Expanding the Regulatory Flood Hazard Area

A defining advancement in the 2025 Code is the expansion of the regulatory flood hazard area to include 0.2-percent annual chance flood zones (the 500-year floodplain). Under the updated provisions in Section R306 of the Residential Code (RCNYS) and Section 1612 of the Building Code (BCNYS), the regulatory framework now applies flood-resistant construction requirements to moderate flood hazard areas—shown on FIRMs as Zone B and Zone X (shaded).

Although the elevation requirement within these 500-year zones remains tied to the base flood elevation (BFE) associated with the 1-percent annual chance flood event, the expansion ensures that a broader set of buildings and infrastructure are evaluated for flood risk and constructed to consistent, resilient standards. For practitioners and communities, this shift represents a meaningful step toward addressing risk beyond the traditional 100-year footprint. Further, the expansion of the regulatory flood hazard area is consistent with a major provision of the newly published national consensus standard for flood resilient buildings, ASCE 24-24.  

Introducing Required Flood Elevation and Integrating Freeboard

The 2025 Uniform Code introduces the new term Required Flood Elevation (RFE)—a unifying concept for establishing elevation requirements across flood hazard areas. As defined in Section R306.1.4, the RFE is established as the greater of:

• The base flood elevation for the applicable flood source, plus:
  • 2 feet of freeboard; and
  • An additional 18 inches for sea level rise in flood hazard areas adjacent to tidal waters; or

• The elevation of the design flood associated with flood hazard areas depicted on a community’s adopted flood hazard map.

The continued requirement for 2 feet of freeboard remains an important buffer above the base flood, enhancing protection against events that exceed minimum expectations, or where regulatory mapping does not keep pace with natural or anthropogenic changes over time. Incorporating freeboard into the Required Flood Elevation calculation reflects longstanding best practices, while the expanded application into moderate hazard zones acknowledges that risk does not stop at the edge of the SFHA.

Accounting for Sea Level Rise in Tidal Areas

A key change to the 2025 Uniform Code is the explicit inclusion of sea level rise (SLR) considerations in tidal coastal areas. As noted in the Regulatory Impact Statement supporting the Code: 

“In both the Residential Code and Building Code, provisions for sea level rise in tidal coastal areas were added that increased the required flood elevation by adding an additional 18 inches in tidal areas over current code requirements, based on recommendations from DEC. This provision is based on the Title 6 Part 490 Projected Sea Level Rise medium sea level rise scenario projections for the 2050s.”
(Regulatory Impact Statement, Appendix B, p. 33,)

The net effect is an additional 18-inch elevation requirement added to the base flood elevation plus freeboard for tidal adjacent areas. This provision is grounded in the New York State Department of Environmental Conservation’s projected SLR medium scenario for the 2050s and reflects a recognition that regulatory design must anticipate emerging conditions—not just historical flood risk.

Technical Considerations and Implementation Guidance

While the expansion of the regulatory flood hazard area and the establishment of the Required Flood Elevation framework are conceptually straightforward, practical challenges remain when multiple flood zones or complex site conditions are present. For example, determining the appropriate base flood reference where adjacent zones have different BFEs, or where AO zones are involved, can present technical ambiguity.

To support consistent interpretation, the New York State Department of Environmental Conservation (DEC) Division of Water has prepared a draft technical bulletin that will soon be published by the New York State Department of State to address these and other unique scenarios.

DEC Division of Water is also updating the model flood damage prevention ordinances and developing a Code Coordinated ordinance to reflect the 2025 Uniform Code provisions, with a goal of assisting communities to align local floodplain management ordinances with updated state requirements.

The post NYS Expands Flood Regulatory Framework with 500-Year and Sea Level Rise Provisions first appeared on Association of State Floodplain Managers.

This article originally appeared on Inside Climate News, a nonprofit, non-partisan news organization that covers climate, energy and the environment. Sign up for their newsletter here.

MANVILLE, N.J.—Richard Onderko said he will never forget the terrifying Saturday morning back in 1971 when the water rose so swiftly at his childhood home here that he and his brother had to be rescued by boat as the torrential rain from the remnants of Hurricane Doria swept through the neighborhood. 

It wasn’t the first time—or the last—that the town endured horrific downpours. In fact, the working-class town of 11,000, about 25 miles southwest of Newark, has long been known for getting swamped by tropical storms, nor’easters or even just a wicked rain. It was so bad, Onderko recalled, that the constant threat of flooding had strained his parents’ marriage, with his mom wanting to sell and his dad intent on staying.

Eventually, his parents moved to Florida, selling the two-story house on North Second Avenue in 1995. But the new homeowner didn’t do so well either when storms hit, and in 2015, the property was sold one final time: to a state-run program that buys and demolishes houses in flood zones and permanently restores the property to open space.

“It’s pretty traumatic to watch your childhood home be bulldozed,” said Onderko, 64 and now the mayor of this 2.5-square-mile borough, which sits at the confluence of two rivers and a placid-looking brook that turns into a raging river when a storm moves through.

His boyhood property—now just a grass lot—is one of some 1,200 properties that have been acquired across New Jersey by the state’s Blue Acres program, which has used more than $234 million in federal and state funds to pay fair market value to homeowners in flood-prone areas who, like the Onderko family, had grown weary of getting flooded over and over again. 

The program, started in 1995, is considered a national model as buyouts are an increasingly important tool for dealing with climate-related flooding. A report this month by Georgetown Climate Center said the program has achieved “significant results” by moving quicker than federal buyout programs, providing a stable source of state funding and shepherding homeowners through the process.

In addition, a report last month by the Natural Resources Defense Council and the Environmental Defense Fund warns that communities may well have to come up with new ways to pay for such initiatives as the Trump Administration continues to downsize government and cut programs. 

Already, the NRDC said, billions of dollars in previously approved Federal Emergency Management Agency (FEMA) resilience grants have been cancelled.

“We need to do a lot of things very differently,” said Rob Moore, an NRDC director who worked on the report, which suggests that states and counties consider using revenue from municipal bonds, local fees and taxes, revolving loan funds, and leveraging insurance payouts to offset some of the reductions in federal funding. 

But Moore said the problem goes beyond funding uncertainty, as the science is showing that the impacts of climate change are “outpacing our efforts to adapt.”

The report, released Nov. 18, cited the Charlotte-Mecklenburg County Storm Water Services, which has acquired some 500 homes in North Carolina in its buyout program, relying largely on stormwater utility fees to fund the sales. New Jersey’s program, Moore said, is a “wonderful example” of a plan that raised money with three bond issues while building a staff that developed a lot of expertise over the years. 

Decades of experience may well come in handy as New Jersey, the nation’s most densely populated state, is likely to experience more significant flooding in the years to come. 

Sea level rose about 1.5 feet along the New Jersey coast in the last 100 years—more than twice the global rate—and a new study by the New Jersey Climate Change Resource Center at Rutgers University predicts a likely increase of between 2.2 and 3.8 feet by 2100, if the current level of global carbon emissions continues. 

Torrential rain storms also have led to massive flooding in inland towns—like Manville—as rivers and streams overflow, sending waves of water into the homes of stunned owners. The stronger storms are attributed by scientists to the Earth’s changing climate, with warming oceans causing rising sea levels and fueling more intense atmospheric activity. 

“Blue Acres has been a pioneering program,” said Robert Kopp, a climate scientist and professor at Rutgers University, calling buyouts a “very important tool” in how the state deals with the flooding repercussions of climate change. 

The program, which so far has benefitted mostly inland rather than coastal communities, is funded with federal money as well as a share of the state’s corporate taxes, providing a consistent infusion of money at a time of uncertainty about the future of federal disaster funding.

Courtney Wald-Wittkop, who manages Blue Acres for the state Department of Environmental Protection, said the program is an important solution for homeowners who have grown weary of repeated flooding. But deciding to give up a home and move away from the flood plain, she said, often takes time. “You have to give them space,” she said, to weigh the financial and personal costs of leaving a home with memories. 

She said the program is known for its novel approach of assigning a case manager to every applicant to help them sort through the issues. “It’s really important that we walk hand in hand with these homeowners,” said Wald-Wittkop.

The program’s goals, however, go beyond the needs of homeowners. The idea is to help reshape the community by returning properties to permanent open space, which can better absorb rain water than impervious surfaces such as concrete, asphalt and buildings. That open space, in turn, is managed—mostly with lawn cutting and brush clearing—by the municipality.

Wald-Wittkop said the program is evolving, and that she would like to make the process move more quickly, provide sellers with more housing assistance, especially outside of flood-prone areas and encourage more community involvement in what to do with the newly acquired open space. 

“We’ve tried to be as innovative as possible,” she said.

With its history of flooding, Manville is one of the towns that has benefitted the most from the state buyout initiative, with some 120 homes in the town sold to the state for about $22 million between 2015 and 2024. Another 53 buyouts are currently underway, according to Wald-Wittkop.

About an hour south, the city of Lambertville was hit hard by Hurricane Ida when a series of creeks overflowed in 2021, stranding residents and business owners in the popular tourist town wherever they happened to be when the massive downpour began. Hours later, residents emerged to stunning destruction. 

“The force of the water was just unbelievable,” recalled Mayor Andrew Nowick, who said 130 properties were damaged and about two dozen homeowners ended up submitting applications for Blue Acre buyouts. Three eventually accepted buyout offers, he said. 

The program, he said, can be attractive for sellers who are ready to move on but he said there was a lot of real soul-searching about the advantage of selling versus repairing homes that were filled with family memories. “These are all hard choices,” said the mayor. 

Incorporated in 1929, Manville was named with a nod to the Johns-Manville Corp., a now-defunct asbestos manufacturer with jobs that transformed the area from a farming community to a factory town. As Manville grew so did the rest of once-rural Somerset County, with more housing, industry and roads. The result was less farmland and open space to absorb the rain and more impervious surfaces that cause substantial water runoff and flash flooding. 

“It’s troubling today to see all the development that has gone on unabated,” said Onderko.

And when Manville floods, it is often epic.

In 1955, Hurricane Diane caused what was called the town’s “worst flood in history,” according to a special edition of the Manville News, which now hangs in Onderko’s office. “RIVER GOING DOWN; BE CALM!” screamed the banner headline. Then-Mayor Frank Baron urged residents not to panic. “You’re not forgotten, no matter where you live,” Baron declared. 

Onderko said getting rescued after Hurricane Doria in 1971 was surreal. Their oil tank came loose from all the water, and he recalled seeing the fuel mix in with the water that was flooding the basement as it approached the first floor. “It was something that you will never forget,” he said.

Later, the remains of Hurricane Floyd caused widespread damage in 1999, as did Hurricane Irene in 2011, but the town largely escaped the fury of Superstorm Sandy, which caused catastrophic damage to parts of New Jersey in 2012.

But then came Hurricane Ida in 2021.

Onderko still chokes with emotion when recalling that night in September 2021 when Ida came roaring through. “It was a war zone,” he recalled in an interview at the borough hall, which was inundated with two feet of water in that storm. “The water came so fast. It was a flash flood event. We were just lucky we didn’t have any loss of life.”

For hours, the mayor and rescue personnel went door to door, urging residents to leave. By the next morning, about 10 to 11 feet of water had flooded the central part of town and surrounding neighborhoods. Two homes and a banquet hall exploded from natural gas leaks, and emergency personnel could not even reach them.

“It took a toll on me,” said Onderko, recalling how he had trouble sleeping and felt “kind of powerless” because of the extent of devastation. 

Wendy Byra and her husband, Thomas Kline, had already moved to higher ground.

Their house had flooded twice and they decided to sell their home to the Blue Acres program. The sale was approved in 2015 for a $185,000 buyout. Byra said a number of their neighbors also applied for the buyout, but had mixed feelings about the amount of money they were offered. 

“A lot of people weren’t happy,” said Byra, recalling that some neighbors thought they should receive more money for their homes. Byra said she and her husband figured they would have a hard time selling on their own, so they accepted the buyout and moved to a home on higher ground, but still in Manville, where she grew up. 

Except when a major flood happens, Onderko said, Manville is a good place to live. So homeowners, even in the two parts of town known for flooding, can go years without having to deal with a water disaster. 

Onderko said residents had long relied on a mix of government help in rebuilding after flooding, but two years after Ida hit in 2021, the state said it would use federal funds only for Blue Acres buyouts of flood-prone properties in Manville. 

Onderko said he and residents were caught off guard by the change in policy. He also believes that elevation and repair remained viable alternatives for some of the houses. The buyouts take time, he said, and the town loses tax revenue from the properties sold via the Blue Acres program. “It doesn’t help the town to lose [tax] rateables,” said the mayor, who said the town also bears the cost of maintaining the open space.

Now in his third term as mayor, Onderko, who lives in a house on higher ground than his boyhood home, seems more like a property manager than municipal executive as he presides over a town that is a mix of neighborhoods. Some are on higher ground and do not flood, but others are in areas that get caught repeatedly in deluges. There, vacant grass lots left from demolished Blue Acres properties are interspersed with homes that have been elevated, repaired or are still in recovery mode. “It’s very frustrating,” said Onderko.

Looking to the future, the mayor said he believes many more homes will be at risk whenever the next flood happens. And Onderko does not sound especially hopeful about how that will go. 

“It’s going to take a miracle to try to save this town,” he said.

The post A New Jersey Buyout Program for Flood-Prone Homes Is a National Model first appeared on Association of State Floodplain Managers.

Through interviews with communities that had recently been provided flood hazard maps developed with 2D modeling, ASFPM found that, in general, local officials were not familiar with 2D modeling and had not received training on how to effectively use the results for managing development. The one exception was a community that became a Cooperating Technical Partner specifically to have more control over the mapping process.

ASFPM learned that the communities were provided maps developed with 2D models, including information on floodways, without clearly understanding the impacts or how to utilize all the data provided to them. To address this gap, ASFPM developed outreach materials to help communities understand how to use 2D modeling data to better manage development.

These new FEMA Risk Map resources include:

• 1D vs. 2D Modeling – Featuring information on the difference between one-dimensional and two-dimensional modeling
• Community Role in the Mapping Process – Offering suggested community involvement during the mapping process, and
• Managing Floodplains with 2D Modeling – Providing detailed guidance on how to best use the flood hazard information provided by 2D modeling.

The Managing Floodplains with 2D Modeling document provides details on how to use the 2D modeling results for managing development. Maps developed using 2D modeling often have evaluation lines that can be used similar to cross sections used in 1D modeling. Included in the guidance are recommendations related to accessing and storing copies of the modeling results, managing development using 2D model results, using evaluation lines and velocity results, reviewing development permit requests, and completing a no-rise analysis.

While these outreach materials should improve community understanding of the mapping process associated with 2D modeling and how to use the results for managing development, ASFPM determined that printed materials alone are not sufficient. A comprehensive training course on 2D Modeling for Floodplain Administrators is needed. ASFPM is in the process of developing this full training course, which should be available by the end of 2026.

The 2D modeling outreach materials were developed with support from FEMA Risk Management.

The post Bridging the Gap: ASFPM Releases Outreach Materials for 2D Modeling first appeared on Association of State Floodplain Managers.

The four policy pillars in the platform are:

• Increase local and state capacity to respond and recover
• Relieve the recovery and mitigation burden for low-income households
• Improve flood mapping and data inputs
• Invest in nature-based hazard mitigation

Over the last decade, Appalachian communities have experienced dozens of devastating flood events and scientific projections show that the region can only expect precipitation events to become more severe. The risk of flooding and the vulnerability of Appalachians to flood impacts are compounded by many factors. Historically, housing and communities in the region have been concentrated along waterways. A history of degraded and mining lands has increased flood risk. Disinvestment in rural communities across Appalachia has also resulted in less accurate flood maps, fewer early warning systems for rising water levels, and few resources to invest in flood reduction measures.

The Appalachian Flood Resilience Coalition is steered by the Amphibian & Reptile Conservancy, the Appalachian Citizens’ Law Center, Appalachian Voices, National Wildlife Federation, ReImagine Appalachia, and Wetlands Watch. More information about the coalition and their work can be found at www.appfloodpolicy.org.

The post Appalachian Flood Resilience Coalition Launched first appeared on Association of State Floodplain Managers.

The Challenge

Laikipia’s terrain and climate make it particularly susceptible to rapid-onset floods, which can devastate communities with little warning. Traditional flood mitigation infrastructure, such as permanent levees and dams, often proves inadequate or unsustainable due to high costs, maintenance challenges, and environmental impacts. Moreover, these structures can exacerbate land-use conflicts and disrupt local ecosystems.​

An Innovative Solution: Portable Flood Barrier

To address these challenges, Laikipia County has piloted the use of portable flood barriers—flexible, water-filled structures that can be rapidly deployed in anticipation of flooding events. These barriers are designed to conform to the natural contours of the land, providing temporary protection against floodwaters. Once the threat subsides, the barriers can be drained, folded, and stored for future use, minimizing their impact on the landscape and allowing for the quick return to normal land use.​

Community Engagement and Implementation

The success of this initiative hinges on strong community involvement. Local disaster response teams, in collaboration with the Water Resources Users Association (WRUA) and other stakeholders, have conducted training sessions and demonstrations to educate residents on the deployment and maintenance of the portable barriers. This participatory approach ensures that the technology is not only effectively utilized but also embraced by the communities it serves.​

Benefits and Early Outcomes

• Flood Mitigation: The portable barriers have effectively diverted floodwaters away from vulnerable areas, reducing damage to homes and infrastructure.​
• Water Storage: By capturing floodwaters, the barriers facilitate the replenishment of local water sources, such as ponds and aquifers, enhancing water availability during dry periods.​
• Environmental Preservation: The temporary nature of the barriers minimizes ecological disruption, preserving natural habitats and promoting biodiversity.​
• Cost-Effectiveness: Compared to permanent structures, portable barriers offer a more affordable and adaptable solution, particularly for resource-constrained settings.​

Relevance to Floodplain Management

Laikipia County’s approach aligns with the principles of adaptive and community-based floodplain management. By integrating flexible infrastructure with local knowledge and participation, the initiative exemplifies a sustainable model for addressing the complexities of flood and drought cycles. This case study offers valuable insights for floodplain managers seeking innovative solutions that balance risk reduction, environmental stewardship, and community empowerment.​

Conclusion

Laikipia County’s experience demonstrates the potential of portable flood barriers as a transformative tool in the face of climate variability. By turning the challenge of flash floods into an opportunity for drought resilience, the county sets a precedent for other regions grappling with similar issues. As climate change continues to intensify weather extremes, such adaptive and inclusive strategies will be crucial in building resilient communities.​

Omar Saleh is the managing director of WaveSave B.V., in the Netherlands.

The post Balancing Floods and Droughts in Kenya: Adaptive Water Management Through Portable Barriers first appeared on Association of State Floodplain Managers.

That’s why ASFPM has developed Model Ordinance Language for ASCE 24-24 Adoption—a practical resource designed to help state and local officials integrate these updated standards into their floodplain management regulations.

This resource highlights four priority areas for adoption:

• Referencing national consensus standards
• Expanding the Flood Hazard Area
• Updating elevation standards
• Strengthening dry floodproofing requirements

By providing clear ordinance language alongside implementation considerations, ASFPM is making it easier for floodplain managers and community leaders to translate national standards into local action.

Download the new resource

ASFPM remains committed to equipping our members with the knowledge and tools they need to reduce flood risk and protect communities nationwide. As a reminder, ASFPM members get free access to the interactive digital version of the ASCE 24-24 standard as part of their member benefit package.

The post New ASFPM Resource Provides Model Ordinance Language for Putting ASCE 24-24 into Practice first appeared on Association of State Floodplain Managers.

The FIM provides near-real-time, high-resolution, street-level visualizations of flood waters to assist NWS forecasters in issuing flood watches and warnings. FIM services are now available to twice as many NWS weather forecast offices with new coverage for:

• Hawaii and the West Coast;
• Portions of South Central Alaska, including the Cook Inlet, Kenai Peninsula, Copper River, and Prince William Sound watersheds;
• The Southwest and Great Plains; and
• The Great Lakes, and interior Southeast.

“Flooding is the most frequent severe weather-related threat, and our costliest natural disaster,” said David Vallee, director, Service Innovation and Partnership Division, NOAA’s National Water Center. “Expanding our FIM availability has been a game-changer in providing actionable, real-time information to emergency and water resource managers, and will expand the delivery of impact-based decision support services to our core partners who work to keep Americans safe and informed.”

FIM helps provide approximate spatial estimates of land area that is covered in water, based on modeled forecast river flows and current conditions, with detailed information on where flooding impacts may occur.

About NOAA’s Flood Inundation Mapping 

FIM services launched in 2023 for 10% of the country, serving portions of Louisiana, New York, Pennsylvania and Texas. In 2024, FIM expanded to cover 30% of the U.S. population, covering areas stretching from the Mid-Atlantic and eastern Great Lakes to the Lower Mississippi Valley and central Gulf Coast region, Washington and parts of Oregon in the Pacific Northwest region, and Puerto Rico and the U.S. Virgin Islands.

The expanded FIM maps are available on the National Water Prediction Service website and in several geographic information system applications. 

There are four unique maps available in near-real-time for the Lower 48 and parts of south-central Alaska:

• National Water Model derived hourly inundation analysis of current conditions
• National Water Model streamflow prediction based five-day inundation forecast
• NWS River Forecast Center (RFC) streamflow prediction based five-day inundation forecast
• Static “categorical” FIM (CatFIM) maps for select NWS River Forecast Points within the FIM domain

FIM services will be slightly different for Hawaii, Puerto Rico, and the U.S. Virgin Islands to capture the fast-response floods on these rivers and streams. As the precipitation forecasting models are different for these areas when compared with the continental U.S., a 48-hour forecast based on National Water Model streamflow predictions will be used to create FIM instead of the five-day flood inundation forecasts from the National Water Model and RFCs.

Looking ahead 

In 2026, FIM will be fully deployed in communities nationwide and available for 110,000 river miles near and downstream of NWS RFC forecast point locations. It will also be available for more than 3.6 million river miles covered by National Water Model forecasts. 

The post NOAA’s Flood Inundation Mapping Tool Expands to 60% of U.S. first appeared on Association of State Floodplain Managers.

Activities eligible for disaster funding 

The FY 2025 Disaster Supplemental Notice of Funding Opportunity is not just about rebuilding—it’s about transforming local economies after disaster, with an emphasis on improving communities’ economic outcomes and resilience to future disasters. This funding opportunity encourages broad-based local engagement and places special emphasis on projects that involve private industry in disaster recovery and economic renewal to ensure the maximum impact for taxpayer funding to support these communities. 

Applicants can choose from three funding pathways based on their recovery stage, capacity, and long-term development vision.  

• Readiness Path: Non-construction projects to build local capacity and prepare for future implementation projects. Readiness projects include funding for recovery strategies, disaster recovery coordinators or other capacity building activities, and pre-development expenses. Grant amounts are expected to range from $250,000 to $500,000. 
• Implementation Path: Standalone construction and non-construction projects that help communities recover from major disasters and advance recovery and growth, improving economic outcomes. Grant amounts are expected to range from $2 million to $20 million for construction projects and $100,000 to $5 million for non-construction projects. 
• Industry Transformation Path: Coalition-led, multi-project portfolios that transform regional economies through industry development. These grants can fund a mix of construction and non-construction projects. Grant amounts are expected to range from $20 million to $50 million.

Projects must be located in, primarily serve, or demonstrably benefit one or more communities in areas that received a major disaster designation occurring in calendar years 2023 and 2024. Check eligibility here

Deadlines vary

Readiness and Implementation grant applications will be accepted and reviewed on an ongoing (rolling) basis until funds are exhausted or the Notice of Funding Opportunity is canceled. Industry Transformation grant applications are due on Tuesday, March 3, 2026 at 5:00 pm Eastern Time. 

Eligible applicants include:

• State, local, and Tribal governments 
• Economic Development Districts 
• Institutions of higher education 
• Economic development organizations
• Public and private non-profits working with local government 
• Public-private partnerships for public infrastructure

To learn more about the program, including how to apply, visit the EDA FY2025 Disaster Supplemental Grant Program page. 

The post EDA Announces $1.45 Billion in Disaster Recovery Grants for FY 2025 first appeared on Association of State Floodplain Managers.

Those interested in joining the committee should apply online here: Committee Application Form | ASCE. Select “SEI” from the “Institute or Committee” dropdown menu, then choose “Flood Resistant Design & Constructions (ASCE/SEI 24).

The deadline to apply is August 18, 2025. Selected committee members will be notified shortly after that date.

The goal of the update is to align with changes made to ASCE 7-28 Chapter 5, to pick up New Business Next Cycle items, to continue updates that were proposed but not incorporated in the ASCE 24-24 cycle.

Objectives

• To provide an up-to-date reference for practicing engineers, architects, authorities having jurisdiction and floodplain managers consistent with ASCE 7 and FEMA Technical Bulletins
• To update coating requirements and corrosion protection for materials
• Edit definitions as required for consistency among codes and standards
• Clarify AO zones with relationship to the building footprint to avoid misinterpretations in the enforcement of provisions
• To consider proposed changes to Flood Design Class of healthcare facilities suggested by the ICC healthcare committee
• Review requirements for Accessory Structures and Functionally Dependent Structures
• To consider current datasets available

As a strong supporter of Flood Resistant Design and Construction, ASCE/SEI 24-24, ASFPM is providing members with free digital access. Learn more

The post ASCE/SEI Seeks Committee Members for ASCE 24 Flood Standards Update first appeared on Association of State Floodplain Managers.

The video was taken at the Lane Valley Road Bridge about six miles upstream from the USGS stream gage at Comfort, TX (08167000). Figure 1 below shows the change in flood stage and discharge from July 2-7 at this stream gage.  On July 4^th the river stage rose 32.5-feet (10-meters) in 2-hours to a peak flood discharge of 177,000 cubic feet per second (cfs)…that’s incredible!

But historically, what magnitude of peak flood discharges have occurred in this region? Research by Asquith and Slade (1995) explored the extreme flood potential for Texas rivers by evaluating peak discharges from 832 sites in natural basins in Texas for over 100 years. They developed extreme peak flood discharge envelope curves for hydrologic regions in Texas by plotting peak discharges and associated contributing drainage areas (see Figure 2 below). This curve defines the upper limit of past peak discharges for a given drainage area. The stream gage on the Guadalupe River at Comfort, TX has a contributing drainage area of 839 square miles and in this hydrologic region the envelope curve equation presents a peak discharge of about 677,000 cfs. In other words, there is the potential for a flood to occur at this location on the Guadalupe River nearly four times higher than the peak flow from the recent July 4^th flood event.

These peak flood events seem massive—and they are—but when viewed in the context of floods that have occurred at this location over the past 125 years, other stories emerge. For instance, Figure 3 below shows annual peak streamflows at this stream gage plotted on a water year basis (Oct to Sept) with their relationship to statistical Annual Exceedance Probability (AEP) flood events. The highest annual peak discharges have consistently occurred in the June to August timeframe — during the summer months — and the July 2025 flood event was the third highest peak discharge at this stream gage since 1900 and 1978, and it was less than a 1% AEP event (100-year flood event). However, in many places along the Guadalupe River, the flooding was observed to exceed the mapped 1% AEP FEMA floodplains (Inal, Charalambous, and Vinick 2025). Having mapped river and coastal floodplains for FEMA flood insurance studies, I realize that these flood hazard boundaries represent a “snapshot in time” and can often be invalidated quickly as floods continue over time.

The 677,000 cfs peak discharge from the peak flood discharge envelope curve described above is “off the chart” below and assigning an AEP to this event by extrapolating the AEPs shown on Figure 3 is highly uncertain. A recommended optimal limit of credible extrapolation for flood discharges estimated from regional streamflow data (such as the extreme peak flood discharge envelope curves) is a 0.1% AEP  event or a 1,000 year flood (Utah State University and U.S. Bureau of Reclamation 1999) and based on an extrapolation of the 4.0% to 0.2% AEP peak discharges this is estimated to be 450,000 cfs. But can this extreme flood ever happen? Statistically, there is an 8% chance that this 1,000-year flood could occur sometime over the 78-year life expectancy of a person in the U.S. (CDC 2025) (National Weather Service 2025).

From Data to Decisions
Now that we have looked at the data, what are some recommendations? Early warning systems? Yes, just do it. Here in Oregon, we have sirens to warn coastal residents in populated areas of potential tsunamis. Also, a recommendation I made back in 2006 is pertinent here. I was involved in the first evaluation of the FEMA National Flood Insurance Program and authored Chapter 11 in the study report “Assessing the Adequacy of the National Flood Insurance Program’s 1 Percent Flood Standard” (Water Policy Collaborative 2006). One observation I made in Section 11.4.1 was that our use of a national uniform 1% AEP flood event “ignores the significant regional variation of floodplain…processes” and “additional considerations should be given to the climatic and geographic characteristics of a flood source” and “a higher standard may be suitable where intense…precipitation events can occur”. I used a graphic showing a plot of peak discharge versus drainage area for the entire U.S. derived from 22,063 streamflow stations, similar to the peak discharge envelope curve for Texas described above, to encourage the use of data more conservative than the 1% AEP flood standard.

So, what should we do? Let’s learn from the past and move forward tailoring our flood hazard mapping to better manage flood risk to people and property. And for our most precious land uses — such as summer camp bunk houses — let’s keep them out of the 1,000-year floodplain, knowing that floods even greater than this one could potentially happen in one’s lifetime.

Kevin Coulton, PE, CFM is a consulting engineer, writer, and photographer living in Portland, Oregon. He can be reached via email at kevin.coulton@gmail.com.

The post Let’s Keep Our Most Precious Land Uses Out of the 1,000-Year Floodplain first appeared on Association of State Floodplain Managers.