By Associated Press

WASHINGTON — A long-awaited study requested by Congress concludes that enlarging Shasta Dam by 18.5 feet is technically and economically feasible, though the Bureau of Reclamation declined to make a formal recommendation to move ahead with the project.

The study found the most viable expansion option would cost an estimated $1.4 billion and provide an economic benefit of $30 million annually from increased salmon populations, water supply, flood control and recreational opportunities.

However, it was unclear who would be willing to take on the cost of construction.

The report said nonfederal alternative financing would have to be secured for a majority of the construction costs before the secretary of interior could recommend the project.

State officials made it clear that the project is ineligible for funding through a recently approved bond proposition.

The federal government typically funds construction of major reservoirs that Congress authorizes and is then repaid from the project’s beneficiaries over the course of several decades.

California voters last year approved $2.7 billion for additional water storage as part of a bond proposition.

Nancy Vogel, deputy secretary for communications at the California Natural Resources Agency, said the project is not eligible for funding from Proposition 1, as funding cannot go to any project that would negatively affect a river protected under the state’s Wild and Scenic Rivers Act.

Raising the dam would inundate portions of the protected McCloud River.

California is in the midst of a four-year drought that has forced tough decisions for many cities and farmers. Gov. Jerry Brown has ordered communities throughout the state to collectively reduce water use by 25 percent.

To prepare for future droughts, some federal and state lawmakers have said securing more water storage through new or expanded reservoirs is critical. They have grown frustrated with how long it has taken for the Bureau of Reclamation to complete feasibility studies on a handful of projects.

Congress first authorized the Shasta study in 1980.

Shasta Lake, the state’s largest reservoir, is located on the upper stretches of the Sacramento River about 160 miles north of Sacramento.

Federal officials looked at an array of options for the dam, from raising the 602-foot concrete structure by 6.5 feet to raising it by 12.5 feet, then to 18.5 feet.

The most beneficial alternative calls for an 18.5-foot increase, adding spawning gravel to the upper Sacramento River and restoring habitat along the river.

The higher lake level would require the relocation of utilities and bridges as well as the modification or total replacement of several marinas, boat ramps and trails.

Expanding the dam by higher than 18.5 feet would require much more extensive and costly relocations, including for Interstate 5, the report said.

The study said the most economically beneficial option would increase the amount of water stored in the reservoir enough to cover 634,000 acres with a foot of water. About a third of that additional water would be used to benefit fish populations.

Members of Congress have been calling for more water storage projects in the state, but their immediate response to the study has been cautious.

“Ensuring that local residents, businesses and infrastructure are given proper consideration is key,” said Rep. Doug LaMalfa, R-Richvale, whose district includes Shasta Lake and surrounding communities. “Should this project move forward, I will work to ensure that those residents and businesses that could be affected are justly compensated and have an opportunity to relocate on the lake.”

Doug Obegi, an attorney with the Natural Resources Defense Council, said raising the dam would destroy sacred tribal sites and provide “virtually no environmental benefits.”