ᐅ Stormwater drainage on the property unclear for building permit/planning permission purposes

Hello everyone,

We have been waiting for our building permit/planning permission for 8 months, and it seems that only one issue remains to be resolved: rainwater drainage.

The following framework conditions apply:
- According to LANUV, the groundwater level is just below the future turf (+41.80m (137.8 ft))
- Planned ground level +41.95m (137.1 ft)
- Ground floor slab height +42.05m (138.1 ft)
- The existing sewer does not have enough capacity for rainwater. Wastewater is not a problem.
- A soakaway is not possible due to the high groundwater level
- 5 new houses are planned along the street between existing buildings
- Communication is difficult as the solution is being coordinated via the developer.

The following alternatives have been considered:
1. New sewer
- Currently not being pursued, as the solution is probably too expensive
2. For a soakaway, the ground would have to be raised by 1.5m (5 feet). This will likely not be approved by the building authority.
3. Infiltration basin combined with a cistern
- Water from the cistern is intended for use in the toilet and washing machine
- Green roofs are planned for some surfaces. For us, this is only possible on the garage, as we are planning a hipped roof
- We have asked if the infiltration basin can be installed in front of the house. However, it seems it will only be allowed in the garden. For whatever reason?!

Currently, only alternative 3 is being pursued. I have the following questions:
- We have a small plot of 380m² (4,090 sq ft). The infiltration basin is supposed to be installed in the garden. What does this mean for the garden? Will the area be unusable?
- How could the infiltration basin possibly be optimized, beautified, or made usable?
- Why is it apparently not allowed to place the infiltration basin in front of the house?
- What are the disadvantages of using rainwater for the toilet and washing machine?

Are there any other ideas on how rainwater drainage could be realized? I would greatly appreciate any tips!

Thank you very much!

mambo1988 schrieb:

- We have a small plot of 380m² (4,086 sq ft). The infiltration basin is planned to be installed in the garden. What does this mean for the garden? Will that area be unusable?
- How could the infiltration basin possibly be optimized, beautified, or made usable?
- Why shouldn’t the infiltration basin be placed in front of the house?
- What are the disadvantages of using rainwater for the toilet and washing machine?

Are there any other ideas on how rainwater drainage could be implemented? I would really appreciate any tips!

The area is usable, for example as a lawn. It just won’t be perfectly level, since it’s a basin.

Placing it in front of the house is possibly avoided because an overflow onto the street might overload the sewer system. An overflow within the garden drains more slowly and is less likely to overwhelm the sewer.

Using rainwater as non-potable water has no disadvantages.

If adjoining properties exist, basins can also be designed jointly. You’ve probably already considered this and mentioned the challenges of communication between property owners.

A direct conversation with the local water authority could also lead to good ideas.

You can also search for research institutes working on this topic. Providing reference plots can save costs and lead to excellent solutions.

I don’t quite understand how it’s possible to build with groundwater up to the turf layer.

When using swales for drainage, you also need at least 1 meter (3 feet) of distance from the groundwater.

Using the space for a washing machine, etc., doesn't make sense. Double piping with switching, filtration, and so on.

A cistern is probably the simplest solution. This way, it can also be used for irrigation.

Wells and groundwater extraction are often not permitted...

Something is definitely wrong here.
Groundwater is almost at the surface.
This is basically a bog; who would classify this as suitable building ground?

Hello everyone,

thanks for the responses. So, the groundwater can rise up to just below the topsoil. Of course, we hope that this normally does not happen. Unfortunately, the plot has already been paid for...

hampshire schrieb:

The area can be used, for example, as a lawn. It is not perfectly level but rather a hollow.
There might be concerns in front of the house that when overflow goes over the street, it could overwhelm the sewer system. Overflow in the garden, however, does not enter the sewer that quickly.
Using rainwater as graywater has no disadvantages.

If there are adjacent plots, the hollows can be shaped together. You have probably already considered that and mentioned the challenges of communication among builders.
A conversation directly with the local water authority could also lead to good ideas.
You could also search online if there is an institute dealing with this topic. Providing reference areas can save costs and lead to great solutions.

Which institutes are you referring to here? And what do you mean by reference areas?