Understanding predation impacts on Delta native fishes


Native threespine sticklebacks pumped from the stomach of a single 22 inch striped bass. The bass was feeding in water being drained from a duck club in Suisun Marsh, The sticklebacks were abundant, concentrated, and confused so were easy prey for the bass. Sticklebacks continue to be one of the most abundant fish in Suisun Marsh. Photos by Teejay O’Rear April 2010.

By Peter Moyle, Andrew Sih, Anna Steel, Carson Jeffres, William Bennett of University of California, Davis.

Will endangered fishes, such as Chinook salmon, delta smelt, and longfin smelt, benefit from control of predators, especially of striped bass? This question is of interest because if the answer is ‘yes’, then predator control might increase the benefits of other actions, such as provision of environmental water for native species. In this blog we express our skepticism of large-scale predator control as a conservation tool, based on eight principles.

  1. Predation ‘problems’ do not have simple solutions.
    Predation is one of many stressors affecting declining species. In ecosystems such as the Delta, predator-prey relationships are complex. Many predators forage opportunistically on whatever prey species are most abundant and accessible at any time and place. As a result, predator control can have unintended consequences.  For example, reducing striped bass populations might cause an increase in important prey species, such as Mississippi silverside, that prey on delta smelt eggs and larvae. In other words, controlling striped bass may backfire and increase predation on delta smelt.  Grossman et al. (2013) have written a good overview of predator-prey dynamics in the Sacramento River. This review provides a basis for the above statements and the conclusion that predator control in the Delta will likely create more problems than it solves. This conclusion can be applied broadly to predator control programs, such as those for invasive mammals.  However, more research could provide a better understanding of predation as a stressor of fish populations, provided that such studies are linked with modeling, focusing on predator-prey interactions in the Delta (similar to work done for the lower Columbia River).
  1. The best long-term strategy for increasing populations of small fish (prey) is to improve the ability of the ecosystem to support them.
    In a healthy ecosystem, multiple predators and multiple prey typically co-exist in dynamic fashion. Prey species such as delta smelt have highly effective predation defense mechanisms that operate best in an environment similar to the one in which they evolved. For the Delta, we suggest that ecosystem recovery efforts should focus on the arc of habitat that includes the Yolo Bypass, the Lindsey-Cache slough region, the Cosumnes-Mokelumne river region, the Sacramento River, Sherman Island and Suisun Marsh (similar to the String of Pearls concept for Chesapeake Bay).  This region is tied together (the string) by the interaction of Sacramento River flows with tidal flows and contains the highest concentrations of native fishes in the upper estuary.
  1. Bypassing problem areas can reduce predation impacts.
    Increasing flows from the Sacramento River down the Yolo Bypass in winter could carry large number of juvenile salmon from upstream areas to productive habitat in the Yolo Bypass. Such flows can also attract fishes such as splittail, and perhaps smelt from the Delta into the Bypass. Fish using the Bypass avoid the rip-rapped channels and likely high predation areas in the western Delta and lower Sacramento River. A similar strategy might work for the San Joaquin River and southern Delta if fish (except smelt) were directed towards the pumping plants and then trucked past predation hot spots in the Delta.  This strategy will only work if predation on trucked fish is reduced by modifying the pumping facilities and adopting different release strategies (#4, #5).
  1. Changing release strategies of captive fish can reduce predation mortality.
    Salmon and other fishes are most vulnerable to predation when they are transported to a release site, usually by truck, and then dumped into the water in large numbers in one place. This release strategy, used by the pumping plants in the South Delta and by many hatcheries, caters to predator behavior, because predators are attracted to concentrations of prey, especially prey that are confused following release. Release strategies need to be developed and carefully monitored, such as slow releases from barges towed at random times of day and night, which do not habituate predators to concentrations of prey. Similar release strategies are needed for hatchery salmon releases as well (#8).
  1. The solution to reducing effects of predation ‘hot spots’ is to move prey around them (see #3) or to reduce their attractiveness to predators.
    Predatory fishes such as striped bass move around a lot.  Therefore, predator control on a hot spot has to be continuous and intensive, because as predators are removed new ones are likely to move in.  However, each hotspot has its own problems that have to be dealt with individually.  For example, Sabal et al. (2016) found striped bass consumed 8-29% of juvenile salmon passing through Woodbridge Irrigation District Dam on the Mokelumne River and reducing the numbers of adult striped bass could temporarily reduce predation rates. It helped that the ‘hot spot’ was some distance upstream from the Delta, where most bass reside. Their conclusion was not that universal striped bass control was needed but that “ …it is important to consider habitat alterations and interactive effects when estimating large-scale predation impacts and when planning local management strategies (p 318).”This conclusion applies to Clifton Court Forebay, which is well-documented as one of the hottest of the predation hotspots.  Striped bass and other predators concentrate there to feed on small fish drawn towards the giant pumps at the state pumping plant. Modifying its structure or operation should be the best way to reduce predation impacts in the forebay. In this light, the National Marine Fisheries Service is currently requiring that both long-term and interim measures to reduce predation on endangered fishes be implemented (letter from Maria Rea to Carl Torgersen, January 22, 2016).  Essentially, NMFS is saying that just studying the problem is no longer a sufficient response to the documented high predation rates at this facility.
  1. Striped bass are not the problem.
    Striped bass get blamed for declines of native fishes because they are an abundant, voracious, non-native predator. Yet striped bass have been part of the Delta ecosystem for nearly 150 years, plenty of time for co-adaptation of predator and prey.  In periods when delta smelt, longfin smelt, and salmon were abundant in the past, striped bass were much more abundant than they are today, suggesting that the same factors that drive native fish declines are also driving striped bass populations.  As generalist, wide-roaming predators, they feed on the most abundant prey available, which is often the result of ‘ringing the dinner bell’ release strategies of captive fish (see #4, above). If striped bass regulate populations of any other fishes, their effects will be mostly on small, consistently abundant prey fishes such as Mississippi silverside and threadfin shad that may compete with or prey on smelt and juvenile salmon.  By reducing competition or predation by silversides or shad on smelt, striped bass might actually have a net positive effect on smelt.  Indeed, other managers have found, to their distress, that reducing top predators has backfired because of this ‘enemy of my enemy is my friend’ effect.  Repeating this error in our system would be unfortunate. All this indicates that programs aimed at direct striped bass control are as likely to have no or negative effects, as to have positive effects, on populations of desirable fishes.
  1. Having a prey species in a predator’s diet does not mean the predator controls the prey’s populations.
    Dietary studies of predators in the Delta have often concentrated in areas where predation is perceived to be a problem, such as predation by striped bass near water diversion structures on salmon in the Delta and Sacramento River or below hatchery release sites. It is not surprising that prey are seen in predator stomachs in those situations. Prey fish have evolved strategies to minimize the effect of predators. For example, a natural predation-reduction strategy of juvenile salmon is to migrate to the ocean in pulses, usually when river flows are high and muddy from run-off. Striped bass and other predators might have stomachs full of juvenile salmon at this time but the percentage of total population is likely to be low. Granted, such strategies may no longer be fully effective under conditions of drought, warm winters and reduced population sizes; however, reduction of overall striped bass predation will likely increase predation by other organisms, taking advantage of whatever increase in prey the absence of striped bass might cause.. In short, a predator control program based mainly on dietary studies is too simplistic to serve as a basis for management to increase prey populations.
  1. Hatchery-reared salmon are exceptionally vulnerable to predation.
    Hatchery salmon start life packed together in cement troughs, with food pellets raining down from above.  This does not give the fish much chance to learn how to avoid predators. They are then either released directly into a river or trucked to a release point in the estuary.  It is scarcely surprising that predators take advantage of these naïve and fat-laden prey, gorging themselves.  Many of these salmon die of stress and other causes. They are then scavenged by unlikely predators such as white catfish.  Studies on the Yolo Bypass indicate that about 30% of hatchery salmon die within a day or two after release into food rich, nearly predator-free environments, in which most wild salmon thrive (Jacob Katz, unpublished data).   Release of hatchery fish into rivers in large numbers mimics, to a certain extent, the predator-swamping strategy used by wild fish.  But the rivers are rarely high and muddy during the release and the fish lack the behavior to avoid predation in clearer water, so predation rates are high.  In short, heavy predation on juvenile hatchery salmon is more a reflection of hatchery practices than of un-natural rates of predation by striped bass and other predators.

Conclusion.  It seems unlikely that a large-scale predator removal program focused on striped bass would have a sustainable, measurable effect on populations of its prey species, specifically protected smelts and salmon. However, if managers deem enough uncertainty exists about the importance of predation as a source of mortality relative to other factors, then an integrated program of empirical studies and modeling should be instituted.   If a control program moves forward despite scientific uncertainty, it should be implemented as an experiment, focusing on data collection and modeling to determine if the program achieves carefully specified objectives.

Further reading

Cannon, T. 2016. Hatcheries Release Salmon Smolts into Low Flows and Warm Water – April and early May, 2016. California Fisheries Blog. May 5, 2016.

Doherty, T.S. and E. G .Richie. 2016.  Stop jumping the gun: a call for evidence-based invasive predator management, Conservation Letters. doi: 10.1111/conl.12251.

Grossman, G., Essington, T., Johnson, B., Miller, J., Monsen, N. and T. Pearsons. 2013. Effects of fish predation on salmonids in the Sacramento River – San Joaquin Delta and associated ecosystems. Report for Cal. Fish Wildlife/Delta Stewardship Council/NMFS. 71pp.

Moyle, P B.   2011. Striped bass control: cure worse than disease?

Sabal, M., S. Hayes, J. Merz, and J. Setka. 2016  Habitat alterations and a nonnative predator, the striped bass, increase native Chinook salmon mortality in the Central Valley, California. North American Journal of Fisheries Management 36:309–320. DOI: 10.1080/02755947.2015.1121938

Sabalow,R. 2016. Should California’s striped bass be vilified as native-fish killers? Sacramento Bee May 6, 2016.

Wunderlich, V. 2015.  Clifton Court Forebay Predation Study.  Bay-Delta Office, California Department of Water Resources.

Posted in Delta, Fish | Tagged , , , , | 2 Comments

SGMA and the Challenge of Groundwater Management Sustainability

By Bill Blomquist

It isn’t just the groundwater that has to be sustainable; it’s the management too.

That’s why the title of this post shifts from the more familiar “sustainable groundwater management” to “groundwater management sustainability.” This perspective doesn’t come from the world of hydrologic or climate or environmental science, but from political science and other disciplines focused on human institutions and behavior.

Along with the development and use of information, the greatest challenge in groundwater sustainability is governance and decision making. Over several decades we have learned that governance is at least as important in environmental management and protection as are science and data. That’s saying a lot, because science and data are critical. Understanding institutions for governing human interactions with the environment and with other humans is at that critical level or greater.

The challenge of governance and decision-making involves dealing with scales and levels, the legal and regulatory framework, and multiple publics and values; also, supporting and institutionalizing innovation, adaptation, and learning. Plainly this is complicated, and like the challenge of information, it is unlikely to be solved once and for all.

The treatment of institutions in policy analysis versus political science

Institutions come up a lot in policy discussions. Policy discussions generally follow this form: “What should we do about X?” Fill in the “X” with the relevant policy topic—groundwater sustainability, mass transit, international terrorism, etc.—and the policy discussion ensues, with varying voices and perspectives advocating one solution or another.

Institutions generally appear in these kinds of policy discussions as prescriptions. They are advocated for their predicted beneficial effects in remedying the illness – the “X” — that’s under discussion.

Got a groundwater problem? Take some private property rights plus a market and call me in the morning, or take a public trust doctrine plus a regulatory agency, or take a comprehensive watershed management authority, or take a public participation process plus some citizen science… etc.

These institutional prescriptions are usually available only in ideal form: well-defined property rights and a well-functioning market, agencies selflessly pursuing the public interest, and so on.

Political science discussions are different. In political science the most important question isn’t, “What should we do about X?” It’s “Who gets to decide what we’re going to do about X, and how?” That leads us into the world of governance and decision making, with its messiness of competing interests, conflicting incentives, rhetorical framing of issues, ideological predispositions, and seemingly endless blocks, countermoves, and end-runs.

To some extent this is a distinction between thinking about institutions as ideal types versus thinking about institutions as problematic human creations. The latter approach involves lifting the hood and applying some diagnostics. That means knowing what to look for and what questions to ask once the hood is up.

Institutional diagnostics—questions to consider if you’re trying to make the management sustainable

To implement the Sustainable Groundwater Management Act (SGMA), people in 127 groundwater basins across California are developing groundwater sustainability agencies (GSAs) that will be required to develop, adopt, and implement groundwater sustainability plans (GSPs). That’s a governance challenge of the first order, and it involves creating new institutions or adapting existing ones for new purposes.

I strongly recommend the recently published report by Kiparsky et al (2016) on criteria for evaluating GSAs: scale, human capacity, funding, authority, independence, participation, representation, accountability, and transparency. Because those are good criteria for evaluating GSAs, they are also good criteria to take into account when designing them.

The authors of that report have done an excellent job of defining and explaining their criteria and their significance. I will add here a few thoughts about one of the criteria they cover—representation—and then add another criterion that is especially important for the notion of “management sustainability.”

Representation is critically important to governance and decision-making. If a GSA will be a new entity, for instance, what will its governance structure look like? Will the members of its governing board represent districts, represent specific constituencies, or serve at large? And if an existing entity is going to assume the responsibilities and gain the authority of a GSA, are there any changes to its internal representation and decision-making structures and processes that should be made?

Either way, will communities or stakeholders within the basin be represented equally or proportionally? If proportionally, relative to what?   Are all stakeholders equal—or, rather, should they all count equally when it comes to making groundwater management decisions? Do some have more weight because of a judgment about their stake in groundwater management? Pumpers, for example, could reasonably be said to have site-specific investments and dependence on the resource to a greater extent than others. On the other hand, if pumpers have primary control over decision-making about an overdrafted groundwater basin, will it always be a situation of “the diet starts tomorrow?” Last but not least, how can the composition of the governing body be adjusted if and when the constellation of interests and uses change?

That brings me to the criterion I’d like to add in designing GSAs and GSPs: adaptability.

An observed fact from the messy world of governance and decision-making is this: no matter how carefully and well we design institutions, we won’t get everything right the first time. Also, conditions will change in ways that alter the fit between what we put in place at one time and what comes along to confront us later.

That will surely be true for the GSAs being designed in the basins starting SGMA implementation now. Despite everyone’s best efforts in constructing these governance structures, there will be errors and surprises. It will be essential to build in processes for modification. People engaged in the hard work of groundwater management in overdrafted basins (Porse 2015) will need to make rules not only for changing groundwater use and managing the basin; they’ll need to make rules for how and when the rules themselves can be changed.

Creating a decision-making body for groundwater management isn’t just solving a problem; it’s writing a constitution. Writing a constitution is an intricate task, where decisions about one element are often linked to and affect other elements. Long-standing and relatively successful constitutions—the sustainable ones, we might say—are the ones that can be adjusted when needed.

SGMA implementation will be hard, in ways that have already been predicted and discussed (Moran and Cravens 2015, Moran and Wendell 2015). By equating it to constitution making, I don’t mean to make it sound even harder. But I think it helps to conceive of it that way. It helps us think beyond the immediate circumstances of the moment and consider the ways in which we are designing a decision making process that will have to address circumstances well beyond this moment. And that, in turn, is likely to make us think now about how we want to be able to adjust then.

As Californians design GSAs and GSPs, they are designing institutions for governance and decision-making. That’s a somewhat different, and I hope useful, way of thinking about the task that lies ahead. Thinking about it that way may help encourage everyone to think about the sustainability of the management as well as of the groundwater.

Bill Blomquist is a Professor of Political Science at Indiana University-Purdue University Indianapolis (IUPUI) in Indianapolis, Indiana.  His areas of research are water resource management, institutions, and the policy making process.

Further Reading

Kiparsky, Michael, Dave Owen, Nell Green Nylen, Juliet Christian-Smith, Barbara Cosens, Holly Doremus, Andrew Fisher, and Anita Milman (2016) Designing Effective Groundwater Sustainability Agencies: Criteria for Evaluation of Local Governance Options. Berkeley, CA: Wheeler Water Institute, UC Berkeley School of Law

Moran, Tara and Amanda Cravens (2015) California’s Sustainable Groundwater Management Act of 2014: Recommendations for Preventing and Resolving Groundwater Conflicts. Stanford, CA: Water in the West Program, Stanford University Woods Institute for the Environment

Moran, Tara and Dan Wendell (2015) The Sustainable Groundwater Management Act of 2014: Challenges and Opportunities for Implementation. Stanford, CA: Water in the West Program, Stanford University Woods Institute for the Environment

Porse, Erik (2015) “The Hard Work of Sustainable Groundwater Management.” California WaterBlog. Posted August 13, 2015.

Posted in Groundwater, Planning and Management | Tagged | 3 Comments

Inevitable Changes to Water in California

By Jay Lund

A shorter version of this piece originally appeared as an op-ed in the Sacramento Bee.

“Denial ain’t just a river in Egypt.” (anonymous)

Water is always important for California, as a dry place with a boisterous economy and unique ecosystems. A growing globalized economy and society historically drive changes in California’s water management that rarely occur quickly or without controversy. Water policy in California has always been about making and resisting change.

California has done comparatively well. Its water system sustains the world’s 7th largest economy of 39 million people with some of the world’s most profitable agriculture in one of the world’s drier places. And California (barely) preserves more of its native ecosystems than most other regions globally with Mediterranean climates, where native ecosystems often have been simply eliminated. California’s successes have not been born from complacency, but from continuous striving and conflict.

California water faces major inevitable changes. These changes are driven by efforts to end groundwater depletion, by sea level rise, global warming and the loss of snowpack, accumulating salts and nitrate in groundwater, new invasive species, and continuing population growth and evolution of California’s globalized economy and agriculture.

The state must prepare for these changes to support a strong economy and a healthy environment, while easing transitions for vulnerable groups.

  • The Sacramento-San Joaquin Delta will export less water and have more open water. The Delta will remain California’s most central and difficult water problem. Some Delta islands and levees are financially unsustainable. With land subsidence, sea level rise, increasing seepage, and earthquakes, their agricultural value is limited and repair costs are high. Some of the most subsided lands in the central and western Delta will permanently flood without unrealistic levels of state subsidies. Delta outflow requirements already reduce water available for Delta water diversions. New flow requirements and climate changes seem likely to further reduce water diversions both upstream and within the Delta. Upstream users will continue to remove much more water than do Delta water exporters and in-Delta water users. Ending groundwater overdraft in the Central Valley will increase demands for water from the Delta.
  • The San Joaquin Valley will have less irrigated agricultural land. The Central Valley south of the Delta is a huge productive agricultural region that currently relies on water from the Delta imports, groundwater overdraft, and reduced outflows from the San Joaquin River. Reductions in those sources will decrease water available to this region by 2-5 million acre feet per year, requiring the fallowing of 500,000-2 million acres of this region’s 5 million irrigated acres. Some of this land will be retired due to salinization and urbanization. Continued shifts to higher value crops, especially orchards, will help maintain agricultural revenues and jobs, as they have during the drought.
  • Urban areas will use less water, reuse more wastewater, and capture more stormwater. Water supply risks and costs will drive cities to use less and capture more local water. These changes will improve water supply reliability and free some water for agriculture and environmental uses, at some cost. But not all actions are equally effective. Water conservation, reuse, and stormwater capture are all effective in coastal areas, which drain to the sea. Reducing landscape irrigation is more effective for inland conservation.
  • Some native species will become unsustainable in the wild despite protective efforts. A warmer climate, combined with continued water and land stress and the dilution of wild genetic stock by hatchery fish and invasive species, will make some native fish species unsustainable in the wild, despite concerted restoration efforts. The entire range of native plant and animal species in California faces similar risks. Not all can be expected to survive. This threat challenges our endangered species laws and their implementation and demands more attention to effective ecosystem management.
  • Groundwater in many agricultural areas will become more contaminated. Modern agriculture applies large quantities of nitrogen fertilizer, much of which enters groundwater as nitrate, a threat to drinking water. Despite improving fertilizer efficiency, farmers often cannot reduce nitrate discharges enough. Ending all nitrate pollution today would leave decades of past discharges flowing toward drinking water wells. This problem is not unique to California, and it is especially worrisome for small, poor, rural communities.
  • Water solutions and funding will become even more local and regional. As federal and state governments experience diminished funding and capability, local and regional agencies are more motivated to address and fund most water problems. Making state and federal regulations more efficient, effective, and supportive of both local and statewide interests in public health, the economy, and environmental protection is a major challenge.
  • Water will be managed more tightly and formally due to economic and environmental pressures. California’s 2014 groundwater legislation will lead many areas to form groundwater sustainability agencies, which will need to account for and manage groundwater, and all water, more tightly. Less cumbersome court, groundwater rights, and water accounting procedures are needed to support this process. In the end, all parties will be more secure in their rights, but the transition will reduce pumping and add costs in problem areas.

Most of these changes will be accompanied by prolonged angst, studies, controversies, and expense. The details of how each change is managed are worth many millions of dollars to individual stakeholder groups. Forward-looking actions can reduce the pain and improve the prospects for water supporting the kind of society, economy, and environment that Californians desire. As always, facing change and thoughtfully preparing for the inevitable will be better than wishfully thinking that California can avoid change.

Jay Lund is director of the UC Davis Center for Watershed Sciences.

A longer earlier version of this piece was published in 2014 at: https://californiawaterblog.com/2014/01/07/resistance-is-futile-inevitable-changes-to-water-management-in-california/


Posted in California Water, Drought, Water Conservation | Tagged | 13 Comments

The Collapse of Water Exports – Los Angeles, 1914

by Jay Lund


Collapse of Los Angeles aqueduct pipeline through Antelope Valley from a major flood in February, 1914 (3-months after the aqueduct’s official opening). LADWP historic photo archives.

“In February, 1914, the rainfall in the Mojave Desert region exceeded by nearly fifty per cent in three days the average annual precipitation.

Where the steel siphon crosses Antelope valley at the point of greatest depression, an arroyo or run-off wash indicated that fifteen feet was the extreme width of the flood stream, and the pipe was carried over the wash on concrete piers set just outside the high water lines. The February rain, however, was of the sort known as a cloud-burst, and the flood widened the wash to fifty feet, carried away the concrete piers, and the pipe sagged and broke at a circular seam. The water in the pipe escaped rapidly through the break under a head of 200 feet, and the steel pipe collapsed like an emptied fire hose for nearly two miles of its length. In some places the top of the pipe was forced in by atmospheric pressure to within a few inches of the bottom. The pipe is ten feet in diameter, and the plates are 1/4 and 5/16 of an inch thick. Many engineers pronounced the collapsed pipe a total loss, and advised that it be taken apart, the plates re-rolled and the siphon rebuilt.

The damage was repaired, however, by the simple expedient of turning the water on after the break was mended, relying on the pressure to restore the pipe to circular form. The hydraulic pressure, under gradually increasing head, restored the pipe to its original shape without breaking any of the joints or shearing the rivets, and a month after the collapse the siphon was as good as new. The total cost of repairing the siphon was only $3,000. It would have cost about $250,000 to take it apart and rebuild it” (LABPSC 1916).


LADWP historic photo archives.

Water management and policy has always faced challenges, even unexpected ones following great technical triumphs. California’s water problems have never been easy.

But sometimes challenges require only creative solutions based on fundamental insights and a willingness, occasionally driven by desperation, to venture forth and adapt.


Jay Lund is the Director of the Center for Watershed Sciences and Professor of Civil and Environmental Engineering at the University of California – Davis.

Further reading

Complete report on construction of the Los Angeles aqueduct, Los Angeles Board of Public Service Commissioners, Los Angeles, CA 1916. (pp. 20-21)

Water and Power Associates. Construction of the Los Angeles Aqueduct

LADWP historic photo archives

YouTube – Construction of the Owens Valley Project

Posted in California Water | Tagged | 4 Comments

Conservation of inland trout populations in California

by Robert Lusardi

This article originally appeared in California Trout’s The Current. For the full issue, click here.

Photo by Mike Wier.

Native fish conservation and recovery is an onerous task.  While there are many threats, hybridization has played an integral role in the demise of numerous inland trout species throughout the western United States.  Nowhere is this more evident than California where introduced rainbow trout have threatened the genetic integrity of California golden trout, Little Kern golden trout, Kern River rainbow trout, Paiute cutthroat trout, and Lahontan cutthroat trout.  Species recovery, however, is challenging.  Managers must often balance short-term goals of reversing a trend towards extinction with long-term species persistence.  These objectives rarely align, in part because they operate at different time scales, but also because threats can shift through time as a result of management intervention.  Lusardi et al. (2015) recently examined this phenomenon in the Little Kern golden trout (Oncorhynchus mykiss whitei), an endemic species to the Little Kern River watershed in the southern Sierra Nevada.  Similar to many western inland trout populations, introductions of coastal rainbow trout greatly reduced the range of Little Kern golden trout by approximately 90% with fewer than 5,000 individuals isolated in five small headwater streams by 1975 (Moyle 2002).  The primary cause of decline was hybridization with introduced rainbow trout.

In order to improve Little Kern golden trout genetics and reduce the threat of hybridization, recovery actions focused on isolating populations with instream barriers (many of which were natural), eradicating hybrid populations using piscicides such as rotenone, and re-establishing unhybridized populations using hatchery fish.  Similar strategies have been used on other California endemic inland trout such as Paiute cutthroat trout.  The strategy was largely successful in slowing the rate of hybridization, with most populations exhibiting minimal rainbow trout genetic influence.  There were, however, consequences associated with these recovery actions.  While the threat of hybridization was greatly reduced, re-introduced Little Kern golden trout populations exhibited very low levels of genetic diversity. Genetic diversity is important because it enables species to adapt to changes in their environment.  If sufficient diversity does not exist, adapting to change becomes a difficult task and the potential for extinction increases.  While resource managers were able to greatly reduce the threat of hybridization in Little Kern golden trout, a new threat of low genetic diversity emerged.


Figure 1: Conceptual model of threat evolution. Dotted lines indicate indirect effects. Positive sign indicates a positive effect or the amelioration of initial threat. Negative sign indicates a negative effect or the creation of a new threat (Lusardi et al. 2015)

In describing the conservation history of the Little Kern golden trout, Lusardi et al. (2015) introduces the term ‘threat evolution’ and defines it as fixing an initial threat (hybridization) through management action, but in so doing creating a secondary threat (low genetic diversity). A review of the literature suggests that the phenomenon has occurred in numerous other western inland trout species.  This points to an inherent difficulty in salmonid recovery.  Immediate action is often required to slow further demise, but those actions might produce new threats which could equally compromise long-term persistence.  This is why adaptive management is an important tool to assist in species recovery.  Management strategies must be flexible in their approach, understanding that different actions can elicit different responses that operate at diverse time scales.


Photo by Mike Wier.

Improving Little Kern golden trout genetic diversity will not be easy.  Defining the entire genetic landscape of the Little Kern Basin appears to be a logical first step.  Resource managers can then focus on removing remaining hybridized populations and promoting connections between isolated unhybridized populations.  In some cases, this may mean altering barriers to promote connectivity or moving fish from one population to another in an effort to improve genetic diversity.  There are risks associated with these types of management actions, but if approached cautiously and within a scientific framework, there are also potentially great benefits.  Establishing Little Kern golden trout refuge populations outside of the basin should also be considered.  Low genetic diversity and small population sizes that currently plague the Little Kern golden trout suggest that the fish is more vulnerable to random events such as disease, wildfire, drought, or further introductions of non-native fish.  Establishing refuge populations would provide insurance against the potential future loss of salmonid biodiversity.

Numerous inland trout populations are threatened by the introduction of non-native rainbow trout.  Recovery of inland trout populations is a difficult task and is, at times, uncertain.  Uncertainty, however, should not mean inaction.  New tools such as structured decision making allow managers to weigh the relative risks and benefits of particular recovery actions and identify uncertainty.  Key to all of this is understanding that the recovery of inland trout populations will take time.  Adaptive management and using the best available science to guide recovery provides the best path forward.

Dr. Lusardi is the UC Davis-California Trout Wild and Coldwater Fish Scientist.  The original article appeared in the September issue of Reviews in Fish Biology and Fisheries.

Further Reading

Lusardi RA, Stephens MR, Moyle PB, McGuire CL, and Hull JM. 2015. Threat evolution: negative feedbacks between management actions and species recovery in threatened trout (Salmonidae). Reviews in Fish Biology and Fisheries 25: 521-535.


Posted in Fish, Planning and Management | Tagged | 1 Comment

California’s Delta-Groundwater Nexus: Delta Effects of Ending Central Valley Overdraft?

By Timothy Nelson, Heidi Chou, Prudentia Zikalala, Jay Lund, Rui Hui, and Josué Medellín–Azuara

Surface water and groundwater management are often tightly linked, even when linkage is not intended or expected. This link has special importance in drier regions, such as California. A recent paper examines the economic and water management effects of ending long-term overdraft in California’s Central Valley, the state’s largest aquifer system.  These effects include changes in regional and statewide surface water diversions, groundwater pumping, groundwater recharge, water scarcity, and resulting operating and water scarcity costs.

The analysis used a hydro-economic optimization model for California’s water resource system (CALVIN) that suggests operational changes to minimize net system costs for a given set of conditions, such as ending long-term overdraft. Based on model results, ending overdraft could induce some major statewide operational changes, including significantly greater demand for Delta exports, more intensive conjunctive-use operations to increase artificial and in-lieu groundwater recharge, and greater water scarcity for Central Valley agriculture. Figure 1 summarizes these changes.


Figure 1 Average annual changes to accommodate ending groundwater overdraft of 1.2 million acre-ft in California’s Central Valley

Ending overdraft in the Central Valley increases economic demands for additional Delta exports, additional groundwater recharge, and additional water market sales, but these are not enough to prevent increased water scarcity to agriculture.

The statewide costs of ending roughly 1.2 maf/yr of groundwater overdraft in the Central Valley are probably at least $50 million per year from additional direct water shortage and additional operating costs. The costs of ending Central Valley overdraft could be much higher, perhaps comparable to the recent economic effects of drought ($1.5 billion/year) (Medellín-Azuara et al. 2015; Howitt et al. 2014).  There is, of course, some uncertainty on both the quantity of Central Valley overdraft and how agencies will manage without it.

Driven by recent state legislation to improve groundwater sustainability, ending groundwater overdraft will have statewide implications for water use and management.  In particular, these implications extend to the Sacramento–San Joaquin Delta, where ending Central Valley overdraft amplifies economic pressure to increase Delta water exports rather than reduce water exports.  California’s largest water management problems are often tied together.

Delta exports and groundwater overdraft in the southern Central Valley have a long intertwined history.  Both the federal Central Valley Project and the State Water Project were developed in part to alleviate groundwater overdraft in the southern Central Valley and improve the sustainability of the region’s agriculture.  The fundamentals of California’s geography, hydrology, and economy of water uses continue to challenge and bind the state and individual regions to balance limited water supplies.

Greater demands for Delta water exports from ending overdraft will probably further complicate potential solutions to Delta problems.  Conversely, the great and perhaps insurmountable difficulties to increasing Delta exports are likely to hinder ending groundwater overdraft in the Central Valley (and increase its costs).  While solving local and regional problems, connections to the statewide system will remain important.  Integrated modeling studies can provide useful insights for these problems, and sometimes insights for solutions.

The authors were or are affiliated with the Department of Civil and Environmental Engineering at the University of California – Davis for this work.  Many have moved on, but some have stayed behind.

Further reading

Nelson, T., H. Chou, P. Zikalala, J. Lund, R. Hui, and J. Medellín–Azuara (2016), Economic and Water Supply Effects of Ending Groundwater Overdraft in California’s Central Valley, San Francisco Estuary and Watershed Science, Volume 14, Issue 1, Article 7, http://dx.doi.org/10.15447/sfews.2016v14iss1art7

Hanak, E., J. Lund, A. Dinar, B. Gray, R. Howitt, J. Mount, P. Moyle, and B. Thompson, Managing California’s Water:  From Conflict to Reconciliation, Public Policy Institute of California, San Francisco, CA, 500 pp., February 2011.

Medellín-Azuara, J., D. MacEwan, R.E. Howitt, G. Koruakos, E.C. Dogrul, C.F. Brush, T.N. Kadir, T. Harter, F. Melton, J.R. Lund,” Hydro-economic analysis of groundwater pumping for California’s Central Valley irrigated agriculture,” Hydrogeology Journal, Vol. 23, Issue 6, pp 1205-1216, 2015.

Howitt, R.E., Medellin-Azuara, J., MacEwan, D., Lund, J.R. and Sumner, D.A. Economic Analysis of the 2014 Drought for California Agriculture. Center for Watershed Sciences, University of California, Davis, CA, 28pp., July 28, 2014.

Posted in Agriculture, California Water, Delta, Groundwater, Uncategorized | Tagged , , , , , | 8 Comments

Sailing the Seas of Data Discovery

by Megan Nguyen

Which display is more engaging to you? The table or the map?


Crop Economics Web Map displaying information at the hydrologic region.

This table shows the total water use of each hydrologic region in California measured in Thousand Acre Feet.

Do you remember a time when you really needed to find something in your room that you know you for certain have but can’t remember where you placed it? And so then you have to search every nook and cranny of your room by hand? That’s what searching for online data feels like.

Data is the currency of science exchange and it is everywhere. As scientists, we deal with data constantly and are either collecting our own or searching for it. Government agencies produce a wealth of data and statistics collected from sensors, gauges, or sometimes simulated by models. However, finding this information is an arduous task as it is often buried deep within a website.

The data diggers are on a quest to find information! After traversing the many links on a website, we finally uncover the coveted data chest. We open it, expecting treasures, only to find ourselves presented with a library of zip files. These files have a secret code of numbers and letters and we are left to unlock their meaning with no cipher. But we can’t give up our search here! We must carry on with our mission. After many attempts, we manage to discover a common pattern between the file names and have unlocked their mystery. We manage to scavenge through the data chest and download what we need. After we process the raw data and refine our analysis, how do we share our data riches to the world? In other words, how do we display our data in a visually appealing manner?

The most common method used to display data is in static forms such as tables, graphs, and charts. Although widely used, a list of numbers in a table is not always the best way to get a message across. Dynamic displays that include color, graphics, or an interactive component can tell a story beyond a simple table or graph. One innovative method of dynamically displaying useful information in an engaging and attractive way is the use of interactive web maps. Web maps invite the user to take action in an interactive framework and explore the data on their own terms.

Our data voyage begins with an investigation into California’s irrigated agricultural use of land and water and its gross value. This information can be found on the California Department of Water Resources website. In its most basic form, the data is a set of excel spreadsheets which contain crop statistics as measured by the California DWR. This data set is consistent and well organized across years and spatial areas, which greatly facilitates translating it into a visual form. Instead of displaying these numbers in a table, Josué Medellin-Azura, Lawrence Li, and myself at the Center for Watershed Sciences recently published online the California Crop Economics Interactive Web Map. We chose to use a web map as an engaging display and invite users to freely explore the information.


Total water use of California at the detailed analysis unit level. Low to high values range from light to dark.

With one glance, a lot can be interpreted from this web map. By combining statistical data to GIS spatial data, we can associate statistics to the location they are related to on a map. As a result, the first thing that immediately stands out is the color gradient which shows the concentration of water usage or crop area based on color intensity. For example, in the map to the left you can see that the Central Valley has the highest total water usage which, makes sense as the Valley is a major hub of agricultural activity.

There are seven variables in the map: total water use, total irrigated crop area, applied water per acre, evapotranspiration of applied water per acre, total revenue, revenue per acre, and revenue per applied water. Each variable (except revenue variables which can only be viewed for revenue regions) can be viewed for different spatial analysis units (consistent with California Water Plan Update) that include, from largest to smallest: hydrologic region, planning area, detailed analysis unit, and revenue regions. The dataset only contains data for California from the years 1998-2010, and can be expanded to include years beyond 2010 when that data becomes available.

The web map has an user friendly interface that features toggle buttons for changing the analysis unit or variable shown as well as a slider to change years. Included in the map are text summary pop ups of each region and a gradient legend. By organizing data in an easily understandable and interactive graphic, a broader audience is able to engage with information in a way that makes it more meaningful, and increases general scientific literacy.

Explore the California Crop Economics Interactive Web Map for yourself!

Megan Nguyen is a GIS researcher at the Center for Watershed Sciences. Her work and interests  revolve around a variety of topics such as drought impacts, flood mitigation, environmental policy, and education outreach.

Posted in Agriculture, Drought, Tools, Uncategorized | Tagged | 6 Comments

ENSO the Wet Season Ends (almost) – March 31, 2016

By Jay Lund

Summary of conditions

March 2016 has been unusually wet, and quite a contrast to February.  The “Godzilla” El Nino this year has been a bit “Gonzo”, but overall has brought a welcome above average precipitation for northern California, after four solid drought years.  The unevenness of the precipitation is some concern, and the depth of remaining surface and subsurface storage drawdown from the drought remains sizable.

Annual precipitation and snowpack are now about average overall for California.  The largest reservoirs in northern California are in good shape, with sizable, about average, snowpacks waiting to trickle down in spring.  Overall, total surface storage in California is about 2.7 million acre-ft below average for this time of year (improved from an 8 maf surface storage deficit in October).  Groundwater will be recharging, as it should this time of year in most places, but groundwater is likely to remain drawn down in much of the southern Central Valley.

California remains in a drought, a bit.  So far, the much-hyped El Nino has brought us largely average precipitation and snowpack.  A huge improvement over the last few years, but not an excuse to forget the lessons of the drought so far.  And who knows what next year will bring.

Here are recent highlights, with links to the California Department of Water Resources’ California Data Exchange Center (CDEC) at http://cdec.water.ca.gov.

Reservoir and Groundwater Storage Conditions

Major reservoirs in northern California are mostly healthy this year, but substantially emptier south of the Delta.

California’s total reservoir storage remains about 2.7 maf (about 2.7 full Folsom reservoirs) less than average for this time of year.  This is a nice improvement from being 8 maf below average in October.  Groundwater statewide will be making some recovery but will be a long way from recovering from drought in many drier areas south of the Delta.

The drought by 2015 depleted total storage in California by about 22 maf cumulatively or nearly a year’s worth of water use in agriculture.  Storage is recovering during this wet season, but still has a good bit to go, probably 12-16 maf of drought storage drawdown remains, mostly from groundwater.




Precipitation and Snowpack


Northern Sierra 8 Station Precipitation Index (inches) (tiny totals, compared to average, in yellow)

Precipitation in most of California is far superior to the last four years of drought.  But we have had some very dry months (February) and some very wet months (March and January).  Southern parts of California, south of the Delta, have had a smaller share of relative water bounty, but are in much better shape than last year.






http://cdec.water.ca.gov/cgi-progs/products/PLOT_ESI.pdf – Sacramento Valley

http://cdec.water.ca.gov/cgi-progs/products/PLOT_FSI.pdf – San Joaquin Valley

http://cdec.water.ca.gov/cgi-progs/products/PLOT_TSI.pdf – Tulare Basin

ns_precip SJ_Precip tulare_precip

Concluding thought

Much better than the last four years, but still a bit of drought. A very wet March, and fairly wet December and January, has helped recover from a dry February and four years of drought. Northern California is in mostly good shape for the coming year.  More southern parts of California are more stressed, but still far better off than the previous four years. Lingering drought effects will continue.  A “Godzilla” El Nino is no guarantee of a drought-buster.

It is unclear if the next year will be a return to drought conditions, but the forecast for April so far seems mostly dry.

UC Davis’ drought seminar series videos are now available at: https://watershed.ucdavis.edu/education/classes/california-water-policy-seminar-series-drought

Jay Lund is Director of the UC Davis Center for Watershed Sciences and Professor of Civil and Environmental Engineering at UC Davis. 

Further Reading

Paul Ullrich (Video): Drought in California: A climatological look at water in a semi-arid landscape. UC Davis School of Law and Center for Watershed Sciences Water Policy Seminar Series, January 13, 2016

Jay Lund (Video): Drought and Water Management in California. UC Davis School of Law and Center for Watershed Sciences Water Policy Seminar Series, January 6, 2016

Peter Moyle and Jay Zeigler (Video): Drought Impacts and Management for Ecosystems. UC Davis School of Law and Center for Watershed Sciences Water Policy Seminar Series, February 1, 2016

Thad Bettner and Robert Roscoe (Video): Local Responses to California’s Drought. UC Davis School of Law and Center for Watershed Sciences Water Policy Seminar Series, February 8, 2016

Posted in California Water, Drought, El Niño, Uncategorized | Tagged | 4 Comments

Water managers drop the ball on Hetch Hetchy

Hetch Hetchy Reservoir has been covered with floating black balls to reduce evaporation and protect water quality

By Nan W. Frobish

Visitors to Yosemite’s iconic Hetch Hetchy reservoir are doing a double-take. Instead of seeing the majestic backdrop of the Sierra Nevada reflected in the pristine mountain water, they are now greeted by millions of black balls that cover the surface.

After four years of record-setting drought and statewide low reservoir levels, concerns developed about evaporation losses and the drought’s effect on water quality for San Francisco’s premier water source. Plans to protect the drinking supply and reduce reservoir evaporation began in 2014, when another year of dry conditions was predicted with no end to the drought in sight.

Inspired by similar measures taken at Ivanhoe Reservoir and the Los Angeles Reservoir in Southern California, 96 million black balls were poured into Hetch Hetchy to limit sunlight penetrating the water surface. Limiting sunlight on the reservoir will reduce both evaporation and the growth of potential contaminants. Given the emergency measures required to mitigate the drought’s effects on municipal water supplies, covering the reservoir was deemed more cost-effective and easier to achieve than constructing additional treatment facilities or implementing additional water conservation actions.

Milly Pore, a spokesperson from the San Francisco PEC, explained, “We are facing long-term concerns about water quality and water supply reliability and estimated that we could save a lot of water and water quality this way.”

“It’s an eye-sore,” said Louie Swan, a recent visitor to the reservoir. “It looks like an oil slick. If this is the best we can come up with to fix water quality, we might as well take the dam down altogether.”

Average 2100 deliveries, scarcity, and scarcity cost associated with O'Shaughnessy Dam removal

Average 2100 deliveries, scarcity, and scarcity cost associated with O’Shaughnessy Dam removal. Null and Lund (2006)

Previous research suggests that dam removal may be a contentious idea whose time has come for the politically charged reservoir. Dr. Sarah Null, a former researcher at the Center for Watershed Sciences, published a study of the effects of dam removal on San Francisco’s water supply. The findings suggest that the dam could be removed with little loss to water supply, but would require additional water treatment costs.

With more and prolonged droughts predicted due to climate change, those water treatment costs are becoming a reality. As water managers and conservationists are becoming aware of the “new normal” for water quality in Hetch Hetchy, dam removal is quietly being revisited.

Hetch Hetchy Reservoir, before black balls were used to cover the water surface

Hetch Hetchy Reservoir, before being black balled

Hetch Hetchy Valley, before O'Shaughnessy Dam was constructed

Hetch Hetchy Valley, before O’Shaughnessy Dam

“It’s a sensitive issue,” said one state agency representative with knowledge of the dam removal talks. “Frankly, we never thought the barriers to dam removal would [be eliminated] by natural conditions. But now that they are, it gives dam removal advocates a stronger position.”

As awareness grows of the recent management activities, local San Francisco residents are voicing additional concerns.

“What are the balls made out of, anyway?” asked Matthew McPhee, a long-time Bay Area resident who was attracted to the city because of its environmental consciousness. “Are they BPA-free? Will sunlight degrade their material? We’re just trading one water quality issue for another.”

The materials used in each black balls are causing some Bay Area residents to question their net effect on water quality

The materials used in each black balls are causing some Bay Area residents to question their net effect on water quality. Photo credit: Irfan Khan, Los Angeles Times

As well as addressing water quality issues, the ‘shade balls’ are also a pilot project to address broader goals set by Governor Brown to reduce evaporation in all of California’s reservoirs.

“Following last year’s 25% reduction in urban water use, we considered requiring that all reservoirs be covered to further save water,” says Rex Kransrose of the Governor’s office. “This year’s wetter conditions delayed this move, but we are glad to see San Francisco leading the way on this.”

“Water supply losses due to evaporation are a major issue,” says Dr. Mollie Luna, a researcher at the Center for Watershed Sciences. “We have enough storage, it’s preventing loss that’s the issue. We’re not sure how effective these shade balls might be, but the drought has shown us that we need to proactively consider many different approaches to secure our water supply.”

Recreational activities bump up against the black ball approach. Image source: www.amusingplant.com

Recreational activities bump up against the black ball approach. Photo credit: Gerd Ludwig, National Geographic

Balancing the ‘shade balls’ with recreational uses is another concern. One option is to phase out municipal supply from reservoirs with the poorest water quality, and gradually transition to solely recreational purposes. The experiment on Hetch Hetchy will provide guidance on whether the ‘shade ball’ approach can be effective for California’s extensive reservoir system.



Nan W. Frobish is an occasional contributor to the California Waterblog and director of life enrichment for the UC Davis Center for Watershed Sciences.

Further reading

A reservoir goes undercover. Los Angeles Times. June 10, 2008

Why Did L.A. Drop 96 Million ‘Shade Balls’ Into Its Water? National Geographic. August 12, 2015

Magin, G.B. and L.E. Randall (1960), Review of Literature on Evaporation Suppression, US Geological Survey, Professional Paper 272-C, U.S. Govt. Printing Office, Washington, DC.

Null SE and Lund JR. 2006. Reassembling Hetch Hetchy: Water supply without O’Shaughnessy Dam. Journal of the American Water Resources Association, Vol. 42, No. 4, pp. 395 – 408, April 2006.

Null, Sarah E., 2016. Water Supply Reliability Tradeoffs between Removing Reservoir Storage and Improving Water Conveyance in California. Journal of the American Water Resources Association (JAWRA) 1-17. DOI:10.1111/1752-1688.12391.

Posted in April Fools' Day, Uncategorized | 20 Comments

“Toilet to tap”: A potential high quality water source for California

Tap closeup with dreaping waterdrop. Water leaking, economy concBy Nathaniel Homan

Reusing water is not a new concept to many Californians. Many municipalities across California have facilities that treat wastewater to high standards, which allows it to be reused for agricultural irrigation, landscape irrigation, and industrial use. Other municipalities, such as the Orange County Water District, treat wastewater even further using advanced technologies, and use the treated wastewater to supplement drinking water supplies by injecting it into underground aquifers. In this manner, they practice indirect potable reuse, or IPR.

However, there is a third method of reusing wastewater that is not currently practiced in California: direct potable reuse, or DPR. DPR is an emerging water supply option which can provide a significant amount of drought resistant, high quality water in arid regions such as California.

In direct potable reuse, advanced treated wastewater is directly introduced into the drinking water system either upstream or downstream of a drinking water treatment plant (see Figure 1). The distinction between indirect and direct potable reuse is that IPR systems include an environmental buffer between wastewater treatment and potable reuse, whereas DPR systems do not.


Figure 1: Comparison of potable reuse schemes (Leverenz, Tchobanoglous, & Asano, 2011)

Environmental buffers are uncontrolled hydraulic systems such as a groundwater aquifers, rivers, lakes, and artificial reservoirs. Historically, environmental buffers were thought to provide additional treatment of recycled wastewater through natural environmental processes. While the concept of additional treatment may have been true in the past, as treatment technologies have matured, the quality of water produced by advanced wastewater treatment has improved. Now, treated wastewater is often of higher quality than the water in the environmental storage buffer. Rather than providing additional treatment, environmental storage buffers can actually degrade the quality of advanced treated wastewater.

Environmental buffers also increase the time between treatment of wastewater and the intake of the treated wastewater to the drinking water system. Use of a buffer allows wastewater treatment plant operators time to respond to monitoring results and prevent water that does not meet treatment standards from entering the potable water system. Some DPR projects include an engineered storage buffer to provide additional residence time for the treated wastewater.

In many situations DPR is a less costly and more efficient reuse scheme than IPR. Many communities may not have access to a large surface reservoir to use as an environmental buffer, or if there is one, the treated wastewater may have to be pumped long distances to reach the reservoir. In IPR systems that use a groundwater aquifer as an environmental buffer, the treated wastewater must be injected underground and later pumped back out. This two-stage process consumes energy and requires the construction of injection wells. For many communities, DPR is a more feasible and cost effective water management strategy.

One such community is Windhoek, Namibia, where DPR has been practiced for over 40 years. Windhoek is located in one of the most arid regions of the world, and it relies on the New Goreangab Water Reclamation Plant to treat wastewater and provide nearly a quarter of its 15 million gallon per day demand for water. More recently, several municipalities in the United States have implemented DPR. The city of Big Springs, Texas, Wichita Falls, Texas, and Cloudcroft, New Mexico, have all implemented DPR projects, while other cities, such as El Paso, Texas, have DPR projects planned in their future. So far, all of the DPR projects in the U.S blend the advanced treated water with raw water before passing the blended water through a conventional drinking water treatment plant. The New Goreangab plant is the only DPR project in the world which introduces the advanced treated water directly into the potable distribution system.

There are many benefits to implementing DPR in California and other arid regions:

  • DPR can increase the amount of available water in California by reusing wastewater that would otherwise be discharged to the ocean. The amount of additional water recoverable in this manner is estimated at 1.2 million acre feet per year – more than the entire storage capacity of Folsom Lake.
  • DPR can increase water supply reliability, as wastewater is not as subject to seasonal and annual variations as other water sources.
  • DPR can increase the quality of drinking water. Because the effluent produced by DPR is of such high quality, if blended with the traditional source water ahead of a drinking water treatment plant, it can improve the quality of drinking water distributed to users.
  • DPR can reduce energy consumption by providing a local source of water for municipalities. A large portion of the cost of water in arid regions comes from the energy required to transport it long distances. While the treatment technologies used for DPR are energy intensive, in areas such as Southern California, the energy required to produce water with DPR is less than that required to transport water from the State Water Project to users (Figure 2).

Figure 2: Power required to supply water to Southern California. It is assumed that power consumption for supply and conveyance of DPR will be close to zero. Adapted from Shroeder et al. (2012).

Many who are opposed to the concept of DPR label it as “toilet to tap,” or “drinking wastewater.” There are several reasons why the perception of DPR as “drinking wastewater” is misleading. First, the treatment technologies used to treat water for IPR and DPR projects produces an effluent which is typically of higher quality than that of the drinking water source (whether groundwater or surface water) for a given municipality. Second, many large municipal areas that would benefit most from DPR projects, such as Los Angeles County, have source water which has already been used by upstream users several times before it reaches the intake to their drinking water treatment plant. In essence, Los Angeles residents are unknowingly practicing “toilet to tap,” but without the careful engineering and safety measures that a real DPR project would incorporate.

While DPR is not yet legal in California, authorities in California have begun investigating DPR as a legitimate water reuse strategy. The California Water Code section 13563 mandates that the State Water Resources Control Board report on the feasibility of developing criteria for DPR by the end of 2016. To accomplish this goal, the SWRCB established an expert advisory committee to hold hearings and gather data in 2014. Progress of the committee can be found here. While legalization of DPR in California is still a ways off, many speculate that it is inevitable.  The acceptance of DPR in Texas and New Mexico, California’s search for new water sources in the current drought, and California’s push towards sustainable technologies are all factors which indicate that DPR will have a future in California.

Nathaniel Homan is earning his Masters degree in Environmental Engineering at UC Davis. He is working with Dr. Peter Green and Dr. Thomas Young to minimize waste from strong base anion exchange systems used to remove hexavalent chromium from drinking water.

Further Reading

Crook, J. (2010). “Regulatory Aspects of Direct Potable Reuse in California.” National Water Research Institute.

Du Pisani, P. L. (2006). “Direct reclamation of potable water at Windhoek’s Goreangab reclamation plant.” Desalination, 188(1-3), 79-88.

Gerrity, D., Pecson, B., Trussell, R. S., and Trussell, R. R. (2013). “Potable reuse treatment trains throughout the world.” Journal of Water Supply Research and Technology-Aqua, 62(6), 321-338.

Harris-Lovett, S. R., Binz, C., Sedlak, D. L., Kiparsky, M., and Truffer, B. (2015). “Beyond User Acceptance: A Legitimacy Framework for Potable Water Reuse in California.” Environmental Science & Technology, 49(13), 7552-7561.

Leverenz, H. L., Tchobanoglous, G., and Asano, T. (2011). “Direct potable reuse: a future imperative.” Journal of Water Reuse and Desalination, 1(1), 2-10.

Shroeder, E., Tchobanoglous, G., Leverenz, H. L., and Asano, T. (2012). “Direct Potable Reuse: Benefits for Public Water Supplies, Agriculture, the Environment, and Energy Conservation.” National Water Research Institute.

Tchobanoglous, G., Cotruvo, J., Crook, J., McDonald, E., Olivieri, A., Salveson, A., and Trussell, S. R. (2015). “Framework for Direct Potable Reuse.” J. J. Mosher, and G. M. Vartanian, eds., WateReuse Research Foundation.

Posted in California Water, Uncategorized, Water Supply and Wastewater | Tagged , , | 3 Comments