Somewhere in your county there is an earthen dam with a high hazard potential classification, an emergency action plan on file with the state, and a notification flowchart whose first phone call lands in your 911 center. There is a fair chance nobody working tonight has opened it, and a better chance the first number on the call list rings an office that closed at five. This piece covers how dams get classified, what an emergency action plan is supposed to contain, what inundation maps can and cannot tell you, how the notification chain breaks, and what to ask a dam owner for before any water is moving.

What is holding back the water in your county

The United States Army Corps of Engineers maintains the National Inventory of Dams, a public database that in recent years has carried records on roughly 92,000 dams meeting the inventory criteria for height, storage and hazard. The count moves as states submit updates and as small structures are added or removed, so pull the current figure from the NID itself rather than quoting mine. What matters more than the total is the ownership mix, because the largest single category in the inventory is private ownership, and privately owned dams outnumber federally owned ones by a very wide margin. The dam upstream of your subdivision is more likely to belong to a homeowners association, a farmer, a quarry or a land trust than to any agency you can reach through the state EOC.

Regulatory authority is split accordingly. The Corps owns and operates several hundred dams of its own and the Bureau of Reclamation several hundred more, the Federal Energy Regulatory Commission regulates dam safety at the hydropower projects it licenses, and everything else falls to state dam safety programs. The Association of State Dam Safety Officials has reported for years that states regulate roughly seventy percent of the dams in the inventory, and ASDSO has also long identified Alabama as the only state without a dam safety regulatory program, which is worth verifying with ASDSO directly if you work in or near that state because the situation has been the subject of repeated legislative attention.

Age is the structural problem underneath all of this. A large share of the inventory was built between the 1940s and the 1970s, including more than eleven thousand watershed dams built with federal assistance through the Department of Agriculture’s small watershed programs, many of which were designed and evaluated for a fifty-year service life that has already run out. The American Society of Civil Engineers has graded the nation’s dams poorly for a long time, awarding a D in its 2021 Infrastructure Report Card, and you should check the current edition for the latest grade and the data behind it. None of that tells you anything about the specific dam above your town, which is why the county-level list from your state program is the document that matters.

Hazard potential classification and what it measures

The federal guidelines for dam safety published by FEMA describe a hazard potential classification system with three classes, generally rendered as low, significant and high. A high hazard potential dam is one where failure or misoperation would probably cause loss of human life. A significant hazard potential dam is one where failure would not probably cost lives but would cause appreciable economic loss, environmental damage, or disruption of lifeline facilities such as a highway or a water treatment plant. A low hazard potential dam is one where failure would cause minimal damage beyond the owner’s own property. States do not all use those words, and some use Roman numerals, some use Category I and Category II, and a few use four tiers, so ask your state program which scheme applies and what each class means in their statute.

The point people miss, including experienced emergency managers, is that the class describes what happens downstream if the dam lets go and says nothing about how likely that is or what condition the structure is in. A brand new, well engineered, well maintained dam above a populated valley is high hazard potential, while a crumbling, seeping, unmaintained farm pond with nothing below it but pasture is low hazard potential. Condition is tracked separately, and the National Inventory of Dams carries a condition assessment field with values such as satisfactory, fair, poor and unsatisfactory, along with a very large number of entries that are simply not rated.

Classification also drifts over time in one direction, because downstream development keeps arriving and almost never leaves. A dam built in 1962 to water cattle becomes a high hazard structure the year a developer puts forty houses in the floodplain below it, and the owner, who has not touched the thing in decades, is suddenly subject to inspection, spillway capacity requirements, engineering studies and an emergency action plan obligation. States handle reclassification on different schedules and with different appeal rights, and the resulting fights over who pays for the upgrade are a routine feature of state dam safety work. For your purposes, the question to put to the state program is which dams in your county have been reclassified in the last ten years and which ones have pending development downstream.

What an emergency action plan actually contains

An emergency action plan is the dam owner’s plan, prepared by or for the owner, filed with the regulating authority, and built around the owner detecting a problem and telling somebody who can warn people. The FEMA federal guidelines on emergency action planning for dams describe the expected elements, and most state programs have adopted a structure close to it: a summary and notification flowchart at the very front, a statement of purpose, a project description, the response process that covers detection, evaluation and classification of the emergency, a general responsibilities section that says who does what, a preparedness section, the inundation maps, and appendices covering the analysis behind the maps and the plan for training, exercising, updating and distributing the document.

The response process is the engine. It defines emergency levels, usually three, along the lines of a non-failure emergency or unusual event, a potential failure situation, and an imminent or actual failure, with the names varying by state. Each level has its own notification path and its own urgency, and the whole design rests on the owner or the owner’s operator recognizing which level applies at two in the morning in the rain. A dam tender who has never exercised the plan is being asked to make a classification decision that will determine whether several thousand people get a phone call, and that is exactly why the training and exercise appendix is not filler.

The preparedness section is where the practical detail lives and where a responder should read first. It should tell you how to get to the dam, who holds the gate key, whether the access road crosses the very stream that will be running high, whether the outlet works can be opened without commercial power, what materials the owner keeps on hand for emergency repair, and what surveillance the owner performs during high water. Update and exercise frequency are set by state rule rather than by federal law, so verify current requirements with your state dam safety program rather than assuming the interval you remember from a class.

The notification flowchart and the number that rings nowhere

The flowchart is one page and it is the only page that runs during the first ten minutes. It lists the people and agencies to be called, in order, with roles and twenty-four-hour telephone numbers, and it almost always designates the local 911 center or the county emergency management agency as the first outside recipient. Everything downstream of that call depends on the person who answers it understanding what was just said, and my experience in dispatch and communications is that this is where the plan most often comes apart, because the caller is an unfamiliar name from an unfamiliar number describing a structure the call taker has never heard of, using words like piping and boil that have no meaning in a CAD incident type list.

The fixes are administrative and cheap. Each high hazard dam in your jurisdiction should exist in CAD as a geocoded premise or hazard record at the dam location, with the dam’s NID identifier, the owner’s twenty-four-hour number, the location of the EAP, and a short note on what to do first, and the same hazard flag should be attached to the downstream road segments that go under water. A dam failure or imminent failure report should have an incident type, so that a call taker is not improvising a category while a reservoir is finding a path through an embankment. Somebody also has to decide in advance how the caller is authenticated, because the first report will not come from a recognized agency line.

Then there is the call-down itself, which decays quietly. Numbers belong to people who retired, agencies consolidate, a county office line rolls to voicemail after hours, and the plan on file with the state was last revised when the previous chief held the position. Dial every number on every flowchart once a year on a night shift, write down who answered and how long it took, and send the results to the owner and to the state program in writing. The other thing to check is whether the notification depends on a single path, since many dam sites sit in poor cellular coverage, and it is a reasonable question to ask an owner whether the operator has a radio, a satellite messenger, or any way to reach you when the cell site on the ridge loses commercial power.

Inundation maps, arrival times, and their limits

Inundation maps in an EAP are usually built from a breach analysis modeled under two conditions. The first is a fair weather or sunny day breach, meaning the dam fails with the reservoir at normal pool and no storm in progress, which produces the scenario with the least warning and the most confusion because there is no rain outside to explain the water. The second is a hydrologic breach, in which the dam fails while passing a large flood, so the downstream channel is already full and the incremental effect of the breach is layered on top of flooding that would have happened anyway. Some plans map both, some map only one, and the difference matters when you are deciding whether an area is already at risk without any failure at all.

The useful content is the arrival time and the maximum depth at named downstream points, together with the outer limit of inundation. A polygon by itself does not tell a deputy anything actionable, while a table saying that the leading edge reaches the state highway bridge in twenty-two minutes and crests at nine feet over the deck tells him when to stop parking on that bridge. Ask for that table explicitly, and ask for it at landmarks your responders actually use, meaning intersections, schools, mobile home parks, nursing homes and campgrounds rather than river miles. Ask for the data as a GIS file rather than a PDF, so your own mapping staff can overlay parcels, count addresses and structures, and pre-draw alerting polygons.

The map carries limits that are worth stating out loud to anyone who will act on it, since it is a modeled estimate built on assumed breach width, breach formation time and downstream channel roughness, and the line drawn on the paper carries real uncertainty that the crispness of the drafting conceals. Inundation mapping prepared for an EAP has no standing under the National Flood Insurance Program and governs nothing about insurance rating or local zoning, and it may be decades old and drawn against a downstream landscape that has since been developed. Distribution is also restricted in many cases, since FERC treats a great deal of dam information as critical energy infrastructure information and numerous states restrict release of inundation mapping under their own statutes, so ask the owner and the state program in writing what you are permitted to share with responders, with schools and facilities in the zone, and with the public.

Four American cases and what each one changed

Kelly Barnes Dam, an earthen structure above Toccoa Falls Bible College in Stephens County, Georgia, failed in the early hours of 6 November 1977 and killed thirty-nine people, most of them students and family members asleep in housing below the falls. The state legislature passed the Georgia Safe Dams Act the following year, creating the classification and inspection framework the state still administers. Anyone working in Georgia should know that the program exists because of a failure inside the state, and the specific lesson for emergency managers is that the population at risk was asleep, indoors, and unaware that there was a dam above them at all.

Teton Dam, a Bureau of Reclamation structure in eastern Idaho, failed on 5 June 1976 during its first filling. Eleven deaths are the figure usually published, along with very large agricultural and property losses across the Snake River plain. The federal response over the following years produced the federal guidelines for dam safety, an interagency coordinating structure, and eventually the National Dam Safety Program Act enacted in 1996, which established the FEMA-administered program that supports state dam safety agencies today and has been reauthorized several times since.

Oroville Dam in California did not fail, and it is still the most instructive recent case in the country. In February 2017 the main spillway chute was damaged during releases, use of the never-before-used emergency spillway produced headcutting erosion that threatened the weir, and on 12 February an evacuation order went out for downstream communities covering a population widely reported at roughly 188,000 people. An independent forensic team commissioned by ASDSO and the United States Society on Dams published its report in January 2018 and attributed the incident to long-standing systemic weaknesses in design, construction, inspection practice and industry-wide dam safety culture rather than to a single operator error. For emergency managers the operational lesson came from the roads, because the order went out in the afternoon and the highways out of the valley jammed within the hour.

Edenville Dam in Michigan failed on 19 May 2020 after days of heavy rain, and the resulting release overtopped Sanford Dam downstream, flooding Midland and prompting the evacuation of roughly ten thousand people with no reported deaths. FERC had revoked the project’s hydropower license in 2018 over the owner’s failure to increase spillway capacity, after which state regulation applied. An independent forensic team reporting in 2022 concluded that the embankment failed through static liquefaction instability of the upstream slope. Separately, Spencer Dam in Nebraska failed in March 2019 during an ice run, killing one person, which is worth knowing because an ice run was not among the failure modes that plan had contemplated.

Rehabilitation money, with the EAP as the gate

Congress authorized a rehabilitation grant program for high hazard potential dams in 2016 legislation, administered by FEMA through the National Dam Safety Program and passed through to state dam safety agencies, and the Infrastructure Investment and Jobs Act of 2021 added substantial funding to it. The eligibility conditions are the reason every emergency manager should care about paperwork sitting in a state office, because the program is generally limited to non-federal dams that are state-regulated, classified high hazard potential, located in a state with a dam safety program, and covered by an emergency action plan that the state has approved. A dam without a current EAP is a dam that cannot compete for the money that would fix it.

Federal mitigation grant programs have changed significantly in the last two years, so ask your state hazard mitigation officer and your state dam safety engineer what is currently open, what the state match requirement is, and which dam projects in your state have actually been funded rather than budgeting against a program name you remember from a conference. State-level programs vary enormously, with some states offering low-interest loan funds or direct grants for dam rehabilitation and others offering nothing at all beyond enforcement.

Removal is a legitimate and frequently cheaper option that local officials tend to overlook. A breach or a full removal of an obsolete dam eliminates the hazard classification, the inspection obligation, the EAP obligation and the liability, and there is an established body of funding and technical support for removal through state agencies, fisheries programs and non-profit organizations. When a small dam owner in your county gets a letter reclassifying their pond as high hazard and cannot afford a spillway upgrade, the conversation about removal is one your emergency manager can usefully start with the state program on the line.

The half of the plan the county has to write

The EAP tells you that water is coming and roughly where it will go, and it stops there, because the owner has no authority to close a road, open a shelter or order anybody out of a house. The county side belongs in an annex to the emergency operations plan you already maintain, and it should name the position authorized to order evacuation, identify the evacuation routes that lead out of the inundation zone rather than along it, list the shelter sites that sit outside the mapped limit, fix the road closure points with their responsible agency, and identify every school, licensed care facility, campground and mobile home park inside the zone with a current contact. Four or five paragraphs of that, written in advance, is worth more than a hundred pages of hazard narrative.

Alerting deserves its own attention because dam breach warning times are short and the message has to be pre-built. If your jurisdiction has IPAWS authority, draw the polygons for each high hazard inundation zone ahead of time, save pre-scripted Wireless Emergency Alert and Emergency Alert System messages that say what the hazard is and what action to take, and confirm with your alerting administrator that the people on duty overnight have current credentials and have practiced in the IPAWS lab environment. Call your National Weather Service forecast office as well and ask how a reported dam failure enters the warning system in your county, who they expect to call them, and what information they need in order to issue a flash flood warning or flash flood emergency with dam failure wording.

Finally, exercise the thing with the owner in the room. A two-hour tabletop with the dam owner or operator, the 911 center, the sheriff’s office, the fire department, the school system and the forecast office will find the stale phone numbers, the locked gate nobody has a key to, the assumption that the state will order the evacuation, and the fact that the shelter you planned to use is in the inundation zone. Responder awareness training is a modest addition to the same effort, since crews sent to check a dam during high water need to know what seepage, boils, sinkholes, new cracking and suddenly muddy discharge look like, who to report them to immediately, and that standing on the downstream toe of a dam that is actively passing water through its embankment is not a survivable place to conduct an assessment.

What to do at your agency

• Have your emergency manager request from the state dam safety program a current list of every dam in the county with its hazard classification, last inspection date, condition rating, EAP status and owner contact, and ask specifically which dams have been reclassified in the last ten years.
• Ask each high hazard dam owner in writing for the emergency action plan, the inundation mapping as a GIS file, a table of arrival times and maximum depths at named downstream landmarks, and a statement of what your agency is permitted to share with responders and the public.
• Have your communications supervisor create a CAD premise or hazard record for each high hazard dam, geocoded to the dam and flagged on the downstream road segments, containing the owner’s twenty-four-hour number, the location of the EAP and the first action for a call taker.
• Dial every number on every EAP notification flowchart once this month on a night shift, log who answered and how long it took, and send the results to the owner and the state program in writing.
• Have your alerting administrator pre-draw IPAWS polygons for each high hazard inundation zone, save pre-scripted WEA and EAS messages for a dam failure, and confirm that every duty officer holds current credentials.
• Add one item to the existing local emergency planning committee agenda asking which position in this jurisdiction is authorized to order an evacuation for a threatened dam and where that authority is written down.
• Have your training officer schedule a two-hour tabletop with the dam owner or operator, dispatch, law enforcement, the school system and your National Weather Service forecast office, using the fair weather breach scenario rather than the storm scenario.

Takeaways

• The National Inventory of Dams maintained by the Corps of Engineers has carried records on roughly 92,000 dams in recent years, most of them privately owned and most of them regulated by state programs rather than by any federal agency.
• A hazard potential classification of low, significant or high describes the consequences of failure downstream and tells you nothing about the condition of the structure or the probability that it fails.
• Classification drifts upward as development arrives below a dam, so ask your state program which dams in your county have been reclassified recently and which have new development pending downstream.
• An emergency action plan belongs to the dam owner and covers detection, classification and notification, while evacuation, road closure, sheltering and public warning remain the county’s responsibility and belong in your own emergency operations plan.
• Inundation maps are modeled estimates with real uncertainty, they have no standing under the National Flood Insurance Program, they may predate current downstream development, and their distribution is often restricted by FERC rules or state statute, so get the sharing permissions in writing.
• Oroville in February 2017 produced an evacuation order covering a population widely reported at roughly 188,000 people without the dam failing, and the independent forensic team commissioned by ASDSO and the United States Society on Dams attributed the incident to systemic weaknesses across design, construction, inspection and industry practice.
• The federal rehabilitation grant program for high hazard potential dams generally requires an approved emergency action plan as a condition of eligibility, which makes a missing EAP both a response problem and a funding problem.
• Requirements for EAP content, update frequency, exercise frequency and inundation mapping vary substantially by state, so verify what applies to you with your state dam safety program rather than relying on any general summary including this one.