Prepared as part of the

U.S. GEOLOGICAL SURVEY SOUTH FLORIDA

PLACE-BASED STUDIES PROGRAM

Methods to Quantify Seepage Beneath

Levee 30, Miami-Dade County, Florida

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 01-4074

0 100 200 FEET

0 25 50 METERS

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

West East

Land Surface

Land Surface

20

10

20

10

Canal

Stage

recorder

Krome

Avenue

Stage

recorder

Seepage

meter

Seepage

meter

G-3579 G-3599

G-3582

G-3583

G-3580

G-3598

G-3581

G-3584

G-3591

G-3592

G-3589

G-3585 G-3590 G-3586

G-3588

G-3597

G-3596

G-3595

G-3297

G-3594

G-3587

G-3593

Water Conservation Levee 30

Area 3B
Methods to Quantify Seepage Beneath

Levee 30, Miami-Dade County, Florida

Prepared as part of the

U.S. Geological Survey South Florida Place-Based

Studies Program

By Roy S. Sonenshein

Tallahassee, Florida

2001

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 01-4074
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

For additional information write to: Copies of this report can be purchased

from:

U.S. Geological Survey

Branch of Information Services

Box 25286

Federal Center

Denver, CO 80225

888-ASK-USGS

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.

Additional information about water resources in Florida is available on the World Wide Web

at http://fl.water.usgs.gov

District Chief

U.S. Geological Survey

Suite 3015

227 North Bronough Street

Tallahassee, FL 32301
Contents III

CONTENTS

Abstract.................................................................................................................................................................................. 1

Introduction ........................................................................................................................................................................... 1

Purpose and Scope....................................................................................................................................................... 2

Description of Study Site............................................................................................................................................. 2

General Hydrogeology and Aquifer Characteristics ......................................................................................... 3

Rainfall and Control-Structure Operation ......................................................................................................... 4

Previous Studies .......................................................................................................................................................... 5

Acknowledgments ....................................................................................................................................................... 6

Data Collection and Evaluation............................................................................................................................................. 6

Data Collection............................................................................................................................................................ 6

Data Evaluation ........................................................................................................................................................... 7

Geologic and Geophysical Data ........................................................................................................................ 7

Vertical Seepage Measurements........................................................................................................................ 8

Surface-Water Discharge Measurements........................................................................................................... 8

Water-Level Data............................................................................................................................................... 10

Quantification of Seepage Beneath Levee 30 ....................................................................................................................... 17

Ground-Water Flow Model ......................................................................................................................................... 17

Model Grid ........................................................................................................................................................ 17

Boundary Conditions......................................................................................................................................... 19

Hydraulic Properties.......................................................................................................................................... 19

Evapotranspiration............................................................................................................................................. 21

Calibration ......................................................................................................................................................... 21

Sensitivity Analysis........................................................................................................................................... 23

Model Results.................................................................................................................................................... 23

Simplified Darcian Approach...................................................................................................................................... 26

Evaluation of Methods to Quantify Seepage......................................................................................................................... 27

References Cited.................................................................................................................................................................... 29

Appendix I: Lithologic Log of Well G-3587......................................................................................................................... 32

Appendix II: Geologic Core Data for Selected Intervals, Well G-3587................................................................................ 35

Appendix III: Geophysical Logs of Wells G-3587 and G-3597............................................................................................ 36

FIGURES

1. Map of southeastern Florida showing location of study site, water-conservation areas, primary canals, 

and hydrogeologic section......................................................................................................................................... 2

2. Map of study area showing study sites, primary canals, levees, control structures, and discharge 

measurement sites ..................................................................................................................................................... 3

3. Hydrogeologic section showing geologic formations, aquifers, and confining units of the surficial 

aquifer system in central Miami-Dade County ......................................................................................................... 4

4. Transect through the central study site showing location of wells, stage recorders, and 

seepage meters........................................................................................................................................................... 5

5. Photographs showing rocks of Pleistocene age in well G-3587, including low-permeability 

complex of the Fort Thompson Formation from 7 to 8 feet below land surface, and highly permeable 

limestone of the Fort Thompson Formation from 17 to 18 feet below land surface................................................. 8

6. Graph showing relations between head difference and change in discharge rate and between head 

difference and seepage rate ....................................................................................................................................... 9

7. Cross sections showing lines of equal hydraulic head in the study area, February to December 1996.................... 11
IV Contents

8. Hydrographs showing water-level or stage elevation, gate openings, and rainfall for selected 

stations from February to December 1996................................................................................................................. 12

9. Hydrographs showing water-level or stage elevation, gate openings, and rainfall for selected 

stations during March, April, and May 1996 and November and December 1996 ................................................... 13

10. Graphs showing average monthly vertical head differences between selected surface-water sites and 

ground-water wells, February to December 1996...................................................................................................... 15

11. Graphs showing average monthly horizontal head differences between selected ground-water wells, 

February to December 1996....................................................................................................................................... 16

12. Model grid showing materials having characteristic hydraulic conductivities used for the model and 

location of model boundary cells............................................................................................................................... 18

13. Model grid showing simulated wet-season flow paths and the water budget for the October 19, 1996 

simulation................................................................................................................................................................... 25

14. Graph showing horizontal flows computed with the analytical approach, February to December 1996 .................. 27

TABLES

1. Inventory data of ground-water wells drilled for the study..................................................................................... 6

2. Seepage and surface-water discharge measurement data........................................................................................ 10

3. Vertical and horizontal head differences, February 1 to December 15, 1996 ......................................................... 14

4. Constant-head boundary conditions used in ground-water flow model.................................................................. 19

5. Material properties used in calibrated flow models ................................................................................................ 20

6. Measured and calibrated water-level data for the ground-water flow model.......................................................... 22

7. Simulated and measured ground-water inflows to Levee 30 canal......................................................................... 23

8. Horizontal flow rates in the ground-water flow model and the Darcian approach at selected 

locations and vertical flow from Water Conservation Area 3B calculated by the ground-water flow model ........ 24

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929−a geodetic datum derived from a 

general adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929.
Introduction 1

Methods to Quantify Seepage Beneath Levee 30, 

Miami-Dade County, Florida

By Roy S. Sonenshein

Abstract

A two-dimensional, cross-sectional, finitedifference, ground-water flow model and a simple 

application of Darcy’s law were used to quantify 

ground-water flow (from a wetlands) beneath 

Levee 30 in Miami-Dade County, Florida. 

Geologic and geophysical data, vertical seepage 

data from the wetlands, canal discharge data, 

ground-water-level data, and surface-water-stage 

data collected during 1995 and 1996 were used as 

boundary conditions and calibration data for the 

ground-water flow model and as input for the 

analytical model.

Vertical seepage data indicated that water 

from the wetlands infiltrated the subsurface, near 

Levee 30, at rates ranging from 0.033 to 0.266 foot 

per day when the gates at the control structures 

along Levee 30 canal were closed. During the 

same period, stage differences between the wetlands (Water Conservation Area 3B) and Levee 30 

canal ranged from 0.11 to 1.27 feet. A layer of 

low-permeability limestone, located 7 to 10 feet 

below land surface, restricts vertical flow between 

the surface water in the wetlands and the ground 

water. Based on measured water-level data, 

ground-water flow appears to be generally horizontal, except in the direct vicinity of the canal. 

The increase in discharge rate along a 2-mile reach 

of the Levee 30 canal ranged from 9 to 30 cubic 

feet per second per mile and can be attributed 

primarily to ground-water inflow. Flow rates in 

Levee 30 canal were greatest when the gates at the 

control structures were open.

The ground-water flow model data were 

compared with the measured ground-water heads 

and vertical seepage from the wetlands. Estimating the horizontal ground-water flow rate beneath 

Levee 30 was difficult owing to the uncertainty in 

the horizontal hydraulic conductivity of the main 

flow zone of the Biscayne aquifer. Measurements 

of ground-water flows into Levee 30 canal, a substantial component of the water budget, were also 

uncertain, which lessened the ability to validate 

the model results. Because of vertical flows near 

Levee 30 canal and a very low hydraulic gradient 

east of the canal, a simplified Darcian approach 

simulated with the ground-water flow model does 

not accurately estimate the horizontal groundwater flow rate. Horizontal ground-water flow 

rates simulated with the ground-water flow model 

(for a 60-foot-deep by 1-foot-wide section of the 

Biscayne aquifer) ranged from 150 to 450 cubic 

feet per day west of Levee 30 and from 15 to 

170 cubic feet per day east of Levee 30 canal. 

Vertical seepage from the wetlands, within 

500 feet of Levee 30, generally accounted for 10 to 

15 percent of the total horizontal flow beneath the 

levee. Simulated horizontal ground-water flow 

was highest during the wet season and when the 

gates at the control structures were open.

INTRODUCTION

In an effort to restore predevelopment flow conditions to the Everglades in southern Florida, water 

managers must balance ecosystem restoration efforts 

with the needs to maintain adequate water supplies for 

public and agricultural use and to prevent flooding. 
2 Methods to Quantify Seepage Beneath Levee 30, Miami-Dade County, Florida

Drainage projects that began in the 1880’s have altered 

the ecosystem in southern Florida. By the early 1990’s, 

only 50 percent of the historical Everglades remained; 

the rest had been drained for agriculture and urban 

development. In response to hurricane-induced flooding of these developed areas of the historic Everglades 

in 1947, the United States Congress authorized the 

Central and Southern Florida Flood Control Project in 

1948. This enormous undertaking required using 

levees, canals, pumping stations, and vast waterconservation areas to control ground-water levels. The 

initial phase of this effort was the construction of an 

interconnected network of levees and adjacent canals 

from central Palm Beach County to southern MiamiDade County (Ogden and Davis, 1994). This network 

of levees and canals (fig. 1) prevents Everglades sheetflow from flooding developed areas to the east.

Accounting for the most substantial sources of 

hydrologic inflows and outflows to and from the Everglades ecosystem is critical to the South Florida PlaceBased Studies Program (McPherson and others, 1995). 

This program is a collaborative effort by the U.S. 

Geological Survey (USGS) working with other Federal, State, and local agencies and Indian Tribes to provide earth-science information needed to resolve landuse demands and water issues in southern Florida. As 

part of this effort, the USGS, in collaboration with the 

U.S. Army Corps of Engineers, conducted a study in 

1995 and 1996 to evaluate methods for quantifying 

seepage beneath Levee 30 and resultant losses from 

Water Conservation Area (WCA) 3B (fig. 1) to the 

underlying Biscayne aquifer. WCA 3B is a major 

source of surface water for Everglades National Park. 

Water impounded in WCA 3B also provides recharge 

for municipal well fields (Sonenshein and Koszalka, 

1996) east and south of Levee 30, and Levee 30 canal 

delivers water to agricultural areas to the south.

Purpose and Scope

The purposes of this report are to: (1) quantify 

the rates of ground-water seepage beneath Levee 30 in 

the west-central part of Miami-Dade County, and 

(2) evaluate the two methods used to quantify seepage 

rates. A two-dimensional, cross-sectional, finitedifference ground-water flow model and an analytical 

model based on Darcy's law were used to estimate 

seepage rates. Geologic and geophysical data, vertical 

seepage data, canal discharge data, and water-level data 

were collected during 1995 and 1996 to aid in the quantification of ground-water seepage beneath Levee 30. 

Comparisons between the methods, field data, and previous studies were made to determine the relative 

accuracy of the different methods. The methods evaluated in this report could serve as a valuable tool for 

water managers in their endeavors to restore historical 

flow patterns in the Everglades ecosystem.

Description of Study Site

The study site is located along Levee 30 in 

Miami-Dade County, Fla., and is about 6.5 mi (miles) 

north of Tamiami Canal (fig. 2). Levee 30, completed 

in 1954, is about 14 mi long and runs north-south along 

the eastern boundary of WCA 3B. Levee 30 canal, 

about 15- to 20-ft (feet) deep and 150-ft wide, parallels 

A

0 5 10 MILES

0 5 10 KILOMETERS





	

	

Levee 30

and canal

Hydrogeologic

section

Miami

Lake

Okeechobee

MiamiDade

County

Everglades

National

Park

WCA 1

WCA

3B

WCA 3A

WCA

2B

WCA

2A

Palm Beach

County

Hendry County Collier County Monroe County

Biscayne Bay

Florida Bay

A




Broward

County

South Florida

ecosystem boundary

Study

site

Atlantic Ocean

Figure 1. Southeastern Florida showing location of study 

site, water-conservation areas (WCA), primary canals, and 

hydrogeologic section.
Introduction 3

Levee 30 about 50 ft to the east. Krome Avenue, a 

two-lane road (not shown in fig. 2), is located about 

200 ft east of the canal. Water in Levee 30 canal may 

flow either northward or southward, depending on the 

status of control structures S-32A and S-337 to the 

north and S-335 to the south. The site is bordered by the 

Pennsuco wetlands to the east (fig. 2), a remnant of the 

Everglades located outside of the levee system that 

confines the water-conservation areas and Everglades 

National Park.

General Hydrogeology and Aquifer Characteristics

The geology and some aquifer characteristics of 

the study site are well defined based on previous geologic analyses (Causaras, 1987) and aquifer tests (Fish 

and Stewart, 1991) from wells located at the site. The 

surficial aquifer system underlies the study site to a 

depth of about 170 ft below land surface (Causaras, 

1987, section A-A′, sheet 1). A section showing the 

hydrogeologic framework of the surficial aquifer system 

in central Miami-Dade County is shown in figure 3.

Dade-Broward Levee and canal

Northwest

Well Field

Pennsuco

wetlands

Water Conservation

Area 3B

Tamiami Canal Levee 31N

and canal S-334 S-336 G-119

S-335

DERM

structure

Northwest

Well Field Canal

Well Field CanalNorthwest

Miami Canal

S-337 S-32A

 	 









	


	





Levee 30 and canal

Study

site

transect

North site

Central site

South site

S-31 S-32

Discharge

measurement

sites Note: Schematic inset

not to scale, arrows indicate

direction of flow through

structures

Levee 30 and canal

Miami Canal

S-31

S-337

S-32

S-32A

0 1 2 3 MILES

0 1 2 3 KILOMETERS

EXPLANATION

CANAL AND LEVEE

CANAL

SURFACE-WATER

CONTROL STRUCTURE

Figure 2. Study area showing study sites, primary canals, levees, control structures, and discharge 

measurement sites.
4 Methods to Quantify Seepage Beneath Levee 30, Miami-Dade County, Florida Approximate location of study site (6 miles north of section) Biscayne aquifer Semiconfining unit Gray limestone aquifer Intermediate confining unit Base of surficial aquifer system

0 5 10 MILES

0 5 10 KILOMETERS

WEST EAST

VERTICAL SCALE GREATLY EXAGGERATED

EXPLANATION

HYDROSTRATIGRAPHICBOUNDARY

A

A

Fort Thompson Formation

Upper clastic unit of Tamiami Formation

Miami Limestone

Fort Thompson Formation

Pamlico Sand

Anastasia Formation Key Largo

Limestone

Hawthorn Formation

Gray limestone of Tamiami Formation

Upper clastic unit of Tamiami Formation

Lower clastic unit of Tamiami Formation Tamiami Formation

Limestone and sandstone of

LITHOSTRATIGRAPHICBOUNDARY

40 FEET

SEA LEVEL

4080

120160200240280

40 FEET

SEA LEVEL4080

120160200240280

Figure 3. Geologic formations, aquifers, and confining units of the surficial aquifer system in central Miami-Dade County (from Fish and Stewart, 1991).

The unconfined Biscayne aquifer, which is the upper part of the surficial aquifer system, underlies the study 

site to a depth of about 60 ft below land 

surface. The Biscayne aquifer is composed primarily of highly permeable 

limestone, including (from land surface 

downward) the: Miami Limestone, 

Fort Thompson Formation, and Key 

Largo Limestone all of Pleistocene age 

and part of the Tamiami Formation of 

Pliocene age. In the wetland areas, a 

thin layer of peat overlies the Biscayne 

aquifer. Below the Biscayne aquifer, 

the surficial aquifer system consists of 

less permeable limestone, sand, and 

sandstone of the Tamiami Formation. 

Hydraulic conductivity was estimated 

to be 29,000 ft/d (feet per day) in the 

Biscayne aquifer and 470 ft/d in the 

Tamiami Formation below the Biscayne aquifer (Fish and Stewart 1991, 

p. 28). Regional water-table maps indicate that ground water flows from west 

to east, perpendicular to and beneath 

Levee 30 (Sonenshein and Koszalka, 

1996, figs. 3 and 4). In an earlier study, 

the Northwest Well Field, which is 

located about 4 mi east of Levee 30 

(fig. 2), had no influence on water levels near Levee 30 (Sonenshein and 

Hofstetter, 1990).

Rainfall and Control-Structure 

Operation

Within the study area, the Biscayne aquifer is recharged by rainfall on 

upland areas that infiltrates to the aquifer directly and by surface water that 

seeps downward through wetland sediments to the aquifer. Annual rainfall in 

southeastern Florida ranges from 30 to 

100 in. (inches) and averages more than 

60 in. (Jordan, 1984, p. 19-20). Rainfall 

follows a seasonal pattern; usually, 

about 70 percent of the annual rainfall 

occurs from June to October (Jordan, 

1984, p. 22). Water stored in the wetlands seeps into the ground during the 

year, recharging the Biscayne aquifer.
Introduction 5

Levee 30 canal was constructed to receive water 

that seeps beneath Levee 30. The canal is well connected to the Biscayne aquifer; however, because sediments on the bottom of the canal are less permeable 

(Miller, 1978), most of the water enters or leaves the 

canal through its nearly vertical sides. Flow in Levee 

30 canal can be both northward and southward depending on the operational status of the four control structures in or adjacent to the canal (fig. 2), ground-water 

levels adjacent to the canal, and the location along the 

canal. Structure S-335, a gated spillway located about 

6 mi south of the study site at the southern end of Levee 

30 canal, is used to control flows into Tamiami Canal 

and Levee 31N canal. The Miami-Dade County 

Department of Environmental Resources Management 

(DERM) structure, a gated spillway located about 

5.25 mi north of the study site, is used to control flows 

into the Northwest Well Field Canal to the east, but 

does not restrict flows in Levee 30 canal. Structure 

S-32A, a gated culvert located about 6.75 mi north of 

the study site at the northern end of Levee 30 canal, is 

used to control flows into Miami Canal downstream of 

structure S-31. Structure S-337, a gated spillway 

located near structure S-32A, is used to control flows 

into Levee 30 canal from Miami Canal upstream of 

structure S-31.

 All structures usually are closed to prevent 

flooding of downstream areas and are only opened 

(under certain conditions) to provide water to downstream areas or to lower water levels in WCA 3B. 

During these periods, flow is toward the open structure 

(S-32A or S-335). When the gates were closed during 

the study period, the head difference ranged from 0.30 

to 1.35 ft across structure S-335, 1.75 to 2.50 ft across 

the DERM structure, 2 to 4 ft across structure S-32A, 

and 0.8 to 2.0 ft across structure S-337. Flows in the 

Northwest Well Field Canal generally were between 

120 and 150 ft3

/s (cubic feet per second) when the 

DERM structure was closed. The downstream gradient 

in the Northwest Well Field Canal resulted in seepage 

from Levee 30 canal around the DERM structure. The 

high head differences across structure S-32A and the 

DERM structure resulted in northward flow in Levee 

30 canal at the study site when all four structures were 

closed.

Previous Studies

Several publications are available that describe 

the evaluation of seepage beneath levees and between 

canals and the Biscayne aquifer in southeastern 

Florida. Seepage beneath a test levee prior to construction of Levee 30 was evaluated by the U.S. Army Corps 

of Engineers (1952). Seepage beneath Levee 30 at its 

northern end was evaluated by Klein and Sherwood 

(1961). Seepage from Lake Okeechobee was evaluated 

by Meyer and Hull (1969) and McKenzie (1973). The 

effect of canal bottom sediments on infiltration into the 

Biscayne aquifer from Miami Canal was evaluated by 

Miller (1978). Ground-water flow beneath Levee 35A 

in Broward County was evaluated by Swayze (1988). 

Chin (1990) used data in the vicinity of Levee 31N 

canal and Snapper Creek Canal Extension to develop a 

method for estimating canal leakage to the Biscayne 

aquifer.

0 100 200 FEET

0 25 50 METERS

ELEVATION, IN FEET ABOVE AND BELOW SEA LEVEL

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

-100

West East

Land Surface

Land Surface

20

10

20

10

Vertical scale exaggerated

Canal

Stage

recorder

Krome

Avenue

Stage

recorder

Seepage

meter

Seepage

meter

G-3579 G-3599

G-3582

G-3583

G-3580

G-3598

G-3581

G-3584

G-3591

G-3592

G-3589

G-3585 G-3590 G-3586

G-3588

G-3597

G-3596

G-3595

G-3297

G-3594

G-3587 (Geophysical logs)

(Geologic log

from Causaras,

1987)

G-3593

Water Conservation Levee 30

Area 3B

(Geologic core and

geophysical logs)

Figure 4. Transect through the central study site showing location of wells, stage recorders, and seepage meters.
6 Methods to Quantify Seepage Beneath Levee 30, Miami-Dade County, Florida

Acknowledgments

The author wishes to express appreciation to the 

many USGS colleagues who assisted in the project. 

John Goebel serviced the continuous recorders and 

processed the data. Robert Mooney installed the seepage meters and assisted with data collection. Steven 

Memberg assisted with data collection. Judson Harvey 

analyzed the seepage meter data. Eduardo Patino and 

Keith Overton obtained discharge measurements. 

Ronald Reese analyzed the geologic core. Gina Tillis, 

Sally Garson, and Lillian Ruiz-Feltman worked on the 

ground-water flow model and assisted with the data 

analysis.

DATA COLLECTION AND EVALUATION

Data collected for use in the models to estimate 

the seepage rate beneath Levee 30 included a geologic 

core, geophysical logs, vertical seepage measurements, 

canal discharge measurements, and continuous groundwater and surface-water-level readings. Aquifer properties were obtained from core permeability and porosity tests. The data were collected and evaluated for use 

in defining model boundary conditions and model 

input parameters and to calibrate the flow model. The 

data also were used as the input values for the simple 

application of Darcy’s law.

Data Collection

A geologic core from 5 to 74 ft below land surface was obtained during the drilling of monitoring 

well G-3587 (fig. 4 and table 1). A lithologic log of the 

core was prepared (app. I), and tests were performed by 

Core Laboratories (1995) on 10 plugs from the core to 

determine permeability and porosity (app. II). Natural 

gamma and resistivity logs were obtained from monitoring wells G-3587 and G-3597 (app. III) using borehole geophysical tools.

Table 1. Inventory data of ground-water wells drilled for the study

[Location of wells shown in figure 4]

Well No. Site identification 

number Latitude Longitude

Well depth

(feet below

land surface)

Remarks

 G-3579 255130080291601 255130 802916 82

 G-3580 255130080291602 255130 802916 17

 G-3581 255130080291301 255130 802913 32

 G-3582 255130080291302 255130 802913 17

 G-3583 255130080291303 255130 802913 11

 G-3584 255130080291101 255130 802911 32

 G-3585 255130080291102 255130 802911 17

 G-3586 255130080291103 255130 802911 12

 G-3587 255130080291104 255130 802911 82 Geologic core and geophysical logs

 G-3588 255130080290601 255130 802906 10

 G-3589 255130080290602 255130 802906 32

 G-3590 255130080290603 255130 802906 17

 G-3591 255130080290605 255130 802906 82

 G-3592 255130080290604 255130 802906 52

 G-3593 255130080290401 255130 802904 17

 G-3594 255130080290402 255130 802904 7

 G-3595 255130080290403 255130 802904 32

 G-3596 255130080290404 255130 802904 52

 G-3597 255130080290405 255130 802904 82 Geophysical logs

 G-3598 255130080290101 255130 802901 17

 G-3599 255130080290102 255130 802901 82
Data Collection and Evaluation 7

Two vertical seepage meters were installed in 

WCA 3B, one about 30 ft west of Levee 30 and the 

other about 500 ft west of the levee (fig. 4). The meters 

were built and operated using the cylinder method 

described by Lee (1977). Similar meters are being used 

in other areas of the Everglades (Harvey, 1996) as part 

of the USGS South Florida Place-Based Studies Program. Seepage measurements were made for 6 days 

between September and December 1996, with a collection period ranging from 1 to 4 hours.

Surface-water discharge measurements were 

made at three sites in Levee 30 canal (fig. 2) under various hydrologic conditions for 6 days from November 

1995 to December 1996: at the transect (central study 

site), about 1 mi south of the transect (south study site), 

and about 1 mi north of the transect (north study site). 

Flow velocities in Levee 30 canal are very low, generally less than 0.2 ft/s (foot per second) when the gates 

are closed. An Acoustic Doppler Current Profiler 

(ADCP), which is capable of measuring very low water 

velocities in three dimensions (Simpson and Oltmann, 

1992), was used to determine the total discharge rate at 

each site. The discharge rate generally was determined 

from the average of a minimum of three measurements 

made at an individual site. The ADCP has been used to 

measure discharges near coastal control structures in 

Miami-Dade County (Swain and others, 1997) and at 

other locations in southern Florida.

Two continuous recording surface-water-level 

(stage) stations and 21 continuous recording groundwater monitoring wells were installed along a transect, 

approximately 1,000 ft long that is perpendicular to and 

bisected by Levee 30 (fig. 4 and table 1). Stage recorders were installed 200 ft west of Levee 30 and in Levee 

30 canal. The wells are located in six different clusters; 

each cluster contains two to five wells with depths 

ranging from 7 to 82 ft below land surface. The five 82-

ft-deep wells were completed in the Tamiami Formation below the Biscayne aquifer; the remaining wells 

were completed in the Biscayne aquifer beneath a hard 

rock layer located from about 7 to10 ft below land surface. All of the wells were completed with 4-in-diameter polyvinyl chloride (PVC) casing with about 2 ft of 

open hole below the casing.

The wells in each cluster ideally should be 

aligned parallel to the levee, and in turn, be parallel to 

the lines of equal hydraulic head. Water-level differences between wells in a cluster then would be solely 

the result of vertical differences, and the Dupuit 

assumption could be validated. Because of the logistics 

of drilling, especially in the wetland areas, this well 

arrangement was not always feasible, with distances up 

to 44 ft between wells in a cluster. Thus, differences in 

water levels between wells within a cluster could be the 

result of horizontal differences, vertical differences, or 

both.

Float wheels and shaft encoders were installed at 

each surface-water station and on each well. Stage and 

ground-water-level data were collected hourly to the 

nearest 0.01 ft using electronic satellite data-collection 

platforms. Tapedown measurements were made every 

1 to 2 months to check the recorded data. Because of 

the low hydraulic gradients, the data were carefully 

verified, and periods of questionable or unreliable data 

were eliminated from the final record. Data were collected over an 11-month period from February to 

December 1996.

An engineer’s level and leveling rod were used 

with standard USGS surveying procedures (Kennedy, 

1988) to establish measuring point elevations at each 

stage recorder and well. The reference datum is the 

National Geodetic Vertical Datum of 1929. Accurate, 

relative water levels were needed for the study because 

of the low hydraulic gradients at the study site. Conditions at the site were not ideal for surveying to the accuracy required for the study, which was due, in part, to 

high water in WCA 3B and relatively large elevation 

changes over a short distance due to the levee. Therefore, differential levels to determine relative measuring 

point elevations were obtained several times during the 

study to verify the differences in measuring point elevations. 

Data Evaluation

Data were evaluated for reliability and for their 

potential use in defining and delineating the groundwater flow model and the simplified Darcian approach. 

The subsequent sections present an evaluation of geologic and geophysical data, vertical seepage measurements, surface-water discharge measurements, and 

water-level data.

Geologic and Geophysical Data

Lithologic and geologic core data for well 

G-3587 from this study (app. I and II), lithologic data 

for well G-3297 from a previous study (Causaras, 

1987), and geophysical borehole logs for wells G-3587 

and G-3597 were used to make a comparative analysis 

between wells and to aid in determining the aquifer 
8 Methods to Quantify Seepage Beneath Levee 30, Miami-Dade County, Florida

layering and properties for use in the models. The natural gamma and electromagnetic induction geophysical 

borehole logs for wells G-3587 and G-3597 are given 

in appendix III. Locations of all wells are shown in 

figure 4.

A comparative analysis of the lithologic and 

geophysical logs between wells indicated little horizontal variability in the geologic properties of the surficial aquifer system. A layer of low-permeability 

limestone less than 2 ft thick (fig. 5A) was present, 

beginning at 7 ft below land surface in well G-3587 and 

at 10 ft below land surface in well G-3297. The low 

permeability of the limestone is evident from the plug 

data presented in appendix II. The top surface of this 

low-permeability zone is a geologic disconformity, 

which is a result of surface exposure caused by minor 

sea-level regression that followed deposition (Scott, 

1997, p. 67). This surface is believed to be the top of the 

Q3 layer of the Fort Thompson Formation (Perkins, 

1977, p. 137-139). Intervals of highly permeable limestone (fig. 5B) characteristic of the Biscayne aquifer 

were present in well G-3587 between 10 and 74 ft 

below land surface, as indicated by the lithologic logs 

(app. I) and the permeability tests (app. II). 

Vertical Seepage Measurements

Vertical seepage data indicated that a considerable amount of water was seeping from WCA 3B into 

the ground water above the low-permeability limestone 

near the levee. The seepage rate at the east meter site 

(30 ft west of Levee 30) averaged five times the seepage rate of the west meter site (500 ft west of Levee 30). 

The seepage rate varied in time at the east and west 

meter sites (fig. 6 and table 2). In December 1996 when 

the canal control structures were open, the seepage rate 

increased at each site with an increase in head difference. However, the seepage rate at the west meter site 

on December 4, 1996, was more than double the average rate of the earlier measurements; whereas the rate 

increase was only 25 percent at the east meter site. 

Thus, the seepage rate is related to the distance from the 

levee and to the head difference between surface and 

ground water.

Surface-Water Discharge Measurements

Surface-water discharge measurements (table 2) 

were used to determine the rate of ground-water 

exchange with Levee 30 canal under various hydrologic conditions. Two factors to be considered when 

evaluating and using the discharge data are: (1) the 

number of measurements (only six sets of measurements were made), and (2) the precision of the measurements. Each discharge rate (table 2) is the average 

of three to five sequential measurements at a site. For 

the higher discharge rates, the range of values at a site 

can be small compared to the differences between sites. 

For the lower discharge rates, the range of values at a 

site can be large compared to the differences between 

sites. Although there was some consistency between 

the measurements, additional measurements are 

needed to verify some of the initial results presented in 

this report.

Discharge rates at the north, central, and south 

study sites (fig. 2) were greatest when the control structures were open, and generally increased in the direction of flow, indicating net inflow of ground water. The 

A

B

Figure 5. Rocks of Pleistocene age in well G-3587, 

including (A) low-permeability complex of the Fort 

Thompson Formation from 7 to 8 feet below land surface, 

and (B) highly permeable limestone of the Fort Thompson 

Formation from 17 to 18 feet below land surface.
Data Collection and Evaluation 9

gate at structure S-32A was open during the first set of 

discharge measurements (November 7, 1995), and the 

gates at structures S-335 and S-337 were open during 

the last set of discharge measurements (December 3, 

1996). Flow was to the north when the gate at structure 

S-32A was open and to the south when the gates at 

structures S-335 and S-337 were open. Flow was to the 

north at all three study sites during the first four sets of 

measurements made when the gates at the structures 

were closed (table 2).

The discharge rate increased in the direction of 

flow for all sets of measurements, except on June 6, 

1996, when there was little difference in discharge rate 

in the canal between the three discharge measurement 

sites. For the other three sets of discharge measurements (February 23, 1996, September 27, 1996, and 

November 27, 1996) made when the gates at the structures were closed, the increase ranged from 9 to 

19 ft3

/s/mi (cubic feet per second per mile). The discharge rate increased between 20 and 30 ft3/s/mi when

HEAD DIFFERENCE, IN FEET,

BETWEEN SURFACE WATER

AND GROUND WATER

SEEPAGE RATE, IN FEET PER DAY

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0 0.05 0.10 0.15 0.20 0.25 0.30

EXPLANATION

West meter (500 feet west of levee)

and well G-3580

East meter (30 feet west of levee)

and well G-3585

HEAD DIFFERENCE, IN FEET,

BETWEEN WATER CONSERVATION AREA 3B

AND LEVEE 30 CANAL

1.50

1.25

1.00

0.75

0.50

CHANGE IN DISCHARGE RATE, IN CUBIC FEET PER SECOND PER MILE IN LEVEE 30 CANAL

0 5 10 15 20 25

Figure 6. Relations between head difference and change in discharge rate and between head difference and seepage rate.
10 Methods to Quantify Seepage Beneath Levee 30, Miami-Dade County, Florida

the gates at the structures were open. The increase in discharge rate has a generally linear relation to the head difference between WCA 3B and Levee 30 canal (fig. 6).

The increase in discharge rate along the 2-mi 

canal reach that encompasses the north, central, and 

south study sites can be attributed primarily to groundwater inflow. The head difference between ground 

water at well G-3588 (near the canal) and Levee 30 

canal stage during the discharge measurements ranged 

from 0.12 to 0.29 ft; the head difference between WCA 

3B and the Levee 30 canal stage ranged from 0.66 to 

1.28 ft (table 2). No rainfall events had an impact on the 

discharge rate before or during the six sets of discharge 

measurements. By comparison, Swayze (1988, p. 14) 

reported an average seepage rate of about 10 ft3/s/mi in 

Levee 35A canal bordering WCA 2B to the north. At 

that site, the head difference between WCA 2B and the 

canal ranged from 4.8 to 6.4 ft. The higher head difference at that site is the result of lower permeabilities in 

the Biscayne aquifer than at the Levee 30 site.

Water-Level Data

Cross sections showing lines of equal hydraulic 

head (fig. 7) and based on ground- and surface-waterlevel measurements depict the overall ground-water 

flow pattern in the study area. Ground-water flow 

appears to be generally horizontal, except in the direct 

vicinity of Levee 30 canal. Ground water from the west 

flows into the canal near the surface, but seems to flow 

beneath the canal with increasing depth. Near the surface, a ground-water divide is almost always present 

between the canal and the easternmost monitoring 

wells. Ground water near the surface immediately east 

of the canal flows toward the canal; the remaining 

ground water flows to the east. The ground-water 

divide is east of the easternmost monitoring wells when 

the gate at structure S-335 is open. Because of the very 

low water-level gradients, interpretation of flow based 

on the cross sections alone is difficult.

Table 2. Seepage and surface-water discharge measurement data

[-- Data not collected]

Date of 

measurement

Discharge1

(cubic feet per second)

Seepage rate

(feet per day)

Stage

(feet above 

sea level)

Water level

(feet above sea level)

Remarks2

North

site

Central

site

South

site

West

meter

East

meter

Water 

Conservation 

Area 3B

Levee 

30 canal

Well

G-3580

Well

G-3585

Well

G-3588

11-07-95 109 81 50 -- -- -- -- -- -- -- Flow to north, gates at 

structure S-32A open

02-23-96 38 -- 19 -- -- 7.87 6.99 7.55 7.24 7.18 Flow to north

06-06-96 41 40 40 -- -- 7.52 6.86 7.27 7.02 6.98 Flow to north

09-23-96 -- -- -- 0.056 0.266 8.49 7.58 8.11 7.79 7.73

09-27-96 54 -- 16 .039 .249 8.41 7.52 8.06 7.74 7.67 Flow to north

10-30-96 -- -- -- .033 .213 8.69 7.77 8.31 7.97 7.92

11-27-96 27 -- 9 .039 .177 8.28 7.41 7.93 7.62 7.58 Flow to north

12-03-96 -265 -282 -310 -- -- 8.20 6.92 7.71 7.27 7.21

Flow to south, gates at 

structures S-335 and 

S-337 open

12-04-96 -- -- -- .092 .292 8.18 6.92 7.71 7.27 7.19 Gates at structures 

S-335 and S-337 open

12-16-96 -- -- -- .072 .207 8.07

8.07

7.03

7.22

7.68

7.69

7.30

7.35

7.26

7.31

Gates open at start of 

seepage data collection but closed during 

measurement. Other 

data collected when 

gates open (top data 

set) and closed (bottom 

data set)

1

Positive discharge values indicate northward flow, and negative discharge values indicate southward flow.

2

Gates at all structures along Levee 30 canal were closed except where noted.
Data Collection and Evaluation 11

10

10

10

10

10

10 10

10

10

10

10

-80

0

-10

-20

-30

-40

-50

-60

-70

0

-10

-20

-30

-40

-50

-60

-70

-80

0

-10

-20

-30

-40

-50

-60

-70

-80

-80

0

-10

-20

-30

-40

-50

-60

-70

0

-10

-20

-30

-40

-50

-60

-70

-80 -80

0

-10

-20

-30

-40

-50

-60

-70

0

-10

-20

-30

-40

-50

-60

-70

-80

-80

0

10

-10

-20

-30

-40

-50

-60

-70

0

-10

-20

-30

-40

-50

-60

-70

-80 -80

0

-10

-20

-30

-40

-50

-60

-70

0

-10

-20

-30

-40

-50

-60

-70

-80

-80

0

-10

-20

-30

-40

-50

-60

-70

8.2

6.9

8.0

8.9

8.4

7.5

8.5

8.4

8.3

8.2

8.1

8

8.05

8.05

7.6

7.5

7.4

7.3

7.2

7.1

7

8

7.8

7.9

7.7

7.6

7.6

6.2

6.4

6.35

6.3

6.25

6.3

6.15

6.15

7.3

7.1

7.05

7.4

7.2

6.9

7

7.7

7.5

7.4

7.3

7.2

7.1

7.9

7.0

Levee 30

Land Surface

Water Conservation

Area 3B Canal Swale

Land Surface

Levee 30

Canal Swale

Water Conservation

Area 3B

Canal

Levee 30

Land Surface

Water Conservation

Area 3B Swale

Levee 30

Land Surface

Water Conservation

Area 3B Canal Swale

Land Surface

Levee 30

Canal Swale

Water Conservation

Area 3B

Canal

Levee 30

Land Surface

Water Conservation

Area 3B Swale

Vertical scale exaggerated

December 4,1996 F

October 19,1996 E

September 16,1996 D

May 18,1996 C

March 25,1996 B

February 23,1996 A

ELEVATION, IN FEET ABOVE AND BELOW SEA LEVEL

Contour interval 0.1 foot. Contour interval 0.1 foot.

Contour interval 0.1 and 0.05 foot.

Contour interval 0.05 foot. Contour interval 0.1 foot.

Vertical scale exaggerated

Vertical scale exaggerated

Vertical scale exaggerated

Vertical scale exaggerated

Vertical scale exaggerated

Contour interval 0.1 and 0.05 foot.

0 100 200 FEET

0 25 50 METERS

0 100 200 FEET

0 25 50 METERS

0 100 200 FEET

0 25 50 METERS

0 100 200 FEET

0 25 50 METERS

0 100 200 FEET

0 25 50 METERS

0 100 200 FEET

0 25 50 METERS

Figure 7. Lines of equal hydraulic head in the study area, February to December 1996.
12 Methods to Quantify Seepage Beneath Levee 30, Miami-Dade County, Florida

A comparison of hydrographs for the surfacewater stations and selected ground-water wells (fig. 8) 

indicates a good hydraulic connection between ground 

water below the low-permeability limestone and 

surface water. Ground-water levels rise rapidly in 

response to increases in the stage in WCA 3B resulting 

from rainfall (fig. 8). Ground-water levels also respond 

rapidly to changes in canal stage. When the gate at 

structure S-335 was open in March, April, and December 1996, the canal stage dropped rapidly (fig. 9), and 

seepage into Levee 30 canal increased. Consequently, 

ground-water levels decreased in all wells. The magnitude of the ground-water-level response decreased with 

distance from the canal. For example, lowering the 

canal stage by 0.4 ft on December 2 resulted in a 0.3-ft 

decline in ground-water levels at wells near the canal 

and a 0.15-ft drop at well G-3580, located more than 

600 ft west of the canal. From March 29 to April 4, 

1996, a mechanism problem caused the gate to close 

slowly. Thus, the canal stage gradually rose, resulting 

in increased ground-water levels.

Stage in WCA 3B also responds to changes in 

canal stage, although the response is much slower than 

the response of ground-water levels. When the gate at 

structure S-335 was open, the rate of stage decline generally was higher than when the gate was closed. This 

is evident in the hydrographs for March and April 

(fig. 9). For example, the rate of stage decline in WCA 

3B increased from 0.013 ft/d to between 0.03 and 

0.04 ft/d, following the opening of the gate at structure 

S-335 in March. When the gate was closing slowly 

from March 29 to April 4, 1996, the stage in WCA 3B 

continued to drop (even though ground-water levels 

were increasing), but at a lower rate of 0.01 ft/d.

Vertical head differences in the ground water 

below the low-permeability limestone were very small 

(fig. 7). The presence or absence of large differences 

may be attributed to the accuracy limits of the measurements and the design of the well clusters. The only 

Gate at structure S-335 open

Nov

Nov

DAILY RAINFALL, IN INCHES

0

2

4

6.5

7.0

7.5

8.0

8.5

9.0

WATER-LEVEL OR STAGE ELEVATION,

IN FEET ABOVE SEA LEVEL

6.0

Water Conservation Area 3B

Levee 30 canal

G-3580

G-3585

G-3590

G-3598

1

3

Feb Mar Apr May Jun Jul

1996

Aug Sep Oct

Feb Mar Apr May Jun Jul

1996

Aug Sep Oct Dec

Dec

Gate at structure S-335

slowly closing

Figure 8. Water-level or stage elevation, gate openings, and rainfall for selected stations from February to December 1996.
Data Collection and Evaluation 13

Gate at structure S-335 open

Gate at structure S-335 open

29 30 1

DAILY RAINFALL, IN INCHES

0

1

2

DAILY RAINFALL, IN INCHES

0

0.5

0.4

0.2

November December

2 3 4 5 6 7 8 9 10 11 14 12 16 13 15

1996

19 20 21 22 23 24 25 26 27 28

29 30 1

November December

2 3 4 5 6 7 8 9 10 11 14 12 16 13 15

1996

19 20 21 22 23 24 25 26 27 28

8.0

6.0

6.5

7.0

7.5

WATER-LEVEL OR STAGE ELEVATION,

IN FEET ABOVE SEA LEVEL

WATER-LEVEL OR STAGE ELEVATION,

IN FEET ABOVE SEA LEVEL

8.5

6.5

7.0

7.5

8.0

Water Conservation Area 3B

G-3580

G-3585

G-3598

G-3590

Levee 30 canal

Water Conservation Area 3B

G-3580

G-3585

G-3598

G-3590

Levee 30 canal

0.1

0.3

March

5 10 15 20 25

1996

15 20 25 31

April

30

May

2

March April

5 10 15 20 25 30

1996

15 20 25 31

May

2

Gate slowly closing

Figure 9. Water-level or stage elevation, gate openings, and rainfall for selected stations during March, April, and May 

1996 and November and December 1996.
14 Methods to Quantify Seepage Beneath Levee 30, Miami-Dade County, Florida

significant vertical difference greater than 0.05 ft was 

found within clusters west of the levee, between wells 

completed below the base of the Biscayne aquifer and 

wells completed within the Biscayne aquifer. At the 

westernmost well cluster, the vertical component of the 

gradient was always downward, and the head difference ranged from 0.02 to 0.13 ft. At the well cluster on 

the western side of the levee, the vertical component of 

the gradient was usually upward, and the head difference was greater than 0.05 ft for 22 percent of the time. 

This head difference may be a result of the upward gradient created by drainage into Levee 30 canal.

Vertical head differences are the controlling 

factor in seepage between wetland surface water and 

ground water. The gradient between the stage in WCA 

3B and ground-water levels is a result of the low-permeability limestone at 7 to 10 ft below land surface. 

Differences between the stage in WCA 3B and groundwater levels (table 3) varied with time and location 

(fig. 10). Much of the variability at a site occurred 

when the stage was near land surface (May 1996) and 

when gates at the control structures were open. From 

June to November 1996, the variability was considerably less, with head differences ranging from 0.19 to 

0.41 ft (between WCA 3B and well G-3580) and 0.45 

to 0.75 ft (between WCA 3B and well G-3584). These 

head differences are substantially less than those for the 

entire period when differences ranged from -0.17 to 

0.48 ft (fig. 10C) and -0.03 to 0.90 ft (fig. 10B). A similar relation can be found between the stage in Levee 30 

canal and ground-water levels in well G-3588 (fig. 

10A); head differences ranged from -0.27 to -0.10 ft 

(June-November) and from -0.39 to -0.04 ft (FebruaryDecember).

The vertical head differences are affected by the 

difference in stage between Levee 30 canal and WCA 

3B. Under current conditions, these differences in stage 

are considerably less than those measured during an 

earlier period in 1959-60 (Klein and Sherwood, 1961, 

p. 11). During 1959-60, the difference in stage ranged 

from 2.2 to 4.7 ft. From February to December 1996, 

the difference in stage ranged from 0.11 to 1.27 ft, suggesting that the vertical seepage rate is considerably 

less now than during the 1959-60 study.

Horizontal ground-water head differences 

between well clusters also varied with time (fig. 11 and 

table 3). Generally, the smallest mean head differences 

occurred in May 1996 when the stage in WCA 3B was 

near land surface. In some instances, the head difference was negative, indicating that the ground-water 

flow direction may have reversed. The values, however, were very low (less than 0.05 ft), and measurement error may have accounted for some of the 

negative head differences that were measured; in particular, the head differences between wells G-3584 and 

G-3590 located west and east of the levee, respectively.

Table 3. Vertical and horizontal head differences, February 1 to December 15, 1996

1

Negative values indicate surface-water head is less than ground-water head; negative values also are given for comparison between two 

surface-water sites where noted. Positive values indicate the opposite.

2

Negative values indicate east-west gradient, positive values indicate west-east gradient.

Surface-water site

Well No.

or surface-water 

site

Vertical head difference (feet)1

Mean Minimum Maximum

Water Conservation Area 3B G-3580 0.30 -0.17 0.48

Water Conservation Area 3B G-3584 .61 -.03 .90

Levee 30 canal G-3588 -.18 -.39 -.04

Water Conservation Area 3B Levee 30 canal .84 .11 1.28

Western well 

No.

Eastern well 

No.

Horizontal head difference (feet)2 Distance 

between wells

(feet)

Mean horizontal 

water-level gradient

Mean Minimum Maximum (feet per foot)

G-3580 G-3583 0.19 0.10 0.27 313 6 x 10-4

G-3583 G-3584 .11 .01 .19 124 9 x 10-4

G-3584 G-3590 .07 -.02 .12 155 4 x 10-4

G-3593 G-3598 .01 -.05 .07 262 4 x 10-5
Data Collection and Evaluation 15

June July Sept

1996

Feb Mar Apr May Aug Oct Nov Dec

June July Sept

1996

Feb Mar Apr May Aug Oct Nov Dec

June July Sept

1996

Feb Mar Apr May Aug Oct Nov Dec

1.0

0

-0.2

0.8

-0.4

0.6

-0.6

0.4

-0.8

0.2

-1.0

-1.2

1.0

0.8

0.6

0.4

0.2

0

0

-0.2

-0.2

HEAD DIFFERENCE, IN FEET

EXPLANATION

Mean

Minimum

Maximum

Levee 30 canal and well G-3588

Water Conservation Area 3B and well G-3584

Water Conservation Area 3B and well G-3580

A

B

C

Figure 10. Average monthly vertical head differences between selected surface-water sites and ground-water wells, 

February to December 1996.
16 Methods to Quantify Seepage Beneath Levee 30, Miami-Dade County, Florida

0.3

0.2

0.1

0

0

June July Sept

1996

Feb Mar Apr May Aug Oct Nov Dec

June July Sept

1996

Feb Mar Apr May Aug Oct Nov Dec

June July Sept

1996

Feb Mar Apr May Aug Oct Nov Dec

June July Sept

1996

Feb Mar Apr May Aug Oct Nov Dec

-0.1

0.2

0.1

0

-0.1

HEAD DIFFERENCE, IN FEET

0.3

0.2

0.1

0.2

0.1

0

EXPLANATION

Mean

Minimum

Maximum

Wells G-3584 and G-3590

Wells G-3583 and G-3584

Wells G-3593 and G-3598

Wells G-3580 and G-3583

(maximum for March is zero)

Figure 11. Average monthly horizontal head differences between selected ground-water wells, February to December 

1996.
Quantification of Seepage Beneath Levee 30 17

Horizontal ground-water head gradients (table 3) 

are a major factor in the variability in the rate of 

ground-water flow. The highest mean horizontal gradient was on the west side of the levee between wells 

G-3584 and G-3583 (table 3); the mean gradient was 

more than double the mean gradient beneath Levee 30 

(wells G-3584 and G-3590) and about 50 percent 

greater than the mean gradient between the western 

pair of wells (wells G-3580 and G-3583). The lowest 

mean gradient was between wells located east of the 

canal (G-3593 and G-3598), with an average gradient 

equal to 10 percent of the average gradient beneath the 

levee (table 3). The variability in the mean horizontal 

gradient by location may be caused, in part, by the variability in the vertical gradient and seepage across the 

low-permeability limestone. Additional research, 

beyond the scope of this study, is needed to further 

evaluate this variability. Mean gradients west of the 

levee, between 6 x 10-4 and 9 x 10-4 ft/ft (feet per foot), 

are about equal to 10 percent of the gradient reported 

for 1960 (Klein and Sherwood, 1961, p. 17). This difference is consistent with the higher difference in stage 

between the canal and WCA 3B in 1960 compared to 

1996.

QUANTIFICATION OF SEEPAGE 

BENEATH LEVEE 30

A numerical ground-water flow model and a 

simple application of Darcy’s law of ground-water 

flow were used to quantify seepage rates beneath Levee 

30 in Miami-Dade County. A description of the two 

approaches and a discussion of the results are described 

herein.

Ground-Water Flow Model

A two-dimensional, cross-sectional, finite-difference, ground-water flow model based on the USGS 

modular, three-dimensional, ground-water flow model 

code MODFLOW (McDonald and Harbaugh, 1988) 

was used to simulate flow in the surficial aquifer system in the vicinity of Levee 30 and seepage into Levee 

30 canal. Although the surficial aquifer system in 

southern Florida contains layers of highly porous and 

dense limestone, it can be modeled as an equivalent 

porous medium, as previously documented through the 

use of aquifer tests (Fish and Stewart, 1991, p. 13-24) 

and through successful calibration of porous-media 

models of the surficial aquifer system (Merritt, 1996; 

Swain and others, 1996). The MODFLOW code is 

capable of simulating ground-water flow in anisotropic, heterogeneous, and layered aquifer systems. A 

block-centered, finite-difference approach is employed 

in the code to simulate ground-water levels and flow, 

using parameter specifications that quantify aquifer 

characteristics (transmissivity, specific yield and storage, and vertical conductance) and aquifer stresses 

(recharge, evapotranspiration, well withdrawals, and 

surface-water interactions). A cross-sectional model 

was used because of the relative horizontal homogeneity of the aquifer characteristics within the surficial 

aquifer system near Levee 30. Because of the constanthead surfaces in the wetlands and the canal and the lack 

of stresses on the ground-water flow system, subsurface flows are generally perpendicular to Levee 30 

canal at the study site.

Steady-state simulations for 6 different days in 

1996 in which flow was believed to be at steady state 

were made to determine the rate of ground-water flow 

beneath Levee 30. The six steady-state periods represented a variety of hydrologic conditions that included 

high and low stages in WCA 3B and high flow in Levee 

30 canal resulting from the gate opening at structure 

S-335. Steady-state simulations were considered adequate because of relatively constant head gradients in 

the flow system over time. Transient conditions, such 

as rainfall or gate openings, may have resulted in the 

invalidation of the assumption of steady-state conditions. There was no rainfall within 2 days of any of the 

days selected for modeling. The control structures were 

open for 2 days prior to and during the December 

simulation.

The Basic package and the Block-Centered Flow 

package were used for the simulation model, and the 

General-Head Boundary and Evapotranspiration packages were used to model boundary conditions. The 

model was evaluated using water-level, discharge, and 

vertical seepage data collected during the study.

Model Grid

The cross-sectional model grid, 1,074 ft in length 

from west to east, consisted of 1 row, 392 columns, and 

29 layers (fig. 12). The model grid contained 11,368 

cells, of which 533 were inactive and 278 were constant-head cells. Locations of the easternmost and westernmost wells (fig. 4) were used to define the extent of 

the model. The western boundary is 500 ft west of the 

levee, and the eastern boundary is 286 ft east of the 
18 Methods to Quantify Seepage Beneath Levee 30, Miami-Dade County, Florida

canal. The water-level data from these wells were used 

to specify accurate boundary conditions, with the 

expectation that these boundaries were at a sufficient 

distance to avoid boundary effects in the area of interest 

(canal and levee). Moving the boundaries farther from 

the canal would have required estimating these boundary conditions. The row was 1 ft wide, the columns were 

2 ft wide near the canal and levee, and 4 or 6 ft wide near 

the edges of the model. The thickness of the model 

(82 ft) was selected to encompass the Biscayne aquifer 

and part of the surficial aquifer system (part of the 

Tamiami Formation) below the Biscayne aquifer. The 

lower part of the model was included to determine if 

flow occurred between the Biscayne aquifer and the 

upper Tamiami Formation. The top 18 layers were 2-ft 

thick, the next 10 layers were 4-ft thick, and the bottom 

layer was 6-ft thick. Relatively smaller dimensions were 

used near the canal and levee in an attempt to model the 

relatively fine-scaled flow patterns anticipated in that 

part of the flow system.

1

10

20

29

26

2

25

4

6

8

Constant Head Boundary and station

G-3580 G-3579 WCA 3B

G-3598 G-3599

Constant Head Boundary and station

No flow boundary

Vertical scale exaggerated 10x

Tamiami Formation

Low-permeability limestone

Open water

Open water

Wetland peat

West

Fort Thompson Formation (lower unit)

Fort Thompson Formation (upper unit)

Miami Limestone

LAYERS

COLUMNS

50 100 150 200 250 300 350

Canal bottom

Canal side

Wetland peat Soil

Levee

0 100 200 Feet

0 25 50 Meters

1 392

East

WCA 3B

Constant Head Boundary and station

(N : C

G

ote anal side and canal bottom are

eneral Head Boundary cells)

Figure 12. Model grid showing materials having characteristic hydraulic conductivities used for the model and location of model 

boundary cells.
Quantification of Seepage Beneath Levee 30 19

Boundary Conditions

Constant-head boundaries were specified in 

layer 1 in WCA 3B and at both the eastern and western 

ends of the grid (table 4). The water surface in WCA 

3B was considered spatially uniform in the study area, 

and stage data from the single site was used for the 

entire boundary. No data were available to indicate any 

difference between stage in WCA 3B and ground-water 

levels above the low-permeability limestone at the 

western boundary. Therefore, the stage value in WCA 

3B at the western boundary was used as the constant 

head in the cells (wetland peat and Miami Limestone) 

above the thin low-permeability limestone. The water 

levels in the shallow wells (well G-3580 at the western 

boundary and well G-3598 at the eastern boundary) 

were used to define the constant head for the cells of the 

low-permeability limestone and Fort Thompson Formation. The water levels in the deep wells (G-3579 at 

the western boundary and G-3599 at the eastern boundary) were used to define the constant head for the cells 

of the Tamiami Formation at the bottom of the model. 

The water level in shallow well G-3598 at the eastern 

boundary also was used to define the constant head in 

the cells of wetland peat in layers 1 and 2 of the model. 

The bottom of the model is a no-flow boundary. 

The General-Head Boundary package was used 

to simulate the hydraulic interaction between the canal 

and the aquifer. Seventy-nine grid cells, each 2 by 2 ft, 

were used to represent the canal (fig. 12, canal side and 

canal bottom cells). The General-Head Boundary 

package requires the use of a conductance term, which 

is equal to the hydraulic conductivity of the river bed 

confining material multiplied by the cross-sectional 

area of flow and divided by the thickness of the 

confining bed. The conductance value for general-head 

cells at the bottom of the canal was set to a relatively 

low value of 1 ft2

/d (square foot per day) because of the 

very fine grained sediment along the bottom. The conductance term for the general-head cells on the side of 

the canal was difficult to determine because there is little if any confining material. The hydraulic conductivity of the bed material for the cells on the side of the 

canal should be similar to the adjacent cell, but the 

thickness of the bed material is difficult to define. 

Therefore, the conductance value for the general-head 

cells on the side of the canal was used as a calibration 

parameter to match the model results to the measured 

fluxes into the canal. The final conductance value used 

in the model for these general-head cells was 

1,000 ft2

/d, which is generally consistent with the 

hydraulic conductivity values of the adjacent cells. The 

stage value in the Levee 30 canal was used as the constant head in the cells specified in the General-Head 

Boundary package.

Hydraulic Properties

Lateral hydraulic conductivity values were initially assigned based on previous aquifer test data from 

well G-3297 (Fish and Stewart, 1991, p. 28), previous 

model results (Chin, 1990; Merritt, 1996; and Swain 

and others, 1996), and the results of the lithologic log 

(app. I) and the geologic core data (app. II) obtained 

from well G-3297. Each grid cell was associated with a 

particular geologic material (table 5); each grid layer 

generally was assigned to the same material (fig. 12). 

Table 4. Constant-head boundary conditions used in ground-water flow model

Date of

measurement

Surface-water stage

(feet above sea level) Water level (feet above sea level)

Remarks Water

Conservation 

Area 3B1

Levee 30 

Canal

Well G-3580

(column 1,

layers 5-25)

Well G-3579

(column 1,

layers 26-29)

Well G-3598

(column 392,

layers 1-25)

Well G-3599

(column 392, 

layers 26-29)

02-23-96 7.87 6.99 7.55 7.48 7.13 7.16 Dry season

03-25-96 7.67 6.91 7.40 7.36 7.04 7.06 Dry season

05-18-96 6.29 6.16 6.41 6.36 6.16 6.16 Dry season

09-16-96 8.45 7.54 8.07 8.01 7.54 7.54 Wet season

10-19-96 8.91 8.02 8.56 8.45 7.99 8.00 Wet season

12-04-96 8.18 6.92 7.70 7.66 7.12 7.14 Gate open

1Also used for column 1, layers 1-4.
20 Methods to Quantify Seepage Beneath Levee 30, Miami-Dade County, Florida

Lateral hydraulic conductivity values were assigned to 

each material type and then modified during the trialand-error calibration process. Materials associated 

with the aquifer were assigned based on the lithologic 

logs obtained from wells G-3297 (Causaras, 1987) and 

G-3587 (app. I). Because of the fine scale grid of the 

model compared with the previous models, there was 

not always a corresponding material in the earlier models to the materials used for this study. Additionally, the 

previous models generally covered a much larger area, 

and average values for a material were used for large 

areas of the model. Thus, the final calibration-derived 

lateral hydraulic conductivities were often different 

than the values for similar material in the previous 

models.

 The open water within WCA 3B and a drainage 

ditch on the eastern side of the model were treated as 

highly permeable material and assigned a calibrationderived lateral hydraulic conductivity of 1,000,000 

ft/d; Merritt (1996) and Swain and others (1996) used a 

value of 3,000,000 ft/d. Levee, wetland peat, and soil 

material were all treated as relatively impermeable 

material and assigned calibration-derived lateral 

hydraulic conductivities of 10, 50, and 100 ft/d 

(table 5), respectively. Previous models used a value of 

10 ft/d for similar material. The low permeability limestone was not modeled in earlier studies, but based on 

the geologic core data, the limestone was treated as 

nearly impermeable, with a lateral hydraulic conductivity of 1 ft/d. The Miami Limestone was assigned a 

calibration-derived lateral hydraulic conductivity of 

1,000 ft/d, less than the 4,500 to 5,000 ft/d used by Chin 

(1990) and Merritt (1996) and the 5,000 to 20,000 ft/d 

used by Swain and others (1996). Based on the lithologic log and the geologic core data, the Fort Thompson Formation was split into an upper unit and a lower 

unit. The upper unit was assigned a calibration-derived 

lateral hydraulic conductivity of 3,000 ft/d, similar to 

the 500 to 5,000 ft/d used by Merritt (1996). The lower 

unit was assigned a calibration-derived lateral hydraulic conductivity of 10,000 ft/d, less than the 20,000 to 

30,000 ft/d used in the previous models and the 

29,000 ft/d estimated for well G-3297 (Fish and 

Stewart, 1991). The lateral hydraulic conductivity of 

29,000 ft/d estimated by Fish and Stewart (1991) 

represents the hydraulic conductivity of the most 

permeable zones. The average value of lateral hydraulic conductivity used for the lower Fort Thompson 

Table 5. Material properties used in calibrated flow models

Material

Lateral hydraulic

 conductivity 

(feet per day)

Thickness1

(feet)

Layer

No.2 Remarks

Open water 1,000,000 2 1 Water Conservation 

Area 3B wetland layer

Open Water 1,000,000 2 2 Drainage ditch, 

eastern edge of model

Levee 10 4 1-2 Thickness of levee required for model

Soil 100 2 1

Wetland peat 50 2 2 Below Water Conservation 

Area 3B open water

Wetland peat 50 4 1-2 Pennsuco wetlands,

eastern edge of model

Miami Limestone 1,000 4 3-4

Low permeability 

limestone 1 2 5

Fort Thompson Formation

(upper unit) 3,000 4 6-7

Fort Thompson Formation

(lower unit) 10,000 50 8-25

Tamiami Formation 500 18 26-29

1

Thickness range given for materials with variable thickness.

2

Some layers consisted of varying materials.
Quantification of Seepage Beneath Levee 30 21

Formation is substantially lower, and thus, the calibrated value of 10,000 ft/d can be considered reasonable. The Tamiami Formation was assigned a lateral 

hydraulic conductivity value of 500 ft/d based on the 

hydraulic conductivity value of 470 ft/d estimated for 

well G-3297 (Fish and Stewart, 1991). Probes of the 

canal bottom indicated a minimum of 2 to 3 ft of very 

fine grained sediment along the bottom. Therefore, 

canal bottom sediments were treated as a nearly impermeable material. Vertical hydraulic conductivity was 

set equal to 10 percent of the lateral hydraulic conductivity for each cell with one exception. The horizontal 

conductivity and vertical conductivity were set to the 

same value for the canal bottom material.

Evapotranspiration

Maximum evapotranspiration rates used in the 

model were obtained from previous work by Merritt 

(1996, p. 90). The maximum evapotranspiration rates 

varied by month, ranging from 0.08 to 0.18 in/d (inches 

per day). A single evapotranspiration rate was used for 

each simulation, but the rate varied between simulations. The evapotranspiration was calculated in the topmost cell not specified as inactive. The elevation of the 

evapotranspiration surface was set to 8 ft, the top of 

layer one. The extinction depth was set to 8 ft, below 

the bottom of the lowest layer (layer three) where 

evapotranspiration was calculated. However, because 

almost half of the surface cells, including the wetland 

cells, were modeled as constant-head cells, it was not 

necessary to specify evapotranspiration rates for these 

cells. Evapotranspiration was between 0.5 and 2 percent of the water budget, and thus, was considered to 

have little effect on the model results and was not considered a critical parameter in the calibration process.

Calibration

The model was calibrated for steady-state conditions for 6 days in 1996 (table 4). All parameters were 

manipulated within expected values during the calibration period. The model showed appreciable sensitivity 

for two parameters: (1) the lateral hydraulic conductivity in the Fort Thompson Formation, and (2) the general-head boundary conductance value for the generalhead cells along the sides of the canal. As previously 

discussed, the conductance value for the general-head 

cells along the sides of the canal is consistent with the 

hydraulic conductivity values of the adjacent cells. 

Therefore, only the lateral hydraulic conductivity in the 

Fort Thompson Formation was estimated using the 

model-calibration process. Because the boundary 

conditions constrained the ground-water levels, model 

output was compared with field measurements of vertical seepage from WCA 3B, ground-water inflows to 

Levee 30 canal, and ground-water levels.

Simulated ground-water levels were compared 

with measured ground-water levels at the 17 wells not 

used for determination of boundary conditions 

(table 6). The difference between the simulated and 

measured values was generally less than 0.05 ft. In 

most instances, the calibrated value was higher than the 

measured value.

Simulated vertical flow rates from WCA 3B to 

ground water were compared with the flow rates measured using the vertical seepage meters. The simulated 

vertical flows were calculated by dividing the model 

cell-by-cell flow term for a representative cell by the 

area of the cell. For the west seepage meter, the modelsimulated value for column 17, about 60 ft east of the 

meter location, was used because of model boundary 

effects. The measured seepage rate at the west meter 

ranged from 0.033 to 0.056 ft/d when the gates at structures S-32A, S-335, and S-337 were closed between 

September and November (table 2). The simulated 

rates in September and October were 0.038 and 

0.035 ft/d, respectively. When the gates at structure 

S-335 were open in December 1996, the measured 

seepage rate at the west meter (table 2) increased to 

0.092 ft/d (table 2), and the simulated rate increased to 

0.048 ft/d.

The simulated rate varied greatly from cell to cell 

near the east meter, with the rate increasing toward 

Levee 30. For example, the simulated seepage rate in 

September was 0.335 ft/d at the east meter (about 30 ft 

west of the levee), 0.195 ft/d at 20 ft west of the meter, 

and 0.615 ft/d at 20 ft east of the meter. The measured 

seepage rate at the east meter ranged from 0.177 to 

0.266 ft/d when the gates at structures S-32A, S-355, 

and S-337 were closed between September and 

November (table 2). When the gates were open at structure S-335 in December, the measured seepage rate at 

the east meter was 0.292 ft/d (table 2), and the simulated rate was 0.445 ft/d.

Simulated inflows to Levee 30 canal obtained 

from the volumetric budget for the model are compared 

herein with the average inflows computed from the 

results of discharge measurements (table 7). The 

simulated inflows were all within the total inflow range 

of measured discharge. On May 18, 1996, results 

indicated considerably lower simulated inflow to the 

canal because very little water was ponded in WCA 3B. 

Discharge measurements were not made in Levee 30 

canal to provide verification of the results.
22 Methods to Quantify Seepage Beneath Levee 30, Miami-Dade County, Florida Table 6. Measured and calibrated water-level data for the ground-water flow model [Measured and calibrated water levels in feet above sea level, -- missing data] Well number Dates of measurement February 23, 1996 March 25, 1996 May 18, 1996 Sepember 16, 1996 October 19, 199

Measured Calibrated Measured Calibrated Measured Calibrated Measured Calibrated Measured Calib

 G-3581 7.39 7.39 7.31 7.26 6.29 6.33 7.87 7.90 8.34 8.3

 G-3582 7.37 7.38 7.28 7.25 6.28 6.32 7.87 7.89 8.34 8.3

 G-3583 7.36 7.37 7.23 7.24 6.26 6.32 7.86 7.88 8.32 8.3

 G-3584 7.23 7.30 7.13 7.18 6.23 6.28 7.76 7.80 8.22 8.2

 G-3585 7.24 7.29 7.12 7.17 6.22 6.28 7.76 7.79 8.22 8.2

 G-3586 7.23 7.28 7.12 7.17 6.24 6.27 7.76 7.78 8.15 8.2

 G-3587 7.27 7.27 7.12 7.16 6.29 6.27 7.79 7.77 8.23 8.2

 G-3588 7.18 7.21 7.08 7.11 6.23 6.24 7.69 7.71 8.16 8.

 G-3589 7.17 7.21 7.06 7.11 -- 6.24 7.69 7.71 8.16 8.

 G-3590 7.17 7.20 7.06 7.10 6.24 6.23 7.67 7.70 8.15 8.

 G-3591 7.15 7.21 7.06 7.11 6.21 6.24 7.66 7.72 8.12 8.

 G-3592 7.19 7.22 7.08 7.11 6.20 6.24 7.67 7.71 8.13 8.

 G-3593 7.11 7.14 7.02 7.04 6.17 6.19 7.58 7.61 8.06 8.0

 G-3594 7.13 7.14 7.03 7.04 6.17 6.19 7.57 7.61 8.07 8.0

 G-3595 7.13 7.14 7.03 7.05 6.18 6.19 7.59 7.61 8.06 8.0

 G-3596 7.10 7.14 7.03 7.05 6.20 6.19 7.60 7.61 8.05 8.0

 G-3597 7.15 7.14 7.05 7.05 6.18 6.19 7.62 7.61 8.08 8.0
Quantification of Seepage Beneath Levee 30 23

Sensitivity Analysis

The sensitivity of the ground-water flow model 

to changes in selected input parameters was determined 

using data for October 19, 1996. Because of the similarities between simulations, a sensitivity analysis was 

not performed for the other simulations. Based on 

results from the calibration process, the lateral hydraulic conductivity in the Fort Thompson Formation was 

determined to have a substantial impact on the estimated seepage beneath Levee 30. The lateral hydraulic 

conductivity in the Fort Thompson Formation was 

doubled and halved for the sensitivity analysis. The 

variables used for analysis were ground-water levels, 

ground-water inflows to the canal, and total flow entering and leaving the model domain. There was no effect 

on the vertical flow from WCA 3B.

Ground-water levels were insensitive to parameter changes and showed a maximum variation of 0.03 ft 

for each sensitivity simulation. (Ground-water levels 

are insensitive to parameter changes because the model 

is constrained by constant-head boundary conditions 

on three sides.) Ground-water inflows to Levee 30 

canal increased and decreased by 24 percent when the 

lateral hydraulic conductivity in the Fort Thompson 

Formation was doubled or halved, respectively. The 

total volumetric flow budget increased by 60 percent 

when the lateral hydraulic conductivity value in the 

Fort Thompson Formation was doubled and decreased 

by 34 percent when the value was halved.

Model Results

The simulations were analyzed based on the 

variation in total horizontal ground-water flow in the 

model layers above the Tamiami Formation (table 8, 

layers 3-25), in vertical seepage from WCA 3B 

(table 8, columns 17-150), and in ground-water flow to 

the canal. During the dry-season simulations in February and March 1996, the horizontal ground-water flow 

on the western side of Levee 30 was 320 and 280 ft3

/d 

(cubic feet per day), respectively, compared to 25 and 

15 ft3

/d, respectively, on the eastern side of the model. 

Table 7. Simulated and measured ground-water inflows to Levee 30 canal

Ground-water flow model

Date

Total inflow

(cubic feet per day 

per foot of canal 

reach)

Stage difference 

between wetlands and 

canal

(feet)

Remarks

02-23-96 307 0.88 Gates at structures closed

03-25-96 273 .76 Gates at structures closed

05-18-96 107 .13 Low water in Water Conservation Area 3B

09-16-96 203 .91 Gates at structures closed

10-19-96 185 .89 Gates at structures closed

12-04-96 432 1.26 Gates at structures open

Measured discharge

Total inflow range

(cubic feet per day,

 per foot of canal reach)

Measurement condition

139 - 311 Gates at structures closed

327 - 491 Gates at structures open
24 Methods to Quantify Seepage Beneath Levee 30, Miami-Dade County, Florida Table 8. Horizontal flow rates in the ground-water flow model and the Darcian approach at selected locations and vertical flow from Wat

calculated by the ground-water flow model [ -- Incomplete water-level data, flow not calculated] Date Total horizontal flow (cubic feet per day)1

1Positive flow is from west to east, and negative flow is from east to west.

Ground

Ground-water flow model

(layers 3 to 25) Darcian approach2

2Analytical flow calculated using a 60-foot section equivalent to ground-water flow model layers 3 to 25. Selected analytical model properties are given below. No 

except for beneath the levee.

Total ground-w

flow to Levee 

canal

(cubic feet

per day)

440 feet west of 

levee

(column 16)

Western side of 

levee

(column 150)

200 feet east 

of canal

(column 370)

West to 

central 

sites3

3West site is represented by well G-3580; central site is represented by wells G-3581, G-3582, and G-3583; and east site is represented by wells G-3584,G-3585, a

Central 

to east 

sites3

Beneath 

levee4

4Beneath levee is represented by Water Conservation Area 3B and Levee 30 canal and wells G-3584, G-3585, and G-3586 (east site) and by wells G-3588, G-3589

levee).

East of 

canal5

5East of canal is represented by wells G-3593, G-3594, G-3595, and G-3598.

6Row 1, columns 17 to 150.7No flow assumed for layer 5.

02-23-96 280 320 25 310 470 260 -20 305 

03-25-96 245 280 15 190 560 240 -30 270 

05-18-96 150 150 65 160 320 -- 30 85 

09-16-96 295 340 140 380 340 330 70 200 

10-19-96 310 355 170 410 360 270 140 185 

12-04-96 390 450 30 410 680 350 20 430 

Model layers

Thickness

(feet)

Lateral hydraulic conductivity

(feet per day)

Site used for water level

Western side of levee

Eastern side of 

levee West Eas

site

Central

site

East

site

3-4 4 1,000 See footnote 4 Water Conservation Area 3B Levee 30 canal See 

5 2 1 See footnote 7 See footnote 7 See footnote 7 See 

 6 - 7 4 3,000 G-3580 G-3583 G-3586 G-3588 G-35

 8 - 18 22 10,000 G-3580 G-3582 G-3585 G-3590 G-35

19 - 25 28 10,000 G-3580 G-3581 G-3584 G-3589 G-35
Quantification of Seepage Beneath Levee 30 25

Vertical seepage from WCA 3B east of the model 

boundary accounted for about 13 percent of the total 

horizontal flow (table 8). Ground-water inflow to 

Levee 30 canal was equal to about 95 percent of the 

total ground-water flow in model layers 3 to 25 on the 

western side of Levee 30. The simulated flow paths 

(fig. 13) show the movement of ground water. All 

ground water above the low-permeability limestone 

and some ground water in the Fort Thompson 

Formation are discharged to Levee 30 canal. Some 

ground water above the low-permeability limestone 

east of Levee 30 canal also is discharged to the canal. 

1

10

20

29

26

2

25

4

6

8

No flow boundary

Vertical scale exaggerated 10x

Tamiami Formation

Low-permeability limestone

Open water

Wetland peat Open water

West

Fort Thompson Formation (lower unit)

Fort Thompson Formation (upper unit)

Miami Limestone

LAYERS

COLUMNS

50 100 150 200 250 300 350

Canal bottom

Canal side

Wetland peat Soil

Levee

0 100 200 Feet

0 25 50 Meters

1 392

EXPLANATION

Simulated wet-season flow path

East

Simulated water-budget component.

ft /d is cubic feet per day 3

Horizontal flow

in layers 3-25

310 ft /d3

Vertical flow

from WCA 3B

45ft /d3

Ground-water flow

to Levee 30 canal

185 ft /d3

Horizontal flow

in layers 3-25

170 ft /d3

Horizontal flow

in layers 3-25

170 ft /d3

Figure 13. Model grid showing simulated wet-season flow paths and the water budget for the October 19, 1996 

simulation.
26 Methods to Quantify Seepage Beneath Levee 30, Miami-Dade County, Florida

During the dry-season simulation in May 1996, the 

horizontal ground-water flow was about half the flow 

as the earlier simulations. Lower flow in May occurred 

because there was almost no ponded water in WCA 3B, 

resulting in vertical seepage of only 5 ft3/d. Groundwater inflow to Levee 30 canal was equal to about 

57 percent of the total ground-water flow in model 

layers 3 to 25 on the western side of Levee 30. 

The horizontal ground-water flow on the western 

side of Levee 30 was higher during the wet-season simulations in September and October 1996 (340 and 

355 ft3

/d) than during the dry-season simulations in 

February and March 1996 (320 and 280 ft3/d). The 

ground-water flow on the eastern side of the model in 

September and October 1996 was about 45 percent of 

the flow on the western side of the levee (table 8). 

Vertical seepage from WCA 3B east of the model 

boundary accounted for about 14 percent of the total 

horizontal flow in February, March, September, and 

October. Ground-water inflow to Levee 30 canal was 

equal to about 95 percent of the total ground-water 

flow in model layers 3 to 25 on the western side of 

Levee 30 during the dry-season simulation, but only 

55 percent during the wet-season simulations.

Horizontal ground-water flow was highest 

(450 ft3

/d) on the western side of Levee 30 in December 1996 when the gates at the control structures were 

open (table 8). Ground-water flow was about 95 percent lower on the eastern side of the model, which is 

similar to the February and March 1996 simulations. 

Vertical seepage from WCA 3B east of the model 

boundary was also highest in December 1996 (table 8), 

but still accounted for less than 15 percent of the total 

horizontal flow. Differences in flow between December and the other periods were a result of the higher gradients between ground-water levels and the canal stage 

caused by the gate openings of the control structures. 

Ground-water inflow to Levee 30 canal was equal to 

almost 95 percent of the total ground-water flow in 

model layers 3 to 25 on the western side of Levee 30.

Simplified Darcian Approach

An analytical approach based on a simple application of Darcy’s law (Heath, 1987, p. 12) was used to 

determine the approximate flow rate in the Biscayne 

aquifer between pairs of monitoring wells from 

February to December 1996 (fig. 14). Darcy’s law is 

expressed by , where Q is the flow rate in 

the aquifer, K is the hydraulic conductivity, is 

the hydraulic gradient, and A is the cross-sectional area 

at a right angle to the flow direction through which 

flow occurs. The primary assumption of this approach 

is that flow is horizontal and vertical flow is negligible 

(Dupuit-Forcheimer assumption). In fact, the groundwater head may vary with depth at the study site, particularly in the vicinity of the levee and canal, indicating vertical flow. The analytical model, however, can 

still provide approximate values for the flow rate at 

points in the aquifer where the effects of Levee 30 and 

its canal are believed to be minimal.

The approximate flow rate was determined using 

the gradients for four cross sections − two sections on 

the western side of Levee 30, one section beneath the 

levee, and one section east of Levee 30 canal (table 8). 

A 60-ft-thick section, equivalent to ground-water flow 

model layers 3 to 25, was used in the calculation. 

Hydraulic conductivity values from the calibrated flow 

model were used. Flow was calculated in each layer 

using water-level data from representative wells 

(table 8). Lateral flow in layers 1 to 3 was considered 

negligible because of the low horizontal hydraulic conductivity and because flow was generally vertical in 

these layers, especially beneath WCA 3B.

The highest flows simulated with the analytical 

model generally were found between the central and 

eastern sites on the western side of the levee (fig. 14). 

The difference between flows at this section and the 

section to the west was greatest during the dry-season 

period from February to April 1996. Total flows 

decreased in sections to the east. The lowest simulated 

flows were east of the canal, as would be expected if 

the canal were acting as a drain. During the dry-season 

period from February to April 1996, these flows 

remained relatively close to zero or were negative, 

indicating water flowing from east to west.

 Because there are no sinks in the flow system 

beneath the levee, the decrease in flows beneath the 

levee can only be explained if vertical flows toward the 

canal are substantial; vertical flows are not accounted 

for in the analytical model. As described earlier, vertical differences in measured ground-water levels were 

minimal. Because of the high hydraulic conductivity, 

however, ground-water gradients coming from differences in ground-water levels below the detection limits 

of the monitoring equipment can result in substantial 

ground-water flows.

Q K ∂x

∂

    = hA

∂x

∂

    h
Evaluation of Methods to Quantify Seepage 27

EVALUATION OF METHODS TO 

QUANTIFY SEEPAGE

Results from the ground-water flow model illustrate the non-uniqueness problem encountered when 

attempting to solve the ground-water flow equation 

. In the analysis presented in this report, 

there are two unknown variables in the equation: the 

flow rate in the aquifer, Q, and the hydraulic conductivity K. By placing constant-head boundaries on three 

sides of the model, the horizontal gradient, , is 

constrained. Q is proportional to K, and thus, any combination of Q and K could match a measured head gradient in the flow model. Thus, it is possible to match a 

measured head gradient by adjusting Q or K. Because 

K cannot be measured exactly and no horizontal aquifer 

flow data, Q, are available for calibration, it is difficult 

to accurately determine the horizontal flow rates using 

this ground-water flow model. The range of values 

used for the lateral hydraulic conductivity in the Fort 

Thompson Formation in the sensitivity analysis, however, is representative of the range of values obtained 

from the aquifer test data from well G-3297 and generally used in modeling the Biscayne aquifer.

The use of constant-head boundaries on three 

sides of the model also constrains the model solution 

for ground-water levels. For example, the parameter 

with the largest effect on the horizontal flow rate based 

on the sensitivity analysis, lateral hydraulic conductivity in the Fort Thompson Formation, had little effect on 

the ground-water levels used to calibrate the model. If 

heads had not been specified for the wetland layer in 

WCA 3B, then an additional unknown would have 

been added to the equation, the net vertical recharge at 

1996

Feb Mar Apr May June July Aug Sept Oct Nov Dec

800

700

600

500

200

300

400

0

100

-100

TOTAL FLOW, IN CUBIC FEET PER DAY

West site west of levee (well G-3580) to central site (wells G-3581 to G-3583)

Central site west of levee (wells G-3581 to G-3583) to east site (wells G-3584 to G-3586)

Beneath levee (wells G-3584 to G-3586 and G-3588 to G-3590)

East of canal (wells G-3593 to G-3595 and well G-3598)

EXPLANATION

Figure 14. Horizontal flows computed with the analytical approach, February to December 1996.

Q K ∂x

∂

    = hA    

∂x

∂

    h
28 Methods to Quantify Seepage Beneath Levee 30, Miami-Dade County, Florida

this boundary, a combination of recharge and evapotranspiration. Vertical recharge rates were measured at 

several locations and compared favorably with modelcalculated rates. Constraining the model using specified head boundaries eliminated the need to include 

estimates of recharge and evapotranspiration rates in 

the model data sets.

Another limitation of the ground-water flow 

model is the methodology and assumptions made in 

determining the flow rate from the aquifer into the 

canal. Because flows to the canal are a major part of the 

total water budget in the model, it is important to estimate these values as accurately as possible during 

model calibration. Flow measurements were made at 

1-mi intervals in the canal; therefore, estimates of seepage values based on measured data were uniform in 

each reach. Additionally, the velocities generally were 

very low (less than 0.2 ft/s) and difficult to measure 

accurately, even with the ADCP equipment that was 

used for the study. Ideally, measurements would have 

been made at intervals less than 1 mi, but the variation 

in flow rate generally was not great enough to measure 

accurately at a smaller interval.

Results based on the numerical model and the 

Darcian approach (table 8) generally were in agreement for flows on the western side of the levee. The 

flows east of the canal, however, differed considerably 

between the two methods. The flows calculated with 

the ground-water flow model ranged from 1.2 to 

2 times the flows calculated with the Darcian approach. 

During periods of lower flow in February and March 

1996, the flows calculated using the Darcian approach 

were toward the canal, in the opposite direction of the 

flows calculated with the ground-water flow model. 

Because of the flat water-level gradient east of the 

canal, the water-level differences cannot be measured 

accurately enough to use in the analytical model over 

the short distance between the well sites used for the 

analytical model.

Results of this study were compared with those 

from previous studies. Stallman (1956, p. 20), estimated seepage at 1,600 ft3

/d/ft (cubic feet per day per 

foot), equivalent to 97 ft3

/s/mi for a 1-ft head difference 

from WCA 3B to Levee 30 canal using an electric 

analog model. Stallman’s results were determined to be 

much higher than those measured for this study, with 

most of the seepage occurring within 200 ft of the 

levee. Analytical models (Stallman, 1956, p. 21) using 

lower vertical permeability resulted in values as low as 

390 ft3/d/ft (24 ft3

/s/mi), which were within the range 

of results obtained for this study. Klein and Sherwood 

(1961, p. 22) used field data collected at a site near the 

northern end of Levee 30 and calculated a flow of 

8,800 ft3/d/ft (540 ft3/s/mi) into the canal for a 10-ft 

head difference. Thus, assuming a linear relation for a 

1-ft head difference, seepage into the canal would be 

880 ft3/d/ft, which again was determined to be much 

higher than the results for this study. In an earlier study 

conducted at Levee 35A in WCA 2B, Swayze (1988) 

used water-budget and analytical approaches to calculate an underflow of 36 x106 ft3

/d for the entire 15.6-mi 

levee or about 440 ft3

/d/ft of levee for a 5.6-ft head difference. This included a loss to Levee 35A canal of 

15.7 x 106 ft3/d for the entire levee or 190 ft3/d/ft of 

levee.

A small-scale test levee (400-ft long) investigation by the U.S. Army Corps of Engineers (1952) near 

Levee 30 resulted in a calculated loss of about 

110 ft3/d/ft (7 ft3/s/mi) for each foot of head difference 

between the ponded surface water and the canal. 

Although the small scale of the test makes it difficult to 

relate to the study area, the results are similar to those 

of the present study.

Based on the results of this study as well as previous studies, additional data are needed to more accurately determine both the total ground-water seepage 

rate beneath Levee 30 and the source of the groundwater flow. Borehole flow-meter measurements can be 

used in uncased boreholes to determine the rate and 

direction of vertical flow in the ground water. Horizontal flow rates may be measured using a tracer test and 

estimates of aquifer porosity. A tracer study was successfully used in Cape Cod, Mass. (LeBlanc, and others, 1991), using an array of closely spaced multilevel 

samplers to map the movement of an induced tracer. 

Finally, data are needed farther than 500 ft west of 

Levee 30 to determine an accurate water budget for 

WCA 3B. The vertical seepage rate throughout WCA 

3B, the lateral extent of influence of Levee 30 canal on 

the vertical seepage rate, and the direction of groundwater flow throughout WCA 3B were not determined 

from the data collected nor the modeling results. Also 

unknown is the extent of the low-permeability limestone and the resulting vertical gradient between the 

ponded water in WCA 3B and the ground water 

beneath the low-permeability limestone.
References Cited 29

REFERENCES CITED

Causaras, C.R., 1987, Geology of the surficial aquifer system, Dade County, Florida: U.S. Geological Survey 

Water-Resources Investigations Report 86-4126, 

240 p., 3 sheets.

Chin, D.A., 1990, A method to estimate canal leakage to the 

Biscayne aquifer, Dade County, Florida: U.S. Geological Survey Water-Resources Investigations Report 90-

4135, 32 p.

Core Laboratories Inc., 1995, Basic rock properties, L-30-

80, No. 9 well, Dade County, Florida: Final report submitted to the U.S. Geological Survey, August 21, 1995: 

Carrolton, Tex., File DAL-95158, 13 p. 

Fish, J.E., and Stewart, Mark, 1991, Hydrogeology of the 

surficial aquifer system, Dade County, Florida: U.S. 

Geological Survey Water-Resource Investigations 

Report 90-4108, 50 p.

Harvey, J.W., 1996, Vertical exchange of ground water and 

surface water in the Florida Everglades: U.S. Geological Survey Fact Sheet 169-96, 2 p.

Heath, R.C., 1987, Basic ground-water hydrology: U.S. 

Geological Survey Water-Supply Paper 2220, 84 p.

Jordan, C.L., 1984, Florida’s weather and climate: Implications for water, in E.A. Fernald and D.J. Patton, eds., 

Water resources atlas of Florida: Tallahassee, Florida 

State University, Institute of Science and Public Affairs, 

p. 18-35.

Kennedy, E.J., 1988, Levels at streamflow gaging stations: 

U.S. Geological Survey Open-File Report 88-710, 42 p.

Klein, Howard, and Sherwood, C.B., 1961, Hydrologic conditions in the vicinity of Levee 30, northern Dade 

County, Florida: Florida Bureau of Geology Report of 

Investigations No. 24, 24 p.

LeBlanc, D.R., Garabedian, S.P., Hess, K.M., and others, 

1991, Large-scale natural-gradient tracer test in sand 

and gravel, Cape Cod, Massachusetts: (1) Experimental 

design and observed tracer movement: Water 

Resources Research, v. 27, no. 5, p. 895-910.

Lee, D.R., 1977, A device for measuring seepage flux in 

lakes and estuaries: Limnology and Oceanography, 

v. 22, no. 1, p. 140-147. 

McDonald, M.G., and Harbaugh, A.W., 1988, A modular 

three-dimensional finite-difference ground-water flow 

model: U.S. Geological Survey Techniques of WaterResources Investigations, book 6, chap. A1, 586 p.

McKenzie, D.M., 1973, Lake Okeechobee seepage monitoring network: U.S. Geological Survey Open-File Report 

73-018, 64 p.

McPherson, B.F., Higer, A.L., Gerould, Sarah, and Kantrowitz, I.H., 1995, South Florida Ecosystem Program of the 

U.S. Geological Survey: U.S. Geological Survey Fact 

Sheet 134-95, 4 p.

Merritt, M.L., 1996, Simulation of the water table altitude in 

the Biscayne aquifer, southern Dade County, Florida, 

water years 1945-89: U.S. Geological Survey WaterSupply Paper 2458, 148 p.

Meyer, F.W., and Hull, J.E., 1969, Seepage tests in L-D1 

Borrow Canal at Lake Okeechobee, Florida: Florida 

Bureau of Geology Information Circular 59, 31 p.

Miller, W.L., 1978, Effects of bottom sediments on infiltration from the Miami and tributary canals to the Biscayne aquifer, Dade County, Florida: U.S. Geological 

Survey Water-Resource Investigations Report 78-36, 

63 p.

Ogden, J.C., and Davis, S.M., 1994, Everglades, the ecosystem and its restoration: Delray Beach, Fla., St. Lucie 

Press, 826 p.

Perkins, R.D., 1977, Depositional framework of Pleistocene 

rocks in south Florida: in Paul Enos and R.D. Perkins, 

eds., Quaternary sedimentation in south Florida: 

Geological Society of America, Memoir 147, Part II, 

p. 131-198.

Scott, T.M., 1997, Miocene to Holocene history of Florida: 

in A.F. Randazzo and D.S. Jones, eds., The geology of 

Florida: Gainesville, University Press of Florida, 

p. 57-68.

Simpson, M.R., and Oltmann, R.N., 1992, Discharge-measurement system using an Acoustic Doppler Current 

Profiler with applications to large rivers and estuaries: 

U.S. Geological Survey Open-File Report 91-487, 49 p.

Sonenshein, R.S., and Hofstetter, R.H., 1990, Hydrologic 

effects of well-field operations in a wetland, Dade 

County, Florida: U.S. Geological Survey WaterResource Investigations Report 90-4143, 16 p.

Sonenshein, R.S., and Koszalka, E.J., 1996, Trends in watertable altitude (1984-93) and saltwater intrusion (1974-

93) in the Biscayne aquifer, Dade County, Florida: U.S. 

Geological Survey Open-File Report 95-705, 2 sheets.

Stallman, R.W., 1956, Preliminary findings on ground-water 

conditions relative to area B flood-control plans, 

Miami, Florida: U.S. Geological Survey Open-File 

Report, 42 p.

Swain, E.D., Howie, Barbara, and Dixon, Joann, 1996, 

Description and field analysis of a coupled groundwater/surface-water flow model (MODFLOW/BRANCH) with modifications for structures 

and wetlands in southern Dade County, Florida: U.S. 

Geological Survey Water-Resources Investigations 

Report 96-4118, 67 p.

Swain, E.D., Kapadia, Amit, Kone, Siaka, and others, 1997, 

Determining discharge-coefficient ratings for coastal 

structures in Dade County, Florida: U.S. Geological 

Survey Water-Resources Investigations Report 97-

4079, 61 p.
30 Methods to Quantify Seepage Beneath Levee 30, Miami-Dade County, Florida

Swayze, L.J., 1988, Ground-water flow beneath Levee 35A 

from Conservation Area 2B, Broward County, Florida: 

U.S. Geological Survey Water-Resources Investigations Report 87-4280, 22 p.

U.S. Army Corps of Engineers, 1952, Part I, Agricultural 

and Conservation Areas − Supplement 5 − Test Levee 

Investigations: Partial Definite Project Report, Central 

and South Florida Project for Flood Control and Other 

Purposes, 28 p., 14 pls.
APPENDIXES
32 Methods to Quantify Seepage Beneath Levee 30, Miami-Dade County, Florida

Appendix I. Lithologic log of well G-3587

[L30-80, site 9, site identification number 255130080291104, prepared by Ronald S. Reese, well completed March 1995, land-surface elevation 

(approximate) - 6 feet above sea level]

Geologic unit and 

Quaternary subaerial 

exposure surface

(Perkins, 1977)

Depth

(feet below

land surface)

Lithology Grain 

size

Permeability

 estimate

Porosity type Description

Q4 No recovery NO DATA Muck

Miami

Limestone 5.0 - 6.0 Calcarenite or 

grainstone Fine Moderate Moldic fine to very fine

Limestone, gray with whitish patches, 

oolitic with fossil fragments, ooids dissolved out, some large vugs filled with 

muck toward the top

Q4 6.0 - 7.0 No recovery NO DATA

Q3 7.0 - 7.5

(fig. 5A) Limestone Fine Very low None to vuggy

Limestone, grayish pink, very dense, well 

cemented, some fine quartz grains, some 

dissolution cavities

 7.5 - 9.0 Sandy 

limestone Fine Low

Intergranular with 

pinpoint vugs 

common

Limestone to sandstone, grayish white; 

well sorted, rounded quartz grains common to predominant, root zone structure

 9.0 - 10.0 Limestone Fine Moderate 

to high

Abundant small 

vugs

Limestone, gray, mottled, becomes broken at base (may be bioturbated), calcarenitic

10.0 - 10.5

Limestone, 

freshwater 

shells

Clay High to 

very high

Large irregular 

vugs

Limestone, gray to grayish brown, fossils 

common in dense matrix, including small 

gastropods, micritic

10.5 - 12.0 No recovery NO DATA

12.0 - 13.5

Limestone, 

freshwater 

shells

Clay Low to 

moderate

Moldic with some 

vugs

Limestone, gray to grayish brown, fossiliferous, clayey, abundant gastropod molds

13.5 - 14.0 Limestone Clay Very low to 

low

Some pinpoint to 

small vugs

Limestone, grayish white, dense, micritic, 

crystal lined vugs, root zone structures, 

grades down into

Fort Thompson 

Formation 14.0 - 16.0 Calcarenite and 

sandy limestone Fine Low to high Intergranular

Limestone, gray, calcarenite, quartz sand 

common in places, churned appearance in 

places, becomes more broken toward 

base, oolitic(?), lost circulation at 14 to 15 

feet

16.0 - 17.0 No recovery NO DATA

17.0 - 18.0

(fig. 5B)

Limestone, 

marine shells Coarse High Abundant moldic and intergranular

Limestone, gray to brownish gray, fossil 

coquina, abundant moldic porosity, gastropods and scallops

18.0 - 20.0

Limestone, 

freshwater 

shells

Clay Moderate Vugs, some large

Limestone, dark-gray to gray, massive to 

mottled, fossiliferous (large gastropods), 

large vertical burrows(?), vugs may not be 

well connected, clayey, micritic, some silt 

and fine sand

20.0 - 20.5 Calcarenite Fine Moderate Intergranular

Limestone, brownish gray, calcarenitic, 

fine grained, micritic, abundant gastropods and clams

20.5 - 22.0 No recovery NO DATA

Q3

22.0 - 22.5 Calcarenite Clay High Vertical vugs 

common

Limestone, mottled light-gray with darkgray patches, vertical or near vertical dissolution features common with infilling of 

dark-gray material as above (18-20 feet), 

matrix is light-gray with fine calcarenite, 

may be some root zone structure
Appendix 33

Q2 22.5 - 23.0 Limestone Clay High Same as above Same as above

Fort Thompson 

Formation

23.0 - 23.5 Limestone, 

marine shells Clay High Same as above Same as above

23.5 - 24.5 Limestone Very fine High Same as above Same as above

24.5 - 25.5 Calcarenite Very fine 

to fine Very high Highly vuggy

Limestone, light-gray, very fine calcarenite, broken into large, irregular, knotty 

chunks, grades into very fine sparite

25.5 - 25.75 Same as above Fine to 

medium Very high Same as above

Limestone, as above, one piece, large 

irregular solution holes, abundant small 

shells and fragments of shells, mostly 

clams

25.75 - 32.0 No recovery NO DATA

32.0 - 33.0

Limestone, 

marine shells to 

calcarenite

Coarse Low Common moldic, 

some large vugs

Limestone, gray to light-gray, calcarenite 

(fine to medium-grained) to shell fragment grainstone, micritic, top foot is relatively dense with whole marine shells

33.0 - 34.0 Same as above Fine to 

medium Moderate Same as above Same as above

34.0 - 34.5 Same as above Coarse High Same as above Same as above

34.5 - 36.5

Limestone, 

freshwater 

shells

Clay Low

Common moldic, 

pinpoint vugs 

common in places

Limestone, gray to brownish gray, mostly 

micrite but some fine-grained calcarenite, 

freshwater gastropods common, large vertical dissolution feature feeds into vertical, curved dissolution surface

36.5 - 37.0 No recovery NO DATA

Q2

37.0 - 37.25

Limestone, 

freshwater 

shells

Clay Very low to 

low

Large vertical 

dissolution features

Same as in 34.5 to 36.5 foot depth interval.

Q1

37.25 - 38.0 Limestone Clay to 

very fine

Very low to 

low Same as above

Limestone, light-gray, micritic to very 

fine grained, dense, may be some sparite, 

root zone structure

38.0 - 40.0

Limestone, 

marine shells to 

calcarenite

Fine to 

coarse

Moderate 

to very 

high

Common moldic

Limestone, gray, shell coquina to shell 

fragment grainstone to calcarenite, fine 

grained with quartz sand has 0.25 foot of 

micrite 0.5 foot from top, which is relatively dense, becomes very broken toward 

base

40.0 - 42.0 No recovery NO DATA

Fort Thompson 

Formation 42.0 - 42.5

Limestone, 

marine shells to 

calcarenite

Coarse High Numerous vugs, 

some large

Limestone, light-gray, similar to 38.0 to 

40.0 foot depth interval, coarse grained, 

micritic, abundant large shell fragments

42.5 - 43.5

Limestone, 

freshwater 

shells to 

calcarenite

Clay to 

very fine Low Moldic

Limestone, brown, micritic, with abundant gastropod molds grading to limestone, light-grayish brown with some 

calcarenite toward base; 3 inches from 

bottom is 0.5 inch thick siltstone bed with 

wavy top and bottom, may be some quartz 

sand above and below it

43.5 - 47.0 No recovery NO DATA

47.0 - 47.25

Limestone, 

freshwater 

shells

Fine Low Moldic

Limestone as in 42.5 to 43.5 foot depth 

interval, grading into calcarenite with 

fine-grained quartz sand

Appendix I. Lithologic log of well G-3587--(Continued)

[L30-80, site 9, site identification number 255130080291104, prepared by Ronald S. Reese, well completed March 1995, land-surface elevation 

(approximate) - 6 feet above sea level]

Geologic unit and 

Quaternary subaerial 

exposure surface

(Perkins, 1977)

Depth

(feet below

land surface)

Lithology Grain 

size

Permeability

 estimate

Porosity type Description
34 Methods to Quantify Seepage Beneath Levee 30, Miami-Dade County, Florida

47.25 - 48.25

Limestone, 

marine shells to 

calcarenite

Fine to 

coarse

High to 

very high

Large vugs 

common

Limestone, light-gray, fine to very coarse 

calcarenite with abundant large shells 

(marine), some well preserved; broken in 

bottom 5 inches

Fort

Thompson 

Formation

48.25 - 49.5 Limestone Clay Low to 

moderate Some large vugs

Limestone, light-chocolate brown, 

micrite, clayey, dense, root zone structure(?) at top, some large near vertical 

vugs, calcarenitic from above filling holes

49.5 - 52.0 No recovery NO DATA

52.0 - 53.5

Limestone, 

marine shells to 

calcarenite

Fine to 

coarse Very high Large vugs

Limestone, gray to gray-brown, shelly 

calcarenite, less shells and more fine 

grained toward base with quartz sand 

common

53.5 - 54.0

Limestone, 

freshwater 

shells

Clay to 

silt Low Moldic

Limestone, light-chocolate brown, silty, 

micritic, abundant gastropods in top half 

and more silty and sandy in bottom half

54.0 - 54.5 Sandy 

limestone

Silt to 

fine Low Intergranular Same as above

Q1 54.5 - 57.0 No recovery NO DATA

57.5 - 58.5

Limestone, 

marine shells to 

sandy

limestone

Fine Low to 

moderate Intergranular

Limestone, dark-gray, sandy to micritic, 

dense, fossiliferous, has solution features 

filled with fine-grained shelly calcarenite

58.5 - 59.5 Calcarenite Coarse Moderate Interparticle

Limestone, dark-gray to brown, conglomerate, abundant large marine shells (broken and transported), sandy matrix, has 

irregular fragments of dark-gray to black 

micritic limestone (?), top surface is irregular and sloping (scour surface?) with 

small coral heads on surface in growth 

position

59.5 - 62.0 No recovery NO DATA

Tamiami 

Formation

62.0 - 62.5

Limestone, 

marine shells to 

calcarenite

Coarse Moderate 

to high Interparticle

Limestone, gray to light-brown, calcarenite, dense, micritic to sparry matrix, bryozoans(?) in places

62.5 - 64.0 Same as above Fine to 

coarse Low Small vugs common

Limestone light- to dark-gray, calcarenite, 

dense, coarsening downward, rock fragment pebbles at bottom

64.0 - 65.5 Same as above Coarse High

Vugs common, 

especially toward 

base

Limestone, dark-gray, conglomerate, rock 

fragment pebbles (black sandy micrite), 

large shells and shell fragments

65.5 - 66.0 Sandy 

limestone Fine High

Large 

interconnected 

vugs

Limestone to sandstone to sand, gray to 

light-brown, mostly fine grained, 

becomes soft and crumbly toward base, 

black pebbles common in places

66.0 - 66.5 Sandstone or 

sand Medium Very high Same as above Same as above

66.5 - 72.0 No recovery NO DATA

72.0 - 74.0 Limestone, 

marine shells Coarse High Very high interparticle

Limestone, gray, coquina, very coarse 

grained, relatively well sorted broken 

shell fragments, fine- to medium-grained 

quartz sand common in places between 

fragments, top 1 inch is very fine grained 

quartz sandstone

74.0 - 77.0 No recovery NO DATA

Appendix I. Lithologic log of well G-3587--(Continued)

[L30-80, site 9, site identification number 255130080291104, prepared by Ronald S. Reese, well completed March 1995, land-surface elevation 

(approximate) - 6 feet above sea level]

Geologic unit and 

Quaternary subaerial 

exposure surface

(Perkins, 1977)

Depth

(feet below

land surface)

Lithology Grain 

size

Permeability

 estimate

Porosity type Description
Appendix 35

Appendix II. Geologic core data for selected intervals, well G-3587

[Data from Core Laboratories Inc. (1995). L30-80, site 9, site identification number 255130080291104, from Core 

Laboratories file DAL-95158, well completed March 1995, land-surface elevation about 6 feet above sea level. 

<, less than the value]

Sample 

No.

Depth interval (feet 

below land surface)

Plug data

Whole core

 porosity

(percent)

Permeability to 

air1

(feet per day)

1Values originally reported in millidarcies.

Porosity2

(percent)

2

Porosity measured on a plug taken from the core.

IV 7.0 - 7.4 <2.44 x 10-7 3.5 Not measured

2V 8.5 - 8.8 0.356 18.2 Not measured

3V 13.3 - 13.9 14.5 18.6 Not measured

4V 17.0 - 17.5 23.2 45.0 47.5

5V 34.0 - 34.4 .478 39.6 36.3

6V 37.3 - 37.8 .888 15.6 Not measured

7V 48.3 - 49.4 1.34 x 10-4 11.2 Not measured

8V 54.2 - 54.4 4.54 30.4 Not measured

9V 58.3 - 58.7 1.68 22.6 Not measured

10V 63.5 - 64.0 6.59 x 10-5 7.2 Not measured
36 Methods to Quantify Seepage Beneath Levee 30, Miami-Dade County, Florida

Depth of plugs for testing

NATURAL GAMMA

(COUNTS)

NATURAL GAMMA

(COUNTS)

RESISTIVITY

(OHM-METERS)

RESIS

(OHM-M

0

G-3587 G-3587 G-3597 G-

0 0 200 100 0 0 

200 250 100 100 200 250 1

20406080

DEPTH, IN FEET BELOW LAND SURFACE

Appendix III. Geophysical logs of wells G-3587 and G-3597