Defensive line question - Waterloo

[CountryBoy]

Let's say I am defending an area that is fronted by a stream. I was thinking of placing my men in line formation behind the stream and pushing skirmishers ahead on the other side of the screen. Is that the best approach? Or is it better to also put the skirmishers behind the stream and the line infantry one hex behind? Does the stream actually do anything? I thought it might perhaps stop charging cavalry? Sorry if this is such a beginner question.