An 800-acre reservoir could be coming to Stanislaus County, but what are the risks?

A federal bill promising $14 million in funding for water storage projects for the Central Valley and Northern California served to place more attention on a proposed reservoir in Stanislaus County.

Rep. Josh Harder, D-Turlock, got the millions included in a massive energy and water infrastructure bill in the House of Representatives. It includes $6 million for the Sites Reservoir near Colusa favored by agribusiness, $4.1 million for the North Valley Regional Recycled Water Program, $2.1 million for the Los Vaqueros Reservoir expansion in Contra Costa County, and $1.5 million for Del Puerto Canyon Reservoir near Patterson.

“The Central Valley has been left behind by funding bills for too long,” said Harder, who discussed the details at Wednesday’s county Water Advisory Committee meeting and acknowledged that the money is a drop in the bucket compared with the billions needed to build the storage projects.

The so-called “Canyon Reservoir” would create an 800-acre lake in scenic Del Puerto Canyon, nestled in the foothills west of Patterson. It could materialize under an aggressive schedule to start construction on the 200-foot-high earthen fill dam in late 2020.

Del Puerto Water District and Central California Irrigation District have developed the reservoir project without many public concerns rising to the surface. That was until Patterson city staff members showed up for Wednesday’s meeting.

Maria Encinas, a city management analyst, asked about a risk assessment for adjacent communities like Patterson. A failure in the dam on Del Puerto Creek, on the west side of Interstate 5, would appear to flood part of the city of 23,700, including perhaps the downtown area in Patterson.

Chris White, executive director of the San Joaquin River Exchange Contractors Water Authority, promised a study of seismic issues and risks before the dam is built. According to a handout on the reservoir project, a fatal flaws feasibility study was completed without finding major issues.

According to the handout, from $2 million to $3 million is needed for environmental studies and a federal feasibility report.

The districts want to use the reservoir to store up to 85,000 acre-feet of water for thirsty farms and for better water management in the San Joaquin-Sacramento Delta. The reservoir would be fairly small compared with a major facility like New Melones, which has a 2.4 million-acre-foot capacity.

Farmers in Del Puerto Water District often are shorted on their federal allocations from the Central Valley Project because of disruptions in pumping water south from the delta. Water pumped from the nearby Delta-Mendota Canal would be held in the canyon reservoir to provide reliable deliveries to West Side farmers in dry years.

White said the districts may take in other partners for the $420 million project and expect to seek funding through the Water Infrastructure for Improvements to the Nation (WIIN) Act of 2016. It pays for conservation and water resources development.

The reservoir would disrupt the scenery for people who drive into Del Puerto Canyon for recreation or sightseeing. Often going from full to empty, the reservoir would offer limited recreation activities, White said

Sal Salerno, president of the Stanislaus Audubon Society, said the different habitat alongside Del Puerto Creek up to Frank Raines Park is excellent for bird-watching. He said the group would need to study the project proposal before taking any position.

The proposed reservoir, extending west of I-5 some 2 1/2 miles into the canyon, could cover ranch land, inundate creekside habitat and put Del Puerto Canyon Road under water for much of the time. Landowners in the area have been contacted by the water districts, White said.

Millions of dollars would be spent relocating Del Puerto Canyon Road and a gas transmission line, officials said.

County Public Works Director David Leamon said the water districts two months ago showed county staff possible routes for the new Del Puerto Canyon Road. One would branch off from Diablo Grande Parkway near the golf resort and climb over the hill to link with Del Puerto Canyon Road west of the reservoir.

Another alternative is realigning the canyon road so it hugs the south shore of the reservoir. “It will cost the districts several million dollars for buying the right of way and construction,” Leamon said.

He said Diablo Grande residents may have something to say about increased traffic near their community. Public discussion needs to take place before the best route for the new road is chosen, he said.

County Supervisor Terry Withrow said the county would cooperate with the process of relocating the road.

White said plans for the canyon reservoir have been in the works for years but were stymied by the lower value of water in previous times. The high market price for water today makes it viable to operate and maintain a private reservoir of this size, White said.

Ken Carlson covers county government and health care for The Modesto Bee. His coverage of public health, medicine, consumer health issues and the business of health care has appeared in The Bee for 15 years.