The Connections, Resiliency, and Management of Flows in the Delta

Tina SwansonAt the end of September, the Friends of the San Francisco Estuary held a conference titled “Bay + Delta + Water: Better Together” in Antioch which brought together over 200 elected officials, agency leaders, and community advocates from around the Bay and Delta to discuss the role that fresh water plays in the San Francisco Bay and the Delta, and to define local solutions or collaborations that can help the struggling system.

One of the presenters during the conference was Tina Swanson, Director of the NRDC’s Science Center, where she works to expand the organization’s scientific capabilities and support its legal and policy work across a range of environmental, public health, and sustainable management issues.  In her presentation, discussed the important work that fresh water does in the estuary and the watershed as a whole, emphasizing the importance of the interconnectedness of the system.

Tina Swanson began by saying that as a scientist, she’s been working on the system for nearly 20 years now. “From a scientific perspective, it’s one of the more fascinating systems out there,” she said. “Today, I want to talk about three concepts: the connections within this system, its resilience, and its management, because I think those are key concepts.”


One of the important things about this system is that you can’t look at any one of these elements in isolation, Ms. Swanson said. “You can’t look at the Bay as a localized entity, you can’t look at the Delta as a localized entity, and you can’t look at water without looking at the landscape over which it’s flowing,” she said. “Everything is connected in this system, and in fact it’s connected beyond the Bay and the Delta, up into the watershed and into the mountains. And the thing that connects it is water.”

It does it in the most obvious ways: water flows downhill, and most of the water that flows into the estuary is coming from the mountains … and while flowing through that system doing all sorts of valuable things from the perspective of a scientist and from the perspective of all of us who care about how this system functions,” she said.

The other connection is that water itself forms a connection between the ocean and all the way back up into the mountains, and that while water is flowing downhill, lots of things are going uphill, in particular, fish,” she said. “There’s a number of fish species that actually move through this connected system from the ocean all the way back up to the mountains, and they’re not just fish, they’re actually doing some really valuable and important ecological things like bringing ocean-derived energy and nutrients up into the mountains, which in fact nourishes our forests.”

Swanson_Page_05These connections are doing a lot of things: the flow is carrying water, it’s carrying nutrients, it’s carrying sediments, it’s carrying pollution, and it tends to go from top to bottom,” said Ms. Swanson. “And while it’s going downhill, the flow is also creating things: it’s creating different types of habitats and it’s creating connections through the corridors between those habitats.”

By doing both of those things – by moving materials through the system and creating these different kinds of habitats, it is driving the function of this vast watershed and this vast ecosystem,” she said. “It’s driving primary and secondary productivity which ultimately supports the fisheries that so many of us value and like to eat; it’s driving water quality, by diluting pollution or pushing the salinity field in the estuary downstream enough so we can draw fresh water from the lowlands. It’s driving things that are little bit more esoteric, like residence time. How long does that molecule of water take to pass through the system, and how long does it reside in the estuary—it’s not only molecules of water, it’s nutrients and pollutants as well.”

By carrying all of these materials, it’s actually tremendously important to maintaining the edges of the system, of the shoreline, in particular the transport of sediment,” she said. “Sediment is very, very important for maintaining stable shorelines, both in the estuary and also in the upper portions of the Delta and the watershed.”

All three of these things: flow, habitat, and function are also themselves inherently connected. So that was my first theme that I wanted you to take home – these connections.”


Graphs are the way scientists tell stories, and so she would be showing a series of graphs that tell a story about the Delta, Ms. Swanson said. She then presented a graph titled Unimpaired Delta Outflow and explained that it means the amount of fresh water that would have flowed through and out the Delta and the estuary if there were no dams and no water diversions. She noted that each year’s outflow is plotted from 1930 to 2013 – the entire, data-rich record for flow conditions in the system.

Swanson_Page_07The very first story that this graph tells is that from year to year, the amount of water that would have flowed into the Delta varies a lot,” she said. “In fact, it varies by an order of magnitude: literally, the driest years are 10 times drier than the wettest years. There is huge variability in this system and it’s been going on forever this way – this is a characteristic of our watershed.”

She pointed out that the red bars are the 20% driest years in the system. “You can see that they’re sort of scattered; we had a bad string in the late 1980s to the early 1990s—many of us will remember that particular drought—we had another drought in the mid-2000s and we’re in the midst of another one now, even though at least in terms of these runoff numbers it actually doesn’t fall to the level of the driest 20%. So there’s a lot of variation.”

The dry years mean poor for the ecological resources in the system, and the fisheries and the productivity of the system is depressed under those dry conditions, she said. “Of course those dry conditions only happen sometimes and they’re always ultimately followed by better conditions when we have more flow going through the system,” she said.  “Keep in mind, though, this is the ‘what would have been’ graph.  This is the amount of water that’s flowing into the system if there were no dams and diversions. It is an estimate, but it’s a pretty darn good one.”

Swanson_Page_08Presenting the next slide, she said, “This is the actual “what is” going on in this system.  This graph is the same period of time, but this is the amount of freshwater flow that actually did flow through from the mountains, through the Delta and into the estuary. I’ve marked in red those years in which the amount of flow that flowed into the Bay was the same or less than the driest 20% of years under unimpaired conditions. And one of the things that you can see really clearly, the story that this graph tells, is that the Bay is seeing a lot more dry years.”

“The Bay doesn’t care about what’s going on in the watershed right now because it doesn’t see that,” Ms. Swanson said. “It sees water that it gets. And these days the water that it gets is chronically drought conditions. And in fact, these are man-made drought conditions.

One of the things this has done is that it has reduced the resilience of this system,” she said. “There are fewer opportunities where conditions are good so that the system can bounce back. That’s what resilience is: being able to bounce back after bad conditions. And so we’ve reduced the opportunities for the system to be able to bounce back because we’re not providing those good conditions, at least with regard to flow.”

Swanson_Page_09Turning to the biological response of the system, she next presented a graph of the results of the Fall Midwater Trawl, with just the first 25 years since the trawl started in 1967. “The story this graph is telling you is that abundance of fish varies a lot,” she said. “It goes down, it goes back up. The vertical bars above each point—those are called error bars and in fact that’s telling you a little bit about the variation among the different species and you can see in some years some species do well, and in other years others do poorly. That’s a resilient response there.”

Swanson_Page_10But this is what we’re seeing in the more recent years,” she said. “In the last decade plus, these species have all collapsed. They no longer have resilience to respond to good conditions and as we’ve seen those good conditions are not being provided for them in this particular system. So we’ve reduced the resilience of this system and if we want to restore it we have to restore that resilience.”


Swanson_Page_12We manage flow in this system with dams, in-river diversions, and Delta diversions, Ms. Swanson pointed out. “We manage flow and we manage that water for very good reasons: flood control and water supply for irrigation and urban uses,” she said. “But it is highly managed, literally down to the drop in many years. The result of that is that we have been progressively over the years taking more and more water out of the system.”

Swanson_Page_13She then presented another slide and said, “This is the volume of water that we’re diverting out of this system each year, whether it’s at the dams or the in-river diversions or the Delta diversions,” she said. “This is the total amount of water that would have flowed into the Bay but didn’t. The first story is that we have been progressively taking more and more water out of this system. Most of the dams and big diversions came online in the ‘50s, ‘60s, and ‘70s.”

The other interesting story this tells is that since then, the amounts of water that we divert out of this system from year to year has become highly volatile and highly variable,” she said. “In some years we’re taking 20 million acre-ft. and in other years we’re taking less than 5 million acre-ft.”

So what is the story underlying this pattern, that’s part of the management story that we need to grapple with as we do a better job managing the system?”

Swanson_Page_14The first thing I want to show you is the low years, where we’re not taking very much water out of the system at all,” she said, presenting the same graph with the dry years circled. “For the most part those were dry, and by that I mean hydrologically dry. These were droughts, and so, in a drought there isn’t as much water so we don’t take as much water out. Those were some of the droughts that the Bay now sees under actual conditions.”

Swanson_Page_16What about these years?” she said, presenting another graph with the peak years circled. “These years where we’re taking huge amounts of water out of the system are the years when we’re refilling our reservoirs, after a dry period when we’ve drained our reservoirs. And in those years many of those years that refilling of the reservoirs, the fact that we’re holding that water back from getting to the Bay, is also creating dry, chronic drought, chronic man-made drought conditions in the system.”

So what I wanted to leave you with is that the system is completely connected,” Ms. Swanson said. “We have pretty much—destroyed is probably too strong, but we’ve certainly depressed the resilience of the system, and that’s going to make our work harder as we try to improve the management of the system in order to balance these needs.”

Thank you very much.”

During the question and answer period, Ms. Swanson was asked, ‘Some people say that fresh water that flows out of the Golden Gate is wasted, is that true?

Short answer, no,” Ms. Swanson replied.  “That has been around for a long time, but in fact, the fresh water passing through the estuary as well as out the Golden Gate is part of the connection in the system and it’s performing a number of really vital functions. And if you want to get totally practical about it, the most important thing it’s doing is it’s holding back the salt wedge in the San Francisco Bay so that we can pump water from the Delta. If there were no water flowing out of the Delta, it would be salty to Sacramento. And so from a practical purpose you have to have it.”

From an ecological purpose, freshwater flow, to speak in scientific geek speak, is what we call a “master driver.” It means it’s a physical environmental condition which drives a lot of other processes and biological responses. And a lot of people talk about flow not being the only problem in the system and that is true. But a lot of the other problems we have identified: invasive species, poor water quality—they’re exacerbated by the flow conditions we have right now, so in fact, it is a master driver, it connects to everything in this system. And part of that connection is the freshwater flow flowing out of San Francisco Bay, which actually has a huge influence on the coastal environment as well.”

Ms. Swanson was asked, ‘How do invasive species contribute to the lack of primary productivity and survival of native fish?’

This is a very heavily invaded system with lots of non-native species that have become established and very abundant,” she said.  “There’s a huge diversity of them, and they affect the ecosystem and native species in a variety of ways. One of the most challenging non-native species that has become established is a tiny little clam that’s become established in Suisun Bay, and it has a substantial impact on the productivity of the system by being a very effective filter feeder; essentially it filters the phytoplankton, the microscopic plankton or plants that form the base of the food web, it filters all of those out so that’s not available as food for the zooplankton which are the important food for the fish, so essentially that’s a competition problem.”

We have other non-native, warm-water bass fish in the Delta that have become very established, it’s actually a very, very popular fishery but those fish don’t belong in the Delta. They live in the Delta now because the environmental conditions in the Delta are now very favorable to them—slow flows, warm temperatures, lots of submerged vegetation in which to hide—it’s not the natural condition for the Delta, and they actually prey on native fish, so there’s a predation problem.”

“I’ll give you a third example, and that is, one of the more problematic invasive plants in the Delta is a submerged vegetation called Egeria. It’s actually an escaped aquarium plant that’s become established in the Delta, and it’s attached to the bottom and it grows up and it essentially just clogs the waterways and it’s transformed what would be an open water channel, which is the kind of habitat favored by a lot of the native species, into this deeply, densely vegetated area where ambush predators like warmwater bass like to sit and wait and grab little fish. It has also reduced the turbidity of the water, which is the cloudiness of the water from the sediment and the silt that’s being transported down from the watershed, and in fact that has also created conditions that are much less favorable for many of the native fish, particularly Delta smelt and lots of times the little larval fish, which really rely on that cloudy water in order for them to be able to hide from predators and to feed properly. That kind of invasive is doing something we call “ecosystem engineering;” literally, the species is engineering and changing the system. So it’s in all these different ways.

“But I want to close by saying that these—I’m going to say almost all of the problematic non-native species that have become established in this system, they’ve gotten here in a variety of ways. But they’ve done well because we’ve changed the characteristics of the environment to conditions that are very favorable for them. They like slow flows, warm temperatures, clear water, and lots of plants, and that’s very favorable for non-native species. Many of the environmental conditions that are now more favorable for them are related to the reductions and the alterations in flows. And in fact, for at least some of these species, short of establishing a commercial fishery for them, and none of those—well, the bass is one—one of the best ways that you can manage these non-natives in the system is to restore some of the dynamic environmental variability into the system, what we as ecologists call “disruptions.” Floods. Even droughts, is its own disruption, the problem is that it’s not a disruption if you’re doing it all the time.”

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