ᐅ How to Build in a 100-Year Floodplain – Extreme Measures

I am currently in the building permit / planning permission process and just found out through a call to the building authority that my property is located in the HQ100 EXTREME risk zone, so I have to take flood protection measures. This requirement has apparently been in effect since 2018 in Baden-Württemberg.

To explain: HQ100 EXTREME means there is a levee protecting my site next to the Danube River, but this levee could break (which seems very unlikely...). Because of this, I need to implement additional flood protection, whatever that may specifically involve. The exact wording states:
“At locations in risk areas outside designated flood zones, where no local land-use plan exists, construction projects may only be built or significantly extended using building methods adapted to the specific flood risk, according to generally accepted technical standards, provided this type of construction is technically feasible given the nature and function of the structure.”

I am building a solid structure without a basement, and my finished floor level is 61cm (24 inches) below this theoretical extreme flood level. I do not want to raise the ground level further. Although this would be technically possible, it would be expensive and would not look good.

I spoke by phone with the responsible official about whether I could build a wall around my property as a possible solution. She said she wasn’t sure if walls that high would be permitted there and reminded me to consider the entrance driveway. She recommended building 81cm (32 inches) higher for safety, but 61cm (24 inches) might be acceptable. However, I got the impression she wasn’t very knowledgeable. Maybe installing barriers or flood gates on the doors could work – I have seen sliding flood barriers online. Overall, this is really frustrating as none of the more than 100 houses nearby (all built before 2018) have anything like this, there has never been an extreme flood, and I think potential damage would probably be less than the cost of these measures. I also have insurance that costs an additional 100€ per year for flood coverage. To be safe, I will probably install my heat pump about 0.5m (20 inches) higher.

Does anyone have experience with this or a good idea on how to solve this as cost-effectively as possible?

I would lift the entire house and then sleep peacefully. All other mentioned measures are basically useless if the water stays there for days after a dam break. Those measures are more suitable for smaller bodies of water where the water rises suddenly and quickly recedes after heavy rain. If a Danube dam breaks, it takes a long time for the water to drain away. Building without a basement is, of course, sensible. Maybe the most important electronics (circuit breaker box, heating controller, router, etc.) can still be installed above the critical level.

Well, if you can get insurance and a building permit/planning permission with these token measures and feel comfortable with it, go ahead – just don’t complain if you end up boating in your living room.

I’m building by a small stream myself and raised the entire house. Problem permanently solved.

Raising the building would be a daily limitation for me. My parents live in the house next door and haven’t experienced any flooding in the last 70 years, only once a few centimeters (inches) of water pressed into the basement next to the shaft, but since then the levee has been raised and widened.
Raising it would also cost €10,000, which could cover insurance payments for 100 years, and I wouldn’t do it without insurance even if I raised the building.

You won't get insurance at that location... or only an unaffordable one.
Besides, I don’t even know what you want now – you already know the situation.
An argument like "others don’t have it either" wouldn't matter to me at all. Climate change, heavy rainfall events, and so on – I would build higher and then take out affordable insurance...

Well, if everyone is equally unprepared and doesn’t make any preparations, at least in the event of a “once-in-a-century flood,” everyone agrees that the taxpayer will have to cover the costs.

This is how all the flood disasters of the last century happened... "It’s never happened before...". Raise it up and that’s that. 10,000 euros is not a huge amount.