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The Rebirth Of Lake Carraizo

by Florencio Marina

March 1, 2000
Copyright © 2000 CARIBBEAN BUSINESS. All Rights Reserved.

Ever since 1994's drought made residents of the San Juan area more appreciative of the water flowing through their pipes every day, Carraizo has become a household name.

After years of postponement, the dredging of Lake Carraizo was formally undertaken in 1997. Weeks Marine was awarded the $60 million dredging contract, which the local legislature provided for through a credit line from the Puerto Rico Government Development Bank (GDB). Eleven million cubic meters of sediment had formed in the dam's bottom since its original construction in 1953, which by 1994 had reduced Carraizo's capacity by 53%--to the point of causing that year's subsequent rationing in the metro area.

A year before the drought, authorities considered throwing extracted sediment over the dam but the lack of clear environmental guidelines back then prevented the EPA and other health and safety organizations from approving such a plan, said Carraizo Project Manager Anibal Camacho.

Prasa chose to build three new dikes in the Rincon, Celada, and Hato Nuevo sectors of Gurabo, to store the sediment.

In 1996, Hurricane Hortense's strong winds and currents removed 800,000 cubic meters of sediment from the lake. Then--between Oct. 1997 and Oct. 1999--another 5 million cubic meters of sediment was removed by dredging.

Camacho added the lake has been restored to its original 75% capacity, which was Prasa's goal.

As part of AFI's special projects, all 8 spillway gates (39 ft. wide and 33 ft. tall) are being replaced, as well as the dam bridge and the trash sluice gate, a project totaling $16.7 million. The gate control system is also undergoing improvements. The new gates will be the same size as the existing ones but will have an ogee lip to protect the gate structure and allow for overtopping, should it become necessary.

The connections between gate members will be welded instead of bolted or riveted, as is the case with the current gates. Existing hoists will be used but the chains will be replaced with stainless steel cables to facilitate maintenance. "In June 1998, the third gate overloaded at the top half and became deformed," said Project Manager Eleanor Allen, also of CH2M Hill.

"It was time to change the 50-year-old gates."

The $16.7 million contract for the replacement of the gates was awarded to Dillingham Construction of California on Jan. 24. Construction is expected to last 26 months replacing one gate at a time. Barrett & Hale of San Juan and ECI of Denver, Colorado designed the new spillway gates, bridge, and trash sluice gate. This portion of the renovation is expected to be completed by April 28.

In addition to those two projects, AFI is also replacing Carraizo's six pumps at a total of $3.2 million. Five of them have a 20 million-gallon-a-day (mgd) maximum capacity and one can handle 30 mgd. Altogether, they currently move 106-110 mgd to the Sergio Cuevas filtration plant due to weakness caused by their five decades of existence. New pumps will each have a 22.5 mgd capacity, meaning all six will be able to move 135 mgd.

Since the capacity of five new pumps will still be greater than the present level, plans are that one pump will serve as backup when needed.

The improvements will also allow maintenance work to be carried out on any one of the pumps, while the other five ensure regular service. The $3.2 million pump replacement project has been awarded to El Dorado Technical and its completion is expected by third trimester 2001.

This Caribbean Business article appears courtesy of Casiano Communications.
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