Debunking the BDCP Myth Debunking

The Bay Delta Conservation Plan (BDCP), a $16--okay, maybe $24--no, wait it could be closer to $57--BILLION dollar plan to produce a more reliable water supply and recover endangered species, is the focus of much speculation, worry, and confusion. And for good reason: not only does the plan involve the construction of some of the largest water infrastructure California has ever seen at an estimated cost that already exceeds the Chunnel, but no one, not even the planners, is really sure that it will do what it promises. In fact, some folks are pretty sure it won't deliver on either of the two co-equal goals of reliability and recovery.

So, understandably there are a fair number of questions surrounding BDCP, and the folks at BDCP have begun a blog to dispel certain "stubborn 'urban myths' that are being perpetuated." We found one of the myth corrections to be woefully inaccurate, and since the BDCP blog does not provide for public comments, we will debunk the debunking here.

From the BDCP blog:

Myth: The BDCP fails to analyze possible effects on San Francisco Bay.

Fact: The BDCP does indeed analyze the effects of the project on San Francisco Bay and other water bodies downstream of the Delta.
Analyses found that because there are no project diversions downstream of the Delta, the only effects of the project on the San Francisco Bay Area would be indirect and related to flow. According to the Department of Water Resources’ Delta Atlas, average tidal flow through the Golden Gate Bridge is 2,300,000 cubic feet per second (cfs) and average tidal flow at Chipps Island is 170,000 cfs. The maximum amount that BDCP would change flows downstream of the north Delta diversions is 9,000 cfs (and most of the time it would be much less). Therefore, at most, BDCP diversions represent only 5 percent of the flows at Chipps Island or less than 0.4 percent of tidal flows at the Golden Gate Bridge. Effects within San Francisco Bay would be within this range, diminishing greatly away from the Delta. Because these changes in flow are so small compared to the tidal range within the Bay, the plan concludes that there would be no effect of BDCP on the San Francisco Bay ecosystem or its native species.

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Don't worry! It'll be a drop in the bucket!

Okay, what does this really mean? Let's break this down:

"Analyses found that because there are no project diversions downstream of the Delta, the only effects of the project on the San Francisco Bay Area would be indirect and related to flow."

The effects of the project on San Francisco Bay are indirect because there will be no construction or habitat restoration activities taking place in the Bay. The indirect effects on San Francisco Bay have to do with BDCP making changes to the rate, timing, and amount of freshwater flow that will reach the Bay. The Bay is part of the San Francisco Bay-Delta Estuary, a mixing zone of fresh and salt water. The Bay-Delta Estuary depends on two types of flow: tidal salt water flows from the Pacific Ocean and freshwater flows from Sacramento and San Joaquin Rivers and smaller tributaries. The ratio of fresh water to salt water in the Bay fluctuates depending on location, time of day, and climate patterns, but both are essential to a healthy, functioning system.

"According to the Department of Water Resources’ Delta Atlas, average tidal flow through the Golden Gate Bridge is 2,300,000 cubic feet per second (cfs) and average tidal flow at Chipps Island is 170,000 cfs. The maximum amount that BDCP would change flows downstream of the north Delta diversions is 9,000 cfs (and most of the time it would be much less)."

The statement above implies that 9,000 cfs of freshwater flow is insignificant compared to tidal flows of 2,300,000 cfs or 170,000 cfs. But this logic conflates freshwater flow with tidal flow. Tidal flows play a different role in shaping the Bay ecosystems than freshwater flows. Comparing freshwater flow to tidal flow is comparing apples to oranges.

To understand the logic used by BDCP better, let's use a baking analogy provided by biologist Jon Rosenfield:

We did study the effect of the baking powder in your muffin recipe, but since the mass of the powder was only a small fraction of the mass of the muffins produced and its effects were indirect, we concluded that the amount of baking powder in your recipe has no effect on the final muffin.

Left: muffin baked with baking powder; right: muffin baked with (oops!) baking soda (2013 Huffington Post)

If we want to compare apples to apples (or muffins to muffins), then we need to compare 9,000 cfs of freshwater flow to be taken by BDCP to total freshwater flow, not tidal flow. The Sacramento River, where the new facilities will be located and a significant source of the Bay's freshwater flow, had an average flow rate of 23,490 cfs during the period 1949-2009. So, to use the same kind of math that the BDCP blog uses, we should say that BDCP would actually be changing freshwater flows on the Sacramento River by 38%.

38% of the Sacramento River paints a very different picture of the impact of BDCP on San Francisco Bay when compared to the example offered by the BDCP blog.

Of course, that's not the entire story. The Sacramento River can run at much higher and lower rates than the average, and the twin tunnels will have to operate under regulations that often will prevent the full diversion rate. Also, while the Sacramento River is the largest source of fresh water (median=85%) to the San Francisco Bay, there are other significant sources such as the San Joaquin River, in-Delta tributaries, and smaller Bay tributaries. Plus, there are many ways in which BDCP's changes to freshwater flows may affect the Bay not captured by this simple equation.

Freshwater flows from the Sacramento and San Joaquin Rivers play an essential role in providing the Bay with nutrients, diluting and dispersing pollutants, reducing water clarity (and thus possibly threats of toxic algae blooms), and lowering salinity for the wide range of fish, birds, and animals that use the Bay. The Bay Delta Conservation Plan owes the people and wildlife of San Francisco Bay more substantial evidence for the conclusion that this large project upstream will have no effect on our region than erroneous "myth" busting.