storms

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Storms and Rising Seas Present New Threats to Unstable SoCal Peninsula

The geologic features of the Palos Verdes Peninsula make it a hotspot for landslides

Bureau of Engineering / City of Los Angeles

November's sea cliff failure took out 600+ feet of roadway and sidewalks.

The latest Palos Verdes Peninsula slide may calve, and the main slide mass is likely to keep “moving oceanward.” That’s according to a preliminary draft of a geotechnical study commissioned by the City of Los Angeles in early winter, but that’s the extent of the news for now. The same report says based on the studies completed to date, the risk of landslide movement behind last November’s slide — landward into a nature preserve and beyond a new chain link fence — is low.

That’s just the latest from an area southwest of downtown L.A. that has been generating geological news for decades. According to a landslides map by the California Geological Survey, the PV Peninsula boasts 175 slides, 49 of them active.

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Planning for the Other “Big One”

Imagine 45 days of rain brought by a series of winter storms so strong and wet that they turned the Sacramento Valley into an inland sea, making the state capital virtually inaccessible. 

Well, that happened in California in the winter of 1861-1862, and scientists say it will happen again, bringing massive flooding, landslides and property damage across the state.

To help emergency agencies plan for such an event, the US Geological Survey released the “ARkStorm Scenario” in Sacramento this week, detailing the repercussions of a storm that produces up to ten feet of rain and forces the evacuations of more than a million people.

“Vast floods would basically take out all the farm land,” said Marcia McNutt, director of the USGS. “They would destroy homes, animals would die, roads would be impassable, infrastructure would be rendered unusable, dikes would fail, levees, would fail.”

Scientists created this hypothetical storm by combining two actual storms, one from 1969 and one from 1986, and putting them back to back.  Together, they rival the 1860′s storm in magnitude, which was the last time California saw a storm this size.
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California Storms: A Dent in the Drought

Spillway at Alpine Lake on Mt. Tamalpais. File photo: Marin Municipal Water District

Spillway at Alpine Lake on Mt. Tamalpais. File photo: Marin Municipal Water District

A version of this post also appears on Dan Brekke’s personal blog, Infospigot. Also see our updated map of reservoir conditions at the end of this post.

By Dan Brekke

Is California’s drought over? OK, let’s take a step back. Yes, I realize one could debate whether the last three years in California actually constitute a drought. But that’s a discussion for another time. For now, I think everyone can agree that we’ve had lower-than-average precipitation for the past three years.

The only reason to ask the question is that, after the first half of the wet season delivered only spotty rain, we’ve had a pretty solid week of downpours. Water is sluicing into our reservoirs, and the hills are greening up. Some counties, like Marin, have water tumbling down the spillways. All of that is a sign of what we think winter should be here.

My favorite water statistic from last week: when the storms were at their heaviest around Lake Shasta, California’s biggest reservoir, water was flowing into the lake at about 500,000 gallons per second. That’s 1.5 acre feet, or about enough for two-to-three “average” households for a year, every second.*

Amazing numbers like that aside, the people who get paid to think about whether the drought is over say “not yet.” Last week, Quest managing editor Paul Rogers wrote a good summary of the situation, for The San Jose Mercury News.

Rogers’ story does contain one bit of quirky California thinking about rain and water, though. He quotes a well established local meteorologist, Jan Null, about where we stand in terms of normal rainfall, saying: “This is a great start, but we need to keep it going.”

Of course, Null recognizes better than most that the amount of rain we get and when we get it is out of anyone’s control. But once you understand the importance of water in California, once you get how crucial the winter rains are, there’s a score-keeping aspect to weather-watching here. It becomes second nature to study the rain gauge and the seasonal precipitation table as an index of performance, a reflection on whether a great collective goal is being attained. Lots of rain means we’re doing well (and that we can put the complexities of water supply out of our minds). A dry spell means we’re failing (and the prospect of hell to pay, or at least the strong possibility of stringent conservation measures).

But in reality, there’s no performance going on. The rain is the rain, and the climate is the climate. California’s rainfall is famously variable. Dry spells can be counted on and the current run of dry years is the third we’ve had since I arrived in Berkeley in the 1970s.

My first California winter, 1976-’77, was bone-dry and was in fact the second year of the driest two-year period ever recorded here. A decade later, from roughly 1986 through 1992, we had another run of dry years. And if our winter rains were to stop now, we’d be in the fourth year of drier-than-normal years. In between these periods we’ve had average years and very wet years and years that didn’t quite hit the average. That might not be too different from anywhere else. The reason it’s a bigger deal here than it might be in, say, Wisconsin, is that we have a six-month dry season. We need to store water to get through that. We have 37 million people and millions and millions acres of farmland that need water, whether it’s falling from the sky or not. Thus the need to believe we can wish the rain to keep going during the wet season and the tendency to feel disappointment when the winter turns into a string of dry, sunny days.

*500,000 gallons per second. Here’s the arithmetic: California Department of Water Resources figures show that in the hour between noon and 1 p.m. on Tuesday, January 19, net inflow into the lake was 66,288 cubic feet per second. That’s the highest inflow figure for any single hour that week. One cubic foot equals 7.48 gallons. 66,288*7.48 = 495,834.24 gallons. One acre-foot = 325,851 gallons. And 495,834.24/325,851 = 1.52 acre-feet. Per second. For the entire 24 hours of the 19th, Lake Shasta’s inflow averaged just over 1 acre-foot a second.


View KQED: California Reservoir Watch in a larger map