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Watersheds and Springsheds

Watersheds

Today, rather than looking at land and water resources as separate, unrelated parts, water managers consider the connections within a watershed or drainage basin. Every part of the Earth’s land surface is within a watershed. Divides (ridges, peaks or areas of high ground) separate watersheds. Because water flows downhill, rain falling on these divides may flow in opposite directions, becoming part of different watersheds. For example, the Brookesville Ridge divides the waterflows between the coastal rivers and the Withlacoochee River basin according to the lay of the land.

A watershed is the land area that contributes runoffThe topographic flow of water from precipitation to stream channels located at lower elevations. Occurs when the infiltration capacity of an area's soil has been exceeded. It also refers to the water leaving an area of drainage. Also called overland flow., or surface water flow, to a water body. The water resources within a watershed are affected primarily by what happens on the land within that watershed. Anything on the land within the watershed, however far from the water body, can eventually reach and impact that water resource. Some examples of contaminantsSomething that contaminates. that may be picked up by water in the watershed are soil particles (suspended materials) and chemicals (dissolved materials), such as nutrientsAny food, chemical element or compound an organism requires to live, grow, or reproduce., herbicides, pesticidesA chemical that kills, controls, drives away, or modifies the behavior of pests., oils and gasoline residuesWhat is left over or remains; the part of a molecule that remains after portion of its constituents are removed. Residues of some contaminants may remain after.

The shape of the land defines a watershed. Water flows both above and below the ground from points of higher elevation to points of lower elevation through the force of gravity. Rainfall that is not absorbed by the soil but flows to a larger body of water is known as runoff; runoff collects in channels such as streams, rivers and canals. The small channels, in turn, flow to larger channels and eventually flow to the sea. These channels or streams are also known as tributaries. The slope of the land, as well as the amount and type of vegetation and soil and the type of land use, determine the rate and amount of runoff that enters a water body. More water soaks through sandy soils than through clayA fine-grained, firm earthy material that is plastic when wet and hardens when heated, consisting primarily of hydrated silicates of aluminum and widely used in making bricks, tiles, and pottery; used for liners in landfills because it is impervious. soils; gentle slopes allow more time for rain to soak into the ground (or to evaporate) than do steep slopes; and natural areas generally allow more water to enter the ground than areas that are covered with houses or pavement. Vegetation also absorbs water and slows its movement.

Florida’s karstAn area of irregular limestone rock formations in which erosion has produced fissures, sinkholes, underground streams, and caverns.
Such terrain is created when ground-water dissolves the limestone.
terrain, as we have in Citrus County, and flat topographyA detailed map of the contours of surfaces of land. sometimes make determining watershed boundaries difficult. In some places the drainage pattern is best described as “disjointed” because streams and rivers do not form continuous channels on the land surface (Mossa 1998) — they may disappear underground in sinks or depressions. Large rivers may form from springs issuing from the surface water watersheds may be quite different from groundwaterWater in the ground. Water that occupies the pore spaces found in some types of bedrock. watersheds. Some portions of Florida are poorly drained (Mossa 1998). There are few or no streams or channels in these areas, and water flows across the surface through extensive swamps or marshes. This is known as sheetflow. Disjointed drainage from these areas without continuous natural channels, may drain into surrounding basins or into the sea through marshes, swamps, ground water or constructed channels. In south Florida’s managed watershed, drainage is by canals more often than by marshes, swamps or ground water. Source: Mossa 1998

In much of south Florida, the natural landscape has been altered with huge public works projects, making the region a managed watershed. Canals, pumping stations and water-control structures, such as dikes and weirs, have altered the watershed. The historic swamps, marshes and associated sheetflow are greatly altered or are replaced by urban development and agriculture and drained by canals. Public and private entities are responsible for water movement, especially the discharge of floodwater.

Springsheds

Black Spring Springs are a “window” into the groundwater flows which emerge to the surface as a spring. The underground flows within a land area that contribute water toa sprng vent or outlet comprise the springshed. Cool in the summer and warm in the winter, the springs are among the most sought-after of all the state’s natural and scenic resources. Most of Florida’s springs are found in the northern half of the state and flow from the Floridan aquifer. As rainwater enters and recharges the aquifer, pressure is exerted on the water already in the aquifer. This pressure causes the water to move through cracks and tunnels in the aquifer. Sometimes this water flows out naturally to the land surface at places called springs.

When the openings are large, spring flow may become the source of rivers. The Ichetucknee is an example of a river created by a spring. Springs also make substantial contributions to the flow of other rivers. Manatee, Fanning, Troy and Blue springs contribute nearly 368 million gallons each day to the Suwannee River. The Coastal Rivers of Citrus County, apart from the Withlacoochee River, originate with spring systems fed from the aquifer. Crystal River/Kings Bay originates with thirty springs to become the second largest spring system in the State.

For thousands of years, Native Americans settled near springs and fished in spring-fed streams. Spanish explorer Ponce de Leon came to Florida seeking a Fountain of Youth, as well as gold and other treasures. Traveling in Florida in 1774, botanist William Bartram described water issuing from one of the springs along the St. Johns River as “perfectly diaphanous,” with fish appearing “as plain as lying on a table before your eyes, although many feet deep in water” (Van Doren 1955). Today, springs are popular with both tourists and residents. Many of Florida’s largest springs have been incorporated into state parks, including Manatee, Homosassa, Silver, Wakulla and Ichetucknee. Wakulla and Silver springs have been popular locations for movies. Majorie Kinnan Rawlings’ The Yearling, as well as more than 100 episodes of the popular TV series Sea Hunt, were filmed at Silver Springs. The Creature from the Black Lagoon and some of the Tarzan movies were shot at Wakulla Springs.

Rain falling onto nearby recharge areasThe area on the Earth's surface that receives water for storage into a particular aquifer. and entering the aquifer is the source of most of Florida’s ground water, which is the source of water flowing from springs. Contrary to popular belief, underground rivers do not carry water into Florida from other states (Spechler and Schiffer 1995). Water in the aquifer flows through the permeable rocks and the various-sized openings in the rocks, rangining size from the microscopic to huge caverns. See Karst terrain. The 320 known springs in the state discharge nearly 8 billion gallons of water each day, more than all the fresh waterWater that is relatively free of salts. used in the state each day (Spechler and Schiffer 1995). Large withdrawals of water from wells near a spring can cause the flow of the spring to become retarded or stop. SiltMineral particle with a size between 0.004 and 0.06 millimeters in diameter. Also see clay and sand. or sedimentsSolid material that has been or is being eroded, transported, and deposited. Transport can be due to fluvial, marine, glacial or aeolian agents. building up in the spring can also cause loss of flow. The only large spring in Florida known to have ceased flowing is Kissengen Spring, about 4 miles southeast of Bartow (Berndt et al.1998). The spring stopped flowing in 1950 (Rosenau et al. 1976).

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