Figure 1. Location of Lee County and figures 2 and 3. [Click on Figure-2 and -3 boxes above to view those figures. Click here to view larger version of Figure 1.]

Historically, freshwater runoff from Cape Coral entered Matlacha Pass estuary as sheetflow. As development occurred on Cape Coral, canals were designed and constructed to collect the freshwater runoff and distribute it as sheetflow through two spreader canal systems into Matlacha Pass. Water managers have expressed concern that altering the freshwater runoff patterns into the pass could have a detrimental effect on salinity distribution which might adversely affect the aquatic system of the pass. Adequate data were not available to evaluate the freshwater flow, its movement, and mixing. The U.S. Geological Survey, in cooperation with the City of Cape Coral, Lee County, and the Florida Department of Environmental Protection, conducted a study from July 1989 to September 1992 to identify three hydrodynamic aspects for managing the estuary.

Figure 2. (above) Bathymetric contours in northern Matlacha Pass, southwestern Florida. [click on numbered area above for larger version of that area]

Figure 3. (above) Bathymetric contours in southern Matlacha Pass, southwestern Florida. [click on numbered area above for larger version of that area]

Purpose and Scope

Description of Study Area

Matlacha Pass is underlain by marine terrace deposits of the Pamlico Sand in Lee County. The Pamlico Sand is characterized as a light-gray to brown, fine- to medium-grained, quartz sand that contains many shells and variable concentrations of clay and silt (Boggess and others, 1981).

The bed topography of Matlacha Pass is relatively flat with the exception of the main channel. The pass is about 13 mi long and about 1.2 mi wide. To the north near the Peace River (not shown) and to the south near the Caloosahatchee River (fig. 3), Matlacha Pass is about 2 mi wide. South of the bridge at Matlacha (fig. 2), the pass narrows to less than 1 mi. The inland coves and bays along the shorelines of Pine Island and Cape Coral (figs. 2 and 3) average less than 2 ft in depth.

Oyster beds and foreshore flats (or sandbars) have developed along the sides of the channel (figs. 2 and 3). These flow obstructions tend to reduce the velocity and turbidity of the water, thereby promoting the colonizations of algae and providing a habitat for small fish and invertebrates (Harris and others, 1983).

The primary vegetative features within Matlacha Pass are the mangrove swamps along the shorelines of Cape Coral and Pine Island (figs. 2 and 3). Red mangroves (Rhizophora mangle) are near the shore and black mangroves (Avicennia germinans) are inland (Harris and others, 1983). The extensive root system of the mangroves prevents erosion and provides protection for fish nurseries. Seagrass beds are abundant in Matlacha Pass and provide food for herbivores and detritivores, shelter for small fish and crustaceans, and serve to stabilize sediments (Harris and others, 1983).

The climate in the Matlacha Pass area is subtropical and humid. The average annual air temperature at Page Field in Fort Myers, 3.5 mi east of Cape Coral, is 74 degrees Fahrenheit, and monthly averages range from 64 degrees Fahrenheit in January to 83 degrees Fahrenheit in August (National Oceanic and Atmospheric Administration, 1978-91). Freshwater discharge is dependent on rainfall, which is distributed unevenly throughout the year. About 60 percent (54 in.) of the average annual rainfall occurs during the wet season (June-September), mostly the result of localized convective storms.