40' Bridge Span - I-Beams or Concrete?

I have bought some land in Ellis County, Texas that needs a bridge across a drainage creek. The creek only has water when it rains, but when it rains IT DRAINS ALOT OF WATER! To that end I feel I need to have 6' clearance, 16' width and a span of 40'. My question is, what weight for 12" x 8" steel I-Beams do I need to use, or would I be better served by placing three 5' x 24' steel culverts with concrete facings and topped with one foot of roadbed?