Rainwater collecting

I have been reading and watching Youtube about swales, trenches etc for conserving rainwater.

I live in southern Spain, hot and very dry in the summer, cold and some rain in the winter. I would like to convert my garden into a small food forest. It seems like a good idea to sort the water situation out before planting or anything.

Looking at my garden it looks like it will naturally collect water without the need for getting the spade out and digging some earthworks as it is walled at the base.

Does this sound right? Here is my dodgy drawing...



Cheers,
Steve

Just at first look, I would be very worried about the house flooding in a rain storm.

The alley is on a slope with a large drain at the bottom. House is a 100 years old with no sign of flooding yet!

It would be awesome to have a way to direct any rain you get off of the roof to your garden beds during any summer showers (if you get them.) Putting in a diverter that directs any rain from the roof to the top of the garden would be the start. Then you want to slow the flow of that rain so it doesn't all run down the slope quickly. If you put in swales every 2m and so that the water can cascade down, you will get maximum absorption. Top view of swales:

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Then, put the plant that like the wettest soil between the swales near the top, and the plants that like the dryest soil in the tops of the swales near the bottoms. This plan would maximize the number of edges in yor yard and you would have a really diverse number of areas to plant in.

interesting, I reckon I can divert the roof's gutter to about 1/3 of the way up the garden and it would flow down with gravity. I would need a way to slow the flow and maybe switch it off at times so I guess it would need some kind of tank

If the pipe size is generous, you don't need much fall. Where I am, septic pipe gets one quarter inch fall per foot (7 or 8 cm per meter, I think). You could squeak by on less, maybe. You could also do the "U" shaped feed to the tank which doesn't have pipe in the air over a long distance, but that has to be drained when freezing is possible. Put your tank as high as possible to allow for some gravity feed. On that slope, a level pad for the tank may be a challenge. Run the tank overflow into your swale system.
Easy to come up with ideas if you don't have to live with the results or do the work, eh?
Gani