A million-dollar project to remove a mountaintop that threatened to cave in on a Turlock Irrigation Canal is nearly complete.
The "daylighting" project saw TID blast away dirt and rock covering a 360-foot long tunnel on TID's upper main canal, which was in danger of collapsing into the canal.
TID Tunnel 2 was originally built in 1891, and then widened to 30 feet in 1914. The concrete base and concrete lined walls withstood the test of time, but the unsupported rock ceiling developed a 40-foot long by 25-foot wide cavity, stretching 17 feet above the former tunnel crown. In 2003 a further 15-foot by 15-foot by 4-foot slab fell from the roof into the canal, mid-summer, at the height of canal flows.
If the entire tunnel had collapsed, the Turlock Irrigation District's upper main canal system could have been shut down indefinitely. Water already in the system at the time of collapse could have overflowed, wiping out nearby homes and washing out large sections of canal.
Per a 1997 TID report, a month-long outage in the heart of irrigation season could cost TID $850,000 - not counting the costs of repairing the canal system. To farmers, a 30 day irrigation outage would result in nearly $14 million in lost revenue.
Work to remove the mountaintop started on Oct. 15, when contractors opted to start excavating the tunnel crown with heavy machinery, rather than blast it down with dynamite. Two weeks later, the crown was removed, and so began three weeks of non-stop treks by 115,000 pound scraper machines to move the rubble away.
Three more weeks of clean-up followed, with excavators carefully removing the last of the dirt and rocks and contractors cleaning up the last of the debris by hand.
Perhaps more surprising than the speed at which a mountain was moved is that no major damage was done to the TID main canal.
"That's amazing," TID Director Michael Frantz said. "All that heavy machinery running atop it and through it, and it didn't break the gunite (the concrete lining of the canal)."
Workers still have some work to do, with a few extremely minor canal repairs, safety fencing installation, and some landscaping still needed.
The entire project is expected to wrap up by Dec. 20, or earlier if expected rains don't come. The daylighting project will finish on budget, at $1 million in cost, assuming no major complications occur in the final days.
On Tuesday, the TID Board of Directors also:
• Approved fee increases for Don Pedro Reservoir visitors.
Day use permits will increase from $9 to $10. Annual passes will increase from $80 to $90, and seniors' annual permits will rise from $45 to $50.
The fee increase is necessary to pay for rising costs, Don Pedro Recreation Agency staff said.
• Approved the District's Ag Water Management Plan, a state-required document which analyzes how TID uses and conserves irrigation water.
The document has been available for public review since Nov. 20. No comments on the plan were received by the District.
• Authorized a shift in TID's investment policy, which will allow accountants to invest in bonds rated in the three highest credit categories, rather than the top two. The change, recommended by an independent third-party auditor, came as rating agencies have recently altered their ratings methodology, and what are now third-tier investments are considered to be as safe as old tier-two ratings.
The new investment policy also allows the District to purchase certificates of deposit from federally-licensed branches of foreign banks, and restricts TID to invest no more than 5 percent of its portfolio in any one entity.