June 11, 2016 Building Permits and Flood Plains

I spent the week studying up on building permit applications. There is a ton of material to read, separating the wheat from the chaff. Applying for the permit itself isn't much of a problem but the fact that we are in the 100 years flood plain. This may add an extraordinary amount of complication to the project.

• The good news: Once we get the  flood plain thing figured we'll get the permit easily.
• The bad news: The flood plain application is complicated, requires a great deal of information, and the County doesn't show their work.

The first thing I need to find is a Base Flood Elevation (BFE). This will tell me how high up off the ground that my floor must be built. I had an engineering study done early on, there is a BFE of 225 feet on it, but this may not be the officially recognized number. Judging from the GPS data on-line the farm is a fairly consistent 228 feet, so I may not actually be in the flood plain after all. None of the maps show the magic number, so I need to figure it out.

FEMA has re-drawn the flood plain map and the changes will take place in July, but they still don't tell you what the number is or how they figured the BFE. I messed around with overlaying maps on top of each other and came up with my own map:

You would be surprised how difficult it was to make this picture.
The numbers are the elevations at each point.

The elevation of almost all of the Farm is 228 feet. The above image shows that creek drops from 217 feet to 215 feet in about a mile as it runs behind the Farm. The Highway has been re-drawn out of the flood plain for the most part, the red used to cover 240 feet. This would mean that, in a one hundred year flood, Manning would be twelve feet under. This cannot be correct, since Manning has never flooded to this extent. FEMA seems to be a bit too cautious in the case of this map.

While I can't find the number, the map gives me enough clues to make a guess and another clue from another source gives me an idea of how they figure where to put the line:
Near as I can tell, the red line runs out at 238 feet. Since the Creek is at 218 feet, and the Tualitin River's peak flood of 1996 (a one hundred year event) was about 19 feet above normal. Since they would have added a foot for safety, and they didn't do any measurements when they drew the map, I figure they just put twenty feet on top of every number on a topographical map.

This is an abstracted flood level to be sure. But the County is going to try and protect the flood plain from development by adding restrictions and conditions of approval. So I may need to have a hydrologist do some calculations, and then apply for a flood plain change before I make my application.

The creek side of the Farm is 229 to 230 feet, roughly thirteen feet or so above the creek. When the flood happened in 1996 the people who once lived here say the creek came up to 227 feet, so it does flood there. But the magic number is what I am after. How high do I have to build the first floor?

Ideally they will let me build at or below 232 feet, but I am guess they will want something like 237 feet, which is nine feet above the dirt. I hope not, it will look worse and I hate stairs. But what I want is an approval and I will pay nearly any cost. If my front porch is nine feet up, the view will be awesome.

As I said above. if I get the flood plain figured, the rest will figure itself. But the idea of jumping this hurdle makes me nervous.

I did look at other things. My plan is still fairly much the same as when I posted in a few days ago.