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Denver • New research shows floods like the one that ransacked northern Colorado two years ago, killing 10 people, might be more common than previously thought — and that could require more homeowners to get flood insurance and trigger more stringent construction rules.

The September 2013 flood caused $3 billion in damage to neighborhoods, highways, farms and oilfields. Nearly 2,000 homes were damaged or destroyed, many in small mountain towns.

Early, rough estimates of the flood indicated it was a 1-in-500 event, meaning the chances of such a deluge in any one year are 1 in 500.

But recently completed studies of the Big Thompson River, St. Vrain Creek and other hard-hit waterways show it was mostly a 1-in-100 event, said Kevin Houck, chief of watershed and flood protection for the Colorado Water Conservation Board.

If a 1-in-100 flood can cause that much havoc, then homes, roads and other infrastructure are more vulnerable than previously believed, he said.

A 1-in-100 flood is sometimes called a 100-year flood, but experts say that's a misnomer. The ratio refers to the chances of such a flood occurring in any single year, based on historical data. A 1-in-100 flood could happen more than once a century.

The Federal Emergency Management Agency is reviewing the new Colorado data and will likely use it to revise its maps designating flood plains — areas that are most prone to flooding, said Ryan Pietramali, FEMA's regional chief of risk analysis.

The maps are important because anyone who has a federally insured mortgage and who lives in a FEMA-designated 1-in-100 flood plain must buy federal flood insurance. If the new maps show a bigger flood plain, more people would have to buy coverage, which averages about $1,300 a year for homes in high-risk areas.

Houck said the reason for the revised expectations isn't climate change or weather patterns but improved data. The previous expectations were based on 30- or 40-year old studies that used methods now considered obsolete. They also had less history to draw from.