Which of the following criteria is essential for grass channel design to avoid erosion?

Flow velocity during storm events is a crucial factor in the design of grass channels to prevent erosion. When designing these channels, understanding the anticipated flow velocity helps in assessing the potential for soil displacement and erosion. High flow velocities can lead to increased shear stress on the channel bed and banks, which can dislodge soil particles and compromise the stability of the channel.

Properly managing flow velocity involves designing the channel with appropriate dimensions, slope, and vegetation cover, which collectively help to slow down the water flow. The grass in these channels acts as a stabilization mechanism, reducing velocities and promoting sediment deposition rather than erosion. Hence, ensuring that flow velocities remain within a safe range is vital to maintaining the integrity and function of the grass channel.