I have four downspouts on the house. Two have downspout extenders that unfortunately have to cross walkways and I'd like to get them out of the way by burying them. Both extenders now drain into garden beds and the walkways are brick, so it'll be easy to pull them up and dig a trench. How deep should that trench be and do I just let the water dump into my garden beds or should there also be some sort of trench with gravel dug there too? What kind of drain pipe material should I use? I sort of would like to be able to disconnect the extension pipe from the downspout when I do gutter cleaning - lots of trees in my neighborhood. Is periodic disconnection at the downspout OK, or will that create problems?

In southern WI, so freeze is an issue. One extender needs to be at least 4' long, the other about 10'. Currently don't have any drainage problems, just the inconvenience and safety hazard of the extenders crossing the main traffic walkways into the back yard.

Thanks in advance for any advice.