Have a few questions on bridges. And wasn't sure which forum to post to! But, went here, since my questions regard G Scale girder bridges. I have 4 Garden Metal Models 12" girder bridges for use outdoors eventually! Before I attempt to install them, somehow, I'm wondering about clearances. As trying to figure out HOW to build the needed abutments! That is, a minimum height, maximum height, or average height above a road, water etc... A couple of mine will be crossing over a small, DRY river bed. Used for water drainage from roof downspouts. Plus, it adds a little variety to the railroad. Anyway, Information appreciated. Thanks.