OAKDALE -- On a slope near Knights Ferry sit rocks that could fall without warning and plug a key canal.
The Oakdale Irrigation District board on Tuesday discussed a proposed tunnel that would bypass this part of the century-old canal system.
The tunnel, more than a mile long and expected to cost about $15 million, would help ensure reliable water deliveries to the portion of the district south of the Stanislaus River.
"It's just a ticking time bomb on the south side," board Chairman Frank Clark said.
The board has yet to decide how to pay for the project, which could start in summer and take nine to 16 months. Options include reserves, a bond issue or water sales to farm or urban users, including the San Francisco area.
The project involves a small part of the South Main Canal, which carries Stanislaus River water bound for farms as far west as Riverbank and almost to Waterford on the south.
This land is about 60 percent of the 55,000 irrigated acres in the OID. It also serves an area north of the river in San Joaquin County.
The South Main Canal winds through an especially steep part of the river canyon. Rocks have fallen into it at least four times over the years, said Gary Jernigan, manager of contracts and special projects at the OID.
If a rockfall happens during irrigation season, usually March to October, crops could go dry for farmers without access to wells.
"They wouldn't have any water for six or seven weeks," Clark said.
The tunnel, 14 feet high and 10½ feet wide, would be built by a contractor with drilling machines and explosives. The excavated material would go into the abandoned canal to create a maintenance road.
The project is part of an estimated $168 million in system improvements outlined in a 2006 plan for the district. They include upgrading canals and tunnels in the Sierra foothills, improving automated controls and water conservation.
A consultant is reviewing the projects and possible financing and could report to the board next month, General Manager Steve Knell said.
Clark said the OID has to be careful about tapping its $47 million in reserves because too low a level could mean higher interest rates on bonds sold to finance projects.
The OID paid for some of its recent upgrades with income from since-ended water sales. One was to Stockton-area domestic users. The other was to the U.S. Bureau of Reclamation for release into the lower Stanislaus fishery.
That water is available for sale to other buyers. This could include nearby farm users, such as the 7,300 acres of new almond orchards proposed to be annexed near Knights Ferry.
The Bay Area city of Brisbane is negotiating to buy about 1 percent of the OID's typical annual supply for at least 50 years.
San Francisco is in talks with the district to buy roughly the same amount as a dry-year backup for 2014. City officials have indicated that they might seek larger deals in the future.
San Francisco also sought water from the Modesto Irrigation District. Its board dropped the idea in September after protest from people concerned about dry-year shortages in the MID service area.
Bee staff writer John Holland can be reached at firstname.lastname@example.org or (209) 578-2385.