Abstract

C-111 Canal in foreground with areas of spoil mound removal. The view is southward towards northeast Florida Bay. [larger image]

Introduction

Florida Bay lies at the southern terminus of the Kissimmee – Lake Okeechobee – Everglades ecosystem. The ecological health of Florida Bay has been of intense public, political and scientific interest in recent years (Fourqurean et al. 1999). Upstream water management activities influence the quantity, quality and timing of water deliveries to Florida Bay, particularly the northeastern portion. The construction of canals for water management in the Florida Everglades dates to the time of the Calusa and Tequesta cultures over 500ybp (Tebeaux 1968). The massive, modern water management system in south Florida was initiated following the devastating hurricane of 1928, during which over 2,000 deaths occurred because of flooding (Light & Dineen 1994). The "South Dade Conveyance System" was constructed as part of the overall water management scheme to protect agricultural interests in the southernmost portion of Dade County, adjacent to Everglades National Park and just north of Florida Bay (Fig. 1). The system removed water from Taylor Slough, the natural overland drainage to Florida Bay, and introduced above normal freshwater flows into Barnes Sound to the east via the C-111 canal. Environmental concerns over the C-111 have existed since it was built (Light & Dineen 1994).

Negotiations between the National Park Service and U.S. Army Corps of Engineers led to changes in both operations and structures within the C-111 basin (USACOE 1992). One part of the 1994 General Re-evaluation Report (GRR), alternative 6a plan (USACOE 1994), was the removal of the berm on the south side of the C-111. Deconstruction of the spoil mounds was started January 13, 1997 with mound 2 and finished with mound 50 on October 31, 1997. Beginning at the US1/C111 Bridge, spoil mounds 2-15 were degraded to 2.0 ft (NGVD 29) and continuing west, spoil mounds 16-50 were degraded to 1.0 ft (NGVD 29, see Fig. 1). This effort was intended to restore overland flow through the marshes and ultimately to northeast Florida Bay. The National Park Service hydrologic evaluation of the berm removal suggest that it is insufficient to significantly restore more natural conditions to the East Panhandle without efforts to improve extent and duration of surface water upstream of the C-111 basin (Hydrology staff, 1993). Here we present an empirical analysis of the effectiveness of the berm removal on water depths in the marshes between the C-111 and Florida Bay.

Objectives and Hypothesis

Here we ask the following questions:

1. For a given stage within the C-111 canal, are marsh water depths higher or lower following the removal of the berm? If the berm was an impediment to flow, marsh depths after berm removal should be higher for a given canal stage.
2. Has the removal of the berm been equally effective across the C-111 basin? The design called for more lowering to the west and less in the east, therefor a spatial pattern to downstream marsh stages might be expected.

Data and Analyses

Figure 1. A collage of three images including a colored map of everglades national park, a small satellite image of a portion of the park including the C111 canal, and a line drawing showing various stations within the C111 canal area. [larger image]

Hydrological monitoring stations within the C-111 basin have been maintained since the 1980’s by staff from Everglades National Park, the USGS Biological Resources Division and the National Audubon Society. Stage within the C-111 canal is monitored by the South Florida Water Management District at the S18C and S197 water control structures (Fig. 1). Here we use water depth data from four marsh stations: Upper and Lower Joe Bay, EPS, and Lower Highway Creek (Fig. 1). These stations form a west to east transect across the C-111 basin. Canal stages were the tailwater stage at S18C and the headwater stage at S197. All stage and depth data were averaged by month. Because of occasional equipment failures not all time series are complete. For any given station to be included in the analysis, at least 25 days of data had to be available. Any station by month combination for which less than 25 days of data were available was excluded from the analysis. The periods of record differed between stations, but in no case were less than eight months available (Table 1). We conducted simple linear regression analyses to relate marsh water depth as a function of canal stage. A separate regression was calculated for the "before" and "after" periods. Western marsh stations were related to stages at S18C and eastern stations to S197.

Results and Discussion

Significant linear relationships were found between marsh water depth and C-111 stage (as either S18C or S197) for all regressions (p< 0.05). However, the strength of the relationship (r2) varied depending on location and time period (Figs. 2-5). An analysis of the "before" and "after" regression equations indicates that, for western and central stations, for a given canal stage, greater water depths are found in the marsh after berm removal. This suggests that removing the berm has had the desired effect of increasing marsh water depths in the west. For the eastern station, however, the opposite was found. For a given canal stage, less water is present in the marsh after berm removal than before. This suggests that less water is moving through the eastern portion of the C-111 basin following berm removal and implies a west-east effectiveness of the project.

(click on files below for larger versions of graphs) Figure 2. [larger image] Figure 3. [larger image] Figure 4 [larger image] Figure 5 [larger image]

Literature Cited

Light, S.S. & J.W. Dineen. 1994. Water control in the Everglades: A historical perspective. PP 47-87 IN Davis, S.M. & J.C. Ogden (Eds.), Everglades: The ecosystem and its restoration. St. Lucie Press, Delray Beach, Florida.

Fourqurean, J.W., M.B. Robblee & L.A. Deegan (Eds.). 1999. Florida Bay: A dynamic subtropical estuary. Dedicated Issue, Estuaries, 22: 345-561.

Tebeaux, C. 1968. 2,000 years of man in the Everglades. University of Miami Press, Coral Gables, Florida.

U.S. Army Corps of Engineers (USACOE) 1990. General Design Memorandum: Modified water deliveries to Everglades National Park, Florida, Parts 1 & 2. Jacksonville, Florida.

U.S. Army Corps of Engineers (USACOE) 1994. Canal 111 (C111) South Dade County, Florida, Final Integrated General Reevaluation Report and Environmental Impact Statement. Jacksonville, Florida.

Hydrology Staff. 1993. Hydrological Evaluation of the Proposed Alternatives for the U.S. Army Corps of Engineers’ General Re-evaluation Report for the C-111 Basin.Technical Report SRNRC 93-4. Homestead, Florida.

Acknowledgements

Jerry Lorenz, of the National Audubon Society, graciously provided marsh depth data for the Lower Highway Creek site. Data for site EPS and other ancillary Everglades National Park hydrologic data were provided by staff at the Park’s South Florida Natural Resources Center. Financial support for our research was provided by the USGS/BRD’s Global Climate Change Program and by the U.S. Department of Interior’s "Critical Ecosystems Studies Initiative" administered by Everglades National Park. Special Thanks to T. Mullins and GIS staff for technical assistance with this poster.

¹ USGS/BRD Florida Caribbean Science Center, Restoration Ecology Branch, Everglades National Park Field Station; email: gordon_anderson@usgs.gov
²USGS/BRD Florida Caribbean Science Center, Restoration Ecology Branch, c/o SERC, Florida International University; email: tom_j_smith@usgs.gov
³SERC, Florida International University; email: nuttlew@fiu.edu

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