French/Trench Drain leading to an inspection chamber

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Hi Guys,

I didn't know whether to post this in Gardening or Building so please excuse if I'm in the wrong area. Our extension is completed, but the back garden slopes uphill away from the side of the house. We tried to grade the land as best we could but there's still a slope of about 2-3 feet over approx. 10m. Next to the house we have a 900mm wide path and there is also the inspection chamber for both our surface and foul water (they are combined in this area).

We get a lot of ponding along this path during heavy rainfall and in the winter, so I need some ideas on drainage. The inspection chamber is very near to the area and is only 18inches deep. The inspection chamber itself is often under water during these downpours. It has 2 unused inlets, one of which faces out from the path onto the sloping garden.

Originally I considered going with 80mm perforated drainage pipe running along the path and running into the inspection chamber. But I only need about 10m of pipe and the minimum lengths to purchase are 25m! So then I thought, what about if I dig a trench drain along the path, increasing in depth towards the chamber. I can then line it with non-woven geotextile sheeting, fill with either pea shingle or pebbles and omit the pipe altogether?

Would this be ok? Whats the best way to prevent soil or pea shingle ingressing into the inspection chamber? Is there an approved method, or can I just cover it with geotex?

Your guidance always much appreciated.
 
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Experts will be along, I'm sure, but I'd ask- is the chamber for foul drainage? If so, does all your other surface water go into it. The water companies often want to keep surface water and sewage separate.
 
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Experts will be along, I'm sure, but I'd ask- is the chamber for foul drainage? If so, does all your other surface water go into it. The water companies often want to keep surface water and sewage separate.
Charliegolf, my original post states that the foul and surface waters are combined in this area.
 
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I would buy the 25mtrs and either bin the leftovers or put 2 parallell lengths in.
 
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