Nevada Irrigation District, which serves two California counties, wants to build a new reservoir on the Bear River to capture rainfall, amid concerns that climate change is shrinking Sierra Nevada snowpack.

Americans have had one primary reason for building dams over the past century: capturing water for growth, whether on farms or in cities.

Now a new dam proposed on California’s Bear River offers another reason: adapting to climate change.

The Centennial Dam project, proposed by the Nevada Irrigation District, is intended to capture rainfall at lower elevations to make up for declining snowpack at higher elevations. It would be built at an elevation of about 2,000 feet between two existing reservoirs on the Bear River – Rollins and Combie – in a region of the Sierra Nevada where winter rainfall can be prolific but snowfall is light.

The district suffered in 2015, along with the rest of California, when winter snowpack nearly vanished completely. On April 1 of that year, at the end of winter, the state Department of Water Resources measured the Sierra snowpack at just 5 percent of average, the lowest ever recorded.

The Nevada Irrigation District that year was forced to buy water from Pacific Gas & Electric Co. out of Rollins Reservoir to serve its customers. That emergency supply – 16,000 acre-feet (19.7 million cubic meters) – cost $1 million and might not be available next time.

The district doesn’t want to have to go begging like that again, said Nick Wilcox, a member of the district’s board of directors.

“We are being seriously impacted now by climate change, and will be more so in the future,” Wilcox said. “This is an attempt to create more mid-elevation storage to capture winter rains for use later in time. We need to control our own destiny.”

Climate change scenarios anticipate, as temperatures rise, more Sierra precipitation will fall as rain rather than snow. That means the mountain snowpack that California has relied upon historically to survive its hot summers may no longer be sufficient.

The Centennial proposal would store 110,000 acre-feet (135.7 million cubic meters) of water by building a dam 275 feet (84m) tall across the Bear River, near the town of Meadow Vista.

That would make it larger than any of the district’s existing 10 reservoirs, and it would be one of the largest dams built in California in some time. For example, Los Vaqueros Reservoir, built by Contra Costa Water District, was 100,000 acre-feet (123.3 million cubic meters) when first constructed in 1998 (and expanded to 160,000 acre-feet).

The district hopes to release a draft environmental impact report on the project in 2017 and start construction for the district’s 100th anniversary in 2021 – hence the “centennial” name.

Although it is hardly the first dam on the Bear River, the project has prompted a number of concerns among local residents and river advocates, including:

Less streamflow for imperiled fish downstream.

It would silence a 6-mile stretch of flowing water that residents enjoy, drowning the popular Bear River Campground operated by Placer County, as well as 25 homes.

It will require a new bridge across the Bear River that could bring more traffic through Meadow Vista.

It would flood dozens of American Indian cultural sites along the river.

“It’s a 19th-century solution to a 21st-century problem,” said Traci Sheehan, coordinator of the Foothill Water Network, a coalition of local groups formed to oppose the dam. “Especially during a time of climate change, you need to be really thoughtful. We believe there are more cost-effective and less environmentally destructive alternatives.”

One of those is meadow restoration, Sheehan said. Sierra meadows have been degraded by more than a century of logging and livestock grazing, reducing their ability to store precipitation.

A number of agencies are working to restore meadows as a water supply solution. The Nevada Irrigation District could do the same thing, Sheehan said, on the 70,000 acres (28,328 hectares) of mountain watershed that help fill its water system today.

Another is conservation. Only 10 percent of the district’s customers are residential or business customers who consume treated water.

The rest are agricultural customers who receive untreated or “raw” water. This water is delivered in a 475-mile (764km) ditch system. Much of this dates to the Gold Rush and a lot of it is unlined, resulting in losses of 10 percent or more due to seepage.

The district has a program to line or pipe its ditches “when feasible,” said general manager Rem Scherzinger. In practice, this means about 2 miles (3.2km) per year, according to a recent report.

“As any responsible agency should, we must explore and utilize all of our resources,” Scherzinger said. “These range from conservation and watershed management to leak loss prevention and the construction of storage facilities to try to protect our community. Centennial is one facet in a holistic approach to survive the coming reality of climate change.”

The district’s treated water customers were required by the state to achieve 33 percent conservation last year because of the drought. They managed 30 percent.

Its raw water customers, however, had no conservation requirement because the state exempted agricultural water users. Although many of the district’s raw water customers are small farmers and ranchers, many are large residential property owners who use the water for other purposes, including landscaping and ponds.

“While we want to make sure farmers get every ounce of water they need for their crops, we believe a lot of agricultural water is going to water the lawns of McMansions,” said Caleb Dardick, executive director of the South Yuba River Citizens League, a small but influential environmental group working to restore river flows for fish and recreation.

An unusual feature of the Nevada Irrigation District system is that it diverts substantial amounts of water from the Yuba River, through a tunnel, into the Bear River, to serve a significant share of its customers in both Nevada and Placer counties.

Dardick worries that if the district doesn’t get the water it needs from the Bear River to fill Centennial Reservoir, it will divert more water from the Yuba River to fill it.

Wilcox said the opposite will actually be true. Building Centennial Reservoir, he said, will allow the district to divert less water from the Yuba to serve its customers in Placer County, who could then be served by Bear River water stored in Centennial Reservoir instead.

As a result, he said, the new reservoir could actually take pressure off the Yuba River.

The project is likely to cost close to $500 million, Wilcox said, which includes the new bridge as well as a possible new hydroelectric unit at Rollins Reservoir, for which the district already has a federal permit. The district would use revenues from electricity sales to help offset construction costs. No rate increases will be needed to pay for the project, he said.

“It is not enough to say, ‘Well, dams are outdated; we hate dams,’” Wilcox said. “Dams are inherently destructive. I grant you that. But they really do provide some water-supply reliability. And our whole society is heavily dependent on infrastructure like that.”

A critical issue for the project is water rights. Nevada Irrigation District actually conceived Centennial Dam in 1927, when it was known as Parker Dam. Wilcox says the State Water Resources Control Board has held water rights for the project “in trust” ever since. But the district does not hold title to the water, which must be granted by the state through a separate hearing process.

A lot has changed since 1927 in California’s understanding of water availability. Estimates from that time of nature’s ability to provide water are now recognized as optimistic. It is also understood that the state has already allocated much more water rights than there is actual water to divert. So it remains to be seen if 110,000 acre-feet of Bear River water is truly still available for a new reservoir.

Shelly Covert, spokeswoman for the Nisenan Tribe’s Nevada City Rancheria, wants the water district to explore every possible alternative before moving ahead with the reservoir.

She said the project will drown cultural sites the tribe has used for millennia. This includes former village sites, places where cremation rituals were performed and where tribal members still go today to harvest natural resources and connect with flowing water.

Known as “momilaj” (mome-lay) in the Nisenan language, flowing water is important to some tribal cultural practices, said Covert, who is also a member of the tribal council.

“I can’t believe that in 2016, our few remaining resources that we still have access to are in danger of being lost again,” she said. “It’s a big deal to change a flowing, rushing river into a big puddle. Water is a living thing, a living being.”