How Would I Calculate Range Here?

[Mad_Dog_of_Fujiwara]

Basically, a character fires a beam attack that we see engulf a large section of a bamboo forest. I'm no good at calcing stuff myself, so I'm wondering what the best method for determining the beam length would be. Or should I just go with a vague "hundreds of meters" or whatever on the profile?

 

[Mr_Sugabz]

I think it's a bit enough to calc if the scene is like that, but on the 2nd Pict I think the distance is at least 30 meters