The idea of breaching the four lower Snake River dams has been around for decades. Fish biologists warned that they shouldn’t even be built, that they would eventually cause the extinction of salmon and steelhead. The Army Corps of Engineers had a very difficult time proving that the dams would provide a positive cost:benefit ratio. Now with salmon abundance at all-time lows , Southern Resident Orcas facing a food shortage, and Bonneville Power Authority in a serious budget crisis, the urgency to breach these four dams has never been greater.
The Army Corps must take a short time to update the 2002 EIS, then begin breaching Lower Granite Dam this fall. The dam removal sequence is Lower Granite, Little Goose, Lower Monumental and finally Ice Harbor.
responsibility and authority
The US Army Corps of Engineers has inherent fiduciary responsibilities to insure existing projects continue to provide economic benefit.
The dams have a Benefit to Cost ratio of 15¢ on the dollar (.15 to 1) in terms of National Economic Development, the standard by which the Corps must measure economic benefit.
The Corps can put the projects into a “non-operational” status. This does not change the project Purpose thus does not need Congressional Authorization.
New dam overtopping modeling software has been developed since the 2002 EIS was drafted which allows a safe breach plan to be created quickly. The breach itself is done in two phases. First, as drawdown of the reservoir is taking place, earth moving equipment, likely two D8 bulldozers and an excavator, will be cutting a notch in the earthen portion of the dam. When drawdown is below spillway crest and the notch cut to that depth, controlled hydraulic breaching will begin which uses the turbine gates to control flow. This takes approximately 8 hours with maximum flows not exceeding high flows normally encountered during spring runoff. Armoring protection and other channelization work can also be accomplished with several pieces of heavy equipment. The entire “construction” effort can easily be accomplished through “Time and Materials” or rental contracts. Details to the breach approach can be found in the 18 Feb 2016 Supplement (unofficial) to Appendix D Natural River
Drawdown Engineers of the 2002 EIS. In short, what the Corps’ Walla Walla District originally estimated would take several years in modeling, engineering, design and contracting and well over $70 million, can be done in a matter of months for around $1 million.
It’s important to remember that complete removal is not necessary. Infrastructure can be left in place, while the earthen abutment is simply breached, or removed with bull dozers (see video below). A free flowing river will heal itself.
Ever wondered what the term “breach” means? Here’s a quick animation that demonstrates each step. You’ll see that the dam infrastructure, the turbines, locks and the spillways remain in place. That’s what makes this method of restoring to a free flowing river so quick and relatively inexpensive.