help reading flood zone map 1

[delagina]

In the attached the legend says zone AH has a flood depth of 1' to 3'.
But when I look at the map, I can't find zone AH.
I only see Zone AE (base flood elevation determined).
Zone AE does not show high the flood is.
This confuse me because almost all the maps I look at only has Zone AE.

How do I correctly read this map.

 

[cvg]

Zone AE does not show high the flood is

Zone AE has base flood elevations determined, so it does show how high the flood is. for instance the Houston ship channel is clearly at a flood stage of 18 feet. I don't believe there are any Zone AH "ponding areas with a depth of 1 - 3 feet" shown on this map or any other types of flood zones.

 

[delagina]

cvg,

on the attached I see the 18' you were saying but right next to it is wingate and mobile street that does not have flood elevation.
if I have small equipment in that area, I don't have to raise the foundation (except for the standard 6" above grade).

thanks,

 

[delagina]

cvg,

I do a lot of foundation equipment for small stations in many places and want to make sure I account for flood level,
like raising the foundation top of concrete above flood level.

is this fema map the resource I should look at or are there other map I should look at?

thanks,

 

[cvg]

you are referencing a Flood Insurance Rate Map (FIRM). according to FEMA, this is "The official map of a community on which FEMA has delineated both the special hazard areas and the risk premium zones applicable to the community." it is intended for use in the National Flood Insurance Program. Using it to set your equipment elevations is a good first step, but may not be adequate. In this case, the elevations were established with a detailed study. So the hydraulics are "good". Some would argue that the hydrology may not be so "good". The map is not intended to show 100-year flood elevations below a foot in depth. So your 6 inch high equipment pad on Wingate Street might be sitting in 11 inches of water. I would suggest that a minimum of 6 inches might not be adequate in every case and you should probably "ground truth" your site before finalizing a design.

 

[delagina]

I'm not familiar with how you "ground truth" the site. Can you explain more the procedure.


Thanks,

 

[cvg]

go out to the site and observe the drainage patterns. look for signs of obvious drainage problems or infrastructure that might have been built to handle flooding through your site. you should be able to get a feel for any potential problems.

 

[ashtree]

Maybe talk to people as well. People next door, or down the street. Use the information they give you cautiously but its another potential source of information.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[delagina]

are you saying there is no map aside from fema link i posted earlier that has base flood elevation?

going to site is not an option most of the time. besides that looks unreliable checking for flood signs.

 

[cvg]

I'm not saying there is no other data on flooding besides a FEMA FIRM on a particular site, but you will have to do the research to find any better information if it exists or do your own analysis.

If you cannot go out to the site and look around, or have it surveyed, than you should be very conservative in your design. It may be unreliable, but sitting at your desk and not gathering any field information is more unreliable.

 

[delagina]

The site is almost always surveyed but I only get topo points for grading the site. I've never received any flood elevation from survey. Are you saying the surveyor can have this flood elevation information?

 

[cvg]

no, I'm saying the surveyor can provide the topo so you can do the analysis

 

[delagina]

I usually only do small sites. when I grade the site I just slope it 2% towards existing ditch or I create a ditch connecting to existing. But I don't know if the whole small site could be flooded even with ditch. If I have information that the whole site say has 2' flood elevation then I can raise my foundation or even the whole site 2' above natural grade. But I don't know where to get that information aside from FEMA map

 

[cvg]

so how do you get your grading and drainage permit without doing any analysis? You just can't rely on FEMA to do that for you.

 

[delagina]

i only do small rectangular sites.. i haven't done anything complicated nor anything requiring any permit..

 

[cvg]

well, most cities do require permits. Houston does

https://edocs.publicworks.houstontx...ng-permits-for-excavations-and-fill-form.html

 

[delagina]

I already told you the projects/sites I worked on so far didn't require me prepare documents for permit.
I have done a dozen of more site grading and none of those I was required to submit or prepare documents for permit.
Most of the sites I do are in open space in the middle of nowhere.

 

[delagina]

I also work in industrial industry not residential.