Help with map making...topic is a valley

I am a noob to modding so I really need some help here lol. So far I am doing well with stuff. Right now I am at a sudden halt because my map has a sunken valley that should be dry,waterfalls going into a small lake and into a ravine. My issue is that when I add the water plane it fills the entire valley and the ravine. Is there a way I can remove the water from where it needs to be removed without removing all the water?

This would kinda stink if it was not possible because i have a map all planned out.

EDIT: Nevermind…I found that I need to make meshes and all that stuff and I am not able to do that. Perhaps I can find someone to take up my ideas and the map layout. Its all going to be posted on the official forums in Workshop Discussions. I have health reasons why I have to give up on making it myself too. I at least learned how to finally get height maps working. Oh well…