The C-111 Canal with structures marked. Notice ENP to the west, Florida Bay and Barnes Sound to the south. Barnes Sound(along with Card Sound) represents 1/3 of all American crocodile nesting in

the continental U.S. Current water quality: FAIR

. Taylor Slough extends more than 20 miles to the coastal mangrove fringe along Florida Bay, and has historically been an important source of fresh water to the central portion of the Bay. **Southeast District**
**Assessment and Monitoring Program** 

# Ecosummary Ecosummary
C-111 Canal

Miami-Dade County March 2003

Currently, the C-111 Canal is the major feature of the C-111 drainage system. For a significant part of its length, it runs east southeast just north of the Panhandle region of Everglades National Park (ENP), in southernMiami-Dade County. The C-111 Basin includes approximately 100 square miles of agricultural land in the Homestead/Florida City area and most of the Taylor Slough Basin, about 100 square miles, mostly withinENP. Canals in the C-111 Basin are operated to provide water supply and flood protection for urban and agricultural areas and deliver flows to Taylor Slough and coastal basins of the Park. At times, the C-111

Canal also receives water from Water Conservation Area 3 (WCA 3) and seepage from Shark River Slough and the headwaters of Taylor Slough from the L-31NCanal through the S-176. It discharges to the Everglades National Park Panhandle, Florida Bay, Manatee Bay and Barnes Sound. A number of structures are utilized to control flow in the basin, including the S-174,S-175, S-176, S-177, S-178, S-18C and, S-197. The S197, located a short distance east of US1, is an outlet

structure from the C-111 Canal to Barnes Sound. During major flood events, all 13 culverts are opened to provide flood protection for the developed portions of

the basin. The existing C-111 Basin drainage system is a modification of the original Central and South Florida (C&SF) project. Initially, the 1947 C&SF Project included levees to protect the C-111 Basin from hurricane driven tides on the south and east and high water in the Everglades on the west. Spillways and culverts in the east andsouth walls of the levee would pass flood control discharges from upstream canals and maintain groundwater levels to prevent saltwater intrusion. After later analysis in 1959, a series of north-south canals that would extend to Barnes Sound, Long Sound and Florida Bay (C-107 through C-112) were proposed to replace the southern levee. Salinity control structures were to

be built between the 1 and 2-foot contours.

Both Everglades National Park and the US Fish and Wildlife Service (FWS) objected to the canals cutting through the Park and discharging to tide. Additional review indicated that the design discharge could not be passed unless the canals were dug into the openwater of the bays. As an alternative, the FWS suggested an east-west canal to connect the C-111 and

C-110 Canals at their southern end to the C-109 Canal, which would discharge into Barnes Sound. This would allow some of the water to spread out through levee gaps and flow across the panhandle of ENP into Florida Bay. During this period, Aerojet General Corp. purchased a large tract of land in the area to construct a rocket engine test facility. Because the canals wouldbe large enough to allow barges to transport rockets to Cape Canaveral, Aerojet also supported the idea of a

canal to connect the C-111 and C-110 Canals to the C109 Canal. Today’s alignment is a version of that concept. Aerojet has since sold it’s property to the South Florida Water Management District (SFWMD).

A design change was also made in the western part of the basin. ENP requested additional flows for Taylor Slough to replace water that had already been diverted from its headwaters by other projects and the lowering of groundwater levels. The L-31W Canal was added to deliver flows to Taylor Slough from western south Dade County. Later the S-332 Pump Station would be

added to assist in this effort.

A major modification was made to the project during construction: since the S–18C, which was to serve as the salinity control structure for the C-111 Canal, was located many miles upstream from the outfall, concerns were raised regarding saltwater moving up the canal.If this occurred, saltwater could contaminate the freshwater aquifer or spill over the south canal bank, flowthrough the levee gaps and impact the freshwater wetlands in the ENP Panhandle. A national campaign by environmental groups to add a structure to the end ofthe canal reached its peak about the time a US Highway 1 bypass, used during construction of a bridge over the canal, was to be removed. A temporary solutionwas reached that left an earthen plug with three culverts in the canal at the bypass site. Although the plug was never removed for navigational purposes, it was removed and replaced a number of times to pass floodcontrol discharges to protect the C-111 Basin’s developed areas. These massive discharges resulted in much environmental harm to Manatee Bay and Barnes Sound, and drained significant amounts of water from ENPand Southern Everglades. In the early 1990s, the S197 Structure, containing thirteen culverts, was constructed to replace the earthen plug.

Prior to construction of the C-111 Canal, the Panhandle

of ENP served as a source of freshwater flows to Florida Bay. Even with the gaps placed in the leveesouth of the canal, natural surface water flow to adjacent wetland areas was restricted and some flow diverted to the east. The reduction of over-bank hydrologic flow resulted in changes in vegetation composition, saltwater intrusion, and loss of desirable fauna.Impounding the wetland system north of the canal altered natural hydrology and consequently impacted water quality throughout the marsh and northeast FloridaBay. As a result, in the early 1990s, a General Reevaluation Report for the C-111 Canal was begun. The Final Report recommended the removal of the spoil mounds from the south side of the east-west leg of the C-111 Canal upstream of US Highway 1; filling of the C-109 and C-110 Canals; and a 1000 foot bridge overTaylor Slough in ENP. Construction of new pump stations S-332A, B, C and D on the L-31N Canal; and a

tieback levee that would extend from S-175 north for

9 1⁄4 miles to near S-332B were recommended. This

levee would form a retention/detention area into which the new pump stations would discharge. A new Pump

Station S-332E and C-111N Canal were recommended to remove water from the C-111 Canal at its junction

with the C-111E Canal and distribute it across the Southern Everglades between the C-111 and US Highway 1. Except for the S-332A and E Pump Stations and the C-111N Spreader Canal, most of these proposals have been constructed, although some in a modifiedform. The tieback levee system has been partially completed.

Additional changes to the C-111 Canal system wererecommended by the Comprehensive Everglades Restoration Plan (CERP), and are included in the C-111NSpreader Canal Project. Modifications consist of enlarging pump station S-332E 10-fold, from 50 cfs to 500 cfs, and extension of C-111N Canal into the ModelLands east of US Highway 1. A stormwater treatment area is proposed to treat water prior to discharging to the Southern Everglades and Model Lands. Additional components of the plan include filling in the

southern reach of C-111 and removal of structures S18C and S-197. These features will improve water deliveries and enhance the connectivity and sheetflowin the Model Lands and Southern Glades areas, eliminate damaging discharges to Manatee Bay and Barnes Sound, and maintain flood protection in the lower south Miami-Dade County area.

An analysis of 1983-96 data (Walker, 1997) reported that inflows to the northern section of C-111 averaged 11,000 acre-ft/yr and contained 97 kg/yr of phosphorus at a concentration of 7 ppb. Inflows to the southernsection of C-111 averaged 45,000 acre-ft/yr and contained 937 kg/yr phosphorus at an average concentration of 17ppb. Walker attributed the higher loads to thesouth reach of the C-111 to “a more substantial agricultural watershed”. Water delivered overland from C-111 through S-18C, S-176, and S-177 structures toFor more informationcontact: The Southeast District SurfaceWater Quality Section in Port St. Lucie at 772/398-2806, or by e-mail:

Dana.Fike@dep.state.fl.us 

### Florida Bay is a triangular shaped, 850 square mile subtropical estuary with an average depth of threefeet. It lies between the southern edge of the Everglades and the Florida Keys with its western side opening directly to the Gulf of Mexico. It is almost entirely enclosed to the south and east except for tidal channels between the Keys. Approximately 80 percent of the Bay is within the boundaries of ENP. Until recently Florida Bay was described byits clear, warm water, lush seagrass beds, and outstanding fishing. In the 1980’s, changes in the Bay’s ecology became apparent. These changes included the extensive death of seagrass beds associated with turbid water, large sustained algal blooms and the death of sea sponges near the Florida Keys.

Florida BayFlorida Bay contained median phosphorus concentrations of 11.8, 11.2 and 8.5 ppb, respectively. Estimates of average annual loads from these three structures based on 1991-96 data was 2813, 129, and 1211 kg/ year. FDEP’s analysis of 1990-2000 SFWMD data collected at S-197 (station AR03) showed a relatively

low mean concentration of ammonia and nitrate nitrogen of 0.06 and 0.04 mg/L, respectively. Mean phosphorus concentration at this site was a low 4 ppb, withonly one of the 62 observed values above 10 ppb. Dissolved oxygen (DO) mean concentration of 5.8 waswell above the State standard for DO of 5.0 mg/L, albeit 7% of the reported values were below 2 mg/l. These low dissolved oxygen concentrations (less than 2 mg/L) all occurred during the warmer months (June thru October); such low oxygen concentrations valuescould potentially result in fishkills in C-111 or in Manatee Bay if water were being released in sufficient quantity. 1990-2000 SFWMD data collected at S-177 (north of S-197) showed a mean concentration of ammoniaand nitrate nitrogen of 0.13 and 0.09 mg/L , respectively. There was a decreasing trend of nitrate nitrogen of 0.01/yr. Mean phosphorus concentration at this site was 0.009 mg/L with no apparent trend. DO mean concentration was 3.5 mg/L with 30 percnet <2.0 and 75 percent <5.0 mg/L. Chlorophyll a mean concentration was 2.1 mg/L.

Most of the discharges from the S-176, S-177 and S18C structures pass to Florida Bay via overland flows

from C-111 southward.