I have a small 50 gallon pond. I'm getting an urge to dig out a stream,
maybe 15-20 foot in length, 18 inches wide, 6-12 inches deep.

I'd lead it to my pond and make that the terminal. Water would pump out
from there and through a tube up to the stream source.

It seems too simple. Anybody running any streams? What problems am I up
against?

I'd like to use some sand in the stream, but assume it would get into
and wreck my pump.

Can I keep my plastic shell pond and join it to a liner for the stream.
Is there a reliable way to do this? Or do I have to remove the shell
and line it all?