Another word for gutter.
Gutter from one roof to another.
The one thing that pretty much everybody agrees on is that at least there should be a downspout to deliver the water to the lower roof and point it in the right direction.
Measure the area of each roof section to calculate gutter size.
How effectively a steep slope asphalt shingle roof sheds rainwater is primarily a matter of roof slope and effective use of flashing including downspouts and gutters.
A hole at the bottom of the gutter or an open gutter end will just splash water around in a heavy rain.
The water is allowed to run on the roof surface and is collected by the lower gutters.
Note also that the valley also sheds its water down the roof surface as well as opposed to into the gutter.