JKTFin
It's a Levada - something typical to Island of Madeira.

It is not really a drain either. The most accurate description (in most cases) would likely be an irrigation aqueduct, but they are usually mapped as drains and I see no reason to change the practice.

They are not seasonal, but they are often  (but not always - GPS tracks or preferably survey required) accompanied by a path. Sometimes it is part of the concrete construction and sometimes earthen right next to the waterway. In either case the center distance between the two is usually under half a meter. As this is less than the possible accuracy from GPS tracks (especially considering the usually steep topology), it makes sense to use single element for mapping. It also simplifies editing considerably.

When Levada crosses roads, the waterway and path often diverge for a few meters and only the path connects to the road.