Flood Zone Discussion – Planning Board Hearing Follow-up

Last night’s Planning Board Public Hearing on the flood zone adoption was interesting to say the least.  It illustrated some of the issues we are trying to address and educate Dennis residents about. In particular, the nature of the changes taking place.

There have been some issues regarding the extent of flood zone expansions raised in Plymouth County. We should leave that discussion to those county officials. Here in Dennis, most of the changes simply carry the flood elevations from the 1986 and 1992 maps through to proper ground elevation contours. This is about 90% of the changes taking place. Where we have increases in flood water elevations, it is generally increases of about 1 foot. Most of our velocity zone changes are small changes as well, and many are the result of modelling of erosion potential. To place this in perspective, all one has to do is look at Dr. Bottero Road and Chapin Beach at the erosion that has taken place in recent years, without a 1% storm.

In the Scott Tyler Road neighborhood off of the Weir Creek, we have a good example of how this is affecting properties both positive and negative. First, the flood map for this area:

Scott Tyler OriginalThis map illustrates the existing A zone (Blue) and the A zone as it will exist with the changes to take effect in July (cross hatched). Base Flood Elevation under the new maps is 11 feet above sea level, existing is an A10 with Elevation 12. Comparing the NGVD29 and the NAVD88 information for this area, we come to a conclusion that there is no change in actual water levels in this area, the difference in elevation between the two analyses is simply the difference between old ground elevation and the new ground elevation. The maps in this area matches base flood elevation to accurate measurements of ground elevation based upon the FEMA LIDAR ground elevation measurements.

The map above illustrates ground elevation contours in 2 foot intervals based upon the town of Dennis LIDAR fly-over conducted for our own GIS efforts. If you look closely, for the most part the Base Flood Elevation splits the difference between the 10 foot and 12 foot contours from our fly-over. The map illustrates areas being added to the flood zone based upon matching flood elevation to actual ground measurements (red below).

Scott Tyler Expand


And areas being removed from the flood zone (red) on the map below.

Scott Tyler Reduction


The property in question last night has a reduction in the flooding of the property. However, it looks to still include parts of the structure in the flood zone.

After the meeting we continued the discussion, here are a few things that need to be explored for these property owners:

  1. They have never been required to buy flood insurance. This raises a question as to whether they should be able to acquire a Preferred Risk Policy if they choose to buy flood insurance now. They have been in a flood zone since the 1986 maps came out. Section 3 of HR 3370 suggests that grandfather rates and Preferred Risk Policies be protected for homeowners who did not have flood insurance and were not required to buy flood insurance. These homeowners should pursue this issue with their insurance representatives after HR 3370 is signed into law this week.
  2. The homeowners were advised to get a survey done of their property. Not only will this be needed to know the correct flood risk of the property and thus flood insurance rates, it will also allow the property owner to know what mitigation efforts they might need to undertake.
  3. After completing the survey, the property owner should consider taking steps to mitigate flooding. The backyard of the property is at about elevation 8. The Base Flood Elevation is at 11 feet. The property owner should look into filling the backyard and bringing it up to, or above elevation 11. While it will not support a Letter of Map Amendment, it will allow the property to seek a lower insurance rate due to having taken mitigation efforts. Additionally, they should look into lifting any utilities in their basement to above base flood elevation. depending upon what they find in their survey, this could, possibly, still be accomplished without moving the equipment out of the basement.
  4. Finally, they should take the necessary steps to make their basement flood resilient. In doing this, there is a special provision in HR 3370 dealing with reductions in rates for flood resilient basements.



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