C-111 Basin Task Force Report - The School of Natural Resources and Environment at the University of Florida

1.0 INTRODUCTION

1.1 Background

In south Florida, controversy has existed among urban, agricultural, fisheries, tourism, and natural resource interests over methods to restore the Everglades National Park and Florida Bay. Currently, elevating the water table and increasing the flow of water to ENP in order to restore more natural hydroperiods is proposed as a solution by the Army Corps of Engineers (COE), South Florida Water Management District (SFWMD), and the Everglades National Park (ENP), based on studies by hydrologists and researchers at those agencies. However, the impact that these water management decisions may have on agriculture in the area has not been addressed to the satisfaction of the local agricultural community. Growers are concerned that recent crop flooding has been exacerbated due to changes in the SFWMD's management of the canal system before and after major rainfall events. In an October 5, 1995 meeting with University of Florida (UF) President John Lombardi and Vice President for Agriculture and Natural Resources Jim Davidson, the growers expressed deep concern that the USACOE and SFWMD plans for future water management in the C-111 basin would further increase the vulnerability of agriculture to high water tables and flooding-induced crop losses.

1.2 Mission of Hydrologic Sciences Task Force

In response to the growers concerns, the University of Florida Institute of Food and Agricultural Sciences formed a multi- disciplinary Working Group to study the situation in South Dade County. The Working Group established three Task Forces, namely the Hydrologic Sciences Task Force, the Crop Research Task Force, and the Extension Task Force. Representatives of the UF College of Engineering, College of Liberal Arts and Sciences, Institute of Food and Agricultural Sciences, and the Florida International University Colleges of Arts and Sciences and Engineering and Design comprise the Hydrologic Sciences Task Force. The purpose of the Hydrologic Sciences Task Force was to review past, present, and proposed water management conveyances, structures and practices in south Dade County, focusing on their impacts on local hydrology in the C-111 basin, and the decision-making process from which they arose. Furthermore, the Hydrologic Sciences Task Force was charged with making recommendations for additional research, including the acquisition of new data and/or additional model development that may improve the planning, design, and operation of water management facilities in south Dade County for the benefit of the natural ecosystem, agricultural, and urban communities.

1.3 Investigative Process

In late 1995 and early 1996 members of the Hydrologic Sciences Task Force met in south Florida with representatives from the SFWMD, ENP, USACOE, USDA, and other agencies to visit the C-111 basin and to discuss the history of water management in the region. The three projects of primary concern were 1) the Experimental Program of Water Deliveries to ENP (a series of seven operational tests being conducted to investigate alternative plans for improved water deliveries to Northeast Shark River Slough and Taylor Slough); 2) the Modified Water Deliveries Project (a construction project to improve water deliveries to Northeast Shark River Slough); and 3) the C-111 Project (a construction project proposed to improve water deliveries to Taylor Slough and Florida Bay).

The Hydrologic Sciences Task Force subsequently obtained the Corps of Engineers (COE) documents that pertained to the Experimental Program of Water Deliveries to ENP, the Modified Water Deliveries Project (MWDP), and the C-111 Project, as well as several SFWMD documents related to the area. Relevant databases at the USACOE and SFWMD were accessed. After reviewing the documents and data files, the Hydrologic Sciences Task Force visited the USACOE in Jacksonville in Spring 1996 to meet with several persons involved with the projects, including hydrologic modelers, project managers, Geographic Information Systems (GIS) personnel, and environmental monitors. Members of the Hydrologic Sciences Task Force also visited the SFWMD in summer 1996 to speak with individuals in their Hydrologic Systems Modeling Division. In addition, representatives from engineering consulting firms with several years of familiarity with the historic and current situation in south Dade County were consulted.

Throughout the process, the Hydrologic Sciences Task Force has sought to understand what has been done and what is planned in the C-111 basin, and what effect these actions will have on the ENP and the agricultural lands east of the Park. This Hydrologic Sciences Task Force Initial Assessment Report summarizes and analyzes many years of work completed by the USACOE, the SFWMD, and the ENP, and makes recommendations for additional work that may improve the planning, design, and operation of water management facilities in the south Dade County area.

2.0 CONCLUSIONS AND RECOMMENDATIONS

The Hydrologic Sciences Task Force on Water Management Issues affecting the C-111 Basin in Dade County, Florida has reviewed historic, existing, and proposed water management practices in south Dade County, focusing on their impacts on local hydrology in the C-111 basin, and the decision-making process from which they arose. This Task Force Report summarizes and analyzes many years of work completed by the USACOE, the SFWMD, and the ENP. Conclusions of this analysis, and recommendations for additional research that may improve the planning, design and operation of water management facilities in south Dade County are summarized below:

2.1 Modeling, Monitoring and Decision-Making Processes

Documentation of the modeling, monitoring, and decision-making processes that went into the Experimental Program of Water Deliveries to ENP, the Modified Water Deliveries Project, and the C-111 Project is voluminous but incomplete and difficult to follow. Retrieval of information from the myriad of planning and design documents pertaining to these projects is an arduous undertaking. The documents are long and repetitive, and yet many are inconsistent, both internally and with other published reports.

To encourage public participation in and acceptance of these projects, and to facilitate outside peer review of the design and decision-making process, the reporting and documentation process must be made more accurate, definitive, and concise. Supplemental summary reports that are easier to read and understand should be developed.

The documentation of the South Florida Water Management Model (SFWMM) used in the USACOE decision-making process is inadequate to enable non-agency personnel to evaluate the validity of the model. The most recent available documentation is an out of date report, written in 1984, that summarizes the physical processes incorporated into the model, and presents results of model calibration/verification time series at several monitoring points at that time. Since then, numerous changes apparently have been made to the model, but no reports are currently available to document these changes or the resulting re-calibrations. Maps of topography, land use, model parameter values, and boundary conditions incorporated into the models actually used in the decision-making process are not available. The procedures used in the calibration/verification process are also not reported.

Publish documentation of the physical processes incorporated into the model, procedures used to calibrate the model, and maps, graphs, and tabular summaries of calibrated parameters, topography, land use, boundary, and initial conditions, and model outputs each time the model is utilized in the decision-making process. According to SFWMD personnel updated documentation of the SFWMM will be released in mid 1997 (Calvin Neidrauer, SFWMD, personal communication, August 2, 1996). We recommend that the SFWMD obtain outside independent peer review of the revised SFWMM documentation and calibration.

The finding of no significant impact for Test 6 and Test 7 of the Experimental Program of Water Deliveries to ENP, and the finding that the C-111 project will maintain or improve flood protection east of both the L-31W and the L-31N/C-111 canals, are based on comparison of modeled hydroperiods and depths of inundation to a hypothetical modeled base condition (or "no-action alternative"). The base condition assumes that canal levels will be operated according to the originally specified design criteria outlined in the USACOE General Design Memorandum Part V, Supplemental 52 (1973), which have never consistently been maintained. Furthermore the base condition in the C-111 model assumes that wet season transfers of water into the C-111 basin at S-331 will be discontinued. This base condition is the legally defined operational plan that will prevail if the current experimental program is discontinued. However, the growers have never actually experienced the base condition. Furthermore their actual experiences under Tests 6 and 7 have not been compared to model results because the model was originally run with rainfall data taken from the 1965 to 1990 data record, and has not been rerun with the actual rainfall that occurred (and is occurring) during these tests. Thus there is no evidence to determine whether the hydroperiods and water depths associated with the modeled base condition, or the modeled alternatives, are compatible with current Dade County agriculture.
Field experiments and modeling studies should be conducted to determine whether the hydroperiods and water depths associated with the modeled base condition, or the modeled alternatives are compatible with current Dade County agriculture.

Broad agreement on operational criteria is critical to the success of the C-111 project, however as of yet, no published operational plan for the project exists. Alternative 6A was recommended for implementation in the C-111 Project, in part, because of the operational flexibility it affords. Nevertheless, it seems prudent to address operational plans and define restoration targets for the project while structural alternatives are being evaluated in order to properly evaluate potential environmental benefits. The proposed C-111 project has the potential to be beneficial to both the natural ecosystem and agriculture, depending on the ultimate operating criteria that are developed. The lack of an operational plan creates anxiety on the part of both agricultural and ENP interests.

Address operational plans for all projects during the evaluation process, not after the preferred alternative is selected. In particular operational plans for the C-111 project should be negotiated and made public as soon as possible. The agricultural community should appoint a technical expert to participate in the operating plan negotiations in order to ensure that their issues and concerns are addressed.

2.2 Analysis of Available Database

Review of historical data shows that groundwater levels in the C-111 basin are inextricably linked to water levels maintained in the L-31N and C-111 canals. The flow of groundwater is predominantly from the northwest to the southeast in the C-111 basin. Thus, groundwater flow is generally in a direction from the canals to the agricultural areas east of the canals, with the elevation of the groundwater table controlled by the height of water in the canals. Only for brief time periods during flooding events is the flow gradient reversed allowing water to flow from the agricultural lands east of L-31N and C-111 into the canals.

Minimum and dry season water levels in the C-111 basin have increased both in the canals and the groundwater since the early 1980s when the construction of the South Dade Conveyance System was completed. The South Dade Conveyance System was intended to provide water supply to Dade County by keeping dry season water levels higher. Wet season importation of water into the C-111 basin at S-331 and S-173 has also increased markedly since the Experimental Program of Water Deliveries to ENP project (a series of operational water management changes intended to restore more natural hydroperiods to ENP) began in 1983.

Due to the small number of extreme events and differences in sampling frequencies in the limited historical data record, it is difficult to determine definitively whether groundwater response to peak rainfall events has changed as a result of the Experimental

Program of Water Deliveries to ENP. A comparison was made of all available groundwater level time series in the C-111 basin east of L-31N and C-111 that had data for the three high water years: 1968-69, 1980-81 and 1994-95. All of these wet years contain events with rainfall depths that roughly coincide with the 1 to 20 day -10 year return period storm for the C-111 basin. Data show that for all three extreme events, groundwater levels increased by 3.5 to 6 feet within one to two days, and the water management system returned the groundwater table to pre-storm levels within approximately two weeks. These data suggest that although 1968-69 was a wetter year in general than 1994-95, pre-storm and peak groundwater levels were in some cases up to two feet higher in the C-111 basin east of L-31N and C-111 in 1994-95 than in 1968-69. In general record high levels in canals and groundwater in the area occurred in 1980-81 as a result of Tropical Storm Dennis.

The hydrologic and geographic data bases in the agricultural area east of the C-111 canal should be enhanced. Installation of additional monitoring stations, development of new geographic information, and further historical and statistical evaluations of the existing data bases is necessary to accurately assess the impact of canal operations on groundwater levels in the agricultural area.

Analyses of historical water quality data show that total phosphorus concentrations within the C-111 basin (both in the agricultural areas and in the ENP) often exceed the 0.011 mg/l (as P) inflow limit for Taylor Slough and the Coastal basins that will become effective

July 1, 2002. Insecticides and herbicides are sporadically found above detection limits in waters of the SFWMD, with the majority of detections being herbicides such as atrazine, ametryn, bromacil and simazine. The insecticide endosulfan, and its metabolite endosulfan sulfate, were detected near ENP in 1995, but have not been detected in water actually entering the ENP. There is insufficient long-term data, however, to determine whether water quality has been affected as a result of the Experimental Program of Water Deliveries to ENP. No modeling studies have been reported that assess the potential impacts of the MWDP and the C-111 Project on the quality of water delivered to the ENP.

The likely future impacts of the proposed C-111 Projects on the quality of water entering the ENP should be more thoroughly examined. This will require additional water quality monitoring, experimental field and laboratory studies, as well as computer modeling studies to evaluate the impacts of agricultural management practices on water quality delivered to the ENP.

2.3 Additional Research Needed:

The environmental restoration benefits to ENP and the sustainability of agriculture in the C-111 basin both depend critically on the operating levels of the canals in the C&SF project. However detailed scientific understanding about how alternative operations will affect ecosystem restoration and the risk of flooding in the agricultural community are lacking.

Detailed scientific understanding about how alternative operations will affect ecosystem restoration and the agricultural community must be developed in order to obtain the broad agreement on operational criteria that is critical to the success of the C-111 project. The proposed C-111 project has the potential to be beneficial to both the natural ecosystem and agriculture, depending on the ultimate operating criteria that are developed.

The environmental restoration benefits of the C-111 Project are unclear. Based on SFWMM 1x1 simulations of 9 alternatives considered for the C-111 Project, ENP staff wrote: "None of the alternatives offered to the Park for evaluation showed any significant increase in hydroperiods or hydropatterns. Restoration goals of returning the wetlands to pre-project conditions at a minimum (i.e., increasing stages in the natural areas and allowing the proper seasonal fluctuation of these stages) remain elusive under the alternatives". Based on the very simple Species Compatibility Score and Hydrohabitat Index used to quantify ecosystem benefits, the selected alternative shows little or no benefit compared to the base case. Also, the USACOE and U.S. Fish and Wildlife Service found that the selected alternative would have no significant effect on endangered species in the affected area.

More thorough analysis of the possible ecological benefits of the C-111 project should be carried out, since little or no benefit to freshwater marshes is documented in the GRR. If no ecological benefit to freshwater marshes can be documented , such benefit should not be offered as a justification for the project. (Note: there may still be ecological benefit to decreasing large freshwater discharges to Barnes Sound, as a result of the flood control aspect of Alternative 6A).

The sustainability of agriculture in the C-111 basin is dependent on the operating levels of canals in the C&SF project. However, at the present time, an analytical tool does not exist to translate groundwater and canal level hydrographs into risk of flooding to specific crops at specific locations in the C-111 basin. The temporal and spatial scales of the SFWMM model used in the USACOE decision-making process are long-term and regional in scope, and thus inadequate to evaluate short-term local-scale impacts of the proposed structural and operational changes to the C&SF project which are of concern to the agricultural community.

A local-scale, event-based hydrologic model is needed to define the risk of flooding to the agricultural community associated with alternative structural and operational plans for the C-111 project. The development of a local-scale model will require a significant amount of field and laboratory work as well as model development to elucidate and simulate important local scale hydrologic processes and parameters. However, such a model could be used to produce maps of flooding probability in the agricultural area associated with alternative structural and operational plans for the C-111 project, which would allow local producers to better plan for the future.

3.0 STUDY AREA

The study area lies in south Florida, entirely within Dade County. Dade County is a rapidly developing area of about 2,000 mi², which includes the city of Miami in the
Northeast and the Everglades National Park (ENP) to the west (Figure 3-1). The general study area that was examined in this report is delineated by Tamiami Trail to the north, 80 degrees and 45 minutes in the Everglades National Park on the west, and the coastline to the east and south. The project study area is bordered by Tamiami Canal to the north, the designated C-111 project boundary in the ENP to the west, Krome Ave on the east, and the coastline on the south. The project area diverges outwards on the east and west side from near the Frog Pond to the coast.

1898	Floods in Greater Miami area Considered equal to or greater than the floods of 1928 and 1947 No detailed records available, mentioned in USACOE-JAX (1995c)
1926	Exceptionally severe flooding No detailed records available, mentioned in USACOE-JAX (1995c)
1928	Floodwaters were on low-lying areas for 105 days Exceeded the 1947 flood in depth, area of inundation, and duration Described in GRR (USACOE-JAX, 1994)
1947	Flooding in September and October Exceptional from standpoint of duration & intensity Several months before floodwaters subsided Described in GRR (USACOE-JAX, 1994), mapped in MacVicar (1983)
1948	Considered fairly severe (more than 1952 and 1953), but less so than 1947 both in rainfall intensity and antecedent storage accumulation Described in GRR (USACOE-JAX, 1994) and USACOE-JAX (1995c)
1952	Not much specific information given As described in GRR (USACOE-JAX, 1994), while comparatively minor, considerable damage resulted from recent developments
1953	Unusually heavy seasonal rainfall combined with a tropical storm, produced about 40 inches of rainfall from June through October While comparatively minor, considerable damage resulted from recent developments as described in GRR (USACOE-JAX, 1994) Also mentioned in USACOE-JAX (1995c)
1957	Unseasonably heavy rains over south-central Florida, Dec 23-25 Much lakefront flooding in late 1957 and January 1958 Considered to be a 1 in 10-year storm (USACOE-JAX, 1995c)
1960	Hurricane Donna, September 1960 September 1960 described as one of the wettest months in SFWMD described in GRR (USACOE-JAX, 1994) and USACOE-JAX (1995c)
1965	Hurricane Betsy, August 1965 Impact in study area unknown, report issued by SFWMD (1965)
1969	Heavy rains in March, especially south shore of Lake Okeechobee Maximum stage was 16.48 ft Mentioned in USACOE-JAX (1995c)
1970-72	Extreme rainfall deficiency in dry season Report issued by SFWMD (Storch, 1972)
1979	Severe storm, April 24-25 Report issued by SFWMD (1979)

Table 3-1 (cont.). Some important hydrologic events in Dade County, south Florida.

YEAR	DESCRIPTION AND INFORMATION
1981	Tropical Storm Dennis, August 16-18 The Homestead and Florida City area reported 20" or more of rainfall The S-28 gauge registered 18.82", exceeding the 100-yr return period Report issued by SFWMD (1982), described in GRR (USACOE-JAX, 1994)
1982	Rainstorm, March 28-29 Report issued by SFWMD (Lin and Jane, 1982) Rainstorm of April 23-26, 1982 Maximum rainfalls of 15.82 inches in Dade County Report by SFWMD (Lin, 1982), described in GRR (USACOE-JAX, 1994)
1983	Severe rainfall event, September 22-25, 1983 Report issued by SFWMD (1983)
1984	Rainfall event, May 22-31 Report issued by SFWMD (1984a) Dry season (Nov. 83-May 84) rainfall 130% of normal Report issued by SFWMD (Lin, 1984) Rainfall event, November 21-26 Report issued by SFWMD (1984b)
1985	Tropical Storm Bob, July 22-24 Report issued by SFWMD (1985)
1988	Succession of heavy rainfall events in south Dade in June Monthly rainfalls of 16.8 inches around Homestead Described in GRR (USACOE-JAX, 1994) Additional storms in south Dade and C-111 basin in August Monthly rainfalls of over 18 inches near S-331 Described in GRR (USACOE-JAX, 1994)
1988-89	Rainfall deficiency, Sept 88-Aug 89, 13 inches below normal Report issued by SFWMD (Marban et al. 1989)
1991	Storm event, January 15-17 Report issued by SFWMD (1991a) Storm event, October 8-10 Report issued by SFWMD (1991b)
1992	Rainstorm, June 23-30 Report issued by SFWMD (1992b) Hurricane Andrew, September No specific reports by SFWMD yet published
1994	Extended wet season Report issued by SFWMD (1995d)
1995	Extended wet season No specific reports by SFWMD yet published

Table 3-2. Completion dates for water management infrastructure in south Dade County.

	Name	Description			Completion Date	Source¹
	L-31N, northern reach	levee and borrow canal			1952	2, page 320
	L-31N, southern reach	levee and borrow canal			8 July 1967	1
	L-31N, enlargement	levee and borrow canal			1978-1979	2, page 320
	L-31W	levee and borrow canal			28 October 1970	1
	C-1	Canal			23 April 1963	3
	C-102	Canal			15 July 1966	3
	C-103	Canal			23 July 1967	3
C-109			Canal	29 April 1974			3
C-109 fill-in (removal)			Canal	April 1996			4
C-110			Canal	29 April 1974			3
C-111			Canal	16 July 1967			3
C-111E			Canal	16 July 1967			3
C-113			Canal	24 April 1970			3
S-331			pump station	1 February 1983			1
S-332, initial 165 cfs			pump station	August 1980			1
S-332, 300 cfs addition			pump station	December 1995			5
S-173			Culvert	8 July 1967			1
S-174			Spillway	20 October 1970			1
S-175			Culvert	28 October 1970			1
S-176			Spillway	8 July 1967			1
S-177			Spillway	16 July 1967			1
S-178			Culvert	16 July 1967			1
S-18C			Spillway	16 December 1971			1
S-194			Culvert	15 July 1966			1
S-196			Culvert	23 July 1967			5
S-197			3 culverts	12 February 1969			1
S-197			expanded to 13 culverts	May 1991			6
G-211			Culvert	May 1991			5

1 Source number 1 is USACOE,1996, Table 3-1

3.3 Operation of Water Management Infrastructure in the C-111 Basin

According to USACOE (1994, page 2-2), the purposes of "the project works" in south Dade are to:

remove 40% of the Standard Project Flood (defined as the flood estimated to occur from the most severe storm reasonably characteristic of the area, excluding extraordinarily rare combinations, and estimated for this project to be 125% of the 100 year storm) runoff from the effective drainage area
reduce the depth and duration of larger floods
provide water control to prevent overdrainage in the area
prevent saltwater intrusion

provide facilities to convey up to 500 cfs to ENP when normal

²it is not apparent what exactly "the project works" are or were (the original infrastructure, of the mid 1960's and early 70's? the ENPSDCS? the present infrastructure?), what "normal runoff" is or was, and what the basis/origin for the 500cfs value is (the only other overall water delivery rate to the eastern ENP discussed in the USACOE documents is the 55,000 acre-feet per year value authorized for the east ENP in 1970, and this corresponds to about 76cfs averaged over the year; see below). Perhaps "the project works" was the pre-ENPSDCS infrastructure, since USACOE (1994, page 2-4) states that the purpose of the ENPSDCS was "conservation and conveyance of water supplies to ENP, and for the expanding agricultural and urban needs", the second part of which goes well beyond point 5 (above) attributed to the "project works".

The 1973 GDM specified design optimum stages for the canals that were designed to accommodate 40% of the Standard Project Flood, and below which canal stages would be permitted to recede 1.5 feet before supplemental water deliveries were initiated. It should be noted that these optimum stages only determine when structures are to be operated, not the levels at which the canals are to be maintained. However, the canals have never been consistently operated according to the 1973 criteria. Operational stages have been changed periodically to suit changing project goals and in response to political pressures.

In June 1970, just before completion of the L-31W borrow canal and the two gates on it (Table 2-1), Public Law 91-282 established a schedule of minimum water deliveries to ENP from the C&SF project (USACOE, 1994, page 2-4). USACOE (1994, page 2-4) states that the minimum annual delivery of 315,000 acre-feet included 270,000 acre-feet to Shark River Slough via the S-12 structures, 37,000 acre-feet to Taylor Slough via the (then-nonexistent) S-332 pump station, and 18,000 acre-feet at (then-nonexistent) S-18C. The fact that the three separate deliveries add up to 325,000 acre-feet (not 315,000) is not explained. It may be that the Shark River Slough allocation is in error, as Light and Dineen (1994, page 66) give 260,000 instead of 270,000 acre-feet for this allocation, with the same stated total (315,000 acre-feet). Throughout the 1970's while the minimum delivery schedule was in effect, water management infrastructure was operated in a fashion that allowed for large seasonal variation in canal water levels (differences of 4-6 ft between wet and dry season, at some structures). Available data indicate that wet season maxima occurred at or very near the design optimum stages (as listed on page 2-3 of USACOE, 1994) on L31-N above S-174 and S-176, and on L31-W above S-175 (See Section 5.3 and Appendix E, this report; ENP, 1995, pages 13-14).

In 1981, after extensive flooding in the C-111 basin from Tropical Storm Dennis, the SFWMD, ENP, and farmers in the C-111 basin developed new operating criteria that constituted the basis for water management in 1982 and 1983 (USACOE, 1994, page 2-6). This included maintaining a wet season stage of 4.5 ft upstream of S-175 and S-177 (the "optimum stages" listed on page 2-3 of USACOE, 1994, but 0.5 ft lower than the "design optimum stage" given on pages 13 and 14 of ENP, 1995), and making dry season water deliveries to keep stages at or above 3 ft, if water was available. However, according to the USACOE there was no intentional lowering of canal stages for the benefit of agriculture (USACOE, 1994, page 2-6). From this time on, there has been a fundamental shift in water management in the C-111 basin, involving higher dry season water levels in most of the canals and groundwater in the C-111 basin, lower wet season water levels in some canals in the C-111 basin, and hence, an overall decrease in the seasonal variability of water levels (See Section 5.3 and Appendix E, this report; ENP, 1995, pages 13-14).

In March 1983, in response to a continuing decline in the ENP’s natural resources, ENP staff requested a series of water management actions that became known as the seven-point plan (SFWMD, 1992a, page 238-239). The seven-point plan included three measures which directly addressed increasing flow to more natural levels in Northeast Shark River Slough (NESRS), south of the southern boundary of WCA 3B. Thus, in addition to the flooding concerns highlighted by Tropical Storm Dennis, the degradation of ENP ecosystems provided a second motivating factor for water management changes in the C-111 basin.

In response, Public Law 98-181 (December 1983) and subsequent acts authorized the USACOE to conduct the Experimental Program of Water Deliveries to ENP (USACOE, 1994, page 2-6 to 2-7). This project has involved a series of iterative field tests for the purpose of collecting hydrologic and biological data under different scenarios, as well as hydrologic modeling. The ultimate goal of the project was to development of an optimum water delivery plan for ENP (USACOE, 1994, page 2-4). The first 5 iterations of the Experimental Program of Water Deliveries to ENP focused on improving water deliveries to Northeast Shark River Slough (NESRS). Iterations 6 and 7 have focused on improving water deliveries to Taylor Slough.

In 1984 farmers in the C-111 basin requested earlier lowering of canal stages near the end of the wet season, arguing that market competition required earlier planting. After coordination meetings with ENP and the farmers, agreement was reached for a 1-year test in which S-175 and S-177 headwater stages were lowered to 3.5 ft by October 15, S-175 stage held there for the entire growing season, and S-177 held at 3.7 ft after planting was complete (USACOE, 1994, page 2-6). ENP (1995, page 12) makes no mention of coordination meetings with ENP, simply stating that "a plan was developed by farming interests in the Frog Pond to artificially lower canal stages".

Also in 1984, two tests were carried out to evaluate the effects of increased water inputs into NESRS: a 30-day dry season test, April 19 to May 18, and 90-day wet season test, August 1 to November 30 (SFWMD, 1992a, p.241). The tests were conducted to see if structures and canals could discharge "sufficient volumes of water" to NESRS and whether these volumes would cause flooding in residential and agricultural areas west of L-31N (SFWMD, 1992a, page 240-241). SFWMD (1992a, page 240-241) also refers to a two-year test, though dates are not given; it is unclear whether this is the same two-year test, ending on June 14, 1987, described by USACOE (1994, page 2-7; see below).

1985 and 1986 saw continuation of the late wet season canal drawdowns started in 1984 (USACOE, 1994, page 2-6). Also, the "Rain-Driven plan for Water Deliveries to the ENP" (USACOE, 1994, page 2-7) began in 1985. This plan seems to refer to the particular implementation of the Experimental Program of Water Deliveries to ENP authorized in December 1983. This plan tied water deliveries to Shark River Slough to precipitation in the previous week, and evaporation over the previous ten weeks, using a statistical correlation between historical weather conditions in WCA 3A and discharge into Shark River Slough (SFWMD, 1992a, page 240). The plan is variously referred to as "the Rain-Driven Water Deliveries to ENP test" (USACOE, 1994, page 2-6), "Rain-Driven plan for Water Deliveries to the ENP" (USACOE, 1994, page 2-7), "the Rain-Driven Plan" (USACOE,

³ the meaning of "sufficient" is unclear, though apparently the volumes discharged during the test were considered sufficient 1994, page 2-7), There had been 6 Addenda to the LOA up to the time of publication of USACOE (1994): Addendum 1 prescribed the operational criteria used in a two-year test ending June 14, 1f987; Addendum 2 prescribed the criteria used through July 10, 1988; Addenda 3, 4, and 5 represented continuations of the criteria in Addendum 2; Addendum 6 contained operational criteria for the Taylor Slough Demonstration Project (see below) (USACOE, 1994, page 2-7).

According to USACOE (1994, page 2-7), the "Taylor Slough Demonstration Project" (which was authorized by Addendum 6 to the LOA, and seems to be equivalent to iteration 6 of the Rain-Driven Plan (USACOE, 1994, p. 1-13)) began in June 1993. This iteration included expansion of pump station S-332, and raising wet season stage in lower L-31N (between S-331 and S-176) from 4.5 to 5 ft (USACOE, 1994, p. 2-7). Iteration 7 of the Rain-Driven Plan began on November 1, 1995, about 5 months after the state of Florida had acquired control of the Frog Pond area from its former owners. Phase 1 of this iteration (currently on-going) involves raising stage in L-31W up to 4.7 ft. Phase 2 will begin with completion of the S-332D pump station (see below). At this time the L-31W stage will not be subject to the upper limit of 4.7 ft (USACOE, 1995b, pages EA-8 to EA-9). It is not known whether iteration 7 involved a seventh addendum to the LOA.

3.4 Proposed Infrastructure Changes in and near Eastern ENP

3.4.1. The Modified Water Deliveries to ENP Project

The Everglades Protection and Expansion Act (Public Law 101-229, passed in 1989) authorized acquisition of 107,600 acres for incorporation into ENP (USACOE, 1994, page 1-13) states that the "Modified Water Deliveries to Everglades National Park project" was also authorized by this same Act, PL 101-229. (Page 3-1 of the same document states that "the Modified Water Deliveries to Everglades National Park (MWD to ENP) Project, [was] authorized in 1989 by PL 98-181", though the reference to PL 98-181 here seems to be a typographical error.) The Modified Water Deliveries to Everglades National Park Project refers to a program of infrastructure modification designed to provide more natural flows to Shark River Slough in ENP (USACOE, 1994, pages 3-1 to 3-2). Thus, it is distinct from its predecessor with a strikingly similar name, the Experimental Program of Water Deliveries to Everglades National Park, authorized in 1983 and involving only operational (not structural) modifications. A key statement clarifying this appears in USACOE (1994, page 3-2): "authority for conducting the Experimental Program of Modified Water Deliveries to ENP expires upon completion of construction of the Modified Water Deliveries to ENP⁴ Project". Thus, authority for the experimental operational program expires when the structural modifications are in place.

In 1992 the USACOE presented a General Design Memorandum (GDM) for the Modified Water Deliveries to Everglades National Park Project (USACOE, 1992) which recommended infrastructure changes and a

⁴ in USACOE (1994) this project is referred to as the "Experimental Program of Modified Water Deliveries to ENP", whereas in USACOE (1995a) and USACOE (1995b) this project is referred to as the "Experimental Program of Water Deliveries to ENP". In this report it will be referred to as the "Experimental Program of Water Deliveried to ENP". Rain-Driven Water Delivery Schedule designed to improve water deliveries to ENP by providing a more natural delivery that more closely simulates historic seasonal flows (USACOE, 1992, page 59). Among other things, the plan proposed in the GDM (USACOE, 1992) would "permit S-331 to return to its design purpose of providing only water supply deliveries southward to Everglades National Park" (USACOE, 1994, page 2-9). The focus of the Modified Water Deliveries Project is north of the C-111 basin (north of S-331) in and near NESRS (see Figure 3-1). A separate project (the "C-111 Project") is underway for infrastructure modification within the C-111 basin, south of S-331 (see below).

Some elements of the Modified Water Deliveries Project were requested by ENP, either specifically or as general goal-oriented requests, in their Seven Point Plan of 1983 (USACOE, 1994, pages 3-1 to 3-2; SFWMD, 1992a, pages 238-239). The Modified Water Deliveries Project calls for (USACOE, 1992, p. 52):

structures to provide a more natural distribution of water in WCA 3A and 3B (the three S-349 and three S-345 structures)
structures to discharge water into NESRS from the southern boundary of WCA 3B (the two S-355 structures)
relocation of structure 334 and raising a portion of the Tamiami Trail (US 41)
removal of the L-67 Extension borrow canal and levee
floodproofing of an air boat camp and two Miccosukee Indian camps

construction of a protective double levee and borrow canal around the northern and western sides of the 8.5 Square Mile area, west of L-31N construction of a pump station (S-357) to remove excess seepage from the protective levee/canal into the L-31N borrow canal
construction of a pump station (S-356) to pump water from the L-31N borrow canal into the L-29 borrow canal, from where it can be released into NESRS at the S-355 structures

Figure 3-1 shows the location of the proposed structural changes. The first two elements of this plan were requested in a general way (not tied to specific structures), and the fourth element in a very specific way, in the ENP Seven Point Plan (SFWMD, 1992a, page 239). However, scientists presently at ENP have reservations about the effectiveness of the overall plan as presented in USACOE (1992) (Robert Fennema, ENP, personal communication, 22 August 1996). USACOE (1992 p. 59) states that an operational plan for the MWDP will be developed during the design and construction period using an iterative process that includes hydrologic modeling, environmental evaluations, and coordination. At the time of preparation of this report construction on the Modified Water Deliveries Project has not yet begun and an operational plan has not yet been published. SFWMD has recently hired a consulting firm to investigate and make recommendations regarding the future of water management in NESRS (Joycelyn Branscome, SFWMD, personal communication, 29 August 1996).

3.4.2. The C-111 Project
Based on continued environmental concerns associated with water deliveries to Taylor Slough and Manatee Bay, and knowledge that agricultural land uses in the C-111 basin were changing from seasonal to year-round crops which require more intensive flood control, the SFWMD requested that the USACOE prepare a GDM to address these issues. However, because of the lengthy process necessary to develop and implement a GDM, the SFWMD developed the C-111 Interim Plan as an intermediate solution to environmental and flood control deficiencies in the C-111 basin (SFWMD, 1995c). The Interim Plan involved the construction of additional gated culverts to control release of waters to Manatee Bay, construction of a new gated control structure on L-31N above S-331, and C-111 gap improvements, as well as a monitoring program to assess the success of the plan.

In 1994 the General Reevaluation Report and Environmental Impact Statement (USACOE, 1994, commonly referred to as the "GRR") was published for the C-111 Project. While the term or name "C-111 Project" is not actually defined in the report (first informal use of the term seems to be on page 1-6, with no definition), it refers to a group of proposed changes to water management infrastructure in the C-111 basin. The stated focus of USACOE (1994) was "to develop the structural plan which provides the greatest flexibility in providing environmental restoration of the study area while maintaining flood control" (USACOE, 1994, page 1-2). USACOE (1994) does not include an operational plan, stating that "a refined operation plan will be developed in coordination with ENP, FWS [U.S. Fish and Wildlife Service], SFWMD, and other agencies prior to project construction" (pages 1-2 and 1-5), and that it was agreed, with ENP and SFWMD, "to develop a plan for the operation of the project during design and construction" (page 5-8). It is not known which preposition ("prior to" or "during") will prove correct.

Development of the various alternatives considered for the C-111 Project is described in some detail in USACOE (1994, pages 5-7 to 5-26). Ten alternatives emerged from an iterative discussion and revision process carried out from 1990 to 1993 among the ENP, USACOE, and SFWMD. Apparently the U.S. Fish and Wildlife Service and C-111 agricultural interests were also involved in at least some of these discussions, with the latter offering one of the final ten alternatives (USACOE, 1994, page 5-26). Of the ten, only nine were actually analyzed by the USACOE in detail. Alternative 8 was eliminated (judging from USACOE, 1994, page 5-43 and Table 5-2) because it required land acquisition (both east and west of L-31N) that was beyond the scope of the C-111 Project. The remaining nine alternatives (numbered 1, 1A, 2, 3, 4, 5, 6, 6A, and 9) were compared to a "base condition" (also referred to as the "no action alternative" and the "future without project condition"; USACOE, 1994, page 5-26) which assumed the same operational criteria (the original design optimum stages specified in the 1973 GDM) but no changes in infrastructure. The alternatives were evaluated, relative to the base condition, for their operational flexibility, cost effectiveness, environmental benefits, and flood damage reduction benefits. Other factors may also have been considered, since these four factors were "not considered all inclusive" (USACOE, 1994, page 5-6).

All the alternatives were determined to provide the same level of flood protection (USACOE, 1994, page 5-94), each offering annual savings of $2.9 million to $3.2 million in flood damage costs, compared to the base condition (USACOE, 1994, page 5-65, Table 5-9). The economic analyses of flood damage expected under each plan were carried out with different amounts of land removed from agricultural production (e.g., no land removed from production for Alternative 1, the western three sections of the Frog Pond removed from production for Alternative 2, and all of the Frog Pond removed from production for Alternatives 3, 4, 5, 6, and 6A; USACOE, 1994, page 5-94). Thus, it is important to recognize that the continued (indeed, the increased) flood protection offered by each alternative relies on the land acquisition and removal from agriculture specified in the alternative. This is discussed in particular for the recommended plan, Alternative 6A. Hydrologic elements of Alternative 6A resulted in highly rated environmental improvements and operational flexibility, though these same features were thought likely to cause an increase in groundwater seepage to the east, reducing flood protection in the Rocky Glades and Frog Pond (USACOE, 1994, page 6-7). Hence, acquisition of these areas is built into Alternative 6A. Table 5-9 of USACOE (1994, page 5-65) shows that Alternative 6A offered the lowest cost of the alternatives which met the operational flexibility criteria (4, 6, 6A, and 9). It had a slightly lower cost than Alternative 6 ($200,000 per year). Alternative 6A was determined by the USACOE to maintain flood protection east of L-31N and C-111, restore natural values in the ENP, restore hydrology of Taylor Slough, and restore the hydrology of SRS.

The proposed modifications for the selected Alternative 6A for the C-111 project are shown in Figure 3-1. These modifications include:

Purchase of all lands in the C-111 basin south of the 8.5 square mile area and west of L-31N and C-111.
An approximately 9.5 mile long detention zone in the Rocky Glades and parallel to L-31N which will hold water above the ground surface and between two new levees. This will maintain a high-water hydraulic ridge which will allow westward seepage of water into the headwaters of Taylor Slough;
Four 300-cfs capacity pump stations along L-31N to pump water from the canal into the detention zone;
Continued operation of pump station S-332 in the L-31W canal;
A new bridge along SR 9336 in the ENP
A spreader canal running east from C-111 to facilitate sheet flow south through the Southern Glades and into the Panhandle of the ENP;
A 50-cfs pump station to pump from C-111 into the spreader canal;
Filling in canals C-109 and C-110 to facilitate sheet flow; and
Degrading of the spoil mounds on the south side of the lower reaches of the C-111 to facilitate sheet flow into the ENP.

Under the C-111 project, floodwaters will be diverted to the ENP instead of being allowed to exit C-111 at S-197, which consists of thirteen culverts near the Manatee Bay area of Florida Bay. The C-111 Project area is considered hydraulically separate from the area affected by the modifications of the Modified Water Deliveries Project; pump station S-331 in the L-31N borrow canal is the intended hydrologic divide. Floodwater north of the C-111 basin will be diverted into the NESRS and floodwater within the C-111 basin will be diverted to Taylor Slough and the Panhandle of the ENP. In the dry season, water could be pumped southward through S-331 if desirable. At the time of preparation of this report C-109 has been filled in, and the S332-D pump station is under construction; however, an operational plan for the C-111 project has not yet been published.

The lack of an operational plan for the C-111 project was sharply criticized by the ENP in 1993, before Alternative 6A existed (USACOE, 1994, Annex F, Technical Report SFNRC 93-4 from the South Florida Natural Resources Center at ENP), but this criticism was not a significant feature of later comments (in 1994), when Alternative 6A existed (USACOE, 1994, Annex F, Appendix A to Technical Report SFNRC 93-4, appendix dated February 1994). For example, ENP staff wrote: "in addition to the proposed structural changes, operational adjustments need to be implemented to properly evaluate potential environmental benefits...These operational changes must be evaluated at the same time as the testing of structural alternatives, or the multiple purposes of the C&SF Project can not be properly balanced" (USACOE, 1994, Annex F, page 10 of Technical Report SFNRC 93-4). Also, "With the addition of larger canals and larger pump capacities, the entire C&SF Project should be operated differently for both flood control and water supply purposes. These changes should be addressed during the evaluation process, not established after the preferred alternative is selected. Operational criteria must be locked in as part of the entire process, otherwise the preferred alternative may not work for most of its intended purpose (viz. the L-31W canal)" (USACOE, 1994, Annex F, page 100 of Technical Report SFNRC 93-4).

The environmental restoration benefits of the C-111 Project are unclear from USACOE (1994). Based on simulations with the South Florida Water Management Model (see Section 4) before Alternative 6A was available, ENP staff wrote: "None of the alternatives offered to the Park for evaluation showed any significant increase in hydroperiods or hydropatterns. Restoration goals of returning the wetlands to pre-project conditions at a minimum (i.e., increasing stages in the natural areas and allowing the proper seasonal fluctuation of these stages) remain elusive under the alternatives" (USACOE, 1994, Annex F, page 99 of Technical Report SFNRC 93-4). Alternative 6A was never actually modeled because the USACOE determined that Alternatives 6 and 6A are hydrologically indistinguishable at the scale of the South Florida Water Management Model (USACOE 1994, page 5-66, and Section 4.2.3 of this report). In Table 5-7 (which summarizes the species compatibility indices for the different alternatives), the environmental benefits of Alternative 6A are given as equal to those of Alternative 6. In addition, the USACOE and U.S. Fish and Wildlife Service found that Alternative 6A will have no significant effect on endangered species in the affected area (USACOE, 1994, pages 6-2 to 6-3). Though Tables 5-6 and 5-7 are presented as the final summary information on the environmental/ ecosystem benefits of the alternatives, Alternative 6A is absent from one and is given as equivalent to Alternative 6 in the other. It is unclear whether the absence of Alternative 6A from Table 5-6 is meant to imply its equivalence to Alternative 6 (as in Table 5-7), though this is probably the case. Adding to the confusion, Tables 5-6 and 5-7 do not contain information for the base condition, but they do contain a column labeled "existing condition", a name which is not one of the three acceptable phrases for the base condition used in modeling comparisons (USACOE, 1994, page 5-26). In summary, it appears (though it is not at all clear) that USACOE (1994) may be presenting Alternatives 6 and 6A as essentially equivalent in the ecosystem benefits to be expected from their hydrologic changes. If this is the case, then it seems the comment above from the ENP (concerning the lack of environmental benefits from any alternative, including Alternative 6) would apply also to Alternative 6A

4.0 HYDROLOGIC MODELING AND ANALYSIS

4.1 Description of the Hydrologic Models

The USACOE, SFWMD, and ENP all use hydrologic computer models to simulate the flow of surface water and groundwater in south Florida. The agencies use these tools to assess the potential impacts of changes in the operation of the ENP-South Dade Conveyance System, and to compare impacts of proposed structural and operational alternatives. The South Florida Water Management Model (SFWMM) is a regional model which was used extensively throughout the evaluation of proposed alternatives for the MWDP and the C-111 Project. In recent years the USGS models MODFLOW and BRANCH have been linked to create the combined groundwater-surface-water model, MODBRANCH, which could potentially be used to simulate smaller scale, local hydrologic conditions. These models and their applications in the Experimental Program of Water Deliveries to ENP Project, the MWDP, and the C-111 Project are described in this section.

4.1.1 South Florida Water Management Model (SFWMM)

The SFWMM was developed by the SFWMD under contract with the USACOE in the late 1970s and early 1980s (USACOE, 1992 p. I). The SFWMM is a regional-scale hydrologic model developed to simulate the integrated system of surface water and groundwater resources in south Florida. This hydrologic system is influenced by man-made canals, structures and levees, climatic and vegetative conditions conducive to high evapotranspiration, flat terrain, and a highly porous and permeable limestone aquifer. Important hydrologic processes incorporated into the SFWMM include evapotranspiration, overland flow, groundwater flow, canal flow, and surface water-ground water interaction. Documentation of an early version of the model, which is now out-of-date, is contained in SFWMD Technical Publication 84-3 (MacVicar et al., 1984). Since publication of this report, numerous changes apparently have been incorporated into the model, but no reports currently exist which document these changes or the resulting re-calibrations. According to SWFMD personnel (Calvin Neidrauer, SFWMD, personal communication, August 2, 1996) documentation of these changes and the model re-calibrations will be released in mid 1997. Since this documentation is not currently available, the following description of the SFWMM is taken strictly from MacVicar et al., (1984).

4.1.1.1 SFWMM 2 x 2 Model

The SFWMM is a large-scale hydrologic numerical model designed to simulate the integrated system of surface-water and groundwater in south Florida. The model uses a square grid network to model the two-dimensional movement of water. A two-by-two (2x2) mile node spacing, and a one day time step is used. Conceptually, SFWMM can be separated into two major components: the hydrologic model and the system management model. The scope of the modeling effort favored the selection of mathematical algorithms that were computationally efficient and whose data requirements could be satisfied without the need for extensive additional fieldwork.

Model Description: The major hydrologic processes and the order in which they are computed are shown in Figure 4-1 (MacVicar et al., 1984). Since all hydrologic processes are modeled independently within one time step, the order of calculation was chosen to handle the most transient phenomena first. Physical assumptions incorporated into the hydrologic model are summarized below:

Surface-water modeling adds specified rainfall and computed surface inflow to beginning surface-water storage in each cell, then subtracts (in order) infiltration, surface outflow, and evapotranspiration.

Infiltration occurs at the maximum rate specified for the cell, until either the available groundwater storage is filled, or all ponded water has infiltrated. The soil column is conceptualized as being totally saturated below the water table and completely dry above the water table. There is no provision for unsaturated soil

ACKNOWLEDGMENTS