What this week’s storms mean for California’s flood control system
While a nearly record-breaking rainy season has battered California’s dams and stretched the limits of local levees, the storms that began to hit Sacramento on Tuesday aren’t expected to put much additional strain on the state’s flood-control system.
Spanning into next week, the storms are expected to drop as much as two inches of rain in Sacramento and two feet of snow in the higher elevations of the Sierra Nevada. But federal weather forecasters said Tuesday they aren’t too worried about widespread problems.
“These series of storms are definitely wet, but they’re not what we saw in January and February, by any means,” said Michelle Mead with the National Weather Service in Sacramento. “They’re more typical of our winter-into-spring storms, meaning we’re getting into that shower and thunderstorm season.”
Those sorts of storms could bring thunderstorms and squalls that can overwhelm local storm drains or roadside ditches for a short time. That was the case Tuesday morning when heavy showers flooded roads across Sacramento, but Mead said the risk of more widespread flooding from a dam breach or levee failure remain minimal.
The reason? After three weeks of mostly dry weather, soils saturated from January’s and February’s soakings have had a chance to dry out. The break in the weather also has given the operators of north state flood-control reservoirs – including the lake behind the badly damaged Oroville Dam – plenty of time to release water so there’s ample room to capture any unexpectedly strong deluges, Mead said.
While this week’s storms aren’t expected to be particularly noteworthy, they come at the tail end of a winter that’s on pace to break precipitation records after California’s five-year drought.
Even after several dry weeks in late February and early March, much of California continues to flirt with record amounts of precipitation for the water year, which runs from October through September.
About 28 inches of rain has fallen in Sacramento since October 1, roughly two inches below total rainfall at the same point in 1983, the wettest water year on record, according to federal data.
This water year’s rainfall totals at Sacramento Executive Airport stood at 181 percent of normal as of early Tuesday morning.
Sierra snowpack levels were at 158 percent of normal on Tuesday – a huge snow year but well below levels seen at this point in 1983, when the snowpack was more than 200 percent of normal. April 1 is typically considered the peak of Sierra snow season.
Thanks to some warmer storms that at times this year brought more rain than snow to the lower Sierra, the Eastern California mountain range remains on pace to break the total precipitation record set in 1983, according to state data.
All that snow in the Sierra is going to extend flood risks into June, particularly in the San Joaquin Valley, where levees below nearly full flood-control reservoirs can get easily overwhelmed by sudden gushes of snowmelt, said Alan Haynes, a hydrologist with the federal California Nevada River Forecast Center.
But barring some unexpected crisis, the seven- to 10-day forecast has Jay Lund, the director of the Center for Watershed Sciences at UC Davis, optimistic the state’s badly battered flood infrastructure will limp into the long dry season without a catastrophe.
“That pretty much gets to the end of the wet season,” he said.
Ryan Sabalow: 916-321-1264, @ryansabalow
This story was originally published March 21, 2017 at 12:50 PM with the headline "What this week’s storms mean for California’s flood control system."