Magnitude and Frequency of Floods in the Suwannee River Water Management District, Florida

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 9 6-4176

Prepared in cooperation with the Suwannee River Water Management District Magnitude and Frequency of Floods in the Suwannee River Water Management District, Florida

By G.L. Giese and M.A. Franklin

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 96-4176

Prepared in cooperation with the SUWANNEE RIVER WATER MANAGEMENT DISTRICT

Tallahassee, Florida 1996 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY Gordon P. Eaton, Director

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Geological Survey.

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 Center 227 North Bronough Street, Suite 3015 Box 25286 Tallahassee, Florida 32301 Denver, CO 80225-0286 CONTENTS

Abstract ...... 1 Introduction ...... 1 Purpose and Scope...... 2 Previous Studies ...... 3 Physical Setting ...... 3 Station Analysis...... 3 Regional Analysis ...... 4 Improved Frequency Estimates By Use Of Weighting ...... 8 Gaged Sites...... 8 Ungaged Sites on Gaged Streams...... 8 Summary ...... 9 References ...... 9 Appendix 1. Station, regional, and weighted T-year flood estimates for the Suwannee River Water Management District ...... 14

Figures 1. Map showing location of Suwannee River Water Management District and stream-gaging stations used for measuring peak discharges ...... 2 2. Map showing physiographic regions within the Suwannee River Water Management District ...... 4 3. Graphs showing elation of flood discharge to drainage area for selected frequencies on the Suwannee River...... 5 4. Graphs showing relation of flood discharge to drainage area for selected frequencies on the Santa Fe River ...... 5

Tables 1. Flood-frequency regression model for the Suwannee River Water Management District ...... 6 2. Probability that a flood of a given recurrence interval will be exceeded during indicated time period ...... 7

CONVERSION FACTORS AND ABBREVIATIONS

Multiply By To obtain

inch (in.) 25.4 millimeter (mm) foot (ft) 0.3048 meter (m) mile (mi) 1.609 kilometer (km) square mile (mi2) 2.590 square kilometer (km2) cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

Contents iii SYMBOLS

Symbol Meaning

Ag Drainage area for gaged site, in square miles

Au Drainage area for ungaged site, in square miles

B1T, B2T, B3T Partial regression coefficients

CT Regression constant

Cv Coefficient of variation DA Drainage area, in square miles EY Accuracy for a flood estimate, in equivalent years of record

KT Pearson Type III deviate LE Channel length, in miles LK Total area of lakes and ponds, in percent of drainage area M Mean of logarithms of the annual peaks N Number of items in a data set n Time interval, in years P Exceedance probability

PN Probability of at least one exceedance within the specified time interval

Qg Estimate from log-Pearson Type III distributions of T-year flood, in cubic feet per second

QR Estimate from regression equation of T-year flood for gaged site, in cubic feet per second

Qru Regional estimate of T-year flood from regression equation for ungaged site, in cubic feet per second

QT Estimate of the T-year flood from log-Pearson Type III distribution in cubic feet per second

Qu Adjusted estimate of T-year flood for ungaged site, in cubic feet per second

Qwt Weighted estimate of T-year flood at gaged site, in cubic feet per second R Multiple correlation coefficient S Standard deviation of the logarithms of annual peaks

SEP Standard-error of prediction SL Channel slope, in feet per mile T Recurrence interval, in years

X1, X2, X3... Independent variables in linear regression

iv Symbols List Magnitude and Frequency of Floods in the Suwannee River Water Management District, Florida

By G.L. Giese and M.A. Franklin

ABSTRACT District) (fig.1) provide vital water-related func- tions. These functions include water- quality treat- Flood-frequency statistics for 2-, 5-, 10-, ment, water supply, flood water conveyance and 25-, 50-. 100-, 200-, and 500-year recurrence attenuation, fish and wildlife habitat, and recre- intervals, based on three methods of analysis, are ational and economic uses. These systems depend presented for 25 continuous-record and seven on the maintenance of the natural variability of the peak flow partial-record gaging stations in the hydrologic cycle as reflected by the magnitude, Suwannee River Water Management District. The duration, and timing of changing streamflow, rising first method, for gaged stations, utilizes station and falling water levels of lakes, rivers, and aqui- records; the second method, for ungaged sites, fers, and interaction of surface and ground waters. Alterations to the natural hydrologic regime by utilizes regional regression analysis; and the third human activities may have adverse effects on the method uses a weighted combination of the natural systems and their functions. However, many station and regional values. Because the weighted aspects of natural-system requirements are poorly values utilize two more or less independent known and must be better understood in order to estimates of the peak flow statistic, they are establish minimum flow and water-level require- considered more accurate than the station ments that will allow adequate water to balance estimates or the regression estimates alone. Also, present and future needs of the natural system with the use of another weighting scheme to improve those of the human population. Quantification of the estimates of flood frequency statistics at ungaged natural hydrologic regime that has shaped the cur- sites is demonstrated. rent natural system is basic to developing this The karstic nature of much of the understanding and achieving this balance. Accordingly, in 1994, the USGS (U.S. Geo- Suwannee River Water Management District logical Survey) and the SRWMD entered into a significantly attenuates flood peaks in some cooperative agreement wherein the USGS agreed to streams by providing substantial subsurface provide, in the course of a long-term program of storage when river stages are high. At such times, investigation, the hydrologic information or tools springs discharging into rivers may reverse flow needed for the SRWMD to establish minimum flow temporarily and become sinks. and water-level requirements for surface and ground waters of the SRWMD. This report, dealing only with flood magnitudes and frequency, is one of INTRODUCTION a planned series of studies intended to accomplish this goal. In recent years there has developed a better The primary motivation for this particular awareness that natural systems such as wetlands, report is to document the high-flow regime of the flood plains, native ecological communities, and natural hydrologic system of the SRWMD. This aquifer recharge areas within the 7,640-square-mile information is available to researchers studying min- SRWMD (Suwannee River Water Management imum inundation requirements for wetlands, estuar-

Abstract 1 84°00′ 30′ 83°00′ 30′ 82°00′

GEORGIA 30°30′ 02326250 02319000 02317620 02317630 02315000 r 02326300 e v Su i wa R nn la e l e i 02319500 Riv c 02326500 02315550 er

u 02315200

A 02326512 02315500 er Riv a Lake n i City f 02326000 n 02324400 02320000 30°00′ co loway er 02321600 E ol Riv h 02320900 n 02324500 e 02321800 02321700 F 02325000

r 02321000 e ta 02321446 v n i a 02320500 S F R e r ve 02321500 02320700 e Ri e h c 02322500 02322000 t 02324000 a

h n i 02322016 e 02323000 S t G U 30′ L F 02323500 r O e v F i R r e M e v e i E n n R X a w a 02313400 I Su s C s a

O s

a c c a W 0 20 40 MILES 02314200 29°00′ 0 20 40 KILOMETERS

EXPLANATION

SUWANNEE RIVER WATER FLORIDA MANAGEMENT DISTRICT LOCATION OF BOUNDARY SUWANNEE RIVER WATER MANAGEMENT 02314200 STREAM-GAGING STATION—And number DISTRICT 02313400 HIGH-FLOW PARTIAL-RECORD STATION—And number 02321446 MISCELLANEOUS SITE—And number

Figure 1. Location of Suwannee River Water Management District and streamgaging stations used for measuring peak discharges. ies, riparian communities, and other ecosystems in Purpose and Scope the SRWMD. These needs are beyond the traditional needs for flood-frequency information in the design This report is presents flood-frequency statistics of drainage structures and bridges, flood-plain zon- for unregulated gaged sites in the SRWMD for which ing, and flow regulation. These traditional needs will 10 years or more of peak flow data were available, also be served by the information in this report. provides means of improving estimates at gaged sites,

2 Magnitude and Frequency of Floods in the Suwannee River Water Management District, Florida and presents methods for estimating peak-flow char- Northern Highlands, the Gulf Coastal Lowlands, and acteristics at ungaged sites. Flood magnitudes are pre- the River Valley Lowlands (fig. 2). The areal extent of sented for 25 continuous-record stations and 7 partial- overbank flooding is generally least in the Northern record gaging stations for recurrence intervals of 2, 5, Highlands and greatest in the River Valley Lowlands. 10, 25, 50, 100, 200, and 500 years, utilizing log-Pear- The SRWMD has a humid subtropical climate. son Type III distributions. Recurrence interval here Rainfall averages about 56 inches per year. July and can be defined as the average number of years between August are typically the wettest months; late spring flood peaks greater than, or equal to, a specified mag- and early fall are the driest. The largest floods, how- nitude. This analysis utilized records up to and includ- ever, have occurred in March or April as the result of ing the 1994 water year. Regression equations for cumulative effects of several consecutive broad fron- estimating flood-frequency characteristics at ungaged tal-type rainfall events over the basin.The largest sites are also presented. Finally, this report includes floods of record on the Suwannee River occurred in methods for improved estimates at both gaged sites March and April of 1948, March 1959, and and ungaged sites on gaged streams. April 1973.

Previous Studies STATION ANALYSIS Frequency curves for individual gaging stations Franklin and others (1994) listed and ranked were developed following the guidelines described in annual peak flows and various consecutive-day high Bulletin 17B, Interagency Advisory Committee on flows for the SRWMD but did not assign frequencies Water Data (1982). A log-Pearson Type III distribu- of occurrence. Stamey and Hess (1993) presented tion function was used to fit annual peak discharges to flood-frequency characteristics of Georgia streams and log-probability curves. The distribution is defined by techniques for estimating magnitude and frequency of the equation: floods in rural basins in Georgia. That report included station analyses and regional regression equations for streams in the upper Suwannee River basin in Georgia. logQT=M+KTS, (1) Bridges (1982) presented flood frequency analyses for Florida stations gaging natural flow, including many of where the stations in the SRWMD. That study also contained QT is the peak discharge for a selected recurrence regional regression equations for estimating flood-fre- interval T, in cubic feet per second; quency characteristics of ungaged streams. Bridge’s M is the mean of the logarithms of the annual report, which utilized records only through the 1978 peaks; water year, is superceded by this report for stations in KT is the Pearson Type III frequency factor the SRWMD. The U.S. Army Corps of Engineers expressed in number of standard deviations (1974) delineated the areal extent of major Suwannee from the mean for a selected recurrence River flooding for the large floods of April 1948 and interval, T; and April 1973. S is the standard deviation of the logarithm of the annual peaks. The computer program J407 (Kirby, 1979) was Physical Setting used to fit the log-Pearson Type III distribution to the annual maximum discharges at each of 25 continuous- The SRWMD, located in the north-central part record and 7 peak-flow partial-record gaging stations of Florida, is one of five water management districts (app. 1). User judgment was exercised in the use of created by the Florida Legislature through the passage this program in determining historic peaks, whether to of the Water Resources Act of 1972. The SRWMD is use station or regional skew coefficents, and interpre- the smallest in area and the most sparsely populated. tation of low and high outliers. The SRWMD is in the Southeastern Coastal Plain Figures 3 and 4 were constructed to examine the physiographic province of the United States, as delin- consistency of flood peaks of different frequencies up eated by Fenneman (1938). The SRWMD is covered to 100 years in a downstream direction on the Suwan- by three physiographic regions of this province--the nee and Santa Fe Rivers. Weighted values of station

Station Analysis 3 84°00′ 83°30′ 83°00′ 82°30′ 82°00′

30°30′

30°00′

EXPLANATION GULF COASTAL 29°30′ LOWLANDS NORTHERN HIGHLANDS

RIVER VALLEY LOWLANDS

SUWANNEE RIVER WATER MANAGEMENT DISTRICT Location of BOUNDARY Suwannee River Water Management District 0 20 40 MILES

29°00′ 0 20 40 KILOMETERS

Figure 2. Physiographic regions within the Suwannee River Water Management District (after SRWMD, 1994). and regional flood peaks were used in the plots. Gen- REGIONAL ANALYSIS erally, for rainfall equally distributed throughout a basin, it is usual to see an increase in flood magnitudes Bridges (1982) performed statewide multiple with increasing drainage area. The decrease in flood regressions on 11 variables to develop relations magnitude between the Luraville and Branford sta- between flood-peak discharges and basin characteris- tions on the Suwannee River is thought to be due in tics. The variables tested were drainage area, channel part to peak attenuation along the channel as cross sec- slope, channel length, mean basin elevation, storage tional area increases in a downstream direction. How- area of lakes and ponds, storage area of lakes, ponds, ever, it is thought that a large part of the attenuation is and swamps, forested area, maximum soil infiltration, through transient stream losses to springs which, at mean annual precipitation, and maximum 24-hour pre- cipitation intensity. The assumed form of the regres- high stream levels, effectively become sinks.The same sion equation used by Bridges was: phenomenon of peak attenuation occurs between Wor- thington Springs and High Springs on the Santa Fe B1 B2 BN River. T T T (2) QT = CTX1 X2 .....XN

4 Magnitude and Frequency of Floods in the Suwannee River Water Management District, Florida 90,000

80,000

70,000

100-YEAR

60,000

50-YEAR

50,000

Suwannee River near Bell (02323000)

Suwannee River at Ellaville (02319500)

Suwannee River at Luraville (02320000)

Suwannee River at Branford (02320500)

Suwannee River near Wilson (02323500) Suwannee River near Benton (02315000) 25-YEAR

40,000 Suwannee River at White Springs (02315500)

Suwannee River at Suwannee Springs (02315550) 10-YEAR 30,000 5-YEAR

20,000 2-YEAR

FLOOD DISCHARGE,10,000 IN CUBIC FEET PER SECOND

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000

DRAINAGE AREA, IN SQUARE MILES

Figure 3. Relation of flood discharge to drainage area for selected frequencies on the Suwannee River.

26,000

24,000 100-YEAR 22,000

20,000 50-YEAR

18,000

16,000 25-YEAR

14,000

12,000 Santa Fe River near Graham (02320700) 10-YEAR

Santa Fe River near Fort White (02322500)

10,000 Santa Fe River near High Springs (02322000)

8,000 Santa Fe River near Worthington Springs (02321500) 5-YEAR

6,000

2-YEAR 4,000

FLOOD DISCHARGE, IN CUBIC FEET PER SECOND 2,000

0 0 100 200 300 400 500 600 700 800 900 1,000 1,100

DRAINAGE AREA, IN SQUARE MILES

Figure 4. Relation of flood discharge to drainage area for selected frequencies on the Santa Fe River. Regional Analysis 5 where did not contribute to significant improvement of either R2 or the standard error of the regression equations in QT is the flood peak discharge (dependent any region of the State. The present (1996) study variable) for recurrence interval of T- adopted Bridges’ regression equation for Region B, years, in cubic feet per second; one of three high flow hydrologic regions Bridges X1 to XN are the basin characteristics (independent defined for Florida. Region B includes the entire variables); SRWMD and is nearly coincident with it. The regres- sion equation for Region B includes only DA and LK CT is the regression constant for a given recurrence interval; and as variables. The equation is: B1T to BNT are the regression coefficients for a given B2 recurrence interval. B1 T 2 T () The regression analysis used R (the square of QT = CTDA LK + 0.6 (3) the multiple correlation coefficient) as a performance criterion. R2 is a measure of the amount of variation in where the independent variable that can be accounted for by Q is the discharge for a recurrence interval of T- 2 T the model. The one-variable model with the highest R years, in cubic feet per second; was produced. Then, the variable that produced the C is the regression constant for a recurrence 2 T greatest increase in R was added to the equation. Each interval, T; variable in the two-variable model was compared to DA is the drainage area, in square miles; each variable not in the model to determine if replac- LK is percentage of drainage area covered by 2 ing one variable with another would improve the R lakes (determined from USGS 7.5-minute coefficient. This procedure continued until the best or 15-minute topographic maps); and two-variable, three-variable, and so forth, model was B1T and developed for each interval of T years. Bridges found B2T are exponents for various recurrence inter- that, statewide, drainage area (DA) accounted for vals. 62 percent of the variance of the dependent variable; The full suite of values for CT, B1T, and B2T is combining DA with lake area (LK) accounted for given in table 1 along with R2 values and standard 80 percent; and, adding channel slope (SL) added only errors for each of the regressions. The standard error 3 percent. (For the SRWMD area, Bridges found that of estimate is the standard deviation of the distribution adding channel slope to the regression equation pro- of residuals about the regression line, meaning that duced insignificant improvement.) All three of these 68 percent of the values are within one standard devia- parameters were determined from available USGS tion of the regression line and 95 percent are within topographic maps. Adding a fourth and fifth variable two standard deviations.

Table 1. Flood-frequency regression model for the Suwannee River Water Management District

Recurrence Exponents Accuracy, Regression Standard interval, Exceedence in equivalent constant R 2 error, in in years probability years of record (C ) B1T B2T percent (T) T (EY)

2 0.5 44.2 0.658 -0.561 0.876 60.9 2 5 .2 113 .614 -.573 .869 59.7 3 10 .1 182 .592 -.580 .863 59.9 3 25 .04 298 .570 -.585 .853 60.9 5 50 .02 410 .556 -.589 .845 61.9 5 100 .01 584 .543 -.591 .836 63.1 6 200 .005 694 .533 -.593 .827 64.4 6 500 .002 936 .521 -.594 .815 66.3 6

6 Magnitude and Frequency of Floods in the Suwannee River Water Management District, Florida Table 1 also gives the accuracy of the regional Bridges (1982) used stations with drainage areas relations in equivalent years of record, which is ranging from 13.9 to 9,640 square miles in developing defined as the number of years of actual streamflow the regression equations for Region B. Lake areas for record required at a site to obtain an accuracy equal to Region B ranged from 0 to 13.26 percent. The regres- the standard error of prediction for the regression esti- sion equations have not been validated outside these mate (Hardison, 1971). Hardison showed that the limits. Also, the regressions are not considered valid equivalent years of actual record required to produce where anthropogehic changes have a significant effect an accuracy for a T-year statistic equal to that of a on flood runoff, such as regulation from dams, levees, regional regression is given by: diversion canals, strip mining operation, and urban development. 100C 2 It is recommended that flood frequency esti- EY = ------V- (4) mates for ungaged sites on ungaged streams be deter- SE P mined by direct application of the regression equation (3) alone in cases where there is no gage upstream or where downstream from the site of interest within a drainage EY is the accuracy of the T-year statistic at a site area range of greater than one-half and less than twice not used in the regression, in equivalent that of the site of interest. The use of the regional years of record; equation is illustrated a follows: CV is the coefficient of variation of annual events, 1) Determine the 50-year flood for station in this case, annual floods; 02321446, Fivemile Creek near Dukes, Flor- SEP is the standard error of prediction in percent. ida, at County Road 18A (fig. 1). Table 2 gives the probabilities that floods of a 2) The DA is 11.80 mi2. The LK is 0.90 percent given recurrence interval will be exceeded during indi- of the drainage area. cated time periods. Note that probabilities are not mul- 3) Equation 3, as determined from table 1 for tiplicative; that is, the probability of a flood of a given the 50-year flood, becomes: recurrence interval occurring during a 5-year period is five times the probability of that magnitude flood not B2 B1 T occurring in any one year. The probabilities are com- T Q = C DA ()LK + 0.6 puted by the formula (Interagency Advisory Commit- T T tee on Water Data, March, 1982): 0.556 -0.58 Q50=410 (11.80) (0.90+0.6)

N Q =1,278 cubic feet per second PN=1-(1-1/T) (5) 50 Appendix 1 shows calculated values of flood where magnitudes from equation 3 for recurrence intervals of PN is the probability of at least one exceedence 2, 5, 10, 25, 50, 100, 200, and 500 years at gaging sta- within the specified time interval; tions. Although it is not recommended that regional N is the time period in years; values derived from equation 3 be used alone where T is the recurrence interval in years. estimates from gaged flows are also available, the fol-

Table 2. Probability that a flood of a given recurrence interval will be exceeded during indicated time period Recurrence Period of time, in years interval, in (N) years (T) 1 5 10 20 25 50 100 200 500 5 0.201 0.67 0.89 0 .99 (2)(2)(2)(2)(2) 10 .10 .41 .65 .89 0.93 (2)(2)(2)(2) 25 .04 .18 .34 .56 .64 0.87 0.98 (2)(2) 50 .02 .10 .18 .33 .40 .64 .87 0.98 (2) 100 .01 .05 .10 .18 .22 .40 .63 .87 (2)

1 Multiply probability values by 100 to obtain percent chance of exceedence. 2Probability greater than 0.99 but less than 1.00.

Regional Analysis 7 lowing section shows how weighting of station and Ungaged Sites on Gaged Streams regional values can be used to improve estimates of flood magnitude and frequency at both gaged and Estimates for ungaged sites near gaged sites on ungaged sites. the same stream can also be improved by weighting techniques. One method (Hannum, 1976) uses a weighted value of the ratio of the weighted and IMPROVED FREQUENCY ESTIMATES BY regional estimate at the gaged site to adjust the USE OF WEIGHTING regional estimate at the ungaged site. This method is suggested when the drainage area at the ungaged site is more than half, but less than twice the drainage area Gaged Sites of the gaged site. Equation 7 or 8 can be used to adjust the regional estimate at the ungaged site with the Flood-frequency estimates based on station anal- weighted estimate from the gaged site depending on ysis and regional regression analysis tend to be inde- the location of the ungaged site relative to the gaged pendent of one another. Therefore, it is to be expected site: that an estimate of frequency characteristics utilizing both estimates is more likely to be closer to the “true” Q =Q [((Q /Q ) -1)*((2A -A )/A ) +1] for site frequency characteristic than either method by itself. u ru wt r g u g At gaged sites, a weighting procedure is recommended downstream from gage (7) which is contained in guidelines of the Interagency Q =Q [((Q /Q ) -1)*((2A -A )/A ) +1] for site Advisory Committee on Water Data (1982). In this pro- u ru wt r u g g cedure, station analysis is weighted by N, the number upstream from gage (8) of years of actual record, and the regression estimate is where weighted by EY, the equivalent years of record of the Qu is the adjusted estimate for ungaged site, in regression analysis, according to the formula: cubic feet per second; Qru is the regional estimate for ungaged site, in LogQwt=(NlogQg+EYlogQr)/(N+EY) (6) cubic feet per second; Qwt is the weighted estimate of the T-year flood at where the gaged site, in cubic feet per second; Qwt is the weighted estimate of the T-year flood at Qr is the regional estimate at gaged site, in cubic gaged site, in cubic feet per second; feet per second; Qg is the T-year flood estimate from log-Pearson Au is the drainage area for ungaged site, in square Type III frequency distribution of annual miles; peaks at gaged site, in cubic feet per second; Ag is the drainage area for gaged site, in square Qr is the regional flood estimate for gaged site, miles. computed from equation 3, in cubic feet per The weighting schemes for equations 7 and 8 are such second; that the weighted station value has full weight at the N is the the number of annual peaks used to station. At sites less than one-half and greater than compute Qg in years; twice Ag, the regional value has full weight. An exam- EY is the accuracy of the regional flood estimate, ple of the use of this weighting technique is as follows: in equivalent years from table 1. 1) It is desired to estimate the 100-year flood for The weighting scheme of equation 6 is such that station 02320900, New River near Raiford at longer periods of record (N) the station record value (fig. 1), an ungaged site on a gaged stream. Its 2 (Qg) carries more and more weight relative to the DA is 96.0 mi ; the percent LK is 0.01.There regional value (Qr). Appendix 1 gives weighted esti- is a gaged site downstream, station 02321000, mates of the T-year floods for each of the 32 gaged New River at Lake Butler. Its drainage area is sites used in the regression analysis. At gaged sites, 191 mi2; the percent LK is 0.03. the weighted estimate is considered to be better for 2) First, determine for the site of interest the design or predictive purposes than either the log-Pear- Regional estimate of the 100-year flood from son Type III estimate alone or the regional estimate equation 3 and the appropriate values from alone. table 1:

8 Magnitude and Frequency of Floods in the Suwannee River Water Management District, Florida B2 B1 T substantial subsurface storage when river stages are T () QT = CTDA LK + 0.6 high. Then, springs discharging into rivers may reverse flow temporarily and become sinks. 0.543 -0.591 Q100=584(96.0) (0.03+0.6)

Q100=Qru=9,150 cubic feet per second. REFERENCES

3) Since the site is upstream from a gage on the Bridges, W.C., 1982, Technique for estimating magnitude same stream, equation 8 applies. Substituting and frequency of floods on natural- flow streams in in equation 8 Qru obtained above for the Florida: U.S. Geological Survey Water-Resources ungaged station and Qwt and Qr for the gaged Investigations Report 82-4012, 45 p. station as obtained from Appendix 1 for the Franklin, M.A., Giese, G.L., and Mixson, P.R., 1994, 100-year flood for New River near Lake Statistical summaries of surface-water hydrologic data Butler: in the Suwannee River Water Management District, Florida, 1906-93: U.S. Geological Survey Open-File Qu=Qru[((Qwt/Qr) -1)*((2Au-Ag)/Ag) +1] Report 94-709, 173 p. Qu=9,150[((18,300/13,300)-1)*((2(96)-191)/191)+1] Fenneman, N.M., 1938, Physiography of eastern United States: New York, McGraw-Hill Book Company, Inc., Qu=9,150[(.3759)*(0.0052)+1] 714 p. Qu=9,150[1.002]=9,170 cubic feet per second. Hannum, C.H., 1976, Technique for estimating magnitude and frequency of floods in Kentucky: U.S. Geological Survey Water-Resources Investigations Report 76-62, SUMMARY 70 p. Hardison, C.H., 1971, Prediction error of regression Flood-frequency statistics were presented for estimates of streamflow characteristics at ungaged 25 continuous-record and 7 high-flow partial-record sites: U.S. Geological Survey Professional Paper 750- stations in the Suwannee River Water Management C, p. C228-C236. District for recurrence intervals of 2, 5, 10, 25, 50, Interagency Advisory Committee on Water Data, 1982, 100, 200, and 500 years, using three methods.The first, Guidelines for determining flood-flow frequency: utilizing station analysis, applied a log-Pearson Type Bulletin 17B of the Hydrology Subcommittee, Office III function to the series of annual peaks. The second of Water Data Coordination, U.S. Geological Survey, method utilized regional relations based on regression Reston, Va., 183 p. of values derived from station analysis with basin Kirby, W. H., 1979, Annual flood-frequency analysis using parameters.Only two basin parameters, drainage area U.S. Water Resources Council guidelines (Program and lake area, were significant enough to include in J407): U.S. Geological Survey WATSTORE User’s final regression equations. Lastly, a weighting method, Guide, v. 4, chap. I-C. utilizing both station and regional values, was used to Marella, R.L., 1995, Water-use data by category, county, improve estimates of flood frequency statistics at and water management district in Florida, 1950-90: U.S. Geological Survey Open-File Report 94-521, gaged sites. The weighted estimate is considered to be 114 p. more accurate than either the station estimate or the Stamey, T.C., and Hess, G.W., 1993, Techniques for regression estimate alone. estimating magnitude and frequency of floods in rural The regression equation can, of course, be used basins of Georgia: U.S. Geological Survey Water- to estimate flood-frequency characteristics at ungaged Resources Investigations Report 93-4016, 75 p. as well as gaged sites. If the ungaged site is on a gaged Suwannee River Water Management District, 1994, Water stream, then the estimate for the ungaged site can be Management Plan: Suwannee River Water improved by transferring information from the gaged Management District, draft of August 8, 1994, 215 p. site to the ungaged site and applying weighting proce- U.S. Army Corps of Engineers, 1974, Suwannee River dures. floods, Florida and Georgia, December 1974: Special The karstic nature of much of the Suwannee Flood Hazard Information Report: U.S. Army Corps of River Water Management District significantly attenu- Engineers, Jacksonville District, Jacksonville, Florida, ates flood peaks in some streams by providing 17 p. and 41 plates.

Summary 9 10 Magnitude and Frequency of Floods in the Suwannee River Water Management District, Florida APPENDIX 1320 9150 3120 8160 3870 6880 4490 6720 4980 55200 60700 57500 34700 57700 38300 40300 57500 41800 31700 55700 37500 56500 44200 61400 47500 130000 105000 118000 120000 102000 118000 111000 103000 1220 7160 2530 7000 2980 5870 3360 5330 3740 45600 49200 47000 30200 47000 32600 34900 46800 35800 86600 98000 27000 45300 31000 99800 84300 98200 86600 45900 81300 36900 49800 39200 107000 1150 6300 2180 4810 2590 4300 2640 4740 2980 38900 36300 38000 26800 42800 28800 30800 42600 31600 91300 79600 86700 23600 41100 27000 85400 77500 84700 70500 41700 67400 31800 45100 34000 1070 4690 1750 3730 1900 3360 2030 3580 2240 32700 28000 31200 23500 33300 24600 26700 33100 27100 76700 62700 71700 20300 31900 22300 72100 61000 71300 56300 32400 54100 26900 34800 28000 /s) 3 (ft 989 3630 1530 2820 1450 2540 1510 2820 1690 26900 22600 25500 20200 27000 21000 22700 26800 23000 63100 51600 59000 17200 25800 18700 59500 50100 58800 43900 26200 42300 22200 28000 23000 874 954 950 2450 1110 1840 1730 1960 1030 19800 16200 19000 15900 19600 16200 17300 19400 17400 46500 38300 44500 13300 18600 13900 44100 37200 43800 29800 18900 29200 16500 20100 16800 Discharge for recurrence interval in years ated period of systematic record; Middle line--regression equation; Bottom l 777 928 640 613 673 1680 1250 1170 1380 14800 11900 14100 12500 14500 12700 13200 14300 13200 34900 28900 33400 10400 13600 10800 33200 28000 33000 20700 13900 20300 12300 14700 12500 800 644 290 577 697 283 6420 8050 8000 7740 7870 7520 7460 6480 7580 7920 6990 16700 19300 16200 18900 10300 (percent) Lake area ) 2 area (mi /s, cubic feet per second] Drainage 3 , square miles; ft 2 11 -- 1680 0 8390 33 -- 2630 .37 7720 69 -- 2430 .31 7510 10 -- 88.6 0.50 617 10 -- 7330 .27 19900 19 -- 2090 0.24 6390 67 -- 6970 .27 19000 29 -- 26.0 1.00 607 63 67 2120 .23 10400 23 -- 220 3.50 262 27 47 1720 0 6920 Years of record Years 1 Systematic Historic 2 5 10 25 50 100 200 500 Name nr Jennings River at Suwannee Springs River at White Springs Suwannee Valley River at Luraville River nr Benton River at Ellaville nr Lebanon Station River nr Pinetta Waccasassa River near Bronson Alapaha River nr Jasper Station, regional, and weighted T-year flood estimates for the Suwannee River Water Management District Station number 02313400 02317630 02317620 Alapaha River 02315550 Suwannee 02315500 Suwannee 02315200 Deep Creek nr 02320000 Suwannee 02315000 Suwannee 02319500 Suwannee 02314200 Creek Tenmile 02319000 Withlacoochee 2 2 ine--weighted or best estimate of T-year flood; mi ine--weighted or best estimate of T-year Appendix 1. III analysis for the indic line--log-Pearson Type relations for each station are presented as follows: Top [Discharge-frequency

12 Hydrogeology of the Surficial and Intermediate Aquifer Systems in Sarasota and Adjacent Counties, Florida 835 2830 1440 3810 2100 3400 7580 9280 8050 2430 1830 2270 37600 12800 33300 22000 20900 21900 31000 19000 27500 30900 18400 28400 91300 92900 11600 10500 11100 124000 104000 119000 107000 689 2140 1100 3170 1650 2860 5990 7210 6300 2070 1430 1910 8310 9400 97000 86400 94600 30900 10200 27700 18400 16800 18200 24300 15000 21900 25600 14800 23600 76800 88200 77900 10100 587 837 9190 1510 2700 1460 2480 4920 6300 5220 1800 1250 1680 8940 7360 8380 79500 79700 79500 26200 23900 15900 15200 15800 19800 13300 18300 21700 13400 20400 66600 80100 67700 492 639 928 7020 9980 1080 2260 1100 2070 3970 4650 4100 1560 1430 7840 5530 7080 64500 63000 64300 21800 20100 13500 11700 13400 15900 14700 18100 10300 17000 56900 64000 57400 /s) 3 (ft 404 798 507 858 718 5600 9410 7800 1830 1670 8250 3110 3560 3200 1320 1190 6770 4320 5930 51400 52100 51500 17600 16200 11300 11200 12300 11400 14600 13700 47700 52700 48000 297 500 335 587 482 3960 8510 6720 8420 8340 5330 7950 1310 1230 5870 9910 2130 2360 2160 1010 4770 5380 2960 4770 36900 38900 37100 12500 11900 10300 36300 39200 36400 Discharge for recurrence interval in years ated period of systematic record; Middle line--regression equation; Bottom l 221 318 240 934 410 878 790 331 720 8890 2900 8450 6540 4890 6460 5740 3700 5480 7290 4260 7030 1480 1590 1490 4320 2060 3730 27500 29600 27800 28000 29600 28100 131 126 202 446 736 735 157 447 1500 4290 2620 3890 1820 2680 2270 3490 1010 2440 17300 16500 17200 17000 (percent) Lake area ) 2 area (mi /s, cubic feet per second] Drainage 3 , square miles; ft 2 25 29 9390 0.49 16400 63 -- 575 2.64 4440 64 -- 1017 1.73 3940 25 -- 191 .03 2770 10 -- 5.12 .05 125 37 -- 94.9 13.26 466 41 -- 868 1.90 3560 63 67 7880 .3019 17000 25 --12 -- 49.1 -- .04 46.0 8.67 163 735 .88 486 2820 Years of record Years 1 Systematic Historic 2 5 10 25 50 100 200 500 Name River nr Bell at Worthington Springs nr Fort White Lake Butler Gainesville nr Graham nr High Springs River at Branford Olustee Creek nr Lulu Swift Creek nr Lake Butler Olustee Creek nr Providence Station, regional, and weighted T-year flood estimates for the Suwannee River Water Management District --Continued Station number 02321600 02321700 02321800 02323000 Suwannee 02321500 Santa Fe River 02322500 Santa Fe River 02321000 New River nr 02322016 Blues Creek nr 02320700 Santa Fe River 02322000 Sante Fe River 02320500 Suwannee 2 2 2 Appendix 1. [Discharge-frequency relations for each station are presented as follows: Top line--log-Pearson Type III analysis for the indic line--log-Pearson Type relations for each station are presented as follows: Top [Discharge-frequency flood; mi ine--weighted or best estimate of T-year

Appendix 13 3910 4630 3250 4390 8890 9240 5680 6290 7960 9160 3300 4490 2690 11800 13000 11500 10300 15500 14300 15100 19000 18400 18900 26600 13700 23700 90100 91700 11100 103000 3360 9330 3870 2770 3580 6420 9070 6720 4120 8020 4500 6890 8870 7600 2680 3520 2930 10300 12900 11500 12500 15000 14700 15000 21800 11000 19600 76900 85300 77800 2950 8280 3340 2420 9080 3040 4940 8000 5220 3180 7020 3640 9950 6120 7930 6710 2250 3100 2480 11000 10400 10800 12400 13100 12500 18200 16800 67500 78700 68600 2540 6230 2780 2090 6810 2490 3740 5980 3920 2410 5200 2630 9290 7960 9010 9910 7630 5370 6020 5560 1860 2320 1970 10100 10100 14800 13700 58600 62300 58900 /s) 3 (ft 2140 4890 2330 1780 5310 2090 2770 4650 2910 1790 3990 1960 7700 6380 7420 7990 7820 7970 6120 4640 4760 4680 1510 1800 1580 11600 10800 50200 51500 50300 1600 3360 1680 1380 3630 1510 1760 3150 1820 1140 2660 1210 5750 4550 5580 5550 5440 5540 7680 4350 7370 3700 3320 3620 1090 1220 1110 39600 38500 39500 Discharge for recurrence interval in years ated period of systematic record; Middle line--regression equation; Bottom l 762 810 796 847 805 1190 2350 1240 1090 2520 1180 1180 2170 1220 1800 4380 3300 4220 3940 3840 3930 5020 3150 4850 2990 2360 2840 31700 29300 31600 660 713 585 840 383 411 434 1160 1230 1050 1760 2500 1950 2030 1670 1970 1210 1840 17200 20800 (percent) Lake area ) 2 area (mi /s, cubic feet per second] Drainage 3 , square miles; ft 2 11 -- 345 2.00 1980 44 -- 198 .85 643 29 -- 160 .42 687 46 -- 120 .37 570 39 -- 60.0 .04 368 20 -- 805 3.00 2590 44 -- 350 .53 2030 38 -- 747 3.00 1990 14 -- 90.7 3.12 437 53 -- 9640 .54 20900 Years of record Years 1 Systematic Historic 2 5 10 25 50 100 200 500 Name nr Perry River nr Perry River at Foley River nr Foley nr Scanlon River nr Cross City at Lamont Aucilla River nr Aucilla Little Aucilla River nr Green- ville River nr Wilcox Station, regional, and weighted T-year flood estimates for the Suwannee River Water Management District --Continued Years of historic record include the period systematic measurements as well intervening years to major flood events. Years Peak-flow partial-record gaging station. 1 2 Station number 02326250 02326300 02326000 Econfina River 02325000 Fenholloway 02324500 Fenholloway 02324400 Fenholloway 02326512 Aucilla River 02324000 Steinhatchee 02326500 Aucilla River 02323500 Suwannee 2 2 Appendix 1. ine--weighted or best estimate of T-year flood; mi ine--weighted or best estimate of T-year [Discharge-frequency relations for each station are presented as follows: Top line--log-Pearson Type III analysis for the indic line--log-Pearson Type relations for each station are presented as follows: Top [Discharge-frequency

14 Hydrogeology of the Surficial and Intermediate Aquifer Systems in Sarasota and Adjacent Counties, Florida