OROVILLE DAM, Thursday noon: Work continues on mitigating erosion; Flows are starting to ramp down

Here’s the latest from the DWR press conference:

BILL CROYLE, Acting Director of DWR: “What I want to do is run through the numbers for the day and status of a number of areas we’ve been talking about the last couple of days.  Our top priority in our unified command structure with the people you see before you and many people that are not in this tent is public safety.  So we have an initial public safety with the threats that we’re mitigating now, and then we have an ongoing effort here to work very hard for this coming spring and summer and fall to make sure that we’re ready for the next wet season as we move through this period.

The lake level continues to decrease.  The lake surface is now at 868’; we started at an elevation of 901’, so the work that we’ve done by discharging at a rate of 55,000-100,000 cfs here in the last number of days has reduced the water level in the reservoir which gives us more flood storage so we can take on these initial storms.  We saw one come last night and we see one coming in the next couple of days.

The inflows to the lake currently are at 25,000 cfs; again those inflows are going to go up and down as we go through our weather conditions.  Yesterday, we had a beautiful day here in Butte County, so the flows went up a little bit.  It got cold overnight and so those dropped back, but on average the inflows are 25,000 cfs.  We expect with a few of these storms coming through the system in the next couple of days that we’ll see these changes in the inflow fluctuate between 25,000 cfs and 45,000 cfs.  This is again far below the amount of water that we’re discharging out of the flood control spillway at the present time, and what we anticipate in the coming days.

We continue to work on our erosion sites in that area on the landside of the emergency spillway.  There are three priority areas that were identified with the various Department, federal, and our third-party contractors in that area that are directing that construction work.  The air operations are on a flyby condition notice, so with this kind of weather, it’s not likely you’ll see the helicopter traffic that we’ve seen in the last few days.  It is amazing how fast they were dumping up until late last night at dark; a helicopter run was every 1 ½ minutes.  It was pretty amazing.

Our ground crews continue to place rock and concrete into those erosion holes in a manner that kind of glues those areas of concern and fills those voids that were generated by the erosion over the top of the dam.  I want to express the mitigation measures that we are resolving is a result of an erosion that occurred by the dam overtopping.  The threat of water moving in or under has been identified as not a threat at this time, so those risks weren’t there from the other sources.  The risk that is now being mitigated is a result of water flowing over the top of the dam and then flowing onto the surface, and during the duration of the flow, eroded some of these gullies which are now being mitigated.

We have three priority sites.  Site 1 is 100% complete.  In other words, that erosion gully is completely filled in and it is armored up.  Site 2 is 25% complete, and Site 3 is 69% complete.  So with the weather conditions, even though they are wet overnight, we continue to make progress in those areas to further mitigate those erosion scores.

Up until 9 am this morning, we were continuing to discharge at 100,000 cfs.  The flood control spillway is stable.  We continue to have a high level of monitoring and surveillance to make sure that as we continue this high rate of discharge given our conditions, that it continues to perform in a manner that we believe is stable and is safe to be able to push this much water through the system.

There has been a lot of work over the last couple of days, and contingency plans are looking at the inflow of the water into the reservoir, not just today but also in the coming weeks.  There was a desire to pull that reservoir down so that we could reduce those flows and be able to access the debris pile that’s build up at the base of the spillway.

As of 9 am this morning, we started ramping down the discharge at 5000 cfs per second every two hours, so that process has started.  Part of our normal procedure, especially now we’re operating emergency action plan, is we provide notice for those downstream so they are aware of what we’re doing.  So the public notice goes out through email and phone messages that are automated that kick out, so every time we turn that dial to reduce that flow, a message is going to go out.  Just because we send a message out to give notice, it doesn’t mean that there is a concern or a problem.  In fact, in this case, it’s a good thing.

Again, as we change the flow, which I mentioned yesterday we were contemplating that adjustment,  now that adjustment is being put in place.  We’re going to get our discharge rate down to 80,000 cfs and we’re going to hold.  So we’re looking at modeling the incoming rainfall, the inflow into the reservoir, and also the dynamics of the flood control spillway itself and our debris pile.  Our contractors are staging in that area so we can start the removal of as much of that material at the bottom of that slope as we can.

The goal is to again manage the inflow and outflow of the reservoir, but also reduce the water level that is pushed up against the Hyatt Power Plant.   Our Department teams and the contractor teams have done an amazing job at waterproofing that facility to ensure that it doesn’t get flooded.  We’re taking additional measures to make sure that we’re doing everything we can to prevent that plant from being flooded and we’ve been successful so far.  The work that we’re doing today to reduce those flows again allows us to get into that lower reach where that debris field has stacked up and start pulling that back so we can let gravity do the work for us and let that water flow out of that pool that’s stacked up against the power plant.  The water proofing measures have been successful; we have redundant systems in place to the extent that that system is leaking or moving a little bit of water into the system, those pumps are removing that water from that plant itself, protecting the operation of the plant for future use.

That plant is important for us to make available so we need to move more of that material away at the bottom of that slope, drop the water level in front of that plant so we can get into normal operations and water conditions on the downstream side, and that allows us to add another way for us to get water out of the reservoir.  So the maximum discharge is the 14,000 cfs, so that adds another dial to our equation in addition to releasing an appropriate amount of water out of the flood control structure, also then we can adjust the discharge rate at the Hyatt Power Plant.  So it’s going to be a little while.  If we can make good progress on our debris file at the bottom of that slope, bring the water down to a level that we can actually use the power plant when it’s deemed safe to assist us in moving the eroded material out of the way and further improving our water conditions up against that plant.  But we will not start that plant until we are sure we can operate it in a safe manner.  That will also help us by activating that plant, deal with our more long-term water supply in this particular area and maintaining our water flow in the Feather River.

That’s an important; it’s a priority part of the work we’re doing, so there’s a lot of mobilization.  We have a number of teams, they are continuing to come in to reinforce our contingency planning, and then the operations part which is executing those plans, so it’s multi-faceted and we have new ideas with different resources coming in to deploy those ideas and again further mitigate the sediment that the erosion and the alluvial fan that has built up there, and then improve the water conditions sitting up against our plant.

We’ve also been able to reestablish some of the debris management that we were doing, like replacing the log booms that were broken away when we increased the flow to further catch the debris that’s coming down or is down and into the diversion pool, so you’ll see boats on the water pulling those trees out of the way or cleaning those log booms.   Yesterday, we made some progress on cleaning trees and debris out of the front of the diversion dam down in the lower reaches.  What that does, it allows us to better operate that system and manage the effects all the way up to the Hyatt Power Plant. So that work has been done, that gives us the ability to make adjustments in this very dynamic environment using adaptive engineering approaches.

We have a lot of people working on this site, agency, third party contractors and our construction crews.  These people are working very hard with long hours, and we want to make sure we have save travel keeping the truck traffic down that helps make sure that we’re safe.  We’re approaching our infrastructure safe, we’re getting in and out of the area below our auxiliary plant, and so all these contractors consult as third parties and the agencies that are coming into this region to assist us to address these concerns are really supporting the bottom line, which is the public safety mission here.  Even though they aren’t here, they are an important part of the entire team, this multi-agency state, federal, local as well as the third party consultants that have been brought here to deal with this.

We have already started our recovery program plan and so we’re putting those people in place, co-locating not only Department but other regulatory agencies and our consultant teams together so we can expedite the site assessment, design, and then future implementation of our measures to get us ready for the next season.

Yesterday, I talked a little bit about how many people are on site and our production rates are relatively the same.  Right now, 96 construction personnel are in place, again we’re at that production rate of about 1200 tons per hour, and again I talked already about the progress we made in those three priority sites.

The latest pictures from Oroville …

The California Department of Water Resources continues to examine and repair the erosion below the Oroville Dam Emergency Spillway. More than 125 construction crews are working around the clock, and placing 1,200 tons of material on the spillway per hour using helicopters and heavy construction equipment at the Butte County site. Photo taken February 15, 2017. Dale Kolke / California Department of Water Resources.

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For all of the Notebook’s coverage of the Oroville Dam spillway, click here.



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