(200) W Ri T1111111,10,11111110 91 by 7V---/tP THE 1971 DROUGHT IN SOUTH FLORIDA AND ITS EFFECT ON THE HYDROLOGIC SYSTEM 600GICAL swi,u ‘10s-roN. v vek AUG 1 r 1974 U. S. GEOLOGICAL SURVEY Water Resources Investigation 12-74 Prepared in cooperation with the FLORIDA DEPARTMENT OF NATURAL RESOURCES .. BIBLIOGRAPHIC DATA 1. Report No. 1 3.'"ecipient's Accession No. SHEET '4. Title and Subtitle `1. Report Date July 1974 The 1971 drought in south Florida and its effect on the hydrologic system. 6. 7. Aurbor(s) 8. Performing Organization Rept. Benson and R. A. Gardner No. M. A. WRI 12-74 9. Performing Organization Name and Address 70. Project/ Task/Work Unit No. U.S. Geological Survey, WRD 325 John Knox Road, Suite F-240 11. Contract/Grant No. Tallahassee, Florida 32303 12. Sponsoring Organization Name and Address 13. Type of Report St Period , Covered Geological Survey, WRD U.S. Final 1970-71 325 John Knox Road, Suite F-240 Tallahassee, Florida 32303 14. 15. Supplementary Notes In cooperation with Florida Department of Natural Resources 16. Abstracts The 1971 dry season rainfall in south Florida was low enough that the public media and concerned public officials unanimously characterized the event as a severe drought. Rainfall over all of south Florida during the 1970 wet season and the 1970-71 dry season was less than 85 percent of normal, as was the 1971 wet season on the heavily populated southeast coast of Florida. Rainfall during the dry season ranged from 20 to 63 percent of normal and recurrence intervals for dry season rainfall of this magnitude ranged from 100 years to several hundred years. Canal flow and ground-water levels reflected the drought conditions but in most cases did not set record lows. NO permanent undesirable effects occurred as i rPqiil r of the rirntielt. 17. Key Words arid Document Analysis. )7o. Descriptors Droughts, Frequency analysis, ground water, storage 17b. Identifiers /Open- Ended Terms Rainfall-frequency, Log Pearson Type III frequency analysis, South Florida 17c. COSA TI 1,i:id/Group 18. Availability Statement 19. •Si..,,,,cy Cias, (i-nis 21- :\o. ut Pages Report) 54 t 'D. s _, ._:.:5 , _i.,;, :... 22. i,..._ No restriction on distribution Page UNC.LASSIF lED FORM NT15-55 (REV. 2.72/ THIS FORM MAY BE REPRODUCED USCOMM.DC :4552.P72 THE 1971 DROUGHT IN SOUTH FLORIDA AND ITS EFFECT ON THE HYDROLOGIC SYSTEM By M. A. Benson and R. A. Gardner U. S. GEOLOGICAL SURVEY Water Resources Investigations 12-74 Prepared in cooperation with FLORIDA DEPARTMENT OF NATURAL RESOURCES July 1974 UNITED STATES DEPARTMENT OF THE INTERIOR Rogers C. B. Morton, Secretary GEOLOGICAL SURVEY Vincent E. McKelvey, Director For additional information write to: U.S. Geological Survey Suite F-240 325 John Knox Road Tallahassee, Florida 32303 CONTENTS Page Ab stract . •000000000•00000000000•• 1 Introduction 2 Characteristics and definition of drought 000090•• 7 The 1971 drought in south Florida .0000.-- 12 Rainfall 14 Rainfall frequency 0 •••••••••••••••• 17 Runoff . OOOOOOO o 0 0-000-0 21 Water levels in Lake Okeechobee 009.00.0000 26 30 Ground-water conditions . Sea-water intrusion . OOOOOOOOO 37 Fires OOOOO 00•0000000000000 38 Cloud seeding OOOOO 0000000000000 40 Summary and conclusions ••••000000 000000 42 References . 45 ILLUSTRATIONS Page Figure 1. Map showing study area and location of rain gages and subareas .0 0 0 0 .0 0 0 OOOOOO 3 2. Graphs showing normal monthly rainfall . .. 4 3. Map showing normal annual rainfall distribution . 5 4 - 8. Graphs showing: 4. Rainfall deficiency May 1970 - October 1971 . 15 5. November to April rainfall frequency for southeast coast of Florida 18 6. November to April rainfall frequency for south-central Florida 0 0 0 0 0 0 0 0 . 19 7. November to April rainfall frequency for southwest coast of Florida O OOOO 0 0 0 • • 20 8. Monthly runoff patterns at six streamflow stations • .• • 0 0 0 0 0 0 .• 0. 0 0 • 23 90 Map showing location of streamflow stations . 25 10. Hydrograph of Lake Okeechobee, 1915-71 27 11. Graph showing number of days water-surface elevation in Lake Okeechobee was at or below in- dicated levels in 1932, 1956, 1962, and 1971 0 0 0 28 12. Hydrographs of selected wells in the study area 0 0 0 0 0 0 . 0 OOOOOOOOO . 0 0 0 0 0 31 Iv ILLUSTRATIONS (Continued) Page Figure 13. Map showing seasonal fluctuation of water levels in the Biscayne aquifer in Dade County 0 0 32 14. Map showing location of wells in study area with 20 to 40 years of record 34 15. Map showing net decline in water levels in Biscayne aquifer, May 1970 to May 1971 35 16. Map showing difference between September 1971 water levels and average water levels in the Biscayne aquifer, Dade County 000. OOOOOO 36 V TABLES Page Table 10 Normal and 1970-71 rainfall and seasonal rainfall deficiencies for south Florida o o . 11 20 December-May runoff at long-term canal flow stations, south Florida 0 0 a •••••••• 24 3. Water levels during drought periods of Lake Okeechobee at St. Lucie Canal 29 VI FACTORS FOR CONVERTING ENGLISH UNITS TO INTERNATIONAL SYSTEM (SI) UNITS The following factors may be used to convert the English units published herein to the International System of Units (SI), Subsequent reports will contain both the English and SI unit equivalents in the station manuscript descriptions until such time that all data will be published in SI units. -By Multiply English units To obtain SI units Length inches(in) 25.4 millimeters(mm) .0254 meters (m) feet(ft) .3048 meters (m) yards (yd) .9144 meters (in) rods 5.0292 meters (m) miles(mi) 1.609 kilometers (km) Area acres 4047 square meters (m2) .4047 *hectares (ha) .4047 square hectometer (hm2) .004047 square kilometers (km2) square miles(mi2) 2.590 square kilometers (lun2) Volume gallons(gal) 3.785 **liters (1) 3.785 cubic decimeters (dm3) 3.785x10-3 cubic meters (m3) million gallons (106 gal) 3785 cubic meters (m3) 3.785x10-3 cubic hectometers (hm3) cubic feet (ft3) 28.32 cubic decimeters (dm3) .02832 cubic meters (m3) cfs-day (ft3/s-day) 2447 cubic meters (m3) 2.447x10-3 cubic hectometers (hm3) acre-feet (acre-ft) 1233 cubic meters (m3) 1.233x10-3 cubic hectometers (hm3) 1.233x10-6 cubic kilometers (km3) Flow cubic feet per second (ft3/s) 28.32 liters per second (l/s) 28.32 cubic decimeters per second (dm3/s) .02832 cubic meters per second (m3/s) gallons per minute (gpm) .06309 liters per second (l/s) .06309 cubic decimeters per second (dm3/s) 6.309x10-5 cubic meters per second (m3/s) million gallons per day (mgd) 43.81 cubic decimeters per second (dm3/s) .04381 cubic meters per second (m3/s) Mass ton (short) .9072 tonne (t) * The unit hectare is approved for use with the International System (SI) for a limited time, ** The unit liter is accepted for use with the International System (SI). VII THE 1971 DROUGHT IN SOUTH FLORIDA AND ITS EFFECT ON THE HYDROLOGIC SYSTEM By M. A. Benson and R. A. Gardner ABSTRACT The 1971 dry season rainfall in south Florida was low enough that the public media and concerned public officials unanimously characterized the event as a severe drought. Rainfall over all of south Florida during the 1970 wet season and the 1970-71 dry season was less than 85 percent of normal, as was the 1971 wet season on the heavily populated southeast coast of Florida. Rainfall during the dry season ranged from 20 to 63 percent of normal and recurrence intervals for dry season rainfall of this magnitude ranged from 100 years to several hundred years. Canal flow and ground-water levels reflected the drought conditions but in most cases did not set record lows. No per- manent undesirable effects occurred as a result of the drought. 1 INTRODUCTION During the early part of 1971, Florida, and particularly south Florida, experienced a memorable drought. It was a drought in the sense that rainfall was markedly deficient, surface and subsurface water levels were critically low, agricultural and domestic water supplies were seriously threatened and wildlife was under severe stress in the area covered by this report (fig. 1). Rainfall records in south Florida show a typical seasonal pattern, a dry winter season and a wet summer season. The graphs in figure 2 show that on the average the dry season begins abruptly in November and continues through April or May, but there is some geographical variation in the start of the wet season. The normal annual rainfall (fig. 3) ranges from 50 to 63 inches (1270 to 1600 mm) and about 75 percent falls in the wet season. If uniformly distributed through the year, the 50 to 63 inches (1270 to 1600 mm) of rainfall would provide year-round abundant supplies. However the bulk of the rainfall during the wet season runs off rapidly to the ocean and thus is not available for use. A large part of the State's agricultural produce is grown during the driest part of the year requiring regular irrigation from surface or subsurface storage. 2 82° 27° LAKE OK EECHOBEE MOORE HAVEN WE8T RM_M BELLE BEACH GLADE • I FORT PAYER", • I CENTRA#_ HENDRY - -COLLIER 1 SOUTH • ; FLORI DA. • PALM BEACH' • • BROWARD • • CO • PARKWAY EVERGLADEO • • 'COHSE/RAMON O I AREA • JA • • f3 %0 7E D ▪%.11 • • CO NOO EXPLANATION •• • • SUBAREA BOUNDARY RAINGAGE LOCATION Figure 1.--Area and location of rain gages and subareas. 10 1111111 1 1111 — 250 5 125 0 111111111 Tri11111 r-1-17-17 0 WEST PALM BEACH BELLE GLADE PUNTA GORDA 10 1 1 1 1 1 1 1 1 —250 5 125 0 1111111 1 1 1-771— l 1 I 1 I 1-1-114111 0 FORT LAUDERDALE MOORE HAVEN FORT MYERS ERS ET CHES 10 IM IN 11111 11 1 1111 1111 I I — 250 L IN 5 —125 MIL —1—.