Bridge Pier layout

Hey Guys,
 I am in need of a bit of input on staking bridge piers. I have staked out new bridges as well as baselines for bridge deck replacements but never a new bridge & peirs) that runs literally next to & at the same elevation as an exiting bridge. That is to say that 1/2 of the new bridge will fall directly in place of the existing bridge. They are going to construct 1/2 of the new deck, switch traffic over to the new section, demo the old bridge & finish placing the remaining half of the new deck on top of the new piers.

My question is how have you guys layed out offsets for new bridge piers that fall in a river that is always flowing & sometimes floods? The bridge I am talking about is 3,000 feet long & about 50' above the water surface.

Thanks

Hard to say without seeing the plans.

First, are there going to be cofferdams erected for the new piers? How deep is the water?

Are the new piers to be built as "extensions" of the existing piers (i.e., a widening of the existing bridge), or are they away from the existing piers, with longer spans?

First the cofferdam sheeting gets laid out, then more accurate layout for footing, bearings, etc., can be marked on the sheeting.

Or, the contractor may have to erect some falsework or temporary platforms for you to set up on.

Completely new piers with a longer span between the new piers than existing. Yes sheet piling will need to be installed as the water is roughly 6' deep. I was thinking that the contractor will build a causeway to get his equipment out to the center of the river.