Oroville 2017

About ten months ago, I was worrying about the Mosul Dam across the Tigris River in far off Iraq. It was constructed on Saddam Hussein's watch but also on a really dodgy foundation. At the moment 10 billion tonnes of water are behind the dam and at least 1 million people are downstream hoping everything will be okay.

Right now in Northern California, they've been having a lot of rain after several years of drought [Lake Oroville just 3 years ago] - dang that climate change! The Oroville Dam is the US's tallest and is made of concrete-faced rubble. The lake behind is full to brimming and so water was let off down a concrete spillway. That GUSH of water - 35,000 cu.ft/sec = 1,000 tonnes/sec has eaten a huge hole in the spillway and the water has topped out the emergency spillway next door. The emergency spillway is just a concrete lip - never used in the 50 years since the dam was topped out 50 years ago - at the top of a rock-and-dirt hillside falling 230m to the Feather River below.  If the water flow undercuts the emergency spillway lip then water will start to lower the hill top possibly catastrophically: a 10m lowering of the lake is conceivable and the lake is 6,000 hectares in extent; that's a lot of acre-feet of water.  Water is coming into the reservoir at an estimated rate of 5,000 tonnes/sec. Weather is forecasting several more storms coming in this week.

160,000 folks downstream of the dam also know that the dam itself consists of an eminently erodable soft centre and they've been ordered to evacuate to higher ground to the north. RTE is still headlining with Maurice McCabe but does cover Oroville on Page 5. I've clipped a pic from RTE to show the was-concrete spillway and the emergency spillway to the left. The dam itself is massively off-camera to the right. Millions of salmon fry in the spawning gravels downstream - they're screwed (sorry). You can pick up enough links to satisfy your further curiosity at Metafilter.
Let's us hope that we don't have a Vajont 1963 , or even an Eigiau 1925 over there.