Over the next month, federal officials will quadruple water releases from Friant Dam as part of the San Joaquin River restoration.

The biggest releases thus far in the program will tell scientists how the previously dried river channel reacts to a stronger flow of water, mimicking spring runoff.

Downstream farmers will be watching closely to see whether underground water tables near the river rise high enough to stunt or kill their crops.

Federal officials will monitor ground-water wells and stay in contact with landowners, said Jason Phillips, restoration program manager for the U.S. Bureau of Reclamation. Officials can slow the flow if needed.

"Nobody knows for sure what will happen," Phillips said.

For decades, sections of the San Joaquin have been dried up downstream of the dam, which was built in the 1940s for irrigation and flood control. Under a 2006 agreement among farmers, environmentalists and federal officials, the river and long-dead salmon runs will be revived over the next several years.

The first revival flow went for six weeks last fall and restarted in February after some maintenance work at Mendota Pool. The flow now will continue until Sept. 30.

Starting next week, water releases will slowly be increased until mid-April, then backed off slowly through May, similar to the timing of spring runoff. Scientists can collect information about the river -- such as water temperature, depth, speed and seepage to surrounding land.

Releases from the dam will peak at 1,445 cubic feet per second next month. That amounts to about 2,800 acre-feet of water daily. Each acre-foot contains a year's supply of water for an average San Joaquin Valley family.

The leading edge of the river now is in the East Side Bypass, northeast of Dos Palos and more than 100 miles downstream of the dam.

The river still must move more than 40 miles to reach the confluence of the Merced River. At that point, the channel would be refilled from the dam to the Sacramento-San Joaquin Delta. The connection is expected this spring.

Farmers along the river last fall were worried about their land, saying not enough ground-water monitoring wells were in place. But federal officials have expanded their network of wells and focused attention on potential trouble spots near Mendota Pool and farther downstream.

Steve Chedester, executive director of the San Joaquin River Exchange Contractors, representing area farm water districts, said growers have noticed improved communications with federal officials.

"We feel we've got a better handle on what's going on now," he said. "When they ramp up the flows next week, we'll be checking it."