USGS Water-Resources Investigations Report 97-4117

Home , Bosque River, Lampasas River, Little River (Texas), Nolan River, Salt Fork Brazos River

ANALYSIS OF MINIMUM 7-DAY DISCHARGES AND ESTIMATION OF MINIMUM 7-DAY, 2-YEAR DISCHARGES FOR STREAMFLOW-GAGING STATIONS IN THE BRAZOS RIVER BASIN, TEXAS

U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 97–4117

Brazos River Basin

TEXAS

GULF OF MEXICO

Prepared in cooperation with the BRAZOS RIVER AUTHORITY ANALYSIS OF MINIMUM 7-DAY DISCHARGES AND ESTIMATION OF MINIMUM 7-DAY, 2-YEAR DISCHARGES FOR STREAMFLOW-GAGING STATIONS IN THE BRAZOS RIVER BASIN, TEXAS

By Timothy H. Raines and William H. Asquith

U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 97–4117

Prepared in cooperation with the BRAZOS RIVER AUTHORITY

Austin, Texas 1997 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY Gordon P. Eaton, Acting 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: Copies of this report can be purchased from:

District Chief U.S. Geological Survey U.S. Geological Survey Branch of Information Services 8011 Cameron Rd. Box 25286 Austin, TX 78754–3898 Denver, CO 80225–0286

ii CONTENTS

Abstract ...... 1 Introduction ...... 1 Purpose and Scope ...... 2 Physical Setting ...... 2 Methods of Analysis ...... 3 N-Day Analysis ...... 4 Statistical Analysis ...... 4 Frequency Analysis ...... 5 Acknowledgments ...... 5 Analysis of Minimum 7-Day Discharges ...... 5 Mann-Kendall Test ...... 5 Wilcoxon Rank-Sum Test ...... 11 Estimation of Minimum 7-Day, 2-Year Discharges ...... 11 Stations With Unregulated Discharge Only ...... 11 Stations With Regulated Discharge Only ...... 11 Stations With Both Unregulated and Regulated Discharge ...... 11 Summary ...... 13 References Cited ...... 14

PLATE

(Plate is in pocket)

1. Map showing locations of streamflow-gaging stations in the Brazos River Basin, Texas

FIGURES

1. Map showing location of the Brazos River Basin, Texas ...... 3 2. L-moment diagram for unregulated and regulated streamflow-gaging stations, Brazos River Basin, Texas ...... 6 3–10. Graphs showing annual minimum 7-day discharges for station: 3. 08099300 Sabana River near De Leon, Texas, water years 1961–86 ...... 7 4. 08083100 Clear Fork Brazos River near Roby, Texas, water years 1963–93 ...... 7 5. 08150000 Big Creek near Needville, Texas, water years 1948–95 ...... 9 6. 08093100 Brazos River near Aquilla, Texas, water years 1941–95 ...... 9 7. 08082000 Salt Fork Brazos River near Aspermont, Texas, water years 1940–95 ...... 10 8. 08091000 Brazos River near Glen Rose, Texas, water years 1924–95 ...... 10 9. 08096500 Brazos River at Waco, Texas, water years 1897–1995 ...... 12 10. 08091500 Paluxy River at Glen Rose, Texas, water years 1948–95 ...... 12

TABLES

1. Reservoirs with normal storage capacities exceeding 5,000 acre-feet, Brazos River Basin, Texas ...... 15 2. Streamflow-gaging stations with at least 10 years of unregulated or 10 years of regulated discharge data, Brazos River Basin, Texas ...... 17 3. Mann-Kendall test results of annual minimum 7-day discharges for streamflow-gaging stations with at least 10 years of unregulated or 10 years of regulated discharge data ...... 21 4. Wilcoxon rank-sum test results of annual minimum 7-day discharges for streamflow-gaging stations with at least 10 years each of unregulated and regulated discharge data ...... 25 5. Estimated minimum 7-day, 2-year discharges for streamflow-gaging stations, Brazos River Basin, Texas ...... 26

iii Analysis of Minimum 7-Day Discharges and Estimation of Minimum 7-Day, 2-Year Discharges for Streamflow-Gaging Stations in the Brazos River Basin, Texas

By Timothy H. Raines and William H. Asquith

Abstract data. The 7Q2 ranges from 33 to 631 cubic feet per second for the eight regulated-only stations on the The minimum 7-day, 2-year discharge (7Q2) mainstem Brazos River. For the seven stations on was estimated for each of 97 streamflow-gaging the mainstem Brazos River with at least 10 years of stations in the Brazos River Basin, Texas, with at unregulated and 10 years of regulated discharge least 10 years of unregulated or 10 years of regu- data, the 7Q2 ranges from 0 to 568 cubic feet per lated discharge data using the Pearson Type III dis- second before regulation and from 0.30 to 670 tribution fitted by L-moment statistics of the annual cubic feet per second after regulation. The 7Q2 minimum 7-day discharges. Forty-six stations have increased during regulation for 19 of the 25 stations at least 10 years of unregulated discharge data only, with both unregulated and regulated data. The 26 stations have at least 10 years of regulated effect of regulation for most stations generally was discharge data only, and 25 stations have at least an increase in the magnitude of the 7Q2. 10 years of unregulated and 10 years of regulated discharge data. INTRODUCTION Statistical tests were applied to the annual minimum 7-day discharges to determine if the Low-flow characteristics of streams are useful unregulated and regulated data have trends; and to evaluate the effects that proposed or existing with- to determine if the data before regulation are drawals or return flows might have on the streamflow and water quality in the basin. Hundreds of permits for significantly different from the data after regula- withdrawals and return flows now exist for streams in tion. Results of the Mann-Kendall test indicate a the Brazos River Basin in Texas, and many new permits significant trend at the 95-percent confidence level are expected to be requested in the future. The effect for 8 of the 46 unregulated-only stations, for 6 of that these withdrawals and the return flows have on the the 26 regulated-only stations, and for 5 stations flow and water quality of receiving streams in the basin before regulation and for 10 stations after regula- is unknown. The minimum 7-day, 2-year discharge1 tion of the 25 stations with both unregulated and (7Q2) is useful in assessing these possible effects. The regulated data. Results of the Wilcoxon rank-sum 7Q2 is used by the Texas Natural Resource Conserva- test indicate a significant difference between the tion Commission to analyze permit applications. Sev- unregulated and regulated annual minimum 7-day eral reservoirs have been constructed in the basin for discharges at the 95-percent confidence level for 16 flood protection, water supply, and recreation. The of the 25 stations with both types of data. effect that the reservoirs have on the low-flow discharge also is unknown. No known previous studies of low- The 7Q2 is zero for 31 of the 46 unregulated- flow frequency have been done for the Brazos River only stations and for 9 of the 26 regulated-only Basin. stations. The 7Q2 also is zero for 9 stations before regulation and for 3 stations after regulation of the 1Annual lowest mean discharge for 7 consecutive days with a 25 stations with both unregulated and regulated 2-year recurrence interval.

Abstract 1 In 1996 the U.S. Geological Survey (USGS), in Administration, 1990). The periods of minimum flow cooperation with the Brazos River Authority (BRA) generally occur in July and August due to low precipi- conducted a study to determine the 7Q2 for streamflow- tation and high evapotranspiration. Statewide droughts gaging stations in the Brazos River Basin using annual during 1932–34, 1938–40, 1947–48, 1950–57, and minimum 7-day discharges. The objectives of the study 1960–67 (Riggio and others, 1987) affected the entire were to (1) determine the 7Q2 for the 97 stations with at Brazos River Basin. The magnitude and duration of least 10 years of unregulated or 10 years of regulated droughts vary over the State. During some droughts data, (2) determine the 7Q2 for the unregulated period only certain regions of Texas are affected. The most and regulated period of the 25 stations with at least 10 severe recorded drought in recent history occurred dur- years of discharge data both before and after regulation, ing 1950–57 and reached its greatest magnitude in the and (3) determine the effects of regulation on the 7Q2 summer of 1956. Several less severe droughts during for the 25 stations. the 1970s and early 1980s affected only parts of the Bra- zos River Basin. Purpose and Scope Thirty-nine reservoirs with normal storage capacities (generally the top of the conservation pool) that This report presents an analysis of minimum exceed 5,000 acre-feet (acre-ft) have been constructed 7-day discharges and estimates of 7Q2 for unregulated in the Brazos River Basin (table 1 at end of report); 10 and regulated streamflow-gaging stations in the Brazos have a normal storage capacity that exceeds 100,000 River Basin and documents the effect of regulation acre-ft. Three of the 39 reservoirs are located on the on the 7Q2. This report is limited to the 97 streamflow- mainstem Brazos River: Possum Kingdom Lake, Lake gaging stations with at least 10 years of unregulated Granbury, and Lake Whitney. or regulated daily discharge data through water year2 The USGS has operated about 140 streamflow- 1995. Statistical tests were applied to the annual mini- gaging stations in the Brazos River Basin during various mum 7-day discharges. The Mann-Kendall test for periods since 1899. Ninety-seven stations have at least monotonic trends3 was applied separately to the unreg- 10 years of unregulated or at least 10 years of regulated ulated and regulated annual minimum 7-day discharges daily discharge data. A regulated station is defined as for all 97 stations. The Wilcoxon rank-sum test for sig- having at least 10 percent of its contributing drainage nificant differences between the median of groups was area regulated by one or more reservoirs. Forty-six sta- applied to the 25 stations with at least 10 years of dis- tions have at least 10 years of unregulated discharge charge data before and after regulation. The Pearson data only, 26 stations have at least 10 years Type III probability distribution was used to estimate of regulated discharge data only, and 25 stations have the 7Q2 for the unregulated and regulated discharge at least 10 years unregulated and 10 years regulated dis- data for all 97 streamflow-gaging stations. charge data (pl. 1). Selected characteristics of the 97 Physical Setting stations are listed in table 2 (at end of report). The contributing drainage areas for the 97 stations range from The Brazos River Basin drains about 45,000 8.65 to 35,773 mi2. Fifteen stations are on the mainstem square miles (mi2), of which more than 35,000 mi2 are of the Brazos River and 41 stations are on 10 major trib- contributing, and extends from northwest Texas to the utaries: Salt Fork Brazos River, Clear Fork Brazos Gulf of Mexico (fig. 1). Mean annual precipitation, River, Paluxy River, Nolan River, North Bosque River, mostly as rainfall, ranges from about 16 inches (in.) in Leon River, Lampasas River, San Gabriel River, Little the northwestern part of the basin to 51 in. at the mouth River, and Navasota River. For all stations, the total and generally increases from west to east (U.S. Depart- record ranges from 10 to 97 years; for those stations ment of Commerce, National Oceanic and Atmospheric with at least 10 years each of unregulated and regulated data, the unregulated record ranges from 10 to 66 years 2A water year is the 12-month period from October 1 through and the regulated record ranges from 11 to 58 years. September 30. The water year is designated by the year in which it Fifty-one of the 97 stations have been discontinued or ends; thus, the water year ending September 30, 1995, is water year 1995. converted to partial-record stations, leaving 46 as cur- 3A monotonic trend means that a variable (the annual mini- rently (1997) active daily streamflow-gaging stations. mum 7-day discharge in this report) increases or decreases over Of the 51 stations with at least 10 years of regulated time, but not necessarily linearly. data, 41 stations are regulated by one or more reservoirs

2 Analysis of Minimum 7-Day Discharges and Estimation of Minimum 7-Day, 2-Year Discharges for Streamflow-Gaging Stations in the Brazos River Basin, Texas 102o 100o

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Brazos River Basin

o 106 o 32o 104

TEXAS

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28o

GULF OF MEXICO

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Figure 1. Location of the Brazos River Basin, Texas. listed in table 1. The remaining 10 stations are regulated streamflow-gaging stations. Statistical tests were by flood-retarding structures with normal storage applied to the annual minimum 7-day discharges to capacities less than 5,000 acre-ft. The areal extent identify trends in the unregulated and regulated dis- of regulation—the percent drainage area considered charge data and significant differences between the regulated—ranges from 11.1 to 99.8 percent. unregulated and regulated discharge data. The 7Q2 for each station was estimated by fitting the annual Methods of Analysis minimum 7-day discharges to a probability distribution. The station 7Q2 was estimated as the discharge for a The annual minimum 7-day discharges were 2-year recurrence interval (0.50 exceedance probabil- computed from daily mean discharge data for the ity). Several different probability distributions were

INTRODUCTION 3 examined to select the most appropriate distribution for rejected in favor of the alternative hypothesis if the the frequency of minimum 7-day discharges in the Bra- p-value4 from the test is less than or equal to the α-level. zos River Basin. The results of the statistical analysis Setting α = 0.05 results in a 5-percent chance and the frequency analysis were used to determine the that the null hypothesis will be rejected when in fact it effect of reservoirs on the 7Q2. is true—that is, the conclusion from the test is that N-Day Analysis there is a trend when the true situation is that there is no trend. Thus the confidence level of the test is 95 N-day discharges are computed as the mean of N percent. consecutive daily mean discharges. The annual minimum 7-day discharge is the minimum mean of any The test yields a correlation coefficient, Kendall’s seven consecutive daily mean discharges in each water tau (τ). The value of τ is influenced by sample size and year. Each successive water year was analyzed to gener- ranges from -1 to +1. τ is a measure of the strength of a ate a time series of annual minimum 7-day discharges trend (strength of the correlation between discharge and for a station. The 7-day analysis was performed using time). For example, if all discharges in a tested time the period of record for each of the 97 streamflow- series decrease with time, τ = -1; whereas if all dis- gaging stations. charges increase with time, τ = +1. The sign of τ thus indicates the direction of the trend. Statistical Analysis If there are no significant differences between The low-flow discharge of a regulated stream unregulated and regulated annual minimum 7-day might be affected by the operation of an upstream discharges for a station, it might be appropriate to use reservoir. Such effects might not be consistent from year the entire period of record for frequency analysis. The to year depending upon the timing and magnitude of Wilcoxon rank-sum test (Helsel and Hirsch, 1992) was reservoir releases. This inconsistency might affect the used to determine if the unregulated annual minimum frequency-analysis assumption that the low-flow dis- 7-day discharges are significantly different from the charges are independent. For this reason, frequency regulated annual minimum 7-day discharges for the analysis typically is used only on unregulated (natural) streams. However, frequency analysis can be used 25 stations with at least 10 years each of unregulated meaningfully on regulated streams if no significant tem- and regulated discharge data. The test is a rank-based poral trends exist in the regulated record and if the oper- procedure to determine whether two groups of data are ational policies remain constant for the period. It is also the same (specifically, whether the two groups have the desirable to test unregulated discharge data for temporal same median). The Wilcoxon rank-sum test in this trends due to natural causes that could affect the application is a two-sided hypothesis test that deter- assumption of independence among low-flow data. mines for a station record whether the unregulated The Mann-Kendall test (Helsel and Hirsch, 1992) annual minimum 7-day discharges are the same as the was used to determine if the annual minimum 7-day regulated annual minimum 7-day discharges (same discharges for unregulated and regulated periods of medians) at the α = 0.05 significance level. The null record have significant trends. The test is a rank-based hypothesis is that the unregulated and regulated dis- procedure (and therefore resistant to the effect of a small charges are the same (same medians); the alternative number of unusual values or "outliers") used to deter- hypothesis is that they are different (median of unregu- mine whether a variable increases or decreases with lated discharges larger or smaller than median of regu- time. The Mann-Kendall test in this application is a two- lated discharges). As in the Mann-Kendall test, the null sided hypothesis test to indicate whether there is an hypothesis is rejected in favor of the alternative hypoth- increasing or decreasing trend in annual minimum esis if the p-value from the test is less than or equal to 7-day discharges at the α = 0.05 significance level. The the α-level. null hypothesis (what is assumed to be true before the test) is that there is no trend; the alternative hypothesis 4 The p-value is the "attained significance level" (the signifi- (the situation anticipated to be true if the data show cance level attained by the data), which is the probability of obtain- that the null hypothesis is unlikely) is that there is an ing the computed test statistic, or one even less likely, when the null increasing or decreasing trend. The null hypothesis is hypothesis is true (Helsel and Hirsch, 1992, p. 108).

4 Analysis of Minimum 7-Day Discharges and Estimation of Minimum 7-Day, 2-Year Discharges for Streamflow-Gaging Stations in the Brazos River Basin, Texas Frequency Analysis logarithmic transformations give greatly increased weight to peaks of small magnitude (low flows). How- The objective of frequency analysis of streamflow ever, when L-moment statistics are used, it is not data is to relate the magnitude of extreme events necessary to use a logarithmic transformation. Also, a to their frequency of occurrence (exceedance probabil- minimum 7-day discharge of zero is possible, which, ity) through the use of a probability distribution. The if present, requires removal from the analysis because data for each station are assumed to be independent the logarithm of zero is undefined. A more complete and identically distributed. The exceedance probability description of frequency analysis using L-moments also can be expressed as a return period or recurrence and the Pearson Type III distribution can be found in interval. A 2-year recurrence interval has a 50-percent Stedinger and others (1993). exceedance probability or a 1-in-2 chance of being equaled or exceeded in any year. Acknowledgments Traditionally, the sample product moments (mean, variance, skewness, and kurtosis) are used to Sheryl Franklin of the BRA provided valuable summarize the data and to fit a probability distribution. review comments during preparation of the report. Another more recent approach is to use L-moment Glenn A. Rivers and Jessica A. Murray of the USGS statistics as introduced by Hosking (1990). The sample assisted with the compilation and processing of the data L-moment estimates (mean, L-variance, L-skewness, used in this report. and L-kurtosis) are linear combinations of the ordered data and do not involve squaring or cubing the values ANALYSIS OF MINIMUM 7-DAY as do the product moments. As a result, the L-moments DISCHARGES are almost unbiased and exhibit small sampling variance, whereas the product moments are highly biased The Mann-Kendall test was used to determine if and can exhibit large sampling variance (Stedinger and the unregulated and regulated annual minimum 7-day others, 1993). discharges have trends. The Wilcoxon rank-sum test was used to determine if the medians of the annual min- An L-moment diagram illustrates the relation imum 7-day discharges before regulation are signifi- between L-skewness and L-kurtosis and is useful in cantly different from those after regulation. determining the most appropriate distribution to fit to the data. Five different distributions were examined Mann-Kendall Test for use in this study: generalized extreme value distribution, generalized logistic distribution, generalized The Mann-Kendall test first was applied to the pareto distribution, log-normal distribution, and Pear- annual minimum 7-day discharges for the 46 stations son Type III distribution. The L-moment diagrams for with at least 10 years of unregulated discharge data only. the unregulated and regulated stations with five differ- A trend for an unregulated station might be the result of ent probability distributions are shown in figure 2. The hydrologic variability, land-use change, or increase or Pearson Type III distribution graphically fits the data for decrease in withdrawals or return flows during the streamflow-gaging stations in the Brazos River Basin period of record. There is a significant trend at the 95- better than the four other probability distributions. percent confidence level for 8 of the 46 stations (table 3 The Pearson Type III distribution is a three- at end of report). Three different trends are apparent parameter probability distribution. The L-moment sta- from graphical examination of the annual minimum 7- tistics of the data are used to estimate the parameters of day discharges for the eight stations. The two stations the distribution. Either the data or logarithmic transfor- indicating a negative trend (negative Kendall’s τ), mations of the data generally are used to estimate the Sabana River near De Leon (fig. 3) and Big Creek near moments (mean, standard deviation, and skewness). Freestone, have a few non-zero minimum 7-day dis- The log-Pearson Type III distribution, recommended for charges at the beginning of the period of record fol- flood frequency analyses (Interagency Advisory Com- lowed by a series of zero discharges. Five of the 6 mittee on Water Data, 1982), uses a logarithmic trans- stations indicating an increasing trend (positive Ken- formation of the measured flood peaks. Logarithmic dall’s τ), Clear Fork Brazos River near Roby (fig. 4), transformations often are effective for reducing skew- California Creek near Stamford, North Fork Hubbard ness of peaks that range over orders of magnitude; but Creek near Albany, San Gabriel River near Circleville,

ANALYSIS OF MINIMUM 7-DAY DISCHARGES 5 1.0

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EXPLANATION GENERALIZED EXTREME VALUE DISTRIBUTION (Stedinger and others, 1993)

GENERALIZED LOGISTIC DISTRIBUTION (Stedinger and others, 1993)

GENERALIZED PARETO DISTRIBUTION (Stedinger and others, 1993)

LOG-NORMAL DISTRIBUTION (three parameter) (Stedinger and others, 1993)

PEARSON TYPE III DISTRIBUTION (Stedinger and others, 1993)

L-MOMENT RATIO FOR CORRESPONDING STREAMFLOW-GAGING STATION (Stedinger and others, 1993)

Figure 2. L-moment diagram for unregulated and regulated streamflow-gaging stations, Brazos River Basin, Texas.

6 Analysis of Minimum 7-Day Discharges and Estimation of Minimum 7-Day, 2-Year Discharges for Streamflow-Gaging Stations in the Brazos River Basin, Texas 1.8

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IN CUBIC FEET IN CUBIC FEET SECOND PER 0.6 ANNUAL MINIMUM 7-DAY DISCHARGE, MINIMUM 7-DAY ANNUAL

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0 1960 1962 1964 1966 1968 1970 1972 1974 1976 1978 1980 1982 1984 1986 Figure 3. Annual minimum 7-day discharges for station 08099300 Sabana River near De Leon, Texas, water years 1961–86.

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0 1962 1964 1966 1968 1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 Figure 4. Annual minimum 7-day discharges for station 08083100 Clear Fork Brazos River near Roby, Texas, water years 1963–93.

ANALYSIS OF MINIMUM 7-DAY DISCHARGES 7 and East Yegua Creek near Dime Box, have below-aver- Seymour, the weight of the evidence against the null age minimum 7-day discharges early in the period of hypothesis is nearly strong enough to reject the null record (probably due to drought) and above-average hypothesis (p-value = 0.053, 94.7-percent confidence discharges late in the period of record. The increasing level) and conclude that a significant trend is present. trends for the five stations represented by the example in Kendall’s τ is negative for 2 of the 5 stations with unreg- figure 4, Clear Fork Brazos River near Roby, probably ulated data and for 1 of the 10 stations with regulated are the result of hydrologic variability. The minimum 7- data. day discharges for the sixth station, Big Creek near Graphical examination of the annual minimum 7- Needville, indicate a substantially increasing trend (fig. day discharges of the five stations with unregulated data 5), which is probably the result of land use changes dur- indicates the presence of two different trends based on ing the period of record. the sign of Kendall’s τ. The two stations with a negative The Mann-Kendall test also was applied to annual Kendall’s τ (Leon River near Hasse and Yegua Creek minimum 7-day discharges for the 26 stations with at near Somerville) have a few non-zero minimum 7-day least 10 years of regulated discharge data only. A trend discharges at the beginning of the period of record fol- for a regulated station might be the result of hydrologic lowed by a series of zero discharges. The decreasing variability, addition of one or more reservoirs, or trends probably are due to hydrologic variability and are changes in operation of the reservoirs. There similar to the trend shown in figure 3, Sabana River near is a significant trend at the 95-percent confidence level De Leon. The three stations with a positive Kendall’s τ for 6 of the 26 stations (table 3). Kendall’s τ is negative (Salt Fork Brazos River near Aspermont, Leon River at for 1 of the 6 stations, indicating a decreasing trend. Gatesville, and Navasota River near Bryan) might be the Graphical examination of the annual minimum 7-day result of minimum 7-day discharges of zero early in the discharges for the Brazos River near Aquilla (fig. 6) unregulated period due to drought. The annual mini- indicates a decrease in the minimum 7-day discharge mum 7-day discharges for the Salt Fork Brazos River during 1969–95 compared to that during 1941–68. Lake near Aspermont are shown in figure 7. The unregulated Whitney was completed in 1951 (table 1); the decrease period of record for this station is 1940–63. might be the result of operational changes in the reservoir in 1969 when the conservation pool was raised. The Graphical examination of the annual minimum results of the Mann-Kendall test for just the 1969–95 7-day discharges of the 10 stations with regulated subset of the data for the Brazos River near Aquilla data indicates that only Brazos River near Glen Rose (p-value = 0.917 and τ = 0.017) indicate no significant seems to be significantly affected by the addition of trend at the 95-percent confidence level. The remaining another reservoir. The minimum 7-day discharges gen- five stations with an increasing trend (Kendall’s τ is pos- erally are larger during roughly the first one-half of the itive), Brazos River near Dennis, North Bosque River at regulated period of record (1941–69) than during Hico, Leon River near Hamilton, Little River near Little roughly the second one-half of the period of record River, and Brazos River near Juliff have a few minimum (1969–95), consistent with the negative Kendall’s τ 7-day discharges that are below average at the begin- (fig. 8). The beginning of generally smaller minimum ning of the period of record and above average at the end 7-day discharges coincides with the completion of Lake of the period of record. The trends for the five stations Granbury in 1969 (table 1). The results of the Mann- are similar to the trend shown in figure 4, Clear Fork Kendall test for 1969–95 for the Brazos River near Glen Brazos River near Roby, and probably are the result of Rose (p-value = 0.162 and τ = 0.194) indicate no signif- hydrologic variability. icant trend. The increasing trend for the regulated period The Mann-Kendall test also was applied to the of the remaining 9 stations (Clear Fork Brazos River at annual minimum 7-day discharges for the 25 stations Nugent, Clear Fork Brazos River at Fort Griffin, Brazos with at least 10 years each of unregulated and regulated River near South Bend, Paluxy River at Glen Rose, discharge data. The test was independently applied to Aquilla Creek near Aquilla, North Bosque River near unregulated and regulated annual minimum 7-day Clifton, North Fork San Gabriel River near George- discharges. There is a significant trend at the 95-percent town, Navasota River near Easterly, Brazos River at confidence level for unregulated data at 5 stations and Richmond) might result from higher minimum 7-day for regulated data at 10 stations (table 3). For the regu- discharges during 1990–95, which are attributed to lated period at one additional station, Brazos River at hydrologic variability.

8 Analysis of Minimum 7-Day Discharges and Estimation of Minimum 7-Day, 2-Year Discharges for Streamflow-Gaging Stations in the Brazos River Basin, Texas 1.4

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0 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 Figure 5. Annual minimum 7-day discharges for station 08150000 Big Creek near Needville, Texas, water years 1948–95.

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0 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 Figure 6. Annual minimum 7-day discharges for station 08093100 Brazos River near Aquilla, Texas, water years 1941–95.

ANALYSIS OF MINIMUM 7-DAY DISCHARGES 9 5.0

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0 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 Figure 7. Annual minimum 7-day discharges for station 08082000 Salt Fork Brazos River near Aspermont, Texas, water years 1940–95.

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100 ANNUAL MINIMUM 7-DAY DISCHARGE, MINIMUM 7-DAY ANNUAL

0 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 Figure 8. Annual minimum 7-day discharges for station 08091000 Brazos River near Glen Rose, Texas, water years 1924–95.

10 Analysis of Minimum 7-Day Discharges and Estimation of Minimum 7-Day, 2-Year Discharges for Streamflow-Gaging Stations in the Brazos River Basin, Texas Wilcoxon Rank-Sum Test zero annual minimum 7-day discharges. Most of these 14 stations are on minor tributaries to the Brazos River. The Wilcoxon rank-sum test was applied to The 7Q2 ranges from 0.02 to 2.8 cubic feet per second annual minimum 7-day discharges for the 25 stations (ft3/s) for 11 of the 46 unregulated stations. The 7Q2 is with at least 10 years each of unregulated and regulated greater than 5 ft3/s for 4 of the 46 unregulated stations discharge data (table 4 at end of report). There is a (Lampasas River near Kempner, Lampasas River at significant difference between the unregulated and Youngsport, San Gabriel River at Georgetown, and San regulated data at the 95-percent confidence level for 16 Gabriel River near Circleville). of the 25 stations. These significant differences most likely are caused by regulation, which might increase or decrease low flow. The graph of annual minimum 7-day Stations With Regulated Discharge Only discharges for Brazos River at Waco (fig. 9) is an example of a station with a significant difference between Eighteen of the 26 stations with at least 10 years unregulated (1899–1940) and regulated (1941–95) data. of regulated discharge data only are on tributaries to The nine remaining stations show no significant differ- the Brazos River. The 7Q2 is zero for 9 stations and ranges from 0.01 to 55 ft3/s for 9 stations. The 7Q2 val- ence between the unregulated and regulated annual min- 3 imum 7-day discharge data, probably because of ues range from 28 to 631 ft /s for the eight regulated- no flow, hydrologic variability, or leakage through the only stations on the mainstem Brazos River. Of the 9 dams. Also, regulation by flood-retarding structures regulated-only stations with 7Q2 of zero, a majority might not significantly affect low flow. The nine sta- of the annual minimum 7-day discharges are zero, tions are Salt Fork Brazos River near Aspermont including 2 stations with all zero annual minimum (fig. 7), Clear Fork Brazos River at Nugent, Clear Fork 7-day discharges. In contrast, of the 17 regulated sta- Brazos River at Fort Griffin, Paluxy River at Glen Rose, tions with the 7Q2 greater than zero, a majority of the Aquilla Creek near Aquilla, Leon River near Belton, annual minimum 7-day discharges are non-zero, includ- North Fork San Gabriel River near Georgetown, Little ing 11 stations with all non-zero annual minimum 7-day River at Cameron, and Brazos River at Richmond. discharges. The graph of annual minimum 7-day discharges for the Paluxy River at Glen Rose (fig. 10) is an example Stations With Both Unregulated and Regulated of a station with no significant difference (p-value = Discharge 0.102) between unregulated (1942–82) and regulated (1983–95) data. Although the results of the Wilcoxon rank-sum test (table 4) indicate no significant difference between ESTIMATION OF MINIMUM 7-DAY, 2-YEAR the unregulated and regulated annual minimum 7-day DISCHARGES discharges for 9 of the 25 stations with both types of discharge record, the 7Q2 was estimated separately for the The 7Q2 was estimated for each of the 97 unregulated and regulated data for all 25 stations streamflow-gaging stations by fitting the Pearson Type because the data were considered to be two independent III distribution to the annual minimum 7-day discharges groups. The 7Q2 is zero for the unregulated data of 9 with a 2-year recurrence interval. The L-moment stations and for the regulated data of 3 stations. Of the statistics of the annual minimum 7-day discharges were 18 stations with both types of data on tributaries to the used to fit the Pearson Type III distribution. The 7Q2 for Brazos River, the 7Q2 ranges from 0.04 to 48 ft3/s for each unregulated and regulated period of record for the the unregulated data of 11 stations (the 7Q2 is zero for 97 streamflow-gaging stations is listed in table 5 (at end the other 7 stations), and the 7Q2 ranges from 0.02 to 54 of report). ft3/s for the regulated data of 15 stations (the 7Q2 is zero Stations With Unregulated Discharge Only for the other 3 stations). The 7Q2 for the seven stations on the mainstem Brazos River ranges from 0 to 568 ft3/s The 7Q2 is zero for 31 of the 46 stations with at for unregulated data and from 0.30 to 670 ft3/s for reg- least 10 years of unregulated discharge data only. Of ulated data. The number or probability of zero annual these 31 stations, a majority of the annual minimum 7- minimum 7-day discharges decreases after regulation day discharges are zero, including 14 stations with all for most of the 25 stations.

ESTIMATION OF MINIMUM 7-DAY, 2-YEAR DISCHARGES 11 600

500

400

300

IN CUBIC FEET PER PER SECOND FEET IN CUBIC 200 ANNUAL MINIMUM 7-DAY DISCHARGE, 7-DAY MINIMUM ANNUAL

100

0 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Figure 9. Annual minimum 7-day discharges for station 08096500 Brazos River at Waco, Texas, water years 1897–1995.

6 IN CUBIC FEET PER SECOND PER FEET IN CUBIC ANNUAL MINIMUM 7-DAY DISCHARGE, 7-DAY MINIMUM ANNUAL 4

0 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 Figure 10. Annual minimum 7-day discharges for station 08091500 Paluxy River at Glen Rose, Texas, water years 1948–95.

12 Analysis of Minimum 7-Day Discharges and Estimation of Minimum 7-Day, 2-Year Discharges for Streamflow-Gaging Stations in the Brazos River Basin, Texas The ratio of regulated 7Q2 to unregulated 7Q2 stations that have been operated in the Brazos River is greater than 1.0 for 13 of the 25 stations (table 5), Basin, 97 have at least 10 years of unregulated or 10 ranging from 1.1 at Little River at Cameron to 30 at years of regulated discharge data. Forty-six stations Brazos River near South Bend, indicating an increase have at least 10 years of unregulated discharge data in the 7Q2 after regulation. There is no significant dif- only, 26 stations have at least 10 years of regulated dis- ference (table 4) between the annual minimum 7-day charge data only, and 25 stations have at least 10 years discharges for 5 of these 13 stations. The ratios for 2 of of unregulated and 10 years of regulated discharge data. these 5 stations with no significant differences (table 4) Fifteen of the 97 stations are on the mainstem Brazos are about 1.0 (1.1 and 1.2) and the ratios for the remain- River, and 41 stations are on 10 major tributaries. ing 3 stations are substantially greater than 1.0, ranging Statistical tests were applied to the annual from 6.4 to 9.5. minimum 7-day discharge data of the streamflow- The ratios for three stations are less than 1.0, gaging stations. On the basis of the results of the Mann- ranging from 0.06 at San Gabriel River at Laneport to Kendall test, there is a significant trend at the 95-percent 0.65 at Leon River near Belton and indicating a decrease confidence level for 8 of the 46 stations with unregu- in the 7Q2 after regulation. There is a significant differ- lated data only, 6 of the 26 stations with regulated data ence (table 4) between the annual minimum 7-day dis- only, and 5 stations for the unregulated period and 10 charges for 1 of the 3 stations (San Gabriel River at stations for the regulated period of the 25 stations with Laneport) with the 7Q2 less than 1.0. both unregulated and regulated data. On the basis of the The ratio is undefined for 9 stations because the results of the Wilcoxon rank-sum test, there is a signifi- unregulated 7Q2 is zero, but the 7Q2 actually increases cant difference at the 95-percent confidence level after regulation for 6 stations; the remaining 3 stations between the unregulated and regulated annual minimum showed no change (7Q2 = 0). There is a significant dif- 7-day discharges for 16 of the 25 stations with at least ference (table 4) between the annual minimum 7-day 10 years unregulated and 10 years regulated discharge discharges for the six stations with an undefined ratio of data. regulated to unregulated 7Q2. There is no significant The 7Q2 is estimated by fitting a probability dis- difference (table 4) between the annual minimum 7-day tribution with a 2-year recurrence interval to the annual discharges for 2 of the 3 stations (Clear Fork Brazos minimum 7-day discharges. The 7Q2 was estimated for River at Fort Griffin and Aquilla Creek near Aquilla); each station with at least 10 years of unregulated or at both have a 7Q2 of zero before and after regulation. least 10 years of regulated discharge data using the The 7Q2 increased during regulation for 19 of the Pearson Type III distribution fitted by the L-moment 25 stations with at least 10 years each of unregulated statistics of the annual minimum 7-day discharges. The and regulated discharge data (table 5). Based on the 7Q2 is zero for 31 of the 46 unregulated-only stations Wilcoxon rank-sum test (table 4), the 7Q2 increased for and for 9 of the 26 regulated-only stations. The 7Q2 also 14 of the 16 stations with a significant difference at the is zero for 9 stations before regulation and 3 stations 95-percent confidence level between unregulated and after regulation of the 25 stations with both unregulated regulated annual minimum 7-day discharges. The effect and regulated data. For the eight regulated-only stations of regulation for most stations generally was an increase on the mainstem Brazos River, the 7Q2 ranges from 3 in the magnitude of the 7Q2. 28 to 631 ft /s. For the seven stations with both unregulated and regulated data on the mainstem Brazos River, 3 SUMMARY the 7Q2 ranges from 0 to 568 ft /s before regulation and from 0.30 to 670 ft3/s after regulation. The 7Q2 The minimum 7-day, 2-year discharge (7Q2) is a increased during regulation for 19 of the 25 stations useful statistic for assessing the effect that proposed or with at least 10 years each of data before and after reg- existing withdrawals or return flows might have on the ulation. On the basis of the results of the Wilcoxon rank- streamflow and water quality of receiving streams. The sum test and the ratios of regulated 7Q2 to unregulated contributing drainage area of the Brazos River Basin is 7Q2, the effect of regulation for most stations generally more than 35,000 mi2. Of about 140 streamflow-gaging was an increase in the magnitude of the 7Q2.

SUMMARY 13 REFERENCES CITED Data Coordination, Hydrology Subcommittee, Bulletin 17B [variously paged]. Helsel, D.R., and Hirsch, R.M., 1992, Studies in environmen- Riggio, R.F., Bomar, G.W., and Larkin, T.J., 1987, Texas tal science 49–Statistical methods in water resources: drought—Its recent history (1931–1985): Texas Water Amsterdam, Elsevier, 522 p. Commission, LP87–04, 74 p. Stedinger, J.R., Vogel, R.M., and Foufoula-Georgiou, E., Hosking, J.R.M., 1990, L-moments—Analysis and 1993, Frequency analysis of extreme events, in estimation of distributions using linear combinations Maidment, D.A., ed., Handbook of applied hydrology: of order statistics: Journal Royal Statistical Society, B, New York, McGraw-Hill, chap. 18. v. 52, no. 1, p. 105–124. U.S. Department of Commerce, National Oceanic and Interagency Advisory Committee on Water Data, 1982, Atmospheric Administration, 1990, Climatological Guidelines for determining flood-flow frequency: data, annual summary, Texas, 1990: Asheville, N.C., Reston, Va., U.S. Geological Survey, Office of Water v. 95, no. 13, 77 p.

14 Analysis of Minimum 7-Day Discharges and Estimation of Minimum 7-Day, 2-Year Discharges for Streamflow-Gaging Stations in the Brazos River Basin, Texas Year began regulation Normal storage (acre-ft) capacity by reservoir by Stream regulated ) 2 area (mi drainage Contributing 17'51" 255 Aquilla Creek 52,400 1983 22'18" 17,623 Brazos River 627,100 1951 24'54" 100 Nolan River 25,600 1964 11'51" 64 Creek Squaw 151,047 1977 41'20" 16,113 Brazos River 153,485 1969 16'08" 461 Pinto Palo Creek 44,100 1964 25'32" 14,030 Brazos River 724,700 1941 36'48" 221 Salt Creek 39,000 1958 58'03" 1,085 Hubbard Creek 318,000 1962 34'52" 368 Creek Paint 57,927 1953 40'05" 470 Big Elm Creek 73,960 1938 23'19" 240 Millers Creek 38,800 1974 18'25" 104 Bitter Creek 2,544 1930 05'01" 689 White River 44,897 1964 , contributing drainage area not available] drainage area not available] , contributing ° ° ° ° ° ° ° ° ° ° ° ° ° ° 5,000 acre-feet, Brazos River Basin, Basin, Texas—Continued River Brazos acre-feet, 5,000 48'44" 97 51'55" 97 17'20" 97 34'46" 97 22'27" 97 38'51" 98 52'20" 98 08'04" 98 49'53" 98 04'44" 99 36'58" 99 26'20" 100 24'32" 99 27'28" 101 ° ° ° ° ° ° ° ° ° ° ° ° ° ° t; --,station; noU.S. Geological NA Survey Reservoir County Latitude Longitude Reservoirs with normal storage capacities exceeding 5,000 acre-feet, Brazos River Basin, Texas Basin, River Brazos acre-feet, 5,000 exceeding normal capacities with Reservoirs storage exceeding capacities with normal Reservoirs storage -- Mineral Wells Lake Parker -- -- 63 RockCreek 7,065 1920 ---- Cisco Lake Daniel Lake Eastland Stephens ------NA 115 SandyCreek Gonzales Creek 11,400 45,000 1948 1923 -- Abilene Lake -- Kirby Lake Taylor Taylor ------102Creek Elm 44 Cedar Creek 45,000 1921 7,620 1928 -- Davis Lake Knox -- -- NA Dutchman Creek 5,395 1959 no. , square miles; acre-ft, acre-fee acre-ft, , square miles; 2 Station Table 1 08093350 Aquilla Lake Bosque 31 08092500 Whitney Lake Bosque 31 08091900 Cleburne Pat Lake Johnson 31 08091730 Creek Reservoir Squaw Somervell 31 08090900 Granbury Lake Hood 32 08090300 Pinto Palo Lake Pinto Palo 32 08088500 Possum Kingdom LakePinto Palo 32 08088400 Graham Lake Young 33 08086400Reservoir Hubbard Creek Stephens 32 08084500 Stamford Lake Haskell 33 08083500 Phantom Fort Hill Lake Jones 32 08083200 Sweetwater Lake Nolan 33 08082800 Millers Creek Reservoir Baylor 33 08080910 Lake White River Crosby 33 Table 1. Table [mi 1. Table

Table 1 15 Year began regulation Normal storage (acre-ft) capacity by reservoir Stream regulated ) 2 area (mi drainage Contributing 19'08" 675 River Navasota 225,400 1978 19'34" 730 River Gabriel San 65,500 1980 34'43" 196 River Navasota 10,000 1962 43'38" 247 RiverGabriel San Fork North 37,100 1980 31'57" 1,313 Lampasas River 235,700 1968 28'28" 3,531 Leon River 457,600 1954 29'09" 1,259 River Leon 59,400 1963 11'51" 1,652 Bosque River 152,500 1965 40'32" 259 River Leon 27,290 1954 ° ° ° ° ° ° ° ° ° 19'30" 96 41'34" 97 38'37" 96 40'03" 97 01'20" 97 06'22" 97 58'07" 98 34'46" 97 21'46" 98 ° ° ° ° ° ° ° ° ° n -- -- 40 Creek Camp 8,400 1949 s -- -- NA Creek Peach 15,227 1975 Reservoir County Latitude Longitude Reservoirs with normal storage capacities exceeding 5,000 acre-feet, Brazos River Basin, Texas—Continued Basin, River Brazos acre-feet, 5,000 exceeding normal capacities with Reservoirs storage ---- GibbonsCreek Reservoir -- Reservoir Harris William Grimes Smithers Lake Bend Fort -- -- Bend Fort ------NA 85 -- Gibbons Creek Creek Oyster 24 Dry Creek 32,084 5,000 1981 1947 18,750 1957 -- Oaks Reservoir Twin --Lake Camp Creek Robertson -- Robertso -- NACreek Duck 30,319 1982 --Lake Bryan Utilities Brazo -- Alcoa Lake Milam -- -- NA Sandy Creek 15,650 1952 ---- Creek Lake Lake Reservoir Creek Tradinghouse McLennan -- McLennan ------39 Creek Tradinghouse NA Manos Creek 37,814 1968 8,500 1953 no. Station 08110470 Limestone Lake Robertson 31 08105600 Granger Lake Williamson 30 08109900 Somerville Lake08110300 Mexia Lake Burleson Limestone -- 31 -- 1,007 Creek Yegua 160,100 1967 08104650 Georgetown Lake Williamson 30 08104050 StillhouseLake Hollow Bell 31 08102000 Belton Lake Bell 31 08099400 Proctor Lake Comanche 31 08095550 Lake Waco McLennan 31 08099000 Leon Lake Eastland 32 Table 1. Table

16 Analysis of Minimum 7-Day Discharges and Estimation of Minimum 7-Day, 2-Year Discharges for Streamflow-Gaging Stations in the Brazos River Basin, Texas Areal extent of extent (percent) regulation Texas Texas— Major reservoirs regulating ort Phantom Hill Lakeort Phantom Hill Lake 21.4 11.8 record Regulated (water years) (water Total record Period No. Period No. (water years) (water ) 2 area (mi buting Contri- drainage or 10 years of regulated discharge data, Brazos River Basin, River Brazos data, discharge regulated of years 10 or 49'40" 20020'24" 1940–49 43811'50" 10 1984–93 24410'49" 10 1,864 1962–95 --13'36" 1925–95 33 -- 042'08" 79.2 6642'17" 382 1966–78 -- 025'53" 279 1940–78 13 1,985 --25'52" 0 1965–89 -- 3424'29" 1964–86 290 0 25 --14'16" -- 23 64.3 1960–86 2,496 --12'47" 1967–89 1957–77 0 1964–86 27 23 --04'51" 1940–95 23 88.8 structures flood-retarding 12 21 0 -- Lake River White -- 251 1966–83 56 25.1 -- 1966–86 18 -- 1964–95 --23'18" -- 32 0 21 Lake River White 228 -- -- 0 34.7 -- 1963–93 -- -- 0 31 -- -- 27.6 0 ------0 ------38'32"13'27" 478 3,98810'11" 1963–95 1925–95 228 33 71 1964–75 1938–95 12 -- 58 F 0 -- 0 ------16'02" 5,97227'53" 1925–95 10448'53" 71 1964–95 1,41647'32" 1964–95 3248'27" 1968–89 205 3251'08" Lake River White 133 22 1969–89 --40'09" 39.1 1964–79 2,199 21 1964–79 -- 0 16 1925–95 11.5 16 -- 1964–79 0 71 16 Abilene Lake 0 1938–95 -- -- 58 F 0 -- -- 76.7 ------° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° 55'51" 99 56'04" 99 33'33" 99 35'08" 101 14'52" 101 02'18" 101 00'29" 100 21'03" 101 10'44" 101 21'22" 100 12'43" 100 17'18" 100 24'03" 100 20'02" 100 14'00" 100 22'59" 100 34'51" 99 19'45" 99 47'15" 100 35'53" 99 34'04" 99 21'08" 99 23'29" 99 41'24" 99 ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° LubbockGarza 33 Garza 33 Stonewall 33 33 nday, Texasnday, Throckmorton 33 Station name County Latitude Longitude River at Lubbock, Texas at Lubbock, River River near Post, Texas River Texas Justiceburg, Texas Aspermont, Streamflow-gaging stations with at least 10 years of unregulated of 10 years least at with stations Streamflow-gaging Streamflow-gaging stations with at least 10 years of unregulated or 10 years of regulated discharge data, Brazos River Basin, River Brazos data, discharge regulated of years or 10 unregulated of 10 years least at with stations Streamflow-gaging , square miles; --, no regulated period of record] period --, no regulated , square miles; no. 2 Station Table 2 08084800 Texas near Stamford, Creek California 08085500 Texas Griffin, at Fort River Brazos Clear Fork 08086050 Shackelford Texasat Moran, Creek Deep Jones 32 32 Shackelford 32 08079500 Brazos Fork Mountain Double Fork North 08079575 Brazos Fork Mountain Double Fork North 08079600 at Brazos River Fork Double Mountain 08080500 near Brazos River Fork Double Mountain 08080540 Texas Creek near Post, McDonald 08080700Texas at Plainview, Draw Water Running 08080950 Texas Girard, near Duck Creek 08081000 Hale Texas near Peacock, River Brazos Salt Fork Garza08081200 Texas near Jayton, Creek Croton Stonewall08081500 Texas Creek near Salt Aspermont, Croton 34 08082000 33 33 Kent Texas near Aspermont, River Brazos Salt Fork Stonewall08082100 King Texas Aspermont, near Creek Stinking 08082180 Stonewall Texas near Knox City, Creek 33 Croton North 33 08082500 TexasSeymour, at River Brazos 33 33 Stonewall Stonewall08082700 Millers Creek near Mu 08083100 33 33 Texas Roby, near River Brazos Clear Fork 08083240 Texas at Hawley, River Brazos Clear Fork Fisher08083245 Baylor Texas near Hawley, Creek Mulberry Jones08083300 Texas near Abilene, Elm Creek 08083400 32 33 Little Elm Creek near Abilene, Texas08084000 Jones 32 Texasat Nugent, River Brazos Clear Fork Jones Taylor Taylor 32 32 32 32 Table 2. Table [mi Table 2. Table Continued

Table 2 17 11.1 86.3 99.1 79.4 99.7 Areal extent of (percent) regulation Texas— Major reservoirs regulating Hubbard Creek Reservoir Creek Hubbard Lake Granbury Lake Whitney Lake 95 13 Aquilla Lake 82.8 record Regulated (water years) Total record Period No. Period No. (water years) (water ) 2 area (mi buting Contri- drainage ed or 10 years of regulated discharge data, Brazos River Basin, River Brazos data, discharge of regulated 10 years or ed 09'52"16'29" 45408'25" 39.3 1963–7500'15" 613 1964–90 1356'52" 280 1967–95 27 1,08945'59" 1963–95 5,697 29 --38'37" 1956–86 13,107 33 -- 1918–82 31 0 1939–95 -- 46 0 1962–86 -- 57 25 0 1962–82 Reservoir Creek Hubbard 1962–95 21 0 Reservoir Creek Hubbard 34 -- Stamford, Lake 99.6 -- 19.0 ------44'40"37'06" 11.843'25" 1959–77 24.218'08" 1959–89 97 14,245 1910'50" 31 1966–89 1925–9555'32" 573 15,671 --39'48" 24 71 1952–76 16,252 -- 1969–95 1941–95 0 25 1924–95 27 55 -- 043'56" Lake Kingdom Possum 72 1964–76 1969–9524'09" 13 0 70.3 27 1941–95 Pinto Palo Lake 17'51" Lake Kingdom Possum 282 1978–95 -- 98.5 55 17,678 Lake, Kingdom Possum -- 1949–95 18 1939–95 89.5 43 -- 1978–95 57 18 80.5 1964–95Reservoir Creek Squaw 1941–95 28 -- 55 Cleburne Pat Lake Lake, Kingdom Possum -- 91.0 -- 35.5 02'04"34'04" 35928'09" 968 1963–95 1,146 1924–95 33 1960–95 72 1968–95 36 28 1968–95 structures 40 flood-retarding 1968–95 28 28 structures 40 flood-retarding 56.3 structures 42 flood-retarding 20.9 18.1 46'37" 410 1948–95 4808'59" 1983–9505'57" 13 57.9 structures 14 flood-retarding 12'04" 1980–92 12.4 22.1 308 1968–79 13 1940–95 12 -- 56 -- 1983– 0 0 ------11'55"13'46" 95.9 1959–79 45.4 1959–73 21 15 1968–79 12 1959–73 structures 14 flood-retarding 15 structures 8 flood-retarding 62.4 49.1 ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° 41'21" 99 42'27" 99 43'58" 99 38'54" 99 50'13" 98 57'36" 98 01'27" 98 22'13" 98 12'43" 98 49'39" 98 51'45" 98 37'51" 98 36'56" 97 16'18" 97 16'12" 97 09'02" 97 48'44" 97 58'41" 98 47'09" 97 40'10" 97 13'53" 97 00'20" 97 55'11" 97 50'40" 97 12'56" 98 04'26" 98 ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° r at Eliasville, Texas Young 32 en Rose, Texas Somervell 32 Station name County Latitude Longitude que River at Hico, Texasque River Hamilton 31 sque River at Valley Mills, Texasat Valley River sque Bosque 31 Streamflow-gaging stations with at least 10 years of unregulat of 10 years least with at stations Streamflow-gaging no. Station 08086150 Texas near Albany, Creek Hubbard Fork North Shackelford08086212 Texas Albany, Creek below Hubbard 32 08086290 Texas Breckenridge, above Creek Big Sandy 08086500 Stephens Texas Creek near Breckenridge, Hubbard 08087300 ShackelfordRive Brazos Clear Fork 08088000 32 32 Stephens Texas Bend, near South River Brazos 32 Young 33 08086100 Texas Creek near Albany, Hubbard Shackelford 32 08088100 Texas Creek at Salt Olney, 08088300 Texas near Graham, Creek Briar 08088450 Big CedarCreek Texas nearIvan, 08089000 Texas Pinto, near Palo River Brazos 08090500 Texas near Santo, Pinto Creek Palo 08090800 Young Young Texas near Dennis, River Brazos Stephens08091000 Pinto Palo near Glen Rose, Texas Brazos River 33 Pinto Palo 33 32 32 32 Parker Somervell08092000 Texas at Blum, River Nolan 08093100 32 Texas near Aquilla, River Brazos 32 Bosque Hill 31 32 08095000 Texas near Clifton, River Bosque North 08095200 Bo North Bosque 31 08091500 Texas at Glen Rose, River Paluxy 08091750 near Gl Creek Squaw Somervell08093250 Creek Hackberry at Hillsboro, Texas 32 08093400 Texas near Abbott, Creek Cobb 08093500 Aquilla Creek near Aquilla, Texas Hill Hill Hill 32 31 31 08093700 Texas at Stephenville, River Bosque North 08094500 Texas Green Creek near Alexander, Erath08094800 Bos North 32 Erath 32 Table 2. Table Continued

18 Analysis of Minimum 7-Day Discharges and Estimation of Minimum 7-Day, 2-Year Discharges for Streamflow-Gaging Stations in the Brazos River Basin, Texas 67.2 84.4 70.1 88.1 Areal extent of extent (percent) regulation Texas— Major reservoirs regulating Lake Whitney Lake Whitney 2 Lake Hollow Stillhouse 99.4 record Regulated (water years) (water Total record Period No. Period No. (water years) (water ) 2 area (mi buting Contri- drainage 39'18"39'21" 40535'06" 83.1 1935–73 563 1968–95 39 1980–90 28 11 -- -- 1980–90 0 11 Georgetown Lake 0 -- 43.9 ------59'17"31'58" 22.236'19" 479 1963–8227'32" 264 1961–86 20 1,26107'16" 1961–86 1,891 2645'42" 1940–91 2,342 26 --53'05" 1926–95 1961–86 52 2626'28" 1951–95 1980–86 455 41 Leon Lake 0 1963–91 3,54200'59" 7 45 29 1951–95 1963–95 Lake Nabors 02'12" Lake Proctor 1924–95 818 33 1963–95 4542'30" Lake Proctor 72 33 33.3 1963–95 1,24029'32" Lake Proctor -- 1964–95 1954–95 1,321 33 -- 1925–80 42 54.1 32 Unknown Lake Belton 1964–89 56 0 99.8 -- 26 95.3 ------0 53.8 1968–89 2 0 0 -- 99.7 ------20'45" 5,22842'40" 1924–95 24841'27" 38 1969–95 133 1963–95 27 1969–95 33 Lake Belton 1980–95 27 16 Georgetown Lake -- 0 67.5 99.6 -- -- 08'16"58'10" 83.5 20,64549'29" 1959–75 20,870 1939–51 17 1966–95 13 1959–75 30 1941–51 17 11 structures flood-retarding 26 1966–95 Lake Kingdom Possum 30 51.1 Lake, Kingdom Possum 68.0 21'56"21'22" 18211'36" 78.2 1960–85 1,65604'22" 1960–85 20,007 26 1960–81 26 1899–1995 22 97 -- 1980–85 1965–81 1941–95 6 17structures flood-retarding 2 55 0 Lake Waco Lake, Kingdom Possum 53.7 -- 99.8 -- ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° 14" 97 ° 41'28" 97 38'45" 97 01'35" 96 10'25" 98 06'50" 98 57'28" 98 47'19" 98 25'58" 97 17'05" 97 04'12" 97 04'54" 98 54'41" 98 57'26" 97 00'06" 97 57'59" 97 39'42" 97 37'32" 97 18'45" 97 17'18" 96 08'02" 96 30'33" 97 33'20" 97 36'04" 97 32'06" 97 39 ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° Williamson 30 Williamson 30 Burlington,Texas Milam 31 Georgetown, TexasGeorgetown, Williamson 30 Station name County Latitude Longitude Georgetown, Texas Georgetown, Texas Streamflow-gaging stations with at least 10 years of unregulated or 10 years of regulated discharge data, Brazos River Basin, River Brazos data, discharge regulated of years or 10 unregulated of 10 years least at with stations Streamflow-gaging no. Station 08105100 Texas near Georgetown, Creek Berry 08105300 Texas near Weir, River San Gabriel Williamson 30 Williamson 30 08099100 Texas near De Leon, River Leon 08099300 Texas near De Leon, Sabana River 08099500 near Hasse, Texas River Leon 08100000 near Hamilton, Texas Leon River 08100500 Comanche at Gatesville, Texas Leon River Comanche08101000 32 Texas at Pidcoke, Creek Cowhouse 32 08102500 Texas near Belton, River Leon Comanche Hamilton08103800 Texas near Kempner, River Lampasas 31 08103900 Coryell Texas near Briggs, Creek Rocky Coryell Fork South 31 08104000 Texas Burnet at Youngsport, River Lampasas Lampasas08104100 31 Texas near Belton, River Lampasas 31 Bell 31 30 Bell 31 Bell 30 31 08098300 Little Pond near Creek 08104500 Texas near Little River, Little River 08104700 near River Gabriel San Fork North 08104900 Georgetown, at River Gabriel San Fork South Bell08105000 at River San Gabriel 30 08097000 Texas Bayou at Mooreville, Cow 08097500 TexasMarlin, near River Brazos 08098290 nearHighbank, Brazos River Texas Falls Falls Falls 31 31 31 08095300 TexasMcGregor, near River Bosque Middle McLennan 31 08095400 Texas near Crawford, Hog Creek 08095600 Texas near Waco, River Bosque 08096500Texas Waco, at River Brazos McLennan McLennan 31 31 McLennan 31 Table 2. Table Continued

Table 2 19 46.8 58.8 44.4 55.7 20.2 69.7 13.5 46.4 40.9 51.4 39.6 49.7 39.5 49.6 39.2 49.3 Areal extent of (percent) regulation Texas— Major reservoirs regulating Lake Whitney Lake Lake Whitney Lake Lake Limestone Lake Lake Limestone Lake Lake Whitney Lake Lake Whitney Lake Lake Whitney Lake Lake Whitney Lake 91 25 Somerville Lake 99.8 record Regulated (water years) Total record Period No. Period No. (water years) (water ) 2 area (mi buting Contri- drainage ed or 10 years of regulated discharge data, Brazos River Basin, River Brazos data, discharge of regulated 10 years or ed 28'23"16'43" 59957'01" 738 1925–76 7,06501'13" 1966–95 1929'10" 1918–95 44.8 29,949 30 1963–73 78 1900–92 -- 1980–95 11 1954–95 16 76 42 Lake Granger 0 Lake Belton 1941–92 -- 52 Lake, Kingdom Possum 0 -- 98.9 50.0 ------54'16"49'02" 23630'26" 244 1963–95 1,009 1963–95 33 1925–91 33 67 -- 1967– -- 0 0 ------32'24"09'18" 195 31,626 1963–95 1967–83 33 17 1967–83 -- 17 Lake, Kingdom Possum 0 -- -- 31'14"27'01" 23919'31" 311 1980–9517'51" 97.2 1966–78 16 968 1979–95 13 1980–95 1925–95 17 16 1966–78 Mexia Lake 71 13 Mexia Lake -- 1962–95 34 Mexia, Lake 0 82.0 63.0 -- -- 11'32" 1,454 1952–94 43 1962–94 33 Mexia, Lake 11'15" 34,314 1939–95 57 1941–95 55 Lake, Kingdom Possum 12'18"45'27" 376 35,441 1964–93 1904–95 30 75 1941–95 -- 55 Lake, Kingdom Possum 0 -- -- 31'58" 35,518 1950–69 20 1950–69 20 Lake, Kingdom Possum 48'45"44'48" 42.834'56" 1948–95 35,773 8.65 1959–79 45 1968–95 21 24 -- 1968–95 -- 24 0 Lake, Kingdom Possum 0 ------° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° 37'43" 97 41'39" 97 49'53" 96 55'52" 97 36'52" 96 20'21" 96 24'26" 96 19'18" 96 25'10" 96 21'40" 96 34'27" 96 30'44" 96 30'25" 96 10'12" 96 52'10" 96 07'44" 96 52'51" 96 34'56" 95 27'19" 95 28'35" 95 30'42" 95 20'58" 95 ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° eestone, Texas Limestone 31 eedville, TexasBend Fort 29 Station name County Latitude Longitude Streamflow-gaging stations with at least 10 years of unregulat of 10 years least with at stations Streamflow-gaging no. Station 08105700 at Laneport, Texas San Gabriel River 08106500 at Cameron, Texas Little River 08108200 Texas Creek near Cameron, Elm North 08109000 Williamson Texas near Bryan, River Brazos 30 Milam Milam 30 Brazos 30 30 08105400 Texas near Circleville, San Gabriel River Williamson 30 08109700 Texas near Dime Creek Box, Yegua Middle 08109800 Creek near TexasDime Box, East Yegua Lee08110000Texas Somerville, near Creek Yegua Burleson 30 30 Burleson 30 08110100 Texas Lyons, near Creek Davidson 08110200 Texas at Washington, River Brazos Burleson Washington 30 30 08110325 Texas Groesbeck, above River Navasota 08110400 Texas near Groesbeck, River Navasota 08110430 Limestone near Fr Big Creek 08110500 Texas near Easterly, River Navasota 31 Limestone 31 Robertson 31 08111000 Texas near Bryan, River Navasota Brazos 30 08111500 Texas near Hempstead, River Brazos Washington 30 08111700 Mill Creek near Bellville, Texas08114000 at TexasRichmond, River Brazos Austin Bend Fort 29 29 08114500 Texas near Juliff, River Brazos Bend Fort 29 08115000 Big Creek near N 08116400 Texas Creek near Rosenberg, Dry 08116650 Texas near Rosharon, River Brazos Bend Fort Bend Fort 29 29 Table 2. Table Continued

20 Analysis of Minimum 7-Day Discharges and Estimation of Minimum 7-Day, 2-Year Discharges for Streamflow-Gaging Stations in the Brazos River Basin, Texas τ ated or 10 10 or ated ated or 10 p-value Kendall’s = 0.050 Trend at Trend α τ zero; --, no data available; <, less than] <, less no data available; zero;--, p-value Kendall’s Unregulated period Regulatedperiod = 0.050 = Trend at Trend α r streamflow-gaging stations with at least 10 years of unregul of 10 years least at with stations r streamflow-gaging unregul of 10 years least at with stations streamflow-gaging r . -, all annual are -, all minimum . 7-day discharges α Station name near Peacock, Texasnear Peacock, -- NO .446 .059 Mann-Kendall test results of annual minimum 7-day discharges fo discharges 7-day minimum annual of results test Mann-Kendall fo discharges 7-day minimum annual of results test Mann-Kendall no. Station Table 3 08079500Lubbock,at Texas Double BrazosRiver Mountain Fork North Fork 08079575near Post, Texas Double BrazosRiver Mountain North Fork Fork 08079600 NO TexasJusticeburg, at Double Brazos River Mountain Fork 08080500near Aspermont, Texas Double Brazos River Mountain Fork 08080540 NO McDonaldPost, Texas Creek near -08080700 Texas at Plainview, Draw Running Water -08080950 NO NO Ducknear Creek Girard, Texas08081000 - Brazos River Salt Fork 08081200 Croton Creeknear Jayton, Texas -08081500 - -Croton Saltnear Aspermont, Creek Texas08082000 near Aspermont, Texas Salt Brazos River Fork -- 08082100 - - Stinkingnear Creek Aspermont, Texas 08082180 -- Texas North CrotonCreek near Knox City, 08082500Texas at Seymour, Brazos River NO08082700 NO Texas Millers Creek near Munday, -- 08083100 -- - TexasRoby, near Brazos River Clear Fork -08083240 Texasat Hawley, Brazos River Clear Fork NO08083245 -- YES Texas MulberryCreek near Hawley, 08083300 NO Elmnear CreekTexas Abilene, 0.349 -08083400 - .001 LittleAbilene,Creek Elm near Texas NO NO08084000 0.152 -at Nugent, Texas Brazos River Clear Fork .46008084800 CaliforniaStamford, Creek near Texas08085500 .758 - -- -- Texas Griffin, at Fort Brazos River Clear Fork 08086050 YES NO -- - DeepTexas Creek at Moran, NO08086100 NO .052 NOTexas Hubbardnear Albany, Creek - .003 .462 .364 - NO .652 NO -- .383 -- .053 .115 0.958 NO -.740 NO .632 -- - -- NO 0.012 YES -- NO - .420 .043 -- .153 .001 .053 -.179 -- -.256 - NO -- .402 .236 NO YES YES - .452 -- .020 -- <.001 NO .121 - .208 .417 .527 -- .075 -- Table 3. Table of years regulated discharge data 3. Table data—Continued discharge regulated of years thanequal or is less to if p-value is significant [Trend

Table 3 21 τ ated or 10 10 or ated p-value Kendall’s = 0.050 Trend at Trend α τ p-value Kendall’s Unregulated periodUnregulated period Regulated = 0.050 Trend at Trend α Station name Station Mann-Kendall test results of annual minimum 7-day discharges for streamflow-gaging stations with at least 10 years unregul of years at 10 least with stations streamflow-gaging for discharges 7-day minimum of annual test results Mann-Kendall no. Station 08086150 Texas North Hubbard Fork Creek near Albany, 08086212 Texas Albany, Hubbard Creek below 08086290 Breckenridge, Texas Big Sandy Creek above 08086500TexasBreckenridge, Hubbard Creek near 08087300 at Eliasville,Texas Brazos River Clear Fork 08088000 near South Bend, Texas Brazos River 08088100 Texas Salt Creek at Olney, 08088300 YES Briar Creek near Graham, Texas08088450 TexasCedar Big near Creek Ivan, 08089000 0.016 nearPinto, TexasPalo Brazos River NO08090500 0.319 NO Pinto Palo Creek near Santo, Texas08090800 -- NO .189 near Dennis, Texas Brazos River 08091000 .344 near Glen Rose, Texas Brazos River 08091500 -- .243 .049 at Glen Rose, Texas River Paluxy 08091750TexasGlen Rose, Creek near Squaw .084 NO -.09708092000 at Blum, Texas Nolan River 08093100 -- .354 near Aquilla, Texas Brazos River 08093250 NO -- Hackberryat Hillsboro, Creek Texas08093400 NO NO NO NO .134 Cobbnear Abbott, Creek Texas 08093500 Aquilla Creek near Aquilla, Texas - .237 .211 NO -08093700 .343 NOTexas at Stephenville, NorthBosque River 08094500 YES NO --Texas Alexander, Green Creek near .190 .09108094800 -.167 0.211 - - at Hico, Texas NorthBosque River 08095000 NO .037 - --Clifton, near Texas North .707Bosque River -0.103 08095200 Mills, Texas at Valley NorthBosque River NO -- .399 .253 - -.074 -- NO -- -- NO -.101 .760 YES NO NO -- - NO .206 .029 YES .003 .229 YES .132 - .248 -- .004 - NO -.274 -- -- NO .244 .027 .147 .603 NO .495 - .705 .305 -- YES .071 YES .252 -.072 -- .014 .004 .156 NO YES -.268 .462 .148 .050 NO YES NO -.167 .265 - .050 .093 .257 .228 - Table 3. years of regulated discharge data—Continued discharge regulated of years

22 Analysis of Minimum 7-Day Discharges and Estimation of Minimum 7-Day, 2-Year Discharges for Streamflow-Gaging Stations in the Brazos River Basin, Texas τ ated or 10 p-value Kendall’s = 0.050 Trend at Trend α τ p-value Kendall’s Unregulated period Regulatedperiod = 0.050 = Trend at Trend α r streamflow-gaging stations with at least 10 years of unregul of 10 years least at with stations streamflow-gaging r Station name Mann-Kendall test results of annual minimum 7-day discharges fo discharges 7-day minimum annual of results test Mann-Kendall no. Station 08095300 Texas near McGregor, Middle Bosque River 08095400 Hognear Texas Crawford, Creek 08095600 TexasWaco, near Bosque River 08096500Texas at Waco, Brazos River 08097000 BayouTexas at Mooreville, Cow 08097500Marlin, Texas near Brazos River 08098290Highbank,Texas near Brazos River 08098300 LittleCreek near Burlington, PondTexas 08099100 NOTexas near De Leon, River Leon 08099300 near De Leon, Texas Sabana River 0.87508099500 near Hasse, TexasRiver Leon -0.02508100000 NO near Hamilton, TexasRiver Leon 08100500Texas at Gatesville, River Leon --08101000 .297 TexasCreek at Pidcoke, Cowhouse 08102500 -- NO --Texas near Belton, River Leon -.17408103800 NO -- Texas near Kempner, Lampasas River -- .29308103900 near CreekTexas Briggs, Rocky South Fork 08104000 -Texas at Youngsport, Lampasas River 08104100 -.114 -- -- YES near Belton, Texas Lampasas River 08104500 Texas near Little Little River, River 08104700 .012 - NOTexas near Georgetown, San GabrielRiver North Fork 08104900 YES -- NO Texas at Georgetown, SanGabriel South Fork River 08105000 -.327 YES NO .072 Texas at Georgetown, San Gabriel River 08105100 .045 NO 0.286 Texas Berry Creek near Georgetown, NO08105300 -- Texas .003near Weir, NO San GabrielRiver -.168 NO .121 -.178 NO -0.169 NO -- .117 NO .665 NO .667 .292 .572 .142 NO .533 -.265 .901 .350 -.018 NO NO -- .959 -.074 .131 -- .661 -.018 .164 NO -.236 -- .736 - .006 -- YES NO .063 .258 NO -- -.047 YES NO .032 .669 - -- .140 .149 <.001 -- -- .082 .259 .045 .156 .683 -.220 NO YES -- .735 -- .046 -.056 .246 NO .876 -.055 Table 3. Table data—Continued discharge regulated of years

Table 3 23 τ ated or 10 10 or ated p-value Kendall’s = 0.050 Trend at Trend α τ p-value Kendall’s Unregulated periodUnregulated period Regulated = 0.050 Trend at Trend α Station name Station Mann-Kendall test results of annual minimum 7-day discharges for streamflow-gaging stations with at least 10 years unregul of years at 10 least with stations streamflow-gaging for discharges 7-day minimum of annual test results Mann-Kendall no. Station 08105400 Texas Circleville, near San Gabriel River 08105700 at Laneport, Texas San Gabriel River 08106500 at Cameron, Texas Little River 08108200 North Elm Creek near Cameron, Texas08109000 near Bryan, Texas Brazos River 08109700Creek near Dime Box, Texas Middle Yegua 08109800near CreekBox, DimeTexas East Yegua 08110000Creek near Somerville, Texas Yegua 08110100 YESTexas near Creek Lyons, Davidson 08110200 Texas at Washington, Brazos River 0.02508110325 NO Groesbeck,Texas above River Navasota 08110400 0.380 NOnear Groesbeck, Texas River Navasota 08110430 .324 Big Creek near Freestone, Texas NO08110500 NO Texasnear Easterly, River Navasota 08111000 - -.209 NOnear Bryan, Texas River Navasota YES -- .131 .95008111500 near Hempstead, Texas Brazos River 08111700 YES .009 .264 -.178 -.006 Millnear Creek Bellville, Texas -08114000 NO at NO Richmond, Texas Brazos River 08114500 -.167 .028 .294 Texas near Juliff, Brazos River --08115000 0.079 -- NO Big Creek near Needville, Texas .094 -- -.12108116400 -- 0.333 -- NOTexas Rosenberg, near Dry Creek 08116650 -- .269 .129 near Rosharon, Texas Brazos River YES NO NO .868 .120 YES .006 .462 -.017 -- .772 -- .011 -.397 .086 NO .043 NO .578 NO NO .432 -- -- YES YES .064 NO .149 .752 NO NO <.001 .103 .001 -.305 -- .231 -.265 -.042 .121 .678 - .387 .256 YES -- NO .191 .040 - -- .055 .191 YES .178 -- .033 NO .347 .333 .145 Table 3. years of regulated discharge data—Continued discharge regulated of years

24 Analysis of Minimum 7-Day Discharges and Estimation of Minimum 7-Day, 2-Year Discharges for Streamflow-Gaging Stations in the Brazos River Basin, Texas of =0.05 p-value α gnificant difference at . <, less than] α harges for streamflow-gaging stations with at least 10 years each years least 10 at with stations streamflow-gaging for harges different if p-value is less than or equal to or equal than less is if p-value different Wilcoxon rank-sum test results of annual minimum 7-day disc 7-day minimum of annual results test rank-sum Wilcoxon Station no. Stationname Si 08082000080825000808400008085500 near Aspermont, Texas Salt Brazos River Fork 08087300Texas at Seymour, Brazos River 08088000 at Nugent, Texas Brazos River Clear Fork 08089000Texas Griffin, at Fort Brazos River Clear Fork 08090500 at Eliasville, Texas Brazos River Clear Fork 08091000South Bend, Texas near Brazos River 08091500 Pinto, TexasPalo near Brazos River 08092000 PintoCreek near Santo, Texas Palo 08093500Glen Rose, Texas near Brazos River 08095000 at Glen Rose, Texas River Paluxy 08096500 NO at Blum, Texas Nolan River 08099500 Aquillanear Creek Aquilla, Texas08100500near Clifton, Texas North BosqueRiver NO NO08102500Texas at Waco, Brazos River YES YES08104700 near Hasse, Texas LeonRiver 08105700Texas at Gatesville, LeonRiver 08106500Texas near Belton, 0.102 LeonRiver YES08109000Texas near Georgetown, San GabrielRiver North Fork YES08110000 at Laneport, SanTexas Gabriel River 08110500 YES at Cameron, Little Texas River .443 .371 YES08111000 <.001 <.001 Bryan, Texas near Brazos River 08114000 NOnear Somerville, Creek Texas Yegua Texas near Easterly, River Navasota YESTexas near Bryan, River Navasota <.001 NO YES at Richmond,Texas Brazos River <.001 NO .010 <.001 YES YES YES .350 NO YES .001 .551 .024 .236 NO <.001 YES YES .001 YES .050 YES NO .329 .0112 .798 <.001 .002 .007 .016 .186 Table 4 Table 4. Table unregulated and regulated discharge data discharge regulated and unregulated are significantly discharges [Unregulated and regulated

Table 4 25 7Q2 Ratio of regulated to unregulated values Non-zero ed and regulated 7Q2 are zero] regulated ed and Annual 7Q Zero values /s) 3 7Q2 (ft ta not available to compute 7Q2; U, ratio of to regulated ta not available values Non-zero Annual 7Q Annual Zero values unregulated 7Q2 undefined because unregulat because 7Q2 undefined unregulated Unregulated period Regulated period /s) 3 7Q2 (ft 7Q2 is zero; Z, ratio of to regulated azos River at Lubbock, Texasat Lubbock, azos River 0 10 0 -- Brazos River near Post, TexasBrazos River 0 6 4 -- /s, cubic feet per second; 7Q, minimum 7-day --, da discharge; ver near Aspermont, Texas near Aspermont, ver 0 47 19 -- 3 Station name Aspermont, Texas .25 0 21 -- Stamford, Texas .03 5 28 -- Estimated minimum 7-day, 2-year discharges for streamflow-gaging stations, Brazos River Basin, Texas Basin, River Brazos stations, streamflow-gaging for discharges 2-year 7-day, minimum Estimated Estimated minimum 7-day, 2-year discharges 2-year streamflow-gaging Basin, Texas—Continued for River stations, Brazos Estimated minimum 7-day, no. Table 5 Station 08085500 Texas Griffin, at Fort Brazos River Clear Fork 08086050 Deep Creek at Moran, Texas08086100 Texas Hubbard Creek near Albany, 0 9 0 0 4 13 10 0 0 2 34 -- -- 24 Z 08079575 Fork Mountain Double North Fork 08079600 Texas at Justiceburg, Brazos River Double Mountain Fork 08080500 Brazos Ri Double Mountain Fork 08080540 Texas Creek near Post, McDonald 08080700 TexasPlainview, at Draw Water Running 08080950 0Girard, Texas near Duck Creek 08081000 near Peacock, Texas Brazos River Salt Fork 08081200 Creek near Croton Jayton, Texas 3308081500 Creek near Salt Croton 08082000 Texas near Aspermont, Brazos River Salt Fork 08082100 0 Texas Stinking Creek near Aspermont, 08082180Texas City, near Knox Creek North Croton 08082500 0 Texas at Seymour, River Brazos 008082700 Texas Millers Creek near Munday, -- -- 08083100 Texas Roby, near 34River Brazos Clear Fork 08083240 13 TexasHawley, at River Brazos Clear Fork --08083245 .08 Texas Creek near Hawley, Mulberry 08083300 0 Elm 0Creek near Abilene, Texas08083400 0 Little Elm Creek near Abilene, Texas 8 008084000 .03 26Texas Nugent, at River Brazos Clear Fork 08084800 near California Creek -- 16 7 -- 13 0 1 .41 0 0 1.4 14 5 2 .05 33 0.03 32 21 0 0 -- 0 29 2 -- 0 6 -- .04 -- 0 19 22 2 32 21 16 4 -- 2 .30 -- -- 0.62 0 9 12 -- 20 -- .38 0 16 U 14 42 2 9.5 08079500 Br Double Mountain Fork North Fork unregulated 7Q2 undefined because unregulated undefined 7Q2 unregulated Table 5. ft 2-year discharge; [7Q2, minimum 7-day, table. at end of Footnote Table 5. Table

26 Analysis of Minimum 7-Day Discharges and Estimation of Minimum 7-Day, 2-Year Discharges for Streamflow-Gaging Stations in the Brazos River Basin, Texas 7Q2 Ratio of Ratio regulated to regulated unregulated values Non-zero Annual 7Q Annual Zero values /s) 3 7Q2 28 0 27 (ft 13 0 27 4.2 1 1 values Non-zero Annual 7Q Annual Zero values Unregulated period Regulated period /s) 3 7Q2 (ft flow-gaging stations, Brazos River Basin, Basin, Texas—Continued River Brazos stations, flow-gaging Station name Stephenville, TexasStephenville, -- 0 11 1 Estimated minimum 7-day, 2-year discharges for stream for discharges 2-year 7-day, minimum Estimated no. Station 08093250Texas Hillsboro, at Creek Hackberry 08093400 Cobb Creek near TexasAbbott, 08093500 Texas Aquilla Creek near Aquilla, 08093700 at North Bosque River 08094500Texas Alexander, near Green Creek 08094800at Hico, Texas Bosque River North 08095000 near Clifton, Texas North Bosque River 08095200Texas Mills, at Valley Bosque River North 0 0 13 0 12 -- 23 0 -- -- .68 20 0 15 -- 29 0 -- 3.1 8 0 7.1 .21 0 5 15 11 1 28 0 Z 17 27 4.6 08086150 Texas Hubbard Creek near Albany, North Fork 08086212 Texas Albany, below Hubbard Creek 08086290 Texas Breckenridge, Big Sandy Creek above 08086500Texas Breckenridge, near Hubbard Creek 08087300Texas at Eliasville, Brazos River Fork Clear 08088000 Texas near South Bend, Brazos River 08088100Texas Olney, at Salt Creek 0.0308088300Texas Graham, Creek near Briar 08088450 11 Texas Big Cedar Creek near Ivan, 08089000 0 Texas Pinto, Palo near Brazos River 008090500 16 --Texas Santo, Creek near Pinto Palo 008090800 32TexasDennis, near Brazos River 08091000 24TexasGlen Rose, near Brazos River 22 1 -- .33 5 11 3 0 -- 0 0 0 -- 12 31 .12 0 0 19 22 9 -- 3.1 10 3 22 0 12 0 2 7 5 18 2 3 0 -- -- 12 -- 24 32 U 0 0 30 33 7 55 0 6 U 27 Z 08091500 at Glen Rose, Texas River Paluxy 08091750 Creek near Glen Rose, Texas Squaw 08092000Texas at Blum, Nolan River 08093100TexasAquilla, near Brazos River .44 -- 8 -- .37 27 5 2.8 10 2.2 4 0 1.2 9 2 18 6.4 26 3.2 Footnote at end of table. Footnote Table 5. Table

Table 5 27 7Q2 Ratio of regulated to unregulated values Non-zero Annual 7Q Zero values /s) 3 7Q2 (ft values Non-zero Annual 7Q Annual Zero values Unregulated period Regulated period /s) 3 7Q2 (ft Station name Burlington, Texas Burlington, 0 20 0 -- ttle River, Texasttle River, -- 55 0 33 Estimated minimum 7-day, 2-year discharges 2-year streamflow-gaging Basin, Texas—Continued for River stations, Brazos Estimated minimum 7-day, no. Station 08099100 near TexasDe Leon, Leon River 08099300 near De Leon, Texas Sabana River 08099500 near Hasse, Texas Leon River 08100000 near TexasHamilton, Leon River 08100500 at Gatesville, Texas Leon River 08101000 Texasat Pidcoke, Creek Cowhouse 08102500 near TexasBelton, Leon River 08103800Texas Kempner, near River Lampasas 08103900 Creek near Texas Briggs, Rocky South Fork 08104000 Texas at Youngsport, Lampasas River --08104100 0Texas Belton, near River Lampasas 08104500 near Li Little River 08104700 14 0Texas Georgetown, near River Gabriel San North Fork --08104900 Texasat Georgetown, Gabriel River San South Fork 08105000 0 .33Texas Georgetown, at River Gabriel San 08105100 20 5 0 Texas Berry Creek near Georgetown, 08105300 9.7 3.1 2Texas Weir, near River Gabriel San 27 .16 31 3 5.5 10 0 -- 0 10 18 .08 -- 0 11 1 20 33 2 26 .75 11 1.9 45 .25 -- 5.3 0 25 2.0 0 -- 11 -- 0 1 2 1.4 -- -- 29 6 22 14 32 -- 37 0 36 4.0 U 14 5.8 16 -- 0 .65 -- 8.8 22 11 0 11 08095300 TexasMcGregor, near Bosque River Middle 08095400 Texas Hog Creek near Crawford, 08095600Texas Waco, near Bosque River 08096500 Texas at Waco, River Brazos 08097000 Texas Bayou at Mooreville, Cow 08097500 Texas near Marlin, River Brazos 08098290 near TexasHighbank, River Brazos 08098300 0.02 Little Pond Creek near 8 .13 18 -- 4 40 ------16 -- 2 40 -- 136 0 0 11 0 198 180 9 55 6 0 0 8 11 30 3.4 Footnote at end of table. at end of Footnote Table 5. Table

28 Analysis of Minimum 7-Day Discharges and Estimation of Minimum 7-Day, 2-Year Discharges for Streamflow-Gaging Stations in the Brazos River Basin, Texas 7Q2 Ratio of Ratio regulated to regulated unregulated values Non-zero Annual 7Q Annual Zero values /s) 3 7Q2 (ft values Non-zero Annual 7Q Annual Zero values Unregulated period Regulated period /s) 3 7Q2 (ft flow-gaging stations, Brazos River Basin, Basin, Texas—Continued River Brazos stations, flow-gaging Station name Dime Box, Texas 0 30 3 -- Cameron, Texas 0 11 0 -- llville, Texas 2.8 0 30 -- Estimated minimum 7-day, 2-year discharges for stream for discharges 2-year 7-day, minimum Estimated 7Q2 based on regulated period 1969–95. regulated period based on 7Q2 1 no. Station 08105400 Texas near Circleville, San Gabriel River 08105700at Laneport, Texas Gabriel River San 08106500 Texas at Cameron, Little River 08108200 North Elm Creek near 08109000TexasBryan, near Brazos River 08109700 near Creek Yegua Middle 08109800TexasBox, Dime near Creek East Yegua 08110000 Creek near Somerville, Texas Yegua 08110100 7.0Texas Lyons, near Creek Davidson 08110200Texas Washington, at Brazos River 1708110325 0 Groesbeck, Texas above River Navasota 08110400Texas Groesbeck, near River Navasota 08110430 48 Big Creek near Freestone, Texas 008110500 19 Texas Easterly, near River Navasota 21908111000 Texas Bryan, near River Navasota 0 008111500 14Hempstead, Texas near Brazos River 08111700 0 0 -- Be near Mill Creek 1808114000 36 TexasRichmond, at Brazos River 008114500Texas 1.0Juliff, near Brazos River -- 38 --08115000 24 15 Texas Big Creek near Needville, 28 --08116400 54 1 Texas Rosenberg, Creek near Dry 08116650 4 428Texas Rosharon, near Brazos River 0 .70 -- 5 15 1 0 0 -- 2 12 .02 41 -- 0.06 6 568 52 10 35 479 5 0 -- 1.1 0 4 15 .27 .01 0 2.0 0 14 1.4 -- -- 14 5 20 17 U 2.2 0 21 2 631 31 8 670 2 34 0 0 -- 0 31 148 2.0 55 -- 579 55 5 U 0 15 1.2 24 Table 5. Table

Table 5 29