Hello All,

I am designing Stream crossing where I have 10′ wide stream. Because of 100 year flow and flood-way condition I am designing 50′ Conspan O series Arch culvert. I am getting different result on design as a bridge and design as a Culvert condition.
I Calculated scour at bride and I am getting 30′ and 25′ scour at left and right over bank, which does not seems right at all.
Question:
1) Which is right method in this situation? Design as bridge or Design as Culvert?
2) If Design as a Culvert( Conspan O series is different then HEC RAS Predefined Conspan Shape) then How do I calc. Scour depth?
3)When Design as a culvert How do I put invert of the Conspan O series Arch Culvert? Because if I buried some depth then it is taking some of Channel Cross section area too.

Thank you in advance for your input here.