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Hernando Today

Preliminary Flood Maps Up For Public Review

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By TONY MARRERO Hernando Today

The Tampa Tribune

Published: September 25, 2008

BROOKSVILLE - The revised versions of the updated flood maps that set off a wave of controversy last year will be up for review in the coming weeks.

The Southwest Florida Water Management District says its improved methodology is producing higher-quality, better-detailed maps. So far, that has resulted in fewer acres the county deemed as floodplain compared to the maps released last fall, said Mark Hammond, director of resource management of the water management district known as Swiftmud.

"We definitely have fewer people affected," Hammond said.

Swiftmud will host workshops throughout the county to give the public a chance to look at the flood maps.

The first is slated for 3:30 p.m. to 7:30 p.m. on Oct. 1 at the District Headquarters, 2379 Broad St., in Brooksville. The workshop will focus on the Powell and Lizzie Hart watersheds. The former is south of downtown Brooksville; the latter extends from north of the city limits into Citrus County.

The Flood Insurance Rate Maps, or FIRMs, try to predict as accurately as possible how much of the county would be underwater in a hundred-year storm event. The maps are used by insurance companies to determine whether a property will require flood insurance.

That's why the outcry was so loud last year when preliminary maps showed a substantial increase of floodplain acreage compared to the last maps created in 1984 by the Federal Emergency Management Agency (FEMA). Many landowners who thought their property had little to no risk of flooding looked at the map and found their piece of the county covered by a blue blob denoting floodwater.

Swiftmud agreed the methodology needed to be improved. The process to update the flood maps is ongoing, but about half the county's 22 watersheds are nearly complete, Hammond said.

The flood plain has expanded in all of the watersheds, and some of that expansion is still "significant," Hammond said.

But the overall expansion is considerably less pronounced than the maps released last year had indicated, according to changes in the 11 or so watersheds that are nearly finished, Hammond said.

In those watersheds, the 1984 maps showed about 30,000 acres in a flood plain. The updated maps released last year had about 65,000 in a flood plain; the revised maps have about 45,000 acres, he said.

Among the methodology changes that are producing better maps, according to Hammond:

• The flood models now take into account a process called infiltration - the rate at which water is absorbed into the sandy soil prevalent in Hernando County, especially on the western and eastern regions.

The failure to account for infiltration was among the biggest concerns that developers and landowners raised last year. The change has definitely caused flood elevations to shrink, Hammond said.

• The models used in most watersheds use a one-day rainfall event to predict flooding, whereas the maps released last year use a multi-day event.

Swiftmud had argued that using the one-day event generally underestimates flooding effects. But further review showed the one-day event is appropriate except where there is data about past multi-day rainfall events that can be factored into the models, Hammond said.

• The new maps include updated topography data compiled by Hernando County and Swiftmud last year using laser-guided radar system.

The new data, collected from an airplane, didn't cause widespread changes to the maps, but was especially helpful in more localized cases where new construction may have altered the lay of the land in an area, Hammond said.

• A new peer-review system has additional engineering firms checking the work of Swiftmud's consultants. The district's Environmental Resource Permitting advisory board also is weighing in on the results.

• And the maps include a higher level of detail, using historical data such as photographs of flooded areas. That kind of evidence "is a lot easier for the public to understand," Hammond said.

The upcoming workshops are the chance for the public to provide more such anecdotal evidence, he said.

The extra work has added to the cost of the project. What had been listed as a $5.3 million tab has increased to $6.1 million, plus the roughly $600,000 cost to acquire the topographical data and the price tag of the additional peer review, which cost Swiftmud $1 million for the work in Hernando and two other counties.

Swiftmud hopes to have at least some of the maps submitted to FEMA by the first of the year. FEMA has its own appeals and process that could take as long as two years, Hammond said.

Reporter Tony Marrero can be reached at 352-544-5286 or lmarrero@hernandtoday.com.

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