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Credit: David Kincaid, Devo Engineering

After the 2004 hurricane season, water levels around Lake Sherwood in Orange County were extremely high.
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Credit: David Kincaid, Devo Engineering

After exploring several alternatives, the Orange County Roads and Drainage division elected to replace one drainage well near Lake Sherwood with four wells 2500 southeast of the existing well.
IMPLEMENTING THE SOLUTION

In December 2004, the R&D Division contracted with Henderson Wilder to construct the replacement drainage wells. The contractor built four 12-inch diameter drainage wells at the east side of Lake Sherwood, south of the East-West Expressway State Road 408. Eighteen-inch diameter steel surface casings were installed to depths from 52 to 55 feet below land surface to serve as outer casings to each of the 12-inch diameter wells. The annular space between each well casing was fully grouted, and the open boreholes were completed to depths of 382 to 455 feet below land surface.

A 36-inch diameter reinforced concrete pipe now serves as the intake pipe to direct the water from the lake to a primary drainage well box, connected to the remaining three well enclosures through 24- and 30-inch diameter concrete pipes. The adjustable weir of the primary well box and the elevation of the casings from each box bottom help sediments to settle, preventing them from entering the aquifer. In addition, each drainwell intake pipe has a bar guard to stop trash and prevent any floating debris from entering.

The construction of the four replacement drainage wells was completed by August 2005 at a total cost of $480,433. The new wells are an improvement over the existing one, as the double casings and grout seal serve to prevent cross-aquifer contamination, and the wellhead enclosures prevent the entry of floating debris. The new drainage wells also are protected against vandalism by means of locked aluminum hatches on each well-head enclosure.

Once the replacement wells were installed, the old well was abandoned in place by sealing it with grout. Hurricane Wilma tested the new wells on Oct. 24, 2005; to the division's satisfaction, the drainage wells effectively controlled Lake Sherwood's levels

An analysis of the recorded water levels at Lake Sherwood from January 2004 to October 2005 shows how efficient the new drainwells were in controlling the water surface elevation of the lake. The maximum-recorded stage at Lake Sherwood was 88.25 feet national geodetic vertical datum (NGVD) in September 2004, during Hurricane Frances. At that time, high water surface elevation caused flooding in the vicinity of the lake, particularly when the lake's normal water level is 69.1 feet NGVD.

However, when Hurricane Wilma discharged heavy rainfall over Orange County, the new wells worked efficiently in controlling the lake level. In November 2005, the highest recorded stage was 76.94 feet NGVD, and no flooding was reported in the area.

Without a doubt, the new drainage wells are serving their purpose. The replacement of the old well has been a successful proactive solution to avoid flooding. Most importantly, the replacement wells have resulted in a better drainage system for the environment.

— Budhu is manager and Torres is engineer III with the Roads and Drainage Division of Orange County, Fla.