N Scale - planning river(s) on a 3 1/2 X 5 layout. Would like suggestions on approximate width of a river on layout of this size.
How long is a string? Got to laugh and not even finish reading the statement.
Rather like asking, "How long is a string?"
You could have a river half the width of the long side of your layout all the way across, and make it a home for two long bridges (and not much else.)
You could have a wide river on one side (with a swing or lift bridge) and switch the smallcraft harbor (fishing boats) from the other side.
At the opposite extreme you could model a glorified rain ruvulet and get it past the tracks through a soda straw pretending to be a culvert.
If you were modeling my neck of the cactus your 'river' would be a concrete channel with a little bit of sand and trash on the bottom. Water flows when it rains - and we have 330+ sunny days a year. Roads and rail lines are supported by big concrete boxes in parallel rows.
Final answer? It all depends on what YOU want the layout to look like.