In his own words: DWR’s principal engineer describes the changes to the Bay Delta Conservation Plan
No doubt, the big story today in the papers will be regarding the changes made to the Bay Delta Conservation Plan that were announced yesterday, but here at Maven’s Notebook, I am always striving to give you something a little different.
Probably the person who can best describe all the changes made to the project is the engineer at the drawing board who is making those changes, and that appears to be Gordon Enas, principal engineer for the Delta Conveyance and Habitat Conservation Program. Here is Mr. Enas, in his own words, describing the changes made to the project.
(Note: For ease of reading, only other people’s words will be in italics. This is pretty much a straight transcription, so I’ve eliminated the ‘Mr. Enas said,’ etc. You can assume words in quotations that are not attributed to someone else are from Mr. Enas. )
Gordon Enas started by saying that the project is going through an ‘optimization’ process which is a normal process that any large infrastructure project goes through. “You start out with some concepts and some ideas and then as you meet with people and as you discuss it with your team, you come up with ways to make improvements, and so this is the process that we’ve been going through the last year to make improvements to the conveyance project.”
He then ran down the changes, starting in the north:
“After discussing with residents, landowners, business owners, and public safety officials around the town of Hood, part of the program is to move Highway 160 temporarily while we are building the three intakes at the northern end of the project, and in doing so we need to construct a detour for Highway 160, so part of our optimization was to move that detour further to the east where we are incorporating an existing railroad embankment. … We feel that due to the impacts to landowners and public access as well as public safety, by moving further to the east and onto this existing embankment, we’ll make a great improvement on that.”
“Another large improvement we’ve made is originally at the north, we were proposing to use that area as a borrow area because we’re building some fairly large intake structures and they need a lot of material to build the foundation pad for them. We were hoping to use that area to the north, but after discussion with landowners there and the reclamation districts, we recognized that we would be greatly impacting some of their irrigation and drainage systems. Also the Stone Lakes Wildlife Refuge mentioned that the property over there is heavily used by sandhill cranes and species that use the refuge for foraging. We’ve eliminated that borrow site from the project.”
“Another thing we’re trying to do is utilize DWR-owned property wherever possible, so the Department currently owns a piece of property just between the third and fifth intakes, and we’ll be using that area, we’ll be concentrating all of our staging, parking, personnel, and office buildings on that piece of property. That will help us reduce the amount of traffic in and around the town of Hood while construction is going on.”
“Another significant impact that we were having on the town of Hood – originally we were proposing to put a pipeline connecting one of the second intakes – the middle one – to our intermediate forebay. We were going to use a traditional construction method of cut and cover, but after again talking to especially the fire chief in Hood, we recognized that it would be a huge disruption to his firehouse, as well as just getting traffic around the area, so now we’ve gone to a option where we’re not going to be using any cut and cover pipelines; we’ll be constructing tunnels for all of our conveyance features. So now we have tunnels running from all the intakes down to our intermediate forebay.”
“Another significant change we’ve made is we’ve reduced the size of our intermediate forebay. We’ve always needed a forebay – when you take water off the river, you have to take it when the water is available, but oftentimes when the water is available in the river, it’s not a good time for us to deliver water to our pumps down at the southern end of the project. We were counting on using the forebay as kind of a regulation basin to handle that mismatch in flows. Also, originally we intended on having a large pumping plant there, and so the size of the forebay was contingent on being able to operate this large pumping plant in a way that minimized the use of power during on-peak times, so we needed a place where we could store water temporarily. Typically what we do is in the evening when the power rates are lower, that’s when we pump water, but with the elimination of the large pumping plant as well as going to a gravity system, the need for a large forebay at the northern end was greatly minimized.”
“In our discussions with landowners, we realized that a forebay at that location seriously impacted the irrigation and drainage systems in the area; it also impacted foraging habitats for sandhill cranes that were flying through the Stone Lakes NWR, and just the size of it was disruptive to landowners, people and the public in the area, so we’ve relocated the forebay further to the east and further south. We’ve also shrunk the size of the forebay from 750 surface acres to down to about 40 acres; now the reason for the forebay mainly is to provide the amount of driving head to push the water down through the tunnels. In doing so, there are benefits to the project; we were able to reduce the length of the large tunnels and we’re also able to relocate the forebay closer to property that’s currently owned by the DWR. … We’ll also be using these areas to store the excavated material that comes out of the tunnel, and possibly also use these for additional sources of borrow material.”
“Moving the forebay to the east also enables us to utilize I-5 as our major corridor for transporting materials and equipment. Originally having it up against the river and moving that kind of equipment and material into the Delta would have a serious impact on local farmers and other operations that go on there, so we think that will be a significant benefit to the Delta communities.”
“One last thing, another benefit, there are several gas wells in the Central Delta, so by moving further to the east, we’ve been able to eliminate the potential of damaging or conflicting with those wells.”
“Moving the forebay to the east necessitated that we move our tunnel alignment to the east; we think it’s a great improvement too because now we can move the tunnel through Staten Island; we think that will be a benefit to the project, for several reasons; mostly it takes us away from Delta legacy communities, it takes us away from having to use privately-owned property, and we think that the excavated material that comes out of the tunnels can be used for habitat restoration projects and levee improvement projects that are currently being planned on Staten Island.”
“As we work our way further to the south, the tunnel alignment pretty much stays the same. Originally we had one of our retrieval areas where we were retrieving tunnel material on Bacon Island and further down here on Victoria Island, but after discussions with folks in Discovery Bay and on Victoria Island, they were concerned that we would have that much tunnel material close to their community, so by realigning the tunnel and also by incorporating our Clifton Court forebay into the project now we’ve eliminated those 2 tunnel disposal areas, and are now going to be using the location just at the very end, the terminus area of the tunnel, to store the tunnel material.”
“Finally, the last significant improvement is incorporating the existing Clifton Court forebay into the project. Originally we had planned not to use the forebay but to use a piece of land on the south as our terminal reservoir. We still need the additional storage space that we lost up at the north end, so by utilizing the forebay, we’re able to still maintain that same capacity that we originally needed but make some needed improvements to the forebay. By incorporating the forebay into the project, we can add some additional reliability to the system and bring the forebay up to current seismic and flood protection standards.”
“The one other thing that we’re currently doing is we’re looking for ways to use the excavated material we take out for the tunnels. We think there’s a significant beneficial use for the material; so we’re currently testing it to see what it takes to use it for engineered backfill and also to use it for habitat restoration projects. And so we’re currently in the process of testing that and hopefully the results from that analysis will show that there’s significant beneficial uses that can come from the material.”
“So just in closing, the optimization process continues. It’s not something that we’ve stopped; it’s ongoing, as we continue to look for opportunities to optimize the project and continue to reduce impacts as we move forward.”
Question: The tunnels have been shrunk from 35 to 30 miles. Are there any changes proposed in actual diameter or dimension of the size of the tunnels?
(Mr. Enas answers) “Yes the original size of the tunnel was 33 feet, interior diameter. That was a pressurized system. When we went to a gravity system, it required us to go to a larger tunnel so that we can allow the water to flow by gravity, so that’s why we increased it to 40 feet where we’re at now. That’s really the size we need to ensure we get adequate flow by gravity.”
Question: What’s the maximum capacity of the 40 feet diameter tunnel?
Mr. Enas: Our design is for 9,000 cfs.
Question: Could it do more than 9,000 cfs?
Mr. Enas: “At 40 feet, you could, but you’d probably have to pump it or pressurize it. So right now we’re planning it on being purely by gravity. If we went back to the other concept where we have a pumping plant at our intermediate forebay, you could possibly push more in it, but really the limiting flow constraint on the system are the three intakes. We’re not putting more intakes in, we’re not increasing the capacity of those intakes, they are still at 9000 cfs.”
“Let me add to that,” said John Laird. “One of the major goals here, when the water project was designed in the 1960s and 1970s, climate change wasn’t as fully understood as it is now, so our real goal in moving the water to do it gravity flow so there is significantly greenhouse gas emissions as part of the process. And the second thing is that the project, as it has been operated the last 40 years, and this one that is proposed, is subject to a permit. The Delta pumps have a capacity that’s greater than what is being exported, but it is limited by what the permit is. We intend to seek a permit that matches that and make sure it matches the 9,000 cfs gravity flow as the maximum.”
Question: Is it 9,000 maximum or is it 9,000 average? I’ve heard the term average a lot. So you would have the capacity to pump 9,000 at certain times when you need it and then lower it to average out to 9,000.
Mr. Laird: The intent is it’s gravity flow and the maximum is 9,000 at gravity flow.
Question: Could you explain what the changes are to Clifton Court forebay … more water in there from the tunnels … ?
Mr. Enas: “There are going to be significant changes to the forebay. What the plan is that the operation of the system will still be a dual system. We will still be making diversions from the south Delta using the existing method of bringing in water through the gates down there, so in order to keep that operation intact, we need to enlarge the forebay, because in order to keep that operation moving, you have to have a certain size forebay. By enlarging it, now we can utilize not only the southern operation but combine that with the north Delta operation. The improvements will be improving the embankment surrounding the forebay, and securing and incorporating the land just at the south and making part of that the enlarged forebay.”
Question: As I understood it before, you were going to take the north Delta water and put it in another storage area before it was put into the aqueduct, so are you going to be putting most of the water from the tunnels into the Clifton Court forebay before it’s put into the aqueduct? Where are you going to be putting the water now?
Mr. Enas: We are providing water in the north part of the forebay for the diversion for the north and that’s considered fish free water but the south part of the forebay still has to use the existing fish facility and that’s why we need to maintain the size we’re currently at.
Question: So are you expanding the size of the Clifton Court forebay or just strengthening it?
Mr. Enas: Yes we are expanding the size. The overall size will be about 2700 surface acres. Currently it’s about 2100, so the southern part of the forebay will be about 1900 surface acres, the northern part of the forebay will be about 800.
Question: So altogether you are expanding the forebay by 600 acres?
Mr. Enas: Correct.
Question: Since the Clifton court forebay is connected to the pumping operation, and the pumping operation has had huge impacts on the south Delta, you are going to be enlarging the forebay, you’re going to be pulling more water from the forebay because it’s bigger, is that going to have an effect on the south Delta?
David Zippin, ICF: “The forebay itself will be split in half. There will be an interior levee constructed to separate the water on the north side of Clifton Court that would be coming in from the north Delta from the water that’s already there being pumped directly from the Delta. There will be separation. The forebay will also be dredged to deepen it slightly to make up for the split to maintain the same capacity that has now for the south Delta water.”
Question: How are the fish screens different than the fish screens currently being used in the south Delta?
Mr. Enas: “The current design for the new intake facilities will be using current state of the art fish screens similar to what is being used in other intakes on the Sacramento River and within the Delta, and they will be designed to a Delta smelt criteria. The existing Skinner Fish Facility in Clifton Court forebay will still remain intact and continue to operate for the south Delta portion of the diversion.”
Question: How will these changes affect the operational flexibility of the system?
Mr. Enas: “The intermediate forebay we were originally proposing was about 750 acres. The little appendage that we were going to add at the bottom of Clifton Court was about 600 acres, so for a total of about 1300 total surface acres. By going to the gravity system, we no longer need again that capacity of the large forebay that was originally based on the need to take water off the river at any time of the day but then hold it until we can get more favorable pumping rates; that really dictated the size of that originally. Then as we started working on this optimization and with the move to a gravity system, we realized we didn’t need that size any longer. Even if we move the water to the south, we still need the ability to be able to hold water until the pumps at the south are available to take it, so we still need some capacity. The math may not add up directly because we no longer are using that north forebay in the same capacity.”
FOR MORE INFORMATION:
- Click here for links to the documents detailing the changes to the project.
Note: Pictures courtesy of the Department of Water Resources.