Are backwater valves always necessary in flood-prone areas?

Since we are currently planning the sanitary stuff, I brought up the topic of backflow valves. We have three spots in the basement where wastewater is discharged outside. For whatever reason, they didn't channel it all to one place.... The plumber says that we are not supposed to have backflow valves. Apparently, they are only needed if rainwater is also discharged into the sewer. That is not allowed in our case, meaning only wastewater is discharged into the sewer. Since we are building in a flood-prone area, I think it is still possible that water could push back through the sewer. What do you think? Do I still need backflow valves then?

Ask the municipality about the maximum backwater level in the sewage system. If you are below or near the maximum backwater level, install a backwater valve. I would at least sleep much more peacefully with that.

As far as I know, the height of the backwater level is simply determined by the height of the manhole covers, regardless of whether rainwater is discharged into them or not. Because the water cannot rise any higher, as it would then flow onto the street through the cover.

If openings (toilets, drains, etc.) are below this level, these connections should be secured by a backwater flap. If drains with blackwater are below, I believe an electric backwater flap must even be installed. If a closure of the flap affects all toilets of a residential unit, a Pumpfix must be installed, which pumps the blackwater into the sewer despite backwater.

Hello

All processes below the backwater level, usually the manhole cover, must be drained via a lifting system.
A backwater valve is not sufficient / professional.

Olli

So we only have the washing machine and a drain basin in the basement. Also a small lifting system that pumps the water away. The construction manager also says that we don't need any backwater valves...

Here is what the basement looks like: