Help with Drainage Planning (with pics!)

[barki]

Hi all,

I'm planning to turn my front garden into the typical modern parking lot.

It's on a slight slope and was previously a mixture of crazy paving & flower beds that relied on natural drainage.

As I hope you can tell from my artistic efforts below, I intend to;

- Pave down the footpath and along the front of the house, I'm using typical budget Riven 600x600x32mm slabs on a wet mortar bed. This base is sloped away from the house and I'm already aware that its close(ish) to the DPC.

- Dig a trench (light green) about 1ft deep (?) and 1ft wide (?) along the 'bottom'. To be filled with coarse gravel.

- Dig a trench for the retaining wall , put a concrete base in, build low wall on top to bring level with existing block driveway.

- Use a whacker on the centre area, then lay membrane and fill with gravel.

- Plant a hedge in the remaining flower bed along the front and shrubs in the other bits.

Here are the photo's from both directions, with and without annotations.

My questions are:

1) Will that trench be enough? (I can't see how else I can route water, without digging up the whole block-paved driveway to join with the drain from the road, which I believe is underneath it.)

2) Will the parking area still drain any water once it's been whackered if I use a permeable membrane (or no membrane at all?)

3) Along the front, i'll be reducing my DPC clearance from about 170mm to about 125mm (although I note that whoever laid the block paving has already reduced it to about 90mm along the side of the house). How criminal is this?

4) I ordered new Riven slabs in 'buff' from Homebase. But upon unpacking them I've realised they are actually a strange mouldy green/brown colour, is this normal? It seems to scratch off the surface like its just discolouring from storage?


Really grateful in advance for anyone's help

 

[Whitling2k]

Do you need planning permission to reduce the permeability of your drive?

It doesn't look like you will be doing if you use gravel - but I reckon it's not a good idea to route it into the drains.

Can you make it into an open-soak away type thing? Google SUDS to see if there are any ideas on there.

If you connect to a drain - I would imagine gravel and other fine sediment getting into the drains and sewers and causing blockages - for you or your neighbours.

Not to mention the increased run-off. One drive will be a minute difference - but 1000s of driveways spread across a drainage basin will make floods slightly higher and slightly quicker. Might be the difference between your river-side friends flooding or not.

 

[barki]

Hi Whitling,

Cheers for the thoughts - I hadnt heard of SUDS, but now a Google it...wow...alot of info!

Is there a rule of thumb about natural drainage, I'd rather do that than divert the water anywhere to be honest (since the only downhill route from my front garden is either under my house, or along the driveway, which is newly(ish) paved.

How cna I work out if what width and depth of trench i'd need to drain that area?



Tom

 

[r896neo]

assuming its just that area and your driveway doesn't also run onto it then i wouldn't bother with the trench.

Gravel on a type 1 sub base will drain ok and if your underlying ground is so poor that it holds water then your trench will not make that process any better.

A soakaway is only useful if the ground will actually drain anyway or you have a clay layer and digging deep enough will get you through it into better draining ground.

You could dig a trial pit and do a perculation test, details on how to do that available at paving expert. com

Your contractor who laid your drive should have told you about suds and you should have a linear drain at the end where it abuts the pavement.