One of the many highlights of my fatherhood experience was when one of my children was assigned a paper on the Hoover Dam.
This meant that for a couple of weeks I could ask during family dinnertime conversations: "How is the dam paper going? Is the dam first draft ready yet? What are you learning from your dam school project?"
Years later, my children still wince about the experience. Well, the dam topic is back again.
Researchers at Resources for the Future have been looking at the issue of old and outdated dams. The National Inventory of Dams (NID) from the US Army Corps of Engineers counts 91,500 dams in the United States with an average age of 57 years.
Some of the dams continue to serve useful purposes: carbon-free power generation, flood protection, drinking water supply, irrigation, creating bodies of water for recreation, and so on.
But many others are both no longer useful and "high-hazard," meaning that there is risk to human life if/when they fail.
For these dams, removal will often be a better option.
Margaret A. Walls and Vincent Gonzales provide a readable overview of the work in "Dismantling Dams Can Help Address US Infrastructure Problems" (Resources, October 2020). For more details, their longer report is "Dams and Dam Removals in the United States" (RFF Report 20-12, October 2020).
The National Inventory of Dams tries to include all dams in the US that meet "at least one of the following criteria:
- High hazard potential classification - loss of human life is likely if the dam fails,
- Significant hazard potential classification - no probable loss of human life but can cause economic loss, environmental damage, disruption of lifeline facilities, or impact other concerns,
- Equal or exceed 25 feet in height and exceed 15 acre-feet in storage,
- Equal or exceed 50 acre-feet storage and exceed 6 feet in height.
These are the relatively big dams. A fuller count of smaller dams from a couple of decades ago suggests that there might be 2.5 million dams in the US as a whole.
The Stanford National Performance of Dams Program also provides useful background information. As their 2018 report on "Dam Failures in the U.S." points out, there was a major surge in dam-building after World War II, which has then slowed to nearly a halt in the last couple of decades.
The Walls and Gonzales report digs into the data from the National Inventory of Dams and reports:
[A] hazard rating is a classification that conveys the consequences should the dam fail or be operated improperly and release water. It is highly dependent on the location of the dam—that is, whether it is located near heavily populated areas—and the size of the reservoir.
Seventeen percent of dams in the NID have a high hazard rating, 12 percent are rated as a significant hazard, 65 percent are considered a low hazard, and 5 percent have an undetermined hazard rating.
Of the high-hazard dams, private entities own the largest share, at 43 percent. Comparing this with private ownership of dams as a whole, however, which is 62 percent, private entities appear to have fewer of the high-hazard dams than do other owner types.
Local governments, for example, own 20 percent of all dams but 29 percent of high-hazard dams, and the federal government owns only 4 percent of all dams but 9 percent of high-hazard dams.
As they point out, removing dams can both reduce the risks of a collapse, and also offer other potential benefits: