Turlock Irrigation District planning a fix for old water tunnel

TURLOCK -- A fix is planned this fall for a 121-year-old irrigation tunnel near La Grange that threatens to collapse.

The Turlock Irrigation District board could vote Tuesday to move ahead with the project, which is expected to cost about $975,000.

The 360-foot tunnel is a tiny part of the distribution system, which has about 250 miles of canals supplying about 146,000 acres around Ceres, Turlock, Hilmar and other towns.

If the tunnel collapsed, the TID could get by for a while with the water stored downstream in Turlock Lake, along with groundwater. The much bigger supply from Don Pedro Reservoir would be lost until emergency repairs could be made.

The district staff recommends "daylighting" the tunnel, which involves removing about 40 vertical feet of soil and rock above it and turning this stretch into an open canal.

The staff expects to clear the project with state and federal agencies next month, then call for bids from construction contractors. The work would be done from October to December, when the system is shut down.

Routine inspection turned up the problem with the tunnel, one of three near La Grange. The TID then took a closer look, including visual inspection, drilling core samples and using a technology called seismic refraction.

The tunnel ceiling is supposed to be 23 feet above the floor. But it is as much as 40 feet where a cavity has developed at the midpoint of the tunnel's length and rock has fallen.

TID officials have said the repair cost is worthwhile in light of the millions of dollars of crop losses that could occur if the water were cut off.

The board will meet at 9 a.m. Tuesday at the district office, 333 E. Canal Drive, Turlock.