Distance water jets 2

Everything you need should be in HEC-14 Hydraulic Design of Energy Dissipators

You can also calculate the distance the water travels by applied physics, if you assume that the water jet behaves as a projectile. Since d=at^2/2, where a is acceleration, then if we replace a = g, and d = H, then, H=gt^2/2, and t=(2H/g)^(1/2), and the horizontal distance X the jet travels is X=Vt.

I usually calculate the distance for the top of the jet, and provide a margin of error in the rip rap length to allow for possible errors in the velocity calculation.

If the slope is so steep that a hydraulic jump is not formed (flow is supercritical in the channel) then you should line the entire channel or provide a cutoff to prevent headcut. If there is a hydraulic jump, then calculate the location and size of the jump and provide erosion protection for some distance past the end of the jump. Again, provide a cutoff. As indicated by bltseatle, HEC14 should provide some guidance. Also, calculate scour depths and provide protection against scour. You could start with HEC6 for this.