Heres what I did with almost the same size creek. I was considering a trailer but nothing came in the price range, looked at the railroad car thing but it was to expensive to transport. I also did not want to spend the money on new lumber for that particular project.
I was driving down the road one day next to the railroad tracks and they were replacing track and had a giant pile of used ties laying next to the track. I mentioned it to a friend and he saw some inspectors going along the track and asked what they were going to do with them and they said "givem to you" /forums/images/graemlins/grin.gif I found about 15 in really good shape so I took those. They must weigh around 300lbs apiece, everything me and a friend could do to lift them on the trailer.
I kept it simple, dug down about 6" to 8" with the loader on both sides of the creek and set them in and filled in the exposed ends. Works like a champ /forums/images/graemlins/cool.gif
The longest one is 13' and shortest was 12'. Good Luck.......