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Some Observations on What Really Drives Water Supply Reliability in California's Delta

Tina Swanson

Posted September 27, 2012

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Yesterday, I posted this piece about California’s recent experiences with its Delta water supply and the challenges that the ongoing Bay Delta Conservation Plan process still faces to develop a plan to meet state-mandated co-equal goals to provide a “reliable water supply” and “protect, restore and enhance the Delta ecosystem.”  I also promised to apply my “simple steps” approach to translate science into plans to solve environmental and resource management problems to the Delta water supply reliability issue.  Here goes….

SThumbnail image for WSrelblog2.PNGtep 1: What have you got? Accepting the underlying premise that the current Delta water supply is unreliable, existing conditions analysis shows that California has three major challenges relevant to the issue.  First, the amount of source water from the rivers and streams that flow to the Delta is finite and variable—we get what Mother Nature gives us and that varies from year to year.  Second, there are structural and functional limitations in the system’s plumbing infrastructure.  Currently, there are large upstream storage facilities on all of the Delta’s nine largest rivers—and contrary to popular opinion, building new dams or enlarging these existing ones does not create new water, it just allows us to rearrange the timing of when water flows into the Delta.  The existing conveyance system, which uses Delta channels to move water to the pumps is old, at risk of catastrophic collapse if Delta island levees fail, and its operations, which reverse natural flows and suck fish (and their food) into the pumps, are harmful to the Delta ecosystem.  Finally, demand for water from the Delta and its upstream watershed has already exceeded the capacity of the river, Delta and San Francisco Bay estuary ecosystems to absorb without substantial and possibly irreversible harm to the valuable ecological, water quality, recreational and commercial services they provide.   The State Water Resources Control Board, the National Academy of Sciences, and the multidisciplinary team of scientists charged with identifying the causes of recent Delta fish declines and the Environmental Protection Agency have all concluded that current flow conditions are insufficient to sustain (much less restore) the ecosystem and its fisheries.  Therefore, in order to meet both co-equal goals, plans to meet the reliable water supply goal are going to have to do it while providing more water for environmental flows.    

Step 2: What do you want?  In California, the phrase “reliable water supply” is like a Rorschach test: some people see only the word “supply” while others focus on “reliable.” Still others confuse “supply” with “demand,” interpreting the goal to mean meeting current or future water demands, or they relate reliability only to the system’s plumbing rather than the supply of water itself.  However, for a plan intended to “provide uninterrupted service” to urban and agricultural water users (the definition articulated by the CALFED Bay-Delta Program nearly ten years ago and since adopted by the Delta Stewardship Council), I would argue that the most effective type of goal would be one that identifies the specific amount of water that can be exported from the Delta on reliable basis, in 95% of years, for example.  And since the plan must simultaneously meet the ecosystem goal, this means that the actual numeric water supply goal will need to be derived from analyses to determine the currently unmet ecosystem needs, rather than as a statement of desired export amounts or even current demand.

Step 3: What are the causes?  The list of factors that affect the ability of the Delta to export water and provide a reliable water supply is not that long.  Runoff to the Delta’s tributary rivers, which varies from year to year, and carryover water stored in reservoirs from previous years constitutes the supply of water available to meet both ecosystem and export needs.  Upstream reservoir storage capacity affects how much runoff can be captured for managed releases for ecosystem needs and export from the Delta and carried over to subsequent years to buffer year-to-year variations in runoff.  Conveyance capacity and physical or environmental restrictions on conveyance operations limit the rates at which water can be exported (and thus annual or seasonal export amounts), while risk of structural failure of Delta levees has implications for long-term reliability of the export system.  Reliability of the export supply is also affected by water management strategies and delivery objectives, for example, management to maximize exports each year versus management designed to reduce year-to-year fluctuations in exports.  Finally, demand in excess of what the system, with its supply, storage and conveyance capacities and its environmental needs, can provide will, by definition, result in unreliable service.   

WSrelblog3.PNGSo what were the causes of the abrupt decline in the Delta water supply in 2008 and 2009 that I described yesterday?  In two words: supply and management.  2008 was the second year of what turned out to be a relatively modest three-year drought.[1]  In 2007, the first dry year, water managers operated the Delta pumps to export 5.6 million acre feet of water, not a record amount but still the 9th highest in nearly 50 years of Delta pumping.  They did this by draining upstream reservoirs filled during the previous wet year and simultaneously shortchanging the estuary of needed freshwater inflows.  When 2008 proved to be nearly as dry as 2007, Delta exports didn’t drop because of pumping restrictions to protect fish, or because fresh water was being “wasted to the sea,” or because of problems with conveyance, or because there was not enough reservoir storage—they fell because there was no water.   And even though 2009 was not as dry as 2007 or 2008, exports remained low because there was still no water

While Mother Nature and our mismanagement of the supply she provides was the immediate cause for the sharp drop in exports in 2008 and 2009, the relentless increase in exports during the past several decades to meet ever increasing demands not only drove the ecosystem towards collapse—it set the stage for greater volatility and unpredictability in Delta exports.  In essence, because demand has exceeded the capacity of the system, increases in exports have reduced the reliability rather than increased it.   

Droughts are a fact of life in California and climate projections suggest that they will become more frequent and intense.  So I’ll leave you to decide how well (or how likely) the recently proposed plan to supplement the existing Delta channel conveyance system with new water intakes and a massive tunnel to convey water under the Delta directly to the pumps will address the existing problems and help meet the state-mandated goal for a reliable water supply.  But it seems ironic that nearly all of the intense discussions and elaborate analyses of the ongoing Delta planning process have revolved around a plan to meet unnamed (but possibly unrealistic) export targets by rearranging the Delta’s plumbing to guard against catastrophic conveyance failure when the real limiting factor driving water supply reliability is probably Mother Nature and the natural limits of a watershed that, unlike Lake Wobegon’s fabled children, cannot produce “above average” runoff every year. 



[1] Respectively, 2007, 2008 and 2009 were the 13th, 15th, and 30th driest years on 82 years.

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Comments (Add yours)

Rogene ReynoldsSep 27 2012 05:41 PM

RE: Unreliability of supply due to earthquake damage to levee system.
Ms. Swanson is so very right-on regarding much in this piece, that I am baffled the misconception regarding our levee integrity shows up here. I have lived in the South Delta (Roberts Island) all my life. Our levees are in better shape now than ever in history. We have never had a levee failure due to earthquake (not in 1906, not during Loma Prieta). Levees like ours survived the Kobe earthquake - there was surface damage, but NO levee failure and NO floods due to levee failure. The earthquake bugaboo is just that - a lie that gets scarier with repitition. Ask the engineers who work with landowners and reclamation districts (in our case Kjeldson, Sinnock, Neudeck). They will tell you the truth about levees and earthquakes.
Thank you for the opportunity to comment on this otherwise informative and well formed article. Rogene Reynolds

Mike HudsonSep 28 2012 10:57 AM

Thank you Tina for putting into words what I have suspected over the last few years: Until we decide what to do with the water, or until we decide what we really need the water for - there is really no way of managing it.

Robert PykeSep 28 2012 12:55 PM

Hi Tina. Rogene Reynolds is correct on the Delta levees and earthquakes issue – this is largely a red herring – but otherwise you are on point. I would only suggest that the definition of water supply reliability needs to be expanded from what you suggest so that it is something like x maf in 9 years out of ten, y maf in 8 years out of 10, and z maf in 7 years out of ten, and so on - harder to convey in talking points but easy to show graphically. That the BDCP or the Delta Stewardship Council has never defined water supply reliability is both amazing and disappointing.

Roland SheppardSep 28 2012 02:47 PM

From My essay, Why Oil Companies Want California’s Water:
At the peak of California production in 1985, Kern County producers needed roughly four-and-a-half barrels of water to produce a single barrel of oil. 
Today, that ratio has jumped to almost eight barrels of water per barrel of oil. This use has been sanctioned despite the three-year drought that has ravaged the valley, causing reductions in the water delivered by the State and Central Valley projects canals. Not only are farmers generally short of water, dozens of small poor agricultural hamlets — including Alpaugh, Seville, East Orosi and Kettleman City — have been forced to tap groundwater. And that groundwater is often contaminated with agricultural pollutants, including arsenic and nitrates. — Oil and Water Don’t Mix with California Agriculture
Shale is found in about one sixth of California. “The Monterey shale overlaps much of California’s traditional crude producing regions. It generally runs in two swaths: a roughly 50-mile wide ribbon running length of the San Joaquin Valley and coastal hills, and a Pacific Coast strip of similar width between Santa Barbara and Orange County.” —A Big Shale Play in California Could Boost the Golden State’s Oil Patch 

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