"up on blocks" mean???

raised up on concrete or wooden blocks so that flood water does not get in.

In your sentence, it does mean that the house was raised up using blocks.

It's can also be an idiom. To put something "up on blocks" is also a way to store something.

Our car is up on blocks until we get back from vacation.


A "block" can also be a way to measure distance in the city.

We live a block from the school.

An automobile can be stored on blocks and the (deflated) tyres ("tires" in the USA) are raised off the ground and therefore will not be permanently deformed by the weight of the stationary vehicle; thus the vehicle is out of service. Sometimes is British slang "up on blocks" is used in this way to mean "not available for use"

'flood waters' and 'high water table' are different things.

In coastal areas with high water tables, houses are built on low pylons with crawl spaces under them. If you watch it being built, it looks like it is up on blocks. If the house was built with a basement, there would be sever water problems. In beach front towns, houses are often built on very high pylons so that flood waters can go under them.

"Up on blocks" can also be a slang term as mentioned above, but that is not what the writer is referring to.