UC Davis water researchers challenged by drought
No Rollin’ on the River
By Chris Bowman
Three straight years of extremely dry conditions can make a river scientist pretty thirsty for data.
Sarah Yarnell hasn’t had a drop in five months on her stream-monitoring project – in a rainforest, no less.
She’s leading a team of researchers with the UC Davis Center for Watershed Sciences that has been watching and waiting for sediment movement in a stream on the redwood-forested coast near Fort Bragg.
Around the start of rainy season last November the group dotted Caspar Creek with brightly painted stones so they could track the transport of free-rolling streambed material as stormwater flows washed it downstream.
The scientists came excruciatingly close to seeing some rock-and-roll action this week as the heavens deigned to unleash a few respectable storms.
But the runoff never arrived in force; the yellow, white and blue marker stones remain pretty much where they planted them.
“It was painful not to see the rocks roll,” said Yarnell, a hydrologist and whitewater rafter who typically begins her day surfing dreamflows.com – a Web site showing real-time flows on rivers in the West.
Last April, Yarnell won a $193,000 National Science Foundation grant to fund three years of streamflow research that could benefit river restoration efforts.
She and fellow rivers researcher Elowyn Yager at the University of Idaho are investigating how unsteady flows characteristic of rivers affect the movement and grain size of sediment – features important to the health of aquatic ecosystems.
Measurements in Caspar Creek and in laboratory experiments will be used to test and validate numerical models used to predict how variable flows influence sediment transport and the size of grains on a riverbed. Such knowledge would help water resource managers properly design improvements to fish habitat below dams, Yarnell said.
Yarnell and her UC Davis research team never imagined they would be this far into the field study with nothing to show for it.
It certainly looked like they would get lucky last Friday night (Mar. 28) when the first big storm in seven weeks finally broke. Buoyed by the forecast, Lucas Siegfried, a doctoral student in hydrology, grabbed his field gear with research assistant Andy Bell. They bolted to Caspar Creek, a 4½-hour drive from Davis.
When they arrived, about 8:30 p.m., the stream was still fairly low but rising fast in pouring rain.
The researchers strung a tarp between two redwoods at the very edge of the bank and settled underneath to keep watch. Their hopes rose with the creek, clocked at 0.5 inch – 1 inch an hour by their depth gage and flow meter.
They knew from previous data that the sediment would start moving at a stream depth of 0.8 feet. Come midnight and still raining, Bell waded into the creek and cocked his headlamp toward the base of the depth gage. He called it out to Siegfried. Zero point seven to point seven five. They weren’t about to call it night now. Time to fire up propane stove.
Like sentinels on graveyard shift, Siegfried and Bell kept alert by regularly checking creek levels between sips of hot chocolate and tea. Hours passed. Rain kept falling. But the Caspar didn’t budge an inch. By sunrise, they called it quits.
“It was pretty heartbreaking because the creek got right up to that threshold (for sediment movement) and just stayed there,” Bell said.
The ground was so dry that it soaked up a lot of the stormwater, Yarnell said. Not enough had drained into the creek.
Not every river researcher got skunked in this week’s storms.
Carson Jeffres' study site on the Cosumnes River south of Sacramento was awash with stormwater runoff, allowing him to net and identify fish.
"A week ago there wasn’t enough water in the river to put in the fish traps,” Jeffres, a fish biologist, said Wednesday. “Today, I caught a nice 4-pound small mouth bass.”
In the Cosumnes River watershed, so much rain fell in such a short time that the ground quickly reached its saturation point. As a result, most of the rainfall drained directly into the river.
In extremely dry conditions, the soil can turn “hydrophobic” – “afraid” of water – researchers said. The first rains don’t penetrate much. The water bounces on the ground and runs right off the surface.
The odds of Caspar Creek’s watershed reaching its infiltration point and producing sizeable runoff this season are diminishing by the day, Yarnell said.
“Unless we get one or two more spring rain events, we’ll have to wait until next winter.”
Chris Bowman is communications director with the Center for Watershed Sciences at UC Davis. He is hydrophilic.