U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2011–3147

December 2011

Prepared in cooperation with the City of Lubbock

Historical Streamflows of Double Mountain Fork Brazos 

River and Water-Surface Elevations of Lake Alan Henry, 

Garza County, Texas, Water Years 1962–2010

Printed on recycled paper

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

with the City of Lubbock, Texas, operates two surface-water 

stations in Garza County, Tex.: USGS streamflow-gaging 

station 08079600 Double Mountain Fork Brazos River at 

Justiceburg, Tex. (hereinafter, Double Mountain Fork 

Brazos station), and 08079700 Lake Alan Henry Reservoir 

near Justiceburg, Tex. (hereinafter, Lake Alan Henry station), 

a water-supply reservoir about 60 miles southeast of Lubbock, 

Tex., and about 10 miles east of Justiceburg, Tex. The Double 

Mountain Fork Brazos River locally is 

also known as the “South Fork Double 

Mountain Fork Brazos River” and is 

often referred to as the “South Fork.” 

The streamflow and water-surface 

elevation data from the two stations are 

useful to water-resource managers and 

planners in support of forecasting and 

water-resource infrastructure operations 

and are used in regional hydrologic 

studies.

The Double Mountain Fork 

Brazos station has a 1,466 square mile 

watershed but a contributing drainage 

area of only 244 square miles. This 

station is currently (2012) the most 

upstream continuous record streamflow 

station in the greater Brazos River 

basin of Texas. The station is upstream 

from Lake Alan Henry, and as a result, 

the Double Mountain Fork Brazos station also provides reservoir inflow data 

(streamflow, in cubic feet per second). 

The Lake Alan Henry station provides 

water-surface elevation of the reservoir, 

which has a 1,617 square mile watershed but a contributing drainage area 

of only 395 square miles. Figure 1 

shows the locations of Lake Alan 

Henry, the Lake Alan Henry station, 

and the Double Mountain Fork Brazos 

station. The Double Mountain Fork 

Brazos River and Sand Creek are 

principal tributaries for the lake. This 

fact sheet highlights some of the data 

and ancillary information collected by the two stations. The data 

for these two stations are available through the USGS National 

Water Information System (U.S. Geological Survey, 2011).

Lake Alan Henry 

The completion of the Lake Alan Henry water-supply 

infrastructure has taken on particular importance because 

of diminished water availability from Lake Meredith near 

Amarillo, Tex. (Blackburn, 2009). Lake Meredith historically 

Figure 1. Location of U.S. Geological Survey surface-water stations in Garza County, Texas.

£

101°10' 101°00'

33°05'

33°00'

Lake Alan Henry

Justiceburg

GARZA COUNTY

KENT COUNTY

JOHN MONTFORD

DAM

Base modified from U.S. Geological Survey digital data, 1:24,000 quadrangles

Universal Transverse Mercator projection, zone 14

North American Datum of 1983

Double Mountain Fork

Brazos River

North Fork Double Mountain Fork Brazos River

¤84

08079600

#

08079700

#

Double Mountain Fork

Brazos River

Sand Creek

EXPLANATION

U.S. Geological Survey continuous

 record surface-water station

08079700#

TEXAS

Amarillo

Lubbock

Lake

Meredith

Study area

Brazos

 River

 Basin

Lake

Alan Henry 

0 2.5 5 MILES

0 2.5 5 KILOMETERS
has been the primary surface-water supply for Lubbock and 

other communities in the region. Construction of the John 

Montford Dam, which impounds Lake Alan Henry, began in 

1991 and was completed in October 1993. The conservation 

pool elevation of the reservoir is 2,220 feet National Geodetic 

Vertical Datum of 1929. The USGS has collected hydrologic 

data at the Lake Alan Henry station since October 1, 1997. 

The first substantial inflows to the reservoir occurred in the 

first half of 1999 and began a period of increasing water-surface 

elevations in the reservoir that lasted about 5 years (resulting in 

a net increase in water-surface elevation of almost 40 feet). The 

reservoir attained conservation-pool elevation (2,220 feet) for 

the first time around October 3, 2004. The original and primary 

purpose of the Double Mountain Fork Brazos station was to 

assess water availability as part of the planning process for 

Lake Alan Henry. After the completion of the reservoir and 

from the mid 1990s onward, the Double Mountain Fork Brazos 

station has provided long-term monitoring of inflows to Lake 

Alan Henry. 

The City of Lubbock (2011) reported that the firm yield 

of Lake Alan Henry is 19,000 acre-feet of water and that the 

reservoir can supply more than 40 percent of the current (2011) 

water-supply needs of Lubbock. The City of Lubbock (2011) 

also reported that some time in 2012 a raw-water pipeline 

from the reservoir to a new water-treatment plant in southeast 

Lubbock is expected to be completed. The new plant will 

contribute drinking water to the municipal distribution system 

in Lubbock. 

Streamflow Data for Double Mountain Fork Brazos River 

Two primary data products for the Double Mountain Fork 

Brazos station are daily mean values (DVs) and instantaneous 

values, also called unit values (UVs), of river stage (height 

referenced to a measurement datum) and more importantly 

streamflow. The daily value data for the station can be accessed 

at http://waterdata.usgs.gov/tx/nwis/dv/?site_no=08079600, 

and the unit-value data can be accessed at http://waterdata.usgs.

gov/tx/nwis/uv/?site_no=08079600. Other data types and 

time periods also can be acquired by using these two Web 

sites. An example figure of DVs for the period of December 1, 

1961 through September 30, 2010 is shown in figure 2, which 

was retrieved through the first Web site shown in this paragraph.

The USGS has previously published several data reports 

(Asquith and others, 2007a, b; Asquith and Heitmuller, 2008) 

that provide summaries of streamflow history throughout Texas. 

The Double Mountain Fork Brazos station is included within 

each of these reports. The top graph in the figure shows that the 

number of days with zero flow represents about 46 percent of 

the water year; streamflows at this station are ephemeral, and 

substantial inflows to Lake Alan Henry occur as storm runoff 

during periods of abundant rainfall. Distinctive patterns in 

number of zero-flow days in water years is evident with some 

water years, particularly before the early 1990s, having fewer 

zero-flow days compared to other water years. Relatively more 

zero-flow days occurred since the early 1990s. The bottom 

graph in figure 3 represents the zero-flow potential by month 

across years. Two peaks representing highest potential for zero 

flow occur around April and July. The months of January and 

December are least likely to have zero-flow conditions.

A summary of annual mean, maximum, minimum, and 

L-scale (a linear measure of variability) statistics of the daily 

mean streamflow for each water year (1963–2010) at the 

Double Mountain Fork Brazos station is shown in figure 4. 

The mean streamflow (top) graph in the figure is perhaps the 

most important from the perspective of water supply. The mean 

annual streamflow is computed as 30.3 cubic feet per second 

(approximately 21,900 acre-feet per year, which compares 

favorably with the City of Lubbock’s [2011] yield for planning of 19,000 acre-feet). The flood event after Hurricane Alex 

(fig. 5), occurring during water year 2010, contributed substantially to the largest annual volume since at least 1963. The 

maximum daily streamflow (top middle) graph demonstrates 

considerable interannual variation in the annual maximum daily 

mean flow, which is typical of many river systems in Texas. The 

minimum daily streamflow (lower middle) graph complements 

figure 3 and shows that zero-flow conditions occur every year. 

Lastly, the L-scale streamflow (bottom) graph shows an apparent consistency in the intraannual variation in streamflow shown 

in the top graph.

Asquith and Heitmuller (2008, p. 556) provided period of 

record and last decade (1997–2007) flow-duration curves for the 

Double Mountain Fork Brazos station. These curves indicate 

(along with a plot of the period of record of DVs from the same 

report) that the streamflow characteristics (statistical properties) 

of the Double Mountain Fork Brazos station above Lake Alan 

Henry during 1997–2007 visually appear similar to those for the 

period of record analyzed (1962–2007). The mean streamflow 

(1962–2007) for the Double Mountain Fork Brazos station is 

reported by Asquith and Heitmuller (2008 p. 557) as about 28 

cubic feet per second. This streamflow value is about the 90th 

percentile of daily flows, which is indicative of a river basin 

for which the storm flow or flood volume represents a critical 

contribution to overall volume (yield) of the Double Mountain 

Fork Brazos River above Lake Alan Henry.

Figure 2. Period of record retrieval of daily mean streamflow for 

U.S. Geological Survey streamflow-gaging station 08079600 Double 

Mountain Fork Brazos River at Justiceburg, Texas, for the period 

December 1, 1961 through September 30, 2010. 
Figure 3. Summary of percentage of zero daily mean streamflow for U.S. Geological Survey streamflow-gaging station 08079600 Double 

Mountain Fork Brazos River at Justiceburg, Texas (modified from Asquith and others, 2007a). 

1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Water year

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

Month

0

10

20

30

40

50

60

70

80

90

100

Percentage of zero streamflow

0

10

20

30

40

50

60

70

80

90

100

Percentage of zero streamflow

EXPLANATION

Mean annual percentage of zero streamflow (46 percent)

Median annual percentage of zero streamflow (47 percent)

Annual percentage of zero streamflow

EXPLANATION

Mean monthly percentage of zero streamflow

Median monthly percentage of zero streamflow

Percentage of zero streamflow for indicated month for a given calendar year
Figure 4. Summary of annual mean, maximum, minimum, and L-scale statistics of daily mean streamflow for U.S. Geological Survey 

streamflow-gaging station 08079600 Double Mountain Fork Brazos River at Justiceburg, Texas (modified from Asquith and others, 2007b). 

1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Water year

1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Water year

1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Water year

1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Water year

0

20

40

60

80

100

Annual mean streamflow,

in cubic feet per second

0

5,000

10,000

15,000

Annual maximum streamflow,

in cubic feet per second

0

0.2

0.4

0.6

0.8

1.0

Annual minimum streamflow,

in cubic feet per second

0

20

40

60

80

100

Annual streamflow L-scale,

in cubic feet per second

EXPLANATION

Mean annual mean streamflow (30.3 cubic feet per second)

Median annual mean streamflow (24 cubic feet per second)

Annual mean streamflow

EXPLANATION

Mean annual maximum streamflow (3,310 cubic feet per second)

Median annual maximum streamflow (2,110 cubic feet per second)

Annual maximum streamflow

EXPLANATION

Mean annual minimum streamflow (0 cubic feet per second)

Median annual minimum streamflow (0 cubic feet per second)

Annual minimum streamflow

EXPLANATION

Mean L-scale of annual streamflow (29.1 cubic feet per second)

Median L-scale of annual streamflow (23.3 cubic feet per second)

Annual L-scale of streamflow
Water-Surface Elevation Data for Lake Alan Henry Reservoir

Two primary data products for the Lake Alan Henry station 

are DVs and UVs of water-surface elevations (http://waterdata.

usgs.gov/tx/nwis/dv/?site_no=08079700 and http://waterdata.

usgs.gov/tx/nwis/uv/?site_no=08079700, respectively). A more 

elaborate summary of the water-surface elevation data than 

available in those data products is shown in figure 6. The figure 

shows that water-surface elevations have met or exceeded the 

Figure 5. Hydrographer performing a measurement of streamflow 

at U.S. Geological Survey streamflow-gaging station 08079600 

Double Mountain Fork Brazos River at Justiceburg, Texas, during 

a large flood event on July 4, 2010, that resulted from the remnants 

of Hurricane Alex (Hydrometeorological Prediction Center, 2010, 

photograph by William H. Asquith). 

conservation pool elevation of 2,220 feet since about 2005 

through the present with substantial inflow events occurring 

about every 2 years. These events are seen as the “spikes” in the 

time series (top graph) exceeding about 2,220 feet. The bottom graph of the figure also shows that the 2010 water year had 

several elevations higher than the mean daily mean and that the 

modest inflow event in late April 2010 and a larger event around 

July 4 set numerous daily maximum elevation values for the 

period of record.

Figure 6. Water-surface elevation National Geodetic Vertical Datum of 1929 (NGVD 29) for U.S. Geological Survey station 08079700 Lake Alan 

Henry Reservoir near Justiceburg, Texas (modified from Asquith and others, 2007c). 

1998 2000 2002 2004 2006 2008 2010

Calendar year

Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept.

Month

2,180

2,190

2,200

2,210

2,220

2,230

Elevation, in feet above NGVD 29 Elevation, in feet above NGVD 29

2,180

2,190

2,200

2,210

2,220

2,230 EXPLANATION

Daily mean elevation above NGVD 29 for

 water year 2010

Mean daily mean elevation above NGVD 29

 for period of record

Maximum or minimum daily mean elevation

 above NGVD 29 for period of record

EXPLANATION

Daily mean elevation above NGVD 29
Publishing support provided by

Lafayette Publishing Service Center

For additional information, contact 

Director, USGS Texas Water Science Center

http://tx.usgs.gov/

gs-w-txpublic-info@usgs.gov 

Cited References

Asquith, W.H., and Heitmuller, F.T., 2008, Summary of annual 

mean and annual harmonic mean statistics of daily mean 

streamflow for 620 U.S. Geological Survey streamflowgaging stations in Texas through water year 2007: U.S. Geological Survey Data Series 372, 1,259 p. (Also available at 

http://pubs.usgs.gov/ds/372/.)

Asquith, W.H., Vrabel, Joseph, and Roussel, M.C., 2007a, 

Summary of percentages of zero daily mean streamflow for 

712 U.S. Geological Survey streamflow-gaging stations in 

Texas through 2003: U.S. Geological Survey Data Series 247, 

721 p. (Also available at http://pubs.usgs.gov/ds/2007/247/.)

Asquith, W.H., Vrabel, Joseph, and Roussel, M.C., 2007b, 

Summary of annual mean, maximum, minimum, and L-scale 

statistics of daily mean streamflow for 712 U.S. Geological 

Survey streamflow-gaging stations in Texas through 2003: 

U.S. Geological Survey Data Series 248, 721 p. (Also available at http://pubs.usgs.gov/ds/2007/248/.)

Asquith, W.H., Vrabel, Joseph, and Roussel, M.C., 2007c, Summary of water-surface-elevation data for 116 U.S. Geological 

Survey lake and reservoir stations in Texas and comparison to 

data for water year 2006: U.S. Geological Survey Data Series 

287, 42 p. (Also available at http://pubs.usgs.gov/ds/287/.)

Blackburn, Elliott, 2009, Water Woes—Officials study possible 

action as Lake Meredith’s water level recedes to 50 feet: 

Lubbock Avalanche-Journal, accessed May 9, 2011, at 

http://lubbockonline.com/stories/061809/loc_452080824.

shtml.

City of Lubbock, 2011, Lake Alan Henry Pipeline Update–

Lubbock’s Water Project Moves Forward: Water Conservation and Education Department, accessed May 5, 2011, at 

http://water.ci.lubbock.tx.us/pdf/news/Advertorial02.pdf.

Hydrometeorological Prediction Center, 2010, Hurricane 

Alex—June 29–July 6, 2010: National Weather Service 

Hydrometeorological Prediction Center, accessed May 

10, 2011, at http://www.hpc.ncep.noaa.gov/tropical/rain/

alex2010.html.

U.S. Geological Survey, 2011, National Water Information 

System, accessed May 2011, at http://waterdata.usgs.gov/tx/

nwis/.

—William H. Asquith and Joseph Vrabel