Crawdads: Naturalized Californians

Sandy, a 4+ year old red swamp crayfish, raised from a newly hatched egg by Marilyn Moyle.

By Peter Moyle

Crayfish, crawdads, crawfish: whatever you call them, they are everywhere in California’s waters and are as tasty as their lobster relatives. They are especially familiar to anglers who peer into the maw of a bass or pikeminnow or flush their stomachs to see what prey caused the bulging belly. Crawdads are familiar to kids wading in streams, who dare each other to catch one without being pinched. River otters love them as food too. I have watched otters dive in Putah Creek and repeatedly come up with one. With each capture, the otter rolls on its back and crunches the crayfish down. The otters appear to be smiling with satisfaction, smacking their lips.  People eating crayfish have the same general appearance.

Crayfish are so integrated into California’s aquatic ecosystems that they might be considered as native if you didn’t know their history. But most are the result of introductions as food for people or as forage or bait for game fish. And most California crayfish live in novel ecosystems. These ecosystems have a biota that is a mixture of native and non-native species living in habitats that are highly altered by the continuous actions of people. Crayfish therefore fit right in, feeding on organic matter, algae, dead fish or anything else they can process, and then being eaten themselves by native predators such as otters, herons and pikeminnows, or by non-native predators such as centrarchid (sunfish family) basses and bullfrogs. However, this integration comes at a cost, especially in less-altered waterways. Non-native crayfish, regardless of species, can (a) displace fish and native crayfish from cover, making them more vulnerable to predation, (b) reduce aquatic plant densities, making water clearer, (c) compete with fish for aquatic invertebrates as food, especially snails, and (d) displace native crayfish from their habitats. How much of all this they do in California ecosystems, however, is not well understood.

The situation with crayfish in California is actually complex because there are three native species and three non-native species. Their status ranges from extinct, to endangered, to being abundant enough to be sustainably harvested. Confusion is further generated by the tendency of many fish biologists (like me), when sampling aquatic habitats, to just refer to crayfish captured as “crayfish” with no reference to species. A second forthcoming crayfish blog will describe how to identify crayfish in California.

California crayfish

Sooty crayfish. The extinct species is the sooty crayfish (Pacifastacus nigrescens) which was found only in a few streams in San Francisco. They disappeared after only a few specimens were collected in the 19th century, presumably victims of rapid urbanization. The story of sooty crayfish is a mystery because if these crayfish were present in the Bay area streams, why weren’t they found throughout streams of the Central Valley, as non-native species are today? But there is no evidence, archeological or otherwise, that crayfish were ever present in most areas that support non-native crayfish today.

Pilose crayfish. An apparent victim of poor field notes is the pilose crayfish (P. gambelii). The species was described from specimens collected in “California” (the complete locality information on the type specimen) by Charles Girard in 1852. While the pilose crayfish is widely distributed across western states, it is not found in California, indicating Girard made a mistake in noting the vague locality (Larson and Olden 2011).

Shasta crayfish. This crayfish (P. fortis) is native to cold, spring-fed streams and rivers of the Pit River system, including Fall River and Hat Creek in northeastern California.  When graduate students from my lab were studying this crayfish in the 1980s and 90s, I was impressed with how different they were in their behavior from other crayfish: they were not aggressive. If there was bucket of live Shasta crayfish being measured, I could stick my hand in the bucket to grab one without looking. Representatives of any other crayfish would grab my fingers or hand with a big claw and hold on until shaken off.  Shasta crayfish did not appear to have the well-developed defensive mechanism of waving their large front claws around while backing into cover. Unfortunately, this lack of aggression has made them an endangered species. Larger, much more aggressive signal crayfish have invaded their habitat. Shasta crayfish now persist only where signal crayfish have not invaded or have been removed.

Signal crayfish (left) vs Shasta crayfish. The more robust, aggressive signal crayfish causes extirpation of Shasta crayfish when it invades their spring habitats. Photo by P. Moyle.

Klamath signal crayfish. This crayfish (P. leniusculus klamathensis) is native to the Klamath River, where it is abundant and widespread. It is possible that crayfish in the Eel River also belong to this subspecies and are native (Riegal 1959). The Klamath signal crayfish is considered to be a subspecies because it can be distinguished by both morphology and genetics from the widespread Columbia signal crayfish. The subspecies itself was introduced into Lake Tahoe and the Truckee River in 1895 where it is thriving, although it has hybridized with non-native Colombia river signal crayfish, so is no longer a distinct taxon in the eastern Sierra Nevada. A 1970 study (Abrahamsson et al. 1970) estimated that Lake Tahoe supported over 5.5. million crayfish; a more recent estimate is over 220 million crayfish, which dominate benthic production and affect everything from water clarity to native fish abundance (S. Chandra, unpublished data). Because these crayfish are resistant to crayfish fungal plague (Aphanomyces astaci), which had destroyed the crayfish fisheries in Sweden, Sweden stocked many of their lakes with crayfish from Lake Tahoe. While crayfish fisheries have been tried in Lake Tahoe, they have not been sustained (S. Chandra, personal communication). It would be an interesting experiment to subsidize a fishery for 10-20 years to see if such a fishery could have a positive effect on the ecology of the lake, including native fish, fisheries, and water chemistry.

These crayfish are now integrated into the ecosystems of Sierra Nevada streams and lakes, for better or worse. Light (2003) found that populations of signal crayfish in Sierra Nevada streams were regulated in part by flow, similar to trout and native fish populations. However, presence of a downstream reservoir that served as a refuge was necessary for recolonization following extreme flow events. Light (2005) also investigated the effects of signal crayfish on the biology of native Paiute sculpin in a small Sierra Nevada stream. While she found some evidence of competition, effects were minor, demonstrating coexistence was possible; presumably flow was more important to regulating crayfish populations than other factors.

(Left) Signal crayfish. USGS photo. and (Right) Shasta crayfish. USFWS photo.  

Columbia signal crayfish. Wide-spread the huge Columbia River basin, this crayfish (P. l. lenuisculus) was introduced into California in the early 1900s by fisheries agencies. Generally, when biologists talk about the signal crayfish, this is the form they are referring to, assuming the two subspecies do not have any ecological differences. The signal crayfish was introduced into Europe as a large, edible crayfish. Unfortunately, the introduced crayfish carried crayfish plague, a disease that pretty much wiped out the native European crayfish (Astacus astacus). This meant that in countries like Sweden, where crayfish are a traditional winter holiday food, crayfish had to be imported. For a while (1970s and 80s), a fishery for signal crayfish in the Delta helped to satisfy the demand. At its peak, the fishery involved an average of 32 boats. But the fishery has apparently disappeared or become small, presumably because cheaper crayfish from other countries or from aquaculture operations have entered the market. However, it is likely environmental change also played a role. Today, signal crayfish appear to be uncommon in the Delta, replaced by red swamp crayfish. When the Delta fishery was doing well, the town of Isleton held an annual crawdad festival. The last time it was held (2008?), the crawdads served were pond-raised and imported frozen from China.

Red swamp crayfish, Natural History of Orange County. Peter Bryant.

Red swamp crayfish. This crayfish (Procambarus clarki) is typically red and does inhabit swamps, where it burrows into the mud. This behavior can cause distress to farmers if the ‘swamp’ happens to be a rice paddy or its levee. On the other hand, farmers who harvest the crayfish consider them to be a bonus crop (Brady 2013). This crayfish is also very versatile, abundant in streams with warm to cool water, variable water quality, and mud to rocky bottoms. It is aggressive and has apparently displaced other crayfish, and an occasional swimmer, in many places where introduced. Introduced into California in the 1930s, it is now the most commonly encountered crayfish in the central and southern parts of the state and subject of a trap fishery in the Delta and Central Valley, mostly for bait.

Buciarelli et al. (2018) demonstrated how red swamp crayfish can change stream ecosystems that historically lacked crayfish. They preyed on or displaced dragonfly larvae in low gradient streams. The dragonfly larvae were more efficient predators on mosquito larvae than crayfish, so fewer dragonflies resulted in more mosquitoes. Red swamp crayfish have also been shown to be aggressive to other crayfish species and appear to have displaced signal crayfish from some streams in Oregon, as well as in Spain (Pearl et al. 2013). This may account for the observation that signal crayfish in California are often confined to cold headwater (trout) streams) when red swamp crayfish are present in the warm lower reaches of the streams.

Virile crayfish, Wikipedia commons.

Virile (Northern) crayfish (Faxonius virilis) are native to much of northeastern and midwestern USA and are one of the most widely introduced crayfish worldwide. They are best known as Orconectes virilis but were recently reclassified as Faxonius virilis by Crandall and de Grave (2017). They have been widely introduced around the western USA, including California, apparently because of their popularity as bait. The first records from the Central Valley were of crayfish in ponds near Chico State College, where they were kept for teaching purposes starting in the early 1940s (Riegel 1959). Today they seem to be common in southern California and abundant in the Central Valley. Virile crayfish, however, can live in a wide variety of habitats including flowing streams, preferring warm water. Like the red swamp crayfish, they create burrows into which they can find refuge as their habitat dries up. The fact their broad habitat requirements are similar to those of red swamp crayfish suggests the two species co-occur and perhaps compete for food and space at times.

General observations

Crayfish had an easy time invading California.  Here are some reasons.

  • People like to eat them or use them as bait for game fish.
  • They are hardy and easy to transport with minimal water.
  • A population can be established by a single ‘berried’ female carrying 100-300 fertilized eggs or newly hatched young. The young can mature in 1-2 years and live up to 5 years, longer in captivity.
  • They can live in a wide variety of streams, reservoirs, and other aquatic habitats, with signal crayfish doing well in cold waters (e.g. trout streams) and red swamp crayfish and virile crayfish widespread in warmer waters.
  • They quickly spread once introduced into a new area, making them nearly impossible to eradicate once established.
  • We have a poor understanding of how crayfish affect aquatic ecosystems and native aquatic species in California.

Because crayfish, especially non-native crayfish, are so widespread and abundant in California, they tend to be taken for granted. They are present in habitats from warmwater ditches to coldwater mountain lakes and appear to be thoroughly integrated into our aquatic ecosystems, even waters like Lake Tahoe. They do especially well in habitats thoroughly altered by people, such as reservoirs, regulated streams, and rice fields. But there is much we don’t know about them. Some potential research questions include:

  • What is the distribution of crayfish species in California today, native and non-native? Such information could allow us to see if they are useful indicators of habitat quality and change. Sampling e-DNA might be a useful approach to this question.
  • Do the species replace one another in different habitats?  Is the red swamp crayfish today the dominant crayfish in most habitats?
  • Are dominant crayfish suppressing invertebrates and plants in streams, lakes, and sloughs throughout California, changing the nature of the ecosystems? This seems to be true in Lake Tahoe.
  • Would removal of crayfish return a given aquatic ecosystem to its original state, favoring native species?
  • Are other crayfish species likely to invade California? For example, the rusty crayfish (Faxonius rusticus) is an ecosystem damaging, aggressive crayfish that is spreading across North America.

Further Reading

Abrahamsson, S.A. and Goldman, C.R., 1970. Distribution, density and production of the crayfish Pacifastacus leniusculus Dana in Lake Tahoe, California-Nevada. Oikos, 21(1): 83-91.

Agerberg, A. and Jansson, H., 1995. Allozymic comparisons between three subspecies of the freshwater crayfish Pacifastacus leniusculus (Dana), and between populations introduced to Sweden. Hereditas122(1): 33-39.

Brady, S. 2013. Incidental aquaculture in California’s rice paddies: red swamp crawfish. Geographical Review, 103(3): 336-354, DOI: 10.1111/j.1931-0846.2013.00002.x

Crandall, K.A. and  S. De Grave, An updated classification of the freshwater crayfishes (Decapoda: Astacidea) of the world, with a complete species list. Journal of Crustacean Biology, 37(5):615–653,

Larson, E.R. & J. D. Olden. 2011. The state of crayfish in the Pacific Northwest, Fisheries 36(2): 60-73.

Light, T., 2003. Success and failure in a lotic crayfish invasion: the roles of hydrologic variability and habitat alteration. Freshwater Biology 48(10): 1886-1897.

Light, T., 2005. Behavioral effects of invaders: alien crayfish and native sculpin in a California stream. Biological Invasions 7(3): 353-367.

McGriff D. 1983. The commercial fishery for Pacifastacus leniusculus (Dana) in the Sacramento-San Joaquin delta. Freshwater Crayfish 5(1): 403-417. DOI: 10.5869/fc.1983.v5.403

Pearl, C., B. McCreary, and M. Adams. 2011. Invasive crayfish of the Pacific Northwest. USGS Fact Sheet 2011-3132. USGS, Corvallis, Oregon.

Riegel, J.A.  1959.The systematics and distribution of crayfishes in California. California Fish and Game 45(1): 29-50.

Rogers, D.C. 2005. Identification Manual to the Freshwater Crustacea of the Western United States and Adjacent Areas Encountered during Bioassessment. EcoAnalysts, Inc. Technical Publication #1. 78 pp.

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Seven conservation lessons I learned in government work

By Andrew L. Rypel

Fig. 1. “Sampling” for bluegill on Lake Monona, Madison, Wisconsin.

Before joining the faculty at UC Davis, I spent the previous five years as a research scientist at the Wisconsin Department of Natural Resources in Madison, Wisconsin. Apparently this experience is somewhat rare among academics. A peer even once described me as “approximating a unicorn”, which I’m still not sure is a good thing or a bad thing! Ultimately, the experience of having lived in both spheres has provided useful perspectives, particularly on the anatomy of successful conservation efforts. So, I’d like to share with you a set of lessons I took from my government work.

  1. Look for questions only science can answer.  Perhaps this seems obvious, but there is much about organisms, habitats, and humans that remains unknown. This is where science is useful. Aldo Leopold (one of the great champions for science-based natural resource management) famously said, “One of the penalties of an ecological education is that one lives alone in a world of wounds.” Indeed this is true. And while it can be quite sad to look upon the ways that humans have violated the natural world, scientific studies shine the path towards novel solutions and futures. It is ultimately okay, if biologists and managers do not know all the answers to every conservation question right now. It is actually one of the exciting features of natural resource jobs – to make important decisions in the absence of complete information where uncertainty is high. Nonetheless, identifying which questions we know and do not know answers to is a key part of the process of building quality policy. Further, as a scientist, identifying high priority science questions in collaboration with decision makers can lead to more impactful and actionable science. This should be a central goal for managers and academics alike – to pursue science that will be useful in decision making.
  1. Long-term data is extremely important. Ecosystems are extraordinarily complicated and flux in unpredictable ways. Some ecological dynamics (like phosphorus-chlorophyll relationships in lakes) show few signs of change up until a threshold is crossed, after which point management is excruciatingly difficult and expensive (Carpenter and Lathrop 2008). Identifying and staying away from these thresholds is key. In other cases, change appears directional and operates in more of a relentless pattern. The warming of aquatic ecosystems over the last century due to climate change has more or less followed this type of dynamic (Sharma et al. 2019). Detecting change in ecosystems is ultimately a tricky proposition, and while there are increasingly better modeling tools available, they will never obviate the need for high quality long-term ecological data. These data are also needed to validate future models. Some of the best long-term ecological datasets available in the USA come from the NSF Long-Term Ecological Research Program (LTER) which tracks key aspects of ecological change at 28 sites across the country. A new NSF program, the National Ecological Observatory Network or NEON will soon also provide useful and standardized data on the heartbeat of ecosystems across the USA. However, other more local examples of long-term monitoring programs have existed for some time. They are more numerous, even coming down to just a single biologist doggedly sampling the same population or ecosystem year after year for the span of a career. These seemingly small efforts generate compound interest and turn enormous conservation profits over time. These are the datasets frequently used to uncover decline of populations and fisheries, the rise of an invasive species, effects of climate change, or impacts of watershed disturbance or water extraction.

As just one California example, if biologists only recently began monitoring the Delta, they might conclude that the Delta Smelt is a naturally rare species. Yet smelt have not always been rare (Börk et al. 2020). Delta Smelt became rare as humans increasingly modified the Sacramento-San Joaquin Rivers and the San Francisco Estuary. Long-term data, notably the fall midwater trawl carried out by an army of dedicated CDFW staff since the 1950s has provided the data necessary to track the decline of smelts, ultimately leading to important efforts to save the species.

Ironically, in tough budget times one of the first things that seems to get cut is monitoring work. It is inherently laborious, time-consuming and expensive. In this author’s opinion, collecting monitoring data is one of the best investments of precious public resources, and often yields some of the best returns on investment. Almost without exception, these activities should be amplified and encouraged rather than cut down.

  1. Money is (unsurprisingly) essential. Conservation activities (monitoring, permitting, grants, science, policy) require funds to conduct and complete. The funding landscape in California is quite different than Wisconsin. For example, fisheries work in Wisconsin is mostly funded through fishing license sales and Sportfish Restoration Act dollars (aka the Dingell-Johnson Act). Those funds are also available in California, but they make up a much smaller portion of the pie. Here, endangered species and water management projects generate the primary funding streams. While this reality is a testament to failed conservation of species (notably fishes) over time, it also provides exceptional opportunity for engaging in cutting-edge conservation practices. As biologists we should all be looking for novel and creative ways to leverage the unique conservation resources of California. However, my personal opinion is that as a collective, we need to get bigger and bolder with our ideas. It is becoming painfully obvious that the status quo in California is simply not working.
  1. Seize the momentum! Government work (but also conservation work is general) is frustratingly slow. It takes hard work, dedication, science and public engagement just to get traction and movement on any given issue. Momentum is an asset. As with any business, staff and leaders move on, budgets change, elections happen and priorities shift. I have seen many projects and teams slowly atrophy and break apart. And this isn’t always anyone’s fault – which make these situations all the more frustrating! The lesson is clear – the time is now. If you can act and move the ball forward on a good science-based conservation policy, you should. Never assume the opportunity to enact change will always be there.
  1. Become an equal opportunity collaborator and conservationist. Unfortunately, people will never agree with you 100% on everything. My experience has been that good policy is not made from getting people to agree with you on everything all the time. Rather, good policy always seems to be strategically built by getting people who don’t agree on everything, to agree on something. I have always been baffled by how birders and duck hunters seem to dislike one another and refuse to work together as much as they could. The arguments usually go something like this (note this is a heuristic and hyperbolic example and certainly not true of all bird people):

Duck hunter: “We buy the licenses and duck stamps that support all the habitat work that the birders are enjoying. They simply aren’t paying their fair share.”

Birder: “That person is wearing camouflage. They must not believe in climate change and are killing birds! Why would anyone do that?!”

Ironically on conservation issues, these two groups are naturally aligned and should be partners. Both groups share a love for birds and waterfowl and are commendably devoted to the preservation and restoration of wetlands. If both camps came together, they would be a definitive force in advancing the conservation needs of declining fish and wildlife in our country. Bringing groups together enlarges the power that any one group might have individually. Uniting factions brings additional financial resources to bear on problems and majority politics suddenly become more realistic. However, such reconciliation necessitates people be open to “working with the other side” and having conversations that are not always totally comfortable.

  1. Get out there! It is exceedingly easy to stay in the office and busy oneself with meetings, reports, and various other administrative duties. However, some of the best experiences I had as a government scientist came from organizing and engaging in public meetings and having conversations with people at boat landings, gas stations and diners.

There was a hashtag that circulated on Twitter several years ago (#actuallivingscientist). It involved scientists introducing themselves as an “actual living scientist” because apparently, so few people know one. But unfortunately there was a twinge of condescension at play here. For example, it’s not really any one of the public’s fault they don’t know a scientist. And are we even reaching those people on social media where the proprietary algorithms tend to bin together people with similar interests? Ironically, the blame if any, should fall squarely with us scientists. As a group, we are simply not great at reaching out and talking plainly with folks. Even in our own families, this can be hard! Of course it would be wonderful if more people knew of the great diversity and talent of scientists and biologists, and I think this was the original intent of the hashtag. It helps reduce fear of science and government employees, and believe it or not, can enhance the science if we learn how to listen. But there is no shortcut (on Twitter or otherwise) to the really hard work of getting out there, meeting people and getting to know them and their lives. Hashtags don’t reach large blocks of the population, and I suspect it may stay that way for some time. For these reasons, in my classes at UC Davis I emphasize how important it is to learn to become excellent scientists AND science communicators. Elements of this topic were explored in a classic book, Escape the Ivory Tower, aimed at academics. However, many of these same principles also apply to government work. 

  1. Anyone can make a difference. Everyone’s work has value and dignity. Government employees do have latitude to make change, suggest change, do simple things, or work to redefine their role to be more effective. These are all opportunities to make a difference in conservation and the public sector. It can be excellent, fulfilling, and worthwhile work.

Furthermore, outside of the government, small groups of citizens can have an out-sized impact if they are motivated and well-organized. In fact, grass roots conservation efforts are often the seeds and engine for real change. In Wisconsin, no one thought about restricting harvest regulations on Muskellunge populations until a small group of concerned anglers and citizens pushed hard for it (Rypel et al. 2016). Government agencies should recognize the rightful and important place of these groups and encourage them as best possible. There are many grass roots conservation organizations in California that pursue excellent science-based natural resource management policies. These folks and their organizations are a treasure to the state and its ecosystems. Margaret Mead may have said it best, “Never doubt that a small group of thoughtful, committed citizens can change the world; indeed, it’s the only thing that ever has.”

For brevity, this is an incomplete list. Maybe some of you have important lessons from your own experiences. If so, please feel free to share them in the comments section below!

Andrew Rypel is an Associate Professor and the Peter B. Moyle and California Trout Chair of coldwater fish ecology at the University of California, Davis. He is a faculty member in the Department of Wildlife, Fish & Conservation Biology and Acting Director of the Center for Watershed Sciences

Fig. 2. Peterson Lake at Dusk, Burnett County, Wisconsin

Further Reading

Baron, N. 2010. Escape from the ivory tower: A guide to making your science matter. Washington, DC: Island Press. 

Bik, H.M. and M.C. Goldstein. 2013. An introduction to social media for scientists. PLOS Biology. 11: e1001535.

Börk, K., A.L. Rypel, and P. Moyle. 2020. New science or just spin: science charade in the Delta,

Börk, K., P.B. Moyle, J. Durand, T.C. Hung, and A.L. Rypel. 2020. Small populations in jeopardy: a delta smelt case study. Environmental Law Reporter. Published Online. 

Carpenter, S.R., and R.C. Lathrop. 2008. Probabilistic Estimate of a Threshold for Eutrophication. Ecosystems 11: 601-613.

Magnuson, J.J. 1990. Long-term ecological research and the invisible present. Bioscience 40: 495-501.

Moyle, P., K. Börk, J. Durand, T. Hung, A.L. Rypel. 2019. Futures for Delta Smelt,

Rypel, A.L., J. Lyons, J.D.T. Griffin, and T.D. Simonson. 2016. Seventy year retrospective on size-structure changes in the recreational fisheries in Wisconsin. Fisheries 41: 230-243.

Sharma, S., K. Blagrave, J.J. Magnuson, C.M. O’Reilly, S. Oliver, M.R. Magee, D. Straile, G.A. Weyhenmeyer, L. Winslow, R. Iestyn Woolway. 2019. Widespread loss of lake ice around the Northern Hemisphere in a warming world. Nature Climate Change 9: 227–231.

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Losing mussel mass – the silent extinction of freshwater mussels

by Andrew L. Rypel

Fig. 1. Sampling a healthy freshwater mussel population in the unregulated Sipsey River, Alabama. Photo credit: Andrew Rypel

Throughout my career I’ve spent some time studying the fascinating ecology and conservation issues of freshwater mussels (Fig. 1). For me, learning about mussels has fortified a recurring theme of the natural world – that everything is connected and that small changes in one part of a system can yield unexpected changes elsewhere, often many years later. More importantly, freshwater mussels are essentially threatened everywhere. And because we don’t often hear about them, it is hard to save them, because public will is so critical to generating change.

What is a freshwater mussel?

Some basics. Freshwater mussels, along with freshwater snails (another taxonomic group in major trouble) are varieties of molluscs. Most molluscs on Earth live in saltwater, however several families live in freshwater. Freshwater bivalves (order Unionidae) are one of the major clades of these species. This group’s fossil record extends back to the upper Devonian (416-365 million years ago or “mya”). In North America, first fossils appear to have emerged in the Triassic (250-200 mya). So these animals are not quite as old as fish (>400 mya), but certainly old.


Now here’s where it gets really interesting. [Caution…your mind may explode like mine once did!] With some exceptions, most juvenile freshwater mussels are obligate parasites on fishes. This means they cannot complete their life cycle without using fish as hosts. Baby mussels (glochidia) attach to the gills and fins of fish hosts. In some cases the host fish for a mussel is highly specific, e.g., mussel species x must use fish species y. In other cases, mussels are generalists which can use a range of fish species. By studying these obscure dynamics, a web of interactions begins to emerge between mussels and fishes that is ecologically vital.

Perhaps more interesting is how mussels transmit the glochidia to the fish. Because mussels are mostly sedentary, they have evolved lures to attract their fish hosts. The lures are often part of the mussel’s mantle and are loaded with magazines of baby glochidia. Once a fish bites the lure, the glochidia are ejected onto the host fish. Some lures are basic while others can be exceedingly ornate. Lures resemble all types of potential fish prey including bluegill, minnows, darters, sculpins, salmon, and aquatic insect larvae. Elaborate superconglutinate lures even emerge from the mussel as though on a mucus string, with the same goal of attracting a host fish to bite. In these cases, the mussel literally appears as though it is “going fishing”. Check out the following video of a mantle lure in action!

Ecosystem services

Freshwater mussels perform a variety of important functions in aquatic ecosystems, well-reviewed by Vaughn 2018. For example, mussels regulate water quality through biofiltration. They also process and store excess nutrients in ecosystems. An interesting thought experiment is to consider the role oysters (a similar group of animals) have in regulating water quality in Chesapeake Bay. According to the Chesapeake Bay Foundation, oysters once filtered the entire ecosystem (estimated ~19 trillion gallons of water) every week. However, with declining oyster abundance, it now takes oysters > 1 year to filter the Bay just once. To what extent do mussels similarly promote water quality in freshwater ecosystems? And what might their losses mean?

Freshwater mussels were important to Native American cultures. Mussels seemed to be highly central to mound-building societies of the midwestern and southern USA. However, shell mounds (or “middens”) were also common on the West Coast, notably in San Francisco – driving down “Shellmound Street” might be one major clue! Shell mounds were created by tribes as sacred ceremonial places and as burial sites. Most mussel shells in archaeological sites are “unworked”, meaning mussels were used as food. But, their low caloric value means mussels were probably supplementary food and used more frequently during times of food scarcity. In the Columbia River, mussels were harvested by tribes well into the 20th century and prepared for consumption mainly by steaming. Shells were also for pottery-making, utensils, and jewelry. Because shells are relatively well-preserved, middens can also reveal how mussels and aquatic ecosystems responded to human activities. For example, one genus of mussels in southeastern USA (Epioblasma spp.) showed relatively constant abundance at archaeological sites over a 5000 year period; but around 1000 years ago, mussel abundances declined rapidly with the rise of maize and bean cultivation. In the last 100 years, Epioblasma spp. have declined substantially further due to ecosystem alterations such that species are now listed under the US Endangered Species Act.

In addition to filtering, mussels support fish populations by engineering benthic habitats to be more suitable for fishes like darters, minnows, dace and sculpins that require firm and complex structures. Mussels also are useful in monitoring water quality because they are among the first species that disappear as water quality declines (Augspurger et al. 2003). Because mussel organs are exposed constantly to ambient environmental conditions, they are figurative “canaries in the coal mine” for aquatic environmental change. Mussels support aquatic and terrestrial foodwebs by providing energy to diverse species including fishes, otters, muskrats, raccoons, waterfowl, crayfish, turtles, frogs, salamanders and people. 

Fig. 2. (Left) Loading mussels on scows along the Mississippi River, IA for use in the pearl button industry. Photo by Hugh M. Smith (1899) in Mussel Fishery and Pearl-Button Industry of the Mississippi River, Bulletin of the United States Fish Commission. (Right) Common cutting technique used in pearl-button manufacturing. Photo from Coker (1921) Fresh-water Mussels and Mussel Industries of the United States, Bulletin of the United States Bureau of Fisheries, vol. 36, 1917-1918.

The market for mother-of-pearl buttons was a leading factor in initial mussels declines and extirpations in North America (Fig. 2). Another factor was pearl hunting, even though pearls from native freshwater mussels are mostly rare and imperfect. Gossip in Rome during the 1st century speculated that one reason Julius Caesar invaded England was to search for pearls in mussels from local streams, and that he returned with a piece of armor decorated in pearls (Haag 2012). In the USA, there were two “pearl rushes” – one in the mid-late 19th century, and a second round in the 1950s related to a new process of culturing pearls in Japan. These rushes had horrible consequences for mussel populations, particularly long-lived species.

Diversity, California & Decline

While Class Bivalvia contains ~20,000 living species worldwide, only ~1000 species are known to live in freshwater, and 850 of these species are in the Order Unionida. Estimates suggest there are ~300 species of freshwater mussels in North America. Like many North American taxa, a diversity hotspot for freshwater mussels is the southeastern USA where a lack of glaciation and a correspondingly old evolutionary landscape promote local evolution and high diversity. 

While freshwater mussel diversity is low in California (3-4 native species), these organisms can be locally abundant. Mussels therefore play underappreciated roles in our ecosystems, and in many locations are apparently in significant decline. Native California mussels include the Western Pearlshell (Margaritifera falcata), the Western Ridged Mussel (Gonidea angulata), the California Floater (Anodonta californiensis), and possibly the Oregon Floater (Anodonta oregonensis) (Fig. 3). The Western Pearlshell is notable for its long life, often exceeding 60 years. These mussels are so old, they can be used to reconstruct past climates, parallel to the ways tree-rings can be used (Black et al. 2015). Ecologically, their host fishes are likely trouts and/or salmon. As recently as 1942, Western Pearlshells were a dominant species in the Truckee River with at least 20,000 individuals surveyed; however only 120 mussels were found recently (Murphy 1942, Howard 2008). Today, the only known populations of Western Pearlshell Mussel in the Tahoe basin are in the Upper Truckee River, Trout Creek, and the Truckee River. Western Ridged Mussels are also native to California and are the dominant native mussel species in the Rocky Mountains and to the West. This species is also in decline across the western USA and sculpins might be a host fish. Finally, the California Floater is common in large rivers and pools of streams. Floaters of the genus Anodonta are frequent specialists on floodplain lakes and pools. We frequently encounter floater shells on banks in the Yolo Bypass and in farm ponds. Speckled dace and sculpin are known host fishes for the California floater (Main et al. 2016), but it is likely that this mussel is a generalist species.

Fig. 3. Photos of native freshwater mussels in California. (Upper Left) Adult and juvenile Western Pearlshells alongside invasive Asian clam. Picture from (Lower Left) Adult specimen of California Floater, photo from (Right) External, internal and hinge of the Western Ridge Shell. Photo from

There is great variation in the life-histories of different freshwater mussel species (Haag and Rypel 2011). Some species are exceptionally long-lived. The freshwater pearl mussel (Margaritifera margaritifera) regularly lives >100 years of age. One specimen from Finland had an estimated age of 162 years – this individual was born 37 years before California became a US State. If you go marine, some bivalves live even longer; a specimen of Arctica islandica from the coast of Iceland in 2006 lived 507 years!

In a classic examination of the conservation status of freshwater mussels in North America, Williams et al. 1993 noted 72% (213 of 297) of species are endangered, threatened or of special concern 21, and 7.1% of species had probably gone extinct. These are the highest rates of imperilment of any other known group of freshwater taxa. According to the Xerces Society, crayfishes, freshwater fishes, amphibians, dragonflies have imperilment rates of 51%, 37%, 36%, and 18% respectively. As another contrast, imperilment rates for flowering plants, mammals and birds are 33%, 16% and 14%, respectively. Mussels are…uniquely endangered.

California problem – California solution?

While mussels are declining globally, the mussel problem is also a California problem. Studies in the Truckee River showed a 99.4% decline in abundances of a long-lived mussel (Murphy 1942, Howard 2008). Howard et al. 2015 re-surveyed 450 historical records from 116 sites throughout California,  showing freshwater mussels re-occured at only 47% of these sites. Mussel losses were especially acute in southern California, with 13 of 14 streams having lost their mussels. Yet while loss of native mussels is occurring in many ecosystems, the addition of invasive mussels is simultaneously wreaking havoc on others. Invasion of the Sacramento-San Joaquin Delta by Asiatic clams (Corbicula spp.) is a commonly-studied mechanism for changing zooplankton and fish communities. The ecology of invasive mussels in California and the West will be a good topic for a future blog post.

Like many natural resource issues, we have inherited and contributed to the freshwater mussel problem, which will require hard and focused work to correct. The mechanisms for losses remain elusive. Commonly cited factors include loss of fish hosts, poaching and overharvest, pollution, invasive species and climate change (Haag 2012). Substantially more basic information is needed on the status and distribution of native mussels in California. Where are our mussels? What are their host fishes? Is there cryptic diversity? What are trends in diversity and abundance? What are the impacts of water and riparian land management and invasive species? How have native fish declines impacted mussels? 

A “mussel-building program” in California could take many shapes. I suggest a draft 4-point plan that might be useful to consider:

1. A statewide inventory: A statewide inventory of freshwater mussel abundance and diversity is long overdue. Currently no native California mussel is listed at the state or federal level as threatened or endangered, even though some of these species are already identified as in jeopardy or extirpated from other Western states. A statewide inventory could occur with a series of targeted grants or directed actions, or using a special research unit within one of the relevant state agencies. These data are needed to assess if some of our native mussel species, populations, and ecosystems should be protected. New environmental DNA (eDNA) tools hold promise for such an endeavor.

2. Sentinel sites: Long-term data shows trends over time. Without these data, scientists have little hope of adequately investigating hypotheses of species declines or developing models for testing potential conservation solutions. A series of sentinel sites (e.g., 10-15) strategically located around the state could monitor freshwater mussel populations over time. Sentinel sites/data would give an immediate benefit to scientists struggling to understand mussel dynamics across our large and complex landscape.

3. Conservation hatcheries?: Some eastern US states are developing mussel hatcheries to recover rare species after habitat issues are corrected. In many cases, older decommissioned hatcheries and aquaculture facilities are being repurposed for conservation aquaculture. Are mussel hatcheries a possibility in California? If mussel species were to become listed at some point, hatcheries may be needed to achieve goals. While hatcheries are never intended to replace natural reproduction, they can be an emergency back-up plan for populations and species.

4. Look for win-wins: Strategic prioritization is needed to locate restoration opportunities that would benefit fishes and freshwater mussels. Because mussels rely on suitable fish hosts, loss of fish hosts from habitats will eventually crash mussel populations. Yet because mussels live long lives, mature adults can subsist for decades without host fishes following landscape fragmentation by dams and other structures. This pattern is often referenced in the ecological literature as a “extinction debt” (Timan et al. 1994). Restarting natural mussel recruitment necessitates recolonization by native fishes. Ecosystems with a high potential for boosting native mussel populations could then be prioritized for restoration. Rehabilitation might include large dam removals, but also could be as simple as adjusting the myriad in-stream culverts that also block fish passage to headwater streams, some of which contain mussels. Strategic prioritization along these lines also ties in with existing mechanisms for restoration funding and climate resilience (e.g., through Propositions 1 and 68). In short, the future of mussels is closely tied to the future of fishes – we need to save them together.

Key lessons can be found when examining the demise of mussels. Healthy lands = healthy watersheds = healthy rivers and lakes often = healthy mussels (and fishes and amphibians and plants) = healthy societies. California has so often been a leader in environmental conservation efforts, and needs to be once again.

Andrew Rypel is an Associate Professor and the Peter B. Moyle and California Trout Chair of coldwater fish ecology at the University of California, Davis. He is a faculty member in the Department of Wildlife, Fish & Conservation Biology and Acting Director of the Center for Watershed Sciences

Fig. 4. Freshwater mussels sampled on a survey of the Marais des Cygnes National Wildlife Refuge 2011. Photo by Tim Menard, USFWS. Downloaded from

Further Reading

America’s freshwater mussels are going extinct — Here’s why that sucks

A freshwater mussel apocalypse is underway – and no one knows why

California floater mussel take fish for an epic joyride

Nature’s britta filter is dying and nobody knows why

Oyster fact sheet

The tiny clams that ate the Bay-Delta

There Were Once More Than 425 Shellmounds in the Bay Area. Where Did They Go?

Scientists find 507-year-old clam. Are older ones out there?

Black, B.A. J.B. Dunham, B.W. Blundon, M.F. Raggon, and D. Zima. Spatial variability in growth-increment chronologies of long-lived freshwater mussels: Implications for climate impacts and reconstructions. Ecoscience 17: 240-250.

Haag, W. R., 2012. North American freshwater mussels: Natural history, ecology, and conservation. Cambridge University Press, Cambridge UK.

Helama, A., and I. Valovirta. The oldest recorded animal in Finland: ontogenetic age and growth in Margaritifera margaritifera (L. 1758) based on internal shell increments. Memoranda Soc. Fauna Fennica 84: 20-30.

Augspurger, T., A.E. Keller, M.C. Black, W.G. Cope, and F.J. Dwyer. Water quality guidance for protection of freshwater mussels (Unionidae) from ammonia exposure. Environmental Toxicology and Chemistry 22: 2569-2575.

Howard, J. K. 2008. Strategic inventory of freshwater mussels in the northern Sierra Nevada Province. Final Report by Western Mollusk Sciences, San Francisco, CA to US Forest Service PSW Regional Office, Vallejo, CA. 65 pp.

Howard, J.K., J.L. Furnish, J.B. Box, and S. Jepsen. 2015. The decline of native freshwater mussels (Bivalvia: Unionidae) in California as determined from historical and current surveys. California FIsh and Game 101: 8-23.

Haag, W.R., and A.L. Rypel. Growth and longevity in freshwater mussels: evolutionary and conservation implications. Biological Reviews 86: 225-247.

Maine, A., C. Arango, and C. O’Brien. Host Fish Associations of the California Floater (Anodonta californiensis) in the Yakima River Basin, Washington. Northwest Science 90: 290-300.

Murphy, G. 1942. Relationship of the fresh-water mussel to trout in the Truckee River. California Fish and Game 28: 89-102.

Timan, D., R.M. May, C.L. Lehman, and M.A. Nowak. Habitat destruction and the extinction debt. Nature 371: 65-66.

Vaughn, C.C. 2018. Ecosystem services provided by freshwater mussels. Hydrobiologia 810: 15-27. 

Williams, J.D. M.L. Warren, K.S. Cummings, J.L. Harris, and R.J. Neves. Conservation Status of Freshwater Mussels of the United States and Canada. Fisheries 18: 6-22.

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Old Readings on California Water

by Jay Lund

1957_map.tiff 2

The California Water Plan. State Dept. of Water Resources, 1957

Today’s water struggles have deep roots.

In our shared summer confinement, we hopefully have some time for some deeper reading on California water.  Here is a small collection of older writings on California water, the youngest of which is still older than me.  Beyond historical interest, these early writings have useful perspectives on water problems today, in the future, and outside California.

These writings illustrate how a society of poor disorganized immigrants experienced abrupt climate change when they moved to California and had to change how they did agriculture, built cities and water systems, and organized water laws and institutions in a new (to them) climate and land.  We still struggle with this condition today, and will in the future.  California society is mostly much richer today, and somewhat more organized.

  1. Alexander, B.S., George H. Mendell, George Davidson (1873) Report of the Board of Commissioners on the Irrigation of the San Joaquin, Tulare, and Sacramento Valleys of the State of California, Washington: G.P.0. Report on irrigation development for the Central Valley, including a wonderful global survey of irrigation projects from around the world.
  2. Austin, Mary (1903), The Land of Little Rain, Houghton, Mifflin and Company, New York, 280 pp. (Text version) On water, life, cultures, landscape, and Native Americans in the Eastern Sierra/Owens Basin.  Includes some early water and irrigation management conflicts.  A very pleasant read.
  3. DWR (1930), California Water Plan, Division of Water Resources, California Department of Public Works, Sacramento, CA.  An excellent strategic presentation, reflecting more than a decade of systematic state studies and discussions, this plan during the Great Depression, shaped the CVP and SWP.  [This document seems to be no long available on a State of California web site.]
  4. Goldschmidt, Walter (1947). As You Sow: Three Studies in the Social Consequences of Agribusiness. Montclair, N.J: Allanheld, Osmun and Co. Publishers, Inc. Excellent readable early work on the anthropology and sociology of rural irrigation-based communities in the Tulare basin – many issues and findings remain relevant.  See recent blog post on this one.
  5. Montgomery, Mary and Marion Clawson (1946), History of Legislation and Policy Formation of the Central Valley Project, United States Department of Agriculture Bureau of Agricultural Economics, Berkeley, CA, March, 264 pp. An excellent history of the early CVP, from a state water project to a federal water project, with struggles over public versus private interests, state projects to supplement declining groundwater and expand irrigated area, and the state’s struggles to regain control of the CVP (while retaining federal funding). [So far, you need to visit a library for this one.]
  6. Banks, Harvey (1953), “Utilization of Underground Storage Reservoirs,” Transactions of the American Society of Civil Engineers, Vol. 118, No. 1, January, pp. 220-234. One of the State Water Project’s main engineers began with excellent analyses and discussions of groundwater.
  7. DWR (1957), The California Water Plan, Bulletin No. 3. Sacramento, California. California Department of Water Resources, May, 1957. This plan could have the subtitle – leave no valley undammed, and set the direction of state water planning until 1983.  [This document seems to be no long available on a State of California web site.]

Many excellent writings on California water are more than 50 years old (pre-dating the popular Cadillac Desert!).

Please suggest additional writings in the comments section, including a web link where available.

Read old to stay sharp.

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

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Fish surveys in the estuary: the whole is greater than the sum of its parts

by Dylan K. Stompe, Peter Moyle, Avery Kruger, John Durand

Fig. 1. Measuring a Sacramento splittail caught in a bottom trawl, Suisun Marsh. Photo: Peter Moyle

The San Francisco Estuary is a dynamic and altered estuary that supports a high diversity of fishes, both native and non-native. These species have substantial recreational, commercial, and intrinsic value to people. Since the 1950s, various agencies and UC Davis have established long-term surveys to track the status of fish populations. These surveys help scientists understand how fishes are responding to natural- and human-caused changes to the Estuary.

Each survey has strengths and weaknesses due to differences in sampling gear and effort, program duration, consistency of sampling, and area sampled. Because of this, it is challenging to understand drivers of change when looking at only a single survey. For example, when considering a single survey with limited sampling area, a decline in catch may be associated with either A) change in the distribution of a species within the Estuary, B) change in characteristics of sampling sites (e.g., deepening or shallowing, invasion of submersed aquatic vegetation) that affects gear efficiency, or C) a true decline in the Estuary-wide abundance of a species.

Surveys are designed to catch different species based on the question under investigation.  Common gear types include midwater trawls, bottom trawls, and beach seines, and each one is better at catching certain species than others (Figure 2). Midwater trawls are generally best at catching pelagic fishes such as juvenile salmon, striped bass, and smelt; bottom trawls do a better job of catching benthic fishes such as Sacramento splittail and gobies; and beach seines are best at catching fishes associated with shallow or weedy-edge habitats, such as largemouth bass and Mississippi silverside.

Fig. 2. Illustration of gear types used in San Francisco Estuary fish surveys.

One of the oldest and most widely cited surveys in the Estuary is the California Department of Fish and Wildlife Fall Midwater Trawl Survey, which was designed primarily to identify trends in striped bass populations. Thankfully, other fish species captured in this and other surveys are recorded as well. As a result, numerous papers have been published identifying periods of declining catch of native and non-native pelagic fishes leveraging the Fall Midwater Trawl data set. However, when data from other surveys are considered, different stories emerge.

We combined data from 14 long-term surveys (Table 1) in a way that allows for basic analysis of trends for up to 167 fish species in a much more spatially and temporally rich manner than could be done with a single survey (Stompe et al. 2020). These surveys use different methods and sample different areas so the total number of fish that they catch is not comparable. However, the trends in catch are comparable among surveys. Using data from multiple surveys in combination shows that some trends for fishes that are present in some surveys are absent or even contradicted by others (Figure 3, 4).

Fig. 3. Trends in pelagic fish catch per unit effort (CPUE) as show by the CDFW Fall Midwater Trawl (right) and aggregative data (left). Notice wide fluctuations in longfin smelt CPUE in the Fall Midwater Trawl versus consistent decline in aggregative data, as well as the steep decline in threadfin shad catch around the year 2001 in Fall Midwater Trawl versus consistent catch in aggregative data. Note that both sets of data show a decline in pelagic fishes in general starting around 1980, followed by a partial recovery, and then another decline starting in about 2001.  Mean annual CPUE calculate as the average catch per trawl or seine pull every year. The blue line denotes the approximate year of invasion by overbite clam, while the red line represents the initiation of the Pelagic Organism Decline (POD, Sommer et al. 2007, Thomson et al. 2010). The horizontal black bars show periods of drought.

For example, average catch per trawl of threadfin shad by the Fall Midwater Trawl declines drastically between 2001 and 2002 (Figure 3, panel B). However, aggregated data revealed that the population did not decline during this time period, and in fact remained relatively stable up until 2007 (Figure 3, panel A; see Stompe et al. 2020 for aggregation methods). The expanded data suggest that the decline in catch per trawl by the Fall Midwater Trawl between 2001 and 2002 was likely the result of changes in threadfin shad distribution or behavior, or changes in sampling station characteristics.

Similarly, if we consider catch per trawl of striped bass in two dissimilar surveys within the Estuary, very different trends appear. Average catch of striped bass per trawl by the Fall Midwater Trawl declines to near zero by the year 2000, while average catch per trawl remains relatively high throughout this same time period in the Suisun Marsh Otter Trawl (Figure 4). The Suisun Marsh Otter Trawl primarily samples shallow and marshy habitats as opposed to many of the deeper and less productive waters sampled by the Fall Midwater Trawl. This differential indicates productive areas such as Suisun Marsh are likely functioning as important and resilient refuges for the fishes of the Estuary.

Fig. 4. Average catch per trawl, by year, of striped bass in the Fall Midwater Trawl (FMWT) and the Suisun Marsh Otter Trawl (SMOT) surveys. Notice how catch by the FMWT declines to near zero by the year 2000 but remains relatively high (yet variable) in the SMOT.

Knowing how species move within the Estuary and what habitats become productive or unproductive over time allows us to make better-informed and more effective management decisions. Each unique survey of the Estuary is an important key to our understanding of fish populations. While certain surveys may appear to have more utility right now, it is impossible to predict which surveys will become invaluable as the Estuary continues to change, new fish species are inevitably listed under the state and federal endangered species acts, and new alien species invade.

Further Reading:

Stompe D.K., Moyle P.B., Kruger A., Durand J.R. 2020. Comparing and Integrating Fish Surveys in the San Francisco Estuary: Why Diverse Long-Term Monitoring Programs are Important. San Francisco Estuary and Watershed Science, 18(2).

Sommer T., Armor C., Baxter R., Breuer R., Brown L., Chotkowski M., Culberson S., Feyrer F., Gingras M., Herbold B., Kimmerer W. 2007. The collapse of pelagic fishes in the upper San Francisco Estuary. Fisheries, 32(6):270-277.

Thomson J.R., Kimmerer W.J., Brown L.R., Newman K.B., Nally R.M., Bennett W.A., Feyrer F., Fleishman, E. 2010. Bayesian change point analysis of abundance trends for pelagic fishes in the upper San Francisco Estuary. Ecological Applications, 20(5):1431-14

This work came from a recently published paper comparing and integrating fish surveys in the SF Estuary (Stompe et al. 2020). It is part of a larger project to evaluate striped bass demography and natural history in the Estuary, funded by California Department of Water Resources.

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SGMA and the Human Right to Water: How do submitted Groundwater Sustainability Plans address drinking water?

by Kristin Dobbin, Darcy Bostic, Michael Kuo and Jessica Mendoza

In 2012 California passed the Human Right to Water (AB 685) which declares all Californians have the right to safe, clean, affordable and accessible drinking water. Two years later during a record-breaking drought, California passed another piece of historic legislation known as the Sustainable Groundwater Management Act (SGMA). To prevent undesirable results from groundwater overdraft, SGMA requires the development of regional Groundwater Sustainability Plans (GSPs) in high and medium priority groundwater basins.

Although only five of 41 GSPs submitted to the Department of Water Resources for review in January mention the human right to water, and only one of those affirmed it as a consideration in their plan, these two policies are closely related. Groundwater contamination and overdraft are both primary factors that limit universal access to safe water in California today. As we look to a future of increased drought under climate change, our ability to maintain adequate groundwater levels is also a grave concern for sustaining the tenuous access of rural residents reliant on single, shallow domestic or public supply wells.

How might SGMA implementation affect environmental justice priorities at this policy intersection? To probe this question our UC Davis research team examined the distribution and extent of drinking water users in critically overdrafted groundwater basins. We then reviewed each of the 41 GSPs posted for public comment to assess how the plans reflect engagement with, and consideration of, those drinking water stakeholders.

We found that critically overdrafted groundwater basins in California cover many different drinking water users including nearly 250 communities and more than 40,000 drinking water supply wells (domestic and municipal). We also found that many submitted GSPs share several major gaps when it comes to drinking water, these include:

  1. Many GSPs lacked Minimum Thresholds for key contaminants that affect public health. For plans that do set thresholds for these constituents, their thresholds are often not aligned with drinking water standards. Many plans failed to discuss the potential impact of these policy decisions on drinking water users.
  2. The Minimum Thresholds for groundwater levels set in submitted GSPs have water levels continuing to decline nearly everywhere. Again, the role of drinking water stakeholders in establishing these minimum standards and their impact on domestic and municipal users is unclear in many GSPs.
  3. GSPs often lacked descriptions of drinking water users in their area. This was particularly true for domestic wells, for which 66% of submitted plans omitted information about the number and/or locations of these beneficial users.
  4. Stakeholder engagement and participation was addressed in most plans yet discussion of how feedback was incorporated into final plans was often lacking. Few plans addressed stakeholder engagement for plan implementation with any detail.
  5. Very few plans (15%) mentioned drinking water affordability, a central tenant to California’s human right to water.
  6. Most plans do not propose projects or management actions with drinking water or Disadvantaged Community (DAC) benefits.

Nonetheless, across these plans we also found important instances where drinking water was thoroughly incorporated. Examples from specific GSPs include aligning Minimum Thresholds for water quality with state drinking water standards; proposing projects that foster water supply reliability for DACs; assessing the risk of, and developing mitigation plans for, negative impacts to shallow domestic wells; and ensuring the integration of drinking water stakeholder voices in decision-making through voting board representation and stakeholder committees. These examples are a clear starting place for further integrating groundwater planning efforts and state environmental justice priorities.

To prevent disproportionate impacts and promote human right to water implementation in the state, current and future GSPs need to more fully address drinking water uses and users. While a growing arsenal of tools can help address drinking water needs in sustainable groundwater planning, doing so will likely require more support by state agencies. Ongoing attention to increasing participation in California water resource management is also crucial to narrowing this gap. In the meantime, given the limited discussion of drinking water in many submitted plans, there is a need for more thorough assessments of the potential drinking water impacts per AB 685.

For more, see the full report available here (also available in español).

Kristin Dobbin is a PhD candidate in the Graduate Group in Ecology at the University of California – Davis.  Darcy Bostic recently received her Masters in Hydrologic Sciences from UC Davis.  Jessica Mendoza and Michael Kuo are undergraduate research assistants in the Center for Environmental Policy and Behavior at UC Davis.

Further Readings

Bernacchi, L. A., Fernandez-Bou, A., Viers, J. H., Valero, J., & Medellín-Azuara, J. (2020). A glass half empty: Limited voices, limited groundwater security for California. Science of The Total Environment, 139529.

Community Water Center. (2019). Guide to Protecting Drinking Water Quality Under the Sustainable Groundwater Management Act.

Dobbin, K. B. (2020). “Good Luck Fixing the Problem”: Small Low-Income Community Participation in Collaborative Groundwater Governance and Implications for Drinking Water Source Protection. Society & Natural Resources, 1-18.

Moran, T. & Belin, A. (2019). A Guide to Water Quality Requirements Under the Sustainable Groundwater Management Act.

Self-help Enterprises, Leadership Counsel for Justice and Accountability, and the Community Water Center (2020). Framework for a Drinking Water Well Impact Mitigation Program.

Water Foundation. (2020). Groundwater Management and Safe Drinking Water in the San Joaquin Valley.



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Drought and the Sacramento–San Joaquin Delta, 2012–2016: Environmental Review and Lessons

by John R. Durand, Fabian Bombardelli, William E. Fleenor, Yumiko Henneberry, Jon Herman, Carson Jeffres, Michelle Leinfelder-Miles, Jay R. Lund, Robert Lusardi, Amber D. Manfree, Josué Medellín-Azuara, Brett Milligan, and Peter Moyle

Droughts are common in California. The drought of 2012-2016 had no less precipitation and was no longer than previous historical droughts (Figure 1), but came with record high temperatures (Figure 2) and low snowpack (Figure 3), which worsened many drought impacts. Water supplies for agriculture and urban users statewide struggled to meet water demands. Conservation and rationing, increased groundwater pumping and a diversified economy helped keep California’s economy robust in most sectors. The drought degraded environmental conditions in the Sacramento-San Joaquin Delta (Delta) as the region became saltier and warmer, invasive weeds spread, and iconic fishes like salmon and Delta smelt had strong declines.

Water demands on the Delta often outstrip its capacity, even in wetter than average years. During the drought, water-demand conflicts increased among human and environmental uses. For example, maintaining Delta outflow and freshwater standards was important to agriculture, drinking water supplies and some sensitive species. To fulfill these downstream needs, upstream water releases from Shasta Reservoir depleted the cold-water pool in 2014 and 2015, increasing Sacramento River temperatures and nearly extinguishing two cohorts of winter-run Chinook salmon.

Fig 1

Figure 1. Cumulative precipitation for water years 2012-2016, compared to average and driest water years (Source: CDEC)

Fig 2

Figure 2. California Mean annual temperature relative to the 20th Century mean (Source: NOAA National Centers for Environmental Information)

Fig 3

Figure 3. California mean April 1 snowpack at Donner relative to the 20th Century mean (Source: CDEC)

To help understand scientific aspects of Delta management during the drought, we reviewed official documentation, reports and data, and spoke with numerous agency managers and scientists (Durand et al. 2020).  State and federal water management priorities for the Delta watersheds were to (1) provide essential human health and safety needs, (2) control saltwater intrusion in the Delta, (3) maintain reservoir capacity, and (4) protect at-risk species. Support for these priorities included reducing reservoir releases, Delta export pumping, and Delta outflow; installing an in-Delta salinity barrier; conserving urban water; reducing agricultural water allotments; increasing salmon hatchery production and trucking; and removing invasive aquatic weeds.

These actions helped maintain the Delta’s environment and its dependent uses.  However, with the exception of a study on the effects of the emergency salinity barrier in the Delta, managers were too occupied with emergency-related responsibilities to apply organized scientific methods to learn and prepare for future droughts.  Our main recommendation is to use the lessons of this drought—and the next—to prepare for the one after that. Indeed, 2020 is another dry year and we may already be in a long-term western US megadrought that will force changes in water policy (Williams et al. 2020). The more we can learn from current and future efforts, the better prepared we will be.

Systematic science-based and stakeholder-inclusive preparation for our future needs to continue despite other pressing priorities. The impacts of the COVID-19 pandemic, related economic hardship, and racial/social injustice are all worsened without effective resource management in our drying, warming climate. The availability of data from long-term monitoring of water quality, plankton and fish populations provide insights when extreme wet and dry periods are compared. Each drought in California’s history has brought changes in water management and policy. As the climate changes, drought effects will become more severe and policies are likely to become rapidly outdated.

We suggest preparing today for anticipated increases in frequency and severity of drought years with the following recommendations:

  1. Pre-drought warnings. Drought timing differs across California’s regions. The Governor’s declaration of drought emergency in 2014 helped solidify a unified response. Preliminary declarations allow diverse water jurisdictions to examine local conditions, and prepare for potential water supply disruptions.
  2. Independent Evaluation. Independent review of water agency data by an interdisciplinary group, such as the Interagency Ecological Program can help managers synthesize and make more environmentally-effective, science-based decisions.
  3. Transparency and Documentation. The internet is a cluttered, unstable place. Recent mandates that support data and policy transparency have increased the clutter, and work at odds to the original intent. For online information to be transparent, professional archivists are needed to ensure that documents and data remain available over time, and do not become dead links.
  4. Scientific Preparation. Drought response often overrode scientific opportunity. The demands on agencies were enormous. Some surveys increased frequency or were extended to monitor drought effects. But to answer long-term questions about the effects of the changing California climate (including droughts), more systematic, science-based  planning is essential.
  5. A Delta drought plan would help managers across agencies organize and prepare resources for the next drought, which might already be beginning. A Delta drought plan should provide a summary of lessons from previous droughts; data analysis; protocols for interagency communication and response; resource deployment and operational contingency plans, with funding and staffing details; and structure to organize a scientific team.
  6. Salinity Barriers. The 2015 Delta salinity barrier program was effective and run like an experiment. Managers should prepare to implement solutions with a similar approach, preparing permits, operational coordination, and scientific monitoring in advance.
  7. Ecosystem Resilience. Vulnerable animal populations become more threatened during droughts. Interventions are less costly and more effective during inter-drought periods. If vulnerable fish stocks and restored habitats are not materially improved between droughts, they are at risk of failing during the next drought.
  8. Salmon hatcheries mostly help to support commercial fisheries, while harming the gene pool of wild stocks, reducing their ability to adapt to changing conditions. This conflict is exacerbated during droughts. More research and a re-thinking of hatchery management is required to separate the needs of competing interests in order to preserve California’s declining salmon heritage, which becomes more vulnerable with each drought.
  9. Climate Change. Preparations must be made for the new California climate: hotter, less snowpack, and with more variable and extreme precipitation. A shift to groundwater storage reliance is taking place and may be helpful in the long term. This will affect the timing and volume of water transport in the Delta, and management responses to emerging stressors.

California’s 2012-2016 drought was practice for future climate change events. The whiplash events of drought followed by flood (e.g., 2017 water year) are unlikely to remain exceptional. In the past century, each drought has brought improvements in water systems and drought management, but at a steep price to environmental conditions in the Delta and its watershed. The shifting climate will exacerbate this trend. Relative to economic, cultural and environmental losses, organized science is cheap. Investing in research can make policy discussions and water investment more effective. A proactive organized campaign to understand and anticipate the changing impact of drought on the Delta and California will help mediate future conflicts and preserve California’s rich natural resources.

Further Reading

Dettinger M, Anderson J, Anderson M, Brown LR, Cayan D, Maurer E. 2016. Climate Change and the Delta. San Franc Estuary Watershed Sci. 14(3). [accessed 2017 Feb 2].

Durand JR, Bombardelli F, Fleenor WE, Henneberry Y, Herman J, Jeffres C, Leinfelder–Miles M, Lund JR, Lusardi R, Manfree AD, et al. 2020. Drought and the Sacramento-San Joaquin Delta, 2012–2016: Environmental Review and Lessons. San Franc Estuary Watershed Sci. 18(2). doi:10.15447/sfews.2020v18iss2art2. [accessed 2020 Jul 17].

Lund J, Medellin-Azuara J, Durand J, Stone K. 2018. Lessons from California’s 2012–2016 Drought. J Water Resour Plan Manag. 144(10):04018067. doi:10.1061/(ASCE)WR.1943-5452.0000984.

Mount J, Gray B, Chappelle C, Gartrell G, Grantham T, Moyle P, Seavy N, Szeptycki L. 2017. Managing California’s Freshwater Ecosystems: Lessons from the 2012-16 Drought. San Francisco, CA: PPIC.

Williams AP, Cook ER, Smerdon JE, Cook BI, Abatzoglou JT, Bolles K, Baek SH, Badger AM, Livneh B. 2020. Large contribution from anthropogenic warming to an emerging North American megadrought. Science. 368(6488):314–318. doi:10.1126/science.aaz9600.

The authors participated in this review of Delta management and science during California’s 2012-2016 drought, from a variety of institutions including UC Davis, UC Cooperative Extension, UC Merced, and the Delta Stewardship Council Science Program (which also provided funding).  We thank the many agency staff and stakeholders who participated in this process.


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106 Years of Water Supply Reliability

by Jay Lund

Water supply reliability is a major policy and management goal in California, and in the rest of the world, today and since the beginning of time.  The goals of reliable water supplies have grown from supporting human health, to supporting economic prosperity, to supporting healthy ecosystems, even when these goals conflict.

Since ancient times, water supply planning, engineering, and operations have sought to provide reliable water supplies.  But until 106 years ago, there was little sophistication on exactly how reliable a water supply would be or should be.

Today, water uses have grown and diversified, and sometimes conflict when water availability is insufficient for all uses.   Water availability will always be limited, despite infrastructure investments, and often will diminish or become more expensive with climate change and evolving environmental and public health standards.

However, perfect reliability is never possible, and high reliability often incurs high economic or environmental costs.  This has long been the dilemma in California.  How do we balance reliability, the costs of improving reliability, and the water shortage costs of unreliability?

Allen Hazen’s 1914 paper established a direction for solving this balancing problem.  His paper, “Storage to Be Provided in Impounding Reservoirs for Municipal Water Supply,” assembled streamflow data for more than a dozen water supplies and examined their reliability for a range of water use levels and a range of reservoir sizes.  These calculations were done by hand.

Realizing that these streamflow records were short, he further fit these reliability results onto “probability paper” (which he invented) to better estimate reliabilities for different extremes, configurations, and demands.

For water wonks with technical or modeling interests, Hazen’s paper remains well worth reading.  Few papers about delivery reliability today thoughtfully synthesize such breadth and detail.  Some of the paper’s main lessons remain relevant for water policy and management:

  • No water supply can be completely reliable (from an engineer or manager’s perspective).
  • Higher reliability requires greater infrastructure costs, with extreme reliabilities incurring extremely large infrastructure and costs.
  • Seasonal and over-year water storage should be considered quite differently. Seasonal storage of water in reservoirs requires less storage capacity per unit of reliable delivery.  Storing water for over-year droughts requires proportionally more storage capacity and costs.  “With a larger reservoir, there is some further gain with increasing size, but in a diminishing ratio.”
  • High levels of reliable supply require larger reservoirs, which are costly and will often take years to refill.
  • Even an infinite reservoir size cannot reliably deliver more than a reservoir’s average annual inflow.
  • Regions with more variable hydrology require greater water storage capacity to supply the same reliability, all else being equal.
  • Climate change is likely, but is hard to estimate. There also seem to be longer-term cycles in runoff records, which are difficult to characterize and predict.
  • Quantifying water shortage amounts is important. Probability distributions of shortage can be more useful than the mere probability of a shortage.  However, probability distributions of shortages are harder to estimate, as shortages are usually rare events.
  • Water reliability analysis is inherently approximate, and it is not worthwhile to overly refine data. “In all hydraulic data the probable error of measurement is considerable. There is, therefore, no justification for the application of extreme refinements in methods of calculation.” Evaporation estimates and data are “less adequate than could be desired.  Nonetheless, some approximations can be reached.”  Longer flow records reduce uncertainty, but do not eliminate it.  Even averages have errors. However, probable errors in such estimates can be quantified.
  • The natural storage in lakes and sandy stream and lake banks can only be approximated, but can “have a great influence on the required storage, especially at relatively low draft [withdrawal] rates. …”.
  • Modeling with monthly flows and operations is somewhat less accurate than daily flows, and tends to under-predict storage needs for a given reliability and other conditions. Weekly time steps correct most of this underestimation.
  • Balancing the cost of improving supplies against shortage costs is needed. Reducing water use or adopting other water supplies can be less expensive than expanding reservoirs to increase water storage, especially for infrequent droughts.
  • Sometimes hedging reservoir releases, to create more frequent small shortages, can be less damaging overall than accumulating a smaller number of large shortages instead.
  • Public displeasure with large drought shortages can lead to infrastructure overinvestment. And the public seeing water spilling from full reservoirs in a few years can encourage the public to think that a supply is not being used to its reasonable limit.
  • Hazen extensively discussed limitations of his methods and findings, and estimated and discussed probable errors in his findings. As he summarized, “frank recognition of the large probable errors in many of the results cannot fail to be advantageous.”

Much of today’s work on water supply reliability would advance to reflect some of the methods and thinking from 1914.

Allen Hazen was a founder of modern urban water supply.  Many aspects of urban water systems today date back to him and the State of Massachusetts’ Lawrence Experiment Station in the late 1800s. This was where Hazen and colleagues worked on fundamentals of water filtration, later expanding as a consulting engineer to fundamentals of pipe network water distribution, reservoir sizing, water metering, utility finance, and overall integration of urban water systems.

We all drink water (mostly reliably) based on his work.  Many of his insights and approaches to water problems remain useful today.

Read old to stay sharp.

Further reading

Hazen, A. (1914), “Storage to be provided in impounding reservoirs for municipal water supply,” Transactions of the American Society of Civil Engineers, Vol. 77, December, pp. 1542-1669.

Hazen, A. (1909 and 1914), Clean Water and How to Get It, New York, J. Wiley & Sons, 252 pp.

Hirsch, R.M. (1978), Risk Analysis for a Water-Supply System – Occoquan Reservoir, Fairfax and Prince Williams Counties, Virginia, Open File Report 78-452, U.S. Geologic Survey, Reston, VA, also in Hydrologic Science Bulletin, Vol. 23, No. 4, pp. 475-505.

Klemes, V. (1987), “One Hundred Years of Applied Storage Reservoir Theory,” Water Resources Management, Vol 1 , pp. 159-175.

Jay Lund is a Professor of Civil and Environmental Engineering at the University of California – Davis.  (Today is the 90th anniversary of Alan Hazen’s death.)

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Summer Reading in the Time of Covid 19

by Peter B. Moyle

Tired of reading about the constant haggling over California water? Or of binge-watching old TV shows? Or, worse, watching the news as the Covid 19 virus spreads in our free country? For relief, I recommend two entertaining yet somewhat off-beat books, reviewed here. The books are very different but both involve fish (if indirectly) and both have central characters (an academic and a thief) you may not like at the end. Both also feature museum collections, the first of fish, the second of birds.

Do Fish Exist?

David Starr Jordan (1851-1931) was a great American ichthyologist and world renowned scientist and educator. Woodcut by Chester Woodhull, ca. 1950.

LuLu Miller’s Why Fish Don’t Exist: A Story of Loss, Love, and the Hidden Order of Life (2020, 195 pp) is a ‘good read’, but the book is more about the latter half of the title than the former. The book follows Miller’s search for order and meaning in a universe where Chaos will eventually win out, no matter what. She focuses in good part on David Starr Jordan, seeing him initially as a person who had an amazingly positive view of life, bouncing back quickly from tragedies (such as the smashing of hundreds of bottles of pickled fish that he had collected over decades, by the San Francisco Earthquake of 1906). Jordan saw order in the universe through his describing and classifying of thousands of fish species. Miller read his entire massive autobiography (Days of a Man)1 to try to understand him and explored his other voluminous writings as well. In his day, Jordan was perhaps the best-known scientist in the USA, if not the world, and a great popularizer of the importance of science.

Miller, however, discovers he was likely involved in a murder to protect his funding and, worse, was a leader in the terrible eugenics movement in the USA1. His view of an orderly universe with Man as the pinnacle of evolution, led to severely flawed reasoning about “unfit” humans and the need to stop them from reproducing. Miller twines her life around Jordan’s story and resolves her own inner turmoil, by and large. At the end, she finds love and order in her personal universe, without fish.

The main title is intriguing and provides an excuse for pleasant meandering of her thoughts. The following discussion of that title could be regarded as a spoiler (but it is not, really). One way that fish don’t exist is through the philosophic idea that a fish species does not exist unless we humans give it a name, so it is part of human consciousness. Miller is basically bemused by this idea. Another way is more academic. She talks about the modern cladist approach (quantitative, computerized) to classification, which shows that the diverse evolutionary lineages that we lump together as ‘fish’ don’t have a common origin2: lampreys, hagfish, sharks, lungfishes, bony fishes. The cladistic approach makes terrestrial vertebrates (e.g., us) a subset of the Osteichthyes, the main lineage of bony fishes that includes most of the 30,000 or so fish species.  Therefore, she opines, fish is not a useful or accurate term. Miller is not a biologist herself and is mildly annoyed by the fact that the fish biologists with whom she talked just accept the problem as not being worth fighting over. Thus, in my text book, I call terrestrial vertebrates “aberrant bony fishes that decided to leave the water and invade the land.” I also say, “Humans are not the pinnacle of evolutionary progress but only an aberrant side branch of fish evolution.” Knowing this, you may want to go and seek your inner fish3.

Still, Miller’s book is worth reading if you are looking for Darwin’s ‘grandeur in this view of life’, want to learn about David Starr Jordan, or just enjoy some good stories about life and love. The book also has curious scratchboard illustrations by Kate Samworth, most featuring Jordan and his mustachios as a fish.

Flies without Fish

Jock Scott salmon fly by Timo Kontio (FlyTying Archive).

Kirk Wallace Johnson’s The Feather Thief: Beauty, Obsession, and the Natural History Heist of the Century (2018, 308 pages) is not about fish or water. Its relationship to both is weak, via fly fishing and the tying of artificial flies that are part of the fly-fishing culture. Even here, the tie-in is tenuous because it centers around artificial salmon flies that were developed in Victorian England. These colorful flies have become valuable collector’s items as art objects and are largely tied today by people who do not engage in angling. Their flies have experienced neither water nor fish. The flies are fairly large, around 3-5 cm, and require small pieces of multiple colorful feathers to be tied together. For such a fly to be genuine, the feathers have to come from wild birds with spectacularly colored feathers, such as birds of paradise. In the community of Victorian salmon fly tiers, such feathers today sell for hundreds of dollars. Dyed chicken feathers will not do.

This book focuses on the theft, by a young champion tier of these flies, of dozens of bird specimens from the British Museum of Natural History. The Museum houses the largest collection of birds in the world, including specimens collected in the 19th century by great naturalists such as Charles Russell Wallace. In just one break-in, the thief took 299 specimens of some of the most beautiful birds in the world in order the pluck feathers from them. The book is the author’s attempt to understand the crime and the criminal, with diversions into subjects such as the deprivations that Wallace experienced in order to collect skins that were stolen and the devastation of bird populations caused by collection of plumes for ladies hats. It reads like a good mystery novel in many respects. The feather thief does get caught eventually but the author’s digging found that crime pays, or at least this crime did. The book does suggest that better security is needed for natural history collections, perhaps even for fish collections.


1 I have a copy, inherited from my father.  It’s only 906 pages long. I have not read it.

2 Miller points out that eugenics has not gone away; forced sterilization laws are still on the books in many states, ignored but not repealed.  When I was an undergrad in the 1960s, the required genetics course I took was called “Genetics and Eugenics” although I don’t recall the prof saying anything about eugenics…

3 Of course, all organisms have a common origin if you go back far enough in time.  What she really means is that cladistics does not result in single category “fish” that is equivalent to amphibians, reptiles, birds, and mammals.

4 See Neil Shubin’s 2009 book, Your Inner Fish: A Journey in to the 3.5 billion-year History of the Human Body.

Further Reading

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Can we talk? New nationwide flood maps provide opportunities for dialogue

by Kathleen Schaefer and Brett F. Sanders

Why Dialogue Matters

For fifty years, Flood Insurance Rate Maps (FIRMs) have unintentionally stifled conversations of flood risk. They have encouraged property-owners and governments at all levels to dwell on map details for one static event, rather than flood risks for a range of events under changing conditions (Soden et al. 2017). Now, First Street Foundation[1] has released a new tool that can change how these conversations develop: Flood Factor, a publicly available online resource to help people understand flood risk for an individual property, area, or region.

For each property parcel, several indicators about flooding are provided by Flood Factor including information about past floods, past flood claims, present-day flood risk, and future risks. This makes it possible to learn if a home has flooded from major recent events, is currently at risk, and how that risk changes over time. This follows previous efforts to bring detailed information on sea level rise into coastal community planning (e.g., Fu et al. 2017).  Importantly, the tool presents an opportunity for fresh dialogue about flooding, including what’s at risk and ways to manage it. There is growing interest in having these types of conversations across the U.S. (National Academies 2019, Sanders et al. 2020).

To frame the timeliness of new flood risk information for dialogue, we can go back to 1968 when Congress passed the National Flood Insurance Act. Community participation in the National Flood Insurance Program (NFIP) and homeowner purchase of a flood policy were initially voluntary (Burby 2001; Horn and Brown, 2017), and the NFIP gave homeowners a more affordable option for insurance than what was available from the private sector (Burby 2001). To determine who would quality, a 1% annual chance risk (or 100-year return period) was selected as the standard, and Flood Insurance Rate Maps (FIRMs) were created to delineate flood hazard zones where properties met the standard. Moreover, community-level dialogue about flooding, and how to manage risks, was part of the plan. As a partnership between federal, state and local government, the NFIP required that communities take responsibility for managing floodplains to reduce the damages of floods and taxpayer liabilities.

But in the ensuing years, major disasters prompted Congress to change the NFIP to a mandatory program. This unintentionally derailed productive conversations about flooding. FIRMs, with the single “in-out” 100-year flood zone boundary, became a battle map. If FEMA announced that it was going to initiate a new study, community leaders would vow to fight the new maps. The contentious nature of the maps made flood risk something no one wanted talk about or pay for. Interest and funding for updating the maps also declined. Today, engineering studies of flood hazards for almost half of California’s communities are over 20 years old. FEMA has designated less than 23% of California’s mapped river miles as ‘valid.’ And, less than 30,000 miles of the State’s estimated 180,000 stream miles have been mapped.

FEMA has worked to develop a more community-friendly mapping process called Risk MAP, and it has shown promise for improving dialogue and deliberations about flooding. However, nationwide implementation of Risk MAP appears cost prohibitive. A study by the California Department of Water Resources (DWR), funded by FEMA, found that implementing the Risk MAP process in California alone would cost $445 million and concluded that much of California would never again see a new FIRM (CA DWR 2013). Indeed, what California and all of the U.S. now have is Flood Factor.

A sample set of depth maps from Flood Factor is shown below in Fig. 1, including a depiction of a past flood, the present-day 500-year return period event, and a future 500-year return period event. Multiple depictions about flooding are important for meeting needs of different end-users of hazard maps (Sanders et al. 2020), and for encouraging end-users of flood hazard information to “wrestle with uncertainty” about flooding (Soden et al. 2017). Whether the resulting dialogue will be productive is unclear.

Flood 1

Fig 1. Sample of past, current and future flood risk for Toledo, Ohio


FloodRISE reveals keys to productive dialogue

Fostering productive dialogue about a societal problem like flooding is challenging. Researchers at UC Irvine tested the value of more detailed flood data, and more intuitive visualizations, in the context of a community-based approach to flood resilience through a program called FloodRISE funded by the National Science Foundation. Working in three coastal sites with different flood hazards (coastal, fluvial and pluvial) and contrasting socio-economic conditions, research showed the importance of fine-resolution data (resolving individual streets and land parcels) for increasing awareness about flooding and building a shared awareness of flooding across subgroups in the community (Cheung et al. 2016, Houston et al. 2019). Research also showed the importance of inclusive and iterative community engagement, which promoted trust, heightened interests, and improved flood model accuracy through input of local knowledge (Luke et al. 2017, Sanders et al. 2020, Goodrich et al. 2020). Iterative community engagement allowed researchers to tailor flooding scenarios, mapped variables and contextual information to the needs and preferences of local end-users including planners, residents, public works managers, developers, natural resource managers, emergency managers, and non-governmental organizations. Hence, a participatory research approach was critical to building trust (Goodrich et al. 2020) and making flood maps that end-users found useful (Luke et al. 2017, Sanders et al. 2020). Examples are shown in Fig.2.

The FloodRISE project also showed that is possible to change power structures that develop around control over the flood mapping process. Dialogue between researchers and diverse groups of end-users triggered “what if” scenarios related to the management and operation of watersheds and flood infrastructure, which were then modeled and mapped (Luke et al. 2017, Goodrich et al. 2020). Historically, such analyses have only been accessible to those with financial resources to hire technical consultants, which excludes many from processes to plan for and respond to flooding.

Flood 2

Fig. 2 Examples of flood hazard maps for Newport Bay including: (left) flood depth for a historical event including photos of flooding; (middle) year 2015 chance of flooding; and (right) year 2035 flood depth corresponding to the 1% annual chance event.  The flood depth scale, dimensioned by the average human body size, is an example of co-production by researchers and end-users.

A contrasting experience with detailed flood maps was reported in Florida, where researchers sought to better understand how information on flooding affected attitudes and opinions about climate change and sea level rise (Palm and Bolsen, 2020). Here, researchers reported that those who viewed detailed flood maps showing future flooding from sea level rise were less likely to believe that climate change was occurring and responsible for increasing coastal flooding—a response linked to political party affiliation. This aligns with a general U.S. trend of polarized views on climate issues and mistrust of scientists around party affiliation (Pew Research Center, 2016).

First Street Foundation Brings Detailed Data to the U.S.

The contrasting California and Florida experiences using detailed flood maps to engage communities in conversations about flooding point to both dangers and opportunities on the horizon for flood management. One danger is that people will not be familiar with the First Street Foundation, and there will be insufficient trust for productive dialogue. Furthermore, mapping errors could undermine trust and perceptions of risk (Cheung et al. 2016, Houston et al. 2019).  Just as FEMA flood maps are prone to errors due to various reasons including data quality, rules about what gets mapped (Wing et al. 2018) and the impacts of political influence (Burby 2006), there will be errors in Flood Factor maps based on limited local knowledge and uncertain models and data. For example, a comparison of FloodRISE and Flood Factor depictions of the 1% annual chance flood zone for Newport Beach, California, where FloodRISE benefitted from extensive local data and knowledge, showed significant differences. Furthermore, most communities do not have a mechanism to dialogue with experts about flood risk, which is critical for building actionable knowledge (Lemos et al. 2018, Goodrich et al. 2020).

On the other hand, major opportunities stem from the potential to engage many more people across the U.S. in contemplating the possibility of flooding, and wresting with uncertainty about what might happen. Furthermore, Flood Factor can not only support national conversations about flooding by policy makers, but serve as a shared reference point for community- and regional-level discussions nationwide. Finally, the form of Flood Factor data, intuitive maps of flood depth for different events, is a much-needed departure from FEMA’s cryptic flood hazard mapping conventions (e.g., Zones AR, X and VE) and terminology (e.g., “floodway”, “special flood hazard area”). These changes are desperately needed so community conversations about flooding focus less on mapping conventions and more about the consequences of flooding and what can be done about it (Sanders et al. 2020).

Kathleen Schaefer is a Ph.D. candidate in Civil and Environmental Engineering at the University of California, Davis. Kathleen’s research is focused on examining community-based alternatives to the NFIP. Brett Sanders, Ph.D. is a Professor of Civil and Environmental Engineering at University of California, Irvine. Dr. Sanders served as Principal Investigator of the the FloodRISE Project, promoting resilience to coastal flooding in Southern California, and leads the Flooding and Poverty Division of the UCI Blum Center for Poverty Alleviation.

Further reading

Burby, R.J., 2001. Flood insurance and floodplain management: the US experience. Global Environmental Change Part B: Environmental Hazards, 3(3), pp.111-122.

Burby, R.J., 2006. Hurricane Katrina and the paradoxes of government disaster policy: Bringing about wise governmental decisions for hazardous areasThe annals of the American academy of political and social science604(1), pp.171-191.

CA DWR. 2013. California Deployment and Mapping Master Plan (Draft). Prepared under Mapping Activity No. 3 executed in 2010 by Atkins. Sacramento, CA: CA Department of Water Resources.

Fu, X., Gomaa, M., Deng, Y. and Peng, Z.R., 2017. Adaptation planning for sea level rise: a study of US coastal citiesJournal of environmental planning and management60(2), pp.249-265.

Goodrich, K.A., Basolo, V., Feldman, D.L., Matthew, R.A., Schubert, J.E., Luke, A., Eguiarte, A., Boudreau, D., Serrano, K., Reyes, A.S. and Contreras, S., 2020. Addressing Pluvial Flash Flooding through Community-Based Collaborative Research in Tijuana, Mexico. Water, 12(5), p.1257.

Horn, Diane P., and Jared T. Brown.  2017. Introduction to the national flood insurance program (nfip). Congressional Research Service. Washington, D.C.

Houston, D., Cheung, W., Basolo, V., Feldman, D., Matthew, R., Sanders, B.F., Karlin, B., Schubert, J.E., Goodrich, K.A., Contreras, S. and Luke, A., 2019. The influence of hazard maps and trust of flood controls on coastal flood spatial awareness and risk perception. Environment and Behavior, 51(4), pp.347-375.

Lemos, M.C., Arnott, J.C., Ardoin, N.M., Baja, K., Bednarek, A.T., Dewulf, A., Fieseler, C., Goodrich, K.A., Jagannathan, K., Klenk, N. and Mach, K.J., 2018. To co-produce or not to co-produce. Nature Sustainability, 1(12), pp.722-724.

Luke, A., Sanders, B.F., Goodrich, K.A., Feldman, D.L., Boudreau, D., Eguiarte, A., Serrano, K., Reyes, A., Schubert, J.E., AghaKouchak, A. and Basolo, V., 2018. Going beyond the flood insurance rate map: insights from flood hazard map co-production. Natural Hazards and Earth System Sciences, 18(4), pp.1097-1120.

National Academies of Sciences, Engineering, and Medicine, 2019. Framing the challenge of urban flooding in the United States. Washington, DC: The National Academies Press.

Palm, R. and Bolsen, T., 2020. Results from South Florida Experiment. In Climate Change and Sea Level Rise in South Florida (pp. 81-92). Springer, Cham.

Pew Research Center, 2016. The politics of Climate.

Sanders, B.F., Schubert, J.E., Goodrich, K.A., Houston, D., Feldman, D.L., Basolo, V., Luke, A., Boudreau, D., Karlin, B., Cheung, W. and Contreras, S., 2020. Collaborative modeling with fine‐resolution data enhances flood awareness, minimizes differences in flood perception, and produces actionable flood maps. Earth’s Future, 8(1), p.e2019EF001391.

Soden, Robert, Leah Sprain, and Leysia Palen. “Thin Grey Lines: Confrontations With Risk on Colorado’s Front Range.” In CHI, pp. 2042-2053. 2017.

Wing, O.E., Bates, P.D., Smith, A.M., Sampson, C.C., Johnson, K.A., Fargione, J. and Morefield, P., 2018. Estimates of present and future flood risk in the conterminous United States. Environmental Research Letters, 13(3), p.034023.

[1] The data was produced by researchers and hydrologists from First Street Foundation; Columbia University; Fathom; George Mason University; Massachusetts Institute of Technology; Rhodium Group; Rutgers University; University of California, Berkeley; and University of Bristol.

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