Landscape Alpha Map Using Splines?


I am trying to make a game environment which is going to be a trench system. I have created the texture i would like to tile across the landscape that unreal engine generated. What i would like to do is use the spline tool to try and create an alpha map with zero opacity. The reason for this is so that i can model my trench system within MAYA and then just adjust the rest of the environment within the game engine. Is this possible?

Thanks for any help.

Would this be adequate?

Or does it need to be a spline?

Spot on mate. great help.