New federal maps identifying the flood hazard here show much more of Miles City, Mont., is in the 100-year flood plain than do the maps being replaced.
The draft maps have three-fourths of the city in the 100-year plain, up from one-third on maps produced in the early 1980s. Property in the 100-year flood plain is deemed to have 1-in-100 chance of flooding in any given year, a classification that can heighten insurance rates and restrict construction and remodeling.
The Corps of Engineers recently released the drafts and will take public comment on them before preparing final maps that Mayor Joe Whalen expects will be complete by year’s end. Whalen has warned that calls for map changes based on economic impact or anything else besides geographic or scientific data are unlikely to be effective.
In the wake of Hurricane Katrina, the corps is reevaluating flood risks in many communities around the country.
Whalen said a report on flood risk here identifies as the greatest threat a potential ice jam that would form in the Yellowstone River and then block the mouth of the Tongue River, causing the Tongue to back up and flood the city.
The Corps of Engineers and the Federal Emergency Management Agency do not recognize dikes now in place. Evaluators found fault with material used when the dikes were built in the 1920s and 1930s, and with vegetation since allowed to grow on them.
The flood news puts Miles City at a disadvantage as the city prepares for growth and the housing needs that involves, Whalen said. Building away from town raises the costly prospect of providing services to relatively distant locations, he said.
“The Corps of Engineers is encouraging Miles City to think creatively about its relationship to the rivers,” Whalen said.
He said rough estimates for the cost of a dike that would protect the entire city range from $20 million to $30 million. Dikes to protect just parts of the city also are a possibility. Other options include dike structures with amenities such as marinas incorporated in the design.
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