Hi,
we’re about to start building soon, and the building permit-free process was not objected to.
However, on the advice of the construction manager, we informed the local authority that rainwater would be infiltrated via a soakaway basin in the garden.
The authority states:
Rainwater must be infiltrated; a calculation of the infiltration system according to ATV-DVWK A-138 is required and must be documented. An infiltration test or an equivalent laboratory test is necessary.
We have no expertise in this matter ourselves. I’ve tried to read up a bit, but the whole topic seems very complex.
As mentioned, we specified a soakaway basin, so the local authority was able to approve it directly and did not have to forward it to the lower water authority.
One neighbor in our new development installed a soakaway tank and prefers it over a basin because it doesn’t create a “wet biotope” in the garden.
Another neighbor who has already built (using the same earthworks company/gardening contractor as we are) installed a trench soakaway system.
Now I’m wondering which option is better or more cost-effective?
Attached is the offer, which also includes the trench soakaway.
The soakaway tank seems to be quite a bit cheaper??
I hope you can help me decide the best infiltration method.
we’re about to start building soon, and the building permit-free process was not objected to.
However, on the advice of the construction manager, we informed the local authority that rainwater would be infiltrated via a soakaway basin in the garden.
The authority states:
Rainwater must be infiltrated; a calculation of the infiltration system according to ATV-DVWK A-138 is required and must be documented. An infiltration test or an equivalent laboratory test is necessary.
We have no expertise in this matter ourselves. I’ve tried to read up a bit, but the whole topic seems very complex.
As mentioned, we specified a soakaway basin, so the local authority was able to approve it directly and did not have to forward it to the lower water authority.
One neighbor in our new development installed a soakaway tank and prefers it over a basin because it doesn’t create a “wet biotope” in the garden.
Another neighbor who has already built (using the same earthworks company/gardening contractor as we are) installed a trench soakaway system.
Now I’m wondering which option is better or more cost-effective?
Attached is the offer, which also includes the trench soakaway.
The soakaway tank seems to be quite a bit cheaper??
I hope you can help me decide the best infiltration method.
RobsonMKK schrieb:
@Evolith That really depends on the soil. What Kf value did you specify?
For a roof area of 140 sqm (1507 sq ft), I calculate 14 boxes. It’s due to a not so great Kf value. So your 24 is almost negligible in comparison. Our particular situation is that we raised the ground by one meter (3.3 ft). So beneath the system, the Kf value would be 0.00009 (I hope the zeros are correct). Around that and somewhat below is gravel, and then there’s the gravel bed. This means water drains very well to the sides, but downward drainage is rather moderate.
So, we specified 160 sqm (1722 sq ft) of roof surface area and nothing else. Otherwise, the water just infiltrates through the ground.
So, we only need to direct the rainwater from the roof to infiltration.
I hope that’s correct.
As mentioned, it also depends on the soil. We indicated gravel (since it’s on a gravel layer); otherwise, it would be sand LAGA Z0.
There is also the regional factor; here, we use n=0.2 and a safety factor fz=1.2.
Why was the tunnel option rejected?
So, we only need to direct the rainwater from the roof to infiltration.
I hope that’s correct.
As mentioned, it also depends on the soil. We indicated gravel (since it’s on a gravel layer); otherwise, it would be sand LAGA Z0.
There is also the regional factor; here, we use n=0.2 and a safety factor fz=1.2.
Why was the tunnel option rejected?
305er schrieb:
I hope that's correct Unfortunately not. You also need to drain the rainwater from the driveway and access path.
305er schrieb:
Why did you decide against the tunnel? Because I would need 16 tunnels instead of 14 soakaway crates. 16 tunnels cover an area of 15 m² (161 sq ft), whereas the soakaway crates only require just under 9 m² (97 sq ft).
Evolith schrieb:
Around it and also a bit underneath is gravel, then there is the gravel bed as well. So the water drains very well sideways, but downward rather moderately. But then, from my point of view, you would still have an underground "soakaway basin" below the infiltration trench that stores water in the gravel and releases it from there. You should have provided a value for the infiltration trench calculation from Graf. The volume for the infiltration trench seems to me more like 10^-5 (probably taken from one of the deeper layers in the soil report). I would recommend a consultation and suggest involving the soil structure. With so much gravel, sand, and crushed stone, I can hardly imagine that.
About the driveway and access paths?
How is that supposed to work? I mean, how am I supposed to collect the water and lead it to infiltration? The soil is permeable, after all.
Our builder only used the 160 square meters (1,722 square feet) of roof area in the original calculation because we specified a retention basin in the building permit / planning permission.
How is that supposed to work? I mean, how am I supposed to collect the water and lead it to infiltration? The soil is permeable, after all.
Our builder only used the 160 square meters (1,722 square feet) of roof area in the original calculation because we specified a retention basin in the building permit / planning permission.
RobsonMKK schrieb:
But then, from my point of view, you would actually have an underground infiltration basin below the soakaway that stores water in the gravel and releases it from there. You must have provided a value for the soakaway calculation to Graf. The volume of the soakaway seems to me more like 10^-5 (probably taken from one of the deeper layers in the soil report). I would suggest having a consultation and discussing the soil structure. With so much gravel, sand, and crushed stone, I find it hard to imagine otherwise.That’s why I had my concerns. The local water authority calculated a basin size of 50m² (3m x 17m x 0.3m (10 inches) deep). I also informed the Graf consultant that we had built up about a meter (3 feet) of crushed stone, but apparently that didn’t register. I probably should give him a call.
305er schrieb:
How is that supposed to work? I mean, how am I supposed to collect the water and lead it to infiltration? The soil is permeable. Very simple, with a catch basin. Wastewater must not be discharged onto public roads (I just had to learn that myself). During heavy rain, your paving won’t absorb the water quickly enough, so you need to install a drain there.
Evolith schrieb:
I probably should give them a call Either that, or look for local companies that can assist with this kind of work. You might also try talking to the building materials supplier that Graf mentioned.
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