The 1971 Drought in South Florida and Its Effect on the Hydrologic System

(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

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.

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 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—. 0 1111111 -7-17-1- 1 1 1 1 0 IN FALL, MIAMI W SO LA BELLE NAPLES AIN R FALL, 10.07

10 AIN fill 1 111 11-11- I - R 5

0 III t -t-_ HOMESTEAD TAMIAMI TRAIL 40 MILE EVERGLADES BEND 10 250

125 0

SOUTHEAST COAST AVERAGE CENTRAL SOUTH FLORIDA AVERAGE SOUTHWEST COAST AVERAGE

Figure 2.--Normal monthly rainfall.

82°

' ST LUCIE COUNTY E COUNTY r MARTIN COUNTY 17

cAttt. 270 LUGE .rte GLADES LAKE purs,Ti•1.79 OKEECHOBEE PALM BEACH CO A GOP DA (1315) MOORE HAVEN 54.62 50. CHARLOTTE CO 06 WEST LEE CO, 4 05At-,1rcHt r 58.75 PALM BLLE '1- BEACH ( 13/37 ) GL ADE0492) (1576)

FORT MYERSI I / 20 53.95 ' ( 1370) HENDRY COLLIER 1

I • \ , PALM BEACH CO CO 1 1' N BROWA RD --wsi P•vA'rcw \1.. Al4 A CO _ _..._._ . \\'''. ., 4,- CO 53.00 E VE Si. ADES PAR•odAl NAPLES FORT LAUDERDALE

(15 - BROWARD lg • DA6E1— •.0

4 .10./.: " RUDES_ CO LLIER co Er ,C NioVR6E CO 0 — 5751 (1461)

C t. oa E E RGIL ADES 62.99 (1600) •

10 20 Milis NAT,IoNA,

EXPLANATION 110 20 30 Km 54.40 (1382) PARK SAMPLING SITE. NUMBER IS NORMAL ANNUAL O RAINFALL,IN INCHES(MM)

Figure 3.--Normal annual rainfall distribution.

5 If water could be stored during wet periods and released

during dry periods, the water management problems of inadequate

rain distribution seemingly could be solved. Yet nature often

conflicts with man's planning: heavy rains may fall during a dry

period, or the wet season of a particular year may have little

rainfall. With sufficient records, normal annual and seasonal

rainfall can be predicted with fair accuracy, but over short

periods rainfall occurs erratically and cannot be predicted ac-

curately more than a few hours in advance.

Although the occurrence of events such as the 1970-71 drought

cannot be predicted, records can be analyzed to determine the average frequency with which they can be expected to occur. These analyses are useful to those responsible for the management of

water resources; therefore, the analyses in this report were under-

taken as a part of the Resource And Land Information Study of

South Florida (U. S. Department of Interior, 1973).

6 CHARACTERISTICS AND DEFINITION OF DROUGHT

Drought is a natural phenomenon of a critical condition, and as such it occupies a place with equal standing among floods, hurricanes, tornados, earthquakes, tidal waves, and other disastrous natural events. All these phenomena are instances of nature departing drastically from its usual course.

Droughts are characterized by long duration when compared to the suddenness of other catastrophes, and their starting and ending times are difficult to identify. Rainfall deficiency is the basic cause of droughts, but there may be a long time lag between deficiencies and visible harmful effects on crops, wildlife, and water supplies.

The dictionary defines drought as (1) a prolonged period of dryness, or (2) a prolonged and chronic shortage. The first definition involves only the supply; the second is more comprehensive and recognizes the needs and the failure to meet the needs as being an integral part of the concept of a drought.

Meteorologists and hydrologists have defined droughts in many different ways, all add to the dictionary definitions by being very specific in defining dryness, or in identifying what constitutes a prolonged period or what the shortages may be with respect to

7 selected needs. Types of drought have been defined as follows

(Suorahmanyam, 1967):

a. Meteorologic drought -- defined only in terms of

precipitation deficiencies in absolute amounts, for

specific durations.

b. Climatological drought -- defined in terms of preci-

pitation deficiencies, not in specific quantities but

as a ratio to mean or normal values.

c. Atmospheric drought -- definitions involve not only

precipitation, but possibly temperature, humidity,

or wind speeds.

d. Agricultural drought -- definitions involve principally

the soil moisture and plant behavior, perhaps for a

specific crop. As Yevjevich (1967) states: "A drought

for tomatoes, for instance, may not be a drought in the

eyes of the grower of potatoes."

e. Hydrologic drought -- defined in terms of reduction of

stream-flows, reduction in lake or reservoir storage,

and lowering of ground-water levels.

f. Water-management drought -- this classification is

included to characterize water deficiencies that may

exist because of the fgTlure of water-management

8 practices of facilities such as integrated water-supply

systems and surface or subsurface storage to bridge

over normal or abnormal dry periods and equalize the

water supply through the year. To a large extent, the

recent drought in the northeastern United States was a

water-management drought. During that drought, large

amounts of water were in storage in aquifers, but means

for withdrawing these supplies had not been developed.

The U.S. Geological Survey has customarily identified droughts on the basis of meterologic records (Thomas, 1962). J. C.

Hoyt (1938) states:

"In general, however, in humid and semiarid States

there are no serious drought effects unless the annual

precipitation is as low as 85 percent of the mean -

that is, unless there is an annual deficiency of 15

percent or more."

Hoyt notes, however, that a deficiency in annual precipitation is not necessarily among the good criteria for determining the existence of a drought since within-year distribution of rainfall is a factor to be considered. He concludes that the seasonal deficiencies would be a better measure of the existence of drought

9 conditions or the lack of them. In this report drought conditions are considered to exist if seasonal rainfall (wet season or dry season) is 85 percent or less of the normal seasonal rainfall.

The study area is divided into three subareas (fig. 1).

They are the southwest coast, central south Florida, and southeast coast. In each subarea four rainfall stations, for which 1941-70 normals have been computed (U, S. Department of Commerce, 1973), were used as the basis for computing normal rainfall and for evaluating rainfall deficiencies during the drought period. Normal monthly rainfall for each subarea was computed as the unweighted average of the normal monthly rainfall of the four stations in the area (table 1). Areal rainfall data used in the frequency study are the averaged seasonal rainfall recorded at the four stations in each area for 1941 to 1971.

10 Table 1. Normal and 1970-71 rainfall and seasonal rainfall deficiencies for south Florida t

Southeast coast rainfall (inches) Central south Florida rainfall (inches) Southwest coast rainfall (inches) Recorded Seasonal Recorded Seasonal Recorded Seasonal 1970-71 percent percent percent percent percent percent Month Normal Recorded normal (normal) Normal Recorded (normal) (normal) Normal Recorded (normal) (normal) wet dry wet dry wet dry I-, Jan. 2.12 3.57 144 1.76 3.57 203 1.77 3.24 183 Feb 2.00 2.87 122 1.96 2.28 116 2.00 1.46 73 Mar 2.73 7.03 204 2.89 11.73 406 2.55 12.57 493 Apr 4.02 .67 15 2.71 .35 13 2.21 .02 1 May 5.82 7.80 153 4.90 5.54 113 4.04 5.85 145 June 7.80 7.49 98 9.15 6.80 74 8.92 6.28 70 July 7.04 3.68 56 78 8.11 7.48 92 85 8.31 6.20 75 82 Aug 7.22 5.06 75 7.51 7.53 100 7.47 5.50 74 Sep 9.68 7.84 81 8.28 4.34 52 8.94 8.17' 92 Oct 8.32 4.58 58 5.14 4.99 97 4.36 2.40 55 Nov 2.79 .34 12 1.41 .14 10 1.36 4.05 298 Dec 2.09 .26 '10 1.47 .24 16 1.37 .27 20 Jan 2.12 .59 24 20 1.76 .58 32 27 1.77 .76 43 63 Feb 2.00 1.02 43 1.96 1.57 80 2.00 1.28 64 Mar 2.73 .33 10 2.89 .51 18 2.55 .37 15 Apr 4.02 .50 12 2.71 .30 11 2.21 .40 18 May 5.82 3.83 75 4.90 4.26 86 4.04 2.25 56 June 7.80 7.57 99 9.15 11.03 120 8.92 5.33 60 July 7.04 4.42 66 74 8.11 6.56 81 99 8.31 6.86 83 95 Aug 7.22 4.91 72 7.51 7.89 105 7.47 9.43 128 Sep 9.68 7.95 83 8.28 6.85 82 8.94 10.51 118 Oct 8.32 5.64 71 5.14 5.96 115 4.36 5.69 131 Nov 2.79 4.87 170 1.41 1.75 124 1.36 .77 59 Dec 2.09 2.79 108 1.47 1.14 78 1.37 .53 39 THE 1971 DROUGHT IN SOUTH FLORIDA

The average rainfall during October varies geographically and ranges from 4 to 9 inches (102 to 229 mm) whereas in November it ranges from 1 to 4 inches (25 to 102 mm). By the end of November

1970 the newspapers were making what seemed to be uncannily accurate predictions of the drought that actually occurred,

Miami Herald, Nov. 27: "A severe drought next

spring is in the making for south Florida.

Nothing can avert it but heavy rains this

winter, which would be very unusual."

Miami Herald, Nov. 30: "With the dry season just

beginning and the rainy season more than six months

away, Central and South Florida teeter on the brink

of a third major drought since 1961."

The predictions are not unduly surprising, however, because the stage for the drought was set at a much earlier date by both the vagaries of nature and the uncertainties inherent in managing water resources with only limited storage capacity available and the necessity of providing for both flood control and water supply with the same storage system.

12 In March 1970 unseasonal heavy rains fell day after day. Over the whole of the Everglades and the southwest coast 12.15 inches

(309 mm) fell, on the average. Rain over the lower east coast averaged 7.03 inches (179 mm). Farms were waterlogged, and deer and other wildlife in the Everglades were critically threatened. The water contained in the storage system of the Central and Southern

Florida Flood Control District was much above schedule prior to the start of the normal rainy season, and the threat of flooding loomed.

The decision was then made to release water from storage to lower water levels to the scheduled elevation in anticipation of the rainy season. Rainfall, however, was deficient (85 percent or less of normal) during the 1970 wet season and the following dry season throughout south Florida, and along the southeast coast during the 1971 wet season (table 1).

Accompanying this period of deficient rainfall were substantial losses from storage in the surface-and ground-water storage systems in the area. The resulting shortages were accompanied by other effects such as landward movement of the salt-water front in the

Biscayne aquifer of southeast Florida and with fires in the

Everglades. These and other characteristics and effects of the drought are discussed in the following sections.

13 Rainfall

During early 1970 south Florida accumulated excess rainfall, averaging from 4 to 10 inches (102 to 254 mm) over the area. There ensued a period of rainfall deficiencies beginning in June 1970 and continuing through the following dry season and along the southeast coast through the 1971 wet season. The length and magnitude of the rainfall deficiencies combined to make this a record drought for south Florida. Rainfall deficiencies for May 1970 through October

1971 are shown in figure 4.

The 1970 wet season rainfall deficiencies in south Florida were, when compared to subsequent events, about uniform over the area with rainfall ranging from 78 to 85 percent of normal. During the ensuing dry season (November 1970 through April 1971) rainfall was 63 percent of normal on the southwest coast, but 27 percent of n ,rmal in central south Florida and 20 percent of normal on the heavily populated southeast coast.

The 1971 wet season saw an abatement of the drought in central south Florida and along the southwest coast with rainfall in those areas 95 percent or more of normal. Rainfall along the southeast coast was 74 percent of normal during the 1971 wet season, less than that of the 1970 wet season. During the 1971-72 dry season, rainfall on the southeast coast was 174 percent of normal and the long period of rainfall deficiency was broken.

14 N_50 20 IIIIIIIIIIIIIIIIIIIIIII

0 0

-20 -50 u) u) cc w w I H 0 -40 111111111111111111111L_i - -100 LIJ z 2 z SOUTH EAST COAST _J >2- _J 0 Z 20 w -50 z U_ >- LL 0 w z 0 w - 0 cr E3 O it cn LLI D 0 _J ix cl- -20 ---50 0 cc u) D CENTRAL SOUTH FLORIDA D u) ___i ___i a_ _J x < 20 D U_ -50 cn z :;;:i J cc J

-20 11111111111 -50 J FMAMJJASOND JFMAMJ JASOND 1970 1971

SOUTHWEST COAST

Figure 4.--Rainfall deficiency May 1970 - October 1971.

15 One particular period is of special interest, the 1970-71 dry period. Although periods of minor rainfall deficiencies are not rare, extreme deficiencies such as the dry 1970-71 season deficiency are very rare; consequently, much of the following discussion is an evaluation of this 6-month period and an evaluation of the average frequency with which a period having the rainfall characteristics of this 6-month period can be expected.

16 Rainfall Frequency

The recorded November to April rainfall for each subarea for 1941 to 1971 was analyzed statistically to develop a frequency relation for each, so as to determine the average recurrence interval of the 1971 dry-period rainfall. Frequency relations could be fitted satisfactorily to the data by using a log-Pearson Type III distribution. This was accomplished by the use of a computer program developed by the U. S. Geological Survey. The developed frequency curves and original data are shown in figures 5 to 7 for each of the three subareas. The fit is good indicating the suitability of the log-Pearson Type III distribution for fitting low-rainfall data such as these.

The computed recurrence interval of the 1971 dry-season rainfall on southwest coast is 100 years. Computed recurrence intervals of the 1971 dry-season rainfall for the southeast coast and central south Florida are several hundred years each. These analyses indicate that the 1971 dry-season rainfall in south

Florida was indeed a rare event.

100 90 2150 80 70 1- 60 1350 50

40 -4 • 950

30 650 t---- •

20 • 450 U) Cc • I- CH

0 . _ 250 ) c L IN

o . + c 190

ALL, -I. _1 . . . 50

NF O COMPUTED VALUE

, ,-.

T 130 AI L • • • + • SELECTED RECORDED VALUES i t I 1 • R 1- HO -4- 1971 RECURRENCE .INTERVAL GR.EATE.R THAN 100 YEARS 4 ---4 CC I_ 90 +1 '971 3 -70 . . i _

2 • -t --f----r- 50

1 T 1 i 1 1 30 , I ___i I , 0.1 I b 10 '?(J 30 40 50 60 70 80 9C, I') 98 99 99.9 PERCENTAGE OF TIME INDICATED VALUE EQUALED OR EXCEEDED

Figure 5.--November to April rainfall frequency for southeast coast of

Florida.

18 100 90 80 2150 70 60

50 1350

40 950 • 30 • 650

20 4 -450 4P (i) I- 4, — 10 -250 El Z 9 - 8 _J a -190 z _J 7 • 60 __J I,- 6 • -130 LI- Zi 5 Z -HO , 4 Cr -90 0 COMPUTED VALUE + 1971 3 + SELECTED RECORDED VALUES -70 1971 RECURRENCE INTERVAL GREATER THAN IOOYEARS 1--- i I- i 1--__L i____ 50

. i --,-- --t-

30 1

0.1 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.9 PERCENTAGE OF TIME INDICATED VALUE EQUALED OR EXCEEDED

Figure 6.--November to April rainfall frequency for south-central Florida.

19 100 . 4_.. 90 - 1----i- 4 4 _i_ 2150 80 i 4 : 70 _ j 1 60 I 1 4 1350 50 ,-- 1 40 .. 1- 950

30 ii . _ 650 —t---

20 ...1, 450

. . . . • U)

CH " -

o 250 _ $) 1

, t IN

o #4- ' It c • • ' 190 . .

---, • • ALL, _ F ...... _ C • 50

i - a 130 AIN o — --f - • R 1 0 COMPUTED VALUE HO 4 --1 + SELECTED RECORDED VALUES • • • " • -4-- • 90 1971 RECURRENCE INTERVAL EQUALS .100YEARS 1971

70 . • • • • • • • • . . . •—

2 . • • • • - • • • • • • . . 50

...... 4--

30 I 0.1 5 1., 20 30 40 50 60 70 80 90 95 98 99 99.9 PERCENTAGE OF TIME INDICATED VALUE EQUALED OR EXCEEDED

Figure 7.--November to April rainfall frequency for southwest coast of

Florida.

20 Runoff

Since the magnitude of the 1971 dry-season rainfall was found

to represent a very rare meteorologic event, it was also of interest

to investigate the corresponding magnitudes of runoff in surface-

water channels. The lack of sufficient storage reserves possibly

might have resulted in deficient runoff in the area and that, on the

average, the surface runoff might have been almost, if not entirely, as deficient as the rainfall.

Runoff in south Florida is highly controlled. Over the years,

water control and management practices have altered natural drainage

patterns by canal construction, damming, diversions, and by transfer

of water between the surface-water and ground-water parts of the

system. In addition, water levels in some wetlands have been

lowered, and artificial surface storage areas (the conservation areas) built, each of which influences evapotranspiration and hence

the runoff. In addition, water use by man has increased steadily.

Therefore, the runoff records through the years represent a

summation of the results of constantly changing conditions.

The monthly runoff pattern in terms of percentage of annual flow was analyzed at seven streamflow stations in south Florida.

These stations had between 29 and 32 years of record.

21 Graphs of monthly flows at six streamflow stations, in percentage

of annual flow, are shown in figure 8. The low-runoff season through

most of south Florida lags the 6-month mow rainfall season by 1

month; that is, the 6-month low-runoff period extends from December

through May.

At six of the seven stations the flow during December-May in

several recent years was lower than that during 1971.

The streamflow records analyzed, except station 02289040

(Tamiami Canal Outlets, levee 67A to 40-mile bend), had dry season

flows during 1971 ranging from 5 to 23 percent of the mean dry

season flow (table 2). Station 02289040 and station 0228906 0

combined are used to measure the southward flow from conservation

areas 3A and 3B (fig. 9). Changes in the facilities for regulating

storage in the two conservation areas have resulted in changes

in the flow regimens at those stations after 1962. The results

of these changes are a factor in the high ratio of the 1971 dry

season flow to average dry season flow for station 02289040. The

combined 1971 dry season flow from stations 02289040 and station

0228906 0 is 17 percent of the combined average dry season flow

(concurrent record 1940 through 1970).

22 21.17 20 1 I 1 1 I STA 02279000 STA 022 88900

0 _J ti_

20 1111111111

STA 02285000 STA 02292000

10 _

0 1 ii 1 1 1 ONDJFMAMJJAS ONDJFMAMJJAS EXPLANATION WATER YEA R WATER YEAR V//A PERIOD OF LOW FLOW

1 1 PERIOD OF HIGH FLOW

Figure 8.--Monthly runoff patterns at six streamflow stations.

23 Table 2. December-May runoff at long-term canal flow stations, south Florida. (mean daily discharge in cubic feet per second)

Average 1971 Ratio of Station Name Length of record Dec.-May Dec.-May 1971 runoff and Number (years) runoff runoff to average

West Palm Beach Canal at West Palm Beach 02279000 30 583 28 0.048

Hillsboro Canal near Deerfield Beach 02281500 30 199 35 .176

North New River Canal near Fort Lauderdale 02285000 30 322 15 .047

Tamiami Canal Outlets 4' 40 mi bend to Monroe 02288900 31 75 15 .200

Tamiami Canal Outlets levee 67A to 40 mi bend 02289040 31 187 208 1.11

Tamiami Canal Outlets levee 30 to levee 67A 02289060 29 1780 117 .066

Caloosahatchee Canal at Moore Haven 02292000 32 1086 248 .228 82°

COUNTY

LAKE OKEECOBEE PUNTA GORDA 02292000 MOORE HAVEN

'yr p CHARLOTTE CO i WEST LEE CO 0,35A/40A, 4E, : LA BELLE BEACH 40,1-- 02279000 FORT MYERS

4111111 IL HENDRY COLLIER 1

22x31500 PALM BEACH

BROWARD

PARKWAY EVERGLADES NAPLES FORT AUCCROAL_E • CONS( RVA,ON AR( 3A 85000 B RDOAW6AE RD t. • L92,04,t, I EvERGLADI'OLLIER CO j °VW 2 8 840 I

EXPLANATION

A GAGING STATION AND NUMBER 02288900 io 2p mil's O I 10 20 30 Kma

Figure 9.--Location of streamflow stations.

25 Water Levels in Lake Okeechobee

During the 1971 drought, the newspapers carried information of the alarming and continuous fall of the water level in Lake

Okeechobee. The information was in terms of either water-level elevation or the number of acre-feet in storage below the scheduled amount. Examination of the previous record of water levels shows that the 1971 levels represented a notable deficiency in scheduled storage, but in no way were they a record-breaking event.

The record of water levels since 1915 shows that comparable periods of low lake stages had occurred in 1934, 1956, and 1962

(fig. 10). Table 3 shows comparative water-level data for these and for the 1971 drought, The minimum water levels were almost the same in 1932 and 1971, but they were slightly lower in 1956 and

1962, The number of days that the levels were below 12 and 11 feet

(3.7 and 3.4m) show that, at least insofar as indicated by storage in

Lake Okeechobee, 1956 and 1962 represented far greater deficiencies in storage than 1971. In addition, during 1932 the lake level was below 12 feet (3.7 m) for 311 consecutive days as compared with

145 days in 1971 (fig. 11, and table 3).

26 LZ

WATER LEVEL,IN FEET ABOVE MEAN SEA LEVEL

011 40 3 = 10 Ca .0. 04 Ot -.I 01 40 l''C,

WATER LEVEL IN METERS ABOVE MEAN SEA LEVEL 1- 11.1 t.L.. LI.1

LAKE LEVEL, IN 12.0 10.0 12.5 10.5 11.0 11.5 Figure 11.--Numberofdays water-surfaceelevationinLakeOkeechobeewas 0 at orbelowindicated levelsin1932, 1956,1962,and1971. 100

NUMBER OFDAYS O D + 200 i 1962 WATERYEAR 1932 WATERYEAR 1956 CALENDARYEAR 1971 WATERYEAR

EXPLANATION 300

H 400 —3.8 3.2 3.6 3.4 3.0

AK LEVEL, IN MET ERS L E Table 3.-- Water levels during drought periods of Lake Okeechobee at St.

Lucie Canal.

Days water Minimum stage

Year level below for the year

12.00 ft 11.00 ft Stage (feet) Date

1932 311 55 10.3 5/17/32

1956 211 132 10.14 8/17/56

1962 224 95 10.22 6/ 7/62

1971 145 70 10.24 6/6-7/71

29 Ground-Water Conditions

Ground-water reservoirs are the immediate source of water for most municipal and part of the agricultural needs. The eastern part of the area depends on a shallow permeable aquifer (Biscayne aquifer) consisting primarily of limestone and sandy limestone which has a direct connection to the sea. The coastal sections contain salty water and the position of the fresh water-salt water interface shifts in response to changes in water levels in the aquifer. The water levels in the aquifer fluctuate in response to rainfall and water- management practices. Canals provide an important source of recharge to the aquifer in areas of large withdrawals of ground water during dry periods (Meyer, 1972).

Annual water-level fluctuations in selected wells in the study area are shown in figure 12. The annual cyclic nature of the water- level fluctuations is evident. The average seasonal range in water- level fluctuations in the Biscayne aquifer in Dade County is shown in figure 13. In north Dade County where water use is concentrated the range in seasonal water levels is relatively small as compared with the range in seasonal water levels to the south. This is attributed to the fact that water-management practices in the north provide for supplying the aquifer with water from conservation area 3 through the canals during the dry season. These facilities Are not yet available to the south part of the county.

30 WATER LEVEL,IN FEET ABOVE MEAN SEA LEVEL WETER LEVEL,IN FEET ABOVE MEAN BEA LEVEL N.) W O O O O [M Fi _ 1 1 _ gur (.7) J ' _ _ @ S D e 12

T .--S ,,,(,- _ el W u) — r- ect o 1 --4 (A

ed -- 0 (-15, c w

ell o u) _ 0 s MJ — _ i SD n C-6 -,4 — th e H st 0 0 0 0 - J S D ud (7)

1 1 ea cy) tD

, O

WATER LEVEL,IN METERS ABOVE MEAN SEA LEVEL

WETER LEVEL, IN FEET ABOVE MEAN SEA LEVEL

O I WATER LEVEL, IN FEET ABOVE OR M

J S D I I BELOW MEAN SEA LEVEL 45 — — 0) — Op — MJSD _ — c r ) — (0

NI r- _ 1 _

co r -4 o --4_ OA — S _ CO — a

_ Z15 c- --.1 -

o1M J S (0 — --.I N) - D - —

I I I

O 57) O WATER LEVEL,IN METERS ABOVE MEAN SEA LEVEL WATER LEVEL,IN METERS ABOVE OR BELOW MEAN SEA LEVEL 80°55' 45' 25' IS' 0°05 26°00 26°Od r BROWARD v COUNTY SNAKE CREEK CANAL DADE Ij COUNTY YNE

CONSERVATION LITTLE CANAL 1,6-„, 3A 5d cq

30' .Y 4 • MD RC rypL. :: ' mot NATI AL...... "...... N ...... ______--„., ...... /' X,. -_,,,„„. .04 0"::7? ---_,..4. 0 Al, AND 5' • 7 PAR, • \ 20 44,4 -,„ L. EXPLANATION — 2--

LINE OF EQUAL AVERAGE SEASONAL WATER-LEVEL FLUCTUATION. DASHED WHERE APPROXIMATELY LOCATED. INTERVALS 0.5 AND I FOOT (0 I5AND 0.30METER) ...... •-• AY 25°10' ; C, A FL 0 POSITION OF AVERAGE DRY SEASON WATER TABLE MEAN SEA LEVEL ELE- u .) o pmftEs VATION

1 0 5 1 10 151KMS 1

Figure 13.--Seasonal fluctuation of water levels in the Biscayne aquifer

in Dade County. 32 Water-level records have been collected in 18 wells in southeast

Florida for 20 to 40 years (fig. 14). In nine of these wells levels have been lower in 2 or more years.

The vulnerability of the Biscayne aquifer to further advances of sea water gave rise to concern about the falling water levels in 1971. The net change in water levels in the Biscayne aquifer in

Dade County between May 1970 and May 1971 is shown in figure 15.

The net decline ranged from 0.5 to 4 feet (0.15 to 1.22 m) and was a foot or more over much of the area. By September 1971 (fig. 16) water levels in all but western Dade County were at or above average elevations.

33 820

27° F-drioTs LAKE OKEECHOBEE PUNTA GORDA

MOORE HAVEN

RIVE A? HARLOTTE CO WEST LEE COG coS!!ArcHre LA BELLE PALM BE AC H

',PALM BEACH - - _

PARKWAY EVERGLADES NAPLES FORT LAUDERDALE Bt

Figure 14.--Location of wells in study area with 20 to 40 years of record.

15 80°55' 4 5' 35, 25' , 80°05 ?6°00 I T 26°00 T —1 BROWARD COUNTY SNAKE CREEK CANALS- — DADE ' COUNTY

0 0 h L AND 'n ;2 2..0

20 1.5

EXPLANATION 1.0 —2.5 LINE OF EQUAL WATER-LEVEL DECLINE. INTERVALS 0.5ANO IFOOT(0.15AN00.30ME- TER) 0.5

SALT WATER FRONT 1971 8,AY 25°10- FLOP Om •

0 5 IpIMILES SALT WATER FRONT 1970 0 g 1 10 15 1KMS

Figure 15.--Net decline in water levels in Biscayne aquifer, May 1970

to May 1971. 35 80055' 45' 35' 25' 15' 800 05. 26°00' 26°00'

r - — - — — - COUNTY SNAKE CREEK CANAL BROWARD _ DADE UNTY

CONSERVATION AREAS 3A 38 5d

LINE OF EQUAL WATER LEVEL RISE (t)OR FALL (--) . INTERVALS 0.5ANO I FOOT(0.15ANO 0.30 / METER)

2 5°I 0

Figure 16.--Difference between September 1971 water levels and average

water levels in the Biscayne aquifer, Dade County.

36 Sea-water Intrusion

The problem of sea-water intrusion into the Biscayne aquifer was considered as a constant threat during the course of the drought.

By March 22, 1971, the U. S. Geological Survey had reported evidence

(Miami Herald) of intrusion in both the Miami Canal and the Little

River Canal in Dade County. On May 1 the city of Miami reported

(Miami Herald) that sea-water intrusion had not affected water from its wells, but had moved to within a mile of them, On May 5 U. S.

Geological Survey hydrologists reported (Miami Herald) that no major well field in Dade County appeared to be endangered by sea-water intrusion.

In addition to showing water-level changes in Dade County, figure 15 also shows the areas of greatest inland movement of salt water in the Biscayne aquifer. The inland movement was greatest in south Dade County where water levels in the interior declined to as much as 1.5 feet (0.46 m) below sea level by May 1971. With the ensuing rainfall water levels began to rise and by September, they had returned to normal as indicated in figure 16. As water levels rose, the increased fresh-water head began to move the fresh-water - salt water interface seaward.

37 Fires

Grass and muck fires and smoke-blackened skies were common during the late months of the 1971 drought. Natural fires occur regularly in south Florida. Many fires are started by lightning and some are started inadvertently by man. Controlled burning is used in land management. On March 22, 1971, the Miami Herald reported that 300 fires had already blackened more than 250,000 acres (101,174 hectares) in Dade, Broward, Palm Beach, and Collier

Counties. However, it said that, "Florida always turns brown at this time of the year. There are always fires." On April 11, 1971, an official of the Central and Southern Florida Flood Control

District said about fires, "So far things haven't been too bad if we had rains now it would be fine." The Washington (D.C.) Post of

May 14 said on its front page that, "By one recent count 7,366 fires have swept 560,518 acres of south Florida this year in the course of the 6-month drought. In wide areas the earth itself is destroyed and the pungent smoke from the burning muck often blackens the skies of Miami."

38 Information furnished by the National Park Service provides data on fires within the Everglades National Park (465,500 acres or 188,365 hectares of fire potential) and an adjacent protection zone outside the Park (266,100 acres or 107,689 hectares).

Records maintained since 1947 show the following acreages burned over by fires during years of many fire occurrences:

Percent of Acres total potential

1950 120,600 16

1962 192,300 26

1963 90,900 12

1971 83,300 11

It is thus seen that since 1947 more extensive burning than in

1971, at least in the Everglades Park area, occurred in 3 other years.

39 Cloud Seeding

The threat of dwindling water supplies led the Central and

Southern Florida Flood Control District to ask (Miami Herald,

December 14, 1970) "that rain-making conferences be set up with

U. S. scientists who have been seeding rain clouds with a view

more towards breaking up hurricanes than breaking droughts." State

officials requested Congress to increase financing for a Miami-based

cloud seeding project with the Experimental Meteorology Laboratory

of the National Oceanic and Atmospheric Administration. In January

tentative clearance was received from Washington to begin such

efforts. However, it was planned to start the actual seeding in

April, when clouds appear of the proper type for seeding.

More than 120 rain gages were installed in an experimental

.area north of Lake Okeechobee. Between April 4 and May 26, a total

of 196 seeding passes were made in the test area (Simpson, Woodley,

and White, 1972). Circumstances prevented the use of controls

and reduced the size of the original test area. The experimental

design did not permit specific conclusions as to the actual amount

of increased precipitation, if any, that resulted from seeding.

40 However, it was estimated by the National Oceanic and Atmospheric

Administration research team that seeding probably increased the precipitation in the test area between 5 and 10 percent during

April and May. The two major conclusions of the study (the first had been anticipated) were: (1) That no, cloud seeding method can break a drought (the proper type of clouds must be present); and

(2) that dynamic seeding can probably provide worthwhile local drought mitigation in Florida, but that its real efficacy remains to be established by continuation of randomized research experiments.

41 SUMMARY AND CONCLUSIONS

The 1971 drought in south Florida received outstanding news coverage during its course and for long afterward. It was considered to be a major crisis and was prominent in the minds of the public and of officials responsible for managing the water resources. Even before it had progressed very far, the possibility of a major water shortage loomed large. The virtual absence of rainfall during the dry season provided strong grounds for the apprehension. Yet a study of the consequences of the very dry dry season and the actual deficiencies that developed show that fears were not entirely justified and that management was successful, in averting or preventing serious results.

The drought period was a very rare event that (within at least part of south Florida) would be expected to recur only at average time periods measured in centuries. In spite of this, the only water shortages that developed were localized. Restrictions in water use were exercised by governing officials toward the end of or following the dry season and for the most part were in the form of requests for voluntary curtailment of water use rather than the application of mandatory restrictions or actual shutting off of supplies,

42 Canal levels were maintained generally no lower than levels previously experienced, in comparison to rainfall that was much less than previously experienced.

Ground-water levels were noticeably affected by the drought.

Low water levels were accompanied by temporary advances of the salt-water front in the Biscayne aquifer in Dade County. Wide fluctuations in water levels in the aquifer are a seasonal phenomenon, however, and by September 1971 water levels in most of the area were at or above average.

The level of Lake Okeechobee, the principal water-storage reservoir, declined, but comparable levels had been reached three other times within the past 55 years (1932, 1956, and 1962). During

1956 and 1962 levels had been slightly lower than in 1971. Based on the number of days the lake level was below 11 and 12 feet

(3.4 and 3.7 m) during the four drought periods, the other three periods represent much more serious deficiencies in storage than did

1971; however, the population and the water demands in 1971 were much greater.

Although fires in 1971 were widespread, data on acreage burned in the Everglades National Park area show that the 1971 acreage burned was exceeded during 3 other years since 1947: 1950, 1962, and 1963.

43 During the drought, there was constant fear on the part of local agencies of serious and irreparable encroachment of the salt- water front. Salt content increased in the lower reaches of some canals and the salt-water front in the Biscayne aquifer temporarily advanced inland about one-half mile (0.8 km) in a part of south

Dade County, However, water from the major well fields that supply the large urban areas did not increase in salinity.

Recurrent fears of drought during each of the dry seasons since

1971 are based on the realization that water needs are increasing rapidly in south Florida, and that shortages may occur at times even though rainfall may be normal for the season. It will be seen that if such shortages occur in a humid region of abundant annual rainfall, they are not droughts except in the sense that water needs and the distribution of rainfall are not balanced. Such balance can be achieved by continual expansion of water-management practices, based on already available techniques, or those that may be developed in the future.

44 REFERENCES

Hoyt, J. C., 1938, Drought of 1936 with discussion on the significance

of drought in relation to climate: U. S. Geol, Survey Water-

Supply Paper 820, 60 p.

Hull, J. E., 1972, Hydrologic conditions during 1970 in Dade County,

Florida: U. S. Geological Survey open-file report, 80 p.

Hull, J. E,, and Wimberly, E. T., 1972, Hydrologic conditions during

1971 in Dade County, Florida: U. S. Geological Survey open-

file report, 104 p.

Meyer, F. W,, 1972, Preliminary investigation of infiltration from

the Miami Canal to well fields in Miami Springs-Hialeah area,

Dade County, Florida: U. S. Geological Survey open-file

report, 85 p.

Simpson, Joanne, Woodley, W. L., and White, R. M,, 1972, Joint federal-

state cumulus seeding program for mitigation of 1971 south

Florida drought: Bull. Amer. Meterological Soc., v. 53, no, 4,

April 1972, p. 334-344.

Subrahmanyam, V. P., 1967, Incidence and spread of continental drought;

World Mete,)rological Organ., Internat. Hydrological Decade,

Reports on WMO/IHD Projects, no. 2, Geneva, Switzerland.

Thomas, H. E,, 1962, The meteorological phenomenon of drought in the

Southwest: U. S. Geological Survey Professional Paper 372-A,

42 p. 45 REFERENCES (Continued)

U. S. Department of Commerce, 1973, Monthly normals of temperature,

precipitation, and heating and cooling degree days 1941-70:

NOAA Environmental Data Service.

U. S. Department of Interior, 1973, Resource and Land Information

for south Dade County, Florida: U. S. Geological Survey Inv.

1-850, 66 p.

Water Resources Council, 1967, A uniform technique for determining

flood flow frequencies: Washington, D. C., Water Resources

Council Bull. no. 15, 15 p.

Yevjevich, Bujica, 1967, An objective approach to definition and

investigation of continental hydrologic droughts: Colorado

State Univ., Hydrology Papers, no. 23, Fort Collins, Colorado,

18 p.

46 co

Er-

cr ru O

,L f3 UNITED STATES DEPARTMENT OF THE INTERIOR POSTAGE AND FEES PAID r-a GEOLOGICAL SURVEY U.S. DEPARTMENT OF THE INTERIOR i-a 325 John Knox Rd., F-240 INT. 413 m Tallahassee, Florida 32303