Years ago, I worked for the Soil Conservation Service. We built mostly "at grade" rock crossings, but did do a few precast concrete crossings.
Questions ;
How deep and wide is the perrenial stream ?
How entrenched is the stream ? How high are the streambanks from the water surface to the top of the bank?
Is the stream/creek bottom soft (sand, mud, etc) or firm (gravelly, rock, etc) ?
Answers to these questions tell me if it's workable or not.
