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Report SFRC 93-03 

Water Management in 

Taylor Slough and 

Effects on Florida Bay 

Everglades National Park, South Florida Research Center, P.O. Box 279, Homestead, Florida 33030 
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Water Management in Taylor Slough 

and Effects on Florida Bay 

By 

Thomas Van Lent, Ph.D., P.E. 

Robert Johnson 

Robert Fennema, Ph.D. 

NATIONAL PARK SERVICE 

SOUTH FLORIDA RESEARCH CENTER 

EVERGLADES NATIONAL PARK 

HOMESTEAD, FL 

November 1993 
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Executive Summary 

Current water management practices in the L-31N, L-31 W, and C-ll1 canals have contributed 

to lower groundwater levels and reduced surface water flows in the Rocky Glades and the Taylor 

Slough marshes. The reduced hydraulic gradients and the truncated periods of flow through the 

Taylor Slough basin are thought to be a major factor contributing to the hypersaline conditions and 

abrupt salinity changes in Florida Bay. 

The progressive lowering of L-31N canal stages from 5.5 to 4.3 feet in response to pressure 

from expanding urban and agricultural development has increased drainage from the marshes in 

Everglades National Park into the bordering canal system. If one looks at the entire reach of L-31N 

from the S-335 to S-176, well over 270,000 acre-ft per year are drained from the western marshes 

into L-31N. Approximately 50,000 acre-ft are returned to Taylor Slough, while 180,000 acre-ft are 

dumped into the lower C-1l1 basin. 

If we focus on the Rocky Glades, the historical headwaters of Taylor Slough, only about 60% 

of the water drained from this area is returned as deliveries to Taylor Slough via S-174. Thus, the 

source of water for S-174 water deliveries to Taylor Slough is primarily from drainage of the local 

Taylor Slough headwaters, not from the regional water supply system. 

Prior to 1981 L-31W canal stages were routinely allowed to reach 5.0 feet. With the increasing 

agricultural activities in the Frog Pond, L-31 W has been held at or below 4.5 feet, and L-31 W is 

used frequently to drain water from the Frog Pond and consequently, Taylor Slough. In a typical 

year, L-31W drains 41,000 acre-ft from Taylor Slough, while S-332 pumps 33,000 acre-ft back into 

Taylor Slough. Moreover, since 1984, L-31W has been artificially lowered to accommodate early 

crop planting times in the Frog Pond. The current operational policy for L-31 W represents a net 

loss of water from Taylor Slough, and a net harm to Everglades National Park. 

This report also contains the analyses of water management operations during three representative storm events affecting the C-111 basin. These case studies indicate that the operational policy 

is to convey storm water from L-31N into C-ll1, rather than into Taylor Slough. As a consequence, 

large volumes of water have been quickly lost from the northern part of the system. overdraining the 

wetlands in Shark Slough, the Rocky Glades, and northern Taylor Slough. The diversion of flows 

from Taylor Slough and into the lower C-ll1 basin has necessitated emergency operations of S-176 

and in addition, forced emergency releases through S-197, damaging Manatee Bay. 

The District, the Corps, and the Park have been working steadily toward an agreement on L31N and L-31 W operations. This report represents the Park staff's preparatory analysis for this 

Taylor Slough demonstration project. vVe present the rationale for raising canal stages as well as 

increasing flows to Florida Bay. By increasing water levels in the wetlands upstream of Florida 

iii 
Bay, more of the water put into Taylor Slough and C-ll1 will actually make it into the Bay. This is 

because if upstream water levels are low, much of the discharges into Taylor Slough will be consumed 

as evapotranspiration and groundwater recharge; if upstream levels are high, then discharges into 

Taylor Slough will immediately bep;in to move downstream as sheet flow. Given the limits to water 

availability, the surest way to increase flows to Florida Bay is to raise stages in the upstream marshes. 

The complete recommendations are found in Chapter 6 on page 75. 

IV 
Abstract 

Taylor Slough has historically been a major contributor of fresh water to Florida Bay. Since 1982, 

progressive lowering of canal stages in and near the headwaters of Taylor Slough has lowered water 

levels throughout southern Dade County, and probably reduced freshwater flow to Florida Bay. The 

primary purpose of this report is to inform Everglades National Park management about the effects 

of changing water management in the L-31N, L-31W and C-111 canal systems on the Park's water 

resources. The report also provides some recommendations on how to protect and improve the 

Park's water resources. 

The analysis is split into six parts. First, we document the operational rules of the water control 

structures along the eastern boundary the Park, along with their evolution, and their effect on 

water levels and flows in and near the Park. Second, we develop water budgets for the canals 

near the Park's eastern boundary, and demonstrate how current operational policies have resulted 

in significant drainage of 'the marshes west of L-31N and L-31 W. Thirdly, we examine the Flood 

Control Project during several wet periods, documenting operations to divert water from Taylor 

Slough into C-l11. Fourth, we look at salinity in Florida Bay and how fresh water inflows affect 

the pattern of salinity. Fifth, we apply the Natural System Model and the South Florida Water 

Management Model to estimate freshwater flows to Florida Bay and how increasing canal stages will 

modify the inflow regime. Lastly, the report concludes with recommendations for water resources 

management to be pursued by Everglades National Park. 

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Acknowledgments 

The authors wish to thank Gordon Anderson, who was responsible for developing the salinity maps 

seen in Chapter 4. Thanks to Gerald Giese of the USGS for his helpful and thorough comments. 

Jim Vearil and Chris Smith of the Corps of Engineers and Ron Mireau of the Sough Florida Water 

Management District provided oral comments. Our particular thanks to Freddy James for his 

organization of the hydrologic data, his calculation of flow volumes and average stages, and especially 

for the development of most of the maps used in this report. 

Claudite iam riVQS, pueri; sat prata biberunt. 

Virgil, Eclogue, iii 111 

Vll 
Contents 

Executive Summary 

Abstract ..... . 

Acknowledgments. 

1 Background 

1.1 The Water Management System ................... . 

1.1.1 Congressional Authorizations and Corps' Design Documents. 

1.1.2 Early Canal Construction in Southwestern Dade County. 

1.2 The South Dade Conveyance System . . . . . . 

1.3 Chronology of Improved ENP Water Deliveries 

1.3.1 Factors Leading to the Experimental Water Delivery Program 

1.3.2 Establishment of the Experimental Water Delivery Program. 

1.3.3 Artificial Canal Drawdowns/the Frog Pond Agreements 

1.3.4 The Experimental Three Party Agreements 

2 Operations in L-31N, L-31W, and C-ll1 

2.1 Operation of the L-31N canal ..... 

2.1.1 Stages in L-31N South of S-331 

2.1.2 Stages in L-31N North of S-331 

2.1.3 Effects of L-31N on the Rocky Glades 

2.1.4 Water Budget of L-31N ....... . 

2.1.5 Supplemental Inflows to the South Dade Conveyance System 

2.1.6 Summary of L-31N analysis 

2.2 Operation of L-31 W ....... . 

2.2.1 Stages in the L-31W canal . 

2.2.2 L-31 W water budget . . . . 

2.2.3 Summary of L-31 W analysis. 

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2.3 Operation of the C-1l1 Canal ......... . 

3 Operation of the SDCS during Storm Events 

3.1 Wet Season, 1988 ................ . 

3.2 Canal Operations and the C-111 Interim Project 

3.2.1 Wet Season Operations 

3.2.2 Dry S<!ason Operations 

3.3 Canal Operations ann the Taylor Slough Demonstration Project 

4 Salinity in Florida Bay 

4.1 Project Flows .... 

4.2 Florida Bay Salinity 

5 Modeling of Flow to Florida Bay 

5.1 Surface Water Flow Comparisons 

5.2 Comparison of Ponded Water 

5.3 Groundwater Flow 

6 Recommendations 

References 

A Calculations 

A.1 Water Budgets 

A.I.1 Data Summaries 

A.2 Calculation of Groundwater Seepage 

A.3 Flow at Context Road . . . . . . . . 

A.3.1 Comparisons of Context Road and S-l73 Stages 

A.3.2 Stage vs. Discharge Relations at Context Road 

B Documents 

C Raw Data 

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60 

63 

63 

65 

69 

69 

70 

73 

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A.2 

A.2 

A.2 

A.17 

A.20 

A.20 

A.24 

B.l 

C.l 
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List of Tables 

1 Canal operational settings for selected C-l11 water control structures. . 

2 Canal operational settings for the L-31W water control structures ..•. 

3 Canal operational settings for selected L-31N water control structures. 

A.l Flow data at S-18C. 

A.2 Flow data at S-173 .. 

A.3 Flow data at S-174 .. 

AA Flow data at S-175 .. 

A.5 Flow data at S-176 .. 

A.6 Flow data at S-194 .. 

A.7 Flow data at S-196 .. 

A.8 Flow data at S-197 .. 

A.9 Flow data at S-331. . 

A.I0 Flow data at S-332 .. 

A.11 Flow data at S-334 .. 

A.12 Flow data at S-335 .. 

A.13 Flow data at S-336 .. 

A.14 Flow data at S-338 .. 

A.15 Annual Inflow and outflow summary for the northern reach of L-31N. 

A.16 Average Stages for selected gages in the northern L-31N basin. 

A.17 Average Stages for selected gages in the southern L-3IN basin. 

A.18 Average Stages for selected gages in the L-31W basin. 

A.19 Measured flow volumes at Context Road. 

A.20 Estimated flow volumes at Context Road. 

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A.S 

A.6 

A.7 

A.8 

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A.lO 

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A.12 

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A.14 

A.IS 

A.16 

A.17 

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A.19 

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A.26 

A.27 
List of Figures 

1 Base Map. . . . . . . . . . . . . 2 

2 Map of the L-31N borrow canal. 18 

3 Stage at S176 headwater. 19 

4 Stages at G-596. ..... 20 

5 Stages at G-596 for the years 1977-1990. . 21 

6 Stage in the L-31N northern reach. . . . 22 

7 Monthly flow volumes at Context Road. 24 

8 Average monthly flow volumes at Context Road. 25 

9 Comparison of annual inflows and outflows to L-31N between S-335 and S-176. 26 

10 Comparison of annual inflows and outflows to L-31N between S-335 and S-331. 27 

11 Estimated regional groundwater gradients in the vicinity of L-31N. . . . . . . . 28 

12 Summary of the average annual water budget for the northern reach of the L-31N canal. 30 

13 Comparison of annual inflows and outflows to L-31N between S-331 and S-176. 31 

14 Estimated regional groundwater gradients in the vicinity of L-31N. 32 

15 Summary of the average annual water budget for the L-31N canal. 33 

16 Comparison of L-31N outflows to deliveries during the dry season. 

17 Comparison of L-31N outflows to deliveries during the wet season. 

18 Comparison of wet and dry season pumping at S-331. 

19 L-31W and vicinity. . ...... . 

20 Stages in the L-31 W borrow canal. 

21 Comparison of stages in L-31W to flows at S-175 .. 

22 Comparison of surface water inflows to surface water outflows in L-31W .. 

23 Average groundwater stages in the vicinity of L-31W. . ...... . 

24 Summary of the average annual water budget for the L-31W canal. . 

25 The basemap of the C-111 Basin .. 

26 Stages at the headwater of 8-177 .. 

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46 

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27 Water Budget for the C-111 canal between S-I77 and S-18C. . 48 

28 Stages in the L-31N basin from July, 1988 to November, 1988. . 51 

29 Total flow volumes in the L-31N borrow canal during August, 1988. 53 

30 Cumulative inflows and outflows L-31N from July, 1988 to November, 1988. 54 

31 Operations of L-31N in June-July, 1992 56 

32 Operations of L-31W in June-July, 1992 57 

33 Operations of L-31N in October-November, 1992 59 

34 Operations of L-31W in October-November, 1992 . 61 

35 Discharges to Taylor Slough and the Eastern Panhandle after Hurricane Floyd, October 12, 1987. .. . . . . . . . . . . . . . . . . 64 

36 Salinity contours 1 day after Hurricane Floyd. . 65 

37 Salinity contours 9 days after Hurricane Floyd. 66 

38 Salinity contours 17 days after Hurricane Floyd. 67 

39 Comparison of calculated surface water flows into southern Taylor Slough and Florida 

Bay. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 70 

40 Average annual hydrographs for surface water flows into southern Taylor Slough and 

Florida Bay. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 71 

41 Comparison of ponded water depths between the managed system and the predrainage condition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

42 Flow direction and magnitude for groundwater in the C-111 drainage basin. 

A.l Temporal Comparison of stages at Context Road and S-176 .. 

A.2 Comparison of stages at Context Road and S-176. . ..... 

A.3 Comparison of estimated and measured stages at Context Road. 

AA Stage vs. Discharge Relation for Context Road. . . . . . . . . . . 

A.5 Comparison of calculated and measured discharges at Context Road. 

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74 

A.21 

A.22 

A.23 

A.24 

A.25 

Chapter 1 

Background 

Taylor Slough has historically been a major freshwater source for Florida Bay. This slough, encompassing more than 158 square miles of freshwater marsh, extends some 20 miles from its upstream 

end north of the Frog Pond to the coastal mangrove fringe along central Florida Bay. The headwaters 

of the slough originate in the Rocky Glades, which forms the hydrologic divide between Shark Slough 

and Taylor Slough. As seen in Figure 1, the largest portion of Taylor Slough and its headwaters are 

located within Everglades National Park, and they represent vital elements of the Park's hydrologic 

system. Besides being a freshwater source for Florida Bay, Taylor Slough and the Rocky Glades are 

critical habitat to several endangered species, and areas essential to the Park's ecosystem. 

The purpose of this report is two-fold. Its primary intent is to inform Park management about 

the effects of past water management practices on the water resources of Everglades National Park. 

The report lays the foundation for a staff recommendation that Park management seek higher canal 

stages, as well as modifications of surface water flows on the eastern periphery of the Park. The 

secondary purpose of this report is to document our examination of the historical hydrologic record. 

This should serve as a baseline for subsequent modeling and analysis of the effects of modifications 

in water management practices in the Taylor Slough, Shark Slough, and lower C-1l1 basins. 

Concern about the decline of Florida Bay has brought the question of water management practices 

to the forefront. The freshwater inflows to Florida Bay are now largely controlled by the Central 

and Southern Florida Project (Project), which is operated by the South Florida Water Management 

District (District). The construction and operation of this complex system of canals and levees has 

brought considerable changes in the hydrologic regime of Taylor Slough and the Rocky Glades. 

Prior to the construction of the Project in western Dade County, water levels in the Taylor 

Slough headwaters were 1.5 to 2.5 feet higher than today [Johnson and Fennema, 1989J. These 

higher water levels kept the northern Taylor Slough marshes inundated for 2 to 3 months each 

1 
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L-67 

EXT 

EVERGLADES 

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CHAPTER 1. BACKGROUND 

Figure 1: Location of Taylor Slough, Florida Bay, and the South Dade Conveyance System. 
1.1. THE WATER MANAGEMENT SYSTEM 3 

year, and sustained sheet flow and groundwater How ,into Florida Bay. The higher water levels 

also maintained more persistent and gradual surface water flows into the downstream wetlands and 

estuary, which presumably produced more gradual salinity fluctuations in the nearshore areas of 

Florida Bay. 

1.1 The Water Management System 

One can conceptually break the ,later management system affecting Taylor Slough and the downstream areas of Florida Bay into three components. The first component is the levees and canals 

forming the Water Conservation Areas (WCAs). The southern-most WCAs are WCA 3A and 3B, 

located just north of Shark Slough along Tamiami Trail. The WCAs were designed to impound and 

store wet season runoff, and control the sheet flows that historically flowed through the Everglades. 

The objective of the Project was primarily twofold: 1) to create a continuous levee system to protect 

the Lower East Coast from the endemic flooding of the Everglades, and 2) to create water supply 

reservoirs for urban and agricultural development. The second component affecting Taylor Slough 

and Florida Bay, and most important to this analysis, is the L-31N, L-31W, and C-111 canal system 

of western Dade County. This canal system captures wet season runoff from the western portion 

of Dade County, and directs these flows southward and westward into Barnes Sound and Florida 

Bay (Figure 1). During the early 1980's, an additional set of water control structures was added to 

this canal system to form the South Dade Conveyance System (SDCS). These modifications were 

added for the purpose of conservation and conveyance of additional dry season water deliveries to 

the eastern portion of Everglades National Park, and for expanding urban and agricultural needs in 

southern Dade County. The third component is the network of canals in the developed portion of 

eastern Dade County. These canals were originally build for drainage, but are now used for water 

supply, flood control, and to control saltwater intrusion. This report concentrates on the effects of 

the L-31N, L-31W, and C-111 canals, since these canals most directly affect Northeast Shark Slough, 

Taylor Slough, and inflows into Florida Bay. 

1.1.1 Congressional Authorizations and Corps' Design Documents 

To ascertain the intent of Congress and to understand how the Project was designed, one must examine the Army Corps of Engineers design documents and record of Congressional action. An excellent 

summary of all of the Project authorizations and features is provided in the Corps of Engineers 1991 

Master Water Control Manual, Volume 1, Authorities and Responsibilities [U.S. Army Corps of Engineers, 1991]. In addition, the Corps has developed a Water Control Plan specifically for the Water 
4 CHAPTER 1. BACKGROUND 

Conservation Areas, Everglades National Park, and the South Dade Conveyance System [U.S. Army 

Corps of Engineers, 1992]. The system of canals and water control structures that deliver surface 

water to the Shark Slough basin were primarily constructed as outflow structures for the Water 

Conservation areas and were authorized by the Flood Control Act of 1948 (PL 80-858). The specific 

design plans and operational objectives of these structures were described in the General Design 

Memorandum (GDM) for Water Conservation Area No.3 [U.S. Army Corps of Engineers, 1960c], 

and in the Detailed Design Memorandums (DDM) for Levees 67 A and 29, Section 3 [U.S. Army 

Corps of Engineers, 1960a], and Levee 29, Sections 1 and 2 and the S-12 Structures [U.S. Army 

Corps of Engineers, 1960b]. 

Several different Congressional acts authorized the canals and control structures that deliver 

water to the eastern basins of the Park. The L-31N levee and associated borrow canal were authorized 

by the Flood Control Act of 1948, as part of the Eastern Protective Levee System. The Flood Control 

Act of 1954 (PL 83-780) authorized construction of the L-31W canal and levee. The Flood Control 

Acts of 1954 and 1962 (PL 86-645) authorized construction of the C-111 canal and levee system and 

improvements to several of the south Dade coastal canals. 

Other more general Congressional Acts affecting the Park include the Flood Control Act of 1968 

(PL 90-483) which authorized construction of the South Dade Conveyance System. The 1968 Act 

specifically directed the Corps of Engineers to modify the existing C&SF Project features for the 

purpose of conserving and conveying additional water supplies for Everglades National Park, and 

expanding agricultural and urban needs. The Minimum Delivery Schedule for Everglades National 

Park was authorized as part of the River Basin Monetary Authorization Act of 1970 (PL 91-282). The 

Supplemental Appropriations Act of 1983 (PL 98-181) modified the schedule of Minimum Deliveries 

to the Park and authorized the Experimental Program of water deliveries to ENP. This experimental 

program was extended two times under the authority of PL 99-190 and PL 100-676. Finally, the ENP 

Protection and Expansion Act of 1989 (PL 101-229) authorized construction of Project modifications 

to improve water deliveries to Shark Slough and to restore more natural hydrological conditions 

within Everglades National Park. 

The design plans and operational objectives for the L-31N, L-31W, and C-ll1 canals and their 

control structures have gone through numerous modifications over the years. The overall operational 

plans for these canals and structures were first described in the Survey Review Reports for South 

Dade [U.S. Army Corps of Engineers, 1961] and Southwest Dade Counties [U.S. Army Corps of Engineers, 1963b]. During the late 1950s through the early 1970s, the Corps prepared three GDMs for 

the study area: (1) Levee 31 and Related Works [U.S. Army Corps of Engineers, 1959], (2) for all of 

South Dade County [U.S. Army Corps of Engineers, 1963c] and (3) for the Conveyance Canals to Everglades National Park and South Dade County [U.S. Army Corps of Engineers, 1973]. In addition, . 
\ 

1.1. THE WATER MANAGEMENT SYSTEM 5 

in 1975 a separate Environmental Impact Statement was prepared for the South Dade conveyance 

canals and the plan for East Coast backpumping [U.S. Army Corps of Engineers, 1975]. Finally, a 

series of Detailed Design Memorandums (DDMs) for the specific reaches and control structures in 

the L-31N, L-31W, and C-ll1 canals were released including: (1) the DDM for Section 1 (lower portion) of the C-1l1 Canal and Control Structure 18C [U.S. Army Corps of Engineers, 1963a], (2) the 

DDM for Sections 2 and 3 of the C-ll1 Canal and Control Structures 176, 177, and 178 [U.S. Army 

Corps of Engineers, 1965], (3) the DDM for the L-31N Canal and Control Structure 173 [U.S. Army 

Corps of Engineers, 1966], (4) the DDM for the L-31W Canal and Control Structures 175 and 175 

[U.S. Army Corps of Engineers, 1967], (5) the DDM for the enlargement of the L-31N Canal, C-1, 

C-103, and Pumping Station 331, built as part of the South Dade Conveyance System [U.S. Army 

Corps of Engineers, 1973], and (6) the DDM for the enlargement of L-29 and L-30, Pumping Station 

332, and Control Structures 194 (modifications), 333, 334, 335, 336, and 338, built as part of the 

South Dade Conveyance System [U.S. Army Corps of Engineers, 1974]. 

1.1.2 Early Canal Construction in Southwestern Dade County 

The original plan of improvement for southwestern Dade County was presented in the Survey Review 

Report for South Dade County [U.S. Army Corps of Engineers, 1961]. The plan called for gravity 

drainage of an area of 227 square miles of southwestern Dade County using a system of 12 primary 

canals. Although the Corps found that the natural drainage in the western portion of south Dade 

was to the southwest (into Taylor Slough), gravity drainage primarily to the south and east (into 

Florida Bay, Barnes Sound, and Biscayne Bay) was found to be most practical. The General Design 

Memorandum (GDM) for South Dade County [U.S. Army Corps of Engineers, 1963c] provided the 

specific design elements for the water management features of southwestern Dade County. The plan 

was designed to provide the area with flood protection up to 40% of the Standard Project Flood 

(SPF), or roughly, a flood event with a 10% chance of occurring in any given year. Runoff from 

the area east of L-31N and north of Homestead was to be drained to Biscayne Bay via six proposed 

canals (C-101 through C-106). The area south of Homestead was to be drained southward into 

Florida Bay and Barnes Sound via six proposed canals (C-107 through C-1l2). During the project 

review, the National Park Service wrote correspondence to the Corps concurring with the plan for 

eastern Dade County, but the Service requested that the area west and northwest of Homestead be 

drained westerly into Everglades National Park. These Park Service objections led to design and 

construction of L-31 W. The Park Service also objected to the southerly extension of the C-llO, CIll, and C-1l2 canals to tidewater, and requested that the canals be terminated at the one- foot 

contour to promote sheetflow. 
6 CHAPTER 1. BACKGROUND 

In response to the written comments of the National Park Service, the Flood Control District, 

and local land developers, the 1961 plan was modified in the 1963 GDM for south Dade County. 

Everglades National Park asked that all excess water west of the divide on the Coastal Ridge be 

drained westward into Taylor Slough. The motivation was to offset the drainage effects of the C&SF 

Project. This was the specific reason why the L-31W canal was added to the 1963 GDM. The works 

were constructed so that, during the design storm, approximately 28 square miles of land east of 

L-31N and west of the Seaboard Airline Railroad would be drained westward into Taylor Slough via 

L-31 W canal. During smaller storms, the contributing areas was expected to increase, and extend 

eastward as far as 5-165 and S-167 (near U.S. Highway 1.) The L-31W levee was build to protect 

the developed areas to the from inundations from Taylor Slough. The Frog Pond agricultural area 

was to be protected by the C-ll1 canal to the east, and further drainage was expected in the form 

of a locally operated, interior drainage system [U.S. Army Corps of Engineers, 1963bl. 

The earliest canal construction in western Dade County began in 1951, with the construction of 

the L-30 and the northern portion of the L-31N canal and levee systems. The levees were built as 

part of the Eastern Protective Levee System, to protect the populated east coast from Everglades 

flooding. In 1961, construction began on the L-29 canal and levee system; its completion in 1962 

largely finished the closure of Water Conservation Areas 3A (WCA 3A) and WCA 3B along the 

northern Park boundary. Initially, there was no surface water connection between the L-29 canal 

and the canal systems making up the western boundary of the urban and agricultural areas (L-30 

and L-31N). Therefore, L-30 and L-31N had no significant flood control or water supply capabilities. 

In 1965, construction began on the remainder of the L-31N canal system. The 1963 GDM 

specifically recommended that the L-31N canal be used "to provide southerly drainage to ENP in 

Taylor Slough for the westerly portion of south Dade County". The benefits of maintaining optimum 

canal stages in these areas was also well known, and structures S-165, S-166, S-167, S-177 and S-178 

were built to maintain groundwater levels as high as possible to promote water conservation. During 

1965, several of the coastal canals (C-1, C-102, and C-103) were extended westward and connected 

to the L-31N canal to improve flood protection for the extreme western agricultural areas and to 

allow for water supply to these basins. The S-173 control structure was added to divide the L-31N 

canal into two reaches: the reach north of S-173 was designed to drain eastward via C-4 and C-1 W, 

while the reach south of S-173 drained southward and westward into the L-31W and C-ll1 canal 

systems. 

The first proposed operating criteria for the southern reach of L-31N and L-31 W canals were 

described in an Army Corps of Engineers letter to the Flood Control District in 1966. At that time, 

the intention was that S-175 and S-176 would remain closed under normal conditions, and L-31N 

would be held as high as 6.5ft msl to promote the discharge of water into L-31W via S-174. Water 
1.2. THE SOUTH DADE CONVEYANCE SYSTEM 7 

would then spill overbank from L-31 W canal into Taylor Slough. Under flood conditions, up to 500 

cfs would be discharged into L-31W via S-174 and out S-175, to maximize Taylor Slough inflows. 

The final authorized operating criteria were modified in the 1967 DDM for the L-31W canal. Under 

these criteria, water would be discharged into the L-31W canal whenever the S-174 headwater stage 

exceeded 5.3ft msl. Structure 176 would remain closed until its headwater stage exceeded 5.5ft msl, 

again to maximize flows into Taylor Slough. Structure 175 was designed to remain closed until its 

headwater stage rose above 4.5 feet [U.S. Army Corps of Engineers, 1967]. When S-332 was added in 

1983, the pump station was authorized to be operated according to the monthly Minimum Delivery 

Schedule, or up to its maximum capacity, with the concurrence of the Corps, the District, and the 

Park. 

In f968 the Corps of Engineers began construction on the L-31 W canal and control structures 

S-174 and S-175. This canal was designed specifically to provide an outlet for a portion of the L-31N 

flood waters and to convey flow to replenish the freshwater supply to the Taylor Slough area of the 

Park. Structure 174 was designed to "maintain optimum water levels up to 6.5 feet in the L-31N 

borrow canal, and discharge up to 500 cfs into the L-31 W borrow canal". Structure 175 was designed 

to "maintain optimum water levels up to 5.0 feet and provide a means of either diverting the borrow 

canal discharge overland into Taylor Slough, or passing it south to be distributed overland from the 

borrow canal south of State Road 27". At this time the system still lacked a direct connection with 

the WCAs, and did not have water control structures capable of moving significant quantities of 

water into southern Dade County. 

1.2 The South Dade Conveyance System 

Concerns by Everglades National Park that more freshwater was needed for Taylor Slough and the 

downstream areas of Florida Bay prompted Congress to authorize construction of the South Dade 

Conveyance System (SDCS) as part of the Flood Control Act of 1968. The conveyance canal system 

was designed to provide supplemental water supply from \Vater Conservation Area 3A to a 524 

square mile area of Dade County, including the Taylor Slough and Eastern Panhandle drainages of 

the Park. The GDM for Conveyance Canals to Everglades National Park and South Dade County 

[U.S. Army Corps of Engineers, 1973] noted that the period from November through May of each 

year was normally a period of insufficient rainfall in south Dade, and that additional dry season 

water deliveries would be required. The Corps also identified the importance of maintaining optimum 

canal stages in the L-31N canal, stating that "deficient water levels in this area create a gt:0undwater 

gradient from adjacent Shark Slough, thereby diverting water that would normally be destined for 

Everglades National Park". In 1975, the Corps completed an Environmental Impact Statement for 
8 CHAPTERl. BACKGROUND 

the SDCS and for the proposed plan for East Coast backpumping [U.S. Army Corps of Engineers, 

1975]. 

The first phase of the SDCS was completed in 1978 with construction of structures 333 and 334 

in the L-29 canal (see Figure 1). The 8-332 pump station in the L-31 W canal was constructed next, 

and it became operational in 1980. The SDCS was finished in 1983; L-31N was enlarged and pump 

station S-331 was completed making the South Dade Conveyance System fully operational. This 

pump station was placed next to the 8-173 divide structure, giving the District the ability to move 

significant volumes of water from the northern end of L-31N into the southern end. All of these 

structural changes were designed to provide additional dry season water delivery capabilities to the 

L-31N and L-31 W canals. 

The Corps estimated that the dry season supplemental flow requirements to the SDCS were 

318,500 acre-feet annually. This represents the average annual inflows that would need to be made 

to the northern reach of the L-31N canal system. Average annual dry season water supply pumping 

needed at S-331 was estimated to be 264,800 acre-feet. Of this amount, a minimum of 55,000 acrefeet would be provided to the Taylor Slough and Eastern Panhandle portions of Everglades National 

Park to meet the Congressionally mandated Minimum Delivery Schedule, which went into effect 

in October 1970 [U.S. Army Corps of Engineers, 1973]. Prior to the construction of S-331, the 

southward movement of water down the L-31N canal was limited to 100 cfs due to the capacity 

of structure S-173. This limited capacity was intentional, since S-173 was constructed as a divide 

structure. Structure 173 was designed to remain closed during flood events, and operated only 

during low water periods. Since the completion of pump station S-331, this operational plan has 

been altered and the S-331 pump station is now routinely used routinely during the wet season to 

provide additional flood protection for the developed areas west of L-31N. 

The Project works in western Dade County were originally designed under the assumption that 

most of the southern C-1ll basin would be undeveloped, and that the land use in the northern developed areas would be primarily seasonal agriculture [U.S. Army Corps of Engineers, 1961]. Canal 

water levels were designed to remain relatively high during the wet season, and were expected to 

recede naturally throughout the dry season. In contrast, expanding urban and agricultural development into the lower-lying areas of western Dade County has pressured the District and the 

Corps to steadily lower water levels in the L-31N, L-31\,y, and C-111 canals over the past 20 years. 

Tables 1-3 provide summaries of the initial operational settings for the control structures in the 

L-31N, L-31W, and C-111 canals and a history of the changes in these operational stages since the 

mid 1960s. Note that wet season water levels at S-176 were approximately 1.2 feet lower than the 

initial design settings. Reduced wet season canal stages at S-176 has lowered water levels in the 

adjacent Rocky Glades l~ading to the drainage of this important wetland system. Since the L-31N 
1.3. CHRONOLOGY OF IMPROVED ENP WATER DELIVERIES 

Date S-176 S-177 Comments 

open static close open static close 

8/65 6.7 6.0 5.8 5.2 4.3 4.1 Design settings (from DDM) 

7/67 6.0 5.5 5.3 4.7 4.5 4.3 Initial settings (op. logs) 

10/67 5.5 5.3 5.0 4.5 4.3 4.0 Unknown reason for change 

6/82 5.0 4.7 4.5 4.2 3.9 3.6 Interagency Agreement 

8/84 4.5 4.3 4.1 4.0 3.8 3.5 NESS 30-day test 

10/84B 3.5 3.3 3.1 Frog Pond draw'rlown test 

3/85° 5.0 4.8 4.6 3.5 3.3 3.1 NESS 2 year test, dry season 

7/85 4.5 4.3 4.1 4.2 3.9 3.6 NESS 2 year test, wet season 

aThe Frog Pond drawdowns continued for 3 additional years (1985-1987) as part of the NESS 

delivery test agreement between the District and the South Dade Farmers. 

bThe Northeast Shark Slough (NESS) experimental water delivery program has continued beyond the original 2 year test under PL 102-229. The wet and dry season operational stages have 

remained the same for the last seven years. 

9 

Table 1: Canal operational settings for selectedwater control structures in the central C-ll1 basin. 

Stages are referenced to ft NVGD. The "open" refers to stages when gates are opened, "close" refers 

to levels when gates are closed, while "static" is the design optimum stage. 

canal system cuts through the Rocky Glades, management of water levels in this reach of the canal 

system largely controls the water levels and inflow volumes to the downstream areas of the Taylor 

Slough basin. 

Note that the initial lowering of operational stages in the L-31N canal occurred in June 1982, 

apparently in response to pressure by urban and agricultural interests in the East Everglades following the flooding caused by Tropical Storm Dennis in August 1981. To our knowledge, there are 

no assessments of the environmental effects of reduced canals stages were made at the time of this 

operational change. In this report, we document the detrimental effects that these lower canal levels 

have had on the resources of Everglades National Park. 

1.3 Chronology of Improved ENP Water Deliveries 

A chronology of events leading to the current iteration of the Experimental Water Delivery Program 

should clarify how operations of the C&SF Project by the Corps and the District has unfolded in 

response to various legistative directives and legal actions. Here, we review the authorizations and 

major operational programs affecting Taylor Slough since 1980. 
10 

Date S-174 

open static 

11/67 5.7 5.5 

3/68 5.5 5.3 

7/71 5.8 5.5 

6/82 4.9 4.5 

8/83 5.0 4.7 

10/84a 

3/85b 5.2 4.9 

7/85 4.7 4.5 

a Same as in Table 1. 

bSame as in Table 1. 

CHAPTER 1. BACKGROUND 

S-175 Comments 

close open static close 

5.3 5.0 Design settings (from GDM) 

5.1 4.5 FCD recommendations 

5.1 4.5 Initial settings (op. logs) 

4.4 4.5 Interagency Agreement 

4Ji 4.5 No reason known 

3.5 Frog Pond drawdown test 

4.7 3.5 NESS 2 year test, dry season 

4.3 4.5 NESS 2 year test, wet season 

Table 2: Canal operational settings for the L-31 W water control structures. 

1.3.1 Factors Leading to the Experimental Water Delivery Program 

Following the implementation of the Minimum Delivery Schedule in 1970, the Park completed a 

number of research studies describing problems that were believed to be related to the inadequacy 

of the fixed monthly water delivery allocations and the impacts of large regulatory flows through 

the S-12 structures. A request by the National Park Service prompted the Senate Committee on 

Environment and Public Works and the House Committee on Public Works and Transportation to 

pass two resolutions in April 1978, to reexamine the practice of providing inflows to the Park. The 

resolutions specifically directed the Corps to examine the operation of the C&SF Project to allow 

for the redistribution of surface water flows back into the northeastern portion of Shark Slough, that 

would more adequately meet the environmental needs in Everglades National Park. The resolutions 

further state that "the investigation shall include, but not be limited to, consideration of structural 

and other appropriate measures to improve the future environmental condition of the Park with 

special regard to providing adequate supply and distribution of water with an acceptable quality to 

the Everglades National Park." 

In August and September of 1981, two extreme rainfall events produced extensive flooding in 

western Dade County, particularly in the unprotected East Everglades area west of L-31N. In June 

of 1982, District lowered the operating criteria in the L-31N canal. It is our understanding that 

this occurred in response to threats of lawsuits by landowners in the East Everglades/south Dade 

area. These changes marked the start of a long period of operational adjustments in the canals that 
1.3. CHRONOLOGY OF IMPROVED ENP WATER DELIVERIES 11 

II S-331/S-173 Water Supply Modea II II 8-331/8-173 Flood Control Modeb II 

Begin pumping when stages drop Pumping based upon water level 

below: at Angel's well 

Structure (HW) Critical Angel's 8-331 HW 

8-174/8-176 4.0 < 6.0 5.0 

8-177 /S-175 3.0 > 6.0 4.5 

8-194/8-196 4.0 Downstream control elevations 

can limit 8-331/8-173: 

8tructure (HW) 8tage 

8-174/8-176 >6.0 

8-177 > 4.3 

8-175 > 5.0 

8-18C > 3.3 

II 8-334/8-335 Water 8upply Mode \I II 8-334/8-335 8tage Maintenance Mode II 

Make releases when stages drop When water supplied not needed, release 

below: to maintain optimum: 

8tructure (HW) Critical 8tructure (HW) Optimum 11aximum 

8-331 3.5 8-334 6.0 7.2 

8-25B/8-22 2.8 8-335 6.0 

a Original operational criteria. 

bSupplemental criteria added as part of 2-year test NESS agreement. 

Table 3: Canal operational settings for selected L-31N water control structures. 
12 CHAPTER 1. BACKGROUND 

boarder the eastern portion of the Park. In September 1982, the Corps completed a draft feasibility 

study and draft Environmental Impact Statement (EIS) for Shark River Slough, as directed in the 

1978 House and Senate Resolutions [U.S. Army Corps of Engineers, 1982]. This was the first official 

document describing the plan to restore surface water flows to the Northeast Shark Slough basin. 

The report was focused directly on the question of the feasibility of using S-333 to mitigate extreme 

high water events in ENP and the redistribution of surface water flows to the full width of the Shark 

Slough flow section. 

In March 1983, following a period of record rainfall and extremely high dry season flows through 

the S-12 structures, the Park presented a Seven Point Plan to the SFWMD Governing Board calling 

for immediate relief from these regulatory releases. The plan called for diverting excess surface 

water flows into Northeast Shark Slough through the use of S-333, construction of new water control 

structures in the L-28 Levee to pass surface water from WCA 3A into the Big Cypress National 

Preserve, installing plugs in the L-67 extension canal to promote sheet flow, and the immediate 

development of an improved water delivery schedule for Shark Slough, based on a more natural 

rainfall-runoff relationship. In late March 1983, the SFWMD and the Corps approved the temporary 

use of S-333 to mitigate severe high water problems in ENP. Structure 333 remained open until the 

middle of June, when concerns were raised related to the potential of increased flooding in the 

East Everglades. Structure 331 flood control operations began in June 1983, prior to our efforts 

to reintroduce surface water flows into Northeast Shark Slough. These operations were not an 

authorized element of the original structure's design. Clearly, the mandate for the South Dade 

Conveyance System, under which S-331 was built, was for water supply and did not include a flood 

control element. 

In June 1983, the Corps, the District, and the Park agreed to establish a field test of improved' 

water deliveries into the western portion of the Shark Slough basin. A Flow Through Plan was 

adopted which established a free flow system of water from WCA 3A into western Shark Slough. 

During the first year, the S-12A, B, and C structures remained open full (S-12D was closed while 

plugs were being installed in the L-67 extension canal). During the second year, ftee flow occurred 

through all of the S-12 structures. The Flow Through Plan produced high sustained flows into 

western Shark Slough throughout the test period and allowed for a more natural dry season recession. 

The plan was discontinued in 1985 because the combination of below normal rainfall and uncontrolled 

flows at the S-12s depleted the water storage capabilities of WCA 3A. 
1.3. CHRONOLOGY OF IMPROVED ENP WATER DELIVERIES 13 

1.3.2 Establishment of the Experimental Water Delivery Program 

In November 1983, Congress passed PL 98-181 authorizing the program of experimental water 

deliveries for Everglades National Park. This enabled the establishment of a series of iterative field 

tests to collect hydrologic and ecologic data, with the ultimate goal of developing optimum water 

delivery plans for ENP. Public Law 98-181 further authorized the Secretary of the Army to acquire 

interest in agricultural lands threatened by the program, and to construct necessary flood protection 

measures in the East Everglades. The Law also required that each iteration would be conducted 

by agreement between the Corps of Engineers, the SFWMD, and ENP, and would not significantly 

impact residential and agricultural interests in the East Everglades. 

Throughout 1983, the SFWMD had been negotiating with representatives of the south Dade 

farmers to establish an agreement to allow for the reintroduction of surface water flows into Northeast 

Shark Slough. In January 1984, the, Corps completed an Environmental Assessment (EA) and 

issued a Finding of No Significant Impact (FONSI) on the plan to reintroduce surface water flows 

into Northeast Shark Slough via the S-333 structure. The Corps FONSI specifically stated that 

"flooding impacts [in the East Everglades] resulting from the proposed plan, however, appear to be 

inconsequential". The Corps' analyses did not show a clear link between S-333 inflows and water 

levels in the East Everglades, but operating criteria to link S-333 releases and groundwater levels in 

the East Everglades were added as a safeguard. 

In March 1983, after repeated discussions with some agricultural representatives failed to produce 

an agreement, the District proceeded with implementation of a 3D-Day field test and opened the 

S-333 spillway. Attorneys for some agricultural interests obtained a temporary restraining order in 

Federal Court and the S-333 gates were closed the same day. The court refused to lift the restraining 

order and directed the two sides to reach an agreement. A formal agreement between the SFWMD 

and the agricultural representatives was signed in April 1984. The agreement stipulated that S-333 

had to be operated according to the Corps EA guidelines, and that S-333 would be closed when 

water levels at G596 were above the Corps specified rule curve. With the agreement the 3D-Day 

field test was re-initiated in late April, 1984. 

In July, 1984 a second agreement was reached between the SFWMD and the representatives of 

the south Dade farmers allowing for a wet season field test of S-333 releases into Northeast Shark 

Slough. An additional set of limiting conditions was added as part of this agreement, these included: 

(1) an agreement by the District to maintain canal water levels at a maximum of 4.5 feet throughout 

the entire reach of L-31N (from S-335 to S-176), and (2) the adoption of additional groundwater 

monitoring wells as measurement points to control the operation of S-333. This 90-Day test was 
14 CHAPTERl. BACKGROUND 

initiated in August 1984 and was interrupted (S-333 closed) for two extended periods, when groundwater levels rose above the trigger well criteria, even with below normal rainfall. Unfortunately, the 

Corps 1984 Environmental Assessment did not address these issues related to the lowering of L-31N 

operational criteria, or the use of S-331 for flood control. 

In June 1985, the Corps of Engineers completed an EA and issued a FONSI on a set of modified 

operating procedures for S-333 and the L-31N canal, similar to those established during the District's 

90-Day wet season test. There are two points of disagreement between the results of the Corps EA 

and the criteria established fo:- the 90-Day test: (1) the EA found that alternatives ~hich allowed 

the groundwater well criteria that triggered S-333 closing to be less restrictive (raised up to 0.4 

feet above the 90-Day test criteria) could be implemented without significantly increasing the risk of 

flooding in the East Everglades, and (2) the operational stages in the L-31N canal upstream of S-331 

could be more flexible (not forced to remain below 4.5 feet) and should be linked with groundwater 

levels in a well closer to the canal system. Both of these adjustments were incorporated, to a 

limited degree, in the 1985 test described below. Three technical studies by the South Florida 

Water Management District have failed to show that there is no clear link between S-333 inflows 

into Northeast Shark Slough and water levels in the East Everglades [MacVicar and VanLent 1984; 

MacVicar 1985; Neidrauer and Cooper 1989]. The District's report on the first two years of the 

Rainfall-Based water delivery plan [Neidrauer and Cooper, 1989] showed that the current lowering 

of L-31N canal stages overcompensates for any impacts caused by the NESS experimental program, 

and produced water levels in the East Everglades that were lower than the pre-test conditions. 

1.3.3 Artificial Canal Drawdowns/the Frog Pond Agreements 

In early 1984 farmers in the Frog Pond area requested that the District develop a plan to lower canal 

water levels in the adjacent canals to allow land preparation and planting to begin in mid October. 

In June 1984, an experimental one-year agreement was signed between Everglades Natiop.al Park and 

representatives of the Frog Pond farmers to allow water levels in the L-31 Wand C-ll1 canals to be 

lowered to 3.50 feet by October 15th, 1984. ENP agreed to the experiment as a way of evaluating the 

effects of L-31 W drawdowns on the water resources of Taylor Slough. Park hydrologists presented 

on the test's findings in a report to the Superintendent in June 1985 and recommended that no 

future drawdowns should be considered [Wagner et al., 1985]. 

Artificial drawdowns in the L-31W and C-ll1 canals were continued after the one-year experiment for three additional years (1985,86, and 87) without the Park's concurrence. This continuation 

was done through agreements between the District and representatives of some south Dade farmers, 
1.3. CHRONOLOGY OF IMPROVED ENP WATER DELIVERIES 15 

related to the Northeast Shark Slough experiment. The Corps of Engineers supported the continuation of drawdowns until 1988, when the Park completed a second technical report describing the 

hydrologic effects of the 1984 through 1986 L-31W canal drawdowns [Johnson et al., 1988]. In June 

1988 the Corps made a statement to the SCWMD Governing Board explaining why they could no 

longer approve the Frog Pond drawdowns. Note that the artificial lowerings of L-31 Wand C-111 

canal stages were never formally evaluated in any of the Corps Environmental Assessments, and 

that artificial drawdowns have continued, most recently in November 1992. 

1.3.4 The Experimental Three Party Agreements 

In July 1985, the Corps of Engineers established the protocol for the Letters of Agreement, requesting written concurrence by the SF\VMD and the Park on implementation of the Experimental 

Program of Water Deliveries to Everglades National Park. The first set of operational criteria for 

the experiment was attached as addendum 1, and included the procedure for implementation of a 

Rain-Driven water delivery formula for the Shark Slough Basin. The operational limitations on the 

use of S-333 and management of L-31N canal water levels were included, but they were slightly 

modified from the findings in the Corps Environmental Assessment. The Park wrote a response 

letter October 9, 1985 asking for additional information concerning the proposed limitations on the 

use of S-333. \Ve also disagreed with the inclusion of the statement that it has been determined 

that high water problems are occurring in the East Everglades, and implying that they were related 

to S-333 operations. We further asked that the consultation and decision protocols related to actions taken to mitigate unanticipated adverse water conditions be clarified. Finally we stated that 

any actions leading to the continuation of the Frog Pond artificial drawdowns be removed from the 

three-party agreement, since these operations were not consistent with the objectives of the water 

delivery experiment. The Corps wrote back to the Park on November 18, 1985 agreeing to remove 

the clause that linked S-333 releases with high water conditions in the East Everglades, but they 

insisted that the Frog Pond drawdown criteria be included in the three party agreement. Several 

interagency meetings were held to resolve these outstanding issues, bllt the Park did not concur with 

the final draft of the three party agreement. Our specific disagreements were related to: (1) the 

inclusion of L-31 Wand C-111 drawdowns for the 1985 and 1986 growing seasons, (2) the continued 

excessive use of S-331 for flood mitigation in the East Everglades, and (3) disagreements related to 

the operational levels in the L-31N canal. Since these issues were not resolved, a letter of concurrence 

was never sent to the Corps. 

A second Letter of Agreement was sent to the Park in December 1987, asking for written concurrence on continuation of the experimental program through December 1988, as authorized by 
16 CHAPTER 1. BACKGROUND 

PL 99-190. The experimental program would be operated according to the criteria in the attached 

addendum 2. The Park did not submit a letter of concurrence because of our opposition to the 

continuation of Frog Pond drawdowns, excessive flood control pumping at S-331, and disagreements 

over the operational criteria in the L-31N canal. A third Letter of Agreement was sent to the Park in 

August 1988, asking for written concurrence on continuation of the experimental program through 

December 1988. The operating criteria in the attached addendum 3 were slightly modified at the 

request of the SFWMD, after the legal agreements with the south Dade farmers had terminated. 

The Park again refused to submit written concurrence because of our continuing disagreements, as 

stated above. 

A fourth Letter of Agreement was sent to the Park, dated April 21, 1989, asking for written 

concurrence on continuation of the experimental program through December 1991, as authorized by 

PL 101-676. The experimental program would be operated according to the criteria in the attached 

addendum 4. In August 1989, the Park transmitted a letter of concurrence on continuation of the 

experimental program. A fifth Letter of Agreement was sent to the Park in February 1992, asking 

for written concurrence on continuation of the experimental program until the Modified Water 

Deliveries improvements are fully implemented. The Park did not submit written concurrence for 

the continuation of the experimental program. The sixth Letter of Agreement was sent to the Park 

in July 1993. To date we have transmitted one letter of concurrence associated with the wet season 

operating plan for the Taylor Slough Demonstration Project. 
Chapter 2 

Operations in L-31N, L-31W, and 

C-lll 

As seen in Tables 1-3, the operation of L-31N, L-31W, and C-111 have been changing since the South 

Dade Conveyance System was completed in the early 1980's. Operational policies for the canals in 

South Dade continue to evolve. In this section, we examine the hydrologic effects of these operational 

policies of the 1980's and 1990's on the marshes in the Rocky Glades, Taylor Slough, and the Park's 

Eastern Panhandle. The analyses in this section are based upon the long-term and average effects of 

the general lowering of canal stages. We limit our investigations to the available hydrologic record. 

\Vhile the hydrologic data base almost certainly contains errors and missing information, it is also 

the most reliable available information on the hydrology of South Dade. Complete calculations for 

analyses in this section are found in Appendix A. 

2.1 Operation of the L-31N canal 

The L-31N canal is conveniently split into two sections. The northern section, defined as the reach 

between S-335 on upstream end and S-331 on the downstream end, cuts through Shark Slough (see . Figure 2.) Surface water and seepage that this canal intercepts would have historically moved west 

into Shark Slough. Structure 331 marks the divide between the southern reach of L-31N, defined 

as the reach between S-331 and S-176. Prior to S-331, structure 173 marked the hydrologic divide; 

areas north of S-173 historically drained into Shark Slough, while areas south of S-173 flowed towards 

Taylor Slough and Florida Bay. 

17 
18 CHAPTER 2. OPERATIONS IN L-31N, L-31W, AND C-ll1 

L-29 

NORTHEAST 

SHARK 

SLOUGH 

Everglades 

National 

PI' 

...... : 

-4 

S-334 S-3 6 

C;lW·· 

C-I02 

Figure 2: Map of the L-31N borrow canal. 

i, 
,', 

2.1. OPERATION OF THE L-31N CANAL 

Operation of Structure 176 on the L-31N Borrow Canal 

8 n---~----~--~----~--~----r----r----.---~--~~--,---~ 

7 

2 

Design Optimum Stage 

5.5 ft msl 

............... Drawdown 6/82 

4.7 ft msl 

o ..... ............. ........ .............................................................................................................................. .. .................. .. 

-I 

19 

1968 1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 

Year 

Figure 3: Stage at S176 headwater. 

2.1.1 Stages in L-31N South of S-331 

We begin analysis of the operational policies in L-31N by looking first at the southern reach, between 

S-331 and S-176. There is more information available for this reach than the northern reach, and 

hence the effects of operations are clearer. Figure 3 is a plot of the stage at the downstream end of 

the L-31N canal. One can clearly discern the changes in operational levels over the past 25 years. 

In the fall of 1981, South Dade was hit with two tropical storms within a month. The rainfall for 

the 1981 wet season was approximately 52 inches, which translates to about a 1-in-25 year rainfall 

total; the Project was designed only for the 1-in-1O year event. Because the storms were locally very 

intense, flooding was extensive in western Dade County. Homeowners and agricultural interests, 

primarily representing the areas east of L-31N, sued the District over their operations in response to 

the storms. Under the threat of litigation, the District lowered S-176 operational stages from 5.5ft 

NVGD to 4.7ft NVGD. 

Canal stages in L-31N were lowered again in August of 1984 from 4.7ft NVGD to 4.3ft NVGD 
20 CHAPTER 2. OPERATIONS IN L-3IN, L-3IW, AND C-11I 

Stages at G-596 

8 

7 

6 

•• 

3 

2 

o ~~~~~~--~~--~~--~~--~~--~~--~~~ 

75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 

Year 

Figure 4: Stages at G-596. See Figure 2 for the location. 

in the wet season as part of an agreement to experiment with water deliveries in Shark Slough. 

Agricultural interests feared increased flooding potential from more flow in Northeast Shark Slough 

and won a concession to lower canal stages as part of a 30-day test. The wet season canal stages have 

remained at 4.3ft NVGD since that time. The Park has often voiced concern over this lowered canal 

stage, and has repeatedly refused to sign the Three-Party Experimental Water Delivery Agreement 

over this issue. 

2.1.2 Stages in L-31N North of S-331 

The stages in the northern reach of the L-31N canal are somewhat sketchy, as the S-173 headwater 

stages are not available on the District's data base. One can infer the operation of the canal, however, 

by looking at nearby wells. One of the longest records available in the area is at G-596, operated 

by the USGS since 1950. Figure 4 is the plot of part of the G-596 time series. The stage histories 

show much the same behavior as seen at S-176. The successive lowering of L-31N stages has reduced 

groundwater levels. Since G-596 is located west of L-31N, one can directly infer that lowering of 
2.1. OPERATION OF THE L-31N CANAL 

8 

Stages at G-596 

7 

6 

••••• • •••• • 

4 

3 

2 L-____ ~ ______ ~ ____ ~ ______ J_ ____ ~ ______ ~ ____ ~ 

1984 1985 1986 1987 

Year 

1988 1989 

Figure 5: Stages at G-596 for the years 1977-1990. 

L-31N stages has generally reduced water levels in the adjacent marshes. 

1990 1991 

21 

Because the G-596 gage is in the marshes west of L-31N, the record is more "noisy." The marsh 

responds quickly to rainfall. However, as seen in Figure 5, the stages are rapidly drawn down 

following storm events. After heavy rains, the stage jumps. Under pre-drainage conditions, these 

high stages would have persisted, and would have resulted in significant surface water flow south and 

west. Under the managed condition, large amounts of water are drained from the area and stages 

brought down, usually within days of the rainfall. 

Some information on L-31N stages is available. Recent headwater stages for S-338 and S-331 

are shown in Figure 6. Both structures have their headwaters in the L-31N northern reach, and 

until 1991, had similar stage readings. The design stage for this reach of the canal is 5.5 ft NVGD. 

However, prior to 1982, stages at G-596, and by implication, L-31N, normally reached 6.5ft in the 

wet season. While this may appear in contradiction to operational policy, the District had little 

capability to modify stages in that canal reach. However, when S-331 became operational, in June 

of 1982, the District could enforce operational stages as 5.5ft NVGD. Table 3 provides the current 

rules for S-331 operation. Most notably, flood control operation of S-331 was not part of the original 
22 

8 

4 

3 

2 

CHAPTER 2. OPERATIONS IN L-31N, L-31W, AND C-lll 

Stage in the Northern Reach of the L-31N Canal 

S-331 HW 

S-338 HW -----. 

80 81 82 83 84 85 86 87 88 89 90 91 

Year 

Figure 6: Stage in the L-31N northern reach. 
2.1. OPERATION OF THE L-31N CANAL 23 

design, and operational rules for flood mitigation have been developed as part of a modified water 

deliveries test to Shark Slough. 

Stages in the upper part of the reach have climbed because of the recent completion of G-211. 

With the completion of the G-211 structure in L-31N just downstream of the C-1W junction (see 

Figure 2), water managers are now able to hold higher water levels in the upper reach of L-31N. 

This should reduce seepage from Northeast Shark Slough, and generally improve hydroperiods in 

the adjacent marshes north of G-211. However, the data required to perform this analysis is not yet 

available on DBHYDRO, the District's hydrologic data base. 

2.1.3 Effects of L-31N on the Rocky Glades 

The effect of lowering canal stages on the marshes to the west of L-31N has been dramatic and 

detrimental. Figure 7 shows the reconstructed monthly flow hydrograph along Context Road (see 

Figure 2.) Context Road is at the southern end of the Rocky Glades and t.he northern extent of 

Taylor Slough. The flow across Context Road essentially represents a surface water contribution to 

Taylor Slough; the USGS in fact published these records as Taylor Slough at Context Road. The 

times series of the flow across Context road is shown in Figure 7. This hydrograph clearly shows 

the drop in surface water flow into the northern reaches of Taylor Slough from the Rocky Glades. 

Since June, 1982, when L-31N was lowered, surface water flows have virtually been eliminated. 

In terms of the average hydrograph, shown in Figure 8, we see a dramatic loss of flow. Prior 

to dropping the canal, we see a fairly typical Everglades hydrograph: peak flows in August and 

September, with a gradual decrease into the dry season. Following the drop in canal stages, sheet 

flow in the headwaters to Taylor Slough has been considerably reduced. 

The explanation is that the ground surface elevations in the area are about 4.7ft NVGD, and 

by holding the canal stages well below the ground level, surface water is drained off into the canal 

rather than flowing south into Taylor Slough. The loss of surface water averages 11,200 acre-ft per 

year, as compared to the 37,000 acre-ft per year mandated for Taylor Slough deliveries. Lowering 

of canal stages in L-31N directly translates to a loss of surface water flow in Taylor Slough. This 

also supports the Park's position that stages in L-31N need to be raised to at least 5.0ft NVGD in 

order to reintroduce any significant surface water flows in the Rocky Glades area. Returning L-31N 

stages to their design flood control optimum of 5.5ft would restore the more desirable hydrograph, 

and would be a step closer to historical hydroperiods. 

Appendix Section A.3 provides more information on how the estimates of flow across Context 

Road were estimated. Although this analysis is predicated on flow information that the USGS 

labels as poor, the results are fully consistent with observations of marsh damage in the areas 
24 CHAPTER 2. OPERATIONS IN L-31N, L-31W, AND C-ll1 

Surface Flow Across Context Road 

20 I I I I I. I I 

Peak Flow: 30,100 acre-ft V 

August 1981 

15 IL-31 N levels dro1212ed ~ 

June 1982 

5 ~ -

o lIL.J II I 11.1. I. .1 III J .II lit L'n. I.hl. II I L .hl I, 

1968 1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 

Year 

Figure 7: Monthly flow volumes at Context Road. The USGS published this data as Taylor Slough 

at Context Road near Homestead, FL. Data is reconstructed from published records; Section A.3 

contains comp~ete details on reconstruction methods. 
2.1. OPERATION OF THE L-31N CANAL 25 

3500 A verage M thl ony Fl ows at ong c ontext R d oa 

3000 

" 

_Average 1968-1982 

8 

.E c:::::JAverage 1983-1991 

~ 2500 

~2 

~~ 2000 

~~ 

0 

:::1l 1500 

~ 1000 

500 

o I n h ~ n h Jan Feb Mar Apr May JUD Jul Aug Sep Oct Nov Dec 

Month 

Figure 8: Average monthly flow volumes at Context Road. 

immediately west of L-31N. Curnutt and Pimm [1993] document an invasion of woody vegetation 

in the Rocky Glades. This vegetation change is induced by loss of surface water in the marsh. 

The result, according to Curnutt and Pimm [1993], has been a loss of Cape Sable seaside sparrows 

(Ammodramus maritima mirabilis) and their habitat in the Rocky Glades. We hypothesize that 

this damage to the habitat of an endangered species is a direct result of lower canal stages. No 

assessment of how lower canal stages would affect the sparrow was ever made, and there is strong 

evidence that lower canal stages has adversely affected their ability to survive. This analysis simply 

corroborates these field observations and links the habitat loss to canal operations. 

2.1.4 Water Budget of L-31N 

The most elementary step in determining the water management implications of canal operations is 

to calculate the water budget. Inflows and outflows are tabulated, with the difference between the 

inflow and outflow being the volume contributed by basin drainage. The water budget is for the canal 

only, not the contributing basin. We have neglected the effects of rainfall and evaporation on the 

canal. All flow data is taken from the District's hydrologic data base, DBHYDRO and reproduced 

in Appendix C. 

Figure 9 is a comparison of the inflows and outflows for theentire reach of the L-31N canal. It is 

immediately apparent that substantially more water is being removed from this canal than is being 

input. That is, the canal serves primarily to drain the basin, not to supply the area with water. Had 
26 CHAPTER 2. OPERATIONS IN L-31N, L-31W, AND C-l11 

~~~~~o~f!.In~fl~o~w~s ~an~d~0~u!!tfl~O~w~s~i~n~th~e~L::;-3~1~N~can~ru~' 450,... 

400 

350 

300 

1:""""""""4 Ioflow _ Outflow 

81 82 83 84 85 86 87 

Year 

88 89 90 91 

Figure 9: Comparison of annual inflows and outflows to L-31N between S-335 and S-176. Inflow is 

S-334 & S-335, while outflow is S-336 & S-338 & S-194 & S-196 & S-176 & S-174. 

the latter been true, one would see many years like 1989, where inflows meet or exceed outflows. 

Between 1983 and 1991, the net drainage by L-31N canal amounted to 210,000 acre-ft per year, on 

the average. As a comparison, the Minimum Delivery Schedule called for a 260,000 acre-ft annual 

delivery to Shark Slough through the S-12 structures. 

The net drainage by the canal explains only part of the picture. Further examination can yield 

more information on the relative impacts to Shark Slough, and the Rocky Glades. vVe therefore 

break the analysis into two components: L-31N north of S-331 and south of S-331. 

Northern Reach of L-31N 

Surface water inflows to the northern reach of the L-31N canal are made through structures 335 and 

334, located on the L-30 and L-29 borrow canals, respectively. These are integral components of 

the South Dade Conveyance System; flows through these structures represent the contribution from 

the regional water supply system. That is, no flood releases are passed through S-334 and S-335, 

as a general rule. Outflows, defined as S-336 + S-338 + S-173 + S-331, represent a combination of 

regional water supply deliveries and drainage. 

The annual inflow and outflow totals for the L-31N between S-335 and S-331 is shown in Figure 10. 

This water budget shows that, except for severe drought years, the northern reach of L-31N is the 

major contributor of water to the downstream basins. On the average, 169,400 acre-ft per year 
2.1. OPERATION OF THE L-31N CANAL 

450 

400 

Q)--- 350 

e~ :l ~ -u 300 ~ ...... '"~ 0 o ell 250 ti:"O 

-a~ :l :l c 0 200 

~t, 

150 

100 

50 

0 

-d 

IT 

Surface Water Inflows and Outflows in the 

Northern Reach ofL-31N 

-

1"""""""",',','1 

I" 

! I: [ I [ 

I 

Ir r- L 

Outflow 

Inflow 

n 

81 82 83 84 85 86 87 88 89 90 91 92 

Year 

27 

Figure 10: Comparison of annual inflows and outflows to L-31N between 8-335 and 8-331. Inflow is 

8-334 & 8-335, while outflow is 8-336 & 8-338 & 8-331 & 8-173. 
28 

NESS 2 

Ave Stage 

6.49 ft msl 

CHAPTER 2. OPERATIONS IN L-31N, L-31W, AND C-lll 

Water Surface Profile 

L-31N 

Ave Stage 

5.03 ft msl 

G-855 

Ave Stage 

4.40 ft msl 

--------------------·:··················t----------------------~---- 3.6 ml 2.0 mi 

Figure 11: Estimated regional groundwater gradients in the vicinity of L-31N. 

was extracted from the basin between 1981-1991. The large withdrawals occurred after 1983; this 

coincides with 8-331 pump station becoming operational. This also demonstrates that 8-331 is 

primarily used for. drainage and flood protection rather than for water supply. If the latter operation 

were predominant, one would see inflows matching outflows, as in the drought year 1989. Instead, 

the huge disparity (outflows average 187% of inflows) indicates that lower canal stages and higher 

pumping rates at 8-331 for flood protection have resulted in enormous losses of water from the 

marshes adjacent to L-31N. 

The average net difference between inflows and outflows into the northern reach of L-31N is 

approximately 200,000 acre-ft per year. This number represents a groundwater seepage contribution 

to the canal from the surrounding area, both east as west of the levee. Also, L-31N has a 1.5 

mile groundwater connection with WCA-3B. While the groundwater flow regime and the surface 

water / groundwater interactions in this area make detailed analysis difficult, one can make some 

general statements about the behavior of groundwater flow in the area. Figure 11 depicts the 

groundwater slopes in the vicinity of the L-31N canal north of 8-331. Clearly, there is a gradient of 

water from west to east. The implication is that, over the long-term, water flows from the marshes 

of Northeast Shark Slough into L-31N, and then out of L-31N as recharge to areas to the east. 

Therefore, it must then be true that Northeast Shark Slough contributes more than the net amount 

of seepage. In other words, Northeast 8hark Slough seepage losses averaged at least a 190,000 acre-ft 

per year contribution to the regional water system. 
2.1. OPERATION OF THE L-31N CANAL 29 

Conservatively assuming that the net groundwater seepage is equal to the amount drained from 

Northeast Shark Slough, we can summarize the annual water budget for the northern reach of L-31N 

for the years 1983-1990 as in Figure 12. This graphic shows, in essence, that large volumes of water 

are drained from Northeast Shark Slough, and then passed down L-31N via S-331. The new G-211 

structure should help reduce these seepage losses. However, this is offset by plans to provide flood 

"mitigation" for the 8.5 sq. mi. residential area in the Rocky Glades. Demands for flood protection 

in areas near L-31N will continue to result in large seepage losses from the marshes in Everglades 

National Park. 

Southern Reach of L-31N 

The annual inflow and outflow totals for the southern reach of L-31N between S-331 and S-176 

are shown in Figure 13. Surface water outflows exceed inflows in nearly every year; more water is 

extracted from the basin than is brought in from the regional system. On the average, outflows are 

115% of inflows. 

The net drainage calculation, however, is incomplete in determining the extent of the effects of 

canal stages on the marshes to the west of L-31N. One can ask the question: What fraction of the 

net drainage comes from the eastern agricultural and urban areas, and what fraction comes from 

the western marshes, i.e, the Rocky Glades and Everglades National Park? With current state of 

knowledge about the groundwater and surface water system in the area, we cannot answer that 

question definitively. However, there are ways of getting estimates of the ratio, and thereby an idea 

of where the canal seepage originates. 

By the fundamental law of groundwater mechanics, the flow of water in the subsurface is proportional to the slope of the water surface. We can therefore estimate the relative importance of 

the eastern and western seepage components by comparing the groundwater slopes. \Ve used two 

gages, G-1502 and G-1363, roughly equidistant and perpendicular to L-31N, to estimate average 

groundwater slopes east and west of the canal. The result is depicted in Figure 14. In effect, the 

marshes contribute more than the net amount, and the canal recharges the areas east of L-31N. That 

is, water is drained from the Rocky Glades and Everglades National Park and is used to recharge the 

agricultural and urban lands east of L-31N. If we were to apply the calculated ratio (see Section A.2) 

and use the average annual net drainage (1983-1990) of 36,300 acre-ft, approximately 71,200 acre-ft 

per year is drained from the Rocky Glades west of L-31N and 34,900 acre-ft per year are recharged 

to the lands east of L-31N. Again, these values should serve to illustrate the relative magnitudes of 

the groundwater flows, and not absolute quantities. They do clearly show that the Rocky Glades 

and Everglades National Park contribute large volumes of water as seepage to L~31N. Thus, raising 

canal stages in L-31N will tend to decrease the loss of water from the Rocky Glades area. This 
30 

L-29 

tional 

Park 

CHAPTER 2. OPERATIONS IN L-31N, L-31W, AND C-lll 

C-4 

10,700 acre-ft 

z 

r--:o--:C-:"-:--

,. ·C;'lW 

,. ___________ ..J 

,-':"'--

1 

, . 

. 1 

I':' --:, 

1 

., 

.1 

Figure 12: Summary of the average annual water budget for the northern reach of the L-31N 

canal, between S-335 and S-331 for the years 1983-1990. The solid arrows represent flows through 

structures, while the shaded arrows represent groundwater seepage into L-31N. 
2.1. OPERATION OF THE L-31N CANAL 

400 

350 

100 

50 

o .... 

80 81 

Surface Water Inflows and Outflows 

in L31N between S331 and S176 

Inflow c::::J 

Outflow me 

r 

82 83 

I 

84 85 86 87 

Year 

88 89 

31 

90 91 

figure 13: Comparison of annual inflows and outflows to L-31N between S-331 and S-176. Inflows 

are S-331 and S-173, while outflows are broken into flow to Taylor Slough (S-174) and outflows east 

and south (S-194 & S-196 & S-176). 
32 

G-1502 

Ave Stage 

5.54 ft msl 

CHAPTER 2. OPERATIONS IN L-31N, L-31W, AND C-111 

G-1363 

Ave Stage 

3.66 ft msl 

~ Water Surface Profile 

L-31N , Ave Stage --""':----... 4.16 ft msl 1--------:nt-i 

·~:··:"'·~:~~~~~:~··········t·················,···.~ 4.2 mt 2.9 mi .... 

Figure 14: Estimated regional groundwater gradients in the vicinity of L-31N. 

will have positive impacts on the marshes in Everglades National Park and the downstream estuary, 

Florida Bay. 

We can summarize the L-31N water budget for the areas south of S-331 for the years 1983-1991 

as in Figure 15. There are several points which we need to emphasize. Firstly, the inflow at S-331/S173 complex largely represents the drainage of Northeast Shark Slough. This is a significant shift in 

operational policy since 1983. Prior to that date, there were only small interbasin transfers. That 

is, little flow was passed between the northern and southern reaches of L-31N. 'With the completion 

of S-331, which was authorized as a water supply structure, the District now moves large volumes of 

water southward out of the Shark Slough basin. This is done primarily to satisfy demands for lower 

L-31N stages. 

Another important point from Figure 15 is the size of the flows eastward through S-194 and S196. Almost 30% of the S-331/S-173 flow is diverted into S-194 and S-196, after which it presumably 

is dumped into Biscayne Bay. These discharges represent flows which historically would have moved 

south and west, but are now diverted to the Atlantic. The lowering of canal stages has forced the 

District to find outlets for the water drained from Taylor Slough and the Rocky Glades, and moving 

it eastward is one alternative. 

The third important feature of Figure 15 is that the contributed flow to Taylor Slough via S-174 

amounts to only 66% of the volume drained from the Rocky Glades. Taylor Slough is therefore 

being deprived of water which would have flowed southward as sheet flow through the slough and 
2.1. OPERATION OF THE L-31N CANAL 

Everglades'. .. ' 

National -:'.' 

Park 

A 

::c 

o 

$: 

m 

l> 

< 

m 

33 

Figure 15: Summary of the average annual water budget for the L-31N canal between 8-331 and 

S-176 for the years 1983-1990. The solid arrows represent flows through structures, while the shaded 

arrows represent groundwater seepage into L-31N. 
34 CHAPTER 2. OPERATIONS IN L-31N, L-31W, AND C-ll1 

into Florida Bay. It also means that the regional water system is not the source for most of the 

water sent to Taylor Slough. Although the SDCS was designed to bring water in from the WCA's 

and the regional system, the historical record shows that the Rocky Glades, not the SDCS, supply 

the water delivered to Taylor Slough. The SDCS operates as designed during drought years, but 

during normal and wet years, it serves primarily to provide flood control and drainage. 

2.1.5 Supplemental Inflows to the South Dade Conveyance System 

Figure 13 shows the annual inflows to the northern reach of the L- 31N canal system (S-334 & S-335) 

for the 1983 through 1991 period. Essentially all of these inflows were made during the dry season 

(November through May) to meet the supplemental water supply requirements of the SDCS. This is 

clearly seen in Figures 16-17. For this period, the average dry season inflow volume to the northern 

reach of the canal was approximately 108,000 acre-feet. (For this analysis, the dry season is defined 

as the months of November through May, which represents the period of deficit rainfall, when inflows 

to the SDCS would be expected [U.S. Army Corps of Engineers, 1973]). In contrast, the GDM for 

the South Dade Conveyance System estimated that the average annual dry season supplemental 

flow requirement to the upper reach of the L-31N canal was 318,500 acre- feet. Note that during 

two extreme drought years, 1985 and 1989, dry season inflows exceeded 250,000 acre-feet, but on 

average the dry season supplemental flows have been less that 34 percent of the Corps estimates. 

According to the design documents of the South Dade Conveyance System [U.S. Army 

Corps of Engineers, 1973], there was no flood control element. The intention was that it function only as a water supply system. However, Figure 17 shows that, since its initial operation in 

1983, the SDCS has been used for flood control, as evidenced by the large wet season pumping 

volumes at S-331. 

The extent of the flood control operation is seen in Figures 18. Here, the wet and dry season 

flow history is summarized for the S-331 pump station for the period from January 1983 through 

December 1991. Figure 18 compares the wet season and dry season pumping at S-331 for the period 

1983-1991. Note that on average, nearly half of the annual flow for S-331 occurred during the 

wet season, and that in the high flow years of 1985, 1986, and 1988 wet season flows accounted 

for 60 to 70 percent of the annual total flow. The use of S-331 for flood control and drainage is 

clearly inconsistent with the original project purpose. Yet, since its construction, S-331 has been 

used as often for flood control as for water supply. This practice adds an additional burden to the 

flood control requirements of the downstream basin, and causes overdrainage of the Northeast Shark 

Slough wetlands. 

As noted earlier, the Corps estimated that the annual average supplemental dry season flow 
2.1. OPERATION OF THE L-31N CANAL 

Dry Season Operation of the 

South Dade Conveyance System 250 r----.---,-----,..----r--....--"--,---r--"-....------,---, 

200 

I

'.:: 

~: 

m InDowo from 

reglooaI oyotem 

• Pumplng.t 

S-331 

1983 1984 198~ 1986 1987 1988 1989 1990 1991 

Year 

35 

Figure 16: Comparison of 8-331 pumping to the inflows from the regional water management system 

during the dry season. In this case, deliveries are the combination of 8-334 and 8-335 flows. 

250 

200 Q)2 E I 

::s ~ 150 - Co) '3- ro 

~o 08 100 u:c 

50 

0 

Wet Season Operation of the 

South Dade Conveyance System 

[] InOows from 

regional system 

I Pumping at 

8-331 

I I[ ? 

1983 1984 1985 1986 1987 1988 1989 1990 • 1991 

Year 

Figure 17: Comparison of 8-331 pumping to the inflows from the regional water management system 

during the wet season. In this case, deliveries are the combination of 8-334 and 8-335 flows. 
36 CHAPTER 2. OPERATIONS IN L-31N, L-31W, AND C-lll 

220.---r---.---.---.----.---.---.---,----.--. 

200 

180 

160 

CIl ..--

Q) ¢:: 140 

S ~ ..:: ti 120 o «:I 

::> 0 100 

~8 LI:::::' 80 

60 

40 

20 

Ell Dry Season Flows 

• Wet Season flows 

O'--~----'"--.--"'----' 

1983 1984 1985 1986 1987 1988 1989 1990 1991 

Year 

Figure 18: Comparison of wet and dry season pumping at S-331. 

requirements for water supply pumping at S-331 were 264,800 acre-feet per year [U.S. Army 

Corps of Engineers, 1973]. Our analyses indicate that the actual dry season supplemental inflows 

averaged 100,500 acre-feet per year. This represents less than 38 percent of the supplemental flows 

expected by the Corps to be provided to the downstream areas of south Dade County. Moreover, 

when we look at the deliveries from the regional water supply system to the SDCS, as in Figure 16, 

we see that in 5 of 9 years, more water was removed from the basin that was delivered. That is, 

L-31N supplied water for downstream uses more than one half of the dry seasons. The dry season 

water supply requirements of south Dade County (including Taylor Slough, the Eastern Panhandle, 

and Florida B~y) need to be re-examined as part of the District's ongoing regional water supply 

planning process. 

2.1.6 Summary of L-31N analysis 

The important aspects of analysis of L-31N are: 

1. Lowering of canal stages in L-31N since 1982 has had a detrimental effect on the Rocky Glades 

marshes. Sheet flow in the late wet season has been virtually eliminated in the headwaters 

of Taylor Slough, as indicated by the estimated flow along Context Road. Raising S-176 

headwater to a minimum of 5.0ft will be a first step toward re-introducing sheet flow in the 

area and recovery of the headwaters of Taylor Slough. 
2.2. OPERATION OF L-31 W 37 

2. The source of water for S-174 deliveries to Taylor Slough is primarily drainage from the upstream L-31N basin, not the regional water supply system. About 66% of the amount comes 

from just upstream, from the Rocky Glades, the headwaters of Taylor Slough. The wet season 

deliveries to Taylor Slough via S-174 are, in effect, simply the rearrangement of water from 

the headwaters (the Rocky Glades) to the northern end of the Taylor Slough. 

3. Even the large volume of surface water inflows to the southern L-31N canal reach via S-331 

do not constitute a significant regional water supply contribution. The majority of this water 

originates as seepage into the northern L-31N canal from Northeast Shark Slough. These 

routine interbasin transfers represent a significant shift in operational policy since 1981. 

4. In the period 1983-1990, the pump station S-331 was used as frequently for flood control 

during the wet season than for water supply during the dry season. This is in contrast to the 

Corps of Engineers design and authorized operation; the pump was intended as a dry season 

water supply structure, with no flood control element authorized. 

5. The dry season deliveries from the regional water supply system to L-31N have averaged 38% of 

design target of 318,500 acre-ft, while average withdrawals from the L-31N have been 198,500 

acre-ft per year, 75% of the design estimate of 264,800. However, approximately half of the 

S-331 pumping is for wet season flood control. In about one half of the dry seasons for which 

we have information, the L-31N basin supplied water for downstream uses. 

2.2 Operation of L-31 W 

The L-31 W west canal is the canal bringing water from the South Dade Conveyance System to 

pump station S-332, which in turn, discharges into Taylor Slough. In 1972, Congress mandated a 

minimum delivery of 37,000 acre-ft per year. L-31 W was constructed for the purpose of bringing the 

minimum delivery allocation to Taylor Slough from the regional water system. Figure 19 depicts the 

major hydrologic features of the area. \Vater enters L-31 W from S-174, and is pumped into Taylor 

Slough at S-332. Structure 175 serves to control the stage in the canal. Structure 175 is also now 

used to provide flood protection to the Frog Pond, although this use is not expressly authorized. 

2.2.1 Stages in the L-31 W canal 

If we examine the historical record of water levels in the L-31W canal (shown in Figure 20), one 

can see an apparent change in the operational policy in 1981. The design optimum stage in L-31W 

is 4.5ft NVGD, but prior to 1981, stages were routinely allowed to reach 5.0ft. The 1981 change 
38 CHAPTER 2. OPERATIONS IN L-31N, L-31W, AND C-l11 

C-103 

C-I13 

S.R. 9336 

S-177 

Figure 19: L-31 Wand vicinity. 
2.2. OPERATION OF L-31 W 

Canal Stages in L31 W 

6.00 r-'--.---r--~~--~--.--.--'---r-~ 

5.00 

... 

£ 

OJ 4.00 ~ 

-g 

.,g:::::;- 3.00 

~8 

r;; $ 2.00 

(Ii 

o 

~ 1.00 en 

0.00 

-1.00 

5.0 ft msl .. _. ~ .... 

~I 

72 74 76 78 80 82 84 86 88 90 

Year 

Figure 20: Stages in the L-31W borrow canal. Shown is the headwater at S-175. 

39 

coincides with a period of extensive West Dade flooding and the beginning of intensive agriculture 

in the Frog Pond. These factors combined to require strict adherence to lower water levels in the 

regional system, emphasizing flood control and drainage. The effect of the South Dade Conveyance 

System is also evident from the higher dry season minimum levels seen after 1982. The effectiveness 

of the water management system at controlling water levels is apparent. Prior to 1981, the canal 

would normally range from 5.0ft to 0.5ft. After 1981, the typical range was between 4.5ft and 2.5ft. 

The narrowing of stage ranges is indicative of an intensely managed system. 

The strict maintenance of L-31W stages since 1981 is accomplished by increased operation of 

S-175. When we compare the stages in L-31W with the flows at S-175, as in Figure 21, it becomes 

apparent that S-175 is now opened so that wet season stages in L-31 W do not exceed 4.5ft. That is, 

S-175 is operated to drain Taylor Slough and the Frog Pond during the wet season, not to provide 

water deliveries to Taylor Slough from the regional system. 

The requirement of not allowing wet season stages in L-31 W to exceed 4.5ft is likely a combination 

of two factors. First, agricultur~l interests in the Frog Pond have objected to any plan to increase 

wet season stages in L-31W. The Park Service agreed in 1983 to a drawdown of the Frog Pond (see 

Table 2, page 10) as part of a test of higher wet season and lower dry season stages. However, the 

increase wet season stage aspect of the experiment waS blocked by the Frog Pond farmers. 

A second factor in the maintenance of L-31 W wet season stages at 4.5ft or lower is a result of the 
40 

.... 

Q) 

ce 

~ 

~ 

<U 

Q),-... 

~ --Vl 

~ a 

-¢:: 

CI) '-' 

.... 

<U 

Q) 

0.0 

c::J 

.... 

CI) 

CHAPTER 2. OPERATIONS IN L-31N, L-31W, AND C-lll 

Canal Stages in L31 Wand Flow at S 175 ~~8~----------------~----~--------------' 

~ ~ Dry Seawn .. 

.... -0 -

~ ] 40 Wet Season c:::J 

§ ~ VJE., 

5.00 - 5.0 ft msl 

---- 4.00 

3.00 

2.00 

1.00 

0.00 

-1.00 

72 74 76 78 80 82 84 86 88 90 

Year 

Figure 21: Comparison of stages in L-31 W to flows at 8-175. 
2.2. OPERATION OF L-31 W 41 

general lowering of L-31N canal stages. When L-31N is held at 4.3 ft, it is not possible to use gravity 

to bring water to L-31W unless L-31W is below 4.3ft, and preferably much lower. To lower L-31W, 

water managers can either a) open S-175 and lower L-31 W stages sufficiently to allow deliveries 

through S-174, or b) close S-174 (disconnecting L-31W from L-31N), and pump S-332. Neither of 

these alternatives is desirable from an environmental standpoint. The former results in lower water 

levels in the marsh, which in turn means shorter hydroperiods. The latter operation extracts water 

from Taylor Slough and then pumps it back in, which is a wasteful recirculation of water. Neither 

of the above operational policies are beneficial to Taylor Slough. 

The lowering of L-31N stages and the use of S-175 to drain L-31 W in the wet season are linked. It 

is clear that raising L-31N stages would also reduce the need to drain Taylor Slough in the wet season. 

Raising canal stages in L-31N would provide more operational flexibility to reduce adverse drainage 

of Taylor Slough and the Rocky Glades. It would help insure that L-31 W is not used to drain the 

marshes to the west, and that deliveries through S-332 do indeed represent a net contribution to 

flows in Taylor Slough. 

2.2.2 L-31 W water budget 

In much the same manner as for L-31N, we can also develop a simple water budget for L-31W. 

Figure 22 compares the total surface water inflows and outflows. The inflow to the canal is S-174, 

while the outflow is the sum of S-175 and S-332. The only time in the available record when inflows 

from S-174 exceeded outflows was in 1989, a drought year. On the average, outflows from S-332 and 

S-175 average double the inflows from S-17 4. The difference between the surface water inflows and 

outflows represents the water drained by L-31 W. In a typical year, 38,000 acre-ft are drained from 

the L-31 W basin. This means that the 37,000 acre-ft minimum delivery schedule can be primarily 

accounted for by groundwater seepage into L-31 W from Taylor Slough. 

Once again, by looking at the average groundwater slopes, one can obtain an estimate on how 

much of the water drained by L-31W comes from Everglades National Park and how much comes 

from the Frog Pond. Figure 23 depicts the typical groundwater gradients in the area. What this 

shows is that in northern Taylor Slough, represented by gageNTS-3, groundwater moves out of the 

marsh and into the canal. Moreover, there is a small difference in stages between the canal and the 

Frog Pond. This small difference indicates that the Frog Pond tends to receive water as seepage 

slightly more often than it contributes water as drainage. Most likely, the amount drained from the 

Frog Pond in the wet season roughly balances the amount the Frog Pond receives from L-31 W in 

the dry season. The low C-111 canal stages on the eastern boundary of the Frog Pond probably 

contribute to a flow out of L-31W through the Frog Pond and into C-lll. 
42 CHAPTER 2. OPERATIONS IN L-31N, L-31W, AND C-1H 

Surface Water 

Inflows and Outflows in L31 W 

160 

Inflow 1""",·"""",',·,1 

140 Outflow_ 

~ 120 

ell v V .. 100 §< -..... ~~ - "0 80 ~ a C ell 

C ::> <I: 60 0 

~ 

"\ Drainage 

by L31W 

40 

20 

0 

80 81 82 83 84 85 86 87 88 89 90 

Year 

Figure 22: Comparison of surface water inflows to surface water outflows in L-31 "V. 

NTS-3 

Ave Stage 

3.61 ft ms! 

r-Water Surface Profile 

\\ L-31W 

Frog Pond 

Gage 

Ave Stage 

3.47 ft ms! 

, Ave Stage 

-'r~......::;::::= 3.48 ft ms! 

~~------~----------~~-- ~ ...... . 

~ 

···········:··~···~:'·················t··············· ........................... . 0.6 m1 1.0 mi 

Figure 23: Average groundwater stages in the vicinity of L-31W. 
2.2. OPERATION OF L-31 W 43 

Figure 24 summarizes the average annual water budget for L-3tW. As an average, many of 

the important operational features are lost, but one can interpret the budget in the following way. 

Because L-31 W canal stages are not allowed to exceed 4.5ft NVGD in the wet season, large volumes 

of water are pulled into L-31W from Everglades National Park and then dumped through S-175. 

Also, inflows at S-174 and outflows at S-332 were not balanced; pumping at S-332 often exceed 

inflows at S-174. To prevent L-31W from draining the marshes in Everglades National Park, S-174 

inflows must meet or exceed the combination of outflows from S-332 and S-175. 

This has important implications on pumping at S-332. If S-332 is used, then an equivalent volume 

must be brought in through S-174. If pumping is increased at S-332, then the increased pumping 

must be offset by increased flows at S-174. Otherwise, pumping amounts to recirculating water in 

L-31W; pumping in L-31W without increasing S-174 deliveries means that the water is pumped out 

of the canal into the marsh, and then seeps back into the canal. Thus, we need to be sure that 

increased pumping at S-332 represents true contribution to Taylor Slough, rat.her than a drainage 

of Taylor Slough. 

If water is brought in through S-174 to match any increased pumping, we must determine if 

increased S-174 flow is the result of extracting water from the Rocky Glades west of L-31N. By 

taking the position that S-174 flows be increased to match pumping at S-332 and that stages in 

L-31N be raised, we are taking positive steps in assuring that plans for increased flow to Florida 

Bay via Taylor Slough do not merely extract water from the Park and reintroduce it downstream. 

2.2.3 Summary of L-31W analysis 

We can summarize the findings of our L-31 W analysis as follows: 

1. Prior to 1981, canal stages in L-31 W were routinely allowed to reach 5.0ft NVGD. After that 

date, stages were held at or below 4.5ft NVGD. 

2. To accomplish this, S-175 was used to drain water from the L-31 W basin during the wet season. 

In an average year, 52,000 acre-ft is passed through S-175. 

3. Current operational policy has the effect of removing 41,000 per year from Taylor Slough, and 

then pumping 33,000 acre-ft back into Taylor Slough via S-332. 

4. Any plan to continue or increase pumping at S-332, using either the existing pump and/or the 

auxiliary pump, will require flows at S-174 which meet or exceed the pumping rate. 

5. Increasing stages in L-31N will allow for increased flexibility in operating L-31W and S-332 for 

the benefit of Taylor Slough. 
44 CHAPTER 2. OPERATIONS IN L-31N, L-31W, AND C-l11 

C-I03 

..... 

Everglades C-ll 

National 

Park 

S.R. 9336 

Figure 24: Summary of the average annual water budget for the L-31 'vV borrow canal for the years 

1983-1990. The solid arrows represent flows through structures, while the shaded arrows represent 

groundwater seepage into L-31 W. 
2.3. OPERATION OF THE C-l11 CANAL 45 

2.::J Operation of the C-l11 Canal 

The lowest reach of the 80uth Dade Conveyance 8ystem is the C-ll1, shown in Figure 25. This 

canal can be broken into three reaches: from 8-176 to 8-177 is the upper reach, 8-177 to 8-18C is the 

middle reach, and from 8-18C to 8-197 is the lower reach. Historically, there was little surface water 

connection between the area north of 8-177 and the wetlands and downstream estuaries of the lower 

C-111 basin. When the C-ll1 canal was constructed in the early 1960's, the canal breached the 

coastal ridge, allowing large volumes of surface water to flow rapidly from northern Taylor 8lough 

into the Eastern Panhandle. For this reason, C-1l1 has an undeniable effect on Florida Bay. Most 

importantly for the Park, the middle reach potentially drains water from Taylor 810ugh. In the lower 

reach, water flows out of the canal, through a series of gaps in the levee south of the C-111 canal, 

and then southward into the Park's Eastern Panhandle. As it stands, this outflow through the gaps 

is the major contributor of overland flow to Florida Bay. 

The hydrologic records from the C-ll1 basin are not as complete or as reliable as those of the 

L-31N and L-31 W canals. Therefore, detailed water budget analyses similar to that performed for 

L-31N and L-31 W will not be reliable. Thus, we will present only some of the raw data, and make 

some general observations. 

Figure 26 shows how the C-ll1 canal adjacent to the Frog Pond has been manipulated since 

records began in 1981. The optimal design headwater at 8-177 prior to 1981 was 4.5ft. 8ubsequent 

operations have reduced the stage to 3.9 in the wet season and 3.3 in the dry season. During drought 

years, such as 1989 and 1990, it has not been possible to maintain the dry season stage, dry season 

stages have averaged much lower than design conditions. These low stages could mean that water 

discharged from 8-175 might seep eastward into C-ll1 around the 8-177 structure (see Figure 26.) 

These lower 8-177 stages often necessitate the closure of 8-174 during storm events. Because 

L-31N stages are much lower than design optima, 8-177 must also be lowered in order to provide 

enough of a gradient for gravity flow southward. 8ince 8-174 has inadequate capacity to pass all of 

the water drained in the L-31N basin, 8-176 must often be opened to dump the storm water into 

C-ll1. When 8-176 and 8-174 are both opened, the net effect is to pull water backwards through 

8-174, through 8-176, and into C-ll1. Thus, with low stages in C-111, it is difficult to simultaneously 

open 8-174 and 8-176 without draining L-31 W. One way to improve the ability to pass storm flows 

through 8-174 and Taylor 810ugh is to return to the design optimum stages of 4.5ft at 8-177 (see 

Table 1 on page 9.) 

Although a water budget for C-111 would be very desirable, the flow data available from the 

District's database indicates clear problems with the record. Figure 27 shows the annual flow volumes 

for the four structures in C-ll1. Of particular concern is that 8-177 flows are less than both the 
46 CHAPTER 2. OPERATIONS IN L-31N, L-31W, AND C-lll 

....... 

....... 

....... I 

U 

C-113 

S-178 

S-l77 ~ 

S-18C 

....... 

....... 

....... I 

U 

....... I 

U 

Everglades National Park 

Figure 25: The basemap of the C-ll1 Basin. 

... 

\ 
2.3. OPERATION OF THE C-ll1 CANAL 47 

Stage at the S-177 Headwater 

5.00 

4.50 ~ Frog Po"" Drnw Dow. 

Test Begins 10/84 

4.00 • 

· • • ,-. 

<l)Vl 3.50 gfS 

cZi¢:: '-" 

3.00 

2.50 

2.00 

1.50 

1.00 

82 83 84 85 86 87 88 89 90 91 92 

Year 

Figure 26: Stages at the headwater of S-l77. 
48 CHAPTER 2. OPERATIONS IN L-31N, L-31W, AND C-111 

Structural Flows in the C-lll Canal 35~ ~--r---~--~--'---~---r---.--~~~--~--~ 

300000 

100000 

5~ 

o '-------'-

80 81 82 83 84 

I::=::I S-17 6 

.. S-l77 

_ S-18C 

WZ2:I S-197 

85 

Year 

86 87 88 89 

Figure 27: Water Budget for the C-111 canal between S-l77 and S-18C. 

90 91 
2.3. OPERATION OF THE C-l11 CANAL 49 

upstream and the downstream structure. This indicates problems with the flow calculations at either 

S-177, S-18C, or most likely, both structures. Moreover, the record for S-197, the southern-most 

structure, are poor. Prior to 1990, the structure consisted of three culverts and an earthen plug. 

Five times from 1981 to 1990, the earthen dam was removed and tens of thousands of acre-ft of 

water flowed into Barnes Sound, unfortunately the flow records during these events are missing from 

the database. 

The C-111 basin is the subject of a number of current investigations. The Park and the District 

are engaged in a joint investigation to document the impacts of the lower C-111 canal system on 

the adjacent wetlands and downstream estuarine environments. This work will result in a set of 

operational and structural recommendations for the C-111 Interim Project. The Park and the 

District are also cooperating in an investigation of the hydrology of the Frog Pond and the adjacent 

areas. We expect these investigations to result in significantly improved estimates of flows at S176, S-174, S-177, S-175, and flows in C-113. This information will be used to recommend improved 

management and operations in L-31N and L-31 \V canals. These efforts will result in a better picture 

of C-111 flows and operations. 
Chapter 3 

Operation of the SDCS during 

Storm Events 

Besides being an integral part of the South Dade Conveyance System, the L-31N borrow canal is 

also used to provide flood protection to southern Dade county. To examine how the SDCS is used 

during storm events, this chapter looks at three individual cases. The first case is the 1988 rainy 

season, which is an example of a storm resulting in the discharge of large volumes of water through 

S-197 into Barnes Sound. This storm also is prior to the adoption of the C-111 Interim Project, 

calling for structural and operational modifications to L·31N and C-l11. The second and third cases 

we examine. are subsequent to the Interim Project, and are comparatively recent. These cases look 

at operations of the L-31N and L-31W canals during June and November, 1992. 

3.1 Wet Season, 1988 

Consider first the 1988 rainy season. Here is an example of a storm which resulted in the opening 

of S-197, which released large volumes of water through C-111 and into Barnes Sound. The 1988 

rainy season represents a situation where, historically, large volumes of freshwater would have gone 

to Florida Bay via Taylor Slough, but were instead diverted into C-111 and into Barnes Sound. 

Figure 28 shows how two gages in the upper Taylor Slough basin responded to the heavy rains 

of August, 1988. Gages G-1363 and G-1502 (see Figure 2 on page 18 for locations) are generally 

indicative of the behavior of the areas east and west of L-31N, respectively. The eastern gage, G1363, reached a peak stage of 8.42ft on August 15. In general, the heaviest rainfall occurred on the 

areas east of L-31N. Even though G-1363 saw heavier rainfall amounts that G-1502, the stage at 

50 
3.1. WET SEASON, 1988 

,,-.... Ocn 

~S 

U5~ '-' 

8 

7 

6 

S 

4 

3 

4 

Rainfall and Stages in the L31N Basin 

from July 1, 1988 to November 30, 1988 

G-1S02 ~ 

G-1363 --+----

L-31N --8·_·· 

7/1 7/1S 7/31 8/1S 8/31 9/1S 9/30 lOllS 10/3111/1S 

Date 

Figure 28: Stages in the L-31N basin from July, 1988 to November, 1988. 

51 
52 CHAPTER 3. OPERATION OF THE SDCS DURING STORM EVENTS 

G-1363 exceeded 5.5ft for only 12 days. The western gage, G-1502, saw smaller increases due to 

rainfall, but also a more persistent stage, with much slower recession. 

Looking at only the August, 1988 flow totals, shown in Figure 29, gives a view of the relative 

magnitudes of the L-31N water budget. The relative seepage contributions are again based upon 

the ratio of groundwater slopes; these estimates should be viewed as very rough. This water budget 

demonstrates a number of points. Firstly, L-31N is used to mitigate high water lev('ls in the areas 

east of L-31N, and does not always recharge this area. However, using L-31N to reduce stages east of 

L-31N has a detrimental impact west of the levee. 'We estimate that seepage from west of the levee 

is approximately 50% higher than that from the east during the month of August, 1988. Secondly, 

even in this wet month, inflows to Taylor Slough via S-174 were probably less than the volume 

removed from the Rocky Glades and Taylor Slough. Even during this storm event, the SDCS did 

not contribute a net volume of water to Taylor Slough and the Rocky Glades. 

Lastly, we again note that the seepage collected in L-31N is largely routed to C-ll1 via S176. This aggravates the high water conditions downstream, potentially increasing the frequency of 

discharges from S-197 in Barnes Sound. Historically, the bulk of late wet season flows went through 

Taylor Slough to Florida Bay; current operational policies tend to put the bulk of late wet season 

flows into the lower C-ll1 basin, the Park's eastern panhandle, and into Barnes Sound. The basis 

for increasing flows to Florida Bay should begin by reducing the drainage of the Rocky Glades and 

Taylor Slough by raising L-31N canal stages, and also by routing high wet season flows into Taylor 

Slough via S-174. 

One way to look at the overall drainage effect of the lower L-31N canal is to examine the 

cumulative inflows and outflows, as in Figure 30. Of interest here are the slopes of the inflow 

and outflow curves, indicative of the discharge. There rate of inflow does not exceed the outflow 

discharge for any significant period. The L-31N canal drains the basin throughout the entire five 

month period, with the rate of drainage more or less constant from July through September. The net 

drainage from July I-November 30 is 58,000 acre-ft. Moreover, one can safely say, based upon the 

fact that heads west of L-31N exceed those east (see Figure 28), that the Rocky Glades and Taylor 

Slough lost at least 58,000 acre to L-31N; most likely, the true value is in the range of 75,000-90,000 

acre-ft for these five months. Contrasting this with the total S-174 volume of 47,500 acre-ft, we again 

see that the SDCS, operating in flood mode, represents a net loss of water from the Rocky Glades 

and Taylor Slough into the lower C-ll1 basin. 
,. 

3.1. WET SEASON, 1988 53 

....J .":. 

~ ~':r.-"~~~ 

Figure 29: Total flow volumes in the L-31N borrow canal during August. 1988. The dark arrows 

represent flow through structures, while the light arrows represent estimated groundwater seepage. 
54 CHAPTER 3. OPERATION OF THE SDCS DURING STORM EVENTS 

Cumulative Inflows and Outflows 

in the lower L31N basin 

from July 1, 1988 to November 30, 1988 

250 ,---.---,----..----r--,----..r----r----r--r-----, 

~i-_~-----------

200 Cumulative Inflows 

Cumulative Outflows 

150 

100 ////-

-- .--

-- 50 /' --

o ~~--~--~--~--~--~--~--~--~~ 

711 7115 7/31 8/15 8/31 9115 9/301011510/311111511130 

Date 

Figure 30: Cumulative inflows and outflows L-31N from July, 1988 to November, 1988. 

3.2 Canal Operations and the C-111 Interim Project 

In December 1988 the South Florida Water Management District proposed a new set of interim 

operational recommendations for the C-ll1 basin. The six proposed structural and operational 

changes were designed to address two major problems in the C-ll1 basin: (1) increased flows into 

the lower C-ll1 basin resulting from implementation of wet season stormwater pumping at S-331, 

and (2) the lack of water management flexibility of the earthen plug at the downstream end of the 

C-ll1 canal. By 1991, two new structural features were added to address these problems. 

To control seepage into the L-31N canal from Northeast Shark Slough, a new water control 

structure (G-211) was constructed immediately south of the intersection of the L-31N and C-1W 

canals. This structure has allowed the District to maintain wet season stages up to 6.0 feet in the 

northern reach of the L-31N canal, which is 1.0 to 1.5 feet higher than design stages. SFWMD 

analyses have shown that the subsequent reduction in seepage losses has significantly decreased the 

frequency, duration, and volume of wet season pumping at the S-331 pump station. 

In 1991 the District modified the earthen plug at S-197 by adding 10 additional gated culverts. 

The installation of an operable structure has allowed gate openings to be more gradual, and eliminated the need to pull the earthen plug. The first test of the benefits of this modification occurred 

in June 1992, following a period of intense rainfall. The new gates were opened gradually, with the 

structure remaining fully open (13 gates out of water) for only three days. The results of this storm 
3.2. CANAL OPERATIONS AND THE C-l11 INTERIM PROJECT 55 

showed that the new operable structure was able to reduce the magnitude, although still substantial, 

and duration of large freshwater releases through S-197 into Manatee Bay. 

3.2.1 Wet Season Operations 

A one and one-half month period, centered on the June 1992 storm, was reviewed to characterize 

wet season canal operations under the C-111 Interim Project. Figure 31 shows daily rainfall, canal 

water level changes, and structure operations for the L-31N canal between G-211 and S-176. The 

daily data on actual canal stages and structure discharges were not available at the time of this 

report, so we used the daily water readings record supplied to the park by the Data r.Ianagement 

Division of the SFvVMD. For this reason. a detailed water budget analysis could not be performed. 

Canal 111 water levels remained low throughout May and early J ~me, following a long period 

of below normal rainfall. During the first two weeks of June structures G-211 and S-331 were 

used to make water supply deliveries to the Taylor Slough and lower C-111 basins. By June 15th, 

downstream stages had reached their allowable optima, and G-211 was closed to prevent overdrainage of Northeast Shark Slough. S-176 headwater stages were maintained at or below the 4.5 

foot wet season criteria throughout the first three weeks of June. 

Canal stages rose rapidly on June 23rd, in response to widespread rainfall associated with a 

stationary, low pressure system. By June 24th, S-331 began flood control pumping, S-176, S-l77, 

and S-18C was opened full, and S-197 had 3 and later 7 gates pulled. On June 26th, G-211 headwater 

stage exceeded 6.00 feet, the gates were opened full, and S-331 pumping was halted to limit inflows 

to the downstream reach of L-31N. By July 6th, upstream water levels had stabilized. G-211 was 

closed and downstream canal water levels had fallen sufficiently to resume S-331 pumping. 

Figure 32 shows the changes in canal stages and gate operations during the same period for 

the structures controlling the L-31\V canal. Stage data from the recorder at NTS-1 is also show 

to demonstrate the close linkage between L-31 vV operations and marsh water levels in Northern 

Taylor Slough. The gate operational records indicate that the L-31 W control structures were fully 

utilized during this storm period. Structure 174 was opened full on June 26th and remained open 

full through mid July. Structure 175 was opened full on June 23rd, and remained fully opened until 

July 6th. Structure 332 was similarly operated at its maximum pumping capacity throughout the 

entire period. 

The early closure of S-176 helped to prevent over-drainage of the Rocky Glades. This is a key 

element of any effort to restore more natural flows to Taylor Slough. Similarly, the prolonged use 

of 8-174 had the beneficial effect of diverting much of the excess flows away from the lower C-111 

canal and into Taylor Slough. The water level record for NTS1 suggests however, that following 
56 

0 

OJ) 

~ ..... 

en "--,, 

I-< -t:/) 

0 8 ..... 

~ 

~ ~ 

"'0 '---' 

~ 

0 

::c 

G-211 

S-331 

S-176 

6.5 

6.0 

5.5 

5.0 

4.5 

4.0 

3.5 

3.0 

2.5 

CHAPTER 3. OPERATION OF THE SDCS DURING STORM EVENTS 

.--------------------------------------------------------,3. 

-- 2. e.S "--,, 

= = 1 ·a C .~ 

~L-LL~~~~---L~--~~~~------L-------~----~~O. 

1 

G-211 

S-331 

S-176 

ci 

7 14 28 7 14 21 

JUD 

21 

JUD 1992 Jul Jul 

Figure 31: Operations of L-31N in June-July, 1992. The stage values are taken from SFWlvlD daily 

water readings. The rainfall is measured at R-3110. 
3.2. CANAL OPERATIONS AND THE C-ll1 INTERIM PROJECT 

b.O S-176 

c .-C 

Il) 

0..Z' Oc S-174 

Il) 

...... 

~ 

0 S-175 

S-332 

(cfs) 

,-----------------------------------------------------.3. 

6.0 

5.5 

5.0 

4.5 

4.0 

3.5 

3.0 

2.5 ..... : 

2.0 

Jun 

10 

0 

10 

0 

3n.O 

0 

165 

0 

7 14 21 28 

Jun 

1992 

7 

Jul 

S-176hw 

S-175hw 

NTS-1 

14 

Jul 

21 

57 

Figure 32: Operations of L-31 W in June-July, 1992. The stage values are taken from SFWMD daily 

water readings. The rainfall is measured at R-3UO. 
58 CHAPTER 3. OPERATION OF THE SDCS DURING STORM EVENTS 

the initial L-31W stage reduction, S-175 and S-332 outflov:s greatly exceeded S-174 inflows. This 

indicates that more attention is needed to track L-31 W operations, or the canal system will continue 

to over-drain the adjacent Taylor Slough marshes. 

3.2.2 Dry Season Operations 

A period of just over two months, from October 1st through early December 1992, was similarly 

reviewed to characterize the dry season canal operations under the C-111 Interim Project. Figure 33 

shows daily rainfall, canal water level changes, and structure operations for the L-31N c.anal bet.ween 

G-211 and S-176. Again the daily data on actual canal stages and structure discharges were not 

available and we relied on the daily water readings record provided by the District. Canal 111 water 

levels were high throughout the early dry season following above normal rainfall in the late wet 

season. Throughout October and the first week of November G-211 stages remained generally at or 

above 6.0 feet, and water supply releases were made into the downstream canal system. The S-331 

pump station passed most of the excess water southward by setting the three units in a syphon 

mode. During this period, S-176 headwater stages remained below 4.8 feet, and the gates Wf're kept 

closed. Structure 174 was left open throughout this period, and the excess water was passed into 

the Taylor Slough basin. 

High rainfall between November 3rd and the 10th raised water levels in the upstream C-111 

basin. In response, G-211 was closed, and S-331 began flood control pumping. By November 10th, 

S-176 was opened to help control stages in the lower reach of the L-31N canal. By November 

17th, additional rainfall prompted the opening of G-211, S-331 began pumping ncar its maximum 

capacity, and the gates at S-176 were opened full. High water conditions persisted through the end 

of November. On December 1st, G-211 was closed, pumping at S-331 was cut back, and S-176 was 

partially closed. 

Figure 34 shows the changes in canal stages and gate operations during the same period for the 

structures controlling the L-31 W canal. Again, NTS1 water levels are included to show the impacts 

of canal operational changes on the adjacent Taylor Slough marsh. vVater supply releases were made 

through S-174 throughout October and early November. On November 12th, S-174 was closed, and 

it remained closed until November 26th, when the headwater stage dropped below 4.8 feet. Structure 

175 was opened full on November 12th, and it remained fully open until December 1st. During this 

period L-31 W water level dropped by more than 1.2 feet, from a high of 4.60 to 3.34 feet. Inflows 

into the L-31W canal were not resumed until S-175 headwater stage dropped below 3.5 feet. The 

early closure of S-174 essentially denied Taylor Slough of any of the benefits that the dry season 

rainfall could have provided. Similarly, the excessive discharges through S-175 artificially forced the 
3.2. CANAL OPERATIONS AND THE C-lll INTERIM PROJECT 59 

~-b!)V) --- ~ E ...... 

!Z) ¢: 

"-" 

..... 

..... 

r---------------------------------------------------------~3 . 

..-

..- 2. ~ ,-.. c:: c:: .~ .- 1. ~ "-"-

~--------~-~--------~~----~----~~~--------------~O. 

6.0 

5.5 

5.0 

4.5 

G-211 HW -- S-331 HW 

S-176HW·-e-··· 

,,

/r----+---+-

.. ~,. .. ;Ir'", 

'" '~----.l 

4.0 ~--------~--------~----~------~----------~~--~--~~ 

1 14 28 

Oct Oct 

1 

Nov 

1992 

14 28 1 7 

Nov Dec 

b!) N ~] c:: I 

'2 0 ~ 

0.. 211 0 

~ ...... 

~ 

Cl 

..... 0.. 

("f) 

("f) 

I 

~ 0.. 3 ~ a 0 !Z) '" .c: 0..0 0 ~ 

'" 

\0 10 

r-

..... I 0 !Z) 

Figure 33: Operations of L-31N in October-November, 1992. The stage values are taken from 

SFWMD daily water readings. The rainfall is measured at R-3110. 
60 CHAPTER 3. OPERATION OF THE SDCS DURING STORM EVENTS 

L-31 W canal system down to the 3.5 foot level, instead of allowing water levels to recede naturally 

into the dry season. The water level record at NTS1 shows that much of the S-175 outflows were 

the result of drainage of the adjacent Taylor Slough marshes. 

3.3 Canal Operations and the Taylor Slough Demonstration Project 

Review of the C-111 canal operations under the interim project guidelines dearly points to the need 

for additional operational improvements to control over-drainage of Northern Taylor Slough. The 

two most important operational changes were included as part of the original recommendations for 

the C-111 Interim Project. First, the operational guidelines for S-176 need to be revised to reflect 

the reduced flood risk to the canal reach between S-331 and S-176 resulting from improved seepage 

control upstream of S-331. The proposed Taylor Slough Demonstration Project calls for raising the 

wet season control elevation at S-176 from 4.3 to 5.0 feet. Second, the pl<l:n calls for increasing the 

pumping capacity of S-332 by an additional 100 cfs. and for more effective use of S-332 during the 

wet season. 

It is clear that the reductions in C-111 canal operational stages over the past ten years were done 

without adequate environmental assessments. It is also apparent that these operational changes 

have detrimentally contributed to the wetland drainage problems in the Taylor Slough basin. For 

these reasons the starting point for all of our restoration efforts should be a return to the original 

authorized canal operational stages. This means that the demonstrat.ion project is at best. a modest 

first attempt to restore historical water levels in the Taylor Slough basin. The 100 cfs increase in 

S-332 pumping capacity should also be viewed as only a first step toward reaching the required flow 

capacity that will most likely be needed in the Taylor Slough basin. Indeed, given the current L-31 W 

operational guidelines, the additional capacity could prove to be detrimental if it is used to quickly 

lower canal stages during periods of high rainfall. Obviously, additional criteria will be needed to 

fully define the operational guidelines of the proposed Taylor Slough Demonstration Project. 

The Park's major goal for the demonstration project is to maintain optimum wet season water 

levels in the L-31N and L-31 W canals, and to allow canal stages to recede naturally into the dry 

season. This will be difficult since it will require adherence to the 5.0 and 4.5 foot optimum criteria 

for S-176 and S-175, whenever excess water is available, while allowing canal water levels to fluctuate 

in response to rainfall. The best approach is to have all outflows from these canals balanced, as much 

as possible, by inflows from their upstream water control structures. To maximize Taylor Slough 

inflows, S-174 should remain open as long as possible, except when closure is needed to maintain 
I """_.' '_, .......... .. 

3.3. CANAL OPERATIONS AND THE TAYLOR SLOUGH DEMONSTRATION PROJECT 61 

4.8 

4.6 

,-.. 4.4 

~ CZl 

~ a 4.2 ..... 

.-----------------------------------------------------~3. 

2. --~ ,-.. Q Q .,... .~ 

I t'l:!'-' .~ 

~--------L--~------~~--~w---~~~~------------~O. 

C/) r:.+:: 4.0 

~ 

Q .-Q 

~ 

0.. 

0 

~ ..... 

t'I:! 

0 

'-' 

3.8 

3.6 

3.4 

3.2 

L-31W ___ 

L-31N --+---. 

NTSI "'.'" 

.. '~ . 

3.0 ~------~----------~--~------~--------~~----~--~ 

1 

Oct 

S-332165 

(cfs) 0 

S-175 

S-174 

10 

S-176 

0 

14 28 

Oct 

1 

Nov 

1992 

14 28 1 7 

Nov Dec 

Figure 34: Operations of L-31W in October-November, 1992. The stage values are taken from 

SFWMD daily water readings. The rainfall is measured at R-3UD. 
62 CHAPTER 3. OPERATION OF THE SDCS DURING STORM EVENTS 

upstream optimum stages, or to control backflows. Similarly, the opening of S-176 should limited, 

so that all excess flows are directed westward into Taylor Slough, except those required to meet the 

delivery needs of the lower C-ll1 basin. 

All gate operational changes should be made as gradually as possible, so that excess stormwater 

is not rapidly forced through the L-31N and L-31 W canal systems. 'When large releases are needed 

to control L-31N canal stages S-174 should be used to the maximum extent possible. When L-31W 

stage reductions are needed, outflows should concentrate on prolonged S-332 pumping, and S-175 

operations should be reduced, as Inuch u.s possible, to short periods of limited releases. During the 

dry season, water supply deliveries should continue to be made to Taylor Slough whenever upstream 

water is available and stages are below 4.5 feet. Once the canal stage has receded to 3.5 feet, S-332 

can be used to maintain L-3IVV water levels. If needed, S-175 releases can be made so that water 

supply and flood control releases through S-174 do not significantly raise L-31 W stages. As quickly 

as possible the three agencies should begin testing and implementation of a new rainfall-based water 

delivery formula for the Taylor Slough basin. In the interim, we should set a target for annual water 

volumes to be split so that approximately 70 percent of the available L-31N flows pass westward 

through S-174 into Taylor Slough. The remaining 30 percent would pass through S-176 to meet the 

environmental needs of the lower C-ll1 basin. 
Chapter 4 

Salinity in Florida Bay 

Concerns about Taylor Slough have become more pressing with the increased attention to problems 

in Florida Bay. There are a number of scientific hypotheses about the cause of t.he observed declines 

in Florida Bay, but one cause generally agreed to be a significant factor is the modification of 

freshwater inflow to Florida Bay. In this chapter, we present some of the available information on 

salinities in Florida Bay and how they are related to flows in Taylor Slough and the lower C-1l1 

basin. 

The data base for salinity in Florida Bay is incomplete. One of the best salinity data sets was 

collected by Dr. ~Iicheal Robblee of the South Florida Research Center subsequent tn Hurricane 

Floyd on October 12, 1987. We begin our presentation of salinity information by examining his 

data. Hurricane Floyd hit the south Florida coast with Category 1 winds. and with approximately 

lOOmm (3.90in) of rain in the areas upstream of Florida Bay, as measured at Homestead. The storm 

was not particularly intense or wet. but does reflect the typical response of the Project to a storm. 

4.1 Project Flows 

We can examine inflows to Taylor Slough and the Eastern Panhandle of the Park by looking at S174, S-18C, and S-197 discharges. These are shown in Figure 35. There are a number of important 

features here. Firstly, note that the operational response to the storm was to shut off water to Taylor 

Slough. Eight days after the storm, S-174 was completely closed, and no water was sent to Taylor 

Slough. Instead, flood water was sent down to C-ll1. The reason for diverting the flood water into 

C-ll1 was probably to increase the rate of drainage in L-31N and the upper C-ll1 basins. By moving 

water south as fast as possible, this decreases the likelihood that the urban and agricultural lands 

will experience any flooding. This operation contradicts the stated operational criteria whereby 

63 
64 CHAPTER 4. SALINITY IN FLORIDA.. DAY 

Figure 35: Discharges to Taylor Slough and the Eastern Panhandle after Hurricane Floyd, October 

12, 1987. 
'\ 

" " " " "-

o 

. 

~IJ 

Florida Bay 

o· 

" 

Figure 36: Salinity contours 1 day after Hurricane Floyd. 

S-174 is opened first. giving Taylor Slough higher priority as a flood release mechanism. 

Secondly, note that the flows to C-111 are much larger than those going to Taylor Slough. For 

October-November. 1987. 9,900 acre-ft went to Taylor Slough, while 83,800 acre-ft went into the 

Panhandle, giving about a 10%-90% split. Compare this to the current minimum delivery schedule 

calling for about a 70%-30% split. Again, this disparity occurs because development pressures force 

the District to dump water south as quickly as possible, rather than move water into Taylor Slough. 

4.2 Florida Bay Salinity 

The effects of these operations on Florida Bay can be seen in Figures 36-38, which are snapshots 

of salinity measurements taken one, nine, and seventeen days, respectively, after Hurricane Floyd. 

These pictures are telling in a number of ways. Firstly, note how the easternmost end of Florida 

becomes fresh very rapidly. \-Vater flows out of the eastern cut-outs on the C-1l1 canal and moves 
66 CHAPTER 4. SALINITY IN FLORIDA BAY 

D 

Q 

o 

Florida Bay 

; 

o· 

Figure 37: Salinity contours 9 days after Hurricane Floyd. 
D 

"-

"-

"-

Florida Bay 

"- - "- 1 o· 

" 

Figure 38: Salinity contours 17 days after Hurricane Floyd. 
68 CHAPTER 4. SALINITY IN FLORIDA BAY 

quickly into the Long Sound/Blackwater Sound region. This area is also bordered to the e"lSt by 

US Highway 1. and on the west by Shell Key. There is little tidal exchange, and the region becomes 

increasingly fresh in response to the C-lll inflows. 

Similarly, one can see a plume of fresh water emanating from Joe Bay, which is directly downstream of the western C-111 cutouts. Clearly, the water coming from C-111 is moving into the 

eastern portion of Florida Bay and the salinities in that region are reflecting this. However, there 

is also indication that the fresh water is not being rapidly mixed, an indication of incomplete tidal 

exchange. That is, the water passed duwn C-111 was not distributed throughout Florida Bay, but 

remained in the shallow embayments of northeast Florida Bay, blocked by shoals and ot.her natural 

obstructions. 

These graphs also demonstrate the effect on Florida Bay of the reduced surface wat.er flows to 

Taylor Slough. Even after this storm event, the areas of Florida Bay south of Madeira and Little 

Nladeira Bays remained at 45 parts per thousand (35ppt is typical marine salinity.) At this time 

of the year, when the largest surface water flows historically occurred. hypersaline conditions would 

not be expected. 

Based upon the size of the contributing area, Taylor Slough contributed much more freshwater 

than the saline marshes to the east. But this pattern has been reversed by current operational 

policies. Moreover. the easternmost areas of Florida Bay have the poorest circulation. so freshwater 

flows are not redistributed throughout the Bay. 

At this point, there is little hard information on historical flow volumes to Florida Bay, and one 

cannot directly determine of the C-111 flows are larger than historical or not. However, one can 

certainly deduce that Taylor Slough flows must have been umch higher than today. The reintroduction of significant Taylor Slough flows will allow freshwater in the areas that are currently the 

most hypersaline. and will help to redistribute flows across the entire Florida Bay/upland marsh 

boundary. 

" " ..•. _." .... ,- . ...... .. -............ '.-"' ................. --.-'" -~. ',-.- ... ~ ...... ... 
Chapter 5 

Modeling of Flow to Florida Bay 

The next step in our a')sessment of the potential impacts of upstream water management on Taylor 

Slough and the downstream areas of Florida Bay was to compare pre- and post-project smface water 

flow volume estimates across a flow line in the lower Taylor Slough basin. The comparison was made 

based on daily surface water flow estimates from the Natural System Model (version 3.6) and the 

South Florida Water i\'1anagement Model (version 1.1) for four grid cells (cells 20-6, 21-6, 22-6, and 

23-6) in the lower Taylor Slough basin. This flow line was chosen for two reasons. First, by choosing 

a flow line well south of the upstream water management system we can reduce any conflicting effects 

caused by groundwater seepage into the L-31N and L-31 \V canals. Second, we wanted to focus on 

the potential surface water flow changes in the southern part of the basin. since these changes will 

have the greatest impact on freshwater flows to Florida Bay. 

5.1 Surface Water Flow Comparisons 

Figure 39 is a comparison of the calculated annual flow hydrographs for the ten year period from 

1980 through 1989. The flows are highly variable but it is clear that the Natural System Model 

predicts that surface water flows would have been much higher that what would be expected under 

current operations. Figure 40 is a comparison of the average monthly surface water flows along the 

same flow line. This plot suggests that substantially more water is needed throughout the year if 

we are to reproduce NSM flow conditions. These are only rough estimates, since problems exist 

with the grid cell resolution and the downstream boundary conditions in both models when they 

are applied to small watersheds like Taylor Slough. However, the estimates are useful and show 

that potentially large volumes of water will be needed to restore natural flow conditions in Taylor 

Slough and ensure the larger, historical flows to Florida Bay. The overdrainage of the head waters of 

69 
70 CHAPTER 5. MODELING OF FLOW TO FLORIDA DAY 

TAYLOR SLOUGH FLOWS 

60r------------------------------------, 

Natural (solid) Annual Mean = 82.000 at 

Managed (dashed) Annual Mean = 31.500 at 

. >. 

\ 1 o " 

80 81 

i 

" !\ 

, i 

Ii 

i 

82 83 84 85 

YEAR 

89 

Figure 39: Comparison of calculated surface water flows into southern Taylor Slough and Florida 

Bay. 

the Taylor Slough basin has most likely contrihuted significantly to the loss of downstream flows by 

reducing the hydraulic gradients throughout the basin. The lowering of the groundwater stage has 

eliminated a large volume of water from storage, which historically contributed to flow to Florida 

Bay well into the dry season. 

5.2 Comparison of Ponded Water 

The spatial distribution of surface water depths for section of the model calculated by the NSM and 

the SF'VVMM is shown in Figure 41 for the "average year" of 1978. Both the driest month, April, 

and the wettest month, October, are plotted to demonstrate how much wetter the sloughs are under 

pre-drainage conditions. The area of the model shown in the figure includes Shark Slough, south of 

the Trail, and Taylor Slough. Almost complete drydowns of the peripheral wetlands of the sloughs, 

as shown occurring in April under managed conditions, seldom occurred under natural conditions. 

During April of this particular year no standing water occurs in the SFWMM over 75% of the 1844 

mi2 area shown in the graphic, which is double the percentage (37%) of dry land in the NSM. Deep 

pools of water were naturally present in and to the north of the Park. These pools slowly drained 
5.2. COMPARISON OF PONDED WATER 

~ r------------------------------------, 

Natural (solid) Annual Mean = 82.000 ac-tt 

Managed (dashed) Annual Mean = 31,500 ac-tt 

'm 

~ # 

} 

I 

:11 

I i :1 

:::s 

.:::~ 

'!i~ 

•. X( 

!~. 

\;1 

il 3 

}~ 

'.::~ 

:~~ ;::: 

tL 1'1 '::~ 

o----~-&~~-&~--~~~~~~~~--.-~ t I. II ::~ }~~ 

JAN FEBMARAPRMAY JUN JULAUGSEPOCTNOVDEC 

MONTH 

71 

Figure 40: Average annual hydrographs for surface water flows into southern Taylor Slough and 

Florida Bay_ 
72 

Natural System 

CHAPTER 5 . . \IODELING OF FLOW TO FLORIDA BAY 

April 1978 

Legend 

o 0) No Dat·~ [] 1 \ Zerc, Dept 

o ~\ 0 <= 0.5 

I]) 3

4 

( O. 5 <= 1. ~ \ 1.0 <= 1. 

~ 5~ 1.5 <= 2. ~ 6 ~ >= 2.0 ft 

Managed System 

Figure 41: Comparison of ponded water depths between the managed system and the pre-drainage 

condition. 
5.3. GROUNDWATER FLOW 73 

southward well into the dry season, keeping the main drainage ways full of standing water. These 

deep pools of water diminished. from 20% of the NSM area covered during April by more than one 

foot of water. to 0.4% of the SFWMM area. 

Although it appears that natural drydowns occurred in April in the wetlands and the headwaters 

of Taylor Slough, the Rocky Glades had up to a foot of water on the surface. The SFWMM shows 

that under current conditions no surface water is present on the Rocky Glades at any time and not 

much water is present in the lower reaches of the Slough. This condition continues well into the wet 

season. when as illustrated by the October plots, the deep water pools are almost non-existent. The 

2 by 2 mile grid size of the models limit their usefulness in small basins such as C-lll. where only 

a few cells simulate the area. Comparison of the NSM and the SF\VMM for these and other time 

periods illustrate profoundly the enormous reductioli in surface water depths and fresh water flows 

which has occurred in the wetlands as a result of the canal system. 

5.3 Groundwater Flow 

The NSM can be used to illustrate general groundwater flow patterns under pre-project conditions. 

Figure 42 is an average of 25 years worth of monthly groundwater flow directions and magnitude. 

East of the coastal ridge, significant quantities of groundwater seep from the ridge into the Atlantic 

Ocean, while the predominant flow patterns along the western side of the ridge are west to southwest. 

The coastal ridge thus acted as a drainage divide for both ground and surface water flows in predrainage conditions. Under managed conditions the pattern west of the ridge has reversed and 

large groundwater flows occur to the east from Everglades National Park into the adjacent drainage 

canals. 

This pattern of groundwater flow is in direct contrast to what is suggested in Figure 9 on 

page 26. This water budget would suggest large seepage losses from the wetlanc!s west of L-31N into 

the developed coastal areas. This is also supported by Leach et al. [1972], who used post-Project 

water levels to document a general eastward and southward movement of groundwater. Figure 42 

suggests the Project has signficantly altered the groundwater flow patterns. Prior to construction 

of the C&SF Project, groundwater moved southward and westward off the coastal ridge. Today, 

seepage flow is predominately eastward. Thus, the seepage losses from wetlands in Taylor Slough and 

Northeast Shark Slough represent the drainage effects of the Project, and not historical groundwater 

flow patterns. 

Chapter 6 

Recommendations 

The primary purpose of this report is to acquaint the Park management staff about hydrologic 

information that most directly affects policy decisions about Taylor Slough and its freshwater inflows 

to Florida Bay. The Park's immediate objectives for improvement and protection of the Park's water 

resources in Taylor Slough, the Eastern Panhandle marshes, and Florida Bay, should be 

• Pursuit of water management policies that increase hydroperiods of the marshes in the Rocky 

Glades and Taylor Slough. Water levels, not flows, are the key indicator of marsh restoration. 

• Establishment of a rainfall-based water delivery formula for flows into Taylor Slough and the 

Eastern Panhandle. 

• Protection of water quality standards for water deliveries to Taylor Slough and the Eastern 

Panhandle. 

The Corps, the District, and the Park have agreed in principle to pursue an experimental test 

of operational policies and structural modifications for Taylor Slough and the C-ll1 basin intended 

to remedy the environmental decline of the past several decades. There are several actions that can 

be undertaken during this first experimental test for Taylor Slough. \Ve recommend that, for this 

initial test: C 

1. The District return canal operations to original design optimum flood control levels in L-31N 

and C-l11. This would require a 5.5ft stage at S-176, 4.5ft at S-l77, and 3.0ft at S-18C. This 

is the single most important recommendation. This signals that environmental protection 

elements of the Project design will be considered co-equal with flood control. 

2. The flood control operations of S-331 need to be curtailed, in conformity to the design objective 

of a dry seaSon, water supply structure. The large interbasin storm water transfers during wet 

75 
76 CHAPTER 6. RECOMMENDATIONS 

periods are inconsistent with efforts to restore historical flow patterns in Taylor Slough and 

the lower C-111 basin. 

3. Keep S-174 open as long as possible, except when closure is needed to maintain upstream 

optimum stages, or to control backflows. Backflows from L-31W to L-31N via S-174 can be 

limited by returning to design flood control optimum stages of 5.5ft NVGD at S-176 and 4.5ft 

NVGD at S-I77. 

4, The op eration of S-176 should be limited, so that all excess flows are directed westward into 

Taylor Slough, except those required to meet the delivery needs of the lower C-lll basin. \Ye 

tentatively propose a 70-30 split of base flows between S-174 and S-176, respectively. As our 

understanding of the hydrology of the C-lll improves, we will be in a better position to have 

more definitive recommendations on Eastern Panhandle needs. 

5. Structure-175 should be operated with 4.7ft open. 4.3ft close, and 4.5ft static operations criteria. That is, gates will open when L-3IW stages exceed 4.7ft, and will close again when stages 

reach 4.2ft. This will reduce the potential of using S-175 for excessive L-31W drawdowns. 

6. Under normal operation, S-175 should be closed. S-332 pumping should be roughly balanced 

with inflows at S-174. This will allow a gradual and more natural recession of L-31 W. 

7. During the dry season. water supply deliveries should continue to be made to Taylor Slough 

and the Eastern Panhandle whenever upstream water is available. \Ye should re-examine the 

role of the SDCS in providing supplemental dry season deliveries, since the current volumes of 

inflows from the regional system are approximately 38 percent of the November to May inflows 

anticipated by the Corps when they designed the Soth Dade Conveyance System. 

8. Storm water that is generated in the C-102 and C-103 canals west of S-194 and S-196, should 

be routed westward into L-31N and then into Taylor Slough. That is consistent with the 

original design of the water management system in southwestern Dade County. If this cannot 

be done, then the demands on the regional water supply system will increase. 

9. All gate operational changes should be made as gradually as possible, so that excess stormwater 

is not rapidly routed through the L-31N and L-31 W canal systems. We should establish a goal 

of conserving as much of this wet season runoff as possible, since this will reduce the need for 

supplemental dry season deliveries for the regional system. 

10. As quickly as possible the Corps, the SFWMD, and the Park should begin testing and implementation of a new rainfall-based water delivery formula for the Taylor Slough basin. 
77 

References 

[Curnutt and Pimm, 1993] J. Curnutt and S. Pimm. Status and ecology of the Cape Sable seaside 

sparrow. Technical Report to the National Park Service under Agreement 5280-2-9021. University 

of Tenilessee. Knoxville, TN, 1993. 

[Johnson and Fennema, 1989] R. Johnson and R. Fennema. Conflicts over flood control and wetland 

preservation in the Taylor Slough and Eastern Panhandle basin of Everglades National Park. In 

Water: Concerns and Succes$es. American Water Resources Association. September 1989. 

[Johnson et al .• 1988] R. Johnson . .1. Wagner, D. Grigsby, and V. Stern. Hydrologic effects of the 

1984 through 1986 L-31(W) canal drawdwons on the northern Taylor Slough basin of Everglades 

~ational Park. Technical Report SFRC-88/01. South Florida Research Center. Homestead, FL, 

1988. 

[Leach et al., 1972] S. Leach, H. Klein. and E. Hampton. Hydrologic effects of water control and 

management of southeastern Florida. Technical Report of Investigations no. 60, Florida Bureau 

of Geology, Tallahassee, FL, 1972. 

(Mac Vi car and VanLent, 1984] T. )"IacVicar and T. VanLent. A thirty day field test of water deliveries to Northea'lt Shark River Slough, April - May, 1984. evaluation report. Technical report, 

South Florida Water Management District, West Palm Beach. FL. 1984. 

[Mac Vicar. 1985] T. :'IacVicar. A wet season field test of experimental water deliveries to Northeast 

Shark River Slough, August - 0l"ovember 1984. Technical Report 85-3. South Florida Water 

Managment District, West Palm Beach, FL, 1985. 

[Neidrauer and Cooper, 1989] C. Neidrauer and R. Cooper. A two year field test of the rainfall 

plan: A management plan for water deliveries to Everglades National Park. Technical Report 

89-3, South Florida Water Management District, West Palm Beach. FL, 1989. 

[U.S. Army Corps of Engineers, 1959] U.S. Army Corps of Engineers. General Design Memorandum, Levee 31 and Related Works, Central and Southern Florida Project, Supplement 30, Part 

V, Coastal Areas South of St. Lucie Canal. 1959. 

[U.S. Army Corps of Engineers, 1960a] U.S. Army Corps of Engineers. Detail De$ign Memorandum, Levees 67A and 29, Section 3 and Control Structure 151, Central and Southern Florida 

Project, Supplement 34, Part I, Agricultural and Conservation Areas, 1960. 
78 CHAPTER 6. RECOM.\IENDATIONS 

[u.S. Army Corps of Engineers, 1960b] U.S. Army Corps of Engineers. Detail Design Memorandum. Levee 29, Sections 1 and 2 and Control Structures 12A, B, C, D, E and 14, Central and 

Southern Florida Project, Supplement 35, Part I, Agricultural and Conservation Areas, 1960. 

[u.S. Army Corps of Engineers, 1960c] U.S. Army Corps of Engineers. General Design Memorandum. Conservation Area No.3, Central and Southern Florida Project, Supplement 33. Part I, 

Agricultural and Conservation Areas, 1960. 

[u.S. Army Corps of Engineers, 1961] U.S. Army Corps of Engineers. Survey Review Report, South 

Dade County, Central and S01j,thern Flor·ida Project, 1961. 

[u.S. Army Corps of Engineers, 1963a] U.S. Army Corps of Engineers. Detail Design Memorandum. Canal 111, Section 1, and Control Structure 18C, Central and Southern Florida Project, 

Supplement 38, Part V, Coastal Areas South of St. Lucie Canal, 1963. 

[u.S. Army Corps of Engineers, 1963b] U.S. Army Corps of Engineers. Survey Review Report, 

Southwest Dade County, Central and Southern Florida Project, 1963. 

[u.s. Army Corps of Engineers, 1963Cj U.S. Army Corps of Engineers. General Design Memorandum, South Dade County, Central and Southern Florida Project, Supplement 37, Part V, Coastal 

Areas South of St. Lucie Canal, 1963. 

[u.s. Army Corps of Engineers, 1965] U.S. Army Corps of Engineers. Detail Design Memorandum, 

Canal 111. Sections 2 and 3; Canal 11 1 (E), and Cvntrol Structures 176, 177, and 178, Central 

and Southern Florida Project. Supplement 43, Part V, Coastal Areas South of St. Lucie Canal, 

1965. 

[u.S. Army Corps of Engineers, 1966] U.S. Army Corps of Engineers. Detail DesigT!- Memorandum, 

Levee 31 (N) and Control Structure 173. Central and Southern Florida Project, SUfJplement 44, 

Part V, Coastal Areas South of St. Lucie Canal, 1966. 

[u.S. Army Corps of Engineers, 1967] U.S. Army Corps of Engineers. Detail Design Memorandum, 

Levee 31{W); Canal 113, and Control Structures 174 and 175, Central and Southern Florida 

Project, Supplement 47, Part V, Coastal Areas South of St. Lucie ((anal, 1967. 

[u.s. Army Corps of Engineers, 1973] U.S. Army Corps of Engineers. General Design Memorandum, Conveyance Canals to Everglades National Park and South Dade County, with Detail Design 

Appendix on Pumping Station 331, and Enlargement of Reaches of Levee 31{N) Borrow Canal, 

C-l and C-103, Central and Southern Florida Project, Supplement 52, Part V, Coastal Areas 

South of St. Lucie Canal, 1973. 
( 

.1 

[u.S. Army Corps of Engineers. 1974] U.S. Army Corps of Engineers. Detail De,~ign Memorandum, 

Level; 29. Section :1. Borrow Canal Enlargement. Pumping Station 332. and Control Structures 

194 (MOD), 333, 334. 335. 3:16. and 838. Central and Southern Florida Project. Supplement 55, 

Part V, Coastal Areas South of St. Lucie Canal, 1974. 

[u.S. Army Corps of Engineers. 1975] U.S. Army Corps of Engineers. Final Environmental Impact 

Statement. South Dade Conveyance Canals and East Coast Backpumping, Central and Southern 

Florida Project. 1975. 

[u.S. Army Corps of Engineers. 1982] U.S. Army Corps of Engineers. Draft Feasibility Report 

and Draft Environmental Impact Statement. Shark River Slough. Central and Southern Florida 

Project. 1982. 

[u.S. Army Corps of Engineers. 1991] FS. Army Corps of Engineers. Alaster Water Control Manual. A uthorities and Responsibilities. Volume 1. Central and Soutlwrn Florida P1"O]f:ct. 1991. 

[u.S. Army Corps of Engineers. 1992] U.S. Army Corps of Engineers. Water Control Plan. Water 

Conservation Areas and Everglades National Park. and ENP - South Dade Conveyance System, 

Central and Southern Florida Project. 1992. 

[Wagner et al.. 1985] J. Wagner, R. Johnson. and D. Grigsby. Effects of the 1984 "Frog Pond" 

drawdown upon northern Taylor Slough water resources, 1985. :-'Ianagement RC'port. 
Appendix A 

Calculations 

This appendix contains the calculations and any summary data required to replicate the calculations 

performed in this analysis. 

A.I Water Budgets 

A.!.! Data Summaries 

Tables A.1-A..14 contain the monthly summary information used in the calculations of water budgets. 

The summaries are based upon the daily data presented in Appendix C. 

In all but two cases, the annual average was calculated over the the period 1983-1990. The two 

exceptions where S-194 and S-196. In each of those cases, only five years of relatively complete 

information was available; therefore, S-194 and S-196 were averaged for the available data. This was 

thought to be a conservative estimate, that is. it underestimates the flow to the east. 

These data also provide the basis for the calculation of the water budgets presented in the text. 

For the L-31 northern reach we defined the inflows and outflows as 

D.SU = Qh. - Q~ut 

Qio = Q5335 + Q5334 

Q5338 + Q5336 + Q5173 + Q5331 

(A.l) 

(A.2) 

(A.3) 

where the superscript u represents the "upper" L-31N basin. For the southern reach of L-31N. the 

inflows and outflows were 

(A.4) 

A.2 
-

II S·18C Flow Volumes (acre-rt) 

II Il Month 

II Year Il Jan I Feb I Mar J Apr May Jun I Jul I Aug I Sop 

68 OM oM OM O~I oM OM OM OM OM 

69 10649 2529 3106 H2O 5794 59310 60-10 17316 294-11 

70 1658 1004 267 0 a 1346 5635 488 548 

71 a a a a a 48 195 53 1191 

72 0 2 a 91 15812 65291 10947 -1261 1970 

73 85 0 a a a 9 2035 125",0 76-10 

74 17 a a a 0 a a a 0 

75 a a a 0 a -1795 11399 71013 0 

76 0 a a 0 10-13 2554-1 1964 13771 14039 

77 a a a 0 2999 12066 0 1997 25127 

78 0 41G5 0 1353 0 0 3537 0 15380 

79 0 0 a 10501 12452 81 2354 0 12147 

80 0 a 0 34 200 1207-1 6686 9328 20525 

81 0 7821 a 0 0 0 0 <16118 58069 

82 0 0 0 133 0 195M7 1638 6226 11075 

83 8277 -19107 59362 31490 3868 36223 13494 31597 59580 

84 0 0 2828 0 7972 12809 21709 29901 34787 

85 2850 1226 1014 575 224 910 42935 20882 .. 6107 

86 9378 686 8773 7922 0 26625 -16985 ,,7727 42738 

87 11566 891 579B 167 .. 790 6456 7323 11463 20513 

88 9188 1666 399 0 2501 56911 30542 90838 35701 

89 2261 863 351 175 204 728 11536 18002 13567 

90 1863 766 407 83 1726 478 2293 25714 13266 

91 2095 0 0 (Jl\f OM OM OM OM oM 

Av~r8ge Annual Total 1983-1990 180732 

Table A.l: Flow data at S-18C. 

- - -

I Oct Nov 

50873 17391 

23441 14724 

1638 689 

925 785 

2307 1164 

H81 391 

a 0 

1839 10-14 

2220 0 

2876 0 

20817 5927 

2874 12 

4374 6085 

21154 0 

32686 22021 

0 26-192 

23683 -lOll 

43286 23421 

4967 8269 

58878 45866 

32490 3654 

5342 2247 

15900 -13-16 

OM OM 

- -- -----------

II 

II II Dec II Total II 

2765 II 71029 

1880 II 115710 

a 13271 

84 3280 

105 101950 

308 25490 

a 17 

0 26219 

a 58580 

0 45065 

0 51178 

3828 44250 

8122 67429 

0 133162 

3293 99665 

964 320"54 

1952 139652 

5534 189565 

5833 209901 

18136 191846 

3231 267120 

2-165 57742 

2733 69573 

OM 2095 

t--

'-

~ 

~ ~ 

b::l 

§ 

~ 

~ 

> w 
II 

II II 

II Year II Jan I Feb I Mar I 

67 OM OM OM 

68 0 OM 0 

69 0 0 0 

70 OM 0 0 

71 0 0 0 

72 0 OM 0 

73 0 0 0 

74 0 0 0 

75 0 0 0 

76 0 OM 0 

77 0 0 0 

78 0 0 0 

79 0 0 0 

80 OM OM OM 

81 OM OM OM 

82 OM OM OM 

83 10318 5433 486 

84 4042 8870 1985E 

85 10969 10487 9483M 

86 6732M 10981 9015 

87 7865 9164 6710 

88 10616 11564 11556 

89 10989E 10747 1\361 

90 OM OM OM 

91 OM 255M 6631 

- - --

5·173 Diecharge (acre-ftl 

Month 

Apr I May _I Jun I Jul I Aug I S.p I Oct 

OM OM OM 0 0 0 0 

0 0 0 0 0 0 0 

0 0 0 0 0 0 0 

0 0 OM 0 0 0 0 

0 0 0 0 0 0 0 

0 0 0 0 0 0 0 

0 0 0 0 0 0 0 

0 0 0 0 0 0 0 

0 0 0 0 0 0 0 

0 0 OM OM OM OM 0 

0 0 OM 0 0 0 0 

0 0 0 0 0 0 0 

0 0 0 0 OM OM OM 

OM OM OM OM OM OM OM 

OM OM OM OM 1908 OM OM 

OM OM OM OM OM OM OM 

H89E 15311 103-10 10457 9303 9751 8612 

4495 10507 8015 6262M OE 5712 6028 

8297 9178 7454 4485E 831E OE 2374E; 

9765 9900 5463E 3017E 916E 3820 11268 

1090lE 6990E 7761E 7488 HIDE 52E 1I09E 

9203 6177E 1200E 1908E 69 ·10467 7694E 

10336 9828E 7135E 2737 4572 3546M OM 

OM OM OM OM OM OM OM 

7179M 147M 4255 6182 4950 4163 5079 

_ A:vera~!_ An!,~~T~~~~~~~=-_19~~ 69888 - -- -----

Table A.2: Flow data at S-173. 

I Nov I Dec 

0 0 

0 0 

oM OM 

0 0 

0 0 

0 0 

0 0 

0 0 

0 0 

0 0 

0 0 

0 0 

0 OM 

OM OM 

OM OM 

2555E 10511 

8561 8114 

6958 10023 

10187 12306 

10362 9354 

58E 5613E 

10225 11270 

OM OM 

OM OM 

5018 OM 

" " II 

II Total II 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

1908 

130·65 

101180 

72898 

86050 

90592 

66120 

71015 

71251 

0 

43861 

r 

*'" 

;s.. 

~ ~ 

~ 

~ 

~ t-o 

CJ 

8 

~ 

g 

~ 
" II II 

II Year II Jan I Feb I Mar I Apr 

11 OM OM OM OM 

72 0 0 0 0 

73 0 0 0 0 

H 0 0 0 0 

75 0 0 0 0 

76 0 0 0 0 

77 0 0 0 0 

78 0 0 0 0 

79 0 0 0 0 

80 0 0 0 0 

81 0 0 0 0 

82 0 0 0 OM 

83 4124 HIS 1785 0 

84 228 1617 956 13M-I 

85 377 0 0 0 

86 0 514 .. 11 0-1 2709 

87 0 0 0 26 

88 0 33. 25-13 4401 

89 4076 3-153 -1633 -IO-IS 

90 6101 6416 .. 846M 39 I 5T\.f 

91 1172l\1 1958M 820 1776 

92 80521\1 3630M oM OM 

--- ------------ -- - - -

5-174 Discharge (acre-h) 

Month 

I May I Jun Jul I Aug I Sep I Oct I OM OM oM 0 0 0 

0 0 0 0 0 0 

0 0 0 0 0 0 

0 0 0 0 0 0 

0 0 0 0 0 0 

0 30 0 0 0 0 

0 0 0 0 256 0 

0 0 0 0 79 0 

0 0 0 0 73 0 

" 101 0 1031 3098 H70 

0 0 0 333i 3429 ·7331 

307M 2440 2797 1853 ",0-12 10796 

0 7976 H87 3316 8335 3158 

3987 8983 7676 12875 6756 3832 

0 3564 40704 1216 107-13 10231 

3178 5927 11191 13170 7299 6 

2511 4967 3907 1539 1706 ~~ 16 

140-1 1-1967 11096 t307SM 1152-1M G163l\1 

3773M 6732 5223M 2135 S119!\f 713. 

3-120M 6066 581 678 3iH6 5647 

2364M oM oM oM 283M 15830M 

OM OM OM OM OM OM 

Aver~~~ A_~?tlal '"!'ot~!~83-~?~~ 47'H~ _______ -- --

Table .-\ .. 3: Flow data at 5-17-1. 

Nov 

0 

0 

0 

0 

0 

0 

0 

0 

0 

30 

1642 

13220 

4112 

0 

2-138 

732 

40 

3777M 

7301 

3416 

51761\1 

OM 

--

-- -- -

II 

II Dpe Total II 

0 0 

0 0 

0 0 

0 0 

0 0 

0 30 

0 256 

0 79 

0 73 

0 5730 

0 1075 

3554 390Q9 

881 42617 

0 48294 

-122 33065 

42 4S871 

565 25077 

..310M 73600 

5945 60175 

2S-I6M <l7B38 

4012M 33391 

OM 11681 

- - -

~ 

..... 

~ ~ 

~ ~ 

to 

§ 

~ 

~ 

;po-. 
II 5-175 Diacharge (acre-h) 

II II Month 

It Year II Jan j Feb I ~lar I Apr Ma,' I Jun Jul I Aug I Sep 

70 OM OM OM OM OM OM OM 0 0 

71 0 0 0 0 0 0 0 0 0 

72 0 0 0 0 0 0 0 0 0 

73 0 0 0 0 0 0 0 0 0 

14 0 0 0 0 0 0 0 0 0 

75 0 0 0 0 0 0 0 0 0 

76 0 0 0 0 0 0 0 0 0 

77 0 0 0 0 0 0 0 0 647 

78 0 192-1 2192 936 0 0 0 0 0 

79 0 0 0 1581 7442 1H01 14116 2930 8061 

80 OM OM 0 220 0 1736M OM 621 0 

81 0 2325 196 0 0 0 0 13367 13918M 

82 0 0 0 OM 148M 8089 1057 0 4780 

83 89-14 17001 10969 12631 1321 16556 4748 11689 18933 

84 970 0 2380 0 5080 )3410 8400 21995 10146 

85 0 0 1023 0 0 0 6805 8569 11524 

86 3880 0 6403 2743 0 9600 18155 20196 10154 

87 2626 0 26-10 0 760 1613 222 2128 1936 

88 532 0 0 464 1379 20603 9908 25006 15031 

89 0 0 0 0 0 0 1960 0 0 

90 0 0 0 0 0 0 32 220 26-16 

91 OM 0 0 OM 6309 8959 7207 15870 20100 

L~~ ~- ~ - - -- ~~era~e ~nnu~! Total !~~-~~~~~~_H_ ~--

Table A.4: Flow data at 5-175. 

- ~ 

Oct Nov 

0 0 

0 0 

0 0 

0 0 

0 0 

0 0 

0 0 

0 0 

0 0 

12379 0 

0 3822 

8723 1381 

17005 20174 

2539 0 

3594 131 

12250 4717 

173 0 

15646 7752 

4792 0 

0 0 

5355 0 

16359 OM 

--- --

-~ 

II 

I Dec II 0 

0 

0 

0 

0 

0 

0 

0 

0 

1260 

3598 

0 

2523 

597 

0 

549 

2225 

3461 

0 

0 

0 

OM 

---

Total 

0 

0 

0 

0 

0 

0 

0 

647 

5052 

60475 

9997 

39910 

54376 

105929 

66106 

45438 

73528 

38783 

77714 

1960 

8253 

74804 

--

;v 

0> 

;:;. 

~ 

~ tl 

~ 

?'-

~ t:-< 

(') 

8 

~ 

::j 

o 

t3 
II 5-176 Discharge (acre·ft) 

" " Month 

II y.., JI Jan 1 F..,.b 1 ~hr L Apr J 1\18)' JUII Jul Aug 

67 OM oM o~t OM OM UM oM OM 

68 OM OM 0 0 1726 33355 12659 0 

69 0 0 0 0 0 25551 339 5492 

70 0 0 0 0 0 504 1640 0 

71 0 0 0 0 0 2674 0 0 

72 0 0 0 a 0 1575 1922 0 

73 0 0 0 0 0 OM 0 2287 

74 0 0 0 OM OM OM 0 0 

75 0 0 0 0 0 0 415 0 

76 0 0 0 0 8M 6613 0 H28 

77 0 0 0 0 0 4891 OM OM 

78 0 0 0 0 0 0 0 0 

79 0 0 0 2255 2-191 0 0 0 

80 8 36 0 0 0 23 .. 0 887 

81 0 0 0 0 0 0 0 22160 

82 0 0 0 7. 391 5693 91 0 

83 2955 28055 -15470 29284 -1901 28658 !'t09S 30078 

84 889 0 73.9 0 7513 5050 1844. 28779 

85 12363 JOS~H 7591 3d:.!2 16364 3812 26521 30681 

86 7272 200 10171 9908 25-130 29655 359il -10068 

87 11722 ·H13 6290 5-159 133tH 10766 12375 1-11-10 

88 8525 7~4 11730 11106 35-11 46505 3dOlOl\1 -I7671M 

89 -Id6-11\1 5552 6696~1 6460 55951\1 13. 12921 10-185 

90 20922 17118M 15773~1 13198M 114211\1 89 87-11M O~I 

91 B59M IS77M SlIH 57-14M 743M O~I OM OM 

92 67771\1 2421M o~1 0~1 OM OM OM OM 

A vl<rllgt:' All nu III Tot al 1983-1990 183-19-1 

TallIe :\.5: Flow data at S-l'G. 

So:P J (kl L Nov 

0 1133 OM 

9233 7950/\.·1 OM 

5082 11853M 5758 

0 0 0 

0 0 0 

0 0 0 

2398 0 0 

a 0 0 

0 0 0 

1·11 0 0 0 

3499M OM OM 

4530 0 0 

3693 7369 0 

7694 4 2198 

36-183 8:.H3 2 

9568 14787 8908 

2J 388 11901 8243 

21862 12516 9007 

40346 42205 20533 

33868 7091 10390 

21953 -18657 5£J·113 

-n 677 29292~1 2354M 

5:H8M 0 7160 

6434M 17219M 550BM 

20-1-11\1 28197 247-1M 

O~I O~I OM 

11 

J Dec II a 

0 

0 

516 

0 

0 

0 

0 

0 

0 

OM 

0 

0 

0 

0 

0 

3467 

12199 

3505 

6744 

27176 

6770M 

14186 

3679 

2948M 

OM 

JI 

II Total 11 

1133 

64922 

54076 

2660 

2674 

3497 

41585 

0 

415 

9-159 

8390 

4530 

15808 

110GO 

66888 

39513 

228495 

123618 

218328 

2173'H 

226746 

247906 

85 .. 02 

120113 

52773 

919B 

;.-

..... 

~ ~ 

~ ~ 

to 

c::: tj 

CJ 

tr:J 

~ 

> 

~ 
--~ --------- ---- -- -- --- -- - -- - -

II 5-194 Discharge (acre-et) 

II II Month 

II Ye .. II Jan I Feb I Mar I Apr May Jun I Jul I Aug Sep I Oct I Nov I 

8~ OM OM OM OM OM OM OM 7966 6790 5659 0 

85 7313 6550 6982 2908 5-1-11 2858 5699 4570 1931 2636 5562 

86 OM OM OM OM OM OM OM OM OM OM OM 

87 580~M 5151 5899 5812 7646 62-16 53-18 4931 5058 6909 7327 

88 6298 6355 7311 6~32 7283 5~05 7619 7710 8230 6522 6173 

89 7363 6710 7730 6873 6893 5292 6625 7910 80H 750~ 6310 

90 5183 4971 5802 3739 1156 6393 7373 6617 6615 6847 6331 

91 5175 4697 5836 6065 6954 6139 OM OM OM OM OM 

Average Annual Total 1983-1990: .. S·128 

Table A.G: Flow data at S-194. 

----

Dec 

1303M 

5086 

OM 

7398 

7289 

5613 

5121 

OM 

--

II~ II Total 

21717 .- 60540 

0 

73528 

82627 

82863 

66148 

34836 

;v 

00 

~ 

~ S 

~ 

~ 

f2 

r 

(") 

8 

~ 

~ o 

t3 
-

II S-196 Discharge (acre-rt) 

II Month 

Year Jan F.b Mar I Apr I May I Jun I Jul I Aug Sep I 

81 OM OM OM OM OM OM OM 752M OM 

82 OM OM OM OM OM OM OM oM OM 

83 OM OM OM oM OM OM OM oM oM 

84 OM OM OM OM OM OM OM 3701 3302 

85 5300 '" 177 4386 1833 3723 1736 3967 3013 1382 

86 OM OM OM OM OM OM OM OM OM 

87 3265M 4659 5006 ·10195 26-16 38-10 3255 3834 3913 

88 2075 466 -551 25011 1160 5<. -3681 -50 -li02 

89 -2210 -3176 -3931 -3295 -3949 ·3822 60S ·202 18·17 

90 <26 1553 1428 107 -1-150 1127 368' 1486 2327 

91 OM OM OM OM 0 OM oM OM OM 

Avertlgt: Annual Total 1983-1990. 115-10 -------

Table A_7: Flow data at 8-196_ 

Oct I Nov I Dec 

OM OM OM 

OM OM OM 

OM OM OM 

39-17 2848 6S9M 

3055 4272 3796 

OM OM OM 

2222 3372 2945 

-3909 -3616 -2717 

1579 859 129 

1751 3100 2664 

OM OM OM 

II 

II Tots.1 

752 

a 

a 

14517 

40640 

0 

43453 

-9136 

-15567 

18409 

0 

/I 

II 

~ 

.... 

~ 

~ ~ 

to 

§ 

C) 

M 

~ 

~ 

io 
-~~ 

-- - - - -

It S·197 Flow Volumee (acre.(t) 

II II Month 

II Year II Jan Feb Mar lAp, May Jun I Jul I Aug sep 

70 OM OM OM OM OM OM OM OM OM 

71 0 0 0 0 0 0 0 0 0 

72 0 0 0 0 1696 6912 3124 1029 553 

73 0 0 0 0 0 0 411E OE OE 

74 OE OE OE OE OE OE OE OE 0 

75 0 0 0 0 0 0 0 609 0 

76 0 OE 0 0 0 0 0 OE OE 

77 0 0 0 0 OE H17 OE OE 0 

78 OE 0 OE 0 0 0 0 0 1837E 

79 OE OE 0 0 4021 OE OE 0 2823 

80 0 0 0 0 0 0 4967 ,,866 16HIE 

81 0 2940 0 0 OE 0 0 60372E 41654E 

82 0 0 0 0 0 10205 1781 0 3779 

83 5935 20761 27801 H99 0 19883E 6206E 9711 32238E 

84 OM OM OM OM OM OM 7168M 2731E 841 

85 OE 0 0 0 0 0 3707 0 12000 

86 0 0 0 0 0 3620 OE 17861 6550 

87 oE 0 OE OE 0 0 OE 0 H91E 

88 OE oE 0 OE OE 20356E OE n022E 2379E 

89 0 0 0 0 0 0 0 0 0 

90 0 0 0 0 0 0 0 0 DE 

91 0 0 0 0 0 OE oE OE 0 

- -- -- - --_._- - --- _ Average Annual Total 1983-1990: 38tl65 

Table A.8: Flow data at S-197. 

-

DC< Nov I OM OM 

0 0 

274 0 

oE oE 

0 0 

0 0 

0 0 

0 0 

1101E OE 

3072 0 

1823E 6702 

26777E OE 

7940 8607 

1250M OM 

0 0 

0 0 

OE 534E 

15-100 5526E 

5718E 0 

0 0 

DE oE 

2327 OM 

- -~ 

II Dec II 

0 

0 

0 

OE 

0 

0 

0 

0 

OE 

0 

0 

OE 

0 

OM 

0 

0 

430E 

OE 

0 

0 

OE 

OM 

- -

Total 

0 

0 

~ 

411 

0 

609 

0 

4717 

2938 

9916 

31769 

131742 

32311 

128583 

10741 

15707 

28995 

23416 

103476 

0 

0 

2327 

r 

...... 

o 

;t. 

~ S 

s:< 

~ 

~ t-< 

C] 

o 

~ 33 
5.331 Discharge (acre.ft) 

Month 

Y~ar Jan Feb Mar Apr May Jun Jul Aug 

82 OM OM OM OM OM OM OM OM 

83 214 26303 57839 26968E 0 9166 2571M 11342 

84 10711 20B09 29196£ 12718 8358 12-166 70911\1 31593£ 

85 25609 20922 14303~1 9586 1355:; 7547 21140E 28808E 

86 4798 403 13914 9515 19665 23708E H385E S7U J E 

87 14273E 14704 10094 104156£ 17137E 23776E 4873 23899E 

88 10665 2751 17677 25442 5004E 37831 E 4H83E 39880E 

89 18742 18656 22562 210-19 20238 15797 11322 10552 

90 19343 19-194 13656 0 688 OM OM OM 

91 13722 584M 1'1-120 16693M OM 6178 -1936 10811 

Average Annual Total 1983-19~O: 20985~ 

Table A.9: Flow data at 8-331. 

Sep Oct Nov 

oM oM 157£ 

11524 12615 13728 

10092 8696 16655 

50542E 46067£ 18728 

40269E 5036 14882 

8263E 46392F. 51065£ 

59317E 16925E 8388 

9340 103·14 10844 

5361 1157-1£ 2180 

16556 160-17 7853 

Dec 

147 

12534. 

20613 

25fil 

45 .... £ 

32736E 

18164M 

61.3 

-I893M 

OM 

Total 

303 

18-1803 

189609 

259359 

241231 

261390 

289629 

175589 

77190 

107800 

~ 

0-. 

~ ~ 

~ ::d 

tl:l 

§ 

G 

M 

~ 

?>' 

...... 

...... 
5-332 Discharge (acre-fll 

Month 

Year Jan Feb M .. Apr M.y Jun Jul Aug I Sep 

80 OM OM OM oM OM OM 0 0 3184 

81 0 2408 0 0 OM 0 0 1035 11159 

82 OM 0 0 0 0 2172 4332 7303 8814 

83 4280 4707 0 0 0 1690 6982 2898 4881 

84 657 292 282 '206 462 7095 6601 189<4 41.41 

85 891 331 234 270 288 6321 5923 2745 .. 784 

86 879 585 262 286 288 4935 7607 2678 6109 

87 873 557 298 264 414 5808 8107 7049 5238 

88 984 601 276 216 -105 3723M OM OM OM 

89 268M 300 60M 46M 511 4628M 73-13 4001 6413 

90 547 498 151 119 IlH S-IS1 5980 5455 6109 

91 940 533 492 536 2803 5622 6701 6204 -46047 

Average Annual Total 1983-1990: 33193 

Taole A.lO: Flow data at S-332. 

-

I Oct I Nov 

2023 0 

5496 2136 

10001 10840 

7160 8297 

6173 4328 

6599 4677 

743-1 3896 

6548 3537 

OM OM 

8458 3180 

7976 4203 

oM OM 

-~ - -

Dec II T~~ 0 '207 

0 22235 

6022 49544 

811 41707 

926 33357 

1144 34207 

871 35828 

990 39741 

OM 6204 

781 35987 

877 38516 

OM :l8479 

;... 

f-' 

N 

~ 

~ ?5 

>:: 

~ 

f2 

r 

(") 

c:::: 

t:--t 

~ 

g 

33 
- - - - ------------_._---

II 5-334 Oi.charge (acre-ft) 

II II Month 

II Year II Jan Feb Mar Ap, May Jun Jui Aug Sep 

78 OM OM OM OM OM OM OM OM oM 

79 0 0 0 15213 0 0 0 0 0 

80 0 0 0 8908 90dS 0 0 0 9101\.1 

81 0 0 0 J 3857 113<10 0 0 778 2 

82 0 1069 10086 10810 0 0 0 0 0 

83 0 0 0 0 0 0 0 0 0 

84 0 0 0 0 2dt14 0 0 0 0 

85 1101-1 16292 31325 31413 47057 20628 0 526 0 

86 0 0 0 0 0 OM 0 0 0 

87 11258 27333E 8144 5720 2551 0 0 0 0 

88 0 0 0 11818 0 0 0 0 0 

89 0 0 0 0 0 0 0 0 0 

90 0 0 0 0 0 0 0 0 0 

91 0 O~I OM OM OE OE 0 0 0 

92 OM OM OM OM OM OM OM OM OM 

Average Annual Total 1983-1990: 2936-1 

Table A.11: Flow data at S-334. 

Oct I Nov 

0 0 

7000 0 

3856 0 

0 0 

958 0 

0 0 

545 1365 

0 0 

0 0 

0 OE 

oE 0 

0 0 

0 0 

OM OM 

OM OM 

II Dec II 

0 

6138 

0 

0 

0 

0 

0 

0 

5040 

0 

0 

0 

0 

OM 

OM 

II 

II Total II 

0 

22882 

22763 

25976 

22923 

0 

-1794 

158256 

5040 

55006 

11818 

0 

0 

0 

0 

~ ...... 

;:t:;: ~ 

~ ~ 

tl:l 

§ 

&5 

~ 

~ ..-

to-' 
',j, 

;1 

II 5-335 Diacharge (acre-h) 

IL JI Month 

II Vear II Jon 1 Feb Mar 1 Apr 1 May 1 Jun 1 Jul .1 Aug 

83 OM OM OM OM OM OM OM OM 

84 3810 360-1.8 10592 0 8142E OE 0 0 

85 39573E 38341 22235 0 OE oE 0 0 

86 0 0 6171 3172 16707E 5423E OE D 

87 0 OE 0 17998E 10590 33097 B239E oE 

88 0 6062 40793 39081 5014 0 0 0 

89 40368 43938 538H 46757 43629 35080 0 0 

90 34273 35987 35919E 1343 0 0 0 0 

91 11548 OM OM 10410M 17561 0 0 0 

92 OM OM OM OM OM OM OM OM 

Average Annual Total 1983-1990: 100055 

Table A.12: Flow data at 5-335. 

Sep 1 Oct 1 Nov J Dec 

OM OM OM 0 

0 0 0 17730 

0 0 0 0 

0 DE 12413 0 

0 0 OE 0 

0 0 2682 35971 

0 0 1248 8037E 

0 0 0 0 

0 OM OM OM 

OM OM OM OM 

._- -

II 

II 

IL Total II 

0 

16383 

100155 

43885 

69924 

129667 

272902 

107522 

39519 

0 

-- -

;... 

...... 

""" 

~ 

~ ~ 

~ 

~ 

&? 

t-< 

Cl 

8 

~ 

g 

~ 
" 

II S-336 Discharge (acre-h) 

II II Month 

II Year II Jan I Ft'b M .. I Ap, I May I Jun I Jul I Aug Sep 

78 OM OM OM 157 12 250 1109 2517 3122 

79 931-1 9693 12002 119-13 3896 7982 6746 7022 6109 

80 6256 5818 6-138 6893 6706 6807 7333 1527 6131 

81 4967 4362 4604 51-43 3354 2-167 3564 26H 169 

82 0 0 1728 "1779 0 3681 5871 6434 4306 

83 0 248 5901 2694 0 0 0 0 0 

84 0 0 0 0 J 097 0 0 0 0 

85 444 7355 7164 460-1 6857 3291 0 0 OM 

86 OM OM 0 0 0 0 0 0 0 

87 OE OE , OE OE OE '-169 0 0 0 

88 0 OE OE 1815 0 -1888 0 0 0 

89 0 3499 7591 5530 5758 5330 0 0 0 

90 43-12 5663 5611 450 0 0 0 0 0 

91 0 0 OM oM OM OM OM OM OM 

92 OM oM OM uM OM OM OM OM OM 

Average Annual Total 1983-1990: 10728 

TallIe .-\_13: Flow data at S-336_ 

OCI I Nov I Dec II 

5701 6744 8142 

6621 6776 6907 

6869 600-1 6137 

-401 0 0 

125 0 0 

0 0 0 

0 0 0 

0 0 OM 

0 0 0 

0 0 0 

0 0 0 

OE 0 oE 

0 0 0 

OM OM OM 

OM OM OM 

Tot!!.) 

27753 

95069 

72919 

30923 

23925 

8842 

1097 

29715 

0 

2-169 

-73 

27708 

16066 

0 

0 

.~ 

;... 

~ 

::s 

~ 

t;1 

~ 

tl:! 

§ 

C) 

trl 

~ 

~ .... 

c:ro 
II 5-338 Discharge (acre-ft) 

II Month 

II V ... II Jan 1 Feb 1 Mar 1 Apr I May Jun Jul 1 Aug I Sep 

79 OM OM 0 726 4580 OE 0 0 0 

80 0 0 1432 3120 2739 1980 1910 3283 3011 

81 0 0 0 0 0 0 0 H09E 10062 

82 0 0 0 0 149 3537 10154 10401 30 .. 5 

83 1392 12173 14390 8013 0 10112 6490 9025 99H 

84 2821M 3404 2214 0 2134 6458 8053 11367 13801 

85 0 0 OE 0 4 375 ·827 512 494M 

86 ",679M 37051.1 5631 3983 0 960 2398 0 3193 

87 5278E 6784E 5615E 6397E 1525E 879 ·1642 0 ·77 

88 8114E 7708 11183 9826 : 252 4566 2118 6292 0 

89 8483 2085 0 0 0 1004 0 0 oM 

90 0 0 0 0 0 0 0 0 0 

91 0 OE 0 0 OE 979M 11796 15459 14254 

92 , OM oM OM OM OM OM OM OM OM 

Average Annual Total 1983-1990; 38650 

Tavie A.14: Flow data at S-338. 

~ 

I Oct I Nov J 2176E 0 

0 0 

6918 2592 

161 i 2 13250 

7373 5655 

13654 1206 

1825 2830 

8146 7151 

635 1853 

4933 2138E 

OM 492E 

0 0 

11406 OM 

OM OM 

II 

JI JI Dec II Total II 

0 7482 

r 11475 

0 25982 

24. 56889 

0 8'1571 

0 65112 

7270 12482 

0 39847 

4126 31371 

5625E 63756 

0 12064 

0 0 

OM 53894 

OM 0 

-

;v 

f-' 

0) 

~ 

~ ~ 

~ 

?'" 

f;2 

t-< 

(J 

~ ~ 

g 

t3 
A.2. CALCULATION OF GROUND1VATER SEEPA.GE A.17 

II Year I Inflow I Outflow I Outflow-Inflow II 

81 i 25.9760 58.8130 -32.8370 

82 22.9230 94.1820 -71.2590 

83 .0000 379.3950 -379.3950 

84 81.1770 328.7160 -247.5390 

I 85 258.4110 387.6050 -129.1940 

86 48.9250 371.6700 -322.7450 

87 124.9300 361.3500 -236.4200 

88 141.4850 424.3270 -282.8420 

89 272.9020 286.6120 -13.7100 

90 107.5220 93.2560 14.2660 

91 39.5190 205.5540 -166.0350 

Table A.15: Ann ual Inflow and outflow slImmary for the northern reach of L-31N. Values are in 10 

O's of acre-ft. 

Qln QS331 + QS173 

Q~ut = QS176 + QS174 + QSI94 + QS196 

where the superscript I represents the ;'!ower" L-31N basin. For L31 \V. the relations are 

Q~ = QS174 

Q:ut = QS332 + QSl is 

A.2 Calculation of Groundwater Seepage 

(A.5) 

(A.6) 

(A.7) 

(A.8) 

(A.9) 

The estimation of the seepage is based upon an application of Darcy's Law. \Ve write the ratio of 

the seepage entering the canal from the east to the that coming in from the west as 

R = 

= 

Qe 

Qw 

-J( b £!lr.. e e 0'" 

-J( b oh", w w 0'" 

(A.lO) 
A.18 .-tPPENDIX .4.. CALCULATIONS 

where h is the head. b is the aquifer depth. and J( is the aquifer hydraulic conductivity. Assuming 

that the aquifer ~onductivities and depths are equal, R can be expresses in discretized terms as 

R ~ 6.Ltv 6.he 

6.Le 6.hw 

IA.11) 

where i:..h is a head difference and 6.L is the distance over which the head difference occurs. This 

ratio can then be used to estimate the relative amounts of seepage from east and west of the canal 

as follows. Since the net seepage is the sum of the eastern and western contributions 

(A.12) 

where i:..S is the net seepage, and the two seepage components are related by 

R = 

(A.13) 

one can find the contribution from the west as 

(A.14) 

Tables A.16-A.18 give some averaged stages for several of the gages in the area. along with the 

distances to the canals. Two of the cases, that of the southern reach of L-31N and L-31 \V. have 

gages which are located approximately perp<'ndicular to the canal and have gages which appear to 

be located in a line parallel to the general regional gradient. For the southern reach of L-31N, we can 

calculate the ratio using G-1502, G-1363, and the average of S-176 headwater and S-331 tailwater 

as indicative of the L-31N stage 

R = 

= 6..L w (H L31N - HG1303) 

6..Le HG1502·-HL31N 

= (4.2) (4.~6 - 3.69) 

2.9 5.<>4 - 4.16 

= 0.49 (A.15) 

For the L-31 \V case, we use the NTS-3 and the "Frog Pond" gages as representative of the groundwater stage, and S-175 headwater as representative of the canal stage, which results in a ratio of 

east to west seepage of 

R = 

6..Lw uhe ---- 6.Le uhw 

= 6.L w ( H L31W - H Frog ) 

6..Le H NTS3 - HL3HV 
:1.2. CALCULATION OF GROUNDWATER SEEPA.GE A.19 

Station Distance to Averaging Average 

Levee (mi) Dates Stage (ftmsl) 

NESS2 3.6 1/1/81-1/15/87 6.49 

1/1/81-7/29/84 6.66 

G-855 2.0 1/1/81-1/15/87 4.40 

1/1/81-7/29/84 4.47 

G-799 6.6 1/1/81-1/15/87 2.96 

1/1/81-7/29/84 2.99 

G-396 0.8 1/1/81-1/15/87 5.14 

1/1/81-7/29/84 5.19 

S-338HW - 1/1/81-1/15/87 4.97 

1/1/81-7/29/84 4.97 

S-338TW - 1/1/81-1/15/87 4.53 

1/1/81-7/29/84 4.60 

S-336HW - 1/1/81-1/15/87 5.09 

1/1/81-7/29/84 5.09 

S-336TW - 1/1/81-1/15/87 5.57 

1/1/81-7/29/84 5.54 

Table A.16: Average Stages for selected gages in the northern L-31N basin. 

Station Distance to Averaging Average 

Levee (mi) Dates Stage (ftmsl) 

G-1502 4.2 1/1/81-12/01/90 5.54 

1/1/81-7/29/84 .5.75 

G-1363 2.9 1/1/81-12/01/90 3.69 

1/1/81-7/29/84 3.65 

S-331HW - 1/1/81-12/01/90 4.23 

" 1/1/81-7/29/84 4.84 

S-174HW - 1/1/81-12/01/90 4.08 

1/1/81-7/29/84 4.55 

Table A.17: Average Stages for selected gages in the southern L-31N basin. 
A.20 APPENDIX A. CALCULATIONS 

I 

Station Dist(1.nce to Averaging Average 

Levee (mi) Dates Stage (ftmsl) 

Frog Pond 1.0 1/1/85-12/31/88 3.47 

NTS-3 0.6 1/1/85-12/31/88 3.61 

S-175HW - 1/1/85-12/31/88 3.48 

Table A.18: Average Stages for selected gages in the L-31W basin. 

= (0.8) (3.48 - 3.47) 

1.0 3.61 - 3.48 

= 0.06 (A.16) 

A.3 Flow at Context Road 

This section outlines the analysis used to reconstruct flows at Context Road (see Figure 19. The 

data was originally published by the United Stages Geological Survey as Taylor Slough at Context 

Road, with the identifier 252948080352700. The notes for the station report the record as poor. The 

station does. however, provide a reasonable indication of the surface water behavior of the Rocky 

Glades prior to t:lC 1982 drawdowns in the L-31N canal. The recorder was removed in 1980 because 

the site was severely vandalized, and proved too difficult to maintain. 

A.3.1 Comparisons of Context Road and S-173 Stages 

The stage recorder for the Context Road station was approximately 1.9mi (3.1km) west of the L-31N' 

canal. approximately 1.?mi (??km) northeast of S-176. One would expect. therefore, that the two 

stages would be similar. Figure A.1 is the historical record for the two stations for the period of 

record of the Context Road gage. The two gages do indeed track closely. \Vhen one plots Context 

Road vs. S-176 headwater, the result is seen in Figure A.2. The two stages are indeed closely related. 

We calculated the relation as 

hContext = 1.1hs176hw - 0.1 (A.17) 

INe can then use this relation to estimate the stages at Context Road for the period where S-176 

information is available. The comparison of the estimated stage and the measured stages for the 

period of record is Figure A.3. 

In 1981. the L-31N borrow canal near S-176 was enlarged. This canal modification may change 

the above relation somewhat. However, enlargement will tend to increase the connection of the canal 
A .. 3. FLOW AT CONTEXT ROAD 

7 

6 

5 

,.-.. 

(!)Cij 

~E 4 ci5¢! '-' 

3 

2 

Stages at S-176 Headwater and Context Road 

; 

" " Jt L{i I ',I : \ :' \ \, , PI 'I Ii ' 

1 " 'I' 

~~ 

1 r,, 

, 

, 

I 

S-176HW 

Context Road -----. 

, " 

, , , , , , , , , ~ I 

" " 

" " " .' j 

A.21 

o ~--------~--------~--------~--------~------~ 

1976 1977 1978 1979 1980 1981 

Year 

Figure A.l: Temporal Comparison of stages at Context Road and S-176 headwater. 
:\,.22 

.... 

~ 

-0 

.... 

0 

u 

~ 

0:: 

"'0 

~ 

0"""" 0::<;; 

>( e 

<l.l¢:: c"-" 

0 

u 

~ 

<l.l 

OJ) 

;3 

CI) 

APPENDIX A. CALCULATIONS 

Stage at S-176 Headwater vs. Stage at Context Road 

7 .-" -. . .•. ... 6 

5 

4 

3 

2 

". ~. 

o ~----~------~----~~----~------~----~------~ 

o 1 2 3 4 

Stage at S-176 Headwater 

(ft msl) 

5 6 7 

Figure A.2: Comparison of stages at Context Road and S-176 headwater. 
.4..3. FLOW AT CONTEXT ROAD 

7 

6 

5 

2 

o 

-1 

1976 

Comparison of Calculated to Measured Stages 

at Context Road 

1977 1978 1979 

Year 

Calculated 

~Mensured 

I \ 

1980 

, 

, , , , , , \.1 I " , " , 

" 

" " " " " 

~ 

A.23 

1981 

Figure A.3: Comparison of estimated and measured stages at Context Road. Eqn (A. I?) relates 

S-176 headwater to Context Road, and S-176 headwater is the basis for the stage estimation. 
.l.24 APPENDIX A. CALCULATIONS 

1000 

'"0 

8 100 

0:: 

0.1 

4.00 

Stage vs. Discharge at Context Road 

4.50 5.00 5.50 

Stage at Context Road 

(ft IDsl) 

6.00 

Figure A.4: Stage vs. Discharge Relation for Context Road. 

6.50 

and to the aquifer. which in turn. will make the canal more efficient at drainage. Thus. (.l.17) will 

continue to overestimate stages at Context Road. 

A.3.2 Stage vs. Discharge Relations at Context Road 

When published stage and discharge measurements at Context Road are plotted, as in Figure A..4, no 

easily discernible relationship is apparent. There are a number of features of importance, however. 

Note that there is very little flow at stages less than 4.5ft. Moreover, the stage vs. discharge values 

exhibit a great deal of scatter. Since the flow actually occurs through a system of culverts, it is 

advisable to use a discharge relation in the form Q = J{ Hm, where J{ and m are coefficients. By a 

linear regression of the data, we obtained the following relation 

{ 

10-8.27 H13.2 

Q= 

o 

H~4.0 

H<4.0 

(A.18) 
J 

A.3. FLOW AT CONTEXT ROAD 

160 

Calculated VS. Measured Discharge at Context Road 

<I) 

~,........ 

o::~ 

~~ 

0 

[i: 

140 

120 

100 

80 

60 

40 

20 

o 

1977 

I 

i 

I 

jli\ , 

1978 

. . I '" \ 

1979 

Year 

Calculated -- Measured -----. 

l 

i 

. . , Ii, I 

I , , 

, 

, 

, 

, 

I 

· , ! 

• : 

1 • . 1,1\ .. f: I tGl " I It I " ::/1' I,tlll," II I, I II ,'I, ~ f 

1980 

Figure A.5: Comparison of calculated and measured discharges at Context Road. 

A.25 

\ 

1981 

where Q is the discharge at Context Road (cfs) and H is the stage at the recorder (ft ms!). Figure A.5 

shows that the reproduced data does a reasonable job of replicating the availahle measurements. 

Table A.19 summaries the available record at Context Road. while Table A.20 is the summary 

of the estimated flow volumes. 
Year .Jan Feb 

76 OM Of"I 

77 0 0 

78 0 18 

79 0 0 

80 0 0 

-, 

---_.- -

Measured Flow Volumes at Cont 

l-.Ionth I 

Mar Apr May .Jun .Jul Aug Sep Oct Nov Dec Total I 

OM OM OM 4040 336 597 2821 809 0 0 8603 

0 0 0 379 0 145 6480 127 0 0 7131 

2 0 0 28 600 217 3543 1098 132 0 5638 

0 1192 2072 248 270 298 2624 4287 79 0 11970 

0 0 0 373 272 184 2778 OM OM 0l-.1 3605 

Average Annual Total 1983--1990: 0 ---- -~-----~ --.-------~-------.--- -----.--~ -

Table A.I!): l\Ieasurcd How volumcs at COlltext Road 

«' 

:v 

t-:> 

O'.l 

;... 

~ 

~ tJ 

~ ;:t:.. 

~ t-< 

(J 

8 

~ 

~ o 

< C/) 
" 

- - -- - -- - - - -- - - -

E.timated Flow Volumu at Con 

Month 

Year Jan Feb Mar Apr Mil)' I Jlln Jul Aug S,-,p Oct I 67 oM oM oM OM OM OM OM OM 34E ""S89E 

68 OE OE oE oE 1,10E 7387£ 3793£ 957E 3832£ 5713E 

69 S2E oE OE OE OE 5045£ nS8E 3614E 3485£ 4108E 

70 10E 6E OE OE OE 1339E 1301E 32E 16E 348E 

71 OE OE OE oE OE OE OE OE 617E 3E 

n OE OE OE oE 259£ 3395£ 1956£ 316E 1197E 2-10£ 

73 oE oE oE oE DE OE 343E 249SE 3556£ 112SE 

74 oE OE oE oE OE OE 116E 969E 276£ S3E 

7S oE OE oE OE OE HE 27-12£ 246E 194£ 141£ 

76 OE OE OE oE 1650£ 110-10£ 2013£ 3675£ 816SE 2427£ 

77 OE OE OE oE 186E 1717£ 22E 671E 5545£ 718E 

78 OE 29E 12E OE Oi:: 364E 689E 976E 38S0E 12S2E 

79 OE OE OE 15SE 1768£ 63E 160E 126E 1-48-1£ 3199£ 

80 2sE 2SE 48E 118E 16SE 2040E 1892E 3232E 2681 E 2466E 

81 3E 69E OE OE OE OE OE 30867E 6826E 279-1£ 

82 OE OE oE oE 142£ 1743E 491E S23E S23E S39E 

83 3HE 281E 152E 283£ OE 22-1£ 133E 403E 312E S93E 

I 84 250E 237E 159£ 19E 81E 619£ 665£ 1IIE 150B. 106E 

85 OE oE 6E OE DE 46E 444E 28DE 453£ 172E 

86 111E OE 117E 107E 39E lODE 149E 3sE 143£ 162E 

87 HSE HE 95E 27E 106E -IOE H3E 188E 263E 4-12E 

88 13-1£ s8E S3E 6sE 167E 930E 3-10£ 2465£ 457£ 170E 

89 57E 16E OE OE oE OE 113£ 175£ 186E 80E 

90 oE OE OE OE 29E 79f: 18SE 247E 218E 213£ 

91 OE OE OE OE DE Of: Of: OE 37E 260£ 

92 UHE OM OM OM OM OM OM D~1 oM OM 

Aven~,ge Annual Tutal 1983-1&90 2216 - - -- - - - -.-----.-~-

Table ,-\.20: Estilllatl'd flow VOhllllCS at COlltext Boat!. 

- -- -

Nil\' 

503E 

1002E 

2948E 

2SE 

195£ 

36E 

OE 

oE 

nE 

347£ 

HE 

263E 

170E 

3102£ 

1698E 

490E 

507E 

42E 

61E 

155£ 

360E 

71E 

OE 

72E 

114£ 

uM 

----------

Dec Total 

oE 5126 

3E :"4397 

178E 22189 

OE 3077 

OE 814 

oE 74100 

OE 7519 

OE 1413 

OE 3389 

OE 29315 

OE 8886 

DE 7433 

284E 7708 

269E 16061 

106E 42362 

398E 4848 

SSIE 3783 

S3E 2491 

S3E ISH. 

138E 1257 

ISSE 2008 

96E 5005 

OE 628 

OE 10·13 

72f: 542 

OM 184 

;t... 

~ 

~ o 

~ 

;t... 

I-:l 

C1 

o 

~ 

~ ~ 

I-:l 

~ 

~ tl 

?> 

~ 

"" 
,. 

~ ~ .. --~.--
Appendix B 

DOClllnents 

This appendix contains various documents and correspondence cited and used within this r<'port. 

The first set of documents are copies documents related to the Experimental 'Vater Deliveries 

program. These documents support the chronology of events described in Section 1.3.4 on page 15. 

The second set of documents are the operations logs obtained from the South Florida 'Vater 

Management District. These documents record the operations of the C&SF water control structures 

for any periods that we have examined in this report. Rather than reproduce this extensive document 

set. these will be available on request by contacting 

South Florida Research Center 

Everglades 'National Park 

.f0001 State Road 9336 

Homestead, FL 33034-6733 

The complete set of operations logs are available from the South Florida Water ;\Ianagement 

District. 

Hydrologic Data Management Division 

Department of Research and Evaluation 

South Florida Water Management District 

P.O. Box 24680 

West Palm Beach, FL 33416-4680 

B.I 

Appendix C 

Raw Data 

In this analysis, the raw hydrologic data \vas obtained from the South Florida Water ;\Ianagement 

District's hydrologic data base, DI3HYDRO. As this data base is continuously updated and modified, we include the data used in the analysis for completeness. All retrievals WE're made between 

November 1 and November 12, 1992, and do not contain modifications made by the District after 

that date. 

Rather than including this lengthy appendix directly in the report. a copy of it may be obtained 

from 

South Florida Research Center 

Everglades National Park 

40001 State Road 9336 

Homestead, FL 33034-6733 

The hydrologic data used here is available from the South Florida Water j\Ianagement District 

by contacting: 

Hydrologic Data Management Division 

Department of Research and Evaluation 

South Florida Water Management District 

P.O. I30x 24680 

West Palm Beach, FL 33416-4680 

Should you need the data used in this analysis, please contact 

Dr. Thomas Van Lent 

Department of Civil Engineering 

C.1 
C.2 

South Dakota State University 

Brookings, SD 57007 

for a distribution on electronic media. 

APPENDIX C. RAW DATA