after probably 25 years of trying different things to cross our creek I finally got it right. We first had a small creek that you could jump across and now due to more homes, more roads, a shoping mall and just good ole' mother nature we have a 20' wide crossing. We had a bridge at one point built out of free telephone poles and 2x12's, worked great until we had a crazy flood, the bridge turned into a raft. I placed a "dead man" on one corner and chained it down so the raft didint get far. We now have 3 concrete culverts with set up like this __O___O___O__, i placed large rocks between them, covered the rocks and culverts with flat sandstone and concrete. The most important thing was to put rocks out into the creek to direct the water into the culverts. You will also need to protect the bank on both sides with rocks or gabion box's to slow down erosion. Cutting down the bank to acess the crossing will also cause erosion, I curently have my ramps packed with clay and that has been very efective.
the only thing we ever paid for in this process was bags of redi mix, the culverts were all free due to cracks, broken flanges, or cut down left overs. Large rocks were the key, when you have a flood the forces that are on a crossing are extreme and unpredictable. good luck