Boolean intersect with plane makes object disappear I'ts been 10 hours of researching, watching tutorials, trial and error and yet i still cannot figure this out.
I have 2 planes, one being my water for my city and the other being the ground. I'm trying to intersect the water with the ground so it will make a little divot like in the image below but every time I do that the mesh disappears or it won't allow me to even intersect it with the Bboolean modifier.
I tried Ctrl+N, removing doubles, making the ground a cube instead of a plane and yet none of these work.
I'll upload the file below but this is just the current lake I've tried out of the 200 other attempts.
The tutorial I'm following is this https://www.youtube.com/watch?v=i4ySFm4ey9U&amp;list=LLZKTEq5R9PWrJvExEVHgTFg&amp;index=5
At 55:36 mark is where I'm stuck.
If anyone could help it would be very appreciated thank you for your time :)
First. The scale of your plane is set to negative.



Press CtrlA in object mode and select apply scale.

Then the river object has inverted normals. 



Make them consistent by pressing ctrl N



Booleans use the direction of the normals to calculate the operation.

Then use Difference to cut out the shape of the river out of the plane:



Some reasons for failed booleans operations: 


Non-Manifold geometry
Inconsistent normals
Booleans don't work with curves or text
The scale for the object uses negative values