TY for fixing my newbie mistake. I was attempting to adjust the boundary rather than create anything new, but I clearly failed.

TY for the culvert assistance. I couldn't figure out how to get it to do that. Also, thanks for the USGS tip. Unfortunately, it shows the creek coming in from the west and then heading south. It definitely comes in from the east by the elementary school, so I have no idea what source they were working off of. Hopefully their mapping to the south is closer to correct!