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Opening the floodgates: Orange County smooths stormwater flow.

Rampant urbanization threatens both the cleanliness and abundance of Florida's water supply--vital to the state's economy. But Florida's Orange County has taken concrete steps to counteract urbanization. It is using various unique and innovative methods to keep water flowing through its canals.

An average of 6,000 people move to the Sunshine State every week, spurring construction of new roads, parking lots, and buildings. Unfortunately, the number of drainage ditches in the county has remained the same.

Rainfall no longer soaks into the ground as readily as before because asphalt and concrete now cover the ground. As a result, rainwater flows off streets three times faster and carries six times more sediment than water running off vegetated areas.

Maintaining a good stormwater management system is the key to preventing flooding and environmental pollution. Stormwater management, however, is proving to be a primary environmental challenge of the 1990s.

As part of Orange County's stormwater management program, the stormwater management department is responsible for controlling vegetation along 110 miles of primary canals, and around eight pumping stations and 96 drain wells. Without drainage efforts, heavy rains would cause widespread flooding for days.

"Our business is not esthetics, but rather the movement of water from point A to point B without flooding someone out," explained Ray Mitchell, the stormwater management department's assistant supervisor. "With an increasing number of people purchasing homes and condominiums along drainage canals, it becomes even more critical to control problem vegetation that can interfere with quick, efficient drainage."

Balancing Act a Challenge

To adapt to changes in runoff and encourage efficient water flow, the department has turned to the use of insects, herbicides, and mechanical measures to control vegetation clogging stormwater drainage systems. One of the biggest challenges the department faces is creating a balance between these methods to develop the most cost-effective, long-term program for controlling vegetation along the canals.

One new approach is the use of insects to suppress vegetation growth, a concept developed by the University of Florida. Different insect species eat the leaves of specific, targeted undesirable plants. If they eat desirable vegetation, they die, says Mitchell. Asian flea beetles, for example, only eat alligatorweed.

Since beetles do not bite and only fly short distances, the department is not concerned about them causing a public disturbance. "Asian flea beetles are helpful, stay near their food source, and are less expensive than using a dragline," Mitchell commented.

"Relocating them is a fairly simple process, and represents the only cost involved with using this method," Mitchell added. The department catches the beetles in sections designated by the Department of Natural Resources (DNR), and releases them in areas heavily infested with alligatorweed. It takes about 500 to 600 beetles to start another population.

"But insects work at Mother Nature's whim," according to Mitchell. "They were getting about 50 percent control three years ago when we got a freak freeze in December, which greatly reduced their population. It will take a couple of years to build up enough beetles before they can make an impact."

Recently, Mitchell worked with the DNR to obtain a special type of moth that eats water lettuce. Mitchell plans on placing the moths in a heavily infested area inaccessible to air boats.

Herbicides Offer Flexibility

A more controllable option to vegetation management is the herbicide invert application. An invert is a mayonnaise-type mixture of oil, water, and herbicide that turns into a thicker, white substance when sprayed. The substance sticks to the plant and the herbicide is then absorbed by its foliage.

Unlike a conventional spray, inverts float and eventually attach to stalks, stems, and leaves of plants growing at the water's edge. As a result, there is minimal material waste. Generally, 3/4 gallon of Rodeo|TM~ herbicide (Monsanto Company, St. Louis, Missouri) is mixed with 4 gallons of I-vod oil in 100 gallons of water. This invert mixture effectively controls cattails, torpedograss, paragrass, and alligatorweed, said Mitchell.

He and his crew operate two Ford Minnesota Warner invert rigs mounted on 4-wheel drive trucks and an air boat. The second air boat has a conventional sprayer that will soon be converted to an invert system. The air boats have 50-gal tanks with pick-up lines to pump water out of canals. This allows workers to mix the materials right at the treatment location.

"We were fortunate to have the budget dollars to purchase the equipment we needed," Mitchell explained. "Our operation is big, and we need a lot of equipment to support it."

The department recently purchased a large Ford truck with a 1,000-gal tank and an invert system with a controlled side-mounted broadcast spray head. Mitchell plans to apply herbicides from the top of the bank to the water's edge to save wear and tear on slope mowers.

"Ultimately, without a herbicide program, we wouldn't be able to maintain any type of long-term vegetation control," Mitchell said. "We want to reach a point where we have the vegetation under control and are then performing only maintenance."

Even though the role of mechanical vegetation control is decreasing in the department, it still exists. "We have eliminated about 75 percent of our trips with the dragline," he explained. "Operating a dragline is about eight times more expensive than a herbicide application on the same area, but then herbicides don't remove sediment and take sand bars out."

The department uses draglines, which are high maintenance machines, to clean debris and sand from canal bottoms. Draglines remove treated vegetation to avoid fish kills due to lack of oxygen. A trip with a dragline is usually followed by the appropriate herbicide applications.

As demands on the stormwater management system increase, Mitchell's department is feeling the crunch of a decreasing budget. "The federal government took all matching funds away from the state of Florida. Basically, our funds have been cut in half, forcing us to do the best we can with the resources we have."

Insufficient funding from conventional sources is a primary reason for stormwater management problems. Local governments wishing to establish funding sometimes implement user fees. Orange County is still in the planning stages of starting a user fee and hopes to have one in place sometime in 1993.
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Title Annotation:Florida
Publication:Public Works
Date:Mar 1, 1993
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