I try to make my own beach waves simulation like the ones one can find over and over on YouTube. In order to test the animation of the fluid waves, I prepared a small test project, in order to be able to bake the fluid fast for different settings. I'm stuck at the problem that whatever I do, the fluid almost completely disappears after 500 frames. Here are two images after baking at frame 1 and frame 500:
I tried many different things like adding surface thickness to the effector objects in my scene or using the "is planar" option (although I have to admit that I don't fully understand the usage of this option...).
This is the fifth incarnation of my beach simulator, in which I build the thickness into the effector objects themself, but it does not work either. I normalized the scale to 1,1,1 like I read in another thread. I totally run out of ideas what the reason for the fluid disappearing could be.
Here is my blend file: 
What am I doing wrong?
Edit:
I tried to add the inflow as Chris suggested. The inflow above the pusher will seriously affect the wave generation and generates chaos.
I understand that the only way to prevent the water from disappearing is to add an inflow.
I did it like this now: 
The chaos is compensated a little bit...
Still, I wonder how all the beautiful beach wave simulations on YouTube are made, where each wave is rolling really beautiful. Or is it just clever editing in the end?!?
