Monday, August 28, 2017

Houston Land Udse Management Issues in Focus

"Banks only require flood insurance if the first finished floor is below the FEMA 100yr floodplain elevation. This is FAR beyond any of our design standards. I'm a certified floodplain manager and very familiar with the topic if you want to ask any wonky questions." ~ Rubygoat

USGS/FEMA just went through a round of updating the flood maps around here.  Surpriselots more flood prone than originally suspected.  This was due to overbuilding.  Channelizing.  Eco-management practices.  I imagine Houston could add the substantial subsidence it has wrought upon itself. 

Do the flood maps adjust for subsidence? 

24 comments:

Rubygoat said...

Pigged.

"We won't change anything. This is beyond the 100 yr storm. The philosophy is that the cost to design everything to withstand an event of this magnitude is greater than the cost to just rebuild it if you happen to get hit. The design standard is set by congress and enacted by FEMA on a federal level. Cities have the option to enforce higher standards, but about the only thing that's designed to this this level are major dams (USACE projects) and even they take pretty regular maintenance to continue that level of saftey (see oroville dam for typical level of maintenance)."

Rubygoat said...

When a new study is done they use the best available data. If it's a developer doing the study then typically that's field survey, but usually it's the latest flown LiDAR which has an on the ground vertical accuracy of 1 to 2 ft. Subsidence would be reflected in this, but the data is very piecemeal and usually very old. Some of the FEMA boundaries are decades old and have just been pulled forward when the maps get revised every 5-10 years or so.

Lawyerliz said...

I'd have both flood insurace and a couple of extra feet th lift a newly build. Not perfect. But helpful.

Rob Dawg said...

FTR, LIDAR is capable of far more precise than a foot or two. We just don't talk about that.

Anyway. http://www.thecamarilloacorn.com/news/2009-01-23/front_page/002.html

City planners agreed with FEMA's preliminary maps, but found "inappropriate predicting" in parts of the city, such as the small bridge across Calleguas Creek at St. John's Seminary.

Mortgage lenders require property situated in a flood zone to have flood insurance.

Believing FEMA's maps were inaccurate, city planners asked the federal agency if Camarillo could submit a more detailed flood model, Fox said.

FEMA agreed, and the city hired a engineer, who finished the report about a year ago. The city submitted the revision to FEMA, which has apparently accepted the revision because the agency has continued with its regular procedure, Fox said.

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Rubygoat, you can probably guess what really happened.

Mike said...

Houston had 10 inches of rain (over two days) and filled up like a bathtub...if that's not a flood plain then why even bother with the mapping??

Mike said...

actually..I was looking at that FEMT map incorrectly earlier...much of Houston is in the "100 year" category (shaded blue on the map)..I was just looking at the "coastal floodplains" earlier (shaded orange)..

http://www.harriscountyfemt.org/

Rubygoat said...

Raw LiDAR is very messy. 15+ million points per sqmi. Every leaf and stick and blade of grass is returned. The inaccuracy comes from filtering out all of the trees and bushes etc. to get to the actual ground elevation.

FEMA trusts the communities to manage their flodplains. There is a city official for every city and county in the nation with the title of Floodplain Administrator. If they participate in the NFIP then FEMA trusts them to administer their flodplains better than any national organization could. If the city generates or approves a 100 yr floodplain then FEMA will incorporate it into the maps. Camarillo knows its floodplains better than FEMA does.

Lawyerliz said...

They had better get a lot of water out there, right away

Rubygoat said...

NOAA should release aerial imagery in a couple days that shows the extent of what actually flooded. I expect the innundation to exceed the 0.2% (500yr) floodplain in Mikes link.

Rob Dawg said...

Have you seen the early images from the still in testing GEOS-16? Incredible.

https://www.nesdis.noaa.gov/content/goes-16-color-composite-images

Rubygoat said...

I love NOAA, they take truly breathtaking imagery.

Rob Dawg said...

Didn't you like my choice of post graphic?

Rubygoat said...

It's almost as breathtaking as the NOAA pics.

Rob Dawg said...

Lol!

LBD said...

Great week end camping. Almost zero TV and cell reception makes life nicer. Now have the RV washed, fueled, reloaded and off on the Southwest loop again. Wife won't go to the gulf coast. I guess she had a bad vibe and it is paying off. What a mess down there.

Lawyerliz said...

Where are these people gonna go.?

Lawyerliz said...

No Gulf Coast left, sorta.

Rob Dawg said...

LBD. Cinco visited the Dawghaus and wuzn't axe murdered or nuttin'. Going past by any chance?

Rubygoat said...

There are a couple reservoirs in houston that are over capacity and will need to open the flood gates to keep the dam safe. They've issued mandatory evacuations for the areas downstream. The reservoir pools are already backed up into the lakeside communities.

LBD said...

Sadly not going in to Kali except to get to Lake Havasu. If I ever do I would be happy to stop by and buy you a beer.

Rob Dawg said...

So far the saving grace is that the port seems mostly intact and should be operating quickly.

All those service poles... That will be a long time repairing. And I wonder how many hadn't yet had their PCB transformers replaced yet. I ask because last i looked replacement less toxic cans were three years plus on back order.

Rob Dawg said...

Carry the conversation over to the new thread. Don't leave your cel phone behind.

Lawyerliz said...

They did it. And it flooded.

Lawyerliz said...

Hub totally agrees