I'm working in an urban area where after the pedestrian/greenway project is complete, there cannot be any (zero) permanent structures in the channel bottom of a jurisdictional stream. We are currently constructing poured in place swale bridges over jurisdictional "ditches" with maybe a span of 4'. A small swale bridge may take 3-4 pours and our contractors hate them because of the time between pours. We are looking for an off the shelf, small, pre-cast structure that we could install in a day or so. Maybe a three-sided box culvert. Loading needs to be at least H25.
Looking for ideas and advise if anyone has ran into similar situations.