mine is similar but no where near the pucker factor, I took 24' x 24" split it in half and made mine.
I only need about 2 feet of fill on top but already have about 3 of gravel just to try and set up so floods go out around the low side. I have some finish work yet to do, time and winter issues mostly.
newest pics. below the culverts are 25" by the tape for ref on sizes of rocks on inlet side.
down stream side there is the bits of the old bridge still visible, I just put culverts under it and used it as a way back & forth till I had the fill up to top of old bridge level. the planks are the old deck I kept there till fill was up to level. I ended up leaving them for now on top just because I have not made u my mind whet to do with them.
It was a toss up about using rocks as base but this place is subject more to a flash flood issues so gravel seems to move around a LOT. taken 100's of yards out of the YARD where it was deposited after flash floods. as you can see it is a shallow enough to have done the ford but would have had to use crete to tie the rock together.
This is the real issue with the culverts, mine was in for a week under the bridge chained to the bridge (which has been washed down stream once in last 15 years & had to be drug back up.)
which put 25 yards of gravel into the park/yard area below the bridge and up stream of it. the stream is dry 25% of the time.
Click any of the pictures to go to the photo bucket folder and see all the picks adding more today.,
Mark