ᐅ Rainwater from the roof – underground drainage for disposal?

Hello,
we are currently in the construction phase of a single-family house, and I am considering where to direct the rainwater from the four downspouts. Generally, there don’t seem to be any major issues in the area with rainwater infiltration. We also do not have a basement.

I must admit I am a beginner in landscaping. So please don’t take my questions the wrong way.

According to the soil report, the groundwater starts at about 3.80 m (12.5 ft). Therefore, we planned to install a water pump (lower costs due to the shallow drilling depth), so a cistern as a water storage tank seems rather pointless.

I was thinking of installing 10 m (33 ft) of drain pipe connected to each of the four roof downspouts, buried underground. Of course, surrounded by gravel and geotextile fabric.

• Is this oversized?
• Should the end of the drain pipe be left open so that in heavy rainfall, the water doesn’t back up and overflow the gutter?
• Do you see any problems with this plan?
• Should I install a backflow valve at the start of the drain pipe to prevent water from backing up into the gutter? But in an extreme case, the water would then run down from the roof because the backflow valve wouldn’t let water flow down.
• Do you have any other suggestions?
• Am I just worrying too much about the rainwater?

Thanks in advance for your help and advice.

Here are additional details from the soil survey:

"Soil group SE -> highly permeable / OH -> permeable: The sands beneath the topsoil or the filled sands have very good infiltration properties down to the respective groundwater level."

"It is also noted that in the development area, due to a reduction in groundwater extraction by the surrounding water utilities in the future, groundwater levels may significantly rise in some places. Therefore, the highest groundwater level is approximately 1.3 m (4.3 ft) below the ground surface."

"In the development area, maximum frost penetration depths of 0.8 m (2.6 ft) are to be expected."

"Infiltration of rainwater is possible from the bottom of the future topsoil layer (e.g., infiltration shaft or infiltration basin). The base of the infiltration system should be located above the highest groundwater level. It may be feasible to collect rainwater in a cistern for reuse and only allow excess water to infiltrate."

vaderle schrieb:

"Infiltration of stormwater is possible starting from the lower edge of the future topsoil (e.g., soakaway shaft or infiltration basin). The base of the infiltration system should be above the maximum groundwater level. It would be advisable to store the collected stormwater in a cistern for potential reuse and only allow excess amounts to infiltrate."

There is your answer. Just a few drainage pipes do exactly: nothing.

Otherwise: sewer connection?

vaderle schrieb:

Do you see any problems with this project?

Hello vaderle

You should first obtain and comply with the applicable regulations. Infiltration does not mean letting water run off uncontrolled and waiting for it to disappear. Infiltration must also be able to handle heavy rainfall without causing the surrounding area to be flooded for hours.

Steven

Possibly also consider adding a cistern. This way, you will have water available for the garden later on.

Steven schrieb:

Hello vaderle

you should first obtain and comply with the applicable regulations. Infiltration does not mean letting water run off uncontrolled and just waiting for it to disappear. Infiltration must also be able to handle heavy rain without flooding the surrounding area for hours.

Steven

Hello Steve,

I understand the need to ensure compliance with legal requirements. However, wouldn’t heavy rain still cause issues even if I didn’t carry out any pipe work? According to the soil report, the ground is very permeable. So water should generally infiltrate well.

@Rick: I did not want a cistern since a water pump is already planned, making the cistern unnecessary because there is enough groundwater and it is not very deep.