How to Restrict flow to some part of Domain
 

Hello, please bear with me .I am a newbie here.
I am working with 2-D fluent. and I am working with gravity waves.Please have a look at the pictures uploaded
https://lh4.googleusercontent.com/-_...2/DSC_0660.jpg

Though the inlet is only at the bottom ,after solution I find that the water seems to fill up the complete domain irrespective of the gravity acting over the domain downwards.

Here is a link of the picture showing the streamlines of flow after solving in Fluent.
https://lh4.googleusercontent.com/-c.../s834/snap.JPG

All I want to study is the effect of the obstacle on the gravity sinusoidal waves I am letting in at the input,when the waves strike the obstacle.Please enlighten me. I did enable Gravity in Problem setup --> General .
Is it compulsory that the flow has to cover the complete domain, once the domain has been meshed completely ?

I need urgent help as I have a project presentation on this.Please enlighten me on this !