[EarthResearcher333]

Water Seepage Discussion - Dark discoloration markings on Finished Dam + two "downslope" large wet areas in early operation

Earthfill embankment dams are known to "settle" in time. All embankment dams have some seepage. Some of the seepage will affect the internal compacted materials if the seepage flow does not destructively erode into internal "channels" or form cracks. An interesting case is revealed in the early days of Oroville Dam. The first photo was taken shortly after the completion of the dam where the reservoir was filled. Notable in this image is dark discoloration markings in stratified areas of the back surface of the dam. The dark discolorations are inferred to be from seepage.

Later, during early operation of Dam, two sections of the backside surface of the dam show remarkable wet areas. Both areas have in common a thin horizontal seam above or upslope. This may infer an internal water seepage flow within the pervious (waterflow capable) fill on the outer zone fill that resulted in the dark discoloration & partial greening of the downslope areas. Note the branching horizontal strips that infer to be branching out from a common layer seam in the construction of the earthfill embankment layering. Today, these areas are dry and have been dry since images going back to the early 2000's. The only area that has persisted is the current "wet area" in the left mid-slope of the dam. (noted per the recent Dam Safety Inspector reports on "investigating" and "taking action" based upon findings).

Photo taken shortly after the completion of the dam where the reservoir was filled. Notable in this image is dark discoloration markings in stratified areas of the back surface of the dam. The dark discolorations are inferred to be from seepage.

Photo taken in early operation of the dam. Notable in this image is two large dark discoloration areas with some greening hue + stratified branching in areas of the back surface of the dam. Note that each has a top horizontal seam above. All of the dark discolorations are inferred to be from seepage.

[EarthResearcher333]

Oroville Earth Fill Dam Design - Drainage Zone (gravel cobble boulders) to collect seepage & Wet Area location

Blueprints reveal the compacted materials within the Oroville Earth fill dam, including a "Drainage Zone" filled with gravels, cobbles, and boulders to collect "seepage". The Drainage Zone is a 20' wide chimney constructed between the Transition Zone and the Pervious Embankment Shell Zone. Any seepage through the two Transition Zones and the center water barrier Impervious Zone is intended to be collected in the Drainage chimney. The Drainage Chimney has a 10' thick horizontal Drainage Zone that leads to a seepage monitoring station at the Toe of the dam. Below this side view blueprint image is the Feather River Embankment Canyon cross-section view. The "Wet Spot Area" is at an elevation that is near the seam abutment elevation of the Feather River Canyon walls. Grouting was performed along the canyon wall abutment. Note that the Palermo Outlet Tunnel is about 100 ft below the "wet spot area" in the canyon rock. If the Drainage Zone Chimney is ineffectual on this side of the canyon wall, then seepage could by bypassing the chimney (going horizontally through) and leveling out at the layer 2 to layer 3 construction boundary compaction seam.

There still is a correlation puzzle on reservoir water levels to the "wet spot" area (i.e. vegetation greenage in the Wet Spot area does not always correlate with reservoir water levels). Most notable was high reservoir water levels at the 2016 inspection date window of photos showing a dry zone & dead grass.