Down sloping garden soaked - Drainage

[Flyer]

Hello,
I am living in Belgium where the drainage problems seem very similar to yours unfortunately! I have found this site very interesting and full of good ideas.
Sorry if I use other units than which you are familiar with...I will try to translate as much as possible though!

Now, my problem :
-down sloping garden below road level, a cut of it would give from left to right :
-road level, slope of 30% (steep!) for 5meters (15feets) then a slope of around 10% for 25 meters (75-80feets). then the slope decreases and there is a small woodhouse on concrete.
-the garden is 6-7 meters wide (about 20 feets)
-the soil is... yes : very heavy clay non- permeable.

No water coming from the road enters the garden as I took all precautions to avoid that but still rain does...and sometimes heavily, you know what I mean!

At the bottom of the high slope : soaked!
Close to the woodhouse : very very soaked!

The garden is still to be created and we would like to avoid grass and make it a series of pads (gravel-dolomie) and fountains. We would like to avoid to improve the soil and all that.

I was more thinking of digging a trench at the base of the high slope with findrain in it and gross gravel to intercept a max amount of water. This trench would be connected to another trench going on the side of the garden , garden has to be resurfaced to get a slope towards that trench, this trench going towards the lowest point (escape of water to a wood). Also, a lower trench in the same manner just before the woodhouse connected to the other trenches for escape of water.

What u think about that ?
How deep those trenches ?
What material in it ? Could we make those trenches as pads of gravel ?
Do I still need to put a perforated plastic hose at the bottom of the trenches ? If yes, why ?

Other ideas, suggestions, please ?

Thank you very much for helping a poor Belgian who is tired of having his feet wet !

Flyer

[Tony McC]

I may have missed something but to where does all this drainage outfall? Where are you getting rid of all the water collected by the fin drain?

Depth of trenches - depends on lie of the land. Minimum 400mm, and deep enough to generate a fall from collection point to outfall.

Materials - 20-5 clean gravel

Pipe - perforated pipe. Not essential but makes for a permanent open channel that ensures free flow of water in times of heaviest flow.

[Flyer]

Thanks for answering.
The outfall is going towards woods (downslope at the end of the garden with lot of trees). "Free" outfall.

Also, can I use the trenches as footpaths using different gravels below and above ? (gross below and finest above).

Flyer

[Tony McC]

Yes - if you use a separation membrane to keep the filter material clean, you can 'top dress' the land drain with any decoratibe gravel to suit the garden.

[Flyer]

Thank you Tony. I will plan the works on paper first and then realize them. I will be back to ask you more or to give a feedback.

Flyer.

[Flyer]

Hello,

I am now busy doing the land drainage in the garden.
So far, 60m trenches 40cm deep by hand, hard work indeed!

Unfortunately I have come accross 3 big roots - 3 to 4 cm diameter approximately. They cross the principal trench.

Would you cut those and proceed or try to go below- above with the drain pipe?

Thanks for your advise.

Flyer

[Tony McC]

Leave them be unless they are directly in the path of the pipe, in which case you need to determine the tree from which they come and assure yourself that it won't fall over and/or die if you were to sever these roots.

[Flyer]

Feedback as promised :
I have finished the drainage of my garden.
Big works by hand but I can already see the difference !
I have now to settle the level and to prepare the soil for planting grass.
Would you have any good link for this ?
Once again, thank you for your good advices. Helped me a lot.
Best regards to all,

Flyer