Going back to prior images before the Main pre-spillway, there are numerous sign of the "HerringBone drain pipe" alignment in Maintenance repair cracks on the surface concrete of the Main Spillway.
Why is this important? The drain pipe, & enveloping drain gravel around the pipe, reduces the thickness of the main spillway slab (see blueprint data posted by abb in post 2,132). This reduction of slab thickness would represent a weaker structural zone vs the full slab height. The very strong indicators of these Maintenance repaired cracks, in a "herringbone" type of pattern, leads to the question of if this is a leading contributor (combined with subsurface erosion, stagnation pressure, WEAK point in concrete slabs from drain design, expansion/contraction stresses, etc).
