I was writing about Oroville Dam and the frightening few days that engulfed [metaphorically!] 200,000 downstream residents when it looked like an emergency spillway might collapse catastrophically. They were compelled to vacate their homes at short notice and spent hours in slow moving convoys heading for higher ground. That apocalyptic situation has been dialled back a notch, because there wasn't as much rain last week as had been forecast and because they had one remaining way to take the pressure off by lowering the reservoir.
It made a lot of people think about how the natural world is prone to floods, avalanches, mudslides, tsunamis, earthquakes and volcanoes and how these can be mind-bogglingly capricious and destructive. In some cases you can do something prophylactic about the danger: early radio warnings that outstrip the tsunami; baffles to dissipate a wall of sliding snow; dams to tame a river. But once you start your interference in the laws of nature, you have to shoulder a lifetime commitment to maintenance. There is now a US-wide process for dismantling hundreds of obsolete dams before they fail [prev, prevlier] but it's costing ready money to achieve; contrariwise, it would cost a lot more in money, lives and anguish to do nothing. If the emergency spillway at Oroville fails it will release a wall of water 10m high which will be like Vajont 1963 all over again. But if Oroville Dam itself failed the water-wall would reach San Francisco: Oroville is just a pile of dirt between two cliffs but it's the highest such, water on one side & air on the other, pile in the USA. Here's a model piled up by the US geological Survey and then trickle-breached. With no Little Hans Brinker to put his arms in the dyke, the whole structure is <spoiler alert> eroded to buggery in short order.
Dwight D. Eisenhower National System of Interstate and Defense Highways was authorised by the Federal Aid Highways Act of 1956 and more or less completed by 1990 a generation later. Look at the project name: it was born at the height of the Cold War on the realisation that the US could not efficiently ship its armed forces from one side of the country to the other to counteract the threat of a a foreign belligerent. It also benefitted the car and gasoline lobby, ensured the demise of the rail network and raised private motor vehicles to the status of chariots of the gods. Not only tanks and armoured personnel carriers use this road network. You can start off down the Massachusetts Turnpike I-90 in Boston and carry on and on and on driving to Seattle, WA 4,861 km further West. The network is truly amazing but the roads are built in, on and across the landscape. They must go up hill and down dale and cross hundreds of rills, streams, becks and rivers. Crossing rivers requires bridges and thousands upon thousands of bridges were built to service the Interstates, not to mention the bridges that have peppered the countryside since the days of horse&buggy.
According to a new graphic produced by WaPo there are 130,000 bridges in the USA which are structurally deficient or functionally obsolete. Let's look at Yuba County which includes the Oroville Dam complex. If there is another compulsory evacuation there are going to be a lot of cars travelling along the same crucial escape routes; you don't want any bridge to collapse under the unwonted weight. But only 68 of the 124 bridges in Yuba County are, according to the Federal register, classified 'good'. In 1983 a bridge on I-95 in Connecticut collapsed at midnight into the Mianus River followed by two semi-trailers and two automobiles. The post-mortem revealed that water seepage had rusted the steel pins that held up the section of the bridge and the weight of two trucks at once had broken the camel's back. There is a lot of steel embedded as rebar in concrete bridges all over the Interstate System; it is now invisble; it is in contact with water leaching through the concrete and it expands as it oxidises; it is a recipe for disaster. President Trump has promised €1,000,000,000,000 to upgrade, update and make safe the US Federal Highway System. Let's hope some of his cronies have stock in civil engineering, steel, cement, tar and/or gravel companies. It is a peculiarity of the US political mindset that Federal tax dollars can buy space-shuttles, tanks, levees and bridges but cannot provide medical treatment to the poor.