Soakaway

[junglejim]

I’m digging a Soakaway and wondering about where to place the inlet pipe and how shallow the runs from downpipes can be. 
The architect has drawn rain water run with 1:80. The longest run is from a French drain and down pipe at the front of the house… approx 30m to Soakaway by this meant the pipe will be about 40cm deep when meeting the Soakaway however assuming that the French drain is at least 150mm then we’re looking at 55cm deep but I suspect will be slightly deeper as 150mm seems shallow. So allowing for a slight increase I think the pipe is likely to come in near the top of the second layer of the Soakaway (3 layers deep.) is this going to be a problem… i don’t really want to do any deeper as already have 1.5m deep to accommodate 3x36cm deep crates.

 

I also need to install a silt trap and conscious that the inlet is likely to be higher than the Rainwater pipe at the moment unless I can extend the silt trap somehow…any help/ideas welcome. 
 

thanks

Edited July 20 by junglejim

[junglejim]

Hoping someone can offer some advice as will be installing tomorrow. Thanks

[Marvin]

16 minutes ago, junglejim said:

Hoping someone can offer some advice as will be installing tomorrow. Thanks

What's going to be above the soakaway? grass? driveway? ...

 

I think ours had to be at least 500mm down to the top....

[junglejim]

Grass on top… drawings say 300mm above crates but aware that’s not enough for the fall depth.

[torre]

Not an expert but isn't the effective depth only measured from the inner of the inlet?

 

[saveasteading]

Only space below the invert counts as soakaway.

If it was to fill above this then the pipes are not emptying. 

As french drains they will drain of course, but then what purpose has the soakaway?

If the water is all clean, then little harm. If dirty then pipes and soakaway will clog in time.

 

I suggest draw it as a cross section, and show water at various levels.

Edited July 21 by saveasteading

[Mr Punter]

Lay the pipe as shallow as possible.  You can go to 1:110 so your 30m run would have about 275mm fall.  If invert at the start is -250mm, this will give an invert at the soakaway of -525mm assuming ground is level at 0mm.

[junglejim]

Thanks all. Managed to dig a little deeper today… the pit looks excessive but means there’s 70cm above the top crate which should be easily doable… next job is to get a silt trap… any recommendations welcome. 

Edited July 22 by junglejim

[saveasteading]

2 hours ago, junglejim said:

next job is to get a silt trap… any recommendations welcome.

You can pay hundreds or adapt a standard catchpit. 

There's a half decent idea on Google, to make your own. But I wouldn't guarantee it and it may need regular cleaning.

I would lay a stack of catchpit units on a concrete base. Pipe in and pipe out at about plus 200mm. The silt should settle.