C.W. Bill Young Regional Reservoir is filled to capacity in this photo taken in 2005. When the reservoir is full it can provide 25 percent of the region’s needs for more than six months.
Tampa Bay Water now knows why the C.W. Bill Young Regional Reservoir has been cracking.
A thorough analysis by consulting engineers revealed the cause of soil-cement cracking to be high water pressures underneath the reservoir’s erosion control liner, according to a report issued on Friday, June 5.
Now that the cause is known, the utility can plan and begin the process for a long-term fix, according to Michelle Rapp, spokesperson for Tampa Bay Water. She said the target date to begin the repair project was June 2012.
Tampa Bay Water outlined the details of the report in a press release that explained the reservoir’s erosion control layer consists of soil-cement that lines the interior and a soil wedge that lies between the soil-cement layer and a deeper geomembrane that protects the rest of the embankment.
The reservoir has been in operation since 2005 and is an intricate part of the region’s drinking water system. During inspections of the reservoir in December 2006, cracking was found in the flat-plate, soil-cement, erosion-control layer linking the reservoir’s interior, according to a fact sheet.
After two years of investigation, Rapp said engineers determined that the soil-cement cracking, soil wedge movement and soil erosion was caused by water becoming trapped in the soil wedge causing high water pressure.
Although the problem has created a situation where the reservoir cannot be filled to its 15.5 billion gallon capacity, inspection and analysis continue to conclude the reservoir is safe, said Gerald Seeber, Tampa Bay Water general manager.
He said short-term patching has allowed continued limited use of the reservoir, but for the long-term more extensive repairs are required.
“Tampa Bay Water’s system was built on a working 15.5 billion gallon reservoir for storage and without it our surface water system becomes vulnerable to surface water shortages,” Seeber said. “The facility is an essential component to the region’s diverse water supply and requires a long-term fix.”
Drought conditions have made the problem at the reservoir even more troublesome. The inability to fill the reservoir to capacity has been an underlying cause for Southwest Florida Water Management District issuing the strict water restrictions for the area.
Rapp said the next step in the process would be board approval to begin work toward finding the best way to fix the problem. The report will be presented to the Tampa Bay Water Board on June 15.
The utility’s engineers propose three basic approaches for the long-term fix, including adding drainage to the soil wedge and replacing the soil cement; adding weight to the existing structure to prevent further movement of the soil cement layer and soil wedge beneath; or removing the soil wedge between the soil cement and geomembrane and reapplying a well-drained, soil-cement, erosion-control layer directly on top of the geomembrane.
Regardless of method, the fix is expected to take several years to complete.
“In order to select the best solution for the best value, Tampa Bay Water will have a competitive design and construction process that will include an independent, expert peer review group as part of the process,” Seeber said. “We want to make sure the focus is on getting it right. Quality and results, rather than schedule, will govern the fix.”
Tampa Bay Water provides wholesale water to the public utility systems of Hillsborough, Pasco and Pinellas counties as well as the cities of New Port Richey, St. Petersburg and Tampa.
- The reservoir holds 15 billion gallons, or 33 times the volume of Raymond James Stadium.
- When full, the reservoir can provide 25 percent of the region’s needs for more than six months.
- The reservoir is two miles long, one mile wide and the circumference at the top of the berm is five miles.
- As part of the mitigation efforts for this project, over 1.5 million plants and trees were planted on the site.
- 8 miles 7-foot diameter pipeline connect the reservoir to the water supply network.
- The reservoir's banks are coated with 16 inches of soil cement to prevent erosion from waves.
- It took 183 days to initially fill the reservoir.
- During construction, more than 150 pieces of heavy equipment were used and more than 150 people employed.
- 13 million cubic yards of earth were moved in total for this project. That is equivalent to one dump truck every minute for two years straight.
- Drilling teams spent 10 months on the site to study the geology and sub-surface conditions and 12,000 man hours were spent collecting data on the site.
- If all the soil borings taken at the site were placed end-to-end, the line would stretch 3 1/2 miles.
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