For what it is worth, I would do this in your situation:
1- Make it only as high as is needed to clear the size pipes you use while at the same time making it a straight enough horizontal path so that you intended trailer etc won't hang up. The idea would be to make it usable while giving the moving water the ability to flow easily over the entire structure during heavy flooding
2- I would backfill the pipes with some sort of sharp stone (as opposed to smooth stone that won't bind on its neighbors)
3- I would cover the backfill (especially on the sides) with either geo matt or some sort of landscape fabric to hold things in place
4- Cover the sides with a significant amount of rip rap style rocks
5- Cover the top with your choice of gravel
What ever you decide, post some pics!
1- Make it only as high as is needed to clear the size pipes you use while at the same time making it a straight enough horizontal path so that you intended trailer etc won't hang up. The idea would be to make it usable while giving the moving water the ability to flow easily over the entire structure during heavy flooding
2- I would backfill the pipes with some sort of sharp stone (as opposed to smooth stone that won't bind on its neighbors)
3- I would cover the backfill (especially on the sides) with either geo matt or some sort of landscape fabric to hold things in place
4- Cover the sides with a significant amount of rip rap style rocks
5- Cover the top with your choice of gravel
What ever you decide, post some pics!