Not sure what the question is exactly, so we´re probably not talking about bridging the streams, rather some bonus in movement points, similar to the bonus in percentage when digging-in? Like, with engineers being next to the stream hex, it costs other units less points to cross it? If something like that, than I´m not aware of any such mechanic.
What is stated in that paragraph from manual is only about building bridges.
So the answer to your question is no, they do not help in any other way except building the bridge.
I hope that helps