopkins, 

1995; Ryder and Ardis, 2002). The underlying aquifers are 

distinguished from one another in large part by the stratigraphic units of the rocks composing the aquifers and the 

relative positions of the units. 

The underlying aquifers are hydraulically connected to 

the Brazos River alluvium aquifer, as indicated by potentiometric-surface maps of the Carrizo-Wilcox, Queen City, and 

Sparta aquifers (Garza and others, 1987). The approximate 

potentiometric-surface map of the Carrizo-Wilcox aquifer 

for 1980 of Garza and others (1987) in the aquifer outcrop 

shows U-shaped potentiometric contours, closed upstream 

and relatively large, across the Brazos River. Similarly, the 

approximate potentiometric-surface map of the Sparta-Queen 

City aquifer (Garza and others [1987] combined the Queen 

City and Sparta aquifers for mapping) for 1980 in the aquifer outcrop shows U-shaped potentiometric contours, closed 

upstream, across the Brazos River. The potentiometric-surface 

maps indicate, in addition to hydraulic connection between 

the Brazos River, the Brazos River alluvium aquifer, and the 

underlying aquifers, that the river is gaining water in the aquifer outcrop areas, which is consistent with the Texas Board 

of Water Engineers (1960) qualitative description of the river 

gaining base flow in the reaches crossing the aquifer outcrops. 

Although no potentiometric surface for the Yegua-Jackson 

aquifer is available, and no potentiometric-surface maps 

Introduction 
Figure 2. Brazos River alluvium aquifer, McLennan County to Fort Bend County, Texas; outcrops of underlying aquifers; and datacollection sites. 

Little

River

Navasota

River

Davidson

Creek

Little Pond

Creek

Middle Yegua Creek

East

Yegua

Creek

Mill

Creek

Yegua Creek

Little Brazos River

Colorado

River

Trinity

River

San

Jacinto

River Neches

River

Brazos

River

B35 B34

T19

T18

B33

B32

B31

B30

T17

B29

T16

T15

B28

B27 T14

B26

B25

B24

B23

T13 B22

B21

B20

B19

B18 T12

B17

B16 B15

T11

B14

T10 B13

B12 B11

B10 B9

T9 B8 B7

B6

T8

B5 T7

B4 T6

T5 B3

T4 T3 T2 B2

T1

B1

B36

S7

S6

S5 S4

S3

S2

S1

BOSQUE

MC LENNAN

FALLS

MILAM

ROBERTSON

BURLESON

BRAZOS

WASHINGTON WALLER

AUSTIN

FORT BEND

HARRIS

AQUIFER

OUTCROP

YEGUA-JACKSON

AQUIFER

OUTCROP

Waco

Bryan

Richmond

Hempstead

Austin

College

Station

Houston

QUEEN CITY

AQUIFER

OUTCROP

SPARTA

GULF COAST

AQUIFER

OUTCROP

CARRIZO-WILCOX

AQUIFER OUTCROP

97° 96° 95°

32°

31°

30°

Albers Equal Area Projection

North American Datum 1983 0 25 50 MILES

0 25 50 KILOMETERS

EXPLANATION

Brazos River alluvium aquifer

Brazos River site and identifier

Tributary site and identifier for gain and loss measurement

Tributary site and identifier for base-flow analysis

B7

T7

S7

Aquifer outcrops 

from Texas Water

Development Board,

2007

 Base Flow and Streamflow Gain and Loss of the Brazos River, McLennan County to Fort Bend County, Texas, 2006
constructed using shallow wells in the outcrops of the Chicot, 

Evangeline, and Jasper aquifers are known to exist, hydraulic 

connection between those aquifers, the Brazos River alluvium 

aquifer, and Brazos River are assumed. 

Acknowledgments

The authors acknowledge the contributions of Barney 

Austin, Robert Mace, and Ali Chowdhury of the Texas Water 

Development Board during the planning of this study. Additionally, the authors acknowledge staff of the Brazos River 

Authority who assisted in identifying appropriate streamflowmeasuring sites and in collecting data. The authors thank the 

numerous property owners who allowed access to measuring 

sites.

Methods

Hydrograph separation using historical streamflow was 

done to estimate base flow. Streamflow data collection and 

streamflow gain and loss computation were done to estimate 

streamflow gains and losses in the reach of the Brazos River 

from McLennan County to Fort Bend County. 

Hydrograph Separation

Hydrograph separation is the process of separating measured streamflow into components resulting either from direct 

surface runoff or from ground-water discharge (base flow). 

Hydrograph separation was done using the USGS computer 

program Hydrograph Separation and Analysis (HYSEP) (Sloto 

and Crouse, 1996). The data used in HYSEP were historical 

(water years 1966–2005) streamflow from 10 USGS gaging stations, three on the Brazos River and seven on selected 

tributaries to the Brazos River (table 1). The HYSEP program 

makes the hydrograph separation process objective by removing inconsistencies inherent in manual methods. Daily mean 

streamflow for each station was input to the HYSEP program. 

Output from the program includes the two components of the 

annual mean streamflow—annual mean surface runoff and 

annual mean base flow. Additionally, HYSEP provides the 

base-flow index (BFI), which is the ratio of the annual mean 

base flow to the annual mean streamflow. The BFI was used 

as a means to graphically compare streamflows (hydrographs) 

from the three Brazos River stations. The graphical comparisons indicate whether the reach between two stations is gaining or losing flow.

Wahl and Wahl (1995) states that caution should be 

used in applying hydrograph separation to data for short-term 

storms or for sites where streamflow is affected by upstream 

regulation, such as reservoir releases. The Brazos River in 

the study area is affected by regulation. Therefore, after using 

HYSEP to make hydrograph separation computations, the 

results were analyzed and judgments made regarding whether 

rises were from storm runoff or from reservoir releases. When 

judged necessary, HYSEP program input was adjusted by 

varying the runoff-timing parameter, and the program was rerun. This iterative process was continued until the results were 

deemed reasonable (that is, periods of reservoir releases were 

categorized by HYSEP as storm runoff).

Streamflow Data Collection

Streamflow data for computation of gains and losses 

were collected from the Brazos River and 19 tributaries to the 

Brazos River during March 6–10, 2006, and during August 

10–18, 2006. The study was separated into two periods to 

collect streamflow data that were representative of two distinct 

hydrologic conditions. March is usually wetter than August 

and demand on water resources (pumpage from the river, the 

alluvium aquifer, and underlying major and minor aquifers) 

is relatively low. August is usually drier and demand on water 

resources is relatively high. 

During the March data-collection period, streamflow 

was measured at 55 sites, 36 on the Brazos River and 19 on 

tributaries (fig. 2; table 2). During the August data-collection period, streamflow measurements were made at 44 of the 

55 sites, 28 on the Brazos River and 16 on tributaries. Water 

temperature and specific conductance also were measured 

during the March data-collection period at 53 and 52 sites, 

respectively. 

Table 1. U.S. Geological Survey streamflow-gaging stations 

on the Brazos River and selected tributaries, McLennan County 

to Fort Bend County, Texas, that provided data for hydrograph 

separation, water years 1966–2005 (October 1965 through 

September 2005). 

[USGS, U.S. Geological Survey]

Site

identifier

(fig. 2)

USGS

station

number

USGS station name

Contributing

drainage 

area 

(square 

miles)

B6 08098290 Brazos River near Highbank, Tex. 20,870

S1 08098300 Little Pond Creek near 

Burlington, Tex.

23.0

S2 08106500 Little River near Cameron, Tex. 7,065

S3 08109700 Middle Yegua Creek near Dime Box, 

Tex.

236

S4 08109800 East Yegua Creek near Dime Box, Tex. 244

S5 08110100 Davidson Creek near Lyons, Tex. 195

S6 08110500 Navasota River near Easterly, Tex. 968

B26 08111500 Brazos River near Hempstead, Tex. 34,314

S7 08111700 Mill Creek near Bellville, Tex. 376

B36 08114000 Brazos River at Richmond, Tex. 35,541

Methods   
Table 2. Sites on the Brazos River and selected tributaries, McLennan County to Fort Bend County, Texas, at which measurements 

for streamflow gain and loss computation were made, March and August 2006—Continued.

Site 

identifier

(fig. 2)

USGS

station number USGS station name

Latitude

(degrees 

minutes 

seconds)

Longitude

(degrees 

minutes 

seconds)

Distance 

upstream 

from mouth 

(miles)

B1 08096500 Brazos River at Waco, Tex. 313209 0970423 401

T1 313210097015800 Tehuacana Creek at SH 6 near Waco, Tex. 313210 0970158 --

T2 312934097045300 Flat Creek at CR 3400 near Robinson, Tex. 312934 0970453 --

B2 312723097020000 Brazos River near Robinson, Tex. 312723 0970200 390

T3 312715096590800 Monas Creek at FM 1860 near Riesel, Tex. 312715 0965908 --

T4 312639097030500 Castleman Creek near Robinson, Tex. 312639 0970305 --

T5 312335097022100 Bull Hide Creek at FM 434 near Golinda, Tex. 312335 0970221 --

B3 312201096572200 Brazos River near Golinda, Tex. 312201 0965722 375

T6 311927097011700 Cow Bayou below FM 434 near Chilton, Tex. 311927 0970117 --

B4 08097500 Brazos River near Marlin, Tex. 311718 0965810 364

T7 311645096584400 Deer Creek at SH 320 near Marlin, Tex. 311645 0965844 --

B5 311437096551300 Brazos River at FM 712 near Marlin, Tex. 311437 0965513 359

T8 311204096523300 Mussel Run Creek near Highbank, Tex. 311204 0965233 --

B6 08098290 Brazos River near Highbank, Tex. 310802 0964929 346

B7 310354096472000 Brazos River below FM 1373 near Baileyville, Tex. 310354 0964720 338

B8 310143096463800 Brazos River above Pond Creek near Baileyville, Tex. 310143 0964638 335

T9 310120096481700 Pond Creek at FM 2027 near Baileyville, Tex. 310120 0964817 --

B9 305836096453800 Brazos River at FM 979 near Calvert, Tex. 305836 0964538 329

B10 305630096451400 Brazos River near Calvert, Tex. 305630 0964514 326

B11 305349096414800 Brazos River at Big Bend near Calvert, Tex. 305349 0964148 317

B12 305158096414500 Brazos River at FM 485 near Hearne, Tex. 305158 0964145 314

T10 304932096443900 Little River at CR 263 near Gause, Tex. 304932 0964439 --

B13 08108500 Brazos River at Valley Junction, Tex. 304938 0963905 309

B14 08108700 Brazos River at SH 21 near Bryan, Tex. 303736 0963238 286

T11 08108990 Little Brazos River at SH 21 near Bryan, Tex. 303827 0963116 --

B15 08109500 Brazos River near College Station, Tex. 303233 0962521 269

B16 302932096201600 Brazos River at Batts Ferry near Wellborn, Tex. 302932 0962016 258

B17 302355096181000 Brazos River near FM 159 near Clay, Tex. 302355 0961810 243

T12 302208096203500 Yegua Creek at FM 50 near Clay, Tex. 302208 0962035 --

B18 302230096175000 Brazos River near FM 1955 near Clay, Tex. 302230 0961750 241

B19 302200096152900 Brazos River at Rogers Plantation near Millican, Tex. 302200 0961529 239

B20 302342096110400 Brazos River near FM 159 near Millican, Tex. 302342 0961104 233

B21 302134096091800 Brazos River at SH 105 near Washington, Tex. 302134 0960918 228

T13 302003096091400 Navasota River below SH 105 near Washington, Tex. 302003 0960914 --

B22 301927096085300 Brazos River below Navasota River near Washington, Tex. 301927 0960853 226

B23 301713096050000 Brazos River at Old River Road near Courtney, Tex. 301713 0960500 219

B24 301313096071200 Brazos River near FM 2726 near Courtney, Tex. 301313 0960712 209

B25 301014096092700 Brazos River near FM 1736 near Hempstead, Tex. 301014 0960927 202

B26 08111500 Brazos River near Hempstead, Tex. 300744 0961115 194

T14 300343096123300 Caney Creek at FM 1371 near Hempstead, Tex. 300343 0961233 --

B27 300217096063400 Brazos River at SH 159 near Hempstead, Tex. 300217 0960634 179

B28 300024096050500 Brazos River near FM 1887 near Hempstead, Tex. 300024 0960505 176

T15 295936096051100 Clear Creek near FM 1887 near Hempstead, Tex. 295936 0960511 --

T16 295637096075400 Piney Creek at FM 331 near Burleigh, Tex. 295637 0960754 --

Table 2. Sites on the Brazos River and selected tributaries, McLennan County to Fort Bend County, Texas, at which measurements for 

streamflow gain and loss computation were made, March and August 2006.

[USGS, U.S. Geological Survey; SH, State Highway; --, not applicable; CR, County Road, FM, Farm Road; IH, Interstate Highway]

   Base Flow and Streamflow Gain and Loss of the Brazos River, McLennan County to Fort Bend County, Texas, 2006
Discrete measurements of streamflow were made using 

USGS methods described in Rantz and others (1982). Where 

conditions allowed (water depths generally less than 3 feet), 

streams were waded and velocity measurements were made 

using rod-mounted acoustic meters (Sontek/YSI, Inc., 2007). 

In all other instances, boat-mounted acoustic Doppler current 

profilers were used to measure streamflow, as described in 

Oberg and others (2005). In-place measurements of water temperature and specific conductance were made using methods 

described by Wilde and Radtke (1998).

Streamflow Gain and Loss Computation

Streamflow gains and losses over the course of a stream 

are measured indirectly by computing the differences in 

streamflow between sites along the stream. Sources of gains 

or losses between two sites (which define a reach), in addition to ground-water inflow or outflow through the streambed, 

include tributary inflow, diversions, return flows, and evaporation. Using these factors, streamflow gain or loss in the reach 

is computed as

G = QD – QU – I + D – R + E, (1) 

where

G = streamflow gain or loss (ground-water inflow or 

outflow);

QD = measured streamflow at the downstream boundary of 

the reach;

QU = measured streamflow at the upstream boundary of the 

reach; 

I = measured inflows from tributaries;

D = measured outflows (diversions) from the reach;

R = return flows to the reach; and

E = evaporation. (Units of all variables are cubic feet per 

second.)

During this study, numerous tributary inflows and one 

diversion were measured directly. However, return flows and 

evaporation were not measured, and those components were 

excluded from equation 1. The magnitude of error associated 

with these exclusions is believed to be minor when compared 

to potential errors associated with the flow measurements. 

For this report, a stream reach is classified as verifiably 

gaining or losing only when the difference between streamflows at the upstream and downstream measuring sites that 

define the reach is greater than the potential error associated 

with the flow measurements. Measurement error is based on 

the rating of the streamflow measurement (excellent, good, 

fair, or poor) by the streamgager (Sauer and Meyer, 1992). 

The rating is based on factors such as cross-section uniformity, 

velocity homogeneity, streambed conditions, and other factors 

that affect the accuracy of the measurement. Measurements 

rated excellent are believed to be within 2 percent of the actual 

flow, good are believed to be within 5 percent, fair are believed 

to be within 8 percent, and poor are believed to differ from the 

actual flow by more than 8 percent. The potential errors associated with each pair of streamflow measurements for a given 

reach were summed to obtain the potential composite error for 

comparison with the computed gain or loss. 

Base Flow

The results of hydrograph separation for three streamflow-gaging stations on the Brazos River, 08098290 Brazos 

River near Highbank (site B6, fig. 2), 08111500 Brazos River 

near Hempstead (site B26, fig. 2), and 08114000 Brazos River 

at Richmond (site B36, fig. 2) for water years 1966–2005 are 

shown in figure 3 and listed in table 3. At the Highbank station, base flow as a percentage of streamflow ranged from a 

high of about 59 percent in 1990 to a low of about 30 percent 

Table 2. Sites on the Brazos River and selected tributaries, McLennan County to Fort Bend County, Texas, at which measurements 

for streamflow gain and loss computation were made, March and August 2006—Continued.

Site 

identifier

(fig. 2)

USGS

station number USGS station name

Latitude

(degrees 

minutes 

seconds)

Longitude

(degrees 

minutes 

seconds)

Distance 

upstream 

from mouth 

(miles)

B29 295431096064800 Brazos River at FM 529 near Burleigh, Tex. 295431 0960648 162

T17 295211096091900 Mill Creek at FM 331 near Burleigh, Tex. 295211 0960919 --

B30 294830096054400 Brazos River at FM 1458 at San Felipe, Tex. 294830 0960544 147

B31 294617096021200 Brazos River at IH–10 near Brookshire, Tex. 294617 0960212 140

B32 294017096011400 Brazos River at FM 1093 at Simonton, Tex. 294017 0960114 125

B33 293820095583200 Brazos River at FM 1489 near Simonton, Tex. 293820 0955832 117

T18 294107095551800 Bessies Creek at FM 1093 near Fulshear, Tex. 294107 0955518 --

T19 293835095525600 Jones Creek at Bois du Arc Road near Fulshear, Tex. 293835 0955256 --

B34 293621095521300 Brazos River at CR near FM 359 near Rosenberg, Tex. 293621 0955213 103

B35 293403095483700 Brazos River at FM 723 near Rosenberg, Tex. 293403 0954837 97

B36 08114000 Brazos River at Richmond, Tex. 293456 0954527 92

Methods 
Figure 3. Base flow and runoff components of streamflow, 1966–2005, from hydrograph separation for (A) 08098290 Brazos River near 

Highbank, Texas; (B) 08111500 Brazos River near Hempstead, Texas; and (C) 08114000 Brazos River at Richmond, Texas. 

1970

1980

19902000

1970

198019902000

1970

1980

19902000

DATE

DATE

DATE

0

4,000

8,000

12,000

16,000

20,000

24,000

28,000

0

4,000

8,000

12,000

16,000

20,000

24,000

28,000

0

4,000

8,000

12,000

16,000

20,000

24,000

28,000

STREAMFLOW, IN CUBIC FEET PER SECOND

A. 08098290 Brazos River near Highbank, Texas

B. 08111500 Brazos River near Hempstead, Texas

C. 08114000 Brazos River at Richmond, Texas.

Runoff

Base flow

Runoff

Base flow

Runoff

Base flow

 Base Flow and Streamflow Gain and Loss of the Brazos River, McLennan County to Fort Bend County, Texas, 2006
Table 3. Results of hydrograph separation for 08098290 Brazos River near Highbank, Texas, 08111500 Brazos River near Hempstead, 

Texas, and 08114000 Brazos River at Richmond, Texas, 1966–2005.

[Q, annual mean streamflow; ft3/s, cubic feet per second; BF, base-flow component; RO, runoff component; BFI, base-flow index (defined as BF/Q)]

Water

year

08098290 Brazos River near

Highbank, Tex. 

08111500 Brazos River near 

Hempstead, Tex.

08114000 Brazos River at 

Richmond, Tex.

Q

(ft3/s)

BF

(ft3/s)

RO

(ft3/s) BFI Q (ft3/s)

BF

(ft3/s)

RO

(ft3/s) BFI Q (ft3/s)

BF

(ft3/s)

RO

(ft3/s) BFI

1966 3,759 1,503 2,255 0.40 8,156 4,596 3,560 0.56 8,792 5,066 3,726 0.58

1967 1,051 565 485 .54 1,822 1,164 658 .64 1,866 1,187 679 .63

1968 5,144 2,195 2,950 .43 12,593 7,534 5,059 .60 13,226 7,597 5,629 .57

1969 2,963 1,354 1,610 .46 7,546 4,619 2,927 .61 8,218 4,974 3,245 .60

1970 2,337 1,161 1,176 .50 6,286 4,312 1,973 .69 6,459 4,453 2,006 .68

1971 572 244 328 .43 1,466 893 573 .61 1,678 941 737 .56

1972 2,253 1,109 1,144 .49 3,703 2,308 1,396 .62 4,374 2,807 1,566 .64

1973 3,611 1,355 2,257 .38 8,186 4,616 3,570 .56 9,282 5,464 3,818 .59

1974 1,552 611 941 .39 6,776 3,447 3,329 .51 7,876 4,266 3,611 .54

1975 4,853 1,815 3,038 .37 12,452 7,560 4,829 .61 13,956 8,735 5,221 .63

1976 1,980 693 1,287 .35 5,400 3,137 2,263 .58 5,817 3,540 2,277 .61

1977 3,643 1,568 2,075 .43 9,958 5,674 4,284 .57 10,740 6,601 4,139 .61

1978 517 233 284 .45 1,564 898 666 .57 1,894 1,038 856 .55

1979 2,970 1,031 1,940 .35 9,722 4,691 5,031 .48 11,487 5,749 5,738 .50

1980 1,218 474 744 .39 3,741 1,917 1,823 .51 4,307 2,284 2,023 .53

1981 1,711 593 1,118 .35 4,541 2,546 1,995 .56 5,053 2,852 2,201 .56

1982 5,150 2,414 2,736 .47 7,360 4,403 2,957 .60 7,829 4,871 2,958 .62

1983 970 363 607 .37 4,491 2,551 1,940 .57 5,462 2,982 2,480 .54

1984 329 162 167 .49 1,216 817 399 .67 1,403 881 522 .63

1985 1,959 865 1,094 .44 6,159 3,384 2,775 .55 6,540 3,775 2,765 .58

1986 2,697 1,002 1,695 .37 7,434 4,332 3,101 .58 8,379 5,144 3,235 .61

1987 4,494 2,298 2,196 .51 11,850 7,997 3,853 .67 13,546 9,318 4,228 .69

1988 690 296 395 .43 1,888 1,350 538 .71 2,184 1,506 678 .69

1989 3,289 1,787 1,502 .54 4,985 3,020 1,966 .61 5,436 3,318 2,118 .61

1990 5,265 3,103 2,162 .59 7,951 5,426 2,525 .68 7,742 5,528 2,214 .71

1991 2,503 1,182 1,321 .47 7,088 4,052 3,035 .57 7,914 4,680 3,233 .59

1992 11,319 6,599 4,720 .58 26,170 18,484 7,685 .71 26,619 20,153 6,466 .76

1993 2,319 1,170 1,149 .50 8,731 5,249 3,482 .60 9,733 5,727 4,006 .59

1994 1,646 736 911 .45 3,399 2,233 1,166 .66 3,718 2,351 1,366 .63

1995 4,474 1,881 2,594 .42 10,508 5,409 5,099 .51 11,676 6,313 5,363 .54

1996 774 346 429 .45 1,638 1,027 611 .63 1,885 1,201 684 .64

1997 6,497 3,337 3,160 .51 13,437 9,607 3,830 .72 13,656 9,880 3,776 .72

1998 2,892 951 1,941 .33 7,207 4,114 3,094 .57 7,735 4,616 3,119 .60

1999 1,273 470 804 .37 7,336 3,467 3,869 .47 8,251 3,940 4,311 .48

2000 506 150 356 .30 1,175 640 536 .54 1,201 667 534 .56

2001 3,253 1,428 1,825 .44 9,390 5,252 4,139 .56 9,662 5,653 4,009 .58

2002 1,849 726 1,122 .39 5,249 3,004 2,244 .57 5,435 3,102 2,333 .57

2003 1,336 499 837 .37 7,758 4,123 3,634 .53 8,515 4,432 4,083 .52

2004 2,605 1,000 1,605 .38 9,805 4,717 5,089 .48 10,115 4,580 5,535 .45

2005 3,719 1,738 1,982 .47 10,877 7,017 3,861 .65 11,280 6,944 4,336 .62

Methods   
in 2000. At the Hempstead station, base flow as a percentage 

of streamflow ranged from a high of about 72 percent in 1997 

to a low of about 47 percent in 1999. At the Richmond station, 

base flow as a percentage of streamflow ranged from a high of 

about 76 percent in 1992 to a low of about 48 percent in 1999. 

The compositions of streamflow at the Highbank and 

Hempstead gaging stations were compared graphically using 

BFI values (tables 3, 4). BFI values for the Brazos River near 

Highbank were graphed relative to corresponding BFI values 

for the Brazos River near Hempstead (fig. 4A). This graph 

shows that for each water year, the BFI value for the Brazos 

River near Hempstead is greater than the corresponding BFI 

value for the Brazos River near Highbank, which indicates that 

a larger percentage of the mean annual flow at the downstream 

gage (Hempstead) than at the upstream gage (Highbank) is 

composed of base flow.

The graph of BFI values in figure 4A does not reflect the 

effect of tributary inflows in the reach between the Highbank 

and Hempstead stations. To include the effect of tributary 

inflows, the results of hydrograph separation (annual mean 

base flow and streamflow) for tributary sites (stations) S1–S6 

(fig. 2) were summed and added to those from the Brazos 

River near Highbank (table 4). The sum of drainage areas for 

these six stations is 8,731 square miles, which accounts for 

about 65 percent of the intervening drainage area between the 

Brazos River near Highbank and the Brazos River near Hempstead stations. The BFI values for the Highbank and tributary 

stations combined were graphed relative to corresponding BFI 

values for the Brazos River near Hempstead (fig. 4B). The 

graph including the effect of tributary inflows is very similar 

to that without the effect of tributary inflows, again indicating 

that more of the mean annual flow at the downstream gage 

(Hempstead) is composed of base flow. 

Data to quantify the potential effects on historical streamflows of diversions, return flows, or other anthropogenic 

activities are not available. To assess whether these factors 

have affected historical streamflows, BFI values were graphed 

relative to time. Figure 4C shows a time series of BFI values 

for the Brazos River near Hempstead station, and figure 4D 

shows time series of BFI values for the Brazos River near 

Highbank station and for the Highbank station plus tributary 

stations. Visual examination of these time-series graphs does 

not indicate any discernible trends. To verify the visual result, 

Mann-Kendall trend tests (Helsel and others, 1992) were run 

on the time series; no significant trends were indicated (at the 

.05 level of significance) (p-value = .49 for the Brazos River 

near Hempstead time series [fig. 4C], p-value = .70 for the 

Brazos River near Highbank time series [fig. 4D], p-value = 

.83 for the Brazos River near Highbank plus tributary stations 

time series [fig. 4D]).

The same process was applied to compare the compositions of streamflow at the Brazos River near Hempstead and 

Brazos River at Richmond gaging stations (fig. 5; table 3). 

Again, annual BFI values for the two gages were compared 

graphically (fig. 5A). This graph shows that for each water 

year, the BFI value for the Brazos River at Richmond is on 

average about the same as the corresponding BFI value for 

the Brazos River near Hempstead, which indicates that the 

percentage of the mean annual flow that is base flow at the 

downstream gage (Richmond) is not noticeably different from 

that at the upstream gage (Highbank).

One USGS streamflow-gaging station is on a tributary 

that enters the Brazos River in the reach between the Hempstead and Richmond stations (site S7, table 1). The drainage 

area for this station is 376 square miles, or about 31 percent of 

the intervening drainage area between the Brazos River near 

Hempstead and Brazos River at Richmond stations. Figure 

5B shows the graph of BFI values for the Brazos River near 

Hempstead plus the tributary station relative to the BFI values 

for the Brazos River at Richmond. The relation in this graph 

is similar to that of the BFIs without the effect of the tributary 

(fig. 5A), although it appears slightly biased toward a larger 

percentage of base flow in streamflow at the Hempstead station than at the Richmond station. Time series of BFI values 

for the Brazos River at Richmond station (fig. 5C) and for the 

Brazos River near Hempstead station and the Brazos River 

near Hempstead station plus the tributary station (fig. 5D) do 

not show discernible trends, which likely indicates diversions, 

return flows, or other anthropogenic activities have not measurably affected streamflow in the reach during 1966–2005. 

Mann-Kendall trend tests run on the time series indicated no 

significant trends at the .05 level of significance (p-value = 

.29 for the Brazos River at Richmond time series and p-value 

= .77 for the Brazos River near Hempstead plus one tributary 

station time series).

Hydrograph separation and graphical evidence from BFI 

values indicate appreciably more base flow as a percentage 

of streamflow at the Hempstead station (about 60 percent on 

average) than at the Highbank station (about 43 percent on 

average). The reach of the Brazos River between the two stations crosses the outcrops of the Carrizo-Wilcox, Queen City, 

Sparta, and Yegua-Jackson aquifers, the probable source of 

the additional base flow. This result is consistent with indications of a gaining reach on potentiometric-surface maps of the 

Carrizo-Wilcox and Queen City-Sparta aquifers of Garza and 

others (1987) and with the Texas Board of Water Engineers 

(1960) qualitative description of the river gaining base flow 

in the reach, as noted previously in the “Description of Study 

Area” section. Hydrograph separation and graphical evidence 

from BFI values also indicate no increase in base flow as a 

percentage of streamflow in the reach of the Brazos River 

crossing the Gulf Coast aquifer (Chicot, Evangeline, and Jasper aquifers) compared to that in the adjacent upstream reach. 

Base flow as a percentage of streamflow at the Richmond 

station is essentially the same as that at the Hempstead station 

(about 60 percent on average).

Streamflow Gain and Loss

Daily mean streamflow of the Brazos River at three stations during the March and August 2006 surveys (08096500 

10 Base Flow and Streamflow Gain and Loss of the Brazos River, McLennan County to Fort Bend County, Texas, 2006
Figure 4. (A) Relation between annual base-flow index for 08098290 Brazos River near Highbank, Texas, and for 08111500 Brazos River 

near Hempstead, Texas; (B) relation between annual base-flow index for 08098290 Brazos River near Highbank, Texas, plus six inflow 

tributary sites, and for 08111500 Brazos River near Hempstead, Texas; (C) time series of annual base-flow index for 08111500 Brazos 

River near Hempstead, Texas, 1966–2005; and (D) time series of annual base-flow index for 08098290 Brazos River near Highbank, Texas, 

1966–2005, and for 08098290 Brazos River near Highbank, Texas, plus six inflow tributary sites, 1966–2005. 

1970 1980 1990 2000

DATE

1970 1980 1990 2000

DATE

BASE-FLOW INDEX FOR

08111500 BRAZOS RIVER NEAR HEMPSTEAD, TEXAS

BASE-FLOW INDEX FOR

08111500 BRAZOS RIVER NEAR HEMPSTEAD, TEXAS

0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75

BASE-FLOW INDEX FOR

08098290 BRAZOS RIVER NEAR HIGHBANK, TEXAS

BASE-FLOW INDEX FOR

08098290 BRAZOS RIVER NEAR HIGHBANK, TEXAS,

PLUS SIX INFLOW TRIBUTARY SITES

BASE-FLOW INDEX BASE-FLOW INDEX

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

(A) (B)

(C)

(D) 08098290 Brazos River near Highbank, Texas

08098290 Brazos River near Highbank, Texas, and six inflow tributary sites

08111500 Brazos River near Hempstead, Texas

Streamflow Gain and Loss 11
BASE-FLOW INDEX FOR

08114000 BRAZOS RIVER AT RICHMOND, TEXAS

0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80

1970 1980 1990 2000

DATE

1970 1980 1990 2000

DATE

BASE-FLOW INDEX FOR

08114000 BRAZOS RIVER AT RICHMOND, TEXAS

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

BASE-FLOW INDEX FOR

08111500 BRAZOS RIVER NEAR HEMPSTEAD, TEXAS

BASE-FLOW INDEX FOR

08111500 BRAZOS RIVER NEAR HEMPSTEAD, TEXAS,

PLUS ONE INFLOW TRIBUTARY SITE

BASE-FLOW INDEX BASE-FLOW INDEX

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

(A) (B)

(C)

(D)

08111500 Brazos River near Hempstead, Texas

08111500 Brazos River near Hempstead, Texas, and 08111700 Mill Creek near Bellville, Texas

08114000 Brazos River at Richmond, Texas

Figure 5. (A) Relation between annual base-flow index for 08111500 Brazos River near Hempstead, Texas, and for 08114000 Brazos 

River at Richmond, Texas; (B) relation between annual base-flow index for 08111500 Brazos River near Hempstead, Texas, plus one 

inflow tributary site, and for 08114000 Brazos River at Richmond, Texas; (C) time series of annual base-flow index for 08114000 Brazos 

River at Richmond, Texas, 1966–2005; and (D) time series of annual base-flow index for 08111500 Brazos River near Hempstead, Texas, 

1966–2005, and for 08111500 Brazos River near Hempstead, Texas, plus one inflow tributary site, 1966–2005. 

12 Base Flow and Streamflow Gain and Loss of the Brazos River, McLennan County to Fort Bend County, Texas, 2006
Table 4. Results of hydrograph separation for 08098290 Brazos River near Highbank, Texas, plus six inflow tributary sites, 1966–2005; 

and 08111500 Brazos River near Hempstead, Texas, plus one inflow tributary site, 1966–2005.

[Q, annual mean streamflow; ft3/s, cubic feet per second; BF, base-flow component; RO, runoff component; BFI, base-flow index (defined as BF/Q)]

Water

year

08098290 Brazos River near

Highbank, Tex., plus six inflow tributary sites1

08111500 Brazos River near Hempstead, Tex., plus one 

inflow tributary site2

Q

(ft3/s)

BF

(ft3/s)

RO

(ft3/s) BFI Q(ft3/s)

BF

(ft3/s)

RO

(ft3/s) BFI

1966 6,822 2,852 3,970 0.42 8,334 4,643 3,690 0.56

1967 1,538 776 762 .50 1,844 1,170 674 .63

1968 9,581 4,300 5,281 .45 12,937 7,567 5,370 .58

1969 5,158 2,199 2,959 .43 7,812 4,677 3,135 .60

1970 4,999 2,716 2,283 .54 6,425 4,347 2,077 .68

1971 1,013 470 543 .46 1,545 910 635 .59

1972 3,176 1,506 1,671 .47 3,889 2,340 1,548 .60

1973 5,778 2,100 3,679 .36 8,591 4,680 3,911 .54

1974 3,966 1,473 2,493 .37 7,182 3,522 3,660 .49

1975 9,858 4,127 5,731 .42 12,902 7,666 5,236 .59

1976 4,099 1,436 2,662 .35 5,580 3,179 2,400 .57

1977 7,184 3,174 4,010 .44 10,431 5,757 4,674 .55

1978 887 423 463 .48 1,661 923 738 .56

1979 5,943 2,047 3,896 .34 10,351 4,776 5,575 .46

1980 2,440 923 1,517 .38 3,892 1,961 1,931 .50

1981 3,464 1,222 2,242 .35 4,689 2,574 2,116 .55

1982 6,376 2,881 3,496 .45 7,583 4,438 3,145 .59

1983 2,417 879 1,538 .36 4,765 2,591 2,173 .54

1984 590 314 275 .53 1,273 839 433 .66

1985 3,654 1,495 2,160 .41 6,320 3,423 2,896 .54

1986 5,535 2,282 3,253 .41 7,671 4,380 3,291 .57

1987 8,886 4,856 4,030 .55 12,240 8,063 4,177 .66

1988 1,297 691 606 .53 2,003 1,379 625 .69

1989 4,295 2,142 2,154 .50 5,061 3,038 2,023 .60

1990 7,122 4,018 3,104 .56 7,979 5,440 2,539 .68

1991 4,495 1,937 2,557 .43 7,357 4,088 3,270 .56

1992 20,987 12,523 8,464 .60 26,836 18,593 8,243 .69

1993 5,174 2,700 2,475 .52 8,731 5,249 3,482 .60

1994 2,636 1,169 1,467 .44 3,399 2,233 1,166 .66

1995 7,552 3,216 4,335 .43 10,508 5,409 5,099 .51

1996 1,237 592 645 .48 1,638 1,027 611 .63

1997 11,872 7,344 4,527 .62 13,437 9,607 3,830 .71

1998 5,701 2,614 3,087 .46 7,207 4,114 3,094 .57

1999 4,067 1,389 2,678 .34 7,336 3,467 3,869 .47

2000 853 289 564 .34 1,175 640 536 .54

2001 6,591 2,936 3,655 .45 9,571 5,294 4,277 .55

2002 3,993 1,649 2,345 .41 5,342 3,032 2,310 .57

2003 3,819 1,472 2,347 .39 8,216 4,191 4,024 .51

2004 5,332 1,979 3,353 .37 10,081 4,784 5,297 .47

2005 8,235 4,293 3,942 .52 11,065 7,065 3,999 .64

1

 Sites S1–S6 (fig. 2, table 1).

2

 Site S7 (fig. 2, table 1).

Streamflow Gain and Loss 13
Brazos River at Waco, 08108700 Brazos River at State 

Highway 21 near Bryan, and 08111500 Brazos River near 

Hempstead) (figs. 6, 7) was relatively stable, except at the 

Waco station during the August survey. At the Waco station, 

streamflow was affected most days during the August survey 

by releases from upstream reservoirs for hydroelectric power 

generation. 

Measurements of streamflow at the 36 sites along the 

main stem of the Brazos River from the March survey (table 5) 

are graphed relative to downstream distance in figure 8. 

Streamflow increases from upstream to downstream except 

at the downstream end of the study reach. An appreciable 

increase in Brazos River flow (173 cubic feet per second) 

occurred between sites B12 and B13 (table 5), the reach bracketing the confluence with Little River, the largest tributary. 

Another large increase in flow (258 cubic feet per second) 

occurred between sites B15 and B16 (river miles 269–258, 

fig. 8) that is not a result of tributary inflow.

Measurements of streamflow at 28 of the 36 sites along 

the main stem of the Brazos River from the August survey 

(table 6) are graphed relative to downstream distance in 

figure 9. The graph shows the same general pattern of increasing streamflow from upstream to downstream, except at the 

downstream end of the study reach, as in the March survey, 

although the minimum flows at the upstream end are larger 

and the maximum flows toward the downstream end are lower. 

Larger minimum flows at the upstream end of the study reach 

likely are the result of releases from upstream reservoirs 

(fig. 7); and lower maximum flows likely are the result of 

generally drier conditions in August. Little River inflow was 

substantially less than in the March survey, and the increase 

in flow between sites B15 and B16 (table 6) also was substantially less than in the March survey. 

Streamflow gains and losses for reaches defined by 

pairs of sites on the Brazos River were computed for 35 

reaches during the March survey (table 7) and for 27 reaches 

Figure 6. Daily mean streamflow for March 1–15, 2006, at (A) 08096500 Brazos River at Waco, Texas; (B) 08108700 Brazos River at State 

Highway 21 near Bryan, Texas; and (C) 08111500 Brazos River near Hempstead, Texas. 

MARCH 2006

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

0

500

1,000

1,500

2,000

0

500

1,000

1,500

2,000

STREAMFLOW, IN CUBIC FEET PER SECOND

0

500

1,000

1,500

2,000

Data-collection period

Data-collection period

Data-collection period

A. 08096500 Brazos River at Waco, Texas

B. 08108700 Brazos River at State Highway 21 near Bryan, Texas

C. 08111500 Brazos River near Hempstead, Texas

14  Base Flow and Streamflow Gain and Loss of the Brazos River, McLennan County to Fort Bend County, Texas, 2006
during the August survey (table 8). Also listed is the potential 

error for each pair of measurements used to compute a gain 

or loss. Only gains or losses in reaches for which the difference between upstream and downstream measurements 

exceeds the potential measurement error are considered 

verified. Based on this criterion, five of 35 stream reaches 

were verifiably gaining streamflow and none were verifiably 

losing streamflow during the March survey (fig. 10). Four 

of the five gaining reaches are in the outcrop areas of the 

Carrizo-Wilcox and Yegua-Jackson aquifers. The reach 

gaining the most flow (B15–B16, 258 cubic feet per second) 

is in the Yegua-Jackson aquifer outcrop. No reason is known 

for the gaining reach at Waco, which is not in an aquifer 

outcrop. 

Figure 7. Daily mean streamflow for August 5–20, 2006, at (A) 08096500 Brazos River at Waco, Texas; (B) 08108700 Brazos River at State 

Highway 21 near Bryan, Texas; and (C) 08111500 Brazos River near Hempstead, Texas. 

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

AUGUST 2006

0

500

1,000

1,500

2,000

2,500

3,000

0

500

1,000

1,500

2,000

2,500

3,000

STREAMFLOW, IN CUBIC FEET PER SECOND

0

500

1,000

1,500

2,000

2,500

3,000

Data-collection period

Data-collection period

Data-collection period

A. 08096500 Brazos River at Waco, Texas

B. 08108700 Brazos River at State Highway 21 near Bryan, Texas

C. 08111500 Brazos River near Hempstead, Texas

Streamflow Gain and Loss 15
Figure 8. Instantaneous streamflow at 36 sites on the Brazos River, McLennan County to Fort Bend County, Texas, March 6–10, 2006. 

Figure 9. Instantaneous streamflow at 28 sites on the Brazos River, McLennan County to Fort Bend County, Texas, August 10–18, 2006. 

16 Base Flow and Streamflow Gain and Loss of the Brazos River, McLennan County to Fort Bend County, Texas, 2006

DISTANCE UPSTREAM FROM MOUTH OF BRAZOS RIVER, IN MILES

450 400 350 300 250 200 150 100 50

Downstream

0

200

400

600

800

1,000

1,200

STREAMFLOW, IN CUBIC FEET PER SECOND

Navasota River

confluence

Little River

confluence

Little Brazos River

confluence

DISTANCE UPSTREAM FROM MOUTH OF BRAZOS RIVER, IN MILES

450 400 350 300 250 200 150 100 50

Downstream

0

200

400

600

800

1,000

1,200

STREAMFLOW, IN CUBIC FEET PER SECOND

Navasota River

confluence

Little River

confluence

Little Brazos River

confluence

16 Base Flow and Streamflow Gain and Loss of the Brazos River, McLennan County to Fort Bend County, Texas, 2006
Little

River

Navasota

River

Davidson

Creek

Little Pond

Creek

Middle Yegua Creek

East

Yegua

Creek

Mill

Creek

Yegua Creek

Little Brazos River

Colorado

River

Trinity

River

San

Jacinto

River Neches

River

Brazos

River

B16 B15

B12 B11

B10 B9

B8

B1 B2

BOSQUE

MC LENNAN

FALLS

MILAM

ROBERTSON

BURLESON

BRAZOS

WASHINGTON WALLER

AUSTIN

FORT BEND

HARRIS

AQUIFER

OUTCROP

YEGUA-JACKSON

AQUIFER

OUTCROP

Waco

Bryan

Richmond

Hempstead

Austin

College

Station

Houston

QUEEN CITY

AQUIFER

OUTCROP

SPARTA

GULF COAST

AQUIFER

OUTCROP

CARRIZO-WILCOX

AQUIFER OUTCROP

97° 96° 95°

32°

31°

30°

Albers Equal Area Projection

North American Datum 1983 0 25 50 MILES

0 25 50 KILOMETERS

EXPLANATION

Brazos River alluvium aquifer

Gaining reach

(No losing reaches)

Site and identifier that define reach

(See table 7)

B15

Aquifer outcrops 

from Texas Water 

Development Board,

2007

Figure 10. Reaches of the Brazos River, McLennan County to Fort Bend County, Texas, identified as gaining or losing streamflow, 

March 6–10, 2006. 

Streamflow Gain and Loss 17
Little

River

Navasota

River

Davidson

Creek

Little Pond

Creek

Middle Yegua Creek

East

Yegua

Creek

Mill

Creek

Yegua Creek

Little Brazos River

Colorado

River

Trinity

River

San

Jacinto

River Neches

River

Brazos

River

B21

B20

B16 B15

B14

B13

B9

B6

B3

B1

BOSQUE

MC LENNAN

FALLS

MILAM

ROBERTSON

BURLESON

BRAZOS

WASHINGTON WALLER

AUSTIN

FORT BEND

HARRIS

AQUIFER

OUTCROP

YEGUA-JACKSON

AQUIFER

OUTCROP

Waco

Bryan

Richmond

Hempstead

Austin

College

Station

Houston

QUEEN CITY

AQUIFER

OUTCROP

SPARTA

GULF COAST

AQUIFER

OUTCROP

CARRIZO-WILCOX

AQUIFER OUTCROP

97° 96° 95°

32°

31°

30°

Albers Equal Area Projection

North American Datum 1983 0 25 50 MILES

0 25 50 KILOMETERS

EXPLANATION

Brazos River alluvium aquifer

Gaining reach

Losing reach

Site and identifier that define reach

(See table 8)

B15

Aquifer outcrops 

from Texas Water 

Development Board,

2007

Figure 11. Reaches of the Brazos River, McLennan County to Fort Bend County, Texas, identified as gaining or losing streamflow, 

August 10–18, 2006. 

18  Base Flow and Streamflow Gain and Loss of the Brazos River, McLennan County to Fort Bend County, Texas, 2006
For the August survey, four stream reaches were verifiably gaining streamflow and two were losing streamflow 

(fig. 11). Because some measurement sites in the March survey were not used in the August survey, the number of reaches 

defined by site pairs is 27, and thus some reaches are longer 

than those of the March survey. Although the August survey 

reaches are not everywhere comparable to the March survey 

reaches, the gaining reaches of the August survey generally 

match those of the March survey—occurring mostly in the 

outcrops of the aquifers. The reach gaining the most flow 

(B6–B9, 194 cubic feet per second) (fig. 11) begins upstream 

from the outcrop of the Carrizo-Wilcox aquifer and contains 

the relatively short gaining reach defined by sites B8 and B9 

(fig. 10) in the outcrop of the Carrizo-Wilcox aquifer from 

the March survey. The reach gaining the second-most flow 

(B13–B14, 134 cubic feet per second) is in the outcrops of the 

Queen City and Sparta aquifers; that reach was not a gaining 

reach in the March survey. The reach defined by sites B15 

and B16 in the Yegua-Jackson aquifer outcrop, which had the 

largest gain during the March survey, gained 73 cubic feet per 

second during the August survey. No reasons are known for 

the streamflow losses that occurred in the reach defined by 

sites B1 and B3 at the upstream end of the study reach and in 

the reach defined by sites B20 and B21 in the outcrop of the 

Gulf Coast aquifer.

The results of the synoptic gain and loss surveys are consistent with the results of the base-flow analysis (hydrograph 

separation) of historical streamflow and with the findings of 

Garza and others (1987) and the Texas Board of Water Engineers (1960). Appreciable increases in streamflow, apparently 

the result of increases in base flow, occur in the reach of the 

Brazos River that crosses the outcrops of the Carrizo-Wilcox, 

Queen City, Sparta, and Yegua-Jackson aquifers. The gain and 

loss surveys also yielded no evidence for appreciable streamflow gains or losses in the outcrop of the Gulf Coast aquifer, 

except for the relatively large, unexplained loss (237 cubic feet 

per second) in the reach defined by sites B20 and B21 in the 

August survey.

Table 5. Instantaneous streamflow, water temperature, and specific conductance for sites on the Brazos River and selected 

tributaries, McLennan County to Fort Bend County, Texas, March 6–10, 2006—Continued. 

Site 

identifier

(fig. 2)

USGS station name Date

Streamflow, 

instantaneous 

(ft3/s)

Water 

temperature 

(°C)

Specific 

conductance 

(μS/cm)

B1 Brazos River at Waco, Tex. March 8, 2006 133 -- --

T1 Tehuacana Creek at SH 6 near Waco, Tex. March 6, 2006 .107 18.0 755

T2 Flat Creek at CR 3400 near Robinson, Tex. March 6, 2006 .802 19.3 384

B2 Brazos River near Robinson, Tex. March 3, 2006 162 20.7 2,580

T3 Monas Creek at FM 1860 near Riesel, Tex. March 7, 2006 .168 17.2 727

T4 Castleman Creek near Robinson, Tex. March 7, 2006 .439 23.8 704

T5 Bull Hide Creek at FM 434 near Golinda, Tex. March 7, 2006 1.00 18.7 925

B3 Brazos River near Golinda, Tex. March 7, 2006 159 21.7 2,240

T6 Cow Bayou below FM 434 near Chilton, Tex. March 7, 2006 2.87 19.2 652

B4 Brazos River near Marlin, Tex. March 9, 2006 182 21.7 2,050

T7 Deer Creek at SH 320 near Marlin, Tex. March 7, 2006 1.06 20.5 854

B5 Brazos River at FM 712 near Marlin, Tex. March 9, 2006 209 23.0 1,850

T8 Mussel Run Creek near Highbank, Tex. March 7, 2006 1.59 20.4 1,400

B6 Brazos River near Highbank, Tex. March 9, 2006 218 21.3 1,860

B7 Brazos River below FM 1373 near Baileyville, Tex. March 9, 2006 223 19.4 2,090

B8 Brazos River above Pond Creek near Baileyville, Tex. March 9, 2006 220 20.8 2,140

T9 Pond Creek at FM 2027 near Baileyville, Tex. March 9, 2006 .180 21.1 2,470

B9 Brazos River at FM 979 near Calvert, Tex. March 6, 2006 295 18.9 2,470

B10 Brazos River near Calvert, Tex. March 7, 2006 254 21.7 2,410

B11 Brazos River at Big Bend near Calvert, Tex. March 7, 2006 301 20.5 2,400

Table 5. Instantaneous streamflow, water temperature, and specific conductance for sites on the Brazos River and selected 

tributaries, McLennan County to Fort Bend County, Texas, March 6–10, 2006. 

[USGS, U.S. Geological Survey; ft3/s, cubic feet per second; °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 °C; --, not available; SH, State 

Highway; CR, County Road; FM, Farm Road; IH, Interstate Highway]

Streamflow Gain and Loss 19
Table 5. Instantaneous streamflow, water temperature, and specific conductance for sites on the Brazos River and selected 

tributaries, McLennan County to Fort Bend County, Texas, March 6–10, 2006—Continued. 

Site 

identifier

(fig. 2)

USGS station name Date

Streamflow, 

instantaneous 

(ft3/s)

Water 

temperature 

(°C)

Specific 

conductance 

(μS/cm)

B12 Brazos River at FM 485 near Hearne, Tex. March 6, 2006 359 21.1 2,240

T10 Little River at CR 263 near Gause, Tex. March 6, 2006 239 22.2 659

B13 Brazos River at Valley Junction, Tex. March 7, 2006 532 20.6 1,660

B14 Brazos River at SH 21 near Bryan, Tex. March 10, 2006 531 20.0 1,630

T11 Little Brazos River at SH 21 near Bryan, Tex. March 10, 2006 35.6 20.3 794

B15 Brazos River near College Station, Tex. March 10, 2006 594 20.6 1,550

B16 Brazos River at Batts Ferry near Wellborn, Tex. March 7, 2006 852 21.0 1,360

B17 Brazos River near FM 159 near Clay, Tex. March 7, 2006 817 23.0 1,510

T12 Yegua Creek at FM 50 near Clay, Tex. March 7, 2006 5.26 23.0 747

B18 Brazos River near FM 1955 near Clay, Tex. March 7, 2006 809 24.2 1,500

B19 Brazos River at Rogers Plantation near Millican, Tex. March 7, 2006 804 22.0 1,700

B20 Brazos River near FM 159 near Millican, Tex. March 7, 2006 898 21.7 1,930

B21 Brazos River at SH 105 near Washington, Tex. March 8, 2006 780 20.3 1,950

T13 Navasota River below SH 105 near Washington, Tex. March 8, 2006 93.0 20.5 566

B22 Brazos River below Navasota River near Washington, Tex. March 8, 2006 854 20.4 1,810

B23 Brazos River at Old River Road near Courtney, Tex. March 8, 2006 892 21.7 --

B24 Brazos River near FM 2726 near Courtney, Tex. March 8, 2006 920 21.8 1,790

B25 Brazos River near FM 1736 near Hempstead, Tex. March 8, 2006 995 22.7 1,740

B26 Brazos River near Hempstead, Tex. March 9, 2006 843 21.4 1,740

T14 Caney Creek at FM 1371 near Hempstead, Tex. March 8, 2006 1.80 23.0 589

B27 Brazos River at SH 159 near Hempstead, Tex. March 9, 2006 922 20.8 1,730

B28 Brazos River near FM 1887 near Hempstead, Tex. March 9, 2006 941 23.5 1,510

T15 Clear Creek near FM 1887 near Hempstead, Tex. March 9, 2006 8.84 21.5 456

T16 Piney Creek at FM 331 near Burleigh, Tex. March 8, 2006 3.58 26.5 199

B29 Brazos River at FM 529 near Burleigh, Tex. March 9, 2006 978 22.5 1,750

T17 Mill Creek at FM 331 near Burleigh, Tex. March 9, 2006 20.8 22.0 513

B30 Brazos River at FM 1458 at San Felipe, Tex. March 8, 2006 963 21.4 1,860

B31 Brazos River at IH–10 near Brookshire, Tex. March 8, 2006 1,130 22.4 1,830

B32 Brazos River at FM 1093 at Simonton, Tex. March 8, 2006 1,090 23.3 1,790

B33 Brazos River at FM 1489 near Simonton, Tex. March 9, 2006 1,010 22.6 1,820

T18 Bessies Creek at FM 1093 near Fulshear, Tex. March 8, 2006 2.48 24.2 320

T19 Jones Creek at Bois du Arc Road near Fulshear, Tex. March 9, 2006 1.00 -- --

B34 Brazos River at CR near FM 359 near Rosenberg, Tex. March 9, 2006 874 22.9 1,790

B35 Brazos River at FM 723 near Rosenberg, Tex. March 9, 2006 930 24.1 1,730

B36 Brazos River at Richmond, Tex. March 9, 2006 871 24.2 1,520

20 Base Flow and Streamflow Gain and Loss of the Brazos River, McLennan County to Fort Bend County, Texas, 2006
Table 6. Instantaneous streamflow for sites on the Brazos River and selected tributaries, McLennan County to Fort Bend County, 

Texas, August 10–18, 2006—Continued.

Site 

identifier

(fig. 2)

USGS station name Date

Streamflow, 

instantaneous 

(ft3/s)

B1 Brazos River at Waco, Tex. August 10, 2006 370

T1 Tehuacana Creek at SH 6 near Waco, Tex. August 10, 2006 0

T2 Flat Creek at CR 3400 near Robinson, Tex. August 10, 2006 .500

B2 Brazos River near Robinson, Tex. -- --

T3 Monas Creek at FM 1860 near Riesel, Tex. August 10, 2006 .020

T4 Castleman Creek near Robinson, Tex. August 10, 2006 0

T5 Bull Hide Creek at FM 434 near Golinda, Tex. -- --

B3 Brazos River near Golinda, Tex. August 10, 2006 320

T6 Cow Bayou below FM 434 near Chilton, Tex. -- --

B4 Brazos River near Marlin, Tex. -- --

T7 Deer Creek at SH 320 near Marlin, Tex. August 10, 2006 0

B5 Brazos River at FM 712 near Marlin, Tex. -- --

T8 Mussel Run Creek near Highbank, Tex. August 11, 2006 1.00

B6 Brazos River near Highbank, Tex. August 11, 2006 396

B7 Brazos River below FM 1373 near Baileyville, Tex. -- --

B8 Brazos River above Pond Creek near Baileyville, Tex. -- --

T9 Pond Creek at FM 2027 near Baileyville, Tex. August 11, 2006 0

B9 Brazos River at FM 979 near Calvert, Tex. August 14, 2006 590

B10 Brazos River near Calvert, Tex. -- --

B11 Brazos River at Big Bend near Calvert, Tex. -- --

B12 Brazos River at FM 485 near Hearne, Tex. August 14, 2006 629

T10 Little River at CR 263 near Gause, Tex. August 14, 2006 61.1

B13 Brazos River at Valley Junction, Tex. August 15, 2006 623

B14 Brazos River at SH 21 near Bryan, Tex. August 15, 2006 757

T11 Little Brazos River at SH 21 near Bryan, Tex. August 15, 2006 8.03

B15 Brazos River near College Station, Tex. August 16, 2006 677

B17 Brazos River near FM 159 near Clay, Tex. August 16, 2006 829

T12 Yegua Creek at FM 50 near Clay, Tex. August 16, 2006 6.59

B18 Brazos River near FM 1955 near Clay, Tex. August 16, 2006 811

B19 Brazos River at Rogers Plantation near Millican, Tex. August 16, 2006 825

B20 Brazos River near FM 159 near Millican, Tex. August 16, 2006 963

B21 Brazos River at SH 105 near Washington, Tex. August 17, 2006 726

T13 Navasota River below SH 105 near Washington, Tex. -- --

B22 Brazos River below Navasota River near Washington, Tex. August 17, 2006 702

B23 Brazos River at Old River Road near Courtney, Tex. August 17, 2006 799

B24 Brazos River near FM 2726 near Courtney, Tex. August 17, 2006 825

B25 Brazos River near FM 1736 near Hempstead, Tex. August 17, 2006 818

B26 Brazos River near Hempstead, Tex. August 17, 2006 807

Table 6. Instantaneous streamflow for sites on the Brazos River and selected tributaries, McLennan County to Fort Bend County, 

Texas, August 10–18, 2006.

[Negative discharge indicates irrigation pumpage from the Brazos River. USGS, U.S. Geological Survey; ft3/s, cubic feet per second; SH, State Highway; 

CR, County Road; --, not available; FM, Farm Road; IH, Interstate Highway]

Streamflow Gain and Loss 21
Table 7. Streamflow gains and losses computed for 35 reaches on the Brazos River, McLennan County to Fort Bend County, Texas, March 6–10, 

2006—Continued. 

Site 

identifier

(fig. 2)

Distance between 

downstream and 

upstream sites 

(mi)

Streamflow, 

instantaneous 

(ft3/s)

Measured inflow 

between downstream 

and upstream sites

(ft3/s)

Difference in 

streamflow between 

downstream and 

upstream sites

(ft3/s)

Gain or loss in 

streamflow between 

downstream and 

upstream sites

(ft3/s)

Potential measurement 

error between 

downstream and 

upstream sites

(ft3/s)

B1 -- 133 -- -- -- --

11 0.91 29.0 28.1 23.6

B2 162

15 1.61 -3.00 -4.61 20.9

B3 159

11 2.87 23.0 20.1 22.5

B4 182

5 1.06 27.0 25.9 31.3

B5 209

13 1.59 9.00 7.41 27.6

B6 218

8 0 5.00 5.00 28.7

B7 223

3 0 -3.00 -3.00 35.4

B8 220

6 0.18 75.0 74.8 47.1

B9 295

3 0 -41.0 -41.0 42.2

B10 254

9 0 47.0 47.0 27.8

Table 6. Instantaneous streamflow for sites on the Brazos River and selected tributaries, McLennan County to Fort Bend County, 

Texas, August 10–18, 2006—Continued.

Site 

identifier

(fig. 2)

USGS station name Date

Streamflow, 

instantaneous 

(ft3/s)

T14 Caney Creek at FM 1371 near Hempstead, Tex. August 17, 2006 0

B27 Brazos River at SH 159 near Hempstead, Tex. August 18, 2006 873

B28 Brazos River near FM 1887 near Hempstead, Tex. August 18, 2006 861

T15 Clear Creek near FM 1887 near Hempstead, Tex. August 17, 2006 3.33

T16 Piney Creek at FM 331 near Burleigh, Tex. August 17, 2006 .07

B29 Brazos River at FM 529 near Burleigh, Tex. August 18, 2006 901

T17 Mill Creek at FM 331 near Burleigh, Tex. August 17, 2006 3.84

B30 Brazos River at FM 1458 at San Felipe, Tex. August 17, 2006 883

B31 Brazos River at IH–10 near Brookshire, Tex. August 17, 2006 884

B32 Brazos River at FM 1093 at Simonton, Tex. August 17, 2006 814

B33 Brazos River at FM 1489 near Simonton, Tex. August 17, 2006 870

T18 Bessies Creek at FM 1093 near Fulshear, Tex. August 18, 2006 0

T19 Jones Creek at Bois du Arc Road near Fulshear, Tex. August 18, 2006 -106

B34 Brazos River at CR near FM 359 near Rosenberg, Tex. -- --

B35 Brazos River at FM 723 near Rosenberg, Tex. August 18, 2006 799

B36 Brazos River at Richmond, Tex. August 18, 2006 696

Table 7. Streamflow gains and losses computed for 35 reaches on the Brazos River, McLennan County to Fort Bend County, Texas, March 6–10, 

2006. 

[Bold font indicates gain or loss that is greater than potential measurement error for that particular reach. mi, miles; ft3/s, cubic feet per second; --, not 

applicable]

22 Base Flow and Streamflow Gain and Loss of the Brazos River, McLennan County to Fort Bend County, Texas, 2006
Table 7. Streamflow gains and losses computed for 35 reaches on the Brazos River, McLennan County to Fort Bend County, Texas, March 6–10, 

2006—Continued. 

Site 

identifier

(fig. 2)

Distance between 

downstream and 

upstream sites 

(mi)

Streamflow, 

instantaneous 

(ft3/s)

Measured inflow 

between downstream 

and upstream sites

(ft3/s)

Difference in 

streamflow between 

downstream and 

upstream sites

(ft3/s)

Gain or loss in 

streamflow between 

downstream and 

upstream sites

(ft3/s)

Potential measurement 

error between 

downstream and 

upstream sites

(ft3/s)

B11 301

3 0 58.0 58.0 43.8

B12 359

5 239 173 -66.0 71.3

B13 532

23 0 -1.00 -1.00 85.0

B14 531

17 35.6 63.0 27.4 90.0

B15 594

11 0 258 258 116

B16 852

15 0 -35.0 -35.0 134

B17 817

2 5.26 -8.00 -13.3 130

B18 809

2 0 -5.00 -5.00 129

B19 804

6 0 94.0 94.0 136

B20 898

5 0 -118 -118 134

B21 780

2 93.0 74.0 -19.0 105

B22 854

7 0 38.0 38.0 140

B23 892

10 0 28.0 28.0 145

B24 920

7 0 75.0 75.0 153

B25 995

8 0 -152 -152 164

B26 843

15 1.80 79.0 77.2 158

B27 922

3 0 19.0 19.0 149

B28 941

14 12.4 37.0 24.6 154

B29 978

15 20.8 -15.0 -35.8 155

B30 963

7 0 167 167 167

B31 1,130

15 0 -40.0 -40.0 178

B32 1,090

8 0 -80.0 -80.0 168

B33 1,010

14 3.48 -136 -139 151

B34 874

6 0 56.0 56.0 144

B35 930

5 0 -59.0 -59.0 144

B36 871

Streamflow Gain and Loss 23
Table 8. Streamflow gains and losses computed for 27 reaches on the Brazos River, McLennan County to Fort Bend County, Texas, 

August 10–18, 2006—Continued. 

Site 

identifier

(fig. 2)

Distance between 

downstream and 

upstream sites 

(mi)

Streamflow, 

instantaneous 

(ft3/s)

Measured 

inflow between 

downstream and 

upstream sites

(ft3/s)

Difference in 

streamflow between 

downstream and 

upstream sites

(ft3/s)

Gain or loss in 

streamflow between 

downstream and 

upstream sites

(ft3/s)

Potential measurement 

error between 

downstream and 

upstream sites

 (ft3/s)

B1 -- 370 -- -- -- --

26 0.52 -50.0 -50.5 34.5

B3 320

29 1.00 76.0 75.0 35.8

B6 396

17 0 194 194 49.3

B9 590

15 0 39.0 39.0 61.0

B12 629

5 61.1 -3.00 -64.1 81.3

B13 623

23 0 134 134 87.7

B14 757

17 8.03 -80.0 -88.0 92.0

B15 677

11 0 73.0 73.0 71.3

B16 750

15 0 79.0 79.0 104

B17 829

2 6.59 -18.0 -24.6 131

B18 811

2 0 14.0 14.0 131

B19 825

6 0 138 138 143

B20 963

5 0 -237 -237 135

B21 726

2 0 -24.0 -24.0 114

B22 702

7 0 97.0 97.0 120

B23 799

10 0 26.0 26.0 130

B24 825

7 0 -7.00 -7.00 131

B25 818

8 0 -11.0 -11.0 130

B26 807

15 0 66.0 66.0 134

Table 8. Streamflow gains and losses computed for 27 reaches on the Brazos River, McLennan County to Fort Bend County, Texas, 

August 10–18, 2006. 

[Bold font indicates gain or loss that is greater than potential measurement error for that particular reach. mi, miles; ft3/s, cubic foot per second; --, not 

applicable]

24  Base Flow and Streamflow Gain and Loss of the Brazos River, McLennan County to Fort Bend County, Texas, 2006
Summary

During 2006–07, the U.S. Geological Survey (USGS), 

in cooperation with the Texas Water Development Board 

(TWDB), did a study to quantify base flow and streamflow 

gains and losses in the Brazos River from McLennan County 

to Fort Bend County, Texas. This report documents the results 

of base-flow analysis (hydrograph separation) of historical 

(1966–2005) streamflow and two synoptic streamflow gain 

and loss surveys of the Brazos River from McLennan County 

to Fort Bend County, Texas, in March and August 2006. 

The study area encompasses a 310-mile reach of the 

Brazos River from Waco in McLennan County to Richmond 

in Fort Bend County and includes selected inflow tributaries 

along the reach. The Brazos River is hydraulically connected 

to the Brazos River alluvium aquifer. Underlying the Brazos 

River alluvium aquifer in laterally adjacent layers generally 

parallel to the coast are two major aquifers, Carrizo-Wilcox 

and Gulf Coast, and three minor aquifers, Queen City, Sparta, 

and Yegua-Jackson. Upstream from the outcrop of the CarrizoWilcox aquifer, the Brazos River alluvium aquifer is underlain 

by rocks not characterized as part of a major or minor aquifer. 

The underlying aquifers are hydraulically connected to one 

another and to the Brazos River alluvium aquifer, as indicated 

by 1980 potentiometric-surface maps of the Carrizo-Wilcox, 

Queen City, and Sparta aquifers that show U-shaped potentiometric contours, closed upstream, across the Brazos River. 

Hydrograph separation was done using the USGS computer program Hydrograph Separation and Analysis (HYSEP). 

The data used in HYSEP were historical (water years 1966–

2005) streamflow from 10 USGS gaging stations, three on the 

Brazos River and seven on selected tributaries to the Brazos 

River. Streamflow data for computation of gains and losses 

were collected during March 6–10, 2006, from 36 sites on 

the Brazos River and 19 sites on 19 tributaries to the Brazos 

River; and during August 10–18, 2006, from 28 sites on the 

Brazos River and 16 sites on tributaries. HYSEP provides the 

base-flow index (BFI), which is the ratio of the annual mean 

base flow to the annual mean streamflow. The BFI was used 

as a means to graphically compare streamflows (hydrographs) 

from the three Brazos River stations. The graphical comparisons indicate whether the reach between two stations is gaining or losing flow.

Streamflow gains and losses for reaches defined by adjacent pairs of Brazos River measurement sites were computed 

as streamflow at the downstream site minus streamflow at the 

upstream site minus inflows from tributaries (plus a diversion 

for one reach). For this report, a stream reach is classified as 

verifiably gaining or losing only when the difference between 

Table 8. Streamflow gains and losses computed for 27 reaches on the Brazos River, McLennan County to Fort Bend County, Texas, 

August 10–18, 2006—Continued. 

Site 

identifier

(fig. 2)

Distance between 

downstream and 

upstream sites 

(mi)

Streamflow, 

instantaneous 

(ft3/s)

Measured 

inflow between 

downstream and 

upstream sites

(ft3/s)

Difference in 

streamflow between 

downstream and 

upstream sites

(ft3/s)

Gain or loss in 

streamflow between 

downstream and 

upstream sites

(ft3/s)

Potential measurement 

error between 

downstream and 

upstream sites

 (ft3/s)

B27 873

3 0 -12.0 -12.0 139

B28 861

14 3.40 40.0 36.6 141

B29 901

15 3.84 -18.0 -21.8 143

B30 883

7 0 1.00 1.00 141

B31 884

15 0 -70.0 -70.0 136

B32 814

8 0 56.0 56.0 135

B33 870

20 -106 -71.0 -35.0 134

B35 799

5 0 -103 -103 120

B36 696

Streamflow Gain and Loss 25
streamflows at the upstream and downstream measuring sites 

that define the reach is greater than the potential error associated with the flow measurements.

Hydrograph separation and graphical evidence from 

BFI values indicate an appreciable increase in base flow as 

a percentage of streamflow in the reach of the Brazos River 

that crosses the outcrops of the Carrizo-Wilcox, Queen City, 

Sparta, and Yegua-Jackson aquifers compared to that in the 

adjacent upstream reach (on average from about 43 percent to 

about 60 percent). This result is consistent with indications of 

a gaining reach on 1980 potentiometric-surface maps of the 

Carrizo-Wilcox and Queen City-Sparta aquifers. Hydrograph 

separation and graphical evidence from BFI values also 

indicate no increase in base flow as a percentage of streamflow in the reach of the Brazos River crossing the Gulf Coast 

aquifer compared to that in the adjacent upstream reach. 

Streamflow gains and losses computed for March 2006 

for 35 reaches defined by pairs of sites on the Brazos River 

indicated that five reaches were verifiably gaining streamflow 

and none were verifiably losing streamflow. Four of the five 

gaining reaches are in the outcrop areas of the Carrizo-Wilcox 

and Yegua-Jackson aquifers. The reach gaining the most flow 

(258 cubic feet per second) is in the Yegua-Jackson aquifer 

outcrop. For the August survey, four stream reaches were 

verifiably gaining streamflow and two were losing streamflow. Although the August survey reaches are not everywhere 

comparable to the March survey reaches, the gaining reaches 

of the August survey generally match those of the March 

survey—occurring mostly in the outcrops of the aquifers. The 

reach gaining the most flow (194 cubic feet per second) begins 

upstream from the outcrop of the Carrizo-Wilcox aquifer and 

ends in the outcrop of that aquifer. The reach gaining the second-most flow (134 cubic feet per second) is in the outcrops of 

the Queen City and Sparta aquifers.

The results of the synoptic gain and loss surveys are 

consistent with the results of the base-flow analysis (hydrograph separation) of historical streamflow. Appreciable 

increases in streamflow, apparently the result of increases in 

base flow, occur in the reach of the Brazos River that crosses 

the outcrops of the Carrizo-Wilcox, Queen City, Sparta, 

and Yegua-Jackson aquifers. The gain and loss surveys also 

yielded no evidence for appreciable streamflow gains or losses 

in the outcrop of the Gulf Coast aquifer, except for one relatively large, unexplained loss (237 cubic feet per second) in 

the August survey.

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References 27

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