Coatings Industry News

Main News Page

Report: Cracking, Spalling Led to Dam Damage

Thursday, April 27, 2017

Comment | More

The California Department of Water Resources has released three reports prepared by consultants in relation to damage incurred by the Oroville Dam spillways earlier this year, revealing that a full fix for the main spillway likely can’t be completed before November, the traditional start of the rainy season.

The three memos, prepared by the Board of Consultants retained by the DWR, were written over the course of the month of March, but were released all at once on Tuesday (April 25). In addition to advice about the coming repairs, they posit a theory that cracking and spalling caused by freezing and thawing were at the heart of what went wrong on the main spillway.

Damaged spillway
Images: Kelly M. Grow / California Department of Water Resources

Newly released reports prepared by the board of consultants retained by the California Department of Water Resources shed light on what likely caused the damage to Oroville Dam's main spillway.

The DWR notes that some reports on the dam cannot be made public because they contain “Critical Energy Infrastructure Information” that is protected as confidential by post-9/11 homeland-security regulations.

The reports recommend prioritizing an interim solution for the main spillway so that the structure is ready to handle the rains by November, but advise that a permanent fix will likely require more work in 2018.

Emergency Spillway Out of Order

The first memo, issued March 10nine days after the Board of Consultants was first convenedcalls for the emergency spillway, which was activated for the first time in February when damage to the main spillway created hazards, to be kept dry until improvements are made.

Emergency spillway
The dam's emergency spillway, which was not paved or covered in any way, was used for the first time in February, leading to erosion; officials are now looking at paving over the hillside with roller-compacted concrete.

The consultants say in the memo that they support a planned geologic investigation to determine what lies under portions of the spillway, and say that the use of compacted clay in some areas of the foundation of the chute slab “calls into question whether portions of the slab that appear undamaged by the failure should be replaced during the restoration.”

Replacement Recommendation, Root Cause

In the second memo, issued March 17, which includes some redacted sections, the consultants say that they favor a total replacement of the upper, damaged part of the spillway this year, prior to November. The lower section of the spillway likely can’t be finished in time for that deadline, but the board recommends laying a foundation that can be used as a temporary measure through the winter, until the work can be finished next year.

The reports indicate that the replacement slab will be constructed of roller-compacted concrete and, where possible, will be made thicker than the original, which in some places was less than a foot thick.

Spillway damage

The board of consultants says cracking and spalling from the freeze-thaw cycle may have led to the damage to the main spillway; cavitation, which had been the subject of speculation soon after the damage appeared, likely played little or no role, the group notes.

The second memo also contains conjecture as to the root cause of the failure of the concrete. The consultants note that damage occurred close to and downstream of a construction joint, and they conclude that the failure “likely occurred as a result of high velocity flow (in the range of 85 to 90 feet per second), penetrating under the slab, causing a strong uplift force and causing the slab to lift, eventually causing all or part of the slab to break away.”

After the initial failure, more foundation material eroded, causing further damage, the report says.

Cracks and spalls in the spillway slab were observed when the most recent repairs were done, in 2009, the report notes, and were likely a product of the freeze-thaw cycle. The spot where the water penetrated under the slab was likely a deep hole like this, the consultants say. They discount the idea that cavitation played a major role, a theory that was brought up by at least one engineer soon after the damage was uncovered.

Paving the Emergency Spillway

The last of the three memos, issued March 31, reiterates much of the advice in the first two, providing further information on seismic concerns and geological information. It also reveals that the board recommended the installation of a concrete or roller-compacted concrete structure on the emergency spillway, which had previously been left unpaved.

When the emergency spillway had to be put into service in February, major erosion of the soil surface occurred, leading to concerns that the weir might fail, leading to an uncontrolled release of water. About 188,000 people downstream of the dam were evacuated from their homes and businesses for more than a day before the danger subsided.

The Board of Consultants currently consists of John J. Cassidy (who holds a Ph. D. in mechanics and hydraulics), Eric B. Kollgaard (a civil engineer), Faiz Makdisi (whose Ph.D. is in geotechnical and geoenvironmental engineering) and Kerry Cato (Ph.D. in engineering geology).


Tagged categories: concrete; Concrete repair; Engineers; Failure analysis; Locks and dams; North America; Quality Control

Comment Join the Conversation:

Sign in to our community to add your comments.

Sauereisen, Inc.


Abrasives Inc.

Axxiom Manufacturing


HoldTight Solutions Inc.

KTA-Tator, Inc. - Corporate Office


Technology Publishing Co., 1501 Reedsdale Street, Suite 2008, Pittsburgh, PA 15233

TEL 1-412-431-8300  • FAX  1-412-431-5428  •  EMAIL

The Technology Publishing Network

PaintSquare the Journal of Protective Coatings & Linings Paint BidTracker

EXPLORE:      JPCL   |   PaintSquare News   |   Interact   |   Buying Guides   |   Webinars   |   Resources   |   Classifieds
REGISTER AND SUBSCRIBE:      Free PaintSquare Registration   |   Subscribe to JPCL   |   Subscribe to PaintSquare News
MORE:      About   |   Privacy Policy   |   Terms & Conditions   |   Support   |   Site Map   |   Search   |   Contact Us