Stormwater
Floodplain Mapping Issues Addressed

Aug 1, 2007

Floodplain Mapping Issues Addressed

As many citizens are aware, the City is undergoing an update for its floodplain mapping.  This mapping project is to establish the limits of what is commonly referred to as the 100-year flood as part of the NFIP (National Flood Insurance Program), of which the City is a participant.  The maps used are referred to as FIRM (Flood Insurance Rate Maps), which delineate the special hazard areas and risk premium zones for a community.  This project is not unique to Madisonville, Hopkins County or even Kentucky, but rather part of a Map Modernization program affecting over 20,000 communities nationwide.

A private engineering consultant, not the City, conducted the recent mapping.  The client in this case was the federal government, specifically, FEMA (Federal Emergency Management Agency), a division of the U.S Department of Homeland Security.

The City's current FIRMs were issued in 1986.  The difference between these maps and the proposed maps are the result of several factors, such as these listed below:

• Additional available data, especially in the form of aerial topography maps.
• More sophisticated computer modeling.
• Changes in weather patterns.
• Additional development, which results in increased stormwater runoff.

The rain event used in the mapping was based on the area's 100-year flood, which translates to a 7.77-inch of rain within 24 hours.  To understand stormwater issues requires an understanding of the different rain events.  For a 100-year flood, it is not, as some may believe, a flood that occurs once every 100 years.  Instead, it is the rainfall event that has a 1% chance of occurring in any one-year.  While this rain event would statistically occur once every 100 years, it could, in fact, occur in back-to-back years, or even twice within the same year.  To check the validity of the values used in the mapping, consider a rain event on March 2, 1997, where Madisonville recorded a 10.25-inch rainfall for the 24-hour period.

In the more recent storm of June 28, 2007, the data was compared with projections and determined to be a 10-year event.  By the definition outlined above, this would mean the amount of rainfall for that event would statistically have a 10% chance of occurring in any one year.  The rainfall data was averaged from several sources.  More or less rain could have occurred depending on the specific location, which was especially true during this event.  Areas where people could not recall previous flooding experienced significant water, while areas that have typically had standing water several times a year had no flood problems.  This was a very localized event, centered in the downtown urban area.

In some cases, property owners have challenged the results of the model.  To do this, private surveyors would collect elevation data to refute the findings by FEMA's consultant, and if upheld, a Letter of Map Revision would be issued to alter the map.  This option has always been available to property owners, even under the older maps, but has been especially utilized with the revised maps of the Map Modernization program.

The NFIP is a pass-through program, where the federal government, not private insurance companies, underwrites flood insurance.  The private insurance companies' role is limited to writing the policy, typically as a service to their existing policyholders.

In the 1930's, insurance companies started to remove flood insurance from their offerings, because of the high risk of insuring properties from floods.  Consequently after, numerous floods in the 1960's the federal government decided to assist property owners that were located in harm's way and began the NFIP.  Insurance actuarial tables, structure ratings and site conditions that would normally be considered would still be applied.  As an example of the application of actuarial tables, consider that a home has a 26% chance of being damaged by a flood during the course of a 30-year mortgage, compared to a 9% chance of damage by fire.  Insurance rates reflect this increased risk.

Currently, the City is waiting for the results of local appeals and protests as well as a Letter of Finalization from FEMA.  The next step in the process would be for the City to adopt the proposed maps, to replace the 1986 maps.  If the City fails to adopt these revised maps, the City will be placed on probation with the NFIP.  This means that people who have purchased flood insurance will be charged an additional fee.  If the City continues to refuse, the City can be suspended from the NFIP, which would also suspend the City from federal disaster relief for any disaster, not just floods.

No one wants to pay money for something they don't feel they need, and especially when they are being required to do so by someone else.  The City understands this point and empathizes with its citizens.  As both a City and as individuals, we have been put in similar situations.  We wish there were options other than opting out of this federal program, however, the program is seen as necessary for the community as a whole.  To assist the citizens and community, the City and Hopkins County have cooperatively applied for a Flood Mitigation Grant that will further study the flood risks and what measure can be employed to minimize the effects.

There is a FEMA website at www.floodsmart.gov where you can find more detailed information on the subject.