Rainwater pipe to drain

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 jon 26 May 2020

I have a rainwater downpipe that at the moment discharges into a bed of gravel through which a land drain (rigid pvc, slotted in its upper part) runs. For various reasons I would now prefer that the water went direct into the drain as I need the immediate area to be as dry as possible. The down pipe drains a 50m² roof and during heavy downpours takes a lot of water. I'm wondering whether to connect the rwp direct to the drain with a Y junction or into some sort of hopper at ground level - I'm not that keen to have it back up the rwp when there's a lot of water about. I'm also thinking that I should replace the section of slotted drain in the immediate vacinity with a non slotted section as a) the area through which it runs will be covered over in the future and therefore there should be no ground water, and b) I don't want it working in reverse and leaking the roof rainwater into the ground. 

Do any experts have any thoughts/opinions on the best way to do this - hopper/no hopper? Change the section of drain? Am I overthinking this...?

Thanks.

 Bacon Butty 26 May 2020
In reply to jon:

I'd connect it to the main drain with a swept bend at the base of the downpipe.
Reducers maybe required.

(non drainage expert)

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 wintertree 26 May 2020
In reply to jon:

I’d want it to dump into an open grate with water trap so there was no way the pressure in the gutter to back flow out of domestic drains if the sewer became blocked.

I’d also check if it’s allowed by my water board or I’d not ask about it on the internet leaving a public record...

 Reach>Talent 26 May 2020
In reply to jon:

I am fairly sure there are rules about discharging to drains, are you talking about going into a surface water drain or a sewer? If it is a sewer irrespective of whether or not it is permitted I would be pretty worried about potentially having 50m2 of catchment feeding into my toilet if someone dead ended the drain with a few wet wipes  

OP jon 26 May 2020
In reply to Reach>Talent:

The drain is a land drain collecting/draining surface water. There are no sewers anywhere in the area. I'm actually coming around to a hopper/grate at ground level to filter out leaves and stuff, which seems sense and which I hadn't considered to begin with (the leaves, I mean). 

Post edited at 12:59
 Rick Graham 26 May 2020
In reply to jon:

After getting money for playing on building sites for the best part of 35 years this seems a bit like work.

But seeing how its you, Jon, here goes .

You are on the right track. A grated gully to trap leaves connected to the land drain sounds good. Connect to a new manhole or saddle / junction on the land drain.

Worth checking how clogged up the gravel/ stone is around the land drain, the material should have plenty of voids.

Most importantly think about the "exceedance flow" or what happens if all the drains are overwhelmed .

If its in France and on your property, I guess you just get on with it discretely. I presume its not too deep and any excavation will not undermine founds.

Rick

Post edited at 13:44
OP jon 26 May 2020
In reply to Rick Graham:

Thanks Rick!

Grated gully is the word I was struggling for! I guess I'll just connect it via a T or a Y to the drain. It's not deep  about 30 > 40cm.

We've just replaced the land drain around the back of the house as the ground was getting damp and found that the guy who'd installed it, laid it on/in a bed of 25mm round gravel/stone... but then simply placed a geotextile over it rather than around the gravel and drain, so mud got into the drain from the sides and blocked it. I don't see any reason that this section will be any different! But as I say I want to replace a section of it with a non perforated pipe anyway.

Yes, it's the sort of thing that needs no permission. Much like most other things here, in fact!

 EdS 26 May 2020
In reply to jon:

do you have combined or separate surface water and foul sewers?

If they are separate you  need authorization of the sewerage undertaker ( water company) to connect --- it may very well be refused as separate systems are where the hydraulic load is already high

OP jon 26 May 2020
In reply to EdS:

No they are separate. This land drain takes uniquely rain/ground water from around the house and discharges into a stream in a ravine on our property, not into a communal rainwater sewer. Regulations regarding these things in rural France are not the same as the UK. I'm just trying to find the best method of getting my rainwater from the roof directly into the drain. It already sort of does this but very indirectly and inefficiently via a soakaway. As I need this area as dry as possible I'd like to do away with the soakaway.

 Rick Graham 26 May 2020
In reply to jon:

Not sure what is available in France but the attributes wanted are a trapped gully which will have a grate on top.

The grate will stop most leaves/ cats/small children . The  sump will trap some silt until it blocks up.

 EdS 26 May 2020
In reply to jon:

Ah - France 

I'd lay a new surface water drain pipe direct to water course - there is a fair likelihood ( if like around here) a land drain (as opposed to a surface water drain) will have a high load in wet weather already

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 daWalt 26 May 2020
In reply to jon:

grated gullies are (potentially) as much of a problem as a solution. they used to be the common method of taking gutter downpipes below ground; but fell out of favor sometime in the 70s. the problem can be, you get as much crap, leaf mulch, windblown debris etc. into the grating as washed down the downpipe. a hopper at ground level is.... a potential maintenance problem. (grates still let a lot of stuff through b.t.w)

more important is access and rodability. if you connect direct to the slotted drain then install a rodding eye too, and check where it goes at the downstream end so you know where it'll rod out.

does the gravel "grip" extend around the perimeter of the building? If so, I suspect the "soakaway" may not be a soakaway but a gravel perimeter drain, to take water away from the buried brickwork of the building. the reason is, if it were a soakaway I would expect the slotts to be on the bottom of the pipe, or all around, to disperse water from the pipe to the gravel. (soakaways have a minimum distance from buildings requirement; 10m?, can't remember of the top of my head) if it's only slots on the top of the pipe, then this'll flow pretty near pipe full before water will escape out.

i'd be inclined, if you're going to connect directly, to ignore the slotts. only in proper pipe full flow will water escape, and during these events everything will be wet in any case. The risk, otherwise, would be actually preventing the gravel from draining

Post edited at 19:18
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 daWalt 26 May 2020
In reply to Rick Graham:

for this type of thing you only need a trap if you are connecting to a combined sewer. again common up until about the early 70s (ish). obviously one would never connect a surface water drain to a foul sewer - that never happens.

the purpose of a trap to provide a smell-barrier. the water in the trap prevents sewer gasses from escaping into your environment (like you have on the bog).

traps are best avoided wherever possible.

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