Florida Rivers: The Physical Environment

Abstract

Florida’s high rainfall and low topographic relief combine to produce a surprising variety of low-gradient streams. The intent of this chapter is to describe physical attributes and processes associated with these lotic environments. I employ the definition of “stream” used by Beck (1965), which is, “a body of water with unidirectional flow of measurable velocity.” This inclusive definition allows the recognition of some unusual Florida stream environments. One of these unusual environments is the Florida Everglades. This so-called “river of grass” is the broadest and shallowest stream for its size on the North American continent. Now interrupted by control structures, the Everglades historically flowed through sawgrass for 150 km from Lake Okeechobee to Cape Sable in a band approximately 50 km wide and mostly less than 1 m deep. The Everglades is just one of many stream systems throughout Florida, whose channels contain sawgrass or other emergent vegetation. The Big Cypress Swamp is characterized by a series of streams including Corkscrew Swamp and Fakahatchee Strand, whose emergent vegetation consists of cypresses and other trees. “Strand” is the term generally used in denoting a channel in which trees grow. “Slough” is more commonly employed to denote a channel clogged with herbaceous or shrubby vegetation such as Taylor Slough, which is peripherally part of the Everglades. Many Florida streams begin as springs with transparent flows that issue abruptly from subterranean sources. The Wakulla and Silver rivers are well known examples. Other streams disappear into the ground. The St. Marks River disappears into a limestone formation for about 500 m before reappearing again (Hendry and Sproul, 1966). The intervening terrain is called a natural bridge and supports a forest of upland trees. Lost Creek begins in a swamp in Wakulla County and flows through flatwoods, primarily pines, for more than 15 km before it disappears entirely. Some streams originate as outfalls from lakes. The Oklawaha River begins at Lake Griffin. Most Florida streams originate in swamps. Their waters are darkly stained by organic acids released as plants decompose. The Suwannee River is a large blackwater stream that drains from the Okefenokee Swamp. Most blackwater streams originate in swamps, but the St. Johns River is exceptional and issues from an extensive complex of marshes. Nicolay (1979) wrote of the St. Johns, “the deep peat marshes act as a giant sponge, storing tremendous quantities of water during the short rainy season and slowly releasing them during the longer dry season.” The St. Johns River is Florida’s longest. Its channel is continuous for at least 320 km, and its headwater marshes extend upstream for another 119 km. The gradient of the St. Johns is exceedingly low. Its water surface elevation 320 km upstream is only 6.1 m above mean sea level (Beck, 1965). The St. Johns River is remarkable among North American rivers for its northward direction of flow. Numerous streams discharge into the Gulf of Mexico from western peninsular Florida and the panhandle. In great contrast, only a few streams flow into the Atlantic Ocean. A principal reason is the St. Johns River, which lies near the coast and captures surface flows before they can reach the Atlantic. To the south, Lake Okeechobee and the Everglades similarly capture potential flows to the Atlantic and redirect them to the Florida Straits and the adjacent Gulf of Mexico. Of course, several canals now discharge from Lake Okeechobee to the Atlantic. Florida’s subtle topographic relief provides little or no apparent distinction between watersheds. For example, the St. Johns and Kissimmee rivers closely parallel each other but flow in opposite directions through nearly flat terrain near Melbourne. Boundaries of Florida’s river basins are mapped (U.S. Geological Survey, 1974; Conover and Leach, 1975). Most sizable streams in the United States are alluvial rivers, sometimes called red or brown water rivers for the color of their turbid load of suspended sediments. Florida has only one stream that is entirely typical of such streams—the Apalachicola River. The Apalachicola is Florida’s largest river in terms of discharge. Formed by the confluence of the Flint and Chattahoochee rivers in extreme southern Georgia, it is the only Florida stream with headwaters in the Appalachian Mountains. All other Florida rivers originate in the Coastal Plain. Headwaters of the Escambia and Choctawhatchee rivers extend to the Fall Line Sand Hills of the inner Coastal Plain of Alabama. Several other rivers begin nearer to the coast within Alabama and Georgia, including the Perdido, Yellow, Ochlockonee, Suwannee, and St. Marys rivers. The latter two streams drain from Okefenokee Swamp. Florida’s other rivers originate within the state, or only their uppermost reaches extend a few kilometers north of the state line (Palmer, 1984).