I Learned about The Cause

Scouring (the removal of sediment from a streambed caused by erosive action of flowing water)
hydraulic gradients

The cause of this collapse was an engineering oversight and failure to detect it during inspection. High speed burms were built upstream to divert water from farmers fields. Because the increase in velocity of water (from man made banks) was not taken into account the size of rocks used to protect the peers at the bottom were not sufficient. It took 20 years but eventually the center support gave because it was exposed to high velocity river water (scour).

Engineers now use electronic sensors in some bridges that warn you when a weakness is detected.