The cost of the tunnels is pegged at $14 billion. The additional $10 billion in costs includes debt service payments and 40 years of expenses for its operation, said Richard Stapler, a spokesman for the state resources agency.

Additional money for habitat restoration in the delta could come from an $11 billion water bond that lawmakers recently deferred until 2014, Stapler said.

Critics called the tunnels an expensive boondoggle and said there are cheaper conservation measures for the delta.

Kate Poole, a senior attorney with the Natural Resources Defense Council, said the plan for the tunnels is "putting plumbing before sensible policy."

"Twenty-first century technology opens up new sources of water, including water conservation and efficiency, recycling and other tools to allow us to reduce our reliance on the delta, allow fish to recover, farmers to farm and people to turn on the tap and rely on good quality water," Poole said.

(Reporting By Jim Christie; Editing by Jonathan Weber and Stacey Joyce)