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A national nonprofit’s newly unveiled “National Flood Risk Assessment” suggests the heart of North Platte has scattered pockets more susceptible to rain-induced flooding than others.

Its authors stress that their work doesn’t mean North Platte was wrong to fight for 14 years to remove citywide flood-insurance mandates.

But two of them said the First Street Foundation’s project aims to further improve awareness of past, present and future flood risks.

For North Platte, that includes fully accounting for flooding risks from heavy rains — with or without Rocky Mountain river runoff — and its low spots where “there’s nowhere for (water) to go,” said Ed Kearns, chief data officer for the Brooklyn, New York-based foundation.

Its searchable “Flood Factor” webpage (floodfactor.com) could help property owners decide whether to buy flood insurance on their own, said Jeremy Porter, director of research and development.

“From an organizational standpoint, we are making this data available so that property owners can make the best decisions about how to protect themselves,” Porter said.

He and Kearns discussed their project with The Telegraph Tuesday in the context of North Platte’s long struggle to reverse a 1979 federal ruling placing its traditional residential areas in the “100-year flood plain.”

That decision triggered a damaging Federal Emergency Management Agency requirement that property owners between the North Platte and South Platte rivers had to buy and maintain federal flood insurance.

North Platte leaders challenged that, based on the valley’s broad, flat terrain and gentle slope and their experiences with rain and the rivers.

Their victory was finalized last October, when FEMA announced the last of four map revisions since 2006 based on more up-to-date scientific information. It took effect in February.

Though some properties inside city limits remain in the 100-year flood plain, virtually all the city’s historic footprint between the rivers has been moved to the 500-year flood plain.

The terms reflect the estimated probability of significant flooding in any given year — respectively, a 1% chance in the 100-year zone and an 0.2% chance in the 500-year zone.

Jim Hawks, who retired in May as North Platte city administrator, led the campaign to update FEMA’s maps during his 16 years in the job.

Hawks, who is on a post-retirement trip, was unavailable for comment on the First Street report. He is also a former Lincoln County surveyor and highway superintendent.

The nonprofit’s report and Flood Factor tool, both released Monday, cites open government data, historic information, decades of research and projections of likely environmental changes for the “lower 48” U.S. states.

For interior states like Nebraska, Porter and Kearns said, their model differs from FEMA’s current approach by factoring in not just river runoff but also flood risks from heavy rains.

Doing so, they said, shows 337 properties inside North Platte’s city limits with a 1% annual risk of significant flooding, compared with 118 in the latest FEMA map from February.

Even First Street’s higher number, however, represents only 3.2% of North Platte’s 10,471 properties. FEMA’s current number is 1.1% of the city’s total.

Those using the Flood Factor tool can search for flood risks by their community’s name, ZIP code or individual address.

Satellite-driven maps within the tool depict only a handful of moderate- to higher-risk property clusters between the two Plattes.

Most within city limits sit closest to the rivers or south of Interstate 80, areas where FEMA’s 100-year flood plain designation persists.

Though First Street’s model also projects flood risks 15 and 30 years from now, it shows North Platte’s number of at-risk properties slightly declining over that time, Kearns said.

A Nebraska Department of Natural Resources engineer said First Street’s project has limitations but can be useful in raising public awareness of flood risks.

“It would be good for planning and mitigating (risks) if a community wanted to do something,” said Shuhai Zheng, DNR’s division head of engineering and technical services.

“But in the meantime, FEMA maps are still the ones to use to determine flood risk.”

Alan Lulloff, chief scientist of the Association of State Floodplain Managers, agreed but also said FEMA’s maps — as North Platte knows — have long been a work in progress.

His organization, based in Madison, Wisconsin, was founded around the same time as FEMA’s 1979 North Platte ruling to push for ongoing improvements in the agency’s mapping.

At that time, U.S. Geological Survey “topographical” maps of an area’s terrain were “kind of the best data we had at the time” to do flood-plain maps, Lulloff said.

But that information wasn’t refined enough, and manually transferring it from topographical maps to flood-plain maps caused errors, he said.

FEMA’s funding and digital tools have greatly improved, Lulloff said, but it still has mapped only about one-third of floodplains along the nation’s rivers and coasts.

That said, it now has “a very vigorous vetting process communities go through to ensure the community has some involvement and say on the mapping that’s developed,” he said.

First Street’s model, Lulloff said, needs more such vetting but uses data and techniques his group supports using to keep improving flood-risk assessments.

Kearns said First Street shares that goal, even as it tries to give people more tools to judge whether building or buying a particular structure makes sense.

“We have the tools and technology now to at least raise the flag” about new concerns, he said.

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