Simulation of a dump in a river
 

Hello everybody.
I am a new user of Openfoam.
I want to simulate the drop of a sluice in a river.
This simulation is for a french kayak association http://lasuze-canoe-kayak.over-blog.com/. We would like to have a static wave at the oulet of the sluice.
The first step is to simulate the flow like it is now, and then to modifie the sluice outlet with a deflector to have a good shape.

I havn't got a lot of knowledge in CFD simulation so i work step by step.
I have made the mesh, take the dambreak tutorial in laminar flow.
The simulation run but i have some problemes.

First one, as you see on the picture, alpha1 is higher than 1 as soon as the simulation beguin. I don't understand why.

Second one, as you see, the level of the volume between sluice outlet and outlet, decrease like in dambreak tutorial. In reality, it is the river, so the level is constant. I have tried to put alpha1 outlet to 1 but I have had error from courent number and i cannot solve it. I think it is another problem.

Have you got an idea?

Thank you.