Water direction and intensity of superficial flow

[CristianNunes_Estevam]

I'm working on maps that the goal is: to display the direction and intensity of surface water flow. I have the DEM for the watershed and generated the direction of flow, but I don't know how to generate the intensity and display the arrows proportionately.
Based on what I researched, I need to generate the intensity data and merge it with the flow direction, and then display the direction and intensity vectors.
Does anyone know how to generate the map of direction and intensity of surface water flow?

Note the direction of flow results in the same size arrows, different from the sample image.