These "depositions" came from "through the dam" flows, just as the Green Wet Area today is from a "through" the dam flow. Flowing water must pass through the "Silts" in two Zone 2 sections and the Clay-clayey soil base in the core. This water flow is maintaining a "bench" flow to get to the Zone 3 surface. In order to maintain an internal "bench" flow there needs to be a form of a non-pervious ratio of material - i.e. high silts, clay, clayey soils. As this water flow "rides" over the time generated formed silts, clay, clayey soils, it brings these fines to the surface at the Green Wet Area.
For the water to even get to the Zone 3 side from the Zone 2 Transition layer, the water has to cross the 20ft wide Drain Zone. Normally, this Drain Zone can handle all of the intended life of the gradual (normal) seepage. This includes the traces of sands and silts and clay clayey soil materials. They would Filter down through this Drain Zone for the life of the dam.
As designed & working correctly, there would be zero pore pressure past the Drain Zone. The normal Phreatic Surface would curve directly into the Drain Zone Chimney.
However, Oroville dam's Drain zone has been "clogged" at the differential settlement area above the Green Wet area. Just as this "clogging", by overwhelming the Drain with Transition zone materials, the "bridge" is a non-pervious rich clog. This same "clogging" effect continued to migrate in the Zone 3 internals. The original layered construction "guided" the early differential "clogged" flows at the sectional layer seams. The more the flow continued through the Core region, the more "clogging" material would deposit in a "flow" bench. So this chain reaction internal clogging effect is the same effect transporting "soil rich" materials to the Green Wet area. There likely is a curvature of this phreatic "guided" bench to where the inner flow disperses in percolation arcs. This forms the baseline estimate in the "stepped" guided layer illustration in the upstream thread. The "outer reach" of these bench guided percolation arcs is where the material + water reaches the Green Wet area. The differing concentrations of clogging material, formed at different arc conditions, creates the staggering of the thinner horizontal seams of concentrated growth within the large green region. IN addition to the arc's the original compaction strata of construction helped form and guide the deposition of thinner horizontal seam strips.
I fully agree that grasses will grow in minimal conditions. But in this case the water cannot reach the outer Zone 3 surface Green Wet area without flowing atop these extended "clogging" transport layers of silts, clays, clayey soils. The extent of the width of the subsurface saturation evacuation of granular "sands" deeper below the Zone 3 layer in the Erosion Zones is overspill from the "deposited" silts, clays, clayey soil material at the Green Wet area elevation and this remaining overspill saturation flow had high enough pore pressure to disassociate the deeper Zone 3 consolidation - thus enabling the formation of the mysterious "size growing" Erosion Channels.
The Erosion channels have been the key to guiding the evidence of "looking inside the dam". The next greatest key was what the dam demonstrated in the original twin differential settlement seams (saturation flows, deposition of high concentration of "fines" creating "dirt patches", clogging the drain zones in two areas to facilitate the Zone 3 penetration, the sectional seam layer preference of water flow, and the subsequent contrast of the "washing" away of the deposited "patches" where there are no Green Areas there today - but it left a "Clean Surface" in additional consolidation with the Zone 3 surface material).
