Conditions on freezing water

Observing the freezing phenomenon of river, here are some questions pop up.

Comparing with pure water, impurity in water will alter melting point, what are the qualitative and quantitative explanation, I know specifically intermolecular interaction like salt and water will change molecular interaction.

Intuitively, stationary water will have higher melting point than running water as latter has higher velocity (Let’s simplify the motion as 1D constant velocity). can anyone determine my guess and give an explicit formula between melting point and fluid velocity. Specifically, is there a critical temperature (other than absolute zero) that no matter how high the velocity of water is, it will freeze.

For a more complicated treatment, will the motion of water effects the melting point? Which means in 3D, acceleration/ constant velocity of linear translation and rotation of fluid, even more, the geometry of container.