y 

to enhance the accuracy of springflow data and identify previously unrecognized hydrologic patterns.

An accurate record of springflow at Barton Springs is important for several reasons. First, Barton Springs is the only know

for the Barton Springs salamander (Eurycea sosorum), a federally-listed endangered species that is dependent on reliabl

to survive. Determination of sustainable Edwards aquifer yields compatible with the survival of the species is impossible w

accurate springflow record. Second, the 3-acre swimming pool fed by Barton Springs is enjoyed by about 340,000 people 

(2003) and is an important tourist attraction. Third, Barton Springs provides a part of Austin's municipal water supply; wat

Barton Springs discharges into Town Lake on the Colorado River about 0.4 mile upstream from one of Austin's three wate

plants. Fourth, flow in Barton Springs reflects water levels in the Barton Springs segment of the Edwards aquifer, which c

(2005) is designated a sole-source aquifer by the U.S. Environmental Protection Agency.

 

This report, prepared by the U.S. Geological Survey, briefly summarizes the results of recent ADV-based velocity and spri

acquisition at Barton Springs and describes an application of velocity monitoring to enhance the accuracy of springflow d

Daily Mean Springflow

The U.S. Geological Survey (USGS), in cooperation with the 

City of Austin, has collected and published daily mean springflow 

for station 08155500 Barton Springs at Austin, Texas (Aragon 

Long and others, 2005), from March 1, 1978, to the present. A 

geographic overview of Barton Springs is shown in figure 1. The 

flow from Barton Springs is the combined flow of Eliza Spring, 

Old Mill Spring, and Main Spring. The flow of Upper Barton 

Spring is not included. Most of Barton Springs flow emerges from 

Main Spring, which is located within the Barton Springs swimming pool about mid-length along the south or right bank (figs. 1, 

2). The photograph in figure 2 shows the pool level down several 

feet for cleaning. Continuous monitoring of springflow at Barton 

Springs is important because the springs are a major discharge 

point of the Barton Springs segment of the Edwards aquifer. The 

springs serve as a major source of drinking water, recreation, and 

endangered species habitat in Central Texas.

The daily mean springflow data published by the USGS for 

station 08155500 represent the longest continuous record of 

water-quantity information available for Barton Springs. Historically, the daily mean springflow has been computed using the 

daily mean gage height derived from continuous 15-minute observations of gage height and a stage-discharge relation developed 

for the station. The stage-discharge relation is developed by using 

aquifer water levels measured near the spring orifice in a nearby 

monitoring well (YD 58–42–903) and manual discharge measurements of Barton Springs flow. The aquifer water levels are used 

(GOES). The data are relayed through various telecom

networks, delivered to a USGS National Water Inform

System (NWIS) server for processing through the sta

relation, and made available on USGS Internet server

time gage height, discharge, and other parameters can 

viewed at http://waterdata.usgs.gov/tx/nwis/uv/?site_

08155500&PARAmeter_cd=00065,00060. A graph o

height and springflow from April 1, 2004, to Septemb

is shown in figure 3. In general, larger springflow is a

with higher gage height. The periods in which the ass

ambiguous or even reversed are the subject of this rep

The specific stage-discharge relation for Barton Sp

empirically developed relation that transforms gage h

springflow for specific water levels of the swimming 

relation is routinely verified and refined through peri

ual) measurement of springflow. The relation represe

step in the process of computing daily mean springflo

2002).

The periodic manual measurement of springflow a

Springs requires three nearly contemporaneous disch

surements on and near Barton Creek: (1) discharge o

Creek below the downstream dam of the pool (fig. 1)

charge of Old Mill Spring, which also is downstream 

pool, and (3) discharge of Barton Creek at a site upst

the pool and downstream from Upper Barton Spring. 

(1) and (2) are added and discharge (3) is subtracted f

to yield the flow from Main, Eliza, and Old Mill Spri

collectively is referred to as Barton Springs flow and 

station 08155500.

About 200 periodic springflow measurements by t

since 1958 have provided data to develop a stage-disc

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact S
2

relation for normal pool (poolfull) levels. The definition of 

pool-full level is ambiguous 

and is known to change with 

historical pool operation. Water 

pressure proportional to the 

level of the pool, where most 

springflow emerges, has substantial influence on computed 

flow from Barton Springs. At 

both scheduled and unscheduled times, water levels in the 

pool are changed at the dam by 

pool staff or changed because 

of overtopping stormflow in 

unpredictable amounts as part 

of typical pool operation, 

maintenance, and Barton Creek 

stormflow accommodation. Complicating matters further, leakage 

to, or inflow from, the Barton Creek bypass culvert (fig. 1) also 

influences pool levels. Experience has shown that the stage-discharge relation “shifts,” which means that subtle changes in pool 

levels produce detectable changes, or shifts, in the stage-discharge 

relation. The shifts necessitate adjustments to the stage-discharge 

relation to maintain accuracy of the daily mean springflow record.

The sensitivity of the stage-discharge relation to pool level 

implies that periodic measurement of springflow always will be 

necessary to produce reliable springflow data. The sensitivity also 

implies that when unpredictable stormflows on Barton Creek are 

larger than the bypass can convey, which results in some of the 

stormflow passing through the pool, the stage-discharge relation is 

not applicable. Stormflow typically increases pool levels by several feet and sometimes in excess of 

10 ft for brief intervals. Furthermore, on 

a semi-regular basis, the pool is temporarily drawn down several feet for several hours to several days for cleaning 

and other maintenance activities, which 

often immediately follow stormflows. 

The stage-discharge relation is not 

applicable during these periods. During 

periods when the stage-discharge 

relation is not applicable, typically the 

two (valid) period-bounding daily mean 

springflow values are prorated by 

straight-line interpolation for each day 

of the period.

Velocity Data for Estimation 

of Daily Mean Springflow

Experimental velocity data (not 

reported here) collected by USGS divers 

at an arbitrary location within the Main 

Spring orifice during September 23–25, 

2003, a period of major pool drawdown, 

showed that the velocity of water flowing from the orifice increased about 40 

percent during the lowered pool conditions. The velocity increase was expected because of less water 

depth in the pool (hydraulic head at the orifice). Interpretation of 

the velocity data strongly indicated that the proration method 

could be enhanced with a complementary method based on velocity-indexing the springflow for periods when the stage-discharge 

relation is not applicable. If the ratio of springflow measured in 

cubic feet per second (ft3

/s) to velocity measured in feet per second (ft/s) can be estimated, then multiplication of this ratio—the 

“discharge/index-velocity ratio” in units of square feet (ft2

)—by 

daily mean velocity would produce an improved estimate of the 

daily mean springflow.

To apply the discharge/index-velocity ratio, on April 1, 2004, 

USGS divers installed a three-dimensional acoustic Doppler 

velocity (ADV) meter on the ceiling of the Main Spring orifice. 

The ADV meter has a combined communication and power cable, which surfaces below a lifeguard tower near the 

orifice (fig. 2) and is connected to the 

DCP at the station. At 4-hour intervals, 

the DCP transmits sixteen 15-minute 

values of x-, y-, and z-velocity, and 

acoustic signal strength. Each 15-minute 

value is computed by 5-minute averaging. The near real-time velocity data can 

be viewed at http://waterdata.usgs.gov/

tx/nwis/uv?dd_cd=24&format=

gif&period=7&site_no=08155500.

The z-component of the velocity data 

is the speed of the water at a point about 

8 ft inside the orifice and is aligned with 

the principal flow direction (out of the 

orifice). The z-component velocity is 

used for velocity in this report. (Normally, the x-component velocity is used 

in ADV applications, but the geometric 

characteristics of the Main Spring orifice required an alternative instrument 

installation.) To appropriately use the 

discharge/index-velocity ratio, additional springflow measurements are 

N

Apartments

Parking lot

Barton Creek

Barton Creek

Main Spring

Old Mill Spring

Upper Barton Spring

Eliza Spring

Barton Springs

 Pool

Bathhouse

Direction of flow

Bypass culvert

Dam

Dam

Well YD–58–42–903

TEXAS

Area

 enlarged

LOCATION MAP

Trail

Road

Flow by type

Ephemeral

Perennial

Underground

Spring

Monitoring well

EXPLANATION

0 300 600 FEET

USGS monitoring well 

YD 58–42–902

(behind tree line)

Springflow discharges 

through faults and fractures

widened by karstification

Most of Barton Springs flow is through this orifice, 

which is the location of the ADV meter.

Figure 1. Barton Springs swimming pool, associated springs, and ancillary elements for springflow 

monitoring, Austin, Texas.

Figure 2. Main Spring and approximate location of 

orifice and monitoring well.
3

needed during and immediately after periods when the pool is substantially below or 

above the pool-full level. The discharge/index-velocity ratio likely will show limited 

variation with changes in both aquifer and pool levels, because the basic geometric 

configuration of the fractured limestone from which springflow emerges does not 

change with time.

Summary of Periods of Daily Mean Springflow Estimation 

During April 1 to September 30, 2004 (183 days), the cumulative springflow of 

Barton Springs exceeded 8.8 billion gallons, and seven periods occurred during 

which the stage-discharge relation was not applicable. The periods totaled 21 days. 

For each (or parts) of the 21 days the stage-discharge relation was not applicable, and 

the daily mean streamflow for each day requires estimation. A time-series graph 

summarizing the April 1 to September 30, 2004, period is shown in figure 4. The 

velocity data were filtered and smoothed to more clearly show temporal trends; occasional unrealistically small velocity spikes in the data thus were suppressed. In general, the velocity data show considerable correlation with the daily mean springflow 

from the stage-discharge relation. Increasing velocity generally is associated with 

increasing springflow. According to the data, when springflow exceeds about 60 ft3

/s 

and the pool is full, the separation between the velocity and the daily mean springflow increases, which indicates that the discharge/index-velocity ratio increases.

Details of the daily mean springflow estimation for the seven periods noted in 

figure 4 follow. 

Period 1, April 29 and 30, 2004—The daily mean springflows for these two poolmaintenance days (fig. 4) were estimated using a discharge/index-velocity ratio of 40 

ft2

 and the daily mean velocity for each day. The estimated values for these two days 

are slightly larger than if the daily values had been estimated through proration with 

April 28 and May 1 springflows. A summary of the estimation is listed in table 1.

Period 2, June 9–18, 2004 (June flood)—The daily mean springflows for these 

10 days (fig. 4) were estimated using a discharge/index-velocity ratio of 37.6 ft2

. 

This ratio was assumed applicable because 37.6 ft2

 is the ratio of a direct measurement of springflow (90 ft3

/s) on June 16, 2004, and contemporaneous velocity data 

from the ADV meter in Main Spring. The pool was drawn down several days by City 

of Austin staff for removal of flood debris and general pool cleaning. A detailed time 

series for the June 9–18, 2004, period is shown in figure 5 and includes both recorded 

velocity data and the filtered and smoothed velocity data. Using the velocity data, the 

additional volume of springflow for the 10 days is about 117 million gallons (shaded 

region in fig. 5).

Period 3, June 30–July 4, 2004 (July flood)—The daily mean springflows for 

these 5 days (fig. 4) were estimated using an assumed discharge/index-velocity ratio 

of 37.6 ft2

 from the June 16, 2004, springflow measurement.

Periods 4–7, July 8, 2004; July 

22, 2004; July 29, 2004; and September 2, 2004—The daily mean 

springflows for these 4 days (fig. 4) 

were estimated by proration and 

not the discharge/index-velocity 

ratio because the drawdown was 

brief and not substantial enough to 

appreciably increase velocity for 

long. These days were regularly 

scheduled pool cleaning days, and 

the stage-discharge relation was 

not applicable for the entire day.

Additional Observations

Some additional observations of 

the velocity data were made. The 

velocity data show a curious and as 

Figure 3. Comparison of gage height and 

computed and estimated daily mean springflow for 

08155500 Barton Springs at Austin, Texas, April 1–

September 30, 2004. GAGE HEIGHT, IN FEET (AQUIFER WATER LEVEL)

SPRINGFLOW, IN CUBIC FEET PER SECOND

2004

Apr. May June July Aug. Sept.

19

20

21

22

23

24

25

26

27

28

30

40

50

60

70

80

90

100

105

15-MINUTE VALUES OF GAGE HEIGHT

DAILY MEAN SPRINGFLOW

EXPLANATION

The apparent spikes in

gage height are real and

reflect the influence of

pool level on nearby

aquifer water levels.

VELOCITY, IN FEET PER SECOND

SPRINGFLOW, IN CUBIC FEET PER SECOND

2004

April

7 14 21 28

May

7 14 21 28

June

7 14 21 28

July

7 14 21 28

August

7 14 21 28

September

7 14 21 28 0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

40

50

60

70

80

90

100

105

FILTERED AND SMOOTHED Z-VELOCITY COMPONENT WITHIN MAIN SPRING

DAILY MEAN SPRINGFLOW FROM STAGE-DISCHARGE RELATION

ESTIMATED DAILY MEAN SPRINGFLOW FROM DISCHARGE/INDEX-VELOCITY RATIO

June flood (pool drawn down)

July flood (pool drawn down)

Estimated daily mean springflow

period and period number.

1

2

3

4

5

6

7

See text for description.

Figure 4. Comparison of z-component of velocity within Main Spring, daily mean springflow derived 

from stage-discharge relation, and estimated daily mean springflow for 08155500 Barton Springs at 

Austin, Texas, April 1–September 30, 2004.

Table 1. Estimation of daily mean springflow using 

discharge/index-velocity ratio and daily mean velocity

[ft/s, feet per second; ft2, square feet; ft3/s, cubic feet per second; --, not available; e, estimated by multiplying 40 ft2 by 

daily mean velocity.] 

Date

Daily mean

velocity

(ft/s)

Discharge/indexvelocity ratio

(ft2

)

Daily mean

springflow

(ft3/s)

April 28 1.49 40 60.

April 29 1.63 -- e65.

April 30 1.56 -- e62.

May 1 1.53 40 61.
4

yet unexplained daily variation on 

April 3–5, 2004 (fig. 6), during the 

end of a period of lower than average springflow. The average springflow during March and April is 

about 68 ft3/s. For 3 consecutive 

days, the velocity was maximum in 

early afternoon and minimum in 

early morning—a 24-hour cycle is 

evident. The daily variation in 

velocity indicates that springflow 

also has daily variation (assuming 

that the ratio between springflow 

and velocity [discharge/indexvelocity ratio] is constant for a 

given day). These data are believed 

to be the first evidence to indicate 

the possibility of potentially daily 

cyclical springflow at Barton 

Springs. The daily velocity variation is not apparent for the 

remainder of the reporting period, April 6–September 30, 2004. 

The source for the daily velocity (and possibly springflow by 

association) variation could be natural or anthropogenic.

Summary

The ADV meter has provided scientifically informative, realtime velocity data from within the orifice of Main Spring in the 

Barton Springs swimming pool for the period April 1, 2004, to 

September 30, 2004. During this period, the daily mean springflow required periodic estimation because the conventional stagedischarge relation is not applicable during periods of pool drawdown or Barton Creek stormflow. A discharge/index-velocity ratio 

(ratio of springflow to velocity) can be used with the velocity data 

to estimate daily mean springflow; this method was used for 17 of 

21 days for the April 1–September 30, 2004, reporting period. 

Although the discharge/index-velocity ratio requires further study, 

the accuracy of springflow estimation at Barton Springs can be 

enhanced with ADV measurements relative to the traditional 

straight-line proration method. Finally, additional observations of 

the data indicate that cyclical daily variation in velocity and hence 

springflow from the Edwards aquifer possibly occurs at Barton 

Springs.

Figure 6. Comparison of z-component of velocity within Main Spring 

and daily mean discharge derived from stage-discharge relation for 

08155500 Barton Springs at Austin, Texas, April 1–13, 2004. VELOCITY, IN FEET PER SECOND

SPRINGFLOW, IN CUBIC FEET PER SECOND

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

April 2004

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

40

45

50

55

60

FILTERED AND SMOOTHED

 Z-VELOCITY COMPONENT

 WITHIN MAIN SPRING

DAILY MEAN SPRINGFLOW

 FROM STAGE-DISCHARGE

 RELATION

Rainfall in Austin area

recharging aquifer and

increasing springflow

and velocity

Daily variation in velocity indicates

that springflow has daily variation.

Figure 5. Comparison of z-component of velocity within Main Spring, daily mean springflow derived 

from stage-discharge rating curve, and estimated daily mean springflow for 08155500 Barton Springs at 

Austin, Texas, June 7–20, 2004.

FILTERED AND SMOOTHED Z-VELOCITY COMPONENT

VELOCITY, IN FEET PER SECOND

SPRINGFLOW, IN CUBIC FEET PER SECOND

June 2004

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

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

40

50

60

70

80

90

100

Z-VELOCITY COMPONENT WITHIN MAIN SPRING

DAILY MEAN SPRINGFLOW FROM STAGE-DISCHARGE RELATION

ESTIMATED DAILY MEAN SPRINGFLOW FROM

Velocity rises as pool

Velocity decreases

as Barton Creek

is lowered in anticipation

of Barton Creek flood

wave (see fig. 3).

flood wave passes

through pool

June 2004 flood Manual springflow measurement

Shaded area represents additional springflow volume

when velocity data are used to estimate springflow.

DISCHARGE/INDEX-VELOCITY RATIO

 WITHIN MAIN SPRING

Selected References

Aragon Long, S.C., Reece, B.D., and Eames, D.R., 2005, Water 

resources data, Texas, water year 2004—Volume 4: U.S. Geological 

Survey Water-Data Report TX–04–4, 363 p.

Morlock, S.E., Nguyen, H.T., and Ross, J.H., 2002, Feasibility of 

acoustic Doppler velocity meters for the production of discharge 

records from U.S. Geological Survey streamflow-gaging stations: 

U.S. Geological Survey Water-Resources Investigations Report 

01–4157, 56 p.

Sauer, V.B., 2002, Standards for the analysis and processing of surfacewater data and information using electronic methods: U.S. Geological Survey Water-Resources Investigations Report 01–4044, 91 p.

Senger, R.K., Collins, E.W., and Kreitler, C.W., 1990, Hydrogeology of 

the northern segment of the Edwards aquifer, Austin region: The 

University of Texas at Austin, Bureau of Economic Geology, 

Report of Investigations 192, 58 p.

Slade, R.M., Jr., Dorsey, M.E., and Stewart, S.L., 1986, Hydrology and 

water quality of the Edwards aquifer associated with Barton 

Springs in the Austin area, Texas: U.S. Geological Survey WaterResources Investigations Report 86–4036, 117 p.

— W.H. Asquith and M.O. Gary 

Any use of trade, product, or firm names is for descriptive purposes only 

and does not imply endorsement by the U.S. Government.

Information on technical reports and hydrologic data related to 

this study can be obtained from:

Director

USGS Texas Water Science Center Phone: (512) 927–3500

8027 Exchange Dr. FAX: (512) 927–3590

Austin, TX 78754–4733 World Wide Web: 

E-mail: dc_tx@usgs.gov http://tx.usgs.gov/