In 200 AD, prehistoric people living near Lake Okeechobee constructed the earliest known canal in North America. According to archaeologists, early Native American societies, such as the one living nearly 2000 years ago in what is now known as Ortona, Florida, constructed canals for fishing and transportation. Similarly, canals constructed by Florida land developers during the twentieth century provide benefits for contemporary denizens.

Today, thousands of miles of canals, and their water control structures, are carved into Florida's landscape, especially in the southeastern parts of the state. Canals are artificial waterways that modify existing rivers or streams, or are dug into wetlands or uplands for navigation, drainage and flood control, irrigation, access, and recreation. Florida canals range from a few feet to hundreds of feet wide and from a few feet to as deep as 35 feet.

Canals provide many benefits to our citizens. Without them, the state from Orlando southward would be unable to accomodate the millions of residents and enterprises that now call south Florida home. Without canals, southern Florida would not be what it is today: a financial, commercial, agricultural and social symphysis of the Western Hemisphere.

However, canals also present many challenges to aquatic plant managers. Aquatic plant management is necessary in canals to keep water flowing. Without regular and frequent management, aquatic plants would clog these systems very quickly, rendering them useless for flood control, navigation and recreation. Jump down for more about plant management in canals.

Ecosystems within river and stream channels that have been widened, deepened, or straightened are forever changed. Altering water flow, bank slope, oxygen and light levels, and bottom composition and structure affects fish and wildlife, as well as plant growth. Canals constructed in wetlands or uplands quickly fill with both native and invasive non-native aquatic plants. Managers must decide how and to what extent aquatic plants should be managed to accommodate the primary as well as the many secondary functions of these artificially constructed waterways.

THIS WEB PAGE INTRODUCES FLORIDIANS to the functions of canals, their benefits, and their management challenges.

Florida is the most likely target for tropical storms and hurricanes of the Atlantic and Gulf of Mexico. These tropical cyclones may drop 20 or more inches of rain in a day's time. Flood control has been an essential purpose for the construction of canals ever since several fatal hurricanes struck southern Florida in the 1920s (some pictures here) that claimed nearly 3,000 lives and caused $75 million ($760 million in 2003 money) in damages. Canals and their large pumps and gates provide flood protection by quickly collecting and moving storm water away from populated areas.

Pump moves water from canal to field	Channels and ditches move water in agriculture

Florida has the fifth largest agriculture industry in the nation. Agriculture boomed with the construction of canals as the water control systems drained fertile land, controlled seasonal flooding, and provided reliable irrigation. Farmers can drain water from their farms during the wet season and retrieve the stored water during the dry season. Major economic crops dependent on south Florida's water control systems include sugarcane (first planted in 1917), peanuts and potatoes (1920s); beans, tomatoes and peppers (1930s); rice (1950s); and St. Augustine grass (1950s). Major citrus groves moved to the area after devastating freezes farther north in Florida during the 1970s and 1980s. Cattle became a major industry in the area in the 1950s.

Navigation lock on Lake Okeechobee	Navigation lock (l) and dam (r) on Lake Tohopekaliga

Navigation throughout the state is facilitated by Florida's canal systems as they provide navigable waterways for commercial and recreational boating to move between lakes, rivers and coasts.

Airboat tours of Florida Everglades	Fishing on the big canals

Unlike central and northern Florida, the southern part of the state has relatively few natural freshwater recreation places. Canals are home to a variety of freshwater game fish, offer thousands of acres of surface area, and are easily accessible to boat and shore fishing.

Cape Coral	Miami	Crystal River

Residential property in Florida has relatively greater real estate value when adjacent to canals. Canalways provide boating access to the ocean and to most of Florida's large public lakes and navigable waters. These canals, which are privately owned, provide valuable property for local government tax rolls, which use part of the tax money for plant management activities in the canals. Residential canals are usually shallow. Not only do residential canals provide drainage and flood control, their spoil is spread next to the canals to raise the elevation of surrounding areas, providing an extra measure of flood protection.

Dams create steps in the river that enable navigation throughout the year by preventing the river from draining in the dry season. River water flows into the pools created by the dam and excess water runs over the dam into the next pool. Dams do not provide flood control. Locks are concrete box-like chambers that enable watercraft to travel from one dammed pool to the next. The gates open and close when water level is equal on both upstream and downstream sides. Filling and emptying of the chamber is conducted by valves within the lock's walls. No pumping is necessary as water flows in and out of the chambers by gravity. Culverts are buried pipes that conduct water underneath roadways, or into canalways. Channels are navigable pathways in waterbodies that are at least nine feet deep. Weirs are crested overflow structures built over canals as a means of measuring water discharge. Three primary types are the rectangular weir, the Cipoletti weir, and the 90-degree v-notch weir.

Here are more canal pictures

PLANT MANAGEMENT IN CANALS

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Canal Jams

Generally, aquatic plant management in canals is the responsibility of the owner or manager of the canal. Each year, millions of dollars are spent for invasive plant management in Florida's canal systems. In 2002, the South Florida Water Management District spent $2 million to manage more than 24,000 acres of nuisance plants in canals. Many millions more were spent on canal plant management by the state, by counties, by other water management districts, by the more-than-200 "special 298" districts, and by farmers and ranchers and other private interests. Here are the managing agencies for canals and other water systems in Florida.

Virtually all canals in Florida are susceptible to serious infestations of plants that alter "hydraulic conductivity", and interfere with navigation, flood control, boating, fishing, and other uses of canals.

Management of both native and invasive plants in Florida's canal systems is integral to water control because aquatic plants greatly affect the hydraulic conductivity (water-handling capacity) of the water control system. Dense vegetation greatly decreases the already limited water flow within a canal system.

The ability of a canal to move water depends on the size of the unobstructed volume where the water passes: the larger the volume, the greater the amount of water that can pass through. The hydraulic efficiency of a canal is measured by the percentage of volume that is unobstructed. Aquatic plant obstruction is measured by Manning's Roughness Coefficient: equation here. For example, a canal that is 47% obstructed with hydrilla is only 53% efficient in water conductivity, which means that the canal can handle only about half the water it was designed to handle.

By incorporating Manning's equation with inches of rainfall, experts can predict the efficiency of a specific canalway, its ability to conduct water, and the amount of water that will overflow into neighborhoods, cities and farmlands during times of rain, flood and hurricane.

In order to keep the water control system functioning, managers must maximize the hydraulic conductivity of canalways by freeing them of vegetative obstructions. Plant managers employ a variety of methods to control aquatic plants in canal systems.

Machine removing plants	Grass carp biocontrol	Applying granular herbicide	Canal Maintenance

Plant destroying and harvesting machines (as described on our mechanical controls page) can provide immediate relief for clogged canals. However, harvesters work slowly and are restricted to the central channel. Sterile grass carp (as described on our biological controls page) is a plant-eating fish that has been used as a biocontrol for submersed plants in canals. However, grass carp must be confined, which is difficult to do in canal situations. The most efficient and most used means of aquatic weed control in canals is the use of herbicides (as described on our herbicidal controls page).

Despite the adverse effects of the various plant management techniques, however, maintaining adequate hydraulic conductivity remains paramount to the proper functioning of canals. The viability of the southern half of the state depends on it.

An unhappy canal

Very long (deep or shallow), and/or dead-end canals usually do not have adequate water circulation. Poor circulation means that inadequate flushing and turnover occurs in many canals. Such conditions lead to decreased dissolved oxygen concentrations; increased pollution loading; decreased plant photosynthesis and growth due to turbidity; excessive accumulation of organic materials and sediments on the canal bottom; accelerated eutrophication; and negative impacts on animal communities.

Dissolved oxygen concentration in canal water decreases as the distance from the canal inlet increases. (Good dissolved oxygen levels in the water are essential to fish and other aquatic animals. Go to the dissolved oxygen page of this web site.) Dissolved oxygen concentrations are statistically related to the mean depth of the water in the canal. Canal water stratifies easily (forms temperature layers), does not circulate much, and exchanges little with the main body of water. Decomposing organic matter along the stagnant canal bottom also depletes the oxygen supply in the water. Some aquatic life can inhabit the shallow, more oxygenated, layers; however, when bottom waters are driven to the surface by upward swelling due to high storm winds, aquatic life often is affected, fish kills may occur. Based on vertical dissolved oxygen profiles and numerical flushing models, the Environmental Protection Agency recommended in 1975 that the appropriate canal depth should be no more than six feet below mean water level

Pollution loading occurs as a result of shoreline development, such as the shorelines of canals. Septic seepage, lawn fertilizers, pesticides and effluent, and oil and gasoline from boats negatively impact canal water quality. Paved parking lots and streets prevent land areas from absorbing polluted runoff, so pollution-laden rainwaters drain directly into canal systems. Inadequate flushing prevents the canal system from dilluting and dispersing pollutants to the receiving waterbody. Contaminants may accumulate on the water surface or build up in canal sediments.

Native wildlife is impacted by canals. Although benthic (bottom-dwelling) animals, fish and plants are frequently abundant in newly constructed canals, the advent of hot weather can result in increased temperatures and dramatic decreases in dissolved oxygen concentrations in the canal water, resulting in heavy mortality of benthic organisms and fish. In cooler weather, animals may recolonize as dissolved oxygen concentrations increase. Most canals are virtually closed bodies of water and serve as nutrient traps, and the accumulation of decaying organic matter on the canal bottom impedes healthy biological production.

For more information on how humans impact our water resources, go to this page on our web site.

Today's New School of "Rational Canal Design"
Many of the environmental and water quality problems posed by canals are the result of hasty construction and poor design. In response to growing concerns over the ecological impacts of canals, researchers have developed a variety of recommendations, primarily in regards to canal design and structure, for the modification of existing canal systems and the construction of new ones.

Canal designers now recommend:

Limit canal construction that connects to shallow lakes with restricted connections to tidal waters.

Include a flow through water exchange system.

Cease construction of dead end canals

Canal depth should be uniform or progressively shallower away from the parent waterbody.

Septic tanks should not be permitted within a canal development.

Stormwater and effluent should be directed away from canal systems.

Nutrients and other contaminants should be reduced (i.e. vegetative buffer zones).

Canals should not interface with aquifers.

Canals should be as wide as possible (in relation to depth and length of canal) and oriented to prevailing winds.

Requirements for navigable depths to shoreline should be eliminated.

Bulkheading should be reduced and sloping banks and native vegetation restored or planted.

Sand and substrates should be diversified.

Eliminate linear and right-angle designs.

Flared inlets should be added to dead end canals that are oriented perpendicular to prevailing winds.

Promote habitat diversity.

Other ideas include: installation of mechanical pumps.

For more information on what you can do to conserve Florida's waters, go to this page on our web site.