In these photos, the river is at high water during the early spring. The Mississippi is typically about 20 feet wide and a foot or two deep for its first few miles downstream of Lake Itasca. The average flow rate is 6 cubic feet of water per second. In contrast, the flow rate under the Crescent City Connection bridges in New Orleans is about 600,000 cubic feet per second. That means that the river grows in size by a factor of 100,000 over the length of its journey to the gulf.
The National Park Service makes the analogy that it would take 10 minutes to fill a semi-truck tanker full of water from the flow of the river coming out of Lake Itasca. In comparison, the river flow at Algiers Point in New Orleans approximately 166 semi-truck tankers per second.
The statistics above are from the Mary Costello book, Climbing The Mississippi River Bridge By Bridge, Volume 2. Costello goes on to say that the original bridge was built in 1968. It has been replaced several times, including once in 1979 when it washed away. The current bridge, installed in 1987, is made of treated wood and has a more substantial base.