Driveway soak away

[Moonshine]

I am putting in a new driveway in, and it needs to have aco drains at the boundary and a soak away as specified by crossing licence.

 

i need to get my head round the how big the soakaway needs to be and the depth of it.

 

From my reading it needs to be at least 2.5m from the boundary as below (blue is the location of the aco),

 

I am unsure of how big the soakaway needs to be (how many crates), what the depth below invert of the aco it needs to be.

 

 

any help would be welcome

[Ferdinand]

I'm quite interested in this.

Would it need a boundary drain if the driveway were permeable?

[Mr Punter]

It is down to how porous your soil is.  For depth go with the minimum the crate people recommend for whatever the heaviest vehicle will be.  Needs to be at least 5m from buildings.

[Moonshine]

36 minutes ago, Ferdinand said:

I'm quite interested in this.

Would it need a boundary drain if the driveway were permeable?

 

It would unlikely not be needed, i have emailed the highways officer to ask if a permeable surface (tarmac ultidrive porous) would be an suitable alternative specification.

 

38 minutes ago, Mr Punter said:

It is down to how porous your soil is.  For depth go with the minimum the crate people recommend for whatever the heaviest vehicle will be.  Needs to be at least 5m from buildings.

 

Soil is not very porous, also just measured it and there is no space for the soakaway to be 5m from a building and 2.5m from the boundary. Also no way to get it into the combined sewer. 

 

It looks like porous is the only sensible solution, lets hope highways also agree! ?

[saveasteading]

It is not widely understood by bc or highways so they might accept the porous surface without further consideration.

 

The purpose of the drain is to prevent your rainwater running over the road where it could cause traffic problems if fast flowing or it freezes.

Also it could find its way to a drain or ditch that may increase flood risk.

 

In your case the rain will go through the surface, reach the ground and run down to the road, then onto it.

 

In permeably surfaced areas such as retail car parks they put a huge thickness of open textured stone underneath to hold the water until it gets away. A soakaway and gully will be cheaper.

But say 100mm of single size stone underneath will help.

 

So that would be up to you to decide. 

 

If going for solid surfacing, then you have to allow for about 60m2 of surface (check) . If it was smaller then there is an allowed  rule of thumb for soakaway size of 10mm rain (in 5 minutes), so perhaps try that first and see if they accept. 

That would be 60 x 0.01 = 0.6m3. 600 litres.