A high hazard dam is one whose failure would probably kill at least one person downstream. The label is about consequences, not condition: a well-maintained structure carries the high hazard tag when enough people live in the path the water would take after a breach, and a deteriorating dam in an empty canyon may carry a lower classification simply because no one lives below it. The United States has roughly 17,400 dams in this category, and the classification triggers the strictest inspection, planning, and liability obligations in the federal dam safety framework.
How the Classification Is Made
The federal system, published as FEMA 333, sorts every dam into one of three tiers based on what would happen if it failed.1Federal Energy Regulatory Commission. Federal Guidelines for Dam Safety: Hazard Potential Classification System for Dams Low hazard dams are those where failure would likely destroy only the owner’s property. Significant hazard dams could cause economic or environmental damage but no deaths. High hazard potential means failure will probably kill one or more people.
Engineers reach that determination through inundation mapping, which uses computer simulations to model how released water would travel, how fast it would move, and how deep it would get at points downstream.2Federal Emergency Management Agency. Federal Guidelines for Inundation Mapping of Flood Risks Associated With Dam Incidents and Failures If the modeled floodwave reaches residential areas, schools, hospitals, or other occupied buildings at dangerous depths and velocities, the dam gets the high hazard label. The analysis accounts for water volume behind the dam, the terrain the water would cross, and the type of structures in its path.
When a Classification Changes
A dam’s hazard classification is not permanent. New housing, commercial buildings, or roads built below an existing dam can push its classification upward, a phenomenon regulators call hazard creep. The dam itself hasn’t changed. The consequences of failure have.
Reclassification has financial teeth. Once a state upgrades a dam to high hazard, the owner faces new requirements: larger spillway capacity, more frequent inspections, and a mandatory emergency action plan.3Federal Emergency Management Agency. Risk Exposure and Residual Risk Related to Dams Bringing a structure originally built to low hazard standards up to high hazard requirements can cost hundreds of thousands of dollars or more. Owners who don’t watch what gets built downstream can be blindsided by a reclassification and the compliance costs that come with it.
Regulatory Framework and Owner Obligations
The National Dam Safety Act, codified starting at 33 U.S.C. § 467, creates a coordinated federal program administered by FEMA.4Office of the Law Revision Counsel. 33 USC 467 – Definitions The law does not directly regulate individual dam owners. It sets baseline standards that state programs must meet to receive federal funding and technical assistance. In practice, your obligations as an owner come from your state, which must satisfy the federal minimums but usually goes further.
Inspections
Federal law requires that state programs have authority to inspect all dams posing a significant threat to life at least once every five years, with provisions for more frequent inspections as needed. For high hazard dams, most states go well beyond that floor. The majority require inspections every one to two years, though a few allow intervals of three to five years. Inspections must be conducted under the supervision of a licensed professional engineer with dam design and construction experience.5Office of the Law Revision Counsel. 33 USC 467f – National Dam Safety Program Inspectors look for seepage, cracking, erosion, settlement, and whether spillways and outlet works are functioning properly.
State agencies also have authority to issue notices requiring owners to perform maintenance, install monitoring instruments, improve security, revise operating procedures, or breach the dam entirely when public safety demands it.5Office of the Law Revision Counsel. 33 USC 467f – National Dam Safety Program Penalties for non-compliance are set at the state level and vary widely, from modest administrative fines to daily penalties that accumulate rapidly.
Emergency Action Plans
Every high hazard dam needs an emergency action plan. Federal grant programs treat an approved EAP as a prerequisite for rehabilitation funding, and virtually every state program requires one.6Office of the Law Revision Counsel. 33 USC 467f-2 – Rehabilitation of High Hazard Potential Dams The plan is the playbook for what happens when something goes wrong. FEMA’s federal guidelines (published as FEMA P-64) recommend notification flowcharts for alerting law enforcement and emergency responders, inundation maps identifying threatened areas, and clear definitions of escalating emergency levels. FEMA also recommends annual seminars and drills with local emergency management, tabletop exercises every three to four years, and functional exercises every five years, each followed by a documented after-action review.7Federal Emergency Management Agency. Federal Guidelines for Dam Safety: Emergency Action Planning for Dams
Federal guidelines also recommend that owners proactively communicate dam failure risks with potentially affected communities, meaning the EAP and inundation maps should reach the people who would need to evacuate.8Federal Emergency Management Agency. Federal Guidelines for Dam Safety
Owner Liability When a Dam Fails
Owning a high hazard dam means continuous legal exposure. Many courts treat dam impoundment as an abnormally dangerous activity, which means the owner can be held liable for damages caused by a failure regardless of how careful they were. The theory traces back to the 1868 English case Rylands v. Fletcher, which held that anyone who collects something likely to cause harm if it escapes is responsible for the consequences. American courts have applied it unevenly. Some states apply strict liability to dam failures. Others, including Arkansas, have declined to extend it, reasoning that maintaining a dam across a natural waterway is neither unusual nor inappropriate to the location.
Whether or not strict liability applies in your state, negligence is always available as a theory of liability. Ignoring inspection findings, deferring spillway maintenance, failing to clear debris, or neglecting to update an emergency action plan all look like negligence in a courtroom. When a failure causes deaths or widespread property destruction, courts can award millions in damages. Gross negligence can bring criminal charges. Professional engineering oversight and documented compliance with every state requirement are the practical protections against catastrophic exposure.
No state currently requires dam owners to carry liability insurance as a condition of ownership, though general liability policies may provide some coverage depending on their terms. Because a single failure can produce liability in the tens of millions, owners should review coverage with a broker who understands infrastructure risk. General liability policies sometimes contain specific exclusions for dam-related losses.
Disclosure When Selling
Disclosure requirements when selling property that includes a dam vary significantly by state. Some states require sellers to disclose known hazards. Others follow the traditional buyer-beware approach. No uniform federal rule requires disclosure of a high hazard classification or outstanding safety orders during a real estate transaction. Buyers should independently check the National Inventory of Dams and contact the state dam safety program to learn about any pending compliance orders before closing.
Finding High Hazard Dams Near You
The National Inventory of Dams, maintained by the U.S. Army Corps of Engineers, is the central database for dam information in the United States. It is open to the public and searchable by dam name, geographic coordinates, or county. Each listing includes the hazard classification, location, size, purpose, type, last inspection date, and condition assessment. Condition ratings range from satisfactory through fair, poor, and unsatisfactory, plus “not rated” for dams that haven’t been formally evaluated. For some dams, the NID also provides flood inundation maps.9U.S. Army Corps of Engineers. National Inventory of Dams State environmental or natural resource departments often provide additional data through their own registries, including smaller structures that don’t appear in the federal inventory.
What a Breach Zone Does Not Mean
Living in a dam breach inundation zone does not automatically place you in a Special Flood Hazard Area on FEMA’s regulatory flood maps. Dam breach inundation maps are primarily dam safety tools used for emergency action planning, and they are generally considered separate from the Flood Insurance Rate Maps that drive mandatory flood insurance purchase requirements.2Federal Emergency Management Agency. Federal Guidelines for Inundation Mapping of Flood Risks Associated With Dam Incidents and Failures The Biggert-Waters Flood Insurance Reform Act of 2012 authorized FEMA to begin identifying dam failure inundation areas on its flood maps, but full implementation has been slow.
If a dam does fail and water damages your property, the National Flood Insurance Program would generally cover the resulting damage, since the NFIP definition of “flood” includes inundation from a breached dam or released spillway.10Federal Emergency Management Agency. Answers to Questions About the National Flood Insurance Program You need an active policy in place before the event. You cannot buy coverage after flooding has begun. If you live downstream of a high hazard dam, flood insurance is worth serious consideration even when your lender doesn’t require it.
Federal Funding for Rehabilitation
Rehabilitating a high hazard dam is expensive, and several federal programs exist to offset the cost.
FEMA High Hazard Potential Dam Grants
The Rehabilitation of High Hazard Potential Dams program, authorized under 33 U.S.C. § 467f–2, provides grants through state dam safety agencies for planning, design, and construction.6Office of the Law Revision Counsel. 33 USC 467f-2 – Rehabilitation of High Hazard Potential Dams To qualify, a dam must be classified high hazard by the state, have an approved emergency action plan, and be determined to fail minimum safety standards. The community where the dam sits must participate in the National Flood Insurance Program and have a hazard mitigation plan.
The program requires a 35 percent non-federal cost share, which can be provided through in-kind contributions. The cost-share requirement is waived entirely for projects benefiting underserved communities. No single dam can receive a grant exceeding $7.5 million or 12.5 percent of the program’s total annual funding, whichever is less. Congress authorized $60 million per year for fiscal years 2021 through 2026.6Office of the Law Revision Counsel. 33 USC 467f-2 – Rehabilitation of High Hazard Potential Dams Grants cannot be used for routine maintenance, hydroelectric modifications, or increasing water supply storage.
USDA Watershed Rehabilitation Program
The Natural Resources Conservation Service runs a separate Watershed Rehabilitation Program for aging dams that no longer meet federal or state safety standards.11Natural Resources Conservation Service. Watershed Rehabilitation Program It provides technical and financial assistance for planning, design, and construction. A local sponsor submits a request and works with NRCS to develop a watershed plan covering environmental impacts, costs, benefits, and maintenance responsibilities.
Corps Water Infrastructure Financing Program
For larger projects, the Corps Water Infrastructure Financing Program offers long-term, low-interest loans for non-federal dam safety work. The minimum project size is $20 million in anticipated costs.12SAM.gov. Corps Water Infrastructure Financing Program Standard projects can borrow up to 49 percent of total costs. Projects serving economically disadvantaged communities can borrow up to 80 percent. Eligible borrowers include state, local, and tribal governments as well as corporations and trusts.