Surface water / soakaway advice

[JackOrion]

One of our planning conditions is to provide details of surface water drainage. The LPA and water company will only allow foul water into the sewer, so we need engineering calcs and drawings showing the soakaway design and location.

 

Site details:

 

• Mainly sloping site

• Soil is very gravelly clay

• Test pits (400 × 400 × 400mm) drained quickly (in under 7 minutes)

• Roof area approx. 120m²

• Paths/driveways will all be permeable

• A few old Victorian garden buildings are on site with lots of old land drains dotted around (it's an old walled garden). No drainage issues anywhere and we've owned the plot a good few years.

 

From what I understand this probably means we need around 3m³ soakaway capacity.

 

We’ve had two drainage engineers visit and both suggested a single soakaway in a flat area (about 5m²) in front of the house. However, that spot isn’t 5m from the house foundations nor is it 5m from a retaining wall further downslope (neighbour’s property), so it seems like it will not meet the usual guidance, and could prove problematic in future.

 

On the other side of the house we have about ½ acre of sloping woodland, with plenty of space but more difficult digging (tree roots present, and will need to be by hand), and then we have a more gently sloping footpath below that.

 

I’m wondering whether splitting the drainage into several smaller / shallower soakaways in the wooded / footpath area might make more sense, which would keep everything well clear of structures.

 

Does that sound like a sensible approach?

Has anyone used any drainage engineers who may be a little more inventive than those who have suggested a single large soakaway, or perhaps have more progressive SUDS experience?

 

Any recommendations / thoughts welcomed.

 

 

Edited 2 hours ago by JackOrion