Even while the recent heatwave is over and warming temperatures are ahead, the central Sierra snowpack remains at nearly 300% of normal, with much of the Truckee River watershed at 200%. The heatwave brought regional-wide record temperatures which accelerated melting of the snowpack, raising the river and enacting a flood watch. This also had officials warning the public to avoid swimming in the river as it is running cold and fast.
With more snowpack melting soon, we wanted to take a chance to see what rising water across the Truckee River looks like, and see what those images can tell us about the river’s health, ecology and development.
“Having a full reservoir is not a guarantee that you’re going to have a full reservoir in August when you’re talking about drawing it down,” explained Dr. Hausner, associate professor at the Desert Research Institute. He has spent over a decade studying the intersection of ecology and hydrology. His work is focused on studying the impacts of climate change on river ecosystems.
“A big year of snowfall, even if we get a slow melt and a lot of water moving downward through that soil, [it] isn’t going to counter decades of drought on a groundwater resource,” explained Hausner. The region needs several more winters similar to this year to fully recharge the groundwater and move the drought needle into the green.
“We don’t have a really good handle on what’s going to happen to precipitation with climate change,” said Hausner. “We know that temperatures in the [Great] Basin are going to get warmer.” Among many different climate models, there is an agreed upon consensus that scientists use to understand what is going to happen to project the future climate. For Hausner, one thing is sure: “precipitation is all over the map.”
This variability impacts the Truckee River ecosystem. Some models have increasing precipitation while others show a decline, or stasis. “So that makes it really difficult to plan for future water resources,” Hausner said.
In March the region had a series of warmer atmospheric storms, leading to what climatologists call rain-on-snow events. Rain melts snow, essentially causing officials to release water from reservoirs and issue flood watches and warnings. In periods of long-term drought, these climate change driver storms make water management quite challenging.
“The other issue that the climate change brings with the Tahoe Basin is we’re not entirely sure what precipitation is going to do from a quantity perspective,” explained Hausner. Scientists do know that the interaction of increasing global temperatures and precipitation is going to lead to a transition from snow to rain. This ultimately means less water for the region.
On top of a reduced snowpack, Hausner said there will most likely be an earlier spring melt off in the future. Many mechanisms behind snowmelt are at play and will feed off one another as the atmosphere warms.
“The clouds disappear and that solar radiation is really what drives the snow melt,” explained Hausner. He added that the bluebird days that we all enjoy are problematic during the winter. “Those are the days that are really responsible for melting off a lot of the snowpack.”
”It’s not the size of the snowpack that is going to be that determining factor for the river and the river ecosystem, but the way that snowpack melts,” explained Hausner. Aside from the first heatwave we had at the end of April, the snowpack has been able to maintain a slow and steady melt, so far.
As the water level rises, the bottom of the riverbed, known as the hyporheic zone, gets more nutrients in the form of oxygenated water from snow melt.
“When you have high flows in the river, you have oxygenated water that’s being pushed into that hyporheic zone,” said Hausner. “It stimulates geochemical cycling, it stimulates the growth of particular algae and bacteria that process some of the contaminants in the water.” He added that high water events, like what we saw recently, have both ecological benefits and drawbacks.
Steamboat ditch is a well-known entity in the Truckee Meadows. This diversion dam allows for a flow of around 50 cubic-feet-per second (cfs). For comparison, the river is currently flowing around 2,400 cfs in Reno.
“[The Truckee River] is a snowmelt-dominated basin, which we take for granted in this area, but that’s relatively rare across the global hydrology,” said Hausner. The watershed is predominantly fed by snow, making future lower snow levels a potential risk to the ecosystem.
Rivers tend to migrate as they meander through a floodplain and during natural high water events, water spills over the riverbank and could potentially erode the floodplain, creating a new course for the river. A braided river is the perfect example of this in action. This process effectively eliminates erosion by slowing the water down and allowing sediment to precipitate out of the water.
“What that does is it concentrates the energy of the water and so rather than having this floodplain to dissipate the energy, this ability to meander, and to cut away parts of the bank, and to deposit parts of the bank and to just move, it has to stay into the same channel,” explained Hausner. This increases the slope of the river and in turn makes the water run faster. Without engineered stabilization, it will erode the river banks through incision.
“It’s no longer connected to that floodplain,” said Hausner. “If you get a big flow through there, it doesn’t then rise up out of its banks and dissipate its energy. It just cuts down even further.”
The health of the river is really dependent on the entire community. It’s where we get our water, both for drinking and irrigation. And water decisions made now can have long-lasting effects.
Credit Richard Bednarski.
Derby dam was solely responsible for draining Winnemucca Lake, a marshland-lake oasis for not just migratory birds, but the Numu, or Northern Paiute people. The lake slowly receded due to restricted flow to Pyramid Lake, Truckee River’s terminus, and was officially cut off when a dam and road were built between the two lakes.
The dam also threatened the health of Kooyooe Pa’a Panunadu, or Pyramid Lake. Within 60 years of water diversion, the lake dropped nearly 90 feet in elevation, placing both the endemic Cui-ui, a species of sucker fish, and Lahontan Cutthroat trout in peril.
After decades of tension and debate, a modern-day water-rights deal was reached amongst the many stakeholders. Originally signed in 2008 and slowed by litigation, the deal will send almost 3,000 acre-feet of water to the Pyramid Lake Paiute Tribe. This will not only benefit the Numu, but the endemic fish, the Cui-ui and Lahontan cutthroat trout.
Stepping out of his scientist shoes, Hausner believes it is not just important to take care of the river for utilitarian reasons, but for ecological ones as well.
“It’s important to not screw up the place where you live, it’s important to sustain wildlife and to live in a way that you can’t avoid your impact on nature,” he explained.
“We can do things as responsibly as we can, but it’s [a] really important thing to keep in mind and it’s worth investing time and effort and money in doing that sustainably.”
