Tampa Bypass Canal — Tampa, Florida

The Tampa Bypass Canal is the flood relief channel that lets high water on the Hillsborough River skip the urban river bends through Temple Terrace and Tampa. According to the Southwest Florida Water Management District (SWFWMD), the canal runs parallel to the river and ends in McKay Bay on the east side of Tampa, carrying water that would otherwise rise through neighborhoods along the lower Hillsborough.

The canal is one piece of what SWFWMD calls the Tampa Bypass Canal System, together with the Hillsborough Flood Detention Reservoir and the Harney Canal. District sources give different lengths depending on where they measure: the project page says approximately 15.7 miles, the SWFWMD recreation page calls it a 14-mile waterway linking the Lower Hillsborough Wilderness Preserve with McKay Bay, and a 2004 District article describes a canal more than 12 miles long built along with six dams, or flood-control structures.

The trigger was the 1960 hurricane season. SWFWMD's history of its first decade records that Hurricane Donna hit Florida with 128-mph sustained winds and massive flooding, and SWFWMD's project page states that Tampa experienced significant river flooding from rainfall, runoff and storm surge. The state response was a new agency: the Florida Legislature created SWFWMD in 1961 by special act to serve as the local sponsor of the Four River Basins, Florida Project, and its Governing Board first met on August 28, 1961, in Tallahassee.

The Four River Basins project was a $57 million flood control plan designed by the U.S. Army Corps of Engineers for a 6,000-square-mile area covering the Hillsborough, Ocklawaha, Peace and Withlacoochee river basins. The Corps designed and built the canals and structures, while the District bought the land and agreed to operate them. For Tampa, that meant land for the bypass canal and large tracts for the Lower Hillsborough River Flood Detention Area, northeast of the city.

The new District organized quickly around local watersheds. By March 1962, SWFWMD reports, its 11 watershed Basin Boards were in place, including boards for the Hillsborough River and Northwest Hillsborough, and the Governing Board and a staff of three met monthly in a rented Brooksville office. Dale Twachtmann, executive director from 1962 to 1972, recalled that the District immediately began buying land for flood control, starting with the right of way for the Tampa Bypass Canal and the acreage for the Lower Hillsborough River Flood Detention Area.

SWFWMD dates engineering and recreation planning for the Tampa Bypass Canal to 1963 and the groundbreaking on its first section to 1966, and a District photograph shows the S-160 Flood Control Structure under construction in 1968. The lower end of the channel follows the Palm River; a SWFWMD release of October 27, 2011 notes that canal construction in the 1960s required significant dredging of the Palm River, which runs from S-160 north of the Selmon Expressway to McKay Bay.

Weather turned the other way while the work went on. From late 1962 into 1963, Hillsborough County and its neighbors were in drought, and the District's first executive director recalled residents asking why money was going to flood control when the problem was a lack of rain. In 1969, SWFWMD asked Congress to expand the Four River Basins project to add a multipurpose water supply role. The District's project page states that the system's design was changed to help the City of Tampa with its public water supply, and the 1960s history quotes the former director saying the change let Tampa use some canal water for drinking water.

One planned feature was dropped. SWFWMD's Lower Hillsborough Wilderness Preserve page notes that a structural reservoir was part of the original plan but was abandoned once the value of natural wetlands for flood storage was understood, leaving the forested detention area northeast of Tampa to hold floodwater instead.

Control starts at Structure S-155. SWFWMD explains that the Hillsborough River flows through a 6.5-mile earthen dam at the edge of the 16,000-acre Hillsborough Flood Detention Reservoir, which stays empty until high water arrives. Closing S-155 stops the river from passing through the dam, the reservoir begins to fill, and District operators then release water back to the river or send it into the canal around Temple Terrace and Tampa.

The District's WaterMatters magazine for November to December 2004 locates S-155 near where the river crosses Interstate 75 just north of Fletcher Avenue. Its two 24-ton gates can redirect all or part of the river, which at that point drains about 452 square miles. Farther downstream, the Harney Canal ties the river to the bypass canal a few miles north of the City of Tampa's dam, and SWFWMD says it is opened when flooding builds below the earthen dam, especially when storm surge blocks the city dam's discharges. When not holding floodwater, more than 7,000 acres of the detention area serve Hillsborough County as a regional park.

The 2004 hurricane season tested the system. After Charley, Frances and Jeanne, rivers flooded across west-central Florida, but SWFWMD reported that homes and businesses on the lower Hillsborough were spared. That year the canal moved more than 200 billion gallons out of the river, an average of 3.5 billion gallons per day, and ran three times for a total of 58 days, compared with a normal pattern of operating once a year.

The flood channel doubles as a reservoir. SWFWMD describes the canals as large linear pools of fresh water that local utilities use, and Tampa Bay Water states that when water is available it skims from the Alafia River, Hillsborough River and Tampa Bypass Canal, treats part of it at the Tampa Bay Regional Surface Water Treatment Plant and stores surplus in the 15.5-billion gallon C.W. Bill Young Regional Reservoir for dry times.

The canal banks are also public land. SWFWMD's recreation page divides the canal at State Road 60: north of SR 60 the water is fresh, motors are limited to 10 horsepower and the reach is a no-wake zone, while south of SR 60 the water is salt and powerboating is unrestricted toward McKay Bay. Access points include Harney Canal Park off US 301, a 12-acre site with a boat ramp and fishing pier run by Hillsborough County Conservation and Environmental Lands Management, and Veterans Memorial Park, where a 0.75-mile paved trail is open to walking, bicycling and inline skating. Bank fishing and hiking along the grassy Tampa Bypass Canal levees are allowed at designated points from sunrise to sunset.