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The Plant & Facilities Engineering Blog is the place for conversation and discussion about mechanical and electrical systems, automation and instrumentation, maintenance and management, and products & services as they relate to plant and facilities operation. Here, you'll find everything from application ideas, to news and industry trends, to hot topics and cutting edge innovations.

Will It or Won't It? The Oroville Dam's Potential Collapse

Posted February 16, 2017 10:25 AM by HUSH
Pathfinder Tags: dam infrastructure Oroville weather

It isn’t too hard to argue that here in the United States we take our infrastructure for granted. Next month, the American Society of Civil Engineers will release its 2017 report card on the state of American infrastructure. ASCE updates the report card every four years. In 2013, the cumulative GPA for the U.S. was a D+, up from a D in 2009. No one is expecting the U.S. to make Honor Roll this year.

One of the lowlights from 2013 was the country’s grades on dams, also a D. It noted that the average age of the 84,000 dams in the U.S. was 52 years old. The number of high-hazard dams—those whose failure may cause loss of life—has steadily risen over the years, all the way up to 14,000. The reasons for this are twofold. Dam construction techniques have improved and old dams just don’t stack up to new evaluations. Also, more people have moved into the low-lying areas that are shielded by dam walls, some of which were built to poorer standards as formerly the area was undeveloped and less important.

Today, one of the most pressing U.S. infrastructure challenges in recent memory continues and the threat of a partial dam collapse persists even as workers attempt to reinforce the dam at this very moment.

After days of rain, on February 7 Oroville Dam officials opened the dam’s spillway so excess water could begin to drain from Lake Oroville, which is at its highest February water level in more than 30 years. The spillway routes water past the dam’s hydroelectric plant as well as bypass valves that had been broken since 2009.

Despite the flushing being well within the spillway’s design limits, operators noticed a hole developing in the spillway. With the lake’s water level rising up to 20 feet per day the spillway had to continue to be used, and gradually the hole grew into a crater. Eventually the debris carried from the 500 ft. x 300 ft. by 50 ft. crater fell into the river below, blocking the outlet of the hydroelectric plant.

State engineers determined that they would need to use the dam’s last resort, its emergency spillway. While it’s not made of concrete like the main spillway, the emergency spillway is a nearby embankment that sits 20 ft. lower than the lip of the dam. On February 11, water crested the edge of the auxiliary spillway. Slowly but surely the water eroded this hillside too, and finally on February 12 an evacuation order was given to 188,000 residents of the Feather River valley. Engineers became less confident in the spillway’s ability to hold as snowpack that is 50% above normal combined with excessive rain. With more rain in the forecast for this week, there is no shortage of wet stuff.

It’s arguable that this disaster-in-the-making could have been prevented. It is well-known that California is in the midst of an epic seesaw drought. Perhaps that is why in 2005, state and federal officials decided not to reinforce the emergency spillway, despite requests from environmental groups including the Sierra Club. What’s notable is that the auxiliary spillway began to erode with water flows of 12,600 ft.³/s, a volume much lower than its specified capacity of 350,000 ft.³/s.

Water flow has finally receded to the point where crews are airlifting and excavating boulders and sandbags into place in the gulley of the auxiliary spillway.

As of Valentine’s Day evening, locals were allowed to return home but were prompted to remain ready for another potential evacuation. The situation at Lake Oroville is tenuous, but appears to be in control for now. The same cannot be said for thousands of other risky dams around the country.

17 comments; last comment on 02/21/2017
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3D Scanning Speeds Assembly Line Changeovers

Posted February 04, 2017 12:00 AM by Engineering360 eNewsletter

A novel application of 3D scanner technology could help to speed retooling of automotive assembly lines. Researchers at Würzburg University are collaborating with a team at Volkswagen AG to streamline changeovers from one model to another.

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Rising Use of Solar Trackers in Grid-Scale PV

Posted January 18, 2017 12:00 AM by Engineering360 eNewsletter

According to a recent report from GTM Research, 12.6 GW of PV trackers will be installed globally this year, up from 5 GW in 2015. As the use of grid-scale photovoltaic (PV) systems continues to grow, a new solar tracking technology can improve production at PV farms by anywhere from 15-30% when compared to a fixed-tilt system.

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2 comments; last comment on 01/19/2017
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Engineer's Guide to Corrosion: Part 3

Posted November 25, 2016 12:00 AM by Engineering360 eNewsletter

Read all three parts of our series on corrosion basics for engineers. Part 1 outlined the basic corrosion mechanism in acid. Part 2 emphasized that most materials in modern steam generators are steel-based. And Part 3 examines corrosion issues, including a discussion of control methods. One approach to inhibit corrosion in carbon steel condensate/feedwater systems is the use of amine, an organic compound derived from ammonia. Ammonia can provide enough alkalinity to also protect the steam generator proper, as long as impurity intrusion is prevented.

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1 comments; last comment on 11/29/2016
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Virtual and Augmented Reality Target the Manufacturing Floor

Posted November 04, 2016 12:00 AM by Engineering360 eNewsletter

Manufacturers are beginning to kick the tires as virtual reality (VR) and augmented reality (AR) become more viable in production environments. The technologies show early promise in reducing error rates and improving productivity. The primary use case, particularly for AR, is remote collaboration or assistance, because it allows users in different locations to see the same thing at the same time. Acting as a "visual wizard," AR and VR can be particularly useful in guiding machine operators or maintenance personnel on actions for which they may not be fully trained or fully understand. However, a steep climb to broader adoption remains.

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