Everglade National Park

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a - General features of the site

Terrestrial surface under sovereignty, excluding wetlands:

3824 sq. km

Wetland surface:

341 ha

Marine surface:

2416 sq. km

b - Physical features

Brief description of the main physical characteristics in the area:

Everglades National Park is part of a large, interconnected freshwater system called the Kissimmee-Lake Okeechobee-Everglades Watershed. This watershed covers almost 11,000 square miles in south-central Florida. Hydrology in the watershed is dominated by a dry season from December to May and a wet season from June to November when 75% of the annual precipitation falls. Rain falls across roughly 22,400 km2 in central and south Florida, which is nearly flat (there is about an inch per mile elevation change from Lake Okeechobee to Florida Bay). Historically, the Everglades system was fed by sheet flow from lakes and wetlands in the northern reaches of the watershed during seasonal rainy periods.

This surface flow moved slowly south into the extensive wetlands that define the Everglades, through the “river of grass,” and on to Florida Bay or the Ten Thousand Islands. This flow was as much as 50 miles wide and ranged from 6 inches to 3 feet in depth, moving about 100 feet per day (33m) from May to October. During the wet season, the landscape was nearly covered with water. Much of the water flows through the unique ridge-and-slough habitat of south Florida. This landscape is characterized by elongated ridges and troughs of limestone and peat. Average water depth is about 1 foot (0.3m) but can be as deep as 3 feet (1m) during the rainy season. In other areas, wet season flows inundate marl prairie habitat and encroach upon pinelands, hardwood hammocks, and other tree islands. As winter approaches, water slows and then ceases form the annual dry season.

Although most habitats dry completely during winter, the ridge-and slough landscape usually retains some of its water, sometimes in shallow pools and sometimes as deep pools, both of which provide valuable aquatic habitat into which many animals retreat until the next rainy season. The watershed has been highly engineered and managed for agriculture, flood control, and supplying water for a growing population. The region is now characterized by large urban centers and highly productive agricultural areas, which have been made possible by the dramatic alterations of the natural hydrology. Beginning in the 1880s, development was assisted by the large-scale drainage of wetlands, construction of channels to carry water to the population centers of the east, and flood control structures.

These efforts would eventually create an extensive system of levees, canals, and water control structures. Direct effects on the park’s hydrology include disruption or elimination of overland sheet flows, changes in the location and timing of flows, and permanent flooding in some areas and permanent drainage of others. Portions of the park now flood more deeply during the rainy season and are drier during the winter. Indirect effects include land subsidence, abnormal fire patterns, and widespread changes in vegetative and animal communities. Canals can also serve as habitats and movement corridors for invasive exotic plants such as hydrilla (Hydrilla verticillata) and water hyacinth (Eichhornia crassipes) and animals like cyclids (Cichlidae) and sailfin catfish (Pterygoplichthys multiradiatus) that impact Everglades’ ecosystems.