“Base Flood Elevation – Zone A”
In the Blue Water area there are two prominent Special Flood Hazard Areas (SFHA) defined on the Federal Insurance Rate Maps (FIRM) that indicate the flooding extents of the 1% chance flood event.
SFHAs marked as Zone AE are the result of a thorough engineering analysis using somewhat sparse, yet survey grade data of the character of the flood source (river, drain, lake etc.). These areas have specific elevations that are associated with the 1% chance flood event and therefore the determination of whether a particular structure would be affected by this event is a relatively straight forward exercise. SFHAs marked as Zone A are a different story altogether.
For any areas designated as Zone A, there has not been a detailed study completed of the flood source using ground data. Therefore, specific elevations cannot be determined. However, the civil engineers tasked with determining the flood extent of a 1% chance flood event can make educated estimates and predictive models based on information that does exist. These potentially unrelated data sources, like USGS quadrangle maps, photogrammetric mapping, and LIDAR data, can be combined by engineers to help determine relative differences in topography.
As an example, suppose the data source is only accurate vertically to the nearest 5 feet. In a particular area the USGS map shows that there is a 5- foot drop in elevation for a creek over three miles. One can make the assumption that the rate of fall is consistent over that three-mile stretch. With no other source of data, that is a reasonable assumption to make. However, if some survey data were included in the analysis it could uncover that there is a ½ mile stretch where the creek falls 3 feet and the rest is extremely flat. This difference will have an effect on the modeling and on the actual extent of the SFHA.
This scenario can be a problem for a potential home buyer. The mortgage lender is requiring their client carry flood insurance due to the fact that the FIRM shows the house, or even just a part of the property, is within Zone A. For the lender, it is important that the house be covered by flood insurance because it is the collateral on the loan. The quoted premium, around $2,500.00 per year, is a deal breaker for the buyer. We know that the extents of Zone A shown on the map are the result of some educated yet undeniably imprecise estimating. We don’t know what the elevation of the 1% chance flood height is for this same reason. How can BMJ Engineers & Surveyors (BMJ) help this situation?
Over the lifetime of this federal program BMJ has developed a very cost effective and helpful method. We:
Review our historic data in the same area from previous submittals to FEMA
Obtain conservative estimates from the Michigan Department of Environmental Quality (MDEQ)
Densify or augment data for submittal to the MDEQ for estimate refining
The next few installments will cover the particulars of these three steps, but if you find yourself in this situation, don’t wait, call BMJ now for a free consultation and quote.
