The disaster at Oroville Dam in California last winter put questions about dam safety in the headlines for the first time in many years. It also inspired dam safety officials in many states to think about the inspection and maintenance programs they use to protect their own dams.
The state of Utah went through its own disaster in 1989 that prompted big changes in the state’s dam safety program. On New Year’s Day, a portion of the Quail Creek Dam near St. George collapsed, causing a flood in the Virgin River channel below that damaged more than 50 homes and forced 1,500 people to evacuate. The earthen dam was relatively small, but it was only three years old and it had experienced seepage problems almost from the moment it was completed.
The following year, the state passed the Dam Safety Act, a new law adopting more rigorous dam inspection procedures and empowering the government to require safety upgrades to dams that no longer meet modern requirements. Those rules are overseen by a unit within the Utah Division of Water Rights.
Water Deeply spoke with David Marble, assistant state engineer for dam safety, to learn more about Utah’s program.
Water Deeply: The Oroville disaster in California was a wake-up call on dam safety for a lot of Americans. What did it make you think about?
David Marble: Anytime you see an event like that, it has to be a wake-up call. That’s the kind of thing we’re working very hard to prevent. Is there something we should be doing that we haven’t done? What was missed? How did this develop? You self-evaluate and try to determine if there’s something we could be doing better to try to determine how to prevent something like that from happening. We’re very interested as to what happened, and if there are some lessons [as to what] we can learn to do better and try to prevent something like that in the future.
Water Deeply: How many dams does Utah have and how do you rate them?
Marble: There’s probably 5,000 or so if you count all the very small ones. Anything about 20 acre-feet in size or less that is considered moderate or low in hazard rating, then we don’t really actively regulate those. We have authority to inspect them if somebody makes us aware of a concern, but they’re not inspected on a regular basis.
Out of those, we regulate around 200 high-hazard dams, around 200 moderate-hazard dams and around 500 low-hazard dams that we regulate from a safety perspective. A hazard rating describes the consequence of failure: If a dam is there and if it were to fail, if people would likely be killed, then the dam is considered high hazard. A moderate-hazard dam is where loss of life is unlikely in a failure, but there would be appreciable property damage. In low-hazard dams, there’s very limited opportunity even for property damage. The way we treat dams is going to vary based on what that hazard rating is.
Water Deeply: How often are these dams inspected?
Marble: High-hazard dams get annual inspections. Moderate-hazard dams every two years and low-hazard dams every five years. It’s a big task that keeps us going. There’s a lot of fieldwork to be done.
We always have somewhere we’ve seen some concerns and have them on a watch list. We have a few with storage restrictions as a result. We probably conduct 300 inspections a year on dams and we always will find anywhere from half a dozen to a dozen repairs that need to happen. There’s routine maintenance, vegetation problems, rodent problems. There’s hardly ever an inspection we do that doesn’t have some maintenance that needs to be done.
Water Deeply: Utah decided to make its maps of dam inundation areas available to the public, in contrast to the federal government and many other states. Why?
Marble: All of our high-hazard and moderate-hazard dams need to have emergency action plans. The inundation maps are pretty specifically geared toward high-hazard dams.
A lot of agencies look at things like inundation maps and consider that to be confidential information. They’re concerned someone may see that information and, in some way, maybe use that in a bad way – terrorism, perhaps.
I think the state of Utah has tended to look a little bit more at it from the perspective that we consider that the information we have is open-record information. And it may be better, especially in the event of an emergency, if the information about where there might be inundation is readily available even way before that emergency develops. Or somebody may say, I want to build a house in that location. We’ve taken the attitude that information ought to be readily available. So anybody can go onto our website and see where the inundation areas are as best we can predict it.
Water Deeply: And besides hazard rating, does the state have some dams in poor condition?
Marble: There are some we have concerns with. One of the proactive things we’ve been doing in our program – and this really started back in 1990 when the new law was written – was to recognize that many of our dams have been in place for a long time. We’ve got dams that are well over 100 years old, and the standards to which those dams were built is appreciably different from what we would approve of now. So we do have an active program now to focus on high-hazard dams.
What we were directed to do in the 1990 legislation was to review the design of all high-hazard dams to determine if they were designed consistent with current safety standards. In many cases, we didn’t know how well some of them were designed. The design information was limited. So after we do our investigation, if we determine a dam does not meet current safety standards, or we could not determine if it does, we send out information to the owner saying you have to conduct an investigation to see what needs to be done to meet current standards.
Water Deeply: That sounds expensive. Does the state have any way to help dam owners cover those costs?
Marble: Since 1997, the state has provided us with some money to go to dam owners and provide grants. They actually cover 80–90 percent of the cost of bringing a dam up to current safety standards.
So there is money provided through the state to upgrade that dam to meet current safety standards. The amount of money we have is not as much as we’d like to see. We upgrade two or three dams a year to meet current safety standards: increasing spillway capacity, increasing stability for earthquake loading – whatever we think is necessary. We’ve done about 50 dams in the past 20 years. There are probably around 10 dams that still need to be done.
Water Deeply: Are your design flood standards changing because of climate change?
Marble: At this point I would say not really. Certainly the issues related to climate change are an important topic. It has a real potential to impact some state standards because of the frequency of big storms.
The Utah standard for high- and moderate-hazard dams is really based on what would be considered the probable maximum precipitation and flooding event. That is science-based information we get from the National Weather Service, and it’s really based on what is the maximum amount of precipitation that can be held in the atmosphere and then released. Since it’s the maximum amount, we’re not really looking at frequency, for example. This is really the most that could happen.
Water Deeply: In some cases, the hazard exists because development has crept in below a dam, right?
Marble: That’s an important concern. We call that hazard creep. You can have a dam, at one time, built with very little below it. Consequently, the hazard potential was not a big concern. Now we’ve got several dams I can point to with aerial photography, and 30 years ago there was very little of concern. And now there’s substantial development below those dams. We’ve had several dams where the hazard rating has had to be increased as a result.