Why is the boolean modifier creating a glitchy mesh instead of cutting into the object? I'm modeling a city and wanted to create a river with help of boolean modifier. I've checked doubles and normals, so I don't know what the problem is when I'm adding a boolean modifier. You can see what's happening and nothing is happening to plane, just glitchy bugs.
If you want to cut something into an object using boolean, the modifier has to be set on the mesh that you want to edit. Not on the stencil object. You also may change the visibility of the scencil object from textured to bounds.

It then should just look like this 

Also i recommend using the BoolTool Addon. It is far more user friendly.