The Army Corps of Engineers is farther along than you may think in breaching or removing the dams on the Lower Snake River, such as Lower Granite Dam and the other dams on the Snake River. They have already completed a study on the feasibility of the Lower Snake dams. The 2010, Lower Snake River Juvenile Salmon Migration Feasibility Report described how the Lower Snake River dams could be breached if it was determined that the benefits of breaching outweighed the negative effects dams have on the environment. For the Corps to consider dam breaching as an option, some species of endangered salmon need to drop below a certain benchmark number. But, dam breaching is not the first option. Dam breaching is the option only if the other options do not work. The first option is “adaptive migration” which is major improvements to fish passage at the dams, which has happened at two of the dams, or maximum transport of juvenile salmon. The purpose of this blog post is to explain how the dams would be breached if that option were selected.
To breach the dams on the Lower Snake, they would remove the earthen section of the dam and leave the concrete section. All the dams on the Lower Snake have an earthen section. To remove the earthen section the Corps would lower the reservoir levels and then slowly work to remove the earthen section until the water level is below the level of the cofferdam. The cofferdams were built to divert the water during the construction of the dams, and they are still there. They would then finish removing the earthen section and breach the cofferdam. They would then remove the rest of the cofferdam. They would keep the concrete in place, in case they decide to build the dam again, and to save money. The picture shows how the dam would look after they remove the earthen section.
Overall, I think that dam breaching is a good option. This publication provides a wealth of information on what needs to be done to remove the dams and how they would go about removing them. The cost of removing the dams would be $19.8 million for removing all four dams. There are many benefits to removing the dams, such as there will be higher salmon returns and the ecosystem will rebound. So, the breaching of the four Lower Snake Dams is the right thing to do to protect the salmon runs and help restore the Snake River ecosystem.
~Patrick