This particular culvert is elevated above the ditch bottom to trap water upstream. The whole area floods during heavy rains due to many field tiles in the watershed of a nearby creek. I suspect the water could have been running at less than half the pipe capacity in a very flat pipe, but I was not there at the time the fish was trapped. The water could even have been running backwards though since this is very possible during flooding. The pond above is a groundwater pond with a small watershed. The critters made fast work of the dead carp, but the spine is still in the pipe months later.