[img]/forums/images/icons/tongue.gif[/img] The nozzle that I described needs at least 200 PSI to really do a good job without wasting all the water. Before you launch this project, do some walking through the yellow pages and see if there is a sewer cleaner guy who has one of those crap-blasters. He might just be willing to take a weekend quasi-vacation in the mountains and give you a decent price on blasting the culvert. [img]/forums/images/icons/crazy.gif[/img] It looks to me as though you may want to build an inlet structure that resembles a manhole with no lid and attach that to the upstream end of the culvert. That would help pond the water and stop the silt. Sometimes we even make a cut out in the inlet tub and put flashboards in the cut out to help control the silt. You add boards as the gully silts in, thereby giving you more interval between cleanouts. I wish I was on site to advise you on this; I have a great deal of experience with reclamation and drainage. [img]/forums/images/icons/smile.gif[/img]
You can buy kits for running PVC under a sidewalk that have a PVC nozzle that glues onto the regular PVC. The idea is to use water and the nozzle on the pipe to bore through, then leave the pipe in place, cut off the nozzle and finish connecting your other pipes. For your purposes, you'll want to pull it back and make more holes, eventually digging everything out and then washing it down with the water stream from the nozzle.
contact your local fire department here in ohio we help clean culverts all the time with our pumpers all we usally ask for is a donation to the department