In cooperation with the Edwards Aquifer Authority 

Streamflow Conditions in the Guadalupe River Basin, 

South-Central Texas, Water Years 1987–2006—An 

Assessment of Streamflow Gains and Losses and 

Relative Contribution of Major Springs to Streamflow 

Scientific Investigations Report 2008–5165 

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U.S. Department of the Interior 

U.S. Geological Survey 
Cover:

Photographs

Top, Canyon Dam and Lake near New Braunfels, Texas (photograph from U.S. Army Corps of Engineers, 

Fort Worth District, http://www.swf-wc.usace.army.mil/canyon/). 

Bottom, Guadalupe River near Hunt, Texas December, 17, 2007 (photograph by Brian Petri, U.S. 

Geological Survey). 

Left, Major spring orifices of Comal Springs in New Braunfels, Texas, January 26, 2007.

Map, Guadalupe River Basin, South-Central Texas, showing location of U.S. Geological Survey gaging 

stations. 
Streamflow Conditions in the Guadalupe 

River Basin, South-Central Texas, Water 

Years 1987–2006—An Assessment of 

Streamflow Gains and Losses and Relative 

Contribution of Major Springs to Streamflow 

By Darwin J. Ockerman and Richard N. Slattery

In cooperation with the Edwards Aquifer Authority

Scientific Investigations Report 2008–5165

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: 2008

For product and ordering information:

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U.S. Government.

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:

Ockerman, D.J., and Slattery, R.N., 2008, Streamflow conditions in the Guadalupe River Basin, south-central Texas, 

water years 1987–2006—An assessment of streamflow gains and losses and relative contribution of major springs to 

streamflow: U.S. Geological Survey Scientific Investigations Report 2008–5165, 22 p. 
iii

Contents

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

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

Purpose and Scope .............................................................................................................................1

Description of Study Area ..................................................................................................................2

Streamflow Conditions .................................................................................................................................2

Streamflow Statistics of U.S. Geological Survey Gaging-Station Data ......................................5

Reported Within-Reach Discharges and Withdrawals .................................................................8

Analyses of Streamflow Conditions for Water Years 1987–2006 .................................................9

Analyses of Streamflow Conditions for Selected Short-Term Periods .....................................12

Summary .......................................................................................................................................................20

References ...................................................................................................................................................21

Figure

1. Map showing Guadalupe River Basin, south-central Texas, locations of U.S. 

Geological Survey streamflow-gaging stations, and locations of stream reaches 

used for analysis of streamflow conditions ............................................................................3

Tables

1. Selected U.S. Geological Survey streamflow-gaging stations, Guadalupe River 

Basin, south-central Texas .........................................................................................................4

2. Stream reaches for which streamflow conditions analyzed, Guadalupe River 

Basin, south-central Texas .........................................................................................................5

 3. Daily streamflow statistics for selected U.S. Geological Survey streamflowgaging stations, Guadalupe River Basin, south-central Texas:

A. Statistics for available period of record ..........................................................................6

B. Statistics for water years 1987–2006 ...............................................................................7

4. Summary of average streamflow conditions for 1987–2006 by stream reach, 

Guadalupe River Basin, south-central Texas ........................................................................10

 5. Average springflows at major springs for selected short-term periods compared 

with long-term flow statistics, Guadalupe River Basin, south-central Texas. .................12

 6. Summary of streamflow conditions for selected short-term periods by stream 

reach, Guadalupe River Basin, south-central Texas ...........................................................14

 7. Comparison of contributions of Canyon Lake releases and flow from major 

springs to streamflow in selected stream reaches for selected short-term 

periods, Guadalupe River Basin, south-central Texas ........................................................20
iv

Conversion Factors and Datum

Inch/Pound to SI 

Multiply By To obtain

Length

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2) 

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

Volume

acre-foot (acre-ft) 0.001233 cubic hectometer (hm3

)

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

°C=(°F-32)/1.8

Datum

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

The U.S. Geological Survey, in cooperation with the 

Edwards Aquifer Authority, assessed available streamflow 

data in the Guadalupe River Basin to determine streamflow 

gains and losses and the relative contribution of flow from 

major springs—Comal Springs, San Marcos Springs, and 

Hueco Springs—to streamflow in reaches of the Guadalupe 

River and its tributaries. The assessment is based primarily on 

long-term (1987–2006) and short-term (January 1999, August 

1999, August 2000, and August 2006) streamflow conditions. 

For each analysis period, the ratio of flow from the major 

springs (measured at the spring source) to the sum of inflows 

(measured at the source of inflow to the river system) is computed for reaches of the Comal River and San Marcos River 

that include springflows from major springs, and for Guadalupe River reaches downstream from Canyon Dam. The ratio 

of springflow to the sum of inflows to the reach is an estimate 

of the contribution of flows from major springs to streamflow. 

For 1987–2006, the ratio of springflow from the major springs 

to the sum of inflows for the most upstream reach that includes 

inflow from all three major springs, Guadalupe River—above 

Comal River to Gonzales, is 27 percent. At the lowermost 

downstream reach, Guadalupe River—Bloomington to the San 

Antonio River, the percentage of the sum of inflows attributed 

to springflow is 18 percent. At that lowermost reach, the ratio 

of Canyon Lake releases to the sum of inflows was 20 percent. 

For the short-term periods August 2000 and August 2006 

(periods of relatively low flow), springflow in the reach Guadalupe River—above Comal River to Gonzales accounted for 

77 and 78 percent, respectively, of the sum of inflows in that 

reach. At the lowermost reach Guadalupe River—Bloomington to San Antonio River, springflow was 52 and 53 percent 

of the sum of inflows, respectively, during August 2000 and 

August 2006 (compared with 18 percent during 1987–2006); 

and during August 2000 and August 2006, the ratios of 

Canyon Lake releases to the sum of inflows were less than 10 

percent (compared with 20 percent during 1987–2006). 

Introduction

The Guadalupe River and its tributaries in south-central 

Texas are a vital source of water for Kerrville, New Braunfels, 

Victoria, and other towns; and the streams supply water for 

farms, ranches, and industry. The Guadalupe River also is a 

popular stream for tubing, canoeing, fishing, and other recreational activities. The Guadalupe River Basin (GRB) includes 

important springs that sustain streamflow and provide habitat 

for several endangered and threatened species.

Streamflow conditions1 in the GRB are affected by 

springflow (spring discharge), rainfall-runoff processes, pointsource discharges, withdrawals for water supply, reservoir 

operations, evapotranspiration, and losses to aquifer recharge. 

A better understanding of how these factors, or changes in 

these factors, affect streamflow conditions can help resource 

managers design watershed-management and operation strategies to optimize use of available water resources. The U.S. 

Geological Survey (USGS), in cooperation with the Edwards 

Aquifer Authority, compiled and analyzed data on streamflow 

conditions to assess streamflow gains and losses and the relative contribution of flow of major springs to streamflow in the 

GRB. 

Purpose and Scope

The purpose of this report is to describe streamflow 

conditions in the GRB—that is, water-budget components of 

stream reaches—that constitute streamflow gains and losses 

and the relative contribution of flow of from major springs to 

streamflow in selected reaches of the Guadalupe River and 

its tributaries. The assessment of streamflow gains and losses 

and the relative contribution of springflow to streamflow is 

based primarily on long-term (20 years) and short-term (four 

1

 “Conditions” in the context of this report refers to water-budget components of stream reaches—upstream flow, downstream flow, and intervening 

gains and losses of flow including gains from major springs. 

Streamflow Conditions in the Guadalupe River Basin, 

South-Central Texas, Water Years 1987–2006—An 

Assessment of Streamflow Gains and Losses and 

Relative Contribution of Major Springs to Streamflow 

By Darwin J. Ockerman and Richard N. Slattery
2 Streamflow Conditions in the Guadalupe River Basin, South-Central Texas, Water Years 1987–2006

1-month base-flow periods) streamflow conditions. Streamflow and springflow data used were collected at 28 streamflow-gaging stations operated by the USGS during water 

years 1987–2006 (October 1986 through September 2006); 

the 1-month base-flow periods were January 1999, August 

1999, August 2000, and August 2006. Permitted, within-reach 

discharge (inflow to the reach) and withdrawal (outflow from 

the reach) data used were reported by the Texas Commission 

on Environmental Quality (TCEQ). 

Description of Study Area

The headwaters of the Guadalupe River form in southwestern Kerr County. From there, the river flows easterly 

for about 250 river miles to Gonzales, then southeasterly for 

another 150 river miles to join the San Antonio River 11 river 

miles upstream from Guadalupe Bay, which is part of the San 

Antonio Bay system (fig. 1). The drainage area of the Guadalupe River is about 10,200 square miles including the San 

Antonio River watershed. The study area—the GRB upstream 

from the confluence of the Guadalupe and San Antonio 

Rivers—comprises 5,974 square miles and excludes the San 

Antonio River Basin. The Blanco River and San Marcos River 

are principal tributaries of the Guadalupe River. Two major 

reservoirs are in the GRB: Canyon Lake is on the Guadalupe 

River in Comal County, about 12 miles northwest of New 

Braunfels. The reservoir impounds runoff from 1,432 square 

miles of drainage area and has 382,000 acre-feet of authorized 

conservation storage (Guadalupe-Blanco River Authority, 

2007a). Construction of the dam and reservoir began in 1958 

and impoundment began in 1964. Coleto Creek Reservoir is 

on Coleto and Perdido Creeks, about 12 miles southwest of 

Victoria. The dam was completed in 1980 and impounds runoff from 507 square miles of drainage area. Conservation storage for the reservoir is 35,060 acre-feet (Guadalupe-Blanco 

River Authority, 2007b). The primary purpose of the reservoir 

is to provide cooling water for electric power generation. 

Major population centers of the GRB include the cities 

of Kerrville, New Braunfels, San Marcos, Seguin, Lockhart, 

Gonzales, Cuero, Luling, and Victoria. The 2007 population 

of the basin was about 589,000 (U.S. Census Bureau, 2007). 

Land use in the basin is predominantly rural. Elevation in the 

study area ranges from about 25 feet (at station 08177520) to 

more than 2,000 feet above sea level in the upstream parts of 

the GRB. 

Three major springs are in the GRB: Comal Springs, San 

Marcos Springs, and Hueco Springs. Comal Springs provides 

most of the flow in the Comal River, which joins the Guadalupe River at New Braunfels. Comal Springs, which discharges 

from several outlets, is the largest spring in Texas and the 

Southwest (Brune, 1975). Long-term average Comal Springs 

flow (water years 1929–2006) is 290 cubic feet per second. 

San Marcos Springs, also with several outlets, provides most 

of the base flow for the San Marcos River, which joins the 

Guadalupe River near Gonzales. This spring is the second 

largest in Texas (Brune, 1975). Long-term average flow for 

San Marcos Springs (water years 1957–2006) is 175 cubic feet 

per second. Hueco Springs is on the west side of the Guadalupe River about 3 river miles upstream from New Braunfels. 

Long-term average flow for Hueco Springs (water years 

1944–2006) is 42 cubic feet per second. Besides these major 

springs east and southeast of Canyon Lake, numerous small 

springs in Kerr County supply much of the base flow in the 

headwater reaches (reaches 1–3, fig. 1) of the Guadalupe River 

(Heitmuller and Reece, 2003).

The climate of the study area is described as subtropical subhumid, characterized by hot summers and mild, dry 

winters (Larkin and Bomar, 1983). Heaviest rainfall tends to 

occur in spring, early summer, and fall, but can occur anytime 

during the year. Periods with large or small amounts of rainfall 

are common, resulting in recurring floods and droughts. The 

following meteorological statistics are from the National 

Weather Service station at New Braunfels (U.S. Department 

of Commerce, 2002): Average annual rainfall (1971–2000) is 

35.74 inches per year. Rainfall greater than 0.01 inch occurs, 

on average, 77 days per year. The average monthly low temperatures range from 35.5 degrees Fahrenheit (°F) in January 

to 70.6 °F in July. Average monthly high temperatures range 

from 61.7 °F in January to 95.3 °F in August. 

Streamflow Conditions

Streamflow conditions in the GRB were analyzed by 

computing surface-water budgets for reaches of Guadalupe 

River and tributary streams. The GRB was divided into a 

network of 27 stream reaches, defined mainly by the locations 

of USGS streamflow-gaging stations. Table 1 lists the gaging stations from which data were compiled for this report, 

including station name and number, county, period of record, 

latitude and longitude, and drainage area upstream from the 

station. The data are in the USGS National Water Information 

System (NWISWeb) (U.S. Geological Survey, 2008). Table 2 

lists each stream reach, including reach number and name, 

upstream and downstream station number, reach length, and 

cumulative drainage area at the downstream station. The locations of the gaging stations and stream reaches are shown in 

figure 1. Thirteen reaches (including the Canyon Lake reach) 

are on the main stem of the Guadalupe River. Fourteen reaches 

are on the tributaries Johnson Creek, Comal River, Blanco 

River, San Marcos River, Plum Creek, Peach Creek, Sandies 

Creek, Perdido Creek, and Coleto Creek. The farthest downstream gaging station used, 08177520 Guadalupe River near 

Bloomington, is a water-stage station, and discharge records 

are not available for the outlet of reach 26. Also, no gaging stations are at the outlets of reach 17 (lower San Marcos 

River), and reach 27 (Guadalupe River from Bloomington to 

the San Antonio River). Outflows from reaches 17, 26 (Guadalupe River—Victoria to Bloomington), and 27 are estimated as 

the sum of upstream gaging-station inflow, intervening runoff 
Streamflow Conditions 3

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0 20 30 40 MILES 10

Guadalupe River Basin upstreamfrom San Antonio River

U.S. Geological Survey streamflowgaging station and number (table 1)

Major springStream reach number (table 2)

EXPLANATION

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11

08165500

TEXAS

Study area

LOCATION MAP

Base modified from U.S. Geological Surveydigital data 1:24,000 quadranglesUniversal Transverse Mercator ProjectionZone 14, Datum NAD83

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18

9

New Braunfels GUADALUPE 

COUNTY

COMAL 

COUNTY

0816871008169000

08168500

08168000

98°05' 98°10'

29°45'29°40'

Inset 2

Comal River

River

Guadalupe Hueco Springs

Comal Springs

0 2 3 4 MILES 1

13

#

14

GUADALUPE

COUNTY

COMAL

COUNTY

CALDWELL

COUNTY

HAYS

COUNTY

0817000008170500

97°50' 97°55' 98°00'

29°55'29°50'

Inset 1

San

River

Blanco River Marcos San Marcos Springs San Marcos

0 2 3 4 MILES 1

30°00'

29°00'

97°00'

98°00'

99°00'

100°00'

REFUGIO

COUNTY

CALHOUN

COUNTY GOLIAD

COUNTY

VICTORIA

COUNTY

KARNES

COUNTY

WILSON

COUNTY

LAVACA

COUNTY

BEXAR

COUNTY

GONZALES

COUNTY

GUADALUPE

COUNTY

BANDERA

COUNTY

REAL

COUNTY CALDWELL

COUNTY

KENDALL

COUNTY

FAYETTE

COUNTY

KERR

COUNTY

HAYS

COUNTY

BASTROP

COUNTY

GILLESPIE

COUNTY

BLANCO

COUNTY

TRAVIS

COUNTY

COMAL

COUNTY

Kerrville

Lockhart

Luling

Victoria

Cuero

Gonzales

San Marcos

San

 Antonio

New

Braunfels

Seguin

Austin

See inset 1

See inset 2

8

10 14

13

26

27

2

20

11

7

18

25

6

22

16

12

24

9

3

21

23

19

15 5

4 1

17

08177520 08177500 08177300

08176900

08176500

08175800

08175000

08174600 08173900

08173000

08172400

08172000

08171300 08171000

08170000

08170500

0816871008169000

08168500

08168000

08167800 08167500

08167000

08166200

08166140

08166000 08165500

08165300

Creek

Johnson

River Blanco

River

Guadalupe

River

Guadalupe

Creek

Plum

River

San Marcos

Creek

Peach

River

SanAntonio

River

Guadalupe

Creek

Sandies

Coleto

Perdido Creek

Creek

San Antonio

Bay

Guadalupe

Bay

Coleto

Creek

Reservoir

Canyon

Lake

Canyon Dam

Hueco Springs

Comal Springs

San Marcos Springs

Figure 1. Guadalupe River Basin, south-central Texas, locations of U.S. Geological Survey streamflow-gaging stations, and locations of stream reaches used for analysis of streamflow conditions. 
4 Streamflow Conditions in the Guadalupe River Basin, South-Central Texas, Water Years 1987–2006

(estimated from adjacent gaged reaches using a unit-runoff 

approach (U.S. Environmental Protection Agency, 2008)—that 

is, by assuming the same discharge per unit area applies in the 

intervening ungaged drainage area as in adjacent gaged drainage areas), and reported within-reach discharges (inflows) 

minus within-reach withdrawals (outflows). 

For each stream reach, streamflow data from the 

upstream and downstream gaging stations were compiled. 

Reported within-reach discharges (for example, wastewatertreatment plant discharges) and withdrawals (for example, 

withdrawals for irrigation or water supply) were summed. 

Measured (gaged) tributary inflows or measured springflows 

also were accounted for. Unreported or unmeasured waterbudget components such as streambed leakage to or from a 

reach were not explicitly accounted for but are included in the 

overall reach gain (or loss), as determined by the difference in 

streamflow measured at the upstream and downstream gaging 

stations. Evaporation and rainfall components of the water 

budgets were computed only for the Canyon Lake reach (U.S. 

Army Corps of Engineers, 2007). The water-budget analyses 

were done for a long-term period, water years 1987–2006, and 

for four short-term, base-flow periods, January 1999, August 

Table 1. Selected U.S. Geological Survey streamflow-gaging stations, Guadalupe River Basin, south-central Texas.

[--, not applicable]

Station name

Station 

number

(fig. 1)

County

Period of 

record1

(water years)

Latitude

(degrees, 

minutes, 

seconds)

Longitude

(degrees, 

minutes, 

seconds)

Drainage 

area

(square 

miles)

North Fork Guadalupe River near Hunt, Tex. 08165300 Kerr 1968–present 30 03 50 99 23 12 169

Guadalupe River at Hunt, Tex. 08165500 Kerr 1966–present 30 04 11 99 19 17 288

Johnson Creek near Ingram, Tex. 08166000 Kerr 1942–present 30 06 00 99 16 58 114

Guadalupe River above Bear Creek at Kerrville, Tex. 08166140 Kerr 1979–present 30 04 10 99 11 42 494

Guadalupe River at Kerrville, Tex. 08166200 Kerr 1987–present 30 03 11 99 09 47 510

Guadalupe River at Comfort, Tex. 08167000 Kendall 1940–present 29 58 10 98 53 33 839

Guadalupe River near Spring Branch, Tex. 08167500 Comal 1923–present 29 51 37 98 23 00 1,315

Guadalupe River at Sattler, Tex. 08167800 Comal 1961–present 29 51 32 98 10 47 1,436

Hueco Springs near New Braunfels, Tex. 08168000 Comal 1945–present 29 45 33 98 08 23 --

Guadalupe River above Comal River at New Braunfels, Tex. 08168500 Comal 1929–present 29 42 53 98 06 35 1,518

Comal Springs at New Braunfels, Tex. 08168710 Comal 1928–present 29 42 21 98 07 20 --

Comal River at New Braunfels, Tex. 08169000 Comal 1929–present 29 42 21 98 07 20 130

San Marcos Springs at San Marcos, Tex. 08170000 Hays 1957–present 29 53 20 97 56 02 --

San Marcos River at San Marcos, Tex. 08170500 Hays 1994–present 29 53 20 97 56 02 49

Blanco River at Wimberley, Tex. 08171000 Hays 1929–present 29 59 39 98 05 19 355

Blanco River near Kyle, Tex. 08171300 Hays 1957–present 29 58 45 97 54 35 412

San Marcos River at Luling, Tex. 08172000 Caldwell 1940–present 29 39 58 97 39 02 838

Plum Creek at Lockhart, Tex. 08172400 Caldwell 1960–present 29 55 22 97 40 44 112

Plum Creek near Luling, Tex. 08173000 Caldwell 1931–present 29 41 58 97 36 12 309

Guadalupe River at Gonzales, Tex. 08173900 Gonzales 1997–present 29 29 03 97 27 00 3,490

Peach Creek below Dilworth, Tex. 08174600 Gonzales 1960–present 29 28 26 97 18 59 460

Sandies Creek near Westhoff, Tex. 08175000 DeWitt 1960–present 29 12 54 97 26 57 549

Guadalupe River at Cuero, Tex. 08175800 DeWitt 1965–present 29 05 25 97 19 16 4,934

Guadalupe River at Victoria, Tex. 08176500 Victoria 1935–present 28 47 34 97 00 46 5,198

Coleto Creek near Schroeder, Tex. 08176900 Goliad 1979–present 28 51 41 97 13 34 357

Perdido Creek near Fannin, Tex. 08177300 Goliad 1979–present 28 45 05 97 19 01 28

Coleto Creek near Victoria, Tex. 08177500 Victoria 1979–present 28 43 51 97 08 18 514

Guadalupe River near Bloomington, Tex. 08177520 Victoria 1999–present 28 39 43 96 57 55 5,816

1

 Present indicates station was active in water year 2008.
Streamflow Conditions 5

1999, August 2000, and August 2006. For each analysis 

period, contributions from the major springs (Comal Springs, 

San Marcos Springs, and Hueco Springs) to the sum of inflows 

are computed for various downstream locations in the Comal, 

San Marcos, and Guadalupe Rivers. 

Streamflow Statistics of U.S. Geological Survey 

Gaging-Station Data

Selected daily streamflow statistics were computed for 

27 active USGS gaging stations in the GRB. Statistics include 

average, or mean, streamflow, 20-percent exceedance streamflow, 50-percent exceedance (median) streamflow, 80-percent 

exceedance streamflow, and 90-percent exceedance streamflow. The percentage exceedance streamflow is defined as the 

daily mean streamflow that was exceeded for the specified 

percentage of time during the analysis period. For example, 

90-percent exceedance streamflow represents a (relatively low) 

daily mean streamflow that was exceeded 90 percent of the 

analysis period. For each gaging station, streamflow statistics 

were computed for two periods. First, statistics were computed 

for the available period of record (table 3A). Second, statistics were computed for water years 1987–2006 (table 3B). 

The period 1987–2006 provides a relatively long-term period 

of record for comparison common among most gages in the 

Table 2. Stream reaches for which streamflow conditions analyzed, Guadalupe River Basin, south-central Texas.

[--, not applicable]

Reach number (fig. 1) 

and name

Upstream 

gaging-station 

number

(fig. 1)

Downstream 

gaging-station 

number

(fig. 1)

Stream 

reach 

length

(miles)

Cumulative 

drainage area 

at reach outlet

(square miles)

1 North Fork Guadalupe River -- 08165300 23 169

2 Guadalupe River—North Fork to Hunt 08165300 08165500 5.9 288

3 Johnson Creek -- 08166000 20 114

4 Guadalupe River—Hunt to Bear Creek 08165500 08166140 8.1 494

5 Guadalupe River—Bear Creek to Kerrville 08166140 08166200 2.3 510

6 Guadalupe River—Kerrville to Comfort 08166200 08167000 24 839

7 Guadalupe River—Comfort to Spring Branch 08167000 08167500 63 1,315

8 Canyon Lake 08167500 08167800 -- 1,436

9 Guadalupe River—Sattler to above Comal River 08167800 08168500 15 1,518

10 Comal River -- 08169000 -- 130

11 Upper Blanco River -- 08171000 60 355

12 Blanco River—Wimberley to Kyle 08171000 08171300 17 412

13 Upper San Marcos River -- 08170500 2.6 49

14 San Marcos River—Kyle to Luling 08170500 08172000 42 838

15 Upper Plum Creek -- 08172400 22 112

16 Plum Creek—Lockhart to Luling 08172400 08173000 23 309

17 Lower San Marcos River 08172000 -- 35 1,358

18 Guadalupe River—above Comal River to Gonzales 08168500 08173900 109 3,490

19 Peach Creek -- 08174600 46 460

20 Sandies Creek -- 08175000 55 549

21 Guadalupe River—Gonzales to Cuero 08173900 08175800 67 4,934

22 Guadalupe River—Cuero to Victoria 08175800 08176500 53 5,198

23 Upper Coleto Creek -- 08176900 36 357

24 Perdido Creek -- 08177300 8.4 28

25 Coleto Creek Reservoir 08176900 08177500 -- 514

26 Guadalupe River—Victoria to Bloomington 08176500 08177520 24 5,816

27 Guadalupe River—Bloomington to San Antonio River 08177520 -- 22 5,974
6 Streamflow Conditions in the Guadalupe River Basin, South-Central Texas, Water Years 1987–2006

Table 3. Daily streamflow statistics for selected U.S. Geological Survey streamflow-gaging stations, Guadalupe River Basin, southcentral Texas.

[ft3/s, cubic feet per second; --, not applicable]

A. Statistics for available period of record

Station name

Station 

number

(fig. 1)

Available 

record 

(water 

years)

Drainage area 

(square 

miles)

Daily mean 

streamflow 

(cubic feet 

per second)

20-Percent 

exceedance 

streamflow

(cubic feet 

per second)

50-Percent 

exceedance 

streamflow

(cubic feet 

per second)

80-Percent 

exceedance 

streamflow

(cubic feet 

per second)

90-Percent 

exceedance 

streamflow

(cubic feet 

per second)

North Fork Guadalupe River near 

Hunt, Tex.

08165300 1968–2006 169 41 37 24 18 15

Guadalupe River at Hunt, Tex. 08165500 1966–2006 288 79 74 49 35 29

Johnson Creek near Ingram, Tex. 08166000 1942–59, 

1961–93, 

1999–2006 

114 26 28 15 8.6 6.0

Guadalupe River above Bear 

Creek at Kerrville, Tex.

08166140 1979–86, 

1999–2006 

494 113 143 92 60 45

Guadalupe River at Kerrville, 

Tex.

08166200 1987–2006 510 152 156 96 62 49

Guadalupe River at Comfort, Tex. 08167000 1940–2006 839 229 245 115 50 28

Guadalupe River near Spring 

Branch, Tex.

08167500 1923–2006 1,315 373 417 159 61 35

Guadalupe River at Sattler, Tex. 08167800 1961–2006 1,436 487 646 215 101 72

Hueco Springs near New Braunfels, Tex.08168000 1945–2006 -- 42 78 35 6.8 .7

Guadalupe River above Comal 

River at New Braunfels, Tex.

08168500 1929–2006 1,518 491 659 233 91 51

Comal Springs at New Braunfels, 

Tex.

08168710 1929–2006 -- 290 356 305 226 177

Comal River at New Braunfels, 

Tex.

08169000 1929–2006 130 303 360 308 226 180

San Marcos Springs at San Marcos, Tex.08170000 1957–2006 -- 175 222 162 120 105

San Marcos River at San Marcos, 

Tex.

08170500 1995–2006 49 196 260 179 120 108

Blanco River at Wimberley, Tex. 08171000 1929–2006 355 145 165 56 21 13

Blanco River near Kyle, Tex. 08171300 1957–2006 412 167 200 52 16 2.0

San Marcos River at Luling, Tex. 08172000 1940–2006 838 415 482 212 118 93

Plum Creek at Lockhart, Tex. 08172400 1960–2006 112 49 17 .82 0 0

Plum Creek near Luling, Tex. 08173000 1931–2006 309 114 40 9.7 3.4 1.7

Guadalupe River at Gonzales, 

Tex.

08173900 1997–2006 3,490 2,120 2,580 1,090 591 454

Peach Creek below Dilworth, 

Tex.

08174600 1960–2006 460 170 39 5.7 1.0 0

Sandies Creek near Westhoff, 

Tex.

08175000 1960–2006 549 140 34 9.8 3.5 1.8

Guadalupe River at Cuero, Tex. 08175800 1965–2006 4,934 2,153 2,270 1,110 635 484

Guadalupe River at Victoria, Tex. 08176500 1935–2006 5,198 1,980 2,140 1,020 564 375

Coleto Creek near Schroeder, 

Tex.

08176900 1979–2006 357 84 37 12 3.1 .93

Perdido Creek near Fannin, Tex. 08177300 1979–2006 28 6.8 .82 .33 .11 .01

Coleto Creek near Victoria, Tex. 08177500 1979–2006 514 115 10 5.1 2.8 2.0
Streamflow Conditions 7

Table 3. Daily streamflow statistics for selected U.S. Geological Survey streamflow-gaging stations, Guadalupe River Basin, southcentral Texas—Continued.

B. Statistics for water years 1987–2006 

Station name

Station 

number

(fig. 1)

Available 

record 

(water 

years)

Drainage 

area 

(square 

miles)

Daily mean 

streamflow 

(cubic 

feet per 

second)

20-Percent 

exceedance 

streamflow

(cubic feet 

per second)

50-Percent 

exceedance 

streamflow

(cubic feet 

per second)

80-Percent 

exceedance 

streamflow

(cubic feet 

per second)

90-Percent 

exceedance 

streamflow

(cubic feet 

per second)

North Fork Guadalupe River 

near Hunt, Tex.

08165300 1987–2006 169 41 40 26 19 16

Guadalupe River at Hunt, Tex. 08165500 1987–2006 288 82 80 53 36 30

Johnson Creek near Ingram, Tex. 08166000 1

1987–93, 

1999–2006

114 37 40 26 19 16

Guadalupe River above Bear 

Creek at Kerrville, Tex.

08166140 1

1999–2006 494 143 156 100 69 57

Guadalupe River at Kerrville, 

Tex.

08166200 1987–2006 510 152 156 96 62 49

Guadalupe River at Comfort, 

Tex.

08167000 1987–2006 839 323 340 158 86 62

Guadalupe River near Spring 

Branch, Tex.

08167500 1987–2006 1,315 565 599 224 109 78

Guadalupe River at Sattler, Tex. 08167800 1987–2006 1,436 612 607 216 115 99

Hueco Springs near New Braunfels, Tex.08168000 1987–2006 -- 49 83 43 14 6.8

Guadalupe River above Comal 

River at New Braunfels, Tex.

08168500 1987–2006 1,518 708 782 298 141 111

Comal Springs at New Braunfels, Tex.08168710 1987–2006 -- 307 382 317 229 186

Comal River at New Braunfels, 

Tex.

08169000 1987–2006 130 327 388 320 230 187

San Marcos Springs at San 

Marcos, Tex.

08170000 1987–2006 -- 189 246 174 118 108

San Marcos River at San Marcos, Tex.08170500 1995–2006 47 196 260 179 120 108

Blanco River at Wimberley, Tex. 08171000 1987–2006 355 202 216 74 32 21

Blanco River near Kyle, Tex. 08171300 1987–2006 412 197 211 52 12 0

San Marcos River at Luling, Tex. 08172000 1987–2006 838 524 597 244 125 106

Plum Creek at Lockhart, Tex. 08172400 1987–2006 112 52 17 .44 0 0

Plum Creek near Luling, Tex. 08173000 1

1987–93, 

2001–06

309 170 67 13 4.8 2.8

Guadalupe River at Gonzales, 

Tex.

08173900 1

1997–2006 3,490 1,900 2,170 964 542 426

Peach Creek below Dilworth, 

Tex.

08174600 2001–06 460 167 46 6.0 1.7 1.3

Sandies Creek near Westhoff, 

Tex.

08175000 1987–2006 549 150 38 9.1 3.1 1.8

Guadalupe River at Cuero, Tex. 08175800 1987–2006 4,934 2,370 2,510 1,090 594 464

Guadalupe River at Victoria, 

Tex.

08176500 1987–2006 5,198 2,500 2,680 1,160 617 485

Coleto Creek near Schroeder, 

Tex.

08176900 1987–2006 357 87 34 8.3 1.8 .40

Perdido Creek near Fannin, Tex. 08177300 1987–2006 28 7.7 .56 .23 0 0

Coleto Creek near Victoria, Tex. 08177500 1987–2006 514 120 7.6 4.8 2.3 1.8

1

 Missing record estimated by regression to calculate statistics for 1987–2006 period.
8 Streamflow Conditions in the Guadalupe River Basin, South-Central Texas, Water Years 1987–2006

GRB. This period was used for long-term mean streamflow 

analyses. Statistics for the available period of record for each 

gaging station are provided for reference and for comparison 

with statistics for water years 1987–2006. 

Daily values from USGS gaging stations used for analysis were obtained from the USGS National Water Information 

System (NWISWeb) (U.S. Geological Survey, 2008). These 

data were collected by the USGS in cooperation with Federal, State, and local agencies, including U.S. Army Corps 

of Engineers, Texas Water Development Board, GuadalupeBlanco River Authority, Upper Guadalupe River Authority, 

and Edwards Aquifer Authority. Accuracy of the streamflow 

records varies in time and by station. Overall, the accuracy of 

the records is considered “good” (excluding estimated values, 

95 percent of the daily streamflows are within 10 percent of 

their true values) (U.S. Geological Survey, 2007). 

Several stations have periods of missing record because 

of discontinuous station operation. Statistics in table 3A were 

computed using only available data. For several stations with 

missing record during water years 1987–2006, statistics in 

table 3B were computed by including estimates of missing record during the 20-year period. These estimates were 

calculated by simple linear regression2

 with data from nearby 

stations, as indicated in the table above. 

The most critical missing record was for station 

08173900 Guadalupe River at Gonzales. This station was 

installed in 1996 and therefore had no record during water 

years 1987–1996. The station is the endpoint for reach 18, 

which is the longest reach in the study area at 109 river miles. 

Reach 18 also includes inflow from the San Marcos River 

2

 The model for simple linear regression is yi = bo + b1xi (Helsel and Hirsch, 

1992, p. 222) where yi is the estimate of missing streamflow on the ith day, 

b0 and b1 are coefficients, and xi is observed daily mean streamflow from a 

nearby station on the ith day, or the sum of observed daily mean streamflows 

from two or more stations.

(reach 17). Without station 08173900, the length of reach 18 

would have been increased to about 176 river miles. 

For stations with periods of record beginning before 

approximately 1950, statistics for the water year 1987–2006 

period generally indicate greater streamflow than statistics 

for the entire periods of record. Two major factors contribute 

to this: First, the historic drought of the 1950s (Bomar, 1995) 

resulted in several years of much-below-normal streamflow. 

Second, the construction of Canyon Dam and Lake in the early 

1960s affected streamflow on the Guadalupe River downstream from New Braunfels. As an example of the effect of the 

1950s drought, mean annual streamflow at station 08167000 

Guadalupe River at Comfort (upstream from Canyon Lake) 

was 323 cubic feet per second during water years 1987–2006. 

However, during 1940–2006, the mean annual streamflow 

was 229 cubic feet per second (about 29 percent less). Comal 

Springs stopped flowing during June–October 1956. During 

the same period, the Guadalupe River from Comfort to New 

Braunfels flowed intermittently. San Marcos Springs reached 

a historical minimum daily mean flow of 46 cubic feet per 

second on August 15, 1956. Streamflow at station 08176500 

Guadalupe River at Victoria was sustained by San Marcos 

Springs and reached a historical minimum daily mean flow of 

14 cubic feet per second on August 20, 1956.

Reported Within-Reach Discharges and 

Withdrawals

Reported (TCEQ permitted), within-reach discharge and 

withdrawal data were obtained from TCEQ. Discharge data 

for 1992–2006 were obtained in the form of monthly totals 

(Robert Organ, Texas Commission on Environmental Quality, 

written commun., 2007). Withdrawal data for 1991–2006 

also were in the form of monthly totals (Ceasar Alvarado, 

Texas Commission on Environmental Quality, written 

Stations with missing record during water years 1987–2006 and stations used in regressions to calculate missing record, Guadalupe 

River Basin, south-central Texas.

Station with missing record Station or stations from which daily mean streamflow 

or sum of daily mean streamflows obtained 

Coefficient of 

determination

08173900, Guadalupe River at Gonzales, Tex. 08168500, Guadalupe River above Comal River at New 

Braunfels, Tex. .96

08169000, Comal River at New Braunfels, Tex.

08172000, San Marcos River at Luling, Tex.

08175800, Guadalupe River at Cuero, Tex.

08166000, Johnson Creek near Ingram, Tex. 08166200, Guadalupe River at Kerrville, Tex. .76

08166140, Guadalupe River above Bear Creek at 

Kerrville, Tex. 08166200, Guadalupe River at Kerrville, Tex. .95

08165500, Guadalupe River at Hunt, Tex.

08173000, Plum Creek near Luling, Tex. 08172400, Plum Creek at Lockhart, Tex. .80
Streamflow Conditions 9

commun., 2007). For both datasets, average monthly totals for 

available periods were used to estimate averages for the entire 

1987–2006 period. For the short-term analysis periods, the 

reported monthly discharge and withdrawal totals were used, 

if available. If totals for a particular monthly period were not 

available, the average monthly inflow and outflow were used 

for the analysis. 

Analyses of Streamflow Conditions for Water 

Years 1987–2006

For each stream reach listed in table 2, computations 

were done to obtain the following streamflow conditions, as 

summarized in table 4:

•	 Average streamflow at upstream and downstream gaging stations

•	 Average measured within-reach inflow from tributaries 

and major springs

•	 Average total within-reach gain or loss of streamflow, 

defined as the difference between average streamflow 

at the downstream station and average streamflow at 

the upstream station

•	 Average reported within-reach discharge inflow

•	 Average reported within-reach withdrawal

•	 Average adjusted within-reach gain/loss of streamflow, 

defined as the average total gain (or loss) plus average 

reported withdrawal minus average measured tributary 

and springs inflow minus average reported discharge 

inflow. This component also includes the sum of 

unmeasured or unreported streamflow components 

entering or exiting the reach. Such components include 

intervening runoff, evaporation, streamflow infiltration 

losses, unreported discharges and withdrawals, and 

streamflow-gaging measurement error. 

•	 Cumulative average reported discharge inflow and 

withdrawal upstream from the reach outlet. These components represent, for each stream reach, the sum of 

all reported inflows and outflows upstream from, and 

including, those in the given reach. So, the cumulative 

inflows and outflows at lowermost reach 27 (Guadalupe River—Bloomington to San Antonio River) would 

represent the sum of reported discharge inflows and 

withdrawals for the entire study area.

•	 Cumulative average springflow from major springs 

upstream from, and including, those in the given reach.

•	 Average sum of inflows to each reach. The sum of 

inflows to the reach is an estimate of the total flow 

entering the river system within, and upstream from, 

the given reach. Inflows are quantified (measured or 

estimated) as they enter the river system. For example, 

measured releases from Canyon Lake enter the Guadalupe River in reach 9 and are considered inflows 

to all reaches of the river including and downstream 

from reach 9 (18, 21, 22, 26, and 27). Other inflows 

include springflows, gaged tributary inflows, reported 

discharges, and intervening runoff and base flow. 

Intervening runoff and base flow were estimated as the 

adjusted gain/loss in the reach.

•	 Ratio of springflow from major springs (Comal, San 

Marcos, and Hueco) to the sum of inflows to the reach, 

expressed as a percentage (for reaches of the Comal 

River and San Marcos River that include springflows 

from major springs, and the Guadalupe River reaches 

downstream from Canyon Dam). The ratio of springflow to the sum of inflows to the reach is an estimate 

of the contribution of flow from major springs to 

streamflow:

Contribution of springs 

 to streamflow 

 

=

∑

Discharge

Inflows

springs

source

, (1)

where 

Dischargesprings = total springflow of major springs, measured 

at the spring source, and

Inflowssource = sum of all inflows (measured at the source 

of inflow to the river system) entering the 

reach of interest. 

The contribution of springs to streamflow can be computed in other ways. Another way to estimate the contribution 

of springflow from major springs to streamflow is to compare springflow, after adjusting for losses (from withdrawals, 

evaporation, seepage) during travel downstream, to streamflow 

measured at the downstream point of interest:

Contribution of 

 springs to = Discharge - Losses

Q

springs springflow

reach

, (2)

 streamflow 

where 

Dischargesprings = total springflow of major springs, 

measured at the spring source;

Lossesspringflow = losses to springflow (from evaporation, 

seepage, or withdrawals) as springflow 

travels downstream to the reach of 

interest; and 

Qreach = measured streamflow in the reach of 

interest. 

Equation 1 involves values of streamflow components 

measured or estimated at the point where they enter the river 

system. Equation 2 involves values of streamflow components 

measured or estimated at the reach of interest. The advantage 

of equation 2 is that the denominator is obtained from measured streamflow. The difficulty with equation 2 is determining, or estimating, losses from springflow as it travels downstream. Also, springflows from the major springs originate 

from three locations and are subject to varying losses under 

different conditions. Given the difficulties associated with 

computing losses to springflow, estimates of the contribution 

of springflow to streamflow were computed using equation 1. 
10 Streamflow Conditions in the Guadalupe River Basin, South-Central Texas, Water Years 1987–2006

Table 4. Summary of average streamflow conditions for 1987–2006 by stream reach, Guadalupe River Basin, south-central Texas. 

[In cubic feet per second except as indicated; --, not applicable;]

Reach number (fig. 1) 

and name

Stream 

length 

(miles)

Average 

streamflow 

at upstream 

gage, or 

reach inlet1

Average measured 

within-reach 

tributary and major 

spring inflow2

Average 

streamflow at 

downstream 

gage, or reach 

outlet3

Average total 

within-reach 

gain/loss4

 1 North Fork Guadalupe River 23 -- -- 41 41

 2 Guadalupe River—North Fork to Hunt 5.9 41 -- 82 41

 3 Johnson Creek 20 -- -- 37 37

 4 Guadalupe River—Hunt to Bear Creek 8.1 82 37 143 61

 5 Guadalupe River—Bear Creek to Kerrville 2.3 143 -- 152 9

 6 Guadalupe River—Kerrville to Comfort 24 152 -- 323 171

 7 Guadalupe River—Comfort to Spring Branch 63 323 -- 565 242

 8 Canyon Lake -- 565 21 612 47

 9 Guadalupe River—Sattler to above Comal River 15 612 49 708 96

10 Comal River -- -- 307 327 327

11 Upper Blanco River 60 -- -- 202 202

12 Blanco River—Wimberley to Kyle 17 202 -- 197 -5

13 Upper San Marcos River 2.6 -- 189 196 196

14 San Marcos River—Kyle to Luling 42 196 197 524 328

15 Upper Plum Creek 22 -- -- 52 52

16 Plum Creek—Lockhart to Luling 23 52 -- 170 118

17 Lower San Marcos River 35 524 170 817 293

18 Guadalupe River—above Comal River to Gonzales 109 708 1,140 1,900 1,190

19 Peach Creek 46 -- -- 167 167

20 Sandies Creek 55 -- -- 150 150

21 Guadalupe River—Gonzales to Cuero 67 1,900 317 2,370 470

22 Guadalupe River—Cuero to Victoria 53 2,370 -- 2,500 130

23 Upper Coleto Creek 36 -- -- 87 87

24 Perdido Creek 8.4 -- -- 10 10

25 Coleto Creek Reservoir -- 87 10 120 33

26 Guadalupe River—Victoria to Bloomington 24 2,500 120 2,680 180

27 Guadalupe River—Bloomington to San Antonio River 22 2,680 -- 2,780 100

1

 Upstream streamflow for reach 27 estimated as (streamflow at downstream outlet of reach 26) + (estimated adjusted within-reach gain/loss) + (reported 

discharges) – (reported withdrawals).

2

 Average within-reach tributary inflows to reach 8, Canyon Lake, also include estimates of ungaged runoff, direct rainfall on lake surface, and evaporative 

losses; average within-reach tributary inflow to reach 8 computed as (estimated ungaged runoff) + (direct rainfall) – (evaporative losses).

3

 Downstream streamflows for reaches 17, 26, and 27 estimated as (streamflow at upstream gaging station) + (within-reach tributary inflow) + (estimated 

adjusted gain/loss) + (reported discharges) – (reported withdrawals). 
Streamflow Conditions 11

Reach 

number 

(fig. 1)

Average 

reported 

within-reach 

discharge 

inflow

Average 

reported 

within-reach 

withdrawal 

Average 

adjusted 

within-reach 

gain/loss5

Cumulative 

average reported 

discharge 

upstream from 

reach outlet

Cumulative 

average reported 

withdrawal 

upstream from 

reach outlet

Cumulative 

average 

springflow 

from major 

springs

Average 

sum of 

inflows to 

reach6

Ratio of 

springflow to 

sum of inflows 

to reach

(percent)

1 0 0.4 41 0 0.4 -- 41 --

2 0 .9 42 0 1.3 -- 83 --

3 0 .7 38 0 .7 -- 38 --

4 0 .05 24 0 2 -- 145 --

5 0 8.6 18 0 11 -- 163 --

6 0 3.7 175 0 14 -- 338 --

7 0 3.6 246 0 18 -- 584 --

8 .1 21 68 .1 39 -- 652 --

9 .4 .2 47 .5 39 49 708 6.9

10 0 0 20 0 0 307 327 94

11 .2 .5 202 .2 .5 -- 202 --

12 0 0 -5 .2 0 -- 202 --

13 0 0 7 0 0 189 196 96

14 5.2 13 139 5.4 13 189 542 35

15 .5 .02 52 .5 .02 -- 52 --

16 1.9 .1 116 2.4 .1 -- 170 --

17 0 .7 124 7.8 14 189 836 23

18 11 39 78 19 92 545 2,000 27

19 .2 .2 167 .2 .2 -- 167 --

20 .3 0 150 .3 0 -- 150 --

21 1.5 1.5 153 21 94 545 2,470 22

22 43 53 140 64 147 545 2,660 20

23 0 0 87 0 0 -- 87 --

24 0 0 10 0 0 -- 10 --

25 0 19 42 0 19 -- 149 --

26 65 83 74 129 249 545 2,940 19

27 0 14 112 129 263 545 3,060 18

4

 Total within-reach gain/loss = (average downstream streamflow) – (average upstream streamflow).

5

 Adjusted gain/loss = (total gain/loss) + (reported within-reach withdrawals) – (tributary and major spring inflows) – (within-reach discharges).

6

 Average sum of inflows to reach = (sum of inflows from entering upstream and tributary reaches, except for reach 9 which only includes streamflow entering 

from upstream reach 8) + (springflow originating within reach, for reaches 9, 10, and 13 only) + (average adjusted within-reach gain/loss) + (reported withinreach discharges).
12 Streamflow Conditions in the Guadalupe River Basin, South-Central Texas, Water Years 1987–2006

For 1987–2006, total and adjusted within-reach gain/loss 

in 26 of 27 reaches is positive—the reaches gained streamflow 

(table 4). Most of the 26 gaining reaches incurred substantial 

gains, likely because of intervening runoff and base flow. 

Reach 12 (Blanco River—Wimberley to Kyle) lost streamflow, 

about 2.5 percent of inflow at the upstream reach boundary. 

Losses in this reach are attributed to infiltration to the Edwards 

aquifer recharge zone (outcrop) (Puente, 1978). Results of 

gain/loss studies by Slade and others (2002) also indicate 

losses to streamflow in reach 12. 

The ratio of springflow from the major springs to the 

sum of inflows for the first reach that includes inflow from 

all three major springs, reach 18 (Guadalupe River—above 

Comal River to Gonzales) is 27 percent. At the lowermost 

downstream reach, 27 (Guadalupe River—Bloomington to 

San Antonio River), the percentage of streamflow attributed 

to springflow is reduced to 18 percent because of the effects 

of tributary inflows (intervening reaches 19, 20, and 25) and 

reported discharges (intervening reaches 22 and 26). 

Flow from Comal Springs into reach 10 (Comal River) 

accounted for about 94 percent of the total inflow to that reach 

during 1987–2006. Flow from San Marcos Springs into reach 

13 (upper San Marcos River) accounted for 96 percent of the 

inflow to reach 13. San Marcos Springs flow was reduced to 

35 percent of the inflow to reach 14 (San Marcos River—Kyle 

to Luling) because of intervening inflow from the Blanco 

River. The contribution of San Marcos Springs to the inflow 

to reach 17 (lower San Marcos River) was further reduced to 

about 23 percent because of the intervening inflow from Plum 

Creek in that reach. Hueco Springs flows into reach 9 (Guadalupe River—Sattler to above Comal River) and contributed 

about 6.9 percent of the inflow to that reach. 

For reach 27, the most downstream reach, cumulative 

average reported discharges accounted for 129 cubic feet 

per second, compared with average sum of inflows of 3,060 

cubic feet per second during 1987–2006; cumulative average 

reported withdrawals were 263 cubic feet per second. Most 

of the reported discharges and withdrawals occur in reach 22 

(Guadalupe River—Cuero to Victoria) and reach 26 (Guadalupe River—Victoria to Bloomington). Additional major 

withdrawals from the Guadalupe River occur downstream 

from reach 27, outside the study area. 

Releases from Canyon Lake (reach 8) averaged 612 cubic 

feet per second during 1987–2006. Compared with cumulative average springflow from major springs (545 cubic feet per 

second) in reach 18 (Guadalupe River—above Comal River 

to Gonzales), Canyon Lake releases (streamflow at outlet of 

reach 8) accounted for a slightly higher percentage of streamflow at downstream reaches. At reach 27, the ratio of Canyon 

Lake releases to average sum of inflows was 20 percent, compared with the ratio of springflow to average sum of inflows of 

18 percent.

Analyses of Streamflow Conditions for Selected 

Short-Term Periods

Analyses similar to those done for 1987–2006 were 

done for four short-term periods: January 1999, August 1999, 

August 2000, and August 2006. These periods were selected 

to represent a variety of relatively steady-state flow conditions, 

including low-flow periods. These analyses provide additional 

understanding of streamflow gains and losses and contributions of springflows to streamflows in the GRB during steadystate and low-flow periods. 

Table 5 shows average springflows at the three major 

springs for the four monthly base-flow periods compared with 

long-term springflow statistics. January 1999 represents a 

Table 5. Average springflows at major springs for selected short-term periods compared with long-term flow statistics, Guadalupe 

River Basin, south-central Texas.

[In cubic feet per second; --, not applicable]

Analysis period Comal Springs San Marcos Springs Hueco Springs Total springs

Short-term analysis period

January 1999 415 312 79 806

August 1999 318 147 25 490

August 2000 177 124 7.7 309

August 2006 213 99 6.0 318

Long-term statistical period 1929–2006 1957–2006 1944–2006 --

Mean 290 175 42 --

20-percent exceedance 356 222 78 --

50-percent exceedance (median) 305 162 35 --

80-percent exceedance 226 120 6.8 --

90-percent exceedance 177 105 .7 --
Streamflow Conditions 13

period when flows from all springs were greater than longterm median springflows. Streamflows upstream from Canyon 

Lake generally were near or greater than median streamflows. 

Streamflows downstream from Canyon Lake, including those 

of tributaries, generally were greater than median streamflows. 

During August 1999 springflow at Comal Springs was 

slightly greater than the long-term median, and flows at San 

Marcos and Hueco Springs were less than their respective 

medians. In August 1999, most streamflows throughout the 

GRB were less than median 1987–2006 streamflows. During 

August 2000 springflows at all springs were low—at or near 

the long-term 90-percent exceedance values. Streamflows 

throughout the GRB also were relatively low. As an example, 

average streamflow at station 08176500 Guadalupe River at 

Victoria was 290 cubic feet per second compared with the 

90-percent exceedance flow of 485 cubic feet per second. 

During August 2006, total springflow was about the same as 

in August 2000, although the distribution of springflow among 

the springs was different. Comal Springs flow was higher in 

August 2006 than in August 2000, whereas Hueco and San 

Marcos Springs flows were lower in August 2006 than in 

August 2000. During August 2006, streamflows throughout 

the GRB were similar to those of August 2000, generally near 

or below 90-percent exceedance values. 

Similar to the 1987–2006 analyses, computations were 

done for each of the short-term periods to obtain the following 

streamflow conditions, as summarized in table 6:

•	 Average streamflow at upstream and downstream gaging stations

•	 Average measured within-reach inflow from tributaries 

and major springs

•	 Total within-reach gain or loss of streamflow, defined 

as the difference between average streamflow at the 

downstream station and average streamflow at the 

upstream station

•	 Reported within-reach discharge inflow

•	 Reported within-reach withdrawal

•	 Adjusted within-reach gain or loss of streamflow, 

defined as the total gain (or loss) plus reported withdrawal minus measured tributary and springs inflow 

minus reported discharge inflow 

•	 Cumulative reported discharge inflow and withdrawal 

upstream from the reach outlet. These components represent, for each stream reach, the sum of all reported 

inflows and outflows upstream from, and including, 

those in the given reach 

•	 Cumulative average springflow from major springs 

upstream from, and including, the given reach

•	 Sum of inflows to each reach. 

•	 Ratio of springflow from major springs (Comal, San 

Marcos, and Hueco) to the sum of inflows to the reach, 

expressed as a percentage (for reaches of the Comal 

River and San Marcos River that include springflows 

from major springs, and the Guadalupe River reaches 

downstream from Canyon Dam). 

During January 1999, streamflow increased for most 

reaches for which gain/loss computations could be made 

(table 6); streamflow decreased in reaches 12 and 25 (indicated either by negative values of average within-reach gain/

loss or by negative values of adjusted within-reach gain/loss). 

During August 1999, streamflow decreased in four reaches (5, 

9, 12, and 15). During the short-term period with the lowest streamflows, August 2000, streamflow decreased in nine 

reaches (4, 5, 6, 7, 9, 12, 14, 15, and 18). Streamflow in 11 

reaches decreased during one or more of the four short-term 

periods. Only in reach 12 did streamflow decrease in all four 

periods. Gains and losses for reach 8, Canyon Lake, and reach 

25, Coleto Creek Reservoir, are affected by reservoir operations and do not take into account storage conditions in the 

reservoir; gain/loss computations only reflect the difference 

between inflows and outflows measured at gaging stations. 

Although inflow exceeded outflow for the Canyon Lake reach 

during each short-term period, storage in the reservoir might 

actually have decreased. 

During the four short-term periods, springflow from 

Hueco Springs accounted for 11–16 percent of the sum of 

inflows in reach 9 (Guadalupe River—Sattler to above Comal 

River). Flow from Comal Springs accounted for all inflows 

in reach 10 (Comal River). In reach 13 (upper San Marcos 

River), flow from San Marcos Springs accounted for all 

inflows during the short-term periods. Downstream in reach 14 

(San Marcos River—Kyle to Luling), springflow was 60–87 

percent of inflows. In the next downstream reach, reach 17 

(lower San Marcos River), springflow was 52–85 percent of 

inflows during the four periods. 

Reach 18 (Guadalupe River—above Comal River to 

Gonzales) is the most upstream reach that includes flows from 

all three major springs. During August 2000 and August 2006 

(periods of relatively low flow), springflow accounted for 77 

and 78 percent, respectively, of inflows in that reach. These 

percentages are considerably greater than the 27 percent that 

springflow accounted for during 1987–2006 (table 4). Farther 

downstream, the contribution of springflow during August 

2000 and August 2006, as during 1987–2006, decreased 

because of tributary inflow and reported discharge inflows. At 

reach 26 (Guadalupe River—Victoria to Bloomington), springflow accounted for 57 and 56 percent of inflows, respectively, 

in August 2000 and August 2006 (table 6). At reach 27 (Guadalupe River—Bloomington to San Antonio River), springflow was 52 and 53 percent of inflows, respectively, during 

August 2000 and August 2006. The comparable percentage at 

reach 27 during 1987–2006 was 18 percent (table 4).

During the short-term periods, reported discharge inflows 

and withdrawals (table 6) were similar to average reported discharge inflows and withdrawals for 1987–2006 (table 4). However, during low-flow periods, discharge inflows and withdrawals account for substantially larger percentages of the sum 
14 Streamflow Conditions in the Guadalupe River Basin, South-Central Texas, Water Years 1987–2006

Table 6. Summary of streamflow conditions for selected short-term periods by stream reach, Guadalupe River Basin, south-central 

[In cubic feet per second except as indicated; --, not applicable or not available]

Reach number (fig. 1) 

and name

Analysis

period

Average 

streamflow 

at upstream 

gage, or 

reach inlet1

Average measured 

within-reach 

tributary and major 

spring inflow2

Average 

streamflow at 

downstream 

gage, or reach 

outlet3

Average 

total 

within-reach 

gain/loss4

 1 North Fork Guadalupe River January 1999 -- -- 24 24

August 1999 -- -- 23 23

August 2000 -- -- 13 13

August 2006 -- -- 13 13

 2 Guadalupe River—North Fork to Hunt January 1999 24 -- 55 31

August 1999 23 -- 39 16

August 2000 13 -- 20 7

August 2006 13 -- 19 6

3 Johnson Creek January 1999 -- -- 33 33

August 1999 -- -- 26 26

August 2000 -- -- 13 13

August 2006 -- -- 11 11

 4 Guadalupe River—Hunt to Bear Creek January 1999 55 33 -- --

August 1999 39 26 69 30

August 2000 20 13 32 12

August 2006 19 11 38 19

 5 Guadalupe River—Bear Creek to Kerrville January 1999 118 -- 121 3

August 1999 69 -- 63 -6

August 2000 32 -- 30 -2

August 2006 38 -- 24 -14

 6 Guadalupe River—Kerrville to Comfort January 1999 121 -- 192 71

August 1999 63 -- 71 8

August 2000 30 -- 23 -7

August 2006 24 -- 25 1

 7 Guadalupe River—Comfort to Spring Branch January 1999 192 -- 280 88

August 1999 71 -- 90 19

August 2000 23 -- 13 -10

August 2006 25 -- 17 -8

 8 Canyon Lake January 1999 280 -12 427 147

August 1999 90 -106 142 52

August 2000 13 -117 56 43

August 2006 17 -108 54 37

 9 Guadalupe River—Sattler to above Comal River January 1999 427 79 564 137

August 1999 142 25 160 18

August 2000 56 7.7 47 -9

August 2006 54 6.0 54 0

See footnotes at end of table.
Streamflow Conditions 15

Texas.

Reach 

number 

(fig. 1) 

Reported 

within-reach 

discharge 

inflow

Reported 

within-reach 

withdrawal

Adjusted 

within-reach 

gain/loss5

Cumulative 

reported 

discharge 

upstream from 

reach outlet

Cumulative 

reported 

withdrawal 

upstream from 

reach outlet

Cumulative 

average 

springflow 

from major 

springs

Sum of 

inflows 

to reach6

Ratio of 

springflow to 

sum of inflows 

to reach 

(percent)

1 0 0.4 24 0 0.4 -- 24 --

0 .5 24 0 .5 -- 24 --

0 .5 14 0 .5 -- 14 --

0 .4 13 0 .4 -- 13 --

2 0 .9 32 0 1.3 -- 56 --

0 1 17 0 1.5 -- 41 --

0 .9 8 0 1.4 -- 22 --

0 .9 7 0 1.3 -- 20 --

3 0 .6 34 0 .6 -- 34 --

0 1 27 0 1 -- 27 --

0 .7 14 0 .7 -- 14 --

0 .7 12 0 .7 -- 12 --

4 0 .04 -- 0 1.9 -- 92 --

0 .05 4 0 2.6 -- 72 --

0 .05 -1 0 2.2 -- 35 --

0 .05 8 0 2.1 -- 40 --

5 0 5.4 8 0 7 -- 100 --

0 6.3 0 0 9 -- 72 --

0 8.6 7 0 11 -- 42 --

0 4.1 -10 0 6 -- 40 --

6 0 3.4 74 0 11 -- 174 --

0 5.2 13 0 14 -- 85 --

0 4.4 -3 0 15 -- 42 --

0 3.9 5 0 10 -- 45 --

7 0 3.4 91 0 14 -- 266 --

0 3.6 23 0 18 -- 108 --

0 3.4 -7 0 19 -- 42 --

0 3.2 -5 0 13 -- 45 --

8 .05 5.8 165 .05 20 -- 431 --

.09 24 182 .09 42 -- 290 --

.09 21 181 .09 40 -- 222 --

.09 70 215 .09 83 -- 260 --

9 .3 .3 58 .4 20 79 564 14

.3 .3 -7 .4 42 25 160 16

.3 .3 -17 .4 39 7.7 47 16

.3 .3 -6 .4 83 6.0 54 11

See footnotes at end of table.
16 Streamflow Conditions in the Guadalupe River Basin, South-Central Texas, Water Years 1987–2006

Table 6. Summary of streamflow conditions for selected short-term periods by stream reach, Guadalupe River Basin, south-central 

Reach number (fig. 1) 

and name

Analysis

period

Average 

streamflow 

at upstream 

gage, or 

reach inlet1

Average measured 

within-reach 

tributary and 

major spring 

inflow2

Average 

streamflow at 

downstream 

gage, or 

reach outlet3

Average 

total 

within-reach 

gain/loss4

10 Comal River January 1999 -- 415 415 415

August 1999 -- 318 318 318

August 2000 -- 179 179 179

August 2006 -- 213 213 213

11 Upper Blanco River January 1999 -- -- 133 133

August 1999 -- -- 25 25

August 2000 -- -- 12 12

August 2006 -- -- 7.5 7.5

12 Blanco River—Wimberley to Kyle January 1999 133 -- 125 -8

August 1999 25 -- 3.2 -22

August 2000 12 -- 0 -12

August 2006 7.5 -- 0 -7.5

13 Upper San Marcos River January 1999 -- 312 312 312

August 1999 -- 147 147 147

August 2000 -- 124 124 124

August 2006 -- 99 99 99

14 San Marcos River—Kyle to Luling January 1999 125 312 496 371

August 1999 3.2 147 151 148

August 2000 0 124 104 104

August 2006 0 99 96 96

15 Upper Plum Creek January 1999 -- 0 12 12

August 1999 -- 0 0 0

August 2000 -- 0 0 0

August 2006 -- 0 0 0

16 Plum Creek—Lockhart to Luling January 1999 12 0 47 35

August 1999 0 0 1.8 1.8

August 2000 0 0 1.8 1.8

August 2006 0 0 1.8 1.8

17 Lower San Marcos River January 1999 496 47 577 82

August 1999 151 1.8 152 1

August 2000 104 1.8 104 0

August 2006 96 1.8 94 -2

18 Guadalupe River—above Comal River to Gonzales January 1999 564 993 1,950 1,390

August 1999 160 470 612 452

August 2000 47 283 242 195

August 2006 54 307 277 223

See footnotes at end of table.
Streamflow Conditions 17

Texas—Continued.

Reach 

number 

(fig. 1) 

Reported 

within-reach 

discharge 

inflow

Reported 

within-reach 

withdrawal

Adjusted 

within-reach 

gain/loss5

Cumulative 

reported 

discharge 

upstream from 

reach outlet

Cumulative

 reported 

withdrawal

upstream from 

reach outlet

Cumulative 

average 

springflow 

from major 

springs

Sum of 

inflows to 

reach6

Ratio of 

springflow to 

sum of inflows 

to reach 

(percent)

10 0 0 0 0 0 415 415 100

0 0 0 0 0 318 318 100

0 0 0 0 0 177 179 100

0 0 0 0 0 213 213 100

11 .2 .4 133 .2 .4 -- 133 --

.2 .5 25 .2 .5 -- 26 --

.2 .5 12 .2 .5 -- 113 --

.2 .5 8 .2 .5 -- 8.0 --

12 0 0 -8 .2 .4 -- 133 --

0 0 -22 .2 .5 -- 26 --

0 0 -12 .2 .5 -- 113 --

0 0 -8 .2 .5 -- 8.0 --

13 0 0 0 0 0 312 312 100

0 0 0 0 0 147 147 100

0 0 0 0 0 124 124 100

0 0 0 0 0 99 99 100

14 6.6 12 64 6.8 12 312 516 60

5.6 14 9 5.8 14 147 187 78

5.6 13 -13 5.8 14 124 142 87

5.9 13 4 6.1 14 99 99 85

15 .4 .02 12 .4 .02 -- 12 --

1.0 0 -1 1.0 0 -- 1.0 --

1.3 0 -1 1.3 0 -- 1.3 --

1.4 0 -1 1.4 0 -- 1.4 --

16 2.3 .1 33 2.7 .1 -- 48 --

1.2 .1 1 2.2 .1 -- 3.2 --

1.9 .1 0 3.2 .1 -- 3.2 --

1.9 .1 0 3.3 .1 -- 3.3 --

17 .8 1.6 35 10 14 312 600 52

.6 2.4 1 9 17 147 192 77

.7 2.2 0 10 16 124 146 85

.7 4.8 0 10 19 99 121 82

18 11 13 399 22 47 806 1,990 41

11 44 15 20 103 490 703 70

11 43 -56 21 98 309 400 77

11 39 -56 21 141 318 406 78

See footnotes at end of table.
18 Streamflow Conditions in the Guadalupe River Basin, South-Central Texas, Water Years 1987–2006

Table 6. Summary of streamflow conditions for selected short-term periods by stream reach, Guadalupe River Basin, south-central 

Reach number (fig. 1) 

and name

Analysis

period

Average 

streamflow 

at upstream 

gage, or 

reach inlet1

Average measured 

within-reach 

tributary and 

major spring 

inflow2

Average 

streamflow 

at downstream gage, 

or 

reach outlet3

Average 

total 

within-reach 

gain/loss4

19 Peach Creek January 1999 -- -- -- --

August 1999 -- -- -- --

August 2000 -- -- -- --

August 2006 -- -- 1.1 1.1

20 Sandies Creek January 1999 -- -- 43 43

August 1999 -- -- 4.2 4.2

August 2000 -- -- 1.5 1.5

August 2006 -- -- .2 .2

21 Guadalupe River—Gonzales to Cuero January 1999 1,950 43 2,180 230

August 1999 612 4.2 672 60

August 2000 242 1.5 282 40

August 2006 277 .2 288 11

22 Guadalupe River—Cuero to Victoria January 1999 2,180 -- 2,210 30

August 1999 672 -- 714 42

August 2000 282 -- 290 8

August 2006 288 -- 296 8

23 Upper Coleto Creek January 1999 -- 0 31 31

August 1999 -- 0 3.4 3.4

August 2000 -- 0 0 0

August 2006 -- 0 1.1 1.1

24 Perdido Creek January 1999 -- -- -- --

August 1999 -- -- -- --

August 2000 -- -- -- --

August 2006 -- -- -- --

25 Coleto Creek Reservoir January 1999 31 2.9 24 -7.0

August 1999 3.4 .3 4.6 1.2

August 2000 0 0 3.9 3.9

August 2006 1.1 0 4.5 3.4

26 Guadalupe River—Victoria to Bloomington January 1999 2,210 24 2,230 20

August 1999 714 4.6 723 9

August 2000 290 3.9 310 20

August 2006 296 4.5 308 12

27 Guadalupe River—Bloomington to San Antonio River January 1999 2,230 -- 2,240 10

August 1999 723 -- 743 20

August 2000 310 -- 347 37

August 2006 308 -- 333 25

1

 Upstream streamflow for reach 27 estimated as (streamflow at downstream outlet of reach 26) + (estimated adjusted within-reach gain/loss) + (reported 

discharges) – (reported withdrawals).

2

 Average within-reach tributary inflows to reach 8, Canyon Lake, also include estimates of ungaged runoff, direct rainfall on lake surface, and evaporative 

losses; average within-reach tributary inflow to reach 8 computed as (estimated ungaged runoff) + (direct rainfall) – (evaporative losses).

3 Downstream streamflows for reaches 17, 26, and 27 estimated as (streamflow at upstream gaging station) + (within-reach tributary inflow) + (estimated 

adjusted gain/loss) + (reported discharges) – (reported withdrawals).
Streamflow Conditions 19

Texas—Continued.

Reach 

number 

(fig. 1) 

Reported 

within-reach 

discharge 

inflow

Reported 

within-reach 

withdrawal

Adjusted 

within-reach 

gain/loss5

Cumulative reported discharge 

upstream from 

reach outlet

Cumulative 

reported 

withdrawals 

upstream from 

reach outlet

Cumulative 

average 

springflow 

from major 

springs

Sum of 

inflows 

to reach6

Ratio of 

springflow 

to sum of inflows to reach 

(percent)

19 0.1 0.2 -- 0.1 0.2 -- -- --

.1 .2 -- .1 .2 -- -- --

.1 .2 -- .1 .2 -- -- --

.2 .2 1 .2 .2 -- 1.2 --

20 .3 0 43 .3 0 -- 43 --

.3 0 4 .3 0 -- 4.3 --

.3 0 1 .3 0 -- 1.3 --

.3 0 0 .3 0 -- 0.3 --

21 2.3 .4 185 24 47 806 2,220 36

2.3 4.1 58 23 107 490 768 64

2.3 2.6 39 24 101 309 442 70

2.3 4.5 13 24 145 318 422 75

22 43 44 31 67 91 806 2,290 35

55 76 42 78 183 490 879 56

38 45 15 62 146 309 422 73

43 83 48 67 228 318 451 70

23 0 0 31 0 0 -- 31 --

0 0 3 0 0 -- 3.0 --

0 0 0 0 0 -- 0 --

0 0 1 0 0 -- 1.0 --

24 -- -- -- -- -- -- -- --

-- -- -- -- -- -- -- --

-- -- -- -- -- -- -- --

-- -- -- -- -- -- -- --

25 0 19 9 0 19 -- 40 --

0 19 20 0 19 -- 23 --

0 19 23 0 19 -- 23 --

0 19 22 0 19 -- 23 --

26 65 83 14 132 193 806 2,410 33

65 83 22 143 285 490 989 50

65 83 34 127 248 309 544 57

65 83 26 132 330 318 565 56

27 0 14 24 132 207 806 2,430 33

0 14 34 143 299 490 1,020 48

0 14 51 127 262 309 595 52

0 14 39 132 344 318 604 53

4

 Total within-reach gain/loss = (average downstream streamflow) – (average upstream streamflow).

5

 Adjusted gain/loss = (total gain/loss) + (reported within-reach withdrawals) – (tributary and major spring inflows) – (within-reach discharges).

6

 Sum of inflows to reach = (sum of inflows from entering upstream and tributary reaches, except for reach 9 which only includes streamflow entering 

from upstream reach 8) + (springflow originating within reach, for reaches 9, 10, and 13 only) + (adjusted within-reach gain/loss) + (reported within-reach 

discharges). 
20 Streamflow Conditions in the Guadalupe River Basin, South-Central Texas, Water Years 1987–2006

of inflows than those during 1987–2006. For example, during 

August 2006 (a low-flow period) combined reaches 22 and 

26 reported discharge inflows accounted for 24 percent of the 

sum of inflows to reach 22. During the same period, withdrawals from reaches 22 and 26 accounted for about 37 percent of 

the sum of inflows to reach 22. During 1987–2006 (table 4), 

combined reach 22 and 26 reported discharge inflows 

accounted for 4.0 percent of sum of inflows, and withdrawals 

accounted for 5.0 percent of sum of inflows to reach 22.

Similar to the computations indicating the contributions 

of springflow to the sum of inflows for selected short-term 

periods (table 6), contributions of releases from Canyon Lake 

(reach 8) to the sum of inflows were computed for selected 

reaches and are shown in table 7. Also shown for comparison 

are the ratios of springflow to the sum of inflows.

In contrast to Canyon Lake releases during 1987–2006 

(table 4), Canyon Lake releases during the short-term periods 

accounted for smaller percentages of the sum of inflows at 

downstream reaches than springflows (table 6). During the 

relatively low-flow periods August 2000 and August 2006 

for reach 27, the ratios of Canyon Lake releases to the sum of 

inflows were less than 10 percent. During those same periods, 

flow from major springs accounted for more than 50 percent 

of the sum of inflows for reach 27. During 1987–2006 for 

reach 27 (table 4), the ratio of Canyon Lake releases to the 

sum of inflows was 20 percent, and the ratio of springflow to 

the sum of inflows was 18 percent.

Summary

The U.S. Geological Survey, in cooperation with the 

Edwards Aquifer Authority, assessed available streamflow 

data in the Guadalupe River Basin (GRB) to determine streamflow gains and losses and the relative contribution of flow 

from major springs—Comal Springs, San Marcos Springs, and 

Hueco Springs—to streamflow in reaches of the Guadalupe 

River and its tributaries. The assessment is based primarily on 

long-term (20 years) and short-term (four 1-month base-flow 

periods) streamflow conditions. 

The GRB was divided into a network of 27 stream 

reaches (13 Guadalupe River and 14 tributary), defined mainly 

by the locations of USGS streamflow-gaging stations. For 

each reach, streamflow data from the upstream and downstream gaging stations and intervening discharges (inflows) 

and withdrawals (outflows) were compiled. Water-budget 

analyses were done for water years 1987–2006 and for four 

short-term, base-flow periods, January 1999, August 1999, 

August 2000, and August 2006. For each analysis period, 

the ratio of flow from the major springs (measured at the 

Table 7. Comparison of contributions of Canyon Lake releases and flow from major springs to streamflow in selected stream reaches 

for selected short-term periods, Guadalupe River Basin, south-central Texas. 

Reach number 

and name

Analysis

period

Average 

streamflow from 

Canyon Lake

(cubic feet 

per second)

Cumulative 

springflow from 

major springs

(cubic feet 

per second)

Sum of inflows 

to reach

(cubic feet 

per second)

Ratio of streamflow from Canyon 

Lake to sum of 

inflows to reach

(percent)

Ratio of 

springflow to

sum of inflows 

to reach

(percent)

18 Guadalupe River—

above Comal River to 

Gonzales

January 1999 427 806 1,990 21 41

August 1999 142 490 703 20 70

August 2000 56 309 400 14 77

August 2006 54 318 406 13 78

22 Guadalupe River—

Cuero to Victoria

January 1999 427 806 2,290 19 35

August 1999 142 490 879 16 56

August 2000 56 309 422 13 73

August 2006 54 318 451 12 70

26 Guadalupe River—

Victoria to Bloomington

January 1999 427 806 2,410 18 33

August 1999 142 490 989 14 50

August 2000 56 309 544 10 57

August 2006 54 318 565 9.6 56

27 Guadalupe River—

Bloomington to San 

Antonio River

January 1999 427 806 2,430 18 33

August 1999 142 490 1,020 14 48

August 2000 56 309 595 9.4 52

August 2006 54 318 604 8.9 53
References 21

spring source) to the sum of inflows (measured at the source 

of inflow to the river system) is computed for reaches of the 

Comal River and San Marcos River that include springflows 

from major springs, and for the Guadalupe River reaches 

downstream from Canyon Dam. The ratio of springflow to the 

sum of inflows to the reach is an estimate of the contribution 

of flow from major springs to streamflow.

For 1987–2006, 26 of the 27 reaches gained streamflow. 

Most of the 26 gaining reaches incurred substantial gains, 

likely because of intervening runoff and base flow. The ratio 

of springflow from the major springs to the sum of inflows 

for the most upstream reach that includes inflow from all 

three major springs, reach 18 (Guadalupe River—above 

Comal River to Gonzales) is 27 percent. At the lowermost 

downstream reach, 27 (Guadalupe River—Bloomington to 

San Antonio River), the percentage of the sum of inflows 

attributed to springflow is reduced to 18 percent because of 

the effects of tributary inflows (intervening reaches 19, 20, 

and 25) and reported (Texas Commission on Environmental 

Quality permitted), discharges (intervening reaches 22 and 

26). 

Compared with cumulative average springflow from 

major springs in reach 18, Canyon Lake releases (streamflow 

at outlet of reach 8) accounted for a slightly higher percentage 

of the sum of inflows at downstream reaches. At reach 27, the 

ratio of Canyon Lake releases to the sum of inflows was 20 

percent, compared with the ratio of springflow to the sum of 

inflows of 18 percent.

The four short-term periods were selected to represent 

a variety of relatively steady-state flow conditions, including 

low-flow periods. During August 2000 and August 2006 

(periods of relatively low flow), springflow in reach 18 

(Guadalupe River—above Comal River to Gonzales), the 

most upstream reach that includes inflow from all three 

major springs, accounted for 77 and 78 percent, respectively, 

of the sum of inflows in that reach. These percentages are 

considerably greater than the 27 percent that springflow 

accounted for during 1987–2006. Farther downstream, the 

contribution of springflow to the sum of inflows during August 

2000 and August 2006, as during 1987–2006, decreased 

because of tributary inflow and reported discharge inflows. 

At the most downstream reach, 27 (Guadalupe River—

Bloomington to San Antonio River), springflow was 52 and 

53 percent of the sum of inflows, respectively, during August 

2000 and August 2006 (compared with 18 percent during 

1987–2006). 

In contrast to Canyon Lake releases during 1987–2006, 

Canyon Lake releases during the short-term periods accounted 

for smaller percentages of the sum of inflows at downstream 

reaches than springflows. During the relatively low-flow 

periods August 2000 and August 2006 for reach 27, the ratios 

of Canyon Lake releases to the sum of inflows were less than 

10 percent (compared with 20 percent during 1987–2006). 

During those same periods, flow from major springs accounted 

for more than 50 percent of the sum of inflows for reach 27 

(compared with 18 percent during 1987–2006). 

References

Bomar, G.W., 1995, Texas weather (2d ed.): Austin, University 

of Texas Press, 275 p.

Brune, G., 1975, Major and historical springs of Texas: Texas 

Water Development Board Report 189, 91 p.

Guadalupe-Blanco River Authority, 2007a, Canyon Lake fact 

sheet: accessed October 10, 2007, at http://www.gbra.org/

Public/CanyonReservoir.aspx

Guadalupe-Blanco River Authority, 2007b, Coleto Creek 

Park and reservoir fact sheet: accessed October 10, 2007, at 

http://www.gbra.org/Recreation/ColetoCreek/Default.aspx

Heitmuller, F.T., and Reece, B.D., 2003, Database of historically documented springs and spring flow measurements in 

Texas: U.S. Geological Survey Open-File Report 03–315, 

1 CD.

Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods 

in water resources—Studies in environmental science 49: 

Amsterdam, Elsevier, 522 p. 

Larkin, T.J., and Bomar, G.W., 1983, Climatic atlas of Texas: 

Texas Department of Water Resources, Limited Printing 

Report LP–192, 151 p.

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

the Edwards aquifer in the San Antonio area, Texas: U.S. 

Geological Survey Water-Resources Investigations Report 

78–10, 34 p.

Slade, R.M., Jr., Bentley, J.T,, and Michaud, Dana, 2002, 

Results of streamflow gain-loss studies in Texas, with 

emphasis on gains from and losses to major and minor 

aquifers: U.S. Geological Survey Open-File Report 02–068, 

136 p., 2 plates.

U.S. Army Corps of Engineers, 2007, Fort Worth–Reservoir 

Control Section: accessed October 10, 2007, at http://www.

swf-wc.usace.army.mil/cgi-bin/rcshtml.pl 

U.S. Census Bureau, 2007, Texas state and county quick facts: 

accessed October 15, 2007, at http://quickfacts.census.gov/

qfd/states/48000.html 

U.S. Department of Commerce, National Oceanic and Atmospheric Administration, 2002, Climatography of the United 

States 81, Monthly station normals of temperature, precipitation, and heating and cooling degree days 1971–2000, 

Texas: Asheville, N.C., National Climatic Data Center, 

v. 41, 88 p.

U.S. Environmental Protection Agency, 2008, Watershed 

academy—Hydrology: accessed September 11, 2008, at 

http://www.epa.gov/owow/watershed/wacademy/wam/

hydrology.html 
22 Streamflow Conditions in the Guadalupe River Basin, South-Central Texas, Water Years 1987–2006

U.S. Geological Survey, 2007, Water-resources data for the 

United States, water year 2006: U.S. Geological Survey 

Water-Data Report WDR–US–2006, accessed January 4, 

2007, at http://wdr.water.usgs.gov/wy2006/search.jsp 

U.S. Geological Survey, 2008, National Water Information 

System (NWISWeb) [for Texas] data available on the World 

Wide Web at http://waterdata.usgs.gov/tx/nwis/nwis 

Publishing support provided by

Lafayette Publishing Service Center

Information regarding water resources in Texas is available at 

http://tx.usgs.gov/
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