Replies

Water Seepage Issue - Answer from "layered" construction of earthen dam? - (problematic "Wet Area" aligns at seam of Layer 2 & 3)

More Clues: The Logistics of moving the fill material conveyor system drove a "layered" construction approach to the main Oroville Dam. At the top of each layer the surface was smooth as observable in early construction photographs. In typical construction, the surfaces would be slightly crested to prevent "pooling" of rainfall. Evidence of this is revealed in the "seam" elevation curve measurements on the outside of the dam. With a slightly sloped crest, and a smooth type of surface to each large step "layer", a moisturized surface exposure (natural rainfall) could occur as one layer is finished before the next layer is started. These factors may explain the unusual horizontal nature of the problematic water seepage. The problem area is right near the seam of the junction sections of the top of Layer 2 and the bottom of Layer 3. The same "layering" may also apply to the impervious core emplacement (stages).

The water issue reveals itself in a recent March 15, 2017 aerial photograph. Very strong greening in horizontal sections reveals a water source. The water source and "greening" also reveals a "sheet" type of dispersal - which would conform to the layer seam formed in the construction of the dam. With the elevation arc cresting of the layers, the inferred source to the water is from the boundary of layer 2 top and layer 3 bottom. The 2017 image reveals that there is little to no greening to the other areas of the dam embankment surface. If precipitation were the source to this "wet area" vegetation, there would be an expectation of other green areas (is little to none).

Oroville Earthen Dam built in sectioned layers - construction image reveal a "smoothing" at a layer elevation point (Layer 1). May form a "seam" from the smoothing. Conveyor system noted in the image.

Layer 1 and Layer 2 revealed in model. Oroville Earthen Dam built in sectioned layers - model infers a planned "smoothing" at a layer elevation point. A type of "seam" may form via the smoothing. Model shows the construction approach to the logistics of relocating a progressive earth fill conveyor system.

Layer 1, Layer 2, Layer 3 revealed in model. Oroville Earthen Dam built in sectioned layers - model infers a planned "smoothing" at a layer elevation point. A type of "seam" may form via the smoothing. Model shows the construction approach to the logistics of relocating a progressive earth fill conveyor system.

Wet Spot returns: visible in 2017 - Notable green vegetation growth in horizontal strips - near seam of Layer 2 top and Layer 3 bottom seam boundary. Picture taken March 15, 2017

If the water is coming through the earthen dam from the reservoir, I would think it is an unfixable problem without draining the swamp so to speak (maybe in more ways than one). It would seem to me that once water found its way into the interior of the earthen dam the gig is up. I know water inside of things can go every which way but loose.

I would think that the swamp would need to be completely drained so they could either do some major repair of the earthen dam or the build a new one.

Is there a better alternative to a dam made of earth when the dam is this massive size?

What other alternatives? A series of smaller dams?

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.

The “surface erosion channels” shown in your 2670 post are a very significant concern. These channels appear to be new, in that they weren’t indicated in previous DWR dam inspection reports, and appear to only be directly below the the horizontal seepage areas, indicating they weren’t caused by surface erosion from the recent heavy rains.

The flow through these seepage pathways would be the greatest when the dam head is the highest. So when the dam was topping out last month, and the cameras were trained on the failure of the main and emergency spillways, the surface of the dam itself may have been eroding on the flip side of the channel. Once you start to get actual movement of material, things can escalate exponentially and uncontrollably, as was shown dramatically with the main spillway.

This would indicate that even if the do expend the mega to gigabucks over a couple years to adequately repair one or both spillways, once the lake level rises enough for those spillways to be operationally used again, there may be sufficient head on the dam to blow it out.

DWR must be aware of whatever dam seepage has or is taking place, as these wet spots were mentioned in previous inspection reports. Yet, they have repeatedly said “the dam is fine”; the only public safety issues are with the spillways.

This would be good fodder for questions at a DWR press conference, or better yet, for one or more of the “independent experts” whom, without CYA issues, might be more objective and honest.