water surface
 

about modeling flow on spilways.when water flows it doesn't have a steady surface .in some places it seems like some small steps on face of the spillway.although i try very small ratio of meshinges,nothing happenes.i have no idea that what the solution is.could you plz help me.thanks.

It depends on how you're analyzing the output. 2-D output will show the calculated surface exactly as it was calculated. 3-D output uses an approximation to create an iso-surface, and the approximation means that 3-D plots do not show the free surface perfectly. I suspect the little steps you're seeing are related to that 3-D approximation. View the spillway in 2-D to check.