DTIC ADA441253: Hydrologic Conditions and Quality of Rainfall and Storm Runoff in Agricultural and Rangeland Areas in San Patricio County, Texas, 2000-2001

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In cooperation with the U.S. Department of Agriculture, Natural Resources
Conservation Service; San Patricio Soil and Water Conservation District;
and The Welder Wildlife Foundation
Hydrologic Conditions and Quality of Rainfall and
Storm Runoff in Agricultural and Rangeland Areas
in San Patricio County, Texas, 2000–2001
Open-File Report 02–291
U.S. Department of the Interior
U.S. Geological Survey
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2002 N/A -
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Hydrologic Conditions and Quality of Rainfall and Storm Runoff in
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Agricultural and Rangeland Areas in San Patricio County, Texas,
2000-2001 5c. PROGRAM ELEMENT NUMBER
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Standard Form 298 (Rev. 8-98)
Prescribed by ANSI Std Z39-18
U.S. Department of the Interior
U.S. Geological Survey
Hydrologic Conditions and Quality of Rainfall and
Storm Runoff in Agricultural and Rangeland Areas
in San Patricio County, Texas, 2000–2001
By Darwin J. Ockerman
U.S. GEOLOGICAL SURVEY
Open-File Report 02–291
In cooperation with the U.S. Department of Agriculture, Natural Resources
Conservation Service; San Patricio Soil and Water Conservation District;
and The Welder Wildlife Foundation
Austin, Texas
2002
U.S. DEPARTMENT OF THE INTERIOR
Gale A. Norton, Secretary
U.S. GEOLOGICAL SURVEY
Charles G. Groat, Director
Any use of trade, product, or firm names is for
descriptive purposes only and does not imply
endorsement by the U.S. Government.
For additional information write to
District Chief
U.S. Geological Survey
8027 Exchange Dr.
Austin, TX 78754–4733
E-mail: [email protected]
Copies of this report can be purchased from
U.S. Geological Survey
Information Services
Box 25286
Denver, CO 80225–0286
E-mail: [email protected]
ii
CONTENTS
Abstract ................................................................................................................................................................................ 1
Introduction .......................................................................................................................................................................... 1
Purpose and Scope .................................................................................................................................................... 3
Description of Study Area ........................................................................................................................................ 3
Texas Water-Quality Standards ................................................................................................................................ 3
Acknowledgments .................................................................................................................................................... 3
Data-Collection Methods ..................................................................................................................................................... 3
Runoff Monitoring .................................................................................................................................................... 4
Water Quality ............................................................................................................................................................ 4
Rainfall Sampling ..................................................................................................................................................... 4
Runoff Sampling ....................................................................................................................................................... 4
Hydrologic Conditions ......................................................................................................................................................... 4
Rainfall ..................................................................................................................................................................... 4
Runoff ....................................................................................................................................................................... 5
Water Quality ....................................................................................................................................................................... 6
Rainfall ..................................................................................................................................................................... 6
Nutrients ........................................................................................................................................................ 7
Rainfall Deposition of Nitrogen .................................................................................................................... 8
Runoff ....................................................................................................................................................................... 9
Nutrients, Major Inorganic Ions, and Trace Elements .................................................................................. 9
Pesticides ....................................................................................................................................................... 11
Bacteria ......................................................................................................................................................... 11
Loads and Yields ........................................................................................................................................... 12
Summary .............................................................................................................................................................................. 12
References ............................................................................................................................................................................ 13
PLATE
[Plate is in pocket]
1. Map showing aerial photograph of agricultural and rangeland watersheds
FIGURES
1. Map showing Coastal Bend area of South Texas and study area ......................................................................... 2
2. Hydrograph showing rainfall, discharge, and subsample-collection timing at watershed site 2 during
storm event, August 30, 2001 ............................................................................................................................... 5
3–5. Graphs showing:
3. Mean monthly rainfall at National Oceanic and Atmospheric Administration (NOAA) weather
station, 1965–2001, and monthly study area rainfall, 2000–2001 ............................................................. 6
4. Comparison of computed and estimated (from regression) total nitrogen deposition for sampled
rainfall events, June 2000–August 2001 .................................................................................................... 9
5. Comparison of runoff concentrations for selected constituents between mixed agricultural
watershed (Moody Creek watershed) and rangeland watersheds (watersheds 1 and 2), 2000–2001 ........ 10
TABLES
1. Rainfall, runoff volumes, and runoff coefficients for runoff events, 2000–2001 ................................................. 7
2. Concentrations of nutrients in rainfall samples, 2000–2001 ................................................................................ 7
CONTENTS iii
3. Summary statistics of selected nutrient concentrations in rainfall samples, 2000–2001 ...................................... 8
4. Event-mean concentrations for selected properties and constituents in runoff samples, 2000–2001 ................... 15
5. Summary statistics of event-mean concentrations for selected constituents in runoff samples, 2000–2001 ....... 18
6. Densities of bacteria in runoff samples, 2000–2001 ............................................................................................. 19
7. Summary statistics of bacteria densities in combined runoff samples, 2000–2001 ............................................. 19
8. Monthly and annual loads of selected constituents in runoff, 2000–2001............................................................ 20
iv
Hydrologic Conditions and Quality of Rainfall and
Storm Runoff in Agricultural and Rangeland Areas
in San Patricio County, Texas, 2000–2001
By Darwin J. Ockerman
Abstract for receiving waters. However, runoff and rela-
tively large bacteria densities represent very brief
During 2000–2001, rainfall and runoff were
and infrequent conditions, and the effect on down-
monitored in one mixed agricultural watershed and
stream water is not known.
two rangeland watersheds in San Patricio County,
Rainfall deposition is a major source of
located in the Coastal Bend area of South Texas.
nitrogen delivered to the study area. Rainfall nitro-
During this period, five rainfall samples were col-
gen (mostly ammonia and nitrate) exceeded the
lected and analyzed for selected nutrients. Ten run-
runoff yield. The average annual rainfall deposition
off samples from nine runoff events were collected
of total nitrogen on the study area watersheds was
at the three watershed monitoring stations. Runoff
1.3 pounds per acre. In contrast, an average annual
samples were analyzed for selected nutrients,
yield of 0.57 and 0.21 pound per acre of total nitro-
major ions, trace elements, pesticides, and bacteria.
gen in runoff exited the mixed agricultural water-
Study area rainfall during 2000 and 2001
shed and the rangeland watersheds, respectively.
was 33.27 and 28.20 inches, respectively, less than
the long-term average annual of 36.31 inches. Total INTRODUCTION
runoff from the study area watersheds during
The Coastal Bend bays and estuaries system of
2000–2001 was 2.46 inches; the regional average is
Texas is one of 28 estuaries in the United States that
about 2 inches per year. Rainfall and runoff during
have been designated as “Estuaries of National Signifi-
the study period was typical of historical patterns,
cance” (Texas Natural Resource Conservation Commis-
with periods of below average rainfall interspersed
sion, 1996). The Coastal Bend bays and estuaries are
with extreme events. Three individual storm events
affected by nonpoint-source runoff from agricultural
accounted for about 29 percent of the total rainfall
land uses within the 12-county Coastal Bend area of
and 86 percent of the total runoff during 2000–
South Texas (fig. 1). Agricultural land uses are predom-
2001. inant on about 88 percent of the Coastal Bend area and
Runoff concentrations of nutrients, major range from cattle grazing to row crop farming. About
ions, and trace elements generally were larger in two-thirds of this agricultural land use is rangeland
the mixed agricultural watershed than runoff con- (Quenzer and others, 1998), the largest single land use
centrations in the rangeland watersheds. Pesticides category in the Coastal Bend area.
were detected in two of eight runoff samples. Three Because information on the characteristics of run-
off from rangeland in the Coastal Bend area is meager,
pesticides (atrazine, deethylatrazine, and triflura-
the U.S. Geological Survey (USGS) studied the hydrol-
lin) were detected in very small concentrations;
ogy and water quality of three watersheds consisting of
only deethylatrazine was detected in a concentra-
14,264 acres of mixed agricultural land and coastal
tion greater than the laboratory minimum reporting
plains rangeland in San Patricio County during January
level.
2000–December 2001. The study was done in coopera-
Bacteria in agricultural and rangeland runoff
tion with the U.S. Department of Agriculture, Natural
is a potential water-quality concern as all fecal
Resources Conservation Service; San Patricio Soil and
coliform and E. coli densities in the runoff samples Water Conservation District; and The Welder Wildlife
exceeded Texas Surface Water Quality Standards Foundation.
Abstract 1
97˚30' 97˚24'
SAN PATRICIO COUNTY REFUGIO COUNTY
ARANSAS
RIVER
MOODY CREEK WATERSHED WATERSHED 1 08189714
Moody NOAA
S 77 Creek 081T8A9E7S11
U
WATERSHED 2
08189710
28˚06'
Moody Creek Creek
South Fork
Chiltipin
0 2 4 6 MILES
EXPLANATION
98˚
Study area C RHEOSKEER VC9O8A˚IN3R0Y'ON MISSION 97˚
Welder Wildlife Refuge 28˚30' 97˚30'
BEE RIVER REFUGIO
08189500 UwWSaatGteeSrr-s qshuteraedlai tbmyo fsultonawdti-aogrnay gainndg naunmdber MNUCECMESULLEN L L CAIVKHEER ICOSTOARIRIKVPERUS08S1k8i9d7m0o0re 08A1ra8n9sa5s00RiverReCfuoBgpaaiAyonoRANSAS
NOAA 28˚ Sinton
Weather station and identifier— SAN PATRICIO
NOAA, National Oceanic and Atmospheric
Administration; TAES, Texas Agricultural Corpus Christi
Experiment Station Corpu s Bay
Christi
DUVAL JIM WELLS NUECES
O
C
27˚30' KLEBERG EXI
M
F
O
F
L
U
G
TEXAS
27˚ BROOKS
Coastal Bend KENEDY
area
LOCATION MAP 0 30 60MILES
Figure 1. Coastal Bend area of South Texas and study area.
2 Hydrologic Conditions and Quality of Rainfall and Storm Runoff in Agricultural and Rangeland Areas in San Patricio County,
Texas, 2000–2001
Purpose and Scope The climate of the area is classified as subtropical
(short, mild winters and long, hot and humid summers).
This report presents the results of a study to
Prevailing winds are from the southeast throughout the
describe hydrologic conditions, to characterize the qual-
year (Baird and others, 1996).
ity of rainfall, and to characterize the quantity and
quality of stormwater runoff in one mixed agricultural
Texas Water-Quality Standards
watershed and two rangeland watersheds in San Patricio
County in the Coastal Bend area of South Texas. Rain-
The Texas Natural Resource Conservation
fall samples were collected in the mixed agricultural
Commission (TNRCC) has designated water-quality
watershed at a streamflow-gaging and water-quality
standards and appropriate uses (such as aquatic life,
station equipped with an automatic rainfall collector.
contact or non-contact recreation, or drinking water) for
Rainfall samples were analyzed for selected nutrients.
specific stream, estuary, and bay segments (Texas Natu-
Runoff samples were collected in each of the three
ral Resource Conservation Commission, 2002). To sup-
watersheds at a streamflow-gaging and water-quality
port the designated use of the water-body segments,
station equipped with automatic water samplers. Runoff
standards for common water-quality indicators such as
samples were analyzed for selected nutrients, major
dissolved oxygen, temperature, pH, dissolved minerals,
inorganic ions, trace elements, and pesticides. Loads
and bacteria have been established for some stream and
and yields of selected constituents entering the receiv-
bay segments. The TNRCC has not developed segment-
ing bays and estuaries from these watersheds were esti-
specific standards for any of the creeks monitored
mated for 2000–2001.
during this study. However, some segment-specific
Description of Study Area standards have been established for the tidal segment of
the Aransas River and Copano Bay, which receive run-
The study area watersheds are delineated on the
off from the study area. The tidal segment of the Aran-
aerial photograph on plate 1. The Moody Creek mixed
sas River is designated for contact recreation and high
agricultural watershed is the largest (13,818 acres). It is
aquatic life. Similarly, the Copano Bay segment is des-
mostly rangeland, but also includes about 2,500 acres of
ignated for contact recreation, high aquatic life, and
cropland in the upper part of the watershed as well as
oyster waters (State of Texas, 2000).
U.S. highway right-of-way. Soils in the Moody Creek
watershed are largely a mixture of sandy loams and clay
Acknowledgments
loams (Soil Conservation Service, 1979). Watersheds 1
and 2 are entirely rangeland and located within the
Special thanks are extended to Dr. D. Lynn
Welder Wildlife Refuge. Watershed 1 is about 97 acres
Drawe, Director of The Welder Wildlife Foundation, for
of loamy sands. Watershed 2 is about 349 acres of clay
valuable project oversight and technical assistance and
soils. The topography of the area is relatively flat with
to Leroy Wolff, U.S. Department of Agriculture, Natu-
altitudes ranging from about 25 feet above mean sea
ral Resources Conservation Service, Sinton, Tex., for
level near the outlets of the watersheds to about 75 feet
indispensable administrative and technical support.
above mean sea level in the upper Moody Creek water-
shed. Vegetation on the rangelands is a mixture of grass
and varying densities of brush and woody vegetation DATA-COLLECTION METHODS
(Drawe, 1997). The study area rangelands are used
for grazing domestic livestock and to provide wildlife USGS streamflow-gaging and water-quality
habitat. sampling stations were installed at the outlets of each of
Creeks in the study area are ephemeral, producing the study area watersheds (pl. 1; fig. 1) in May 2000 and
runoff only after heavy rains. The streamflow-gaging operated through December 2001. The Texas Agricul-
stations in watersheds 1 and 2 are located at the edge of tural Experiment Station (TAES) in Corpus Christi has
fields (grassed ditches) that typically are dry. The lower operated a weather station near watershed 1 since
reach of Moody Creek is inundated by backwater from November 15, 2000. The wildlife refuge staff monitors
the tidal reach of the Aransas River. All study area a National Oceanic and Atmospheric Administration
watersheds drain to the tidal segment of the Aransas (NOAA) weather station (also near watershed 1) from
River and then to Copano Bay (fig. 1). which rainfall data have been collected since 1965.
DATA-COLLECTION METHODS 3
Runoff Monitoring samples also were analyzed for dissolved phosphorus,
total phosphorus, and dissolved orthophosphate phos-
Water-surface elevation (stage) was continuously
phorus. Field measurements of pH, conductivity, and
recorded during runoff events at all three streamflow-
alkalinity also were made for selected samples.
gaging stations using a gas-bubbler and pressure trans-
ducer system (Rantz and others, 1982). At Moody Runoff Sampling
Creek (station 08189710), tidal backwater conditions
Automatic water samplers collected runoff sam-
result in a variable relation between stage and dis-
ples during storm events. When streamflow-monitoring
charge. An acoustic doppler velocimeter also was used
to measure stream velocity. Correlations between stage, equipment detected runoff, automatic samplers were
activated to collect discrete aliquots (subsamples). Ali-
velocity, and measured discharge were used to develop
quots were collected at a pre-programmed rate depend-
the discharge rating and to compute continuous dis-
charge at this station (Patino and Ockerman, 1997). ing on the station. Aliquots were collected at 30-minute
intervals at watersheds 1 and 2. Aliquots were collected
Relations between stage and runoff (discharge) were
hourly at the Moody Creek watershed, where runoff
developed at watersheds 1 and 2 (stations 08189711 and
duration was longer. At the end of the runoff event, the
08189714, respectively) by making independent dis-
aliquots from each station were combined into a single
charge measurements (Buchanan and Somers, 1969;
discharge-weighted composite sample (one sample
Kennedy, 1984).
from each station). The volume of each aliquot added to
Water Quality the composite sample was proportional to the stream
discharge at the time of the aliquot collection. Thus, the
Water-quality samples were collected from two analysis of the composite samples yielded EMCs that
sources. Rainfall samples were collected primarily to represent the discharge-weighted average concentra-
determine rainfall nitrogen delivered to the study area. tions during the runoff event. Figure 2 shows a rainfall-
Runoff samples were collected to characterize runoff discharge hydrograph of a runoff event at watershed 2
quality and to estimate constituent loads and yields on Aug. 30, 2001, and shows the timing of subsample
transported to receiving waters. collection.
After runoff samples were collected, they were
Rainfall Sampling
chilled and bottled, necessary preservatives were added,
and the samples were shipped overnight to the NWQL.
Rainfall samples were collected at the Moody
Samples were analyzed for nutrients, major inorganic
Creek station by an automatic rainfall collector. The
ions, trace elements, and dissolved pesticides.
collector is equipped with polyethylene buckets that are
In addition to the subsamples, discrete grab sam-
covered when rainfall is not occurring to prevent con-
ples were collected. These samples were analyzed for
tamination and evaporation of the sample. A moisture
bacteria at the USGS office in San Antonio, Tex.
sensor activates a mechanism to uncover the collection
bucket when rainfall begins and to cover the sample
HYDROLOGIC CONDITIONS
when rainfall ends. About 0.2 inch of rain was required
to provide sufficient sample volume for analysis. Rain-
Rainfall
fall samples were collected as single event-composite
samples during rainfall events and therefore represent Annual rainfall statistics were computed from
rainfall event-mean concentrations (EMCs). The sam- rainfall data measured at the NOAA weather station
ples were retrieved as soon as possible after a rainfall (pl.1; fig.1). The 37-year (1965–2001) average annual
event, chilled, and shipped overnight to the USGS rainfall is 36.31 inches with a minimum of 15.49 inches
National Water Quality Laboratory (NWQL) in Denver, in 1989 and a maximum of 59.46 inches in 1983. The
Colo., for analysis. standard deviation of annual rainfall, 10.09 inches, indi-
Rainfall samples were analyzed for the following cates relatively large differences in annual rainfall.
forms of nitrogen: ammonia, dissolved organic, total Study area rainfall (average of data from NOAA
organic, and nitrite plus nitrate. Total nitrogen concen- and TAES weather stations [pl. 1; fig. 1] during 2000
trations were computed for each sample as the sum of and 2001 was 33.27 and 28.20 inches, respectively.
ammonia, total organic, nitrite, and nitrate nitrogen. The Monthly rainfall was below normal during 16 of the
4 Hydrologic Conditions and Quality of Rainfall and Storm Runoff in Agricultural and Rangeland Areas in San Patricio County,
Texas, 2000–2001