As evidence has been presented that the Erosion channels are slowly getting wider, yet DSOD Inspectors have not been able to observe any water in these channels when the Green Wet area is saturated, what is happening? Processed imagery data reveals that "fines" (sands, & tiny minus gravel) are being removed and causing the underlying cobble & rock to be further exposed & remain or even loosen and tumble. Yet the channels are gradually deepening and widening (Imagery data). Where are these "fines" going?
DSOD inspection reports do not reveal any discovery of piled up "sands" accumulating at the bottom seam of the hillside. With the numerous individual Erosion channels averaging from 5 feet to 7 feet wide, and the combining of these erosion channels measuring from 20.55 ft wide and greater; with the length of the channels, the depth (from shadows & cobble boulder increased exposure), surely there must be a volume of accumulation of material somewhere?
Could it be possible that the "fines" are migrating downward in a form of an "intergranular seepage"? If so, this would require a "granular" migration chain reaction from a subsurface sequence of "void" channels that these "fines" may migrate into. Then what formed these deeper "granular voids"?
Eventually rainfall percolation movement of these "fines" should eventually stack up and backfill to the surface. If so, then why do the Erosion channels keep growing? The only answer would be that a bigger subsurface condition has either already occurred or is continuing to occur. This "subsurface" condition would had to have been a large area migration of deep subsurface "fines" that were ported deeply downward & went somewhere. Looking at the full square footage of the Erosion channel area, if this whole swath was scoured in a capillary type of vertical downward migration erosion of "fines", this would allow the individual Erosion channels to form as they have - naturally from rainfall. The key difference is that the rainfall is not "pushing" the fines downhill, but is facilitating the "percolation migration" of these fines into the Zone 3 fill.
The original forces of a large hillside saturation, and likely combined with some rainfall at the time, are the only positive hydraulic pore pressure conditions that could upwardly "disassociate" the original construction consolidation of the fines in the Zone 3 fill. More so, the saturation likely was from a wide area subsurface flow. This subsurface flow, of a higher hydraulic pore pressure, would have the ability to "migrate fines" downward in a bottom-up back erosion condition where the "fines" ended up inside of the bottom horizontal Drain Zone. This Drain Zone would easily accept the migration of "fines", from a strong subsurface flow, as the Drain Zone is comprised of gravels, cobbles, and boulders - plenty of space for a large volume of "fines" to be deposited. As long as the Drain Zone is able to accept this continued "depositing", the upper strata of Zone 3 areas will be micro honeycombed with flow channels for more "fines" - simply by a mix of rainfall entering the erosion channels, eroding & migrating more surface fines into the channels + then percolation downward. This process also deepens the channels as more fines are eroded and carried downward via percolation. (note: the average "flow" of water would be thin as there would be a continuous percolation absorption compared to a normally "combined" flow in a typical channel - thus the missing DSOD information on why there are no "piles" of accumulation at the bottom of the hillside seam.. the "thinness" of a channel flow, in a heavy rainstorm, would be determined by the percolation rate absorption to sq ft deposition rate of the precipitation).
What this reveals is that there is likely a wide area "flow" condition below the Green Wet Area that is unseen. If this subsurface flow contains silts, soils, clays or clayey "fines" from the Transition Zone or the Core, this too would be "unseen" as this flow over time would be deep under the Zone 3 surface. This a key reason why there are no thick greening areas in these "Erosion channels" - there is no upward surface deposition of a vegetative soil base. All of the "fines" migration is evidenced as a downward percolation flow.
