The substructure is the supporting part of a bridge.  For this project there are five piers and, of course, two abutments.  The piers will be built first.  This process is usually: build a cofferdam and pump the water out, drive the piling, pour the footing, pour the column, and pour the pier cap.

Pouring the pier column
Setting the forms
First Pier Complete
Pile Driving
Insulated Forms
Second Pier Complete
Building the Cofferdam
Rebar stockpile
Five Piers