I need to simulate the flow of a river, to do small scale hydrodynamics testing on a partially submerged water wheel / paddle wheel design. The typical water tunnel setup will not work, because we are interested in the flow near the surface. The water wheel is half in the water, and half out. Anyone have any suggestions? I have been trying to use a long open topped gutter and pump the water in one side, and out a drain on the other. But, I get turbulence reflecting backwards because the water is bouncing back before exiting out of the drain port. How can I get a smooth flow / current, like a river with both air space and a water surface, without using a closed system that is based on water pressure? In my current open topped gutter setup; should I be using an open end hose pushing the water in the proper direction, or should I use a diffused filter? Or will both get reverberation flow regardless? Thanks so much in advance. Appreciate the advice.