Multiple Depth Layers

So I figured out how to create my depth layers. I created a "mud pit" and saved the level. I now need a "sand pit." I created this sand pit and replaced the .PNG. Now my "mud pit" has no depth. Do I need to create all my depth layers at once? Or can I name and rename each layer? Usually its Mapname.ter.depth.png So could I do Mapname.mud.ter.depth and Mapname.sand.ter.depth.

 

I must be doing something wrong. When I edit my .png they are in my documents. Each png is separate grass, mud, sand, rockdirt. I opened my mud pit file Mapname_layerMap_4_Mud.png I made my mud pit and replaced the original map png. My sand pit file is under Mapname_layerMap_5_BeachSand.png I have to open separate and edit separate. And when I go to save this file it over writes my mud pit depth. A simple 4x4 park is turning into a huge therapy bill. lol

 

That is how they come out after exporting them, now you have to make them into one *png* file ( take the mud one and the sand one, and make them into one png file in a photo editing software)