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Compensatory Flood (FRINGE) Storage
Posted by brad-ott on February 9, 2020 at 2:23 pmWhen did this become a thing that began to be enforced?
16 years ago when I last was involved in this sort of situation, compensatory flood (WAY) storage was the only conversation that I recall.
a-harris replied 4 years, 2 months ago 6 Members · 8 Replies- 8 Replies
Referring to a No-Rise Certificate?
I have never heard of such a certificate, but thanks.
I am referring to a single family development on the same property on the other side of the creek 16+ years ago being allowed to fill in the fringe. The local municipality is now requiring compensatory flood storage for any fill in the fringe on the remaining side of the creek, effectively killing the same type project.
They say, what was allowed then, would not have been allowed today.
I want to be careful to draw a clear distinction here between the following terms:
floodway
flood fringe
Had the same thing here a couple of years ago. Resolved by removing the same yardage as was filled in the form of a boat ramp. Worked well for all.
What we typically refer to as the floodway gets expanded to include the fringe areas as well when bureaucracy wants to dissuade people from doing anything where floodwaters could be involved. About 25 years ago we hit this problem with a city who did not want a certain (unfavored) business man putting an extension on his insurance office building. The 500 year flood coloration on the FIRM barely touched the south end of his existing building and he wanted to add on to the south. Roughly 20 feet by 30 feet of concrete with about two inches of depth of potential flood waters. When the river would grow to touch his building, the far side of the river would be nearly two miles distant across prime farm ground on the far side. I attempted to expose the city fathers to the term “infinitesimal” but they really didn’t care. They didn’t like the guy.
My first introduction to the no-rise certificate involved a case of river gravel being excavated from within the river channel. The argument was that by introducing a large hole in the bottom of the river the flow characteristics would be altered in such a way that flow would be impeded causing a slight rise in the flood level upstream. They also did not like the creation of a ramp area so dump trucks could easily drive down onto the gravel beds during low flow to haul away the gravel. This was a cut back into the bank area, not an obstruction in the channel itself.
I believe you have encountered a case of bureaucrats discouraging any changes within the entire flood zone. Removing obstructions (dirt, trees, concrete, etc.) near the planned project that equate to the same or larger volume than that required to achieve the client’s goals may still be seen as a detriment to the flood zone, in their opinion. They believe they have no authority higher than themselves, so do as they say or end up doing nothing.
Some days life sucks. Common sense is not always terribly common.
FEMA sets the minimum requirements and local jurisdictions are free to set higher standards. Doing so is supposed to reward the entire jurisdiction with lower flood insurance rates.
In the county where I do most of my work, they have chosen to regulate to the 500yr and minimum floor elevations are typically one or two feet higher. We can fill half the width of the flood fringe but God help you if you put a shovel of dirt on the other side of that arbitrary line.
Thanks for these helpful responses, fellas.
Been in the NFIP regs for a long while. The trouble is the local CFMs follow the County CFMs, follow the State CFMs, follow the Federal CFMs who are subcontracted. There’s a bit of difference in the interpretations and changes as the information is handed downstream.
I was once required to provide compensatory storage for a coastal floodplain by the local Conservation Commission. Absolute idiocy. I am now often required to provide stone trenches when proposing impervious surfaces to make sure the floodwaters will soak into the ground. The funny thing about sand is that the groundwater rises with the floodwaters and those stone trenches will be full by the time the water passes over the surface. Absolute idiocy.
Unless your client needs structural fill or some flavor of dirt that is not already on the property, propose to regrade with nothing coming in or going out. Then you are pretty safe to say that you have meet the compensatory storage requirements.
Having any detainmet system in place will cause flooding in new areas
When they are well designed they will slow erosion better and slow the drain waters as they head downstream
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