I recently agreed to fill in my neighbor's ditch (along the road) for him. The ditch is only about 2' deep. I will be using 12" plastic corrugated pipe. My question is...Is it necessary to install gravel under the pipe? I am leaning toward not using any gravel because I dont really see a purpose for it. All of the neighbors I have talked to used gravel under their pipes but dont necessarily know why. What do you think? Thanks for the help!