Explainer: How the U.S. Evaluates and Upgrades High-Hazard Dams

Water infrastructure is largely invisible until it fails. Across the United States, more than 92,000 dams hold back reservoirs, provide hydroelectric power, and mitigate seasonal flooding. Yet, the average age of these structures has quietly crept past 65 years, pushing many beyond their original design lifespans. For downstream communities, the integrity of these earthen and concrete barriers is the only thing standing between a normal Tuesday and a catastrophic inundation.[1]

The scale of the challenge is mapped by the National Inventory of Dams, maintained by the U.S. Army Corps of Engineers. Within that database, nearly 17,000 structures are currently classified as "high-hazard potential." This designation is frequently misunderstood by the public; it does not mean a dam is structurally deficient or on the verge of collapse. Rather, it is a strict consequence-based metric indicating that if the dam were to fail, the resulting floodwaters would likely cause a direct loss of human life.[1]

As suburban development expands into formerly rural valleys and floodplains, the number of dams meeting this high-hazard criteria has more than doubled over the past two decades. A dam built in 1950 to protect a remote agricultural basin might now sit upstream from a sprawling subdivision, instantly elevating its hazard classification without a single crack forming in its spillway.[1]

Evaluating and maintaining this vast network falls largely to state dam safety programs, which oversee approximately 69% of the dams in the national inventory. Every state except Alabama operates a regulatory program responsible for inspecting dams, enforcing safety standards, and ensuring that owners maintain up-to-date Emergency Action Plans.[1]

The financial reality of dam rehabilitation is daunting. In its 2025 Report Card for America's Infrastructure, the American Society of Civil Engineers upgraded the nation's dams from a D to a D+. While this slight improvement reflects recent federal investments and heightened regulatory attention, the underlying math remains severe. The Association of State Dam Safety Officials estimates that bringing the nation's nonfederal dams into a state of good repair would cost $165.2 billion.[1][3]

Addressing just the most critical, deficient high-hazard dams—of which there are over 2,300—would require an estimated $37.4 billion. This massive backlog is driven by the fact that over 56% of U.S. dams are privately owned. Many belong to homeowners' associations, defunct mining companies, or local water districts that lack the capital to undertake multi-million-dollar structural overhauls.[1][3]

To help bridge this gap, the federal government intervenes through the Federal Emergency Management Agency. FEMA administers the National Dam Safety Program, which provides essential training, technical assistance, and state assistance grants to help state regulators bolster their inspection capabilities.[2]

More directly, FEMA manages the Rehabilitation of High Hazard Potential Dams (HHPD) Grant Program. Authorized by the Water Infrastructure Improvements for the Nation Act, this program provides technical, planning, design, and construction grants specifically targeted at eligible non-federal high-hazard dams.[2]

To qualify for HHPD funding, a dam must be classified as high-hazard, fail to meet minimum state safety standards, and possess an approved Emergency Action Plan. The grants require a non-federal cost-share of at least 35%, meaning local sponsors must still generate significant capital to unlock federal assistance.[2]

Despite its critical mission, the HHPD program's funding levels highlight the disparity between federal resources and local needs. For fiscal year 2026, FEMA announced $11.4 million in available HHPD grant funding. While these funds are vital for the specific projects they support, they represent a microscopic fraction of the $165 billion national rehabilitation backlog.[2][3][4]

Consequently, the burden of dam safety remains overwhelmingly local. State dam safety officials are chronically stretched thin; on average, a single state inspector is responsible for overseeing 190 existing dams. This personnel shortage complicates efforts to enforce compliance and guide private owners through the complex engineering required for structural upgrades.[3]

Despite the financial and logistical hurdles, the dam safety sector has achieved significant victories in emergency preparedness. The most notable success is the widespread adoption of Emergency Action Plans across high-risk watersheds.[1]

An EAP is a formal document that identifies potential emergency conditions at a dam and specifies pre-planned actions to minimize property damage and loss of life. These plans include detailed inundation maps showing exactly where water will flow if the dam breaches, allowing local emergency managers to establish evacuation routes and warning protocols.[1]

As of recent assessments, over 81% of high-hazard-potential dams now have an EAP on file, a marked increase from previous decades. In many states, compliance has reached 90% or even 100%. This means that even if a dam cannot be immediately repaired due to funding constraints, the downstream community is significantly better prepared to evacuate safely if a crisis occurs.[1]

Looking forward, the engineering community is increasingly focused on risk-informed decision making. Rather than treating all deficient dams equally, regulators use advanced modeling to prioritize rehabilitation funds for structures that pose the highest combined risk of failure and downstream consequence.[2]

In cases where a dam no longer serves a vital economic or flood-control purpose, removal is becoming an increasingly favored option. Decommissioning an obsolete dam eliminates the safety hazard entirely, restores natural river ecology, and is often less expensive than bringing a deteriorating structure up to modern safety standards.[3]

Ultimately, securing the nation's water infrastructure requires a systems-level approach. It demands sustained funding, rigorous local enforcement, and a public that understands the silent, towering structures operating in their watersheds.[1][3]