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 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.
Annual rainfall over the SFWMD averaged 53.0 inches from 1915 to 1995, with a standard deviation of 7.4 inches (Sculley, 1986, page 48-49; SFWMD, 1996) (Figure 3-2). Annual precipitation over the Everglades National Park (ENP) rainfall basin defined by the SFWMD (corresponding roughly to the ENP boundaries, not including Florida Bay) averaged 55.5 inches, with a standard deviation of 9.9 inches, from 1941 to 1985 (Sculley, 1986, page 44-45). There is appreciable annual variability in rainfall, with roughly 75% of annual rainfall occurring in the wet season that includes the period from May 1 through October 31. There also is appreciable annual variability, and there have been several reports published on short-term and long-term floods and droughts in the study area (Table 3-1).
The amount of evapotranspiration is typically 70-90% of rainfall, on an annual basis (Duever et al., 1994, page 233). While evaporation from an open water surface is generally highest late in the dry season (a time of low humidity and high wind speed), evapotranspiration is highest during the wet season due to high water availability, high temperature, and high plant growth rates (Duever et al., 1994, page 233).
Essentially all of Dade County is underlain by a highly permeable "surficial aquifer system", consisting of, from top to bottom, the Biscayne aquifer, a clastic semi-confining unit, the gray limestone aquifer, and a lower clastic unit (Fish and Stewart, 1991, page 10). The entire system is roughly 250 ft thick in the C-111 basin, while the wedge-shaped Biscayne aquifer is about 40-80 ft thick (thicker toward the southeast) (Fish and Stewart, 1991, plates H and I, page 38). Canals in the C-111 basin only partially penetrate the Biscayne aquifer, the most permeable portion of the surficial aquifer system.
The Biscayne aquifer consists of several limestone formations composed predominantly of marine limestone, with lesser amounts of fresh-water limestone and sand (Fish and Stewart, 1991; Causarus, 1987). The two formations in the study area are the Miami limestone and the underlying Fort Thompson formation (Fish and Stewart, 1991; Genereux and Guardiario, 1996). Both limestone formations have large pores due to extensive secondary solution (Fish and Stewart, 1991). Recent hydrogeological investigations in the Frog Pond area (Figure 3-1) showed that the overall thickness and hydraulic conductivity of the Biscayne aquifer are about 46 ft and 25,000 ft/day, respectively (Genereux and Guardiario, 1996). Thickness and hydraulic conductivity for the Miami limestone are 16 ft and 49,000 ft/day, respectively; corresponding values for the Fort Thompson formation are 30 ft and 13,300 ft/day (Genereux and Guardiario, 1996).
Water is under unconfined conditions in the Biscayne aquifer and the water table fluctuates in direct response to variations in precipitation (Miller, 1990). This aquifer is the principal source of water for all of Dade County, as well as Broward and southeastern Palm Beach Counties. An average of about 786 mgd was withdrawn from the Biscayne aquifer in 1985, and withdrawals have increased since (Miller, 1990). Because the groundwater interacts appreciably with surface water, the aquifer is readily susceptible to contamination. The top of the aquifer is at or near the land surface, and its base is somewhat irregular but generally slopes downward toward the coast to a maximum depth of about 240 feet below sea level near Boca Raton. The Biscayne aquifer extends underneath Biscayne Bay, creating the potential for saltwater intrusion.
The water table surface of the Biscayne aquifer resembles the land surface, being highest under higher areas including the Water-Conservation Areas and a topographic ridge in eastern Palm Beach County, and it is lowest near the coast. The general movement of water in the Biscayne aquifer is seaward. Well-field pumping in eastern Broward and Dade Counties supplying Miami and Fort Lauderdale has caused cones of depression. Such excessive groundwater withdrawal has locally reversed the natural flow direction, thereby increasing the possibility of saltwater encroachment (Miller, 1990). The water table fluctuates rapidly in response to variation in recharge (precipitation), natural discharge, and pumpage from wells. Natural discharge is by seepage into streams, canals, or the ocean; by evaporation; and by transpiration.
The Flood Control Act of 1968 (Public Law 90-483) authorized the Everglades National Park - South Dade Conveyance System (ENPSDCS) to provide changes to the water management infrastructure in and near the C-111 basin. These changes included addition of pump stations S-331 and S-332 and enlargement of the L-31N borrow canal (USACOE, 1994, pages 2-4 and 1-11) for the purpose of "conservation and conveyance of water supplies to ENP, and for expanding agricultural and urban needs" (USACOE, 1994, page 2-4). A General Design Memorandum (GDM) for the ENPSDCS was issued by the USACOE in 1973, and construction was initiated on this project in 1976. S-331 was the last element of the ENPSDCS to be completed, in February 1983. There have been only four significant infrastructure changes since that time: the expansion of S-332 from its original capacity of 165 cfs to 465 cfs, the addition of the G-211 gate on the L-31N borrow canal, the upgrade of S-197 from 3 to 13 culverts, and the removal of C-109 (Table 3-2).
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 ENPÔs 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 NESRS3 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, 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, 1987; 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.
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
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):
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)5. 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).
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:
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.
2 It 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".
3 the meaning of "sufficient" is unclear, though apparently the volumes discharged during the test were considered sufficient
4 in USACOE (1994) this project is reffered 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".
5 ENP have questioned the merit of this plan which calls for circuitous pumping of water (i.e. pumping water out of the 8.5 square mile area then re-releasing it into Northeast Shark river Slough, from where it will flow directly back into the 8.5 square mile area) to sustain development in the 8.5 square mile area.
6 Coordination with whom is not specified. However a process similar to the one used in the Experimental Program of Water Deliveries to ENP is referenced, so presumably coordination will be between the USACOE, the SFWMD, and the ENP.
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