We had a similar problem with the road into our shooting range. Talked to the county about a culvert - no way! Couldn’t get approval for concrete either. One of our members had a connection with local gravel pit...he made a call for all of the big mud rock we could get. During a dry spell we dug out a pit about 4-6 ft deep across the crick and pushed in the mud rock and put large gravel on top of that. Water occasionally flowed over top but it just washed the big gravel into the downstream side and we replaced it. Last years floods backed water up over top of the fence posts in that area but the bed rock stayed put and it took very little work to get back passable.

Good luck with a tough problem!

“My horn is full and my pouch is stocked with ball and patch. There is a new, sharp flint in my lock and my rifle and I are ready. It is sighted true and my eyes can still aim.”
Kaywoodie