Good point! Yes the culvert should be grated. It is about a 4'-0" diameter pipe ... so scampering inside is quite doable. This is part of a Storm Runoff Drainage System which is a completely separate system from the sewer. The culvert empties into a concrete channel along side a walking and horse trail.
The open culvert is on the other side of this bridge (the bridge supports a four lane roadway). The left side is for water and the right side is for horses and people.
we grate off everything over 18". crazy what you can fit inside such a seemingly small hole. i like that they've separated the open culvert from the horses & hiking path.