Turbidity and Insights on Flow-Habitat-Fish Abundance Curves in Policy-making

by Jay Lund

California’s water policy community continues to be embroiled on how best to manage what remains of California’s native aquatic ecosystems, particularly for the Sacramento-San Joaquin Delta and its tributaries.  One aspect of this controversy is the dedication and use of habitat and flow resources to support native fishes.

There is general agreement that California’s native fishes need both water and aquatic habitat.  After this, water management for native ecosystems becomes more complex, uncertain, and controversial.

Various authors have produced or explored relationships between native fish abundance, flow, and habitat for California’s Sacramento-San Joaquin Delta (see some under further readings below).  For policy-making, there is a tendency and probably a need to simplify the world by trying to believe such relationships.  Scientifically, the policy insights from such relationships might be quite limited, but such curves might have some utility nonetheless for helping us stagger towards better management.

Consider the alternative general fish abundance-outflow-habitat curves in the figure: flow-habitat-abundance curves

Axes. Even the axes for this plot will be a gross simplification.  For net outflow, it is quite important to know: a) when outflows occur seasonally, together with Delta inflow conditions, b) internal Delta flow conditions, c) the recent time history of Delta inflow and internal flow, and d) upstream habitat conditions that supply nutrients, prey, and young for species of interest.  Similarly, the habitat area is a gross amalgam of different types of habitat being managed differently in different parts in the Delta and upstream to provide different habitat, food, and nutrients at different times of year suitable for different native species.  Such grotesque simplification is a cost of the simplicity needed to start organizing a problem.

Thresholds for extinction.  On the diagram, there should be general agreement that some minimum thresholds of Delta outflow and habitat are needed for native species to subsist (dotted lines).  We should despair on knowing such thresholds exactly.  Thresholds for extinction are unlikely to be fixed and could easily vary with species, hydrologic conditions, antecedent conditions, and how these annual conditions are managed seasonally and locally within the Delta.  These thresholds should be seen something like vibrating limits, where even getting near them increases risks for extinction and costs for future species recovery.  Quantifying such limits as policies will be unavoidably controversial and scientifically perilous.

More fish and habitat help fish abundance.  There is general agreement that more flows and more habitat, if properly managed seasonally and geographically, should lead to more fish.  Consider the dashed diagonal line on the diagram, along which fish abundance always increases with northeast movement.

Substitution of resources for fixed fish abundance.  Now pick some arbitrary point on the diagonal, beyond the zone of certain extinction, a point that supports a fish abundance of n with equal dedications of aggregated habitat and flow.  Is this the best way to have an abundance of n fish?  Maybe a little more flow with a little less habitat (or vice versa) might result in more fish or less economic cost for providing flow and habitat for n fish?

Four possible shapes for a habitat-flow-fish abundance curve are suggested for achieving n fish.  These are curves A, B, C, and D on the diagram. These curves would shift outward for greater fish populations, and inward towards the extinction thresholds for smaller fish populations.  (For explication, the quantification of fish here is just as grotesque, averaged, and un-nuanced as the quantification of flow and habitat. These curves also vibrate stochastically, implying some probability of stable recovery increasing with higher populations.)

No substitution of flow and habitat.  Curve A shows no possibility for substituting flow for habitat in supporting fish.  Here, each fish needs fixed amounts of both habitat and flow, with fish abundance limited only by the most limiting resource.  Any extra flow or habitat above the limiting amount is wasted, except that, given uncertainties, an additional resource reduces the likelihood that resource is limiting, but makes it more likely that other resources are limiting.

Fixed rate of substitution.  If a constant fixed substitution of flow for habitat exists, then line C describes how flow and habitat trade-off to produce a fixed aggregated fish abundance.  From a management perspective, if flow is more easily gotten politically or economically than habitat, then fixed substitutability would lead investing all in flow (as near the threshold as one dared), to get the most fish.

Substitutions that encourage balance.  Where the total habitat and flow consists of heterogeneous sub-areas of habitat and flow with different abilities to support fish abundance, then some substitutability of flow and habitat will occur from investments in different mixes of sub-areas.  So spatial heterogeneity could create a degree of substitutability, perhaps like curve B.  For this curve, fish abundance would likely increase quickly as one exceeds a flow or habitat extinction threshold, and be maximized with a balancing of fish and flow investments.  For curve B, maintaining a given fish abundance n with less and less flow or habitat requires more rapid increases in the other resource to compensate (perhaps across different sub-areas), until the extinction threshold is approached.

Some substitutions encourage extremes.  If additional flow or habitat above an extinction threshold only slowly improves fish abundance, then curve D seems the likely flow-habitat-abundance curve shape.   This seems a perilous ecosystem to manage because, like the linear case of curve C, one is tempted to maximize abundance by investing all in flow or habitat (not both) as close to the extinction threshold of the other resource as one dares.

Keep out of the zone of extinction.  Of course, this discourse is only useful if enough flow and habitat resources exist to escape the zone of extinction, defined by the thresholds.  Indeed, one needs to invest in both resources to be far from them, as their exact locations vary with time and have uncertainty.

Other important things.  Alas, this diagram tempts suggests that flow and habitat (even as grossly considered here) are the only important factors.  The management of invasive species, ocean conditions, climate change, and other things may shift these curves with time, gently or abruptly.

Conclusions.  So, what can be learned from this?

  1. Managing flow and habitat for native Delta fishes is an unavoidably grotesque, complex, and uncertain problem. Whatever policies and management are adopted will probably not work as hoped for.  So a considerable effort is needed in developing institutions, resources, science, and synthesis that can adaptively manage.
  2. If we think we know the general shape of the substitutability of flow and habitat in supporting fish abundance, it leads us to either investing predominantly one resource or the other as near the extinction threshold as we dare if substitutability is constant (curve C) or concave (curve D), with more balanced investments in flows and habitat if there is no substitution (curve A) or weak substitution (curve B). The shape of substitution trade-offs determines the best strategic approach.
  3. If there is no substitutability of flow and habitat for fish abundance (curve A), yet both are vital, then it is important to seek the proper balance of resources. A balanced strategy also is best, but less strongly, if increasing flow or habitat would be needed to make up for a scarcity of the other (curve B) and both resources are costly.
  4. In all cases, managers should stay away from the extinction zone. Some flow-habitat-abundance shapes tempt one to find and manage at the edge of extinction edge, despite its instability.  For these substitution shapes (curves C and D), how close should we dare get to the extinction threshold?
  5. To find the proper balance and avoid extinction thresholds requires vigorous science-based adaptive management, based on ecological or mechanistic theory and models supported by field data and experiments.
  6. Although these general policy lessons have some value, settling on an initial resource policy and allocation can obscure the more difficult problems of how to manage these resources locally within the Delta seasonally and inter-annually. This more challenging detailed level of management and science must be workable for the ideal curve shapes and policies discussed above to hold true.

Hopefully this adds more insight than turbidity.

Jay Lund is the Director for the Center for Watershed Sciences and Professor of Civil and Environmental Engineering at the University of California – Davis.  This blog benefited (probably not enough) from conversations with John Durand, Peter Moyle, Wim Kimmerer, and Cathryn Lawrence.

Further readings

Bennett, W.A., and P. B. Moyle.  1996.  Where have all the fishes gone: interactive factors producing fish declines in the Sacramento-San Joaquin estuary. Pages 519-542 in J. T. Hollibaugh, ed. San Francisco Bay: the Ecosystem. San Francisco: AAAS, Pacific Division.

Grimaldo, L. F., T. Sommer, N. Van Ark, G. Joes, E. Hoilland, P.B. Moyle, B. Herbold, and P. Smith. 2009. Factors affecting fish entrainment into massive water diversions in a freshwater tidal estuary: Can fish losses be managed? North American Journal of Fisheries Management 29:1253-1270.

Hanak, E., J. Lund, A. Dinar, B. Gray, R. Howitt, J. Mount, P. Moyle, and B. Thompson. 2011.   Managing California’s Water. From Conflict to Reconciliation.  PPIC, San Francisco. 482 pp.

Healey, M., W. Kimmerer, G. M. Kondolf, R. Meade, P. B. Moyle, and R. Twiss. 1998.  Strategic plan for the Ecosystem Restoration Program. CALFED Bay-Delta Program, Sacramento. 252 pp.

Kimmerer, W. (2002), “Physical, Biological, and Management Responses to Variable Freshwater Flow into the San Francisco Estuary,” Estuaries Vol. 25, No. 6B, p. 1275–1290 Dec.

Kimmerer, W., E. Gross, and M. MacWilliams (2009), “Is the Response of Estuarine Nekton to Freshwater Flow in the San Francisco Estuary Explained by Variation in Habitat Volume?,” Estuaries and Coasts (2009) 32:375–389.

Kimmerer, W., T. Ignoffo . K. Kayfetz, and A. Slaughter (2018), “Effects of freshwater flow and phytoplankton biomass on growth, reproduction, and spatial subsidies of the estuarine copepod Pseudodiaptomus forbesi,” Hydrobiologia 807:113–130.

Lund, J., E. Hanak, W. Fleenor, W., R. Howitt, J. Mount, and P. Moyle. 2007. Envisioning futures for the Sacramento-San Joaquin Delta. San Francisco: Public Policy Institute of California. 284 pp. http://www.ppic.org/main/publication.asp?i=671

Moyle, P. B., R. Pine, L. R. Brown, C. H. Hanson, B. Herbold, K. M. Lentz, L. Meng, J. J. Smith, D. A. Sweetnam, and L. Winternitz.  1996.  Recovery plan for the Sacramento-San Joaquin Delta native fishes. US Fish and Wildlife Service, Portland, Oregon.  193 pp.

Nobriga, M. and J. Rosenfield (2016), “Population Dynamics of an Estuarine Forage Fish: Disaggregating Forces Driving Long-Term Decline of Longfin Smelt in California’s San Francisco Estuary,” Transactions of the American Fisheries Society, Volume 145, 2016 – Issue 1

 

Posted in Uncategorized | Leave a comment

Is it drought yet? Dry October-November 2019

by Jay Lund

So far, October and November 2019 has been the driest (or almost the driest) beginning of any recorded water year with almost zero precipitation. (The 2020 water year began October 1, 2019 – so you might have missed a New Year’s party already.)

Should we worry about a drought yet?

Yes, this is California, where droughts and flood can happen in any year, and sometimes in the same year.  Water managers should always worry about drought (and floods) at all times in all years, especially during the November-March wet season.

No, not especially anyway, because we are still early in the 2019 wet season, most precipitation falls later in the water year, and there is not strong correlation between October-November precipitation and total water year precipitation.

The California Department of Water Resources does a great job assembling current and historical data on water conditions, updated daily on the California Data Exchange Center website.  It is a wonderful data playground.

Plotting historical 1921-2018 northern Sierra precipitation for October+November against water year total precipitation gives the following scatter-plot, correlation, and statistics.

Water year precip scatter plot

Having little precipitation in October + November still means the year overall could be wet or dry, but averages a bit drier

From this plot, statistically, every inch lost in October+November precipitation averages 1.4 inches less total water year precipitation for the northern Sierras.  Since October+November averages 9.3 inches of precipitation historically, if it does not rain for the rest of November (a storm is in the forecast), then we would have on average 13 inches less than average northern Sierra precipitation this year. (Average historical northern Sierra precipitation is 50 inches.)  Although this is not good news, it is not doom.  Given the high variability of California’s climate and poor correlation between monthly precipitations, anything could happen.

It is comforting that California’s reservoirs are relatively full today, which provides something of a buffer against dry years and shorter droughts.  And the last few wetter years also have refilled groundwater some from the last drought.

The these recent dry months lengthened this year’s fire season (if anyone had not noticed).  With a warming climate and more houses in fire-prone areas, any fire season extension due to dry weather becomes increasingly threatening.

Overall

Will California have a drought? Yes.

Is the next drought beginning this year?  Perhaps, but probably not.  Still, water managers should (and usually do) prepare for drought, even if recent months had been wet – because it will become dry eventually.

I am looking forward to rain (and hopefully snow).  A good storm is forecast for later this week, so we get at least some precipitation in November, slightly improving odds of a wetter year.

Jay Lund is a professor of civil and environmental engineering and director of the Center for Watershed Sciences at UC Davis. 

Further Reading

Lund, J. (2015), “The California Drought of 2015: January,” CaliforniaWaterBlog.com, January 5, 2015.

California Weather Blog, http://www.weatherwest.com/

L’Heureux, M., “Seeing Red Across the North Pacific Ocean”, October 23, 2019: https://www.climate.gov/news-features/blogs/enso/seeing-red-across-north-pacific-ocean  A recent discussion on Pacific blobs affecting drought in California.

Posted in Uncategorized | Leave a comment

Some more water management truisms (Part II)

by Jay Lund

Fate of old professors

Decaying matter from which truisms emerge

Here is part two of a partial collection of truisms on water management.  These ideas seem obviously true, but still offer insights and perspective.  Original sources are mostly unknown (but apocryphal citations are common).  Any that I think are original to me, are probably not.

  1. Progress and effectiveness occur somewhere between complacency and panic. Complacency never befriends progress.  Panic can be motivating, but often betrays improvement.
  2. Everyone wants a better water system, and everyone agrees someone else should pay for it.
  3. Integration is easy to say, but is hard to do. So “integration” is said often.
  4. Involvement is not integration, but can be a start.
  5. You touch everything when you touch water. And in the American West, when you touch water, someone will become defensive.
  6. Some import drinking water from Fiji, Italy, or France, but not to irrigate crops.  Water is heavy and expensive to move, so it is usually cheaper to move food than water.
  7. People often pollute water by adding artificial coloring (blue, green, grey, black, etc.). Water is more clearly understood without verbal turbidity.
  8. ‘The meek shall inherit the Earth but not its water rights.’ – @WaterWired (apologies to J. Paul Getty)
  9. “No single raindrop believes it is to blame for the flood.” – E. L. Kersten
  10. Water obeys physical laws immediately, far faster than human courts.

Further reading

Lund, J. “Some Water Management truisms, Part I,” CaliforniaWaterBlog.com,

Jay Lund is a Professor of Civil and Environmental Engineering at the University of California, Davis.  I am frightened by how many more sayings remain on my list.  (Making such lists seems a symptom of being an old professor, which is another list to publish elsewhere someday.)

Posted in Uncategorized | Leave a comment

Night of the Living Dead Salmon

by Kelly Neal and Gabe Saron

Fish 1

Adult Chinook salmon carcass picked up by the Carcass Crew. Photo Credit: Kelly Neal

On a cool and misty morning somewhere south of Redding, California, jet boats roar across the tranquil Sacramento River. Armed with tridents, machetes and poleaxes, it seems akin to a scene from an action movie; except that “California Department of Fish and Wildlife” is painted on the boats. One by one, the boats peel out of formation and hole up in eddies and backwaters beside the main river channel. Then, they wait.

Once a pale shadow is spotted within the murky depths of the riverbed, someone onboard thrusts a trident into the water and sinks its barbed prongs into something fleshy. Then, they raise it back out of the water and pivot the catch toward the bow. Glistening in the morning light, covered in welts and sores with blood streaming, a creature resembling something from a horror films slaps onto the deck. The catch lands on a measuring board and the team flies into action, calling  “Fork length: 870mm, male, spawned, disk tag ready.”

It is an adult Fall Run Chinook Salmon, just past the end of its life cycle. It takes on a zombie-like appearance as it consumes its own body for energy on the journey upstream to spawn. After spawning, the fish died and continued decomposing before crossing paths with the Carcass Crew.

Aboard the jet boats, the fishy bodies are dissected in the name of science. With knives and forceps, researchers extract eyeballs and otoliths (ear stones) from the fish. Putrid carcass residue spills across the bow and splatters the boots and pants of the team. Eyeless and mutilated, the fish is clamped with a metal tag and tossed back into the current. This floating horrorshow is one example of the length that people will go to understand and protect Chinook salmon.

Fish2

Salmon carcasses for dissection.  Photo credit: Kelly Neal

This fish was, despite being slaughtered after its death, one of the lucky ones. It completed its life cycle in a largely hostile landscape: it survived variable ocean conditions, slipped past salmon fishermen, and avoided Delta water diversions on its way upstream to spawn. Something of a feat since only thousands of salmon are able to make the journey homeward now, when millions once did (Gresh 2011). Its tissues bear chemical traces from the waterways and food webs that sustained it across its lifespan. Its metal tag helps researchers compute the total number of returning adults by comparing the number of tagged to recaptured carcasses. This carcass is part of a massive effort to quantify how many spawning adults return, and what helps them survive the long watery journey.

Scientists aren’t the only ones looking for salmon carcasses. All along the Pacific Coast, organisms of all trophic levels, and even the next generation of juvenile salmon, sustain themselves on nutrient-rich carcasses. In Salmon streams in Alaska and the Pacific Northwest, bears and wolves feast on carcasses and carry their leftovers into adjacent riparian forests. This enables trees to uptake the nutrients of decaying fish. Marine-derived nutrients can restructure entire forest ecosystems, and provide nutrient-limited headwaters a pathway for growth (Naiman 2009).

Fish 3

Bobcat feasts on a Chinook salmon carcass on the Sacramento River. Photo credit: Eric Holmes

In California’s Central Valley, much of the water and its nutrients are appropriated for agriculture. In 2018, the Pacific Fishery Management Council estimated 108,000 returning Chinook Salmon adults in California’s Central Valley (Pacific Fishery Management Council, 2019). Assuming the average adult Chinook Salmon weighs 20kg and contains about 5% Nitrogen, Chinook Salmon delivered roughly 126 metric tons of marine-sourced nitrogen fertilizer to the Central Valley last year. Isotopic tracing has shown that these nutrients make their way into wine grapes, and possibly other crops, irrigated from salmon streams (Moyle and Merz 2006). This Halloween, consider something truly spooky: when you prepare a fresh salad or pour a glass of Pinot Grigio, you might be giving second life to the carcass of a long dead Chinook Salmon. Cheers!

Kelly Neal and Gabe Saron are Junior Specialists at the UC Davis Center for Watershed Sciences. 

Further Reading 

Gresh T., Lichatowich, J., Schoonmaker., P. An Estimation of Historic and Current Levels of Salmon Production in the Northeast Pacific Ecosystem: Evidence of a Nutrient Deficit in the Freshwater Systems of the Pacific Northwest. Fisheries 25:1. 2000

Merz, J. and P. Moyle, Salmon, Wildlife and Wine: Marine-Derived Nutrients in Human Dominated Ecosystems of Central California. Ecological Applications 16(3) 2006.

Ogaz, Mollie, The Spawning Dead: Why Zombie Fish are the Anti-Apocalypse, CaliforniaWaterBlog.com October 29, 2017.

Pacific Fishery management Council. Review of 2018 Ocean Salmon Fisheries. 2019.

Pinay, G., O’Keffe, T., Edwards, R., Naiman, R., Nitrate removal in the Hyporheic Zone of a Salmon River in Alaska.” River Research and Applications 25. 2009

Posted in Uncategorized | Leave a comment

The Dreamt Land by Mark Arax: We’re all complicit in California’s water follies

by Ann Willis

(Arax photo/Joel Pickford)

We are all sinners. At least, that’s the impression Mark Arax leaves in The Dreamt Land: Chasing Water and Dust Across California. What’s bold, and distinguishes this book from others about California, is that Arax grapples with a history that we’re still in the midst of creating, rather than reflecting on sins long past and easily put away as the transgressions of others. In that way, he leaves us both illuminated and uncomfortable, for we must ask ourselves: Are we complicit? Or an agent of the rigged system? For there doesn’t seem to be much safe space for innocence.

The voices that resonate through this story are not so much oft-told tales of William Mulhullond and the Owen’s Valley Water Grab or dam excesses under Floyd Dominy, though those episodes are given their due in the chapters that describe the era of extraction and rerouting of California’s waterways. Rather than dwell on overtold stories, Arax introduces new voices, including his. 

Part of what makes this book compelling and widely appealing is that Arax doesn’t shy away from his unwonkiness. His first awareness of California water was, like most people, tangential to some other part of everyday life. Arax’s grandmother pointed to irrigation ditches crisscrossing Fresno and urged young Arax to promise never to play near one, 

“…because I would lose my balance and fall in and, like the poor sons of the Mexican farmworkers, no one would hear my screams or be able to save me. The men who ran the irrigation district wouldn’t shut off the valve and drag me out until the growing season was over, she told me. When I asked her why, she said the flow of one irrigation ditch meant more to the valley than the body of one silly little boy.” (The Dreamt Land, pg. 46)

The Sacramento – San Joaquin Delta, as seen from a ship traveling through the Stockton Ship Channel on September 24, 2013. Photo by Florence Lo, California Department of Water Resources

Arax seems to rearrange fragments of childhood memories, like his grandmother’s warning or a strange tool that his grandfather kept in a drawer, as though twisting a kaleidoscope so that when they refocus, they are framed by the powers that control the flow of California’s rivers. It’s as though, with his education of California water, a secret is revealed and Arax suddenly sees his family’s history more clearly. As pieces of his heritage come into focus, Arax guides us to forces that shaped his story, showing us how his story is also ours. If we eat here, drink here, live here, we are touched by the deep state of California water. And within that deep state, there is as much indifference to us as to a silly little boy in a ditch.

Stewart and Lynda Resnick might take issue with that assessment. That’s the implication suggested in “Kingdom of Wonderful,” the chapter on a carpetbagger’s rise and success in California agriculture. While reading about growers like the Resnicks, I’m reminded of dynasties like the Rockefellers and Carnegies: families whose wealth from industrial transgressions seems distant while their philanthropic legacies endure in museums, performance centers, public land, and libraries. Woven into the Resnicks’ empire-building activities are considerable philanthropic and community programs, including an $80 million charter school serving students from the poorest towns in the West. Nevertheless, the agricultural practices underpinning such philanthropy stand in stark relief. When a billion-dollar nut harvest signals the start of inhaler season for local farmworkers who can’t drink their own tap water and reside in what neurologists call “Parkinson’s Alley,” it’s hard to accept philanthropy as proportional penance.

Arax doesn’t just level his judgement on the agricultural barons of Kern County. He dismisses any notion of bystanders’ innocence, too:

“When the rivers were content, the people were content…They had no interest in hiring engineers who could tell them at what cubic feet their rivers flowed, a science that might allow them to better prepare for the next fit of weather. In times of good nature, they cared not to be reminded of ill nature. In the desire to forget, their memories were able to play such tricks that when flood and drought returned, they were genuinely perplexed.” The Dreamt Land, pg. 171

The south fork of Lake Oroville, California’s second largest reservoir, in September 2014. Photo by Kelly M. Grow/California Department of Water Resources.

From regulators down to the public, Arax holds a mirror up to all and shows us the reflection of those either willfully indifferent to over-consumption or too cowed to wield power to regulate it. The consequences of that indifference or impotence are playing out today, such as the on-going effort to raise of Shasta Dam. Part of the genius of Arax’s book is how it juxtaposes California’s settlement history with today’s conflicts. The Dreamt Land shows that California’s water war is a long game in which formidable players have staked their ground and simply wait for the right combination of opportunity and luck to press their advantage. 

Mark Arax will speak on November 18th, 4-5:30pm at the UC Davis Student Community Center multi-purpose room. You can register at the Eventbrite link. The book lecture is free and open to the entire campus community and the public. Please feel free to forward the Eventbrite invitation to others who may be interested.

Ann Willis is a researcher at the Center for Watershed Sciences and a PhD candidate in civil engineering. She holds fellowships with the National Science Foundation GFRP, John Muir Institute for the Environment, and Southwest Climate Adaptation Science Center.

Further reading

Arax, Mark. 2019. The Dreamt Land

Reisner, Marc. 1986. Cadillac Desert

Water is for fighting over? – a review of John Fleck’s recent book. California Waterblog.

Posted in Agriculture, California Water, Drought, education, Stressors, Sustainability | Tagged | 1 Comment

Can we understand it all?

How we get water in our homes

This is my favorite water cartoon.  It depicts how well the public (and elected officials) will ever understand how water systems work.

Today, as individuals we understand only a little about the detailed world around us (cell phones, medical technology, monetary policy, politics, international trade, law, etc.).  We operate with amazing Neolithic brains in a modern world, relying mostly on others for details.

Public education and outreach matters, of course, as seen during the drought, but our expectations must be reasonable.  In our complex society and economy, with many important distractions, most people will only learn a lot about water systems if they fail.  Civilization requires that most people not worry about water.  The cartoon signals the success of typical water systems, which allows people to think about other things.

Water professionals and managers face similar challenges from the great complexity inside the dashed water system box.  Filling in details inside the cartoon box quickly “goes fractal” with seemingly endless agencies, regulations, institutions, specialists and specialized components, and their interactions.  No one, not even dedicated water wonks, can completely understand most water systems.

Still, modern water systems have been rather successful for public health and economic prosperity.  But for everyone individually, how water gets to our homes will be an opaque or at best translucent box.  Complexity grows as water management expands to include environmental and ecological systems.  Managing this complexity becomes a struggle for managers and the society as a whole.  We can only succeed if we work well together – this struggle is the hard price of success.

Now I must return to struggling with my smarter-than-me-phone.

Jay Lund

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

Posted in Uncategorized | 1 Comment

Some water management truisms, Part I

by Jay Lund

Here is a partial collection of truisms on water management.  These are common ideas that seem obviously true (particularly in the western US), but still offer insights and perspective.  The original sources of these are unknown (although apocryphal citations are common).  Any that I think are original to me, are probably not.

  1. Water flows downhill, but uphill towards money.
  2. There is rarely a shortage of water, but often a shortage of cheap water.
  3. Some water is essential to life. But too much is also unhealthy.
  4. Silver bullets tend to sink in water.
  5. Progress is when the new problems are less bad than the old problems would have become.
  6. Your water use is a “grab” and a “waste.”  My water use is a need, a nab, and a sacred right.
  7. Water is often like money and manure – if you spread it around, many good things can grow, but heaping it all in one place can cause big problems.
  8. Irrigation inefficiency can be good for aquifer water quantity, but bad for aquifer water quality, defying simple judgements.
  9. Some changes in water availability with climate change are easily expected, and some will be unexpected. We won’t know the changes exactly for decades after they have become noticeable, if ever. Changes also are unlikely to be constant, or to end.
  10. A dedication of water and land alone is slightly more likely to create a desirable ecosystem than pile of wood, steel, and concrete is to create a home or a bridge. Resources must be organized and artfully employed, as well as provided, to get what we want.
Posted in Uncategorized | 2 Comments

Management’s eternal relevance

by Jay Lund

Just a brief, and slightly pedantic, blog post this week on the importance of liberal education and broad thinking for those want to solve real problems, illustrated with a bit of history.

Engineers and physical scientists will know Claude-Louis Navier from his work on the fundamental equations of fluid mechanics (the Navier-Stokes equations) (1822). These are some of the scariest equations seen in most undergraduate engineering and science educations.

But the early French engineers did not merely derive equations that we still struggle to learn and apply.  They also founded modern engineering as an approach to organized problem-solving, an approach picked up by many disciplines. As the French state was keen to rationalize (and centralize) national military and infrastructure systems, they faced many fundamental intellectual and organizational, and technical challenges. So early French engineers were as involved in construction, management, education, and policy as they were in what we too-narrowly think of today as “engineering” calculations (Langins 2004).

Navier was a bridge inspector, a developer of fundamental equations of fluid and solid mechanics, and a policy thinker on the organization and economic analysis of public works. His 1832 paper, “On the Execution of Public Works, Particularly Concessions,” Navier compares different fundamental approaches for financing public works – local funding, state funding, state funding repaid with user fees, and private concessions. We face these issues today, and always.  He also discusses the analysis and public scrutiny desirable for evaluating such proposals.  His ideas remain fundamental and of enduring relevance for all manner of water infrastructure and projects, including local and regional water projects, local projects for safe drinking water, water storage projects, water as a human right, and privatization and community ownership.  Navier’s 1832 paper is seen by some historians of economics as among the earliest formal work on benefit-cost analysis and the economic management of public works (Ekelund and Hebert 1999).

Navier was not alone in having fundamental contributions spanning very different fields. Navier’s younger colleague Jules Dupuit is known today in groundwater and engineering for his contributions to flow modeling (which came from his work on sewers). But Dupuit’s more fundamental contribution was developing the idea of “consumer’s surplus” taught in every undergraduate economics class (1844). The famous economist and political philosopher Hayek, traces socialism to early French engineers. (Today’s modern engineering profession was developed orignally to serve the state, not the private sector.)

Talented engineers and physical scientists should not fear or disdain economics, policy, and social sciences. Many fundamentals in these fields were developed by the same folks who developed the fundamentals of engineering and physical and social science. As the early French engineers discovered, a broad range of fundamentals are important to combine for effective organized problem-solving.

There is ever a need to bring technical and social organization together for effective problem-solving. This is important for the professions, as well as governmental deliberations.

Further readings

Dupuit, Jules. “On the Measurement of the Utility of Public Works.” Translated by R. H. Barback from the Annales des Ponts et Chaussees, 2d ser., Vol. VII (1844) in the International Economic Papers, No. 2. London: Macmillan Co., 1952; reprinted in Kenneth J. Arrow and Tibor Scitovsky, eds., Readings in welfare economics, 1969.

Ekelund, R.B. Jr. and R.F. Hebert (1999), The Secret Origins of Modern Microeconomics – Dupuit and the Engineers, University of Chicago Press, Chicago, IL.

Hayek, F.A. (1944), The Road to Serfdom.

Langins, J. (2004), Conserving the Enlightenment: French Military Engineering from Vauban to the Revolution, MIT Press.

Navier, C-L (1832), “On the Execution of Public Works, Particularly Concessions,” ANNALES des PONTS ET CHAUSSÉES, N°. XXXV.1st Series, 1st Semester (1832) (translated poorly from the original French by Jay Lund): French original: https://gallica.bnf.fr/ark:/12148/cb34348188q/date1832

Navier, C-L Wikepedia article, English. https://en.wikipedia.org/wiki/Claude-Louis_Navier

Navier, C-L Wikepedia article, French https://fr.wikipedia.org/wiki/Henri_Navier

 

Posted in Uncategorized | 1 Comment

The long and winding road of salmon trucking in California

Spawning Chinook salmon at Nimbus Hatchery on the American River (image by Barry Lewis)

By Dr Anna Sturrock

Trucking juvenile hatchery salmon downstream is often used in the California Central Valley to reduce mortality during their perilous swim to the ocean. But is it all good? Researchers at UC Berkeley, UC Davis, UC San Francisco and NOAA Fisheries published an article in Fisheries this month exploring the history and implications of salmon trucking in a changing climate.

When I moved from England to California in 2012 to start a postdoctoral position at UC Santa Cruz, I distinctly remember the feeling of awe. Everything was on a bigger scale, and anything seemed possible. The patches of green English fields were replaced by never-ending rows of crops and fruit trees, gold-scorched hills, and craggy mountains. Our calmer, smaller waterways were replaced by fast-flowing rivers fed by dams the size of skyscrapers. Even the ocean waves were bigger here. When I started hearing about behemoth pumps that sucked so much water they reversed the river direction, and baby salmon hitching rides in trucks, I wasn’t sure if people were being serious. It turns out they were.

California is a land of plenty, boasting diverse, beautiful, vast landscapes and an abundance of natural resources. It also hosts a diverse and ambitious population of visionary thinkers with an unparalleled can-do attitude. Undeterred by its wildly variable Mediterranean climate of long, hot, dry summers and multi-year droughts, or wet, stormy winters that often flooded major towns, Californians have created a network of imaginative engineering solutions to store and move water around the state. One of the most transformative solutions to manage its boom-bust weather patterns was to build huge dams along the foothills of the Sierra Nevada to store winter rains and snow, providing water ‘banks’ to sustain domestic and agricultural users through the long, dry summers and droughts. These dams provide significant benefits to humans, supplying water to extensive agri-business and urban populations. However, the diversion of water, particularly during droughts, and the fragmentation of river habitats has drastically affected many aquatic species. For example, migratory fishes like Chinook (or King) salmon are often prevented from ascending the rivers to high elevation habitats where they would literally chill over the summer, eliminating the historically dominant spring run salmon from most Central Valley streams.

To mitigate for lost salmon production above the dams, five production hatcheries were built between 1944 and 1970 – Coleman National Fish Hatchery, and four state-operated hatcheries – Nimbus, Mokelumne, Feather, and Merced River Hatcheries. When I first moved here I wasn’t totally sure what hatcheries were: European media tends to focus on fish farms (where fish are kept in pens until they end up on your plate), generating horror stories about over-crowding, sea lice and escapees. So I was pleasantly surprised when I first visited a hatchery and talked to the people working there. I liken hatcheries to salmon IVF clinics (Fig. 1). Only these IVF clinics are not just addressing parent fertility issues, but providing luxury birthing suites, daycares and calorific dinners to the babies that would have otherwise been supported by the upstream habitat. Hatcheries then release the babies into the wild, typically once they have grown into smolts (‘fat toddlers’) to complete an otherwise natural life cycle.

The objectives of this study were to explore (a) when, where, and how many hatchery juveniles were released each year, (b) whether release patterns had changed through time, and (c) where these fish ended up if they were lucky enough to survive to adulthood.

Spawning Chinook salmon at Nimbus Hatchery on the American River (image by Barry Lewis)

In the early years (1940s to 1960s) everything was fairly low key compared with today – hatcheries tended to allow their youngsters to swim directly into the adjacent river where they would mingle with the wild fish, and they would swim to the ocean together (Fig. 2; also see our accompanying web app). In intermediate years (1960s to 1990s), the hatcheries intensified their role. For example, it was not a popular option to cull excess production (more babies than the hatchery could support), so – particularly in wet years – juveniles were often trucked to small, remote creeks that do not typically support their own salmon populations (e.g., Secret Ravine, Doty Ravine). Most of these fish were tiny and unmarked so we don’t really know what became of them – their offspring are probably an interesting study in themselves. However, over time managers and stakeholders got wise to the poor survival of juveniles during their perilous migration through the Sacramento-San Joaquin River Delta – historically, a diverse, mosaic of wetland habitats, now a channelized water conveyance system packed with introduced predators and contaminants. Thus, from 1980 onwards, trucking hatchery salmon directly to the ocean really took off, particularly during droughts. The argument is that chauffeuring fish past mortality hotspots (typically worse during droughts) gives them a survival advantage that boosts commercial and recreational fisheries. The idea of putting fish into a truck was a real culture shock for me. Faced with the same issues in the UK, I am pretty sure Boris Johnson would shrug his weary shoulders, mumble something incoherent, and we would all just have to tolerate low returns (of both hatchery and wild salmon) after droughts. Here, in historic drought year 2015, almost all the hatchery salmon produced (about 26.5 million individuals) were loaded into trucks and driven to the Delta, bays, or ocean (Fig. 2). That takes a lot of people, gas, and money. It also creates an even wider survival gap between hatchery and wild fish, contributing to the dominance of hatchery fish on nearly all Central Valley rivers.

Fig. 2 Densities (numbers) of hatchery salmon released during years characterized by (1) On-site releases (represented by each hatchery’s first release year); (2) non‐natal releases (spreading them out – e.g., in wet year 1998); or (3) trucking them to the bay (e.g., drought year 2015). ‘Bay’ indicated by a dashed line. Hatchery codes: COL = Coleman, FEA = Feather, NIM = Nimbus, MOK = Mokelumne, MER = Merced. Figure from Sturrock et al. (2019). If you want to download the release data or explore it in more depth, check out the accompanying web app.

Another consequence of trucking is that trucked salmon are much more likely to stray into other hatcheries or rivers when they return to spawn. Normally, young salmon create olfactory maps when they swim to the ocean, sequentially recording the smells they encounter along the way. If they are among the lucky few that survive to adulthood, they use these olfactory memories like street signs to find their way home. Trucked salmon have large gaps in their maps, making it harder for them to navigate home. We analyzed tagging data for salmon released by the five hatcheries since the start of the Constant Fractional Marking Program (an excellent program involving system-wide tagging of 25% of hatchery releases and increased tag recovery efforts to see who came back and where). We found that the further the salmon were trucked from the hatchery, the more likely they were to stray into a different river when they came back (Fig. 3). The effect was most extreme for hatcheries on smaller, more distant rivers, and when natal stream flows were lower during the period of return. We also found that fish returning at older ages were more likely to stray. These older individuals may simply be more forgetful, but it is more likely that their longer ocean residence time correlated with larger changes in the freshwater environment (i.e., their map became ‘outdated’), particularly in the Central Valley’s highly engineered waterways.

 Why do we care about straying? Some level of straying is natural and can help maintain genetic diversity, expand range boundaries, and recolonize impacted habitats. However, in a natural system, most individuals return home, allowing populations to adapt to local stream conditions (e.g., thinner individuals in shallower spawning grounds) and increase fitness (i.e., more babies per adult). The main concern is that excessive straying (often >80% of trucked juveniles strayed as adults) eliminates existing local adaptation, makes it harder for local adaptation to re-evolve, and can introduce maladapted genes into recipient populations. Excessive straying can also have more immediate impacts. For example, after Coleman (the biggest producer in the system) trucked all their fish to the Delta in 2015, so many of these fish strayed elsewhere when they returned in 2017 that Coleman was unable to meet its production goals (i.e., make enough babies for the next generation). Some argue that Central Valley salmon – being at the edge of the species distribution and more prone to drought and disturbances – might have higher baseline straying rates than their northerly counterparts. However, we found that the hatchery fish released on-site had “normal” straying rates, averaging 0.3% to 9.1% (i.e., if reducing straying rates were the only objective, then releasing on-site does seem to work).

Fig. 3 Observed (circles) and predicted (lines) straying indices of California Central Valley hatchery fish as a function of transport distance and return age (other model covariates averaged). Indices based on coded wire tag recoveries from brood years 2006–2012 (this study; circles) and 1980–1991 (Niemela 1996; crosses). Circles sized by the logged number of tag recoveries (used to weight model). Predicted straying rates for 3‐year‐old fish at minimum and maximum natal stream flows during the return period indicated by dashed lines (specifically, the range of mean October–November flows in return years 2008–2015, displayed above each plot). River distance from each hatchery to the bay indicated by an arrow (note, MER did not perform bay releases during the years examined). Hatchery codes defined in Fig. 2. Figure from Sturrock et al. (2019).

Hatcheries are often controversial and not everyone likes them. But without the Central Valley production hatcheries there would not be much of a salmon fishery in California, and – managed well – they could hold the key to salmon persistence in a rapidly changing climate. Trucking may help supplement the fishery in a given year, but it comes at a cost (impeding local adaptation and increased competition for food, mates, habitat – both from straying and the survival advantage provided by the trucking itself). Long-term, the combination of such high straying rates and such a large survival imbalance could reduce the stability of these populations and the fishery.

Fig. 4 Ranse Reynolds (retired CDFW Nimbus Hatchery Manager) at his home after interviewing him about some of the more vaguely described release locations.

Today, we are at an ecological tipping point, and California’s climate is predicted to become increasingly volatile and prone to hotter, longer droughts. To counter this uncertainty perhaps we should consider managing our fish and environment using a cautionary, risk-spreading approach that promotes long-term resilience, even if this occasionally leads to short-term losses in returns. Ideally, we would manage salmon stocks for both resilience and abundance, by (1) reducing straying rates of hatchery fish (e.g., using flow-through barges, segregation weirs, terminal fisheries, and attraction flows) and (2) enhancing the abundance and survival of natural-origin salmon (e.g., by increasing habitat carrying capacity via restoration and flow management). Many fish and water agencies, NGOs, stakeholder groups, and hatcheries are already exploring ways to achieve both objectives. Coleman and Mokelumne hatcheries have led the way in experimenting with alternative release strategies, and we are encouraged to see other hatcheries also trying broader release periods, and releasing fish closer to the hatchery in recent years. Such experiments may be expensive and challenging to perform, but – if carefully coordinated and repeated across water years – they will be crucial to informing management decisions in the future.

Central Valley Chinook salmon are at the edge of the species range and are clearly a tough breed – having already persisted in the face of multiple human impacts and extreme droughts. By trying new tools and working as a team – coordinating across watersheds, managers and stakeholder groups – we may be able to alleviate some of the issues we have created, and help these tough fish persist in a rapidly changing world.

Acknowledgements

This study built on the painstaking work carried out by Eric Huber transcribing decades worth of data from hatchery release reports into an electronic database. My first task was to add GPS coordinates to often incredibly vague site descriptions (e.g. “Misc.” or “Dry Creek” – do you know how many Dry Creeks there are in California?!). This involved a lot of interviewing (hassling) current and retired hatchery employees. I remember Anna Kastner digging out hand-drawn maps from the 70s from the Feather River Hatchery basement, Marc Provencher going through piles of physical planting receipts at Coleman, and Ranse Reynolds (retired Nimbus Hatchery manager – Fig. 4) and his wife Joyce, zooming around google maps from their home in Woodland while their grandkids played with my son. The historical insights were fascinating, and I was encouraged by how forthcoming and helpful everyone was. I cannot thank you enough. Thanks also to my dad, Barry Lewis, for the wonderful pictures of Nimbus Hatchery. Thanks also to Arnold Ammann, Walt Beer, Mark Clifford, Laurie Earley, Fred Feyrer, Brett Galyean, Ted Grantham, Scott Hamelberg, Tim Heyne, Paula Hoover, Rachel Johnson, Brett Kormos, Dave Krueger, William Lemley, Joe Merz, Carl Mesick, Cyril Michel, Kevin Niemela, David Noakes, Gary Novak, Bob Null, Mike O’Farrell, Kevin Offill, Jim Peterson, Corey Phillis, Rhonda Reed, Edward Rible, Paco Satterthwaite, Ole Shelton, Jim Smith, Ted Sommer, Bruce Sturrock, Lynn Takata, Mike Urkov, Judy Urrutia, Dan Webb, Peter Westley, Michelle Workman, and Steve Zeug for their comments, advice, support, and/or provision of data. Funding was provided by the CDFW Ecosystem Restoration Grant (E1283002), the Delta Science Fellowship Program (Award no. 2053) and CDFW Water Quality, Supply and Infrastructure Improvement Act of 2014 (CWC §79707[g]) (P1596028). I am also indebted to the massive efforts of all my coauthors – Stephanie Carlson, Will Satterthwaite, Kristina Cervantes‐Yoshida, Eric Huber, Hugh Sturrock, Sébastien Nusslé – and to my other mentor, Rachel Johnson, for giving me my first proper job, taking me to my first hatchery, and inspiring my obsession with salmon!

Anna Sturrock (@otolithgirl) is an Assistant Project Scientist at the Center for Watershed Sciences using natural and applied tags to reconstruct fish growth and habitat use. She is passionate about science communication and data visualization, and providing empirical data to support and inform natural resource management. Senior co-authors Drs Stephanie Carlson and Will Satterthwaite can also be found in the twittersphere as @fishteph and @satterwill.

Further reading

Sturrock, A. M., Satterthwaite, W. H., Cervantes-Yoshida, K. M., Huber, E. R., Sturrock, H. J. W., Nusslé, S., & Carlson, S. M. (2019). Eight Decades of Hatchery Salmon Releases in the California Central Valley: Factors Influencing Straying and Resilience. Fisheries, doi:10.1002/fsh.10267 (linked here)

Web app to visualize the release data across time and space: https://baydeltalive.com/fish/hatchery-releases

Huber, E. R., & Carlson, S. M. (2015). Temporal trends in hatchery releases of fall-run Chinook salmon in California’s Central Valley. San Francisco Estuary and Watershed Science, 13(2) (linked here)

Niemela (1996) – Effects of release location on contribution to the ocean fishery, contribution to hatchery, and straying for brood years 1987-1991 fall Chinook salmon propagated at Coleman National Fish Hatchery. USFWS. Northern Central Valley Fish and Wildlife Office, Red Bluff (linked here)

California Hatchery Scientific Review Group (2012). California Hatchery Review Report. Prepared for the USFWS and PSMFC (linked here)

Posted in Uncategorized | 2 Comments

Providing Flows for Fish

pic1.jpg

Putah Creek below Putah Creek Diversion Dam, December, 2014, a drought year.  The stream flows are regulated in part to support a diverse native fish fauna, including Chinook salmon.

by Peter Moyle

A reality in California and the American West is that people are competing with fish for water. We humans are winning the competition.  However, because there are moral, aesthetic, and legal obligations to provide fish with water in streams, biologists like me often get asked the question “Just how much water do the fish need, anyway?” This, of course, is the wrong question because the best reply is  “all of it!” if you consider the stream flows under which each fish species evolved, that often varied from raging torrents to gentle summer trickles across a single year.   The question may then switch to, “well, what is the minimum flow we need to provide to keep the fish alive?”  This is also the wrong question because if you keep a stream fish assemblage on minimum flows for a long enough period, most native species will likely disappear. In their place will be trout raised in hatcheries and non-native species like fathead minnows and green sunfish; these fish will live in a highly degraded habitats, signified by dead riparian trees and stagnant pools. A more useful question is “what is the optimal flow regime that will allow a diverse native fish fauna and other biota to thrive, while providing water for use by people?”

Attempts to find an answer to the last question, usually by simple, cheap hydrologic methods, have dominated stream flow disputes over fish for decades.  While some regions now typically use holistic approaches, in the USA and few other countries there remains heavy reliance on mechanistic approaches such as the Instream Flow Incremental Methodology (IFIM) and its modeling companion PHABSIM.  Frankly, these methods don’t work very well, because they are based on some untenable assumptions and on simplified models that bear little resemblance to ecological reality. Without trying to explain them further, lets just say they are likely to work best in a ditch that contains only rainbow trout.  So what does work for most streams?  There are several good options, which are explained in a new book Environmental Flow Assessment : Methods and Applications by John Williams,  Peter Moyle, Angus Webb, and Mathias Kondolf (2019, Wiley Blackwell, 220 pages).  You will note that I am a co-author so you may want to read this summary with some skepticism.

pic2

It is not by accident that the two chapters of the book following the introductory chapters are primers on flow and life in rivers and streams.   These chapters make the point that flowing waters are beautifully complex both physically and biologically, so it is rather naïve to think that a simple hydrologic model will suffice to determine flows needs for desirable aquatic life  (or even just fish).

The next chapter (5) deals with tools for environmental flow assessment (EFA). It shows that we don’t have to be content with standard hydrologic models because there are so many options these days, of intellectual tools, models, concepts and approaches that be used for EFA. Examples of new approaches to EFA that the book describes include Bayesian networks and hierarchical Bayesian models, of growing interest in biological systems.  Of course, tools are only as useful as the users make them.  “Ultimately, successful EFA depends on clear and critical thinking; the human brain is the most important tool for environmental flow assessment (p. 51).”

Once the myriad of tools available for EFA are in hand, there are many options for methods to determine environmental flows. Chapter 6 classifies these options and provides a critique of how and when each one is useful; the methods range from very simple to very complex. Any of them can be misused, of course, but most methods, preferably holistic ones, can be adapted to local situations.  The latter is important because no two streams are exactly alike so when a study is proposed, diverse options should be considered.

This is also true for the use of models in flow assessment, which seem ubiquitous. They are often used as if they can, by themselves, provide definitive solutions to a flow problem.   Because of this, the book (Chapter 7) provides a lengthy discussion on modeling and model testing.  It‘s the kind of background we hope everyone involved in an EFA relies on from the beginning. But the most basic lesson here is that: “Models are best used in EFA to help people think, not to provide answers (p. 141).”

Nowhere in the EFA universe are models more important than when looking at the how rivers are regulated below dams. Indeed, most EFAs are done on regulated streams.  Historically, most EFAs were couched as water vs fish, with little attention paid to inevitable geomorphic simplification of fish habitat that dams cause. Dams reduce sediment inputs, stabilize stream channels, and eliminate most high flows events. These processes are important for allowing stream channels to support diverse riparian and aquatic habitats for fish and all other aquatic life (Chapter 8).  Maintaining a ‘living stream’ below a dam is hugely challenging, but possible if an adaptive attitude is maintained towards EFMs.

Much of the book is critical of common methods for EFA. However, Chapter 9 presents a highly workable approach for the typical case where limited data are available, so expert opinion becomes more important for developing a flow regime that favors desirable species, usually fish.  The trick is to use structured methods to turn expert opinions (including those from published papers and reports) into a conceptual model of the situation. The conceptual model can then be quantified as a Bayesian Network Model. This model can be continuously improved as more data becomes available.  Ideally these data would be collected from the stream being modeled, by monitoring the effects of an initial flow regime. This results in a ‘feed back loop’ of more data making the model more useful followed by further manipulation of the study stream.  Eventually, the greatly improved data set will allow a more powerful Bayesian hierarchical model to be used.

The final chapter is short but contains the statement  “We have also emphasized that EFA is human activity and so subject to human behavior.”   This idea should be kept mind even when evaluating abstract hydrologic models. The book ends with a long checklist of things to keep in mind when conducting an EFA.

Because the book is aimed a broader audience than the people who just conduct EFAs, we made an effort to keep the language as concise, jargon–free and as clear as possible, given our own deep interests in the issues. In fact, clear writing is key to good EFAs, especially plain-word summaries of technical reports.

It is hard to over-emphasize the need for improved and innovative assessments of environmental flows in California’s streams, because there are over 1400 large dams in the state. Most dams need periodic reassessment of their flows for aquatic life, especially fish.  Climate change, with longer droughts and bigger floods, will create more disputes over managing the limited water supply. Improved understanding of the EFA options available should make settling such disputes in an amicable fashion more likely.

Further reading

Williams,  J., P. Moyle, A. Webb, and M. Kondolf (2019), Environmental Flow Assessment : Methods and Applications (Wiley Blackwell, 220 pages).  https://www.amazon.com/Environmental-Flow-Assessment-Applications-Restoration/dp/1119217369

 

 

 

Posted in Uncategorized | 1 Comment