California Water Commission: A progress report on DWR’s System Reoperation Study
At the October meeting of the California Water Commission, Ajay Goyal, Chief of the Department of Water Resources Surface Storage Investigations branch, briefed Commission members on the status of the Department’s System Reoperation Study. The study, mandated by SB X2 1 in 2008, seeks to identify potential strategies for the reoperation of statewide flood protection and water supply systems that will improve water reliability, reduce flood hazards, provide ecosystem benefits, address climate change impacts, and improve water quality.
Ajay Goyal began by saying that the inspiration for this presentation came from the presentation a few months earlier a water commission meeting which included a discussion on the connection between surface water and groundwater storage, and he felt that some of the work underway with the System Reoperation Study was relevant.
Mr. Goyal then explained the study that was authorized in 2008 by Senate Bill X2 1. The Department was directed by the legislature to conduct planning and feasibility studies to identify potential options for the reoperation of the state’s flood protection and water supply systems that will optimize the use of existing facilities and groundwater storage capacity, and to also consider appropriate climate change scenarios. The legislature also directed that the study be designed to determine the potential to simultaneously achieve the objectives of water supply reliability, ecosystem enhancement, and flood protection by integrating flood protection and water supply systems, reoperating existing systems in conjunction with effective groundwater management, and improving existing water conveyance systems.
- Phase 1: Plan of Study (completed 2011): Phase 1 was to develop a plan which included identifying objectives, developing measures, and building blocks, as well as identifying two dozen scenarios to set strategies for reoperation which included reoperating reservoirs on various river basins in conjunction with groundwater and also forecast-based operations, he said.
- Phase 2: Strategy Formulation and Refinement (completed 2014): In Phase 2, we took the two dozen strategies and working in cooperation with stakeholders, we narrowed it down to four strategies, he said. We also did a trade-off analysis, looking at what tradeoffs there are if we were to improve only one aspect, for example, if we were to do ecosystem enhancement using water from the reservoir, what impact could it potentially have, he said.
- Phase 3: Preliminary Assessments of Strategies (completion anticipated in 2015): In Phase 3, we are doing analysis of the four strategies identified in Phase 2.
- Phase 4: Reconnaissance Level Assessments of Strategies (completion anticipated in 2016)
“In Phase 2, we started off by first of all identifying the reservoirs in the various river basins which could be considered for reoperation,” said Mr. Goyal. “We made a list of all these reservoirs: they include Shasta, Oroville, Folsom, New Don Pedro, Pardee, Comanche, New Exchequer, and Friant, and we also considered CVP-SWP integration.” The reservoirs would be reoperated in conjunction with groundwater in the Sacramento and San Joaquin Valley, as well as Southern California, he said.
They next had vetting sessions with the owners of all the surface storage reservoirs, including the Army Corps of Engineers, Reclamation, Metropolitan, Friant, EBMUD, Merced Irrigation District, Modesto and Turlock Irrigation Districts, he said. They also met with NMFS, TNC, Water Research Foundation, irrigation and groundwater districts in the Sacramento Valley, San Joaquin Valley, and Southern California.
“One thing we learned is that several reservoirs didn’t have much flexibility for reoperation,” he said. “For example, when Friant is drawn down to dead pool; it doesn’t have much flexibility. And some reservoirs are going through FERC relicensing, and the owners did not want to participate.”
“We found that in San Joaquin Valley, in Kern and in Southern California, there is ample space in those well-managed groundwater banks for extra storage,” he said. “Roughly it’s about 3 MAF of storage space. What they are limited by is surface water. They want more surface water to fill those banks.”
The list of strategies was then narrowed down to four: reoperating Oroville, reoperating Shasta, reoperating New Exchequer or Lake McClure, and looking at integrating the Central Valley Project and the State Water Project; all strategies include a groundwater component, he said. There were three reoperation components identified: supplementing ecosystem flows, doing conjunctive groundwater management, and operating the reservoirs based on a five-day forecast.
Mr. Goyal then described each component in more detail.
- Supplemental ecosystem flows: Supplemental flows could be used by salmonids for spawning, rearing, to reduce predation or thermal stress, and could be used to benefit Delta smelt and splittail. They could also be used to create geomorphic flows in the river or to implement riparian habitat establishment.
- Conjunctive groundwater management: How this can be applied depends on whether you are north of Delta or south of Delta. In Northern California, the groundwater table is high and is recharged naturally through precipitation or irrigation; here, the conjunctive management would likely be groundwater substitution wherein the users of surface water would use groundwater during critical and dry years, making that water available for other uses. In Southern California, the groundwater table is low, so they are limited by access to surface water; replenishment could be done by spreading basins, injection wells, or providing surface water in lieu of pumping, which is the preferred way.
- Forecast reoperation: Typically a reservoir has a dead pool, conservation storage space, and space for flood control water. Mr. Goyal presented a typical flood control diagram, explaining that the Army Corps of Engineers requires the surface reservoirs to be brought down in November to maintain flood control space from November through March to be able to capture flood inflows. “The idea is that we would, based on a five day forecast, encroach into the flood space or encroach into the conservation space, depending on what the forecast is like,” he said. “If it’s going to be clear and sunny and we don’t expect much inflow, then we would encroach into the flood space for just the five day period, and if we see there’s a lot of precipitation or we expect a lot of inflows, then we would encroach into the conservation space and release the water to create more space to capture flood flows.”
Mr. Goyal explained that they next did a tradeoff analysis to test the flexibility of the system using Oroville and Shasta, evaluating releases of supplemental flows from 25,000 acre-feet to 500,000 acre-feet during spring months from each of the reservoirs, and similarly did conjunctive management with groundwater substitution in the Sacramento Valley or Feather River basin ranging from 25 to 100,000 acre-feet; they also combined several cases for each of the reservoirs.
“One thing that we found is that we don’t have much flexibility in the system, and the system is highly optimized so there are tradeoffs,” he said. “If you tried to provide ecosystem flows, then we noticed that there is less water left in storage and that impacts cold water pool, water supply and hydropower generation, and the impact carries from year to year.”
He then presented an example of the reoperation of Lake Oroville where the target was to release ecosystem flows of 100,000 acre-feet. “We met the target in wet and above normal years, so on average, it was about 27,000 acre-feet we were able to release for supplemental ecosystem flows, but what happened is it impacted storage in Oroville; end of September storage on average was down by about 25,000 acre-feet, so you can see the impact right away. And there was a minor increase in other reservoirs, and there was also an impact in the exports.”
We then overlayed conjunctive management by groundwater substitution in Feather River basin with a target of 100,000 acre-feet. “We did this during dry and critical years, and this improved the storage in Oroville and also improved exports, and we were able to do the same amount of ecosystem flows,” Mr. Goyal said. “Then we overlayed onto this analysis the forecast based operations with 5 day forecasts. We encroached up to a maximum of 25% into the flood storage space, and 25% encroachment equals the release capacity of the reservoir in 5 days, so we were able to increase storage in Oroville by 24,000 acre-feet, and also improve exports a little bit and still be able to do ecosystem flows. Of course, forecast-based operations mean you are taking more risks.”
“Key observations are that existing reservoirs have very limited flexibility, and releasing ecosystem flows will impact storage in the reservoirs which impacts cold water pool, water supply and also hydropower,” he said. “Forecast-based operations does improve flexibility and it comes at the cost of risk, but no other costs. Then forecast-based operations along with conjunctive management would facilitate enhancement of the three objectives we had for the study.”
“Another good things is that through this process, we have developed analytical framework for integrated analysis for surface and groundwater storage, and this could be useful in future studies when we do surface storage planning studies or groundwater, we can do them together,” he added.
They will next incorporate the scenarios with climate change, with proposed Delta conveyance, and with the flood control and ecosystem benefits, as well as continue refining the conjunctive management opportunities, he said.
“One more thing I would like to mention here, Kamyar [Givetchi] and I have been discussing the issue about depleted groundwater basins in southern California,” said Mr. Goyal. “His advice is that maybe for future planning studies, we should consider recharge of depleted groundwater basins as an objective of the project, and maybe even, because of the very low groundwater tables, and of course with some rules, that this recharge of depleted groundwater basins be made a public benefit. It depends on how the water will have to be used; they would have to have different rules for it, but something for consideration.”
“I appreciate the last comment,” said Commissioner Orth. “I think the way you presented it suggests that that’s not a practice that is being pursued in the south Valley and it absolutely is the foundation of conjunctive management in the south Valley is to try and capture the flood flows when they are available and get them through in-lieu, although usually when the flood flows are coming, there’s not a whole lot of irrigation demand, so either through the in lieu, to do on-farm flood water utilization which is a new project being pursued, or the traditional recharge basins. I’m a little aware, but maybe for the benefit of the commissioners, expand a bit on the beneficial use issue that you refer to, because that’s fairly critical. It’s an impediment right now to utilization of surface waters for groundwater recharge.”
“For recharge of groundwater basins, the way we recharge are either those regions put users of groundwater on surface water, which is in-lieu, or inject surface water into the ground, or thirdly we have spreading basins,” replied Mr. Goyal. “Now the issue is that those groundwater tables are so far depleted … there is subsidence happening because of that which impacts not just the users – it impacts the whole region. We will have structural damages as a result of depletion; same thing with land, so because it’s going to affect the public at large, you might want to consider recharge of groundwater basins as a public benefit. And maybe this new groundwater legislation might help us developing rules for this groundwater recharge.”
“I think this is a really good point and something we need to think carefully about in lieu of both the bond and upcoming regulations for the groundwater legislation in terms of how we characterize a public benefit as it relates to groundwater recharge or groundwater banking operations,” said Commissioner Saracino. “What we don’t want to do is get into a situation where we’re looking at a project that provides recharge for local benefit and somehow that becomes a ‘public benefit’ so for the benefit of everyone out there considering applying for funds, we really need to think about how to characterize groundwater projects in terms of their public benefits . I don’t think we’ve done much of that yet in our development of the regulations.”
“The bill AB 1471 does have in the beginning in its findings that investments to expand groundwater storage and reduce and reverse overdraft and water quality impairment of groundwater basins provides extraordinary public benefit, so the legislature, I think, has said they believe that reversing overdraft would be a public benefit, and actually one that may be greater than the other public benefits identified,” said Commissioner Delfino. “It’s something I think that the Commission will, may, upon passage of the bond if it passes, may need to take into great consideration, which is why I think this presentation is so very interesting.”