The Delta, in 3-D

Jay Lund, UC Davis Professor of Engineering
 

Time and tide wait for no man, and change in the Delta won’t wait for a computer model either.

Continued land subsidence and sea level rise, increasing likelihood of a major earthquake, and rising chances of major floods all pose serious threats to subsided islands in the central and western Delta.  The economics of many deeply subsided Delta islands also imply that many islands will be abandoned by their owners when they next fail (Lund et al. 2010; Suddeth et al. 2010).  This extends the ongoing historical pattern of island failures and abandonments from Big Break (1927),  Franks Tract (1938), Mildred Island (1983), and Liberty Island (1998), all now major recreation and wildlife areas.

The western and central parts of the Delta will become different than they are today, with more flooded islands.  Both flooded islands and sea level rise introduce important three-dimensional features to Delta water quality, flows and ecosystems.  Water will flow into and through these flooded islands in complex ways.  Water in the islands will stratify, with different quality at different depths and different locations.  All of the flow in these islands will be driven by and, in turn, affect the conditions of adjacent channels. These three-dimensional aspects bedevil current one-dimensional models being used for most Delta studies.

To anticipate and adapt to a very different future, Delta planning and operational studies need a more substantial and coherent basis in hydrodynamic modeling.  This would include more systematic development of bathymetric data, additional one and two dimensional modeling studies, and ultimately a widely-available three-dimensional model of hydrodynamics, salinity and water quality. Without such modeling, it will be difficult to evaluate, design and plan major operational and infrastructure changes in the Delta for the coming decades. It will also be more difficult to understand the interaction of flows, water quality and habitats needed to improve the functioning of the Delta’s ecosystem.

Some effective and insightful applications have been made of 3-D models for the California Delta.  The technology is proven, but requires additional application and data development to become more widely available.  However, despite several well-intentioned efforts, this needed technology is not developing quickly or coherently.  Instead, we continue to see fragmented, inefficient and somewhat ineffective development.

Efforts to bring coherence to these efforts have been stilted by agency balkanization and poorly coordinated investments by major state and federal agencies.  The greater Sacramento-San Joaquin Delta region is blessed with considerable hydrodynamic modeling expertise, as much or more than anywhere else in the world.  This expertise is underutilized and too often pitted against itself, rather than being more gainfully employed to develop a better common understanding of the Delta and potentially promising solutions.

Without better modeling capability, including effective use of well-developed and accessible three-dimensional modeling, it will be all too easy to attack the basis of a variety of long-term Delta plans and supporting environmental documentation.  We need these models not only to defend proposals for change, but also to develop and implement effective solutions.  Scientifically, we also need the insights of more timely and widely available three-dimensional modeling to test and develop a wide variety of hypotheses about how the Delta ecosystem functions now and might better function in the future.

We all have an interest in better understanding how the Delta of the future will perform in terms of water flows and quality.  We will be substantially in the dark without upgrading our models to reflect expected future conditions. The changes coming to the Delta require better preparation than we can currently provide, despite the earnest efforts of many.

True adaptive management depends upon extensive modeling of alternatives and future conditions; our current fragmented efforts at system modeling are one aspect where an effective adaptive management program for the Delta has little existing foundation.

Computer modeling is unglamorous to most, but designing major facilities or programs in California without systematic and detailed modeling would be negligent and risky.  The Delta is a complex place and is becoming more complex.  Successful plans and policies need to better reflect emerging changes.  We should not finalize and evaluate detailed plans for the Delta without the benefits of more realistic hydrodynamic and water quality modeling.  This is an urgent need (alas, one of many).

RMA2 simulation of conductivity (μS/cm) distribution caused by flooding of 5 islands in the western Sacramento-San Joaquin Delta. Colors represent conductivity range of 500 to 30,000 μS/cm.

Further reading:

Lund, J., E. Hanak, W. Fleenor, W. Bennett, R. Howitt, J. Mount and P. Moyle (2010), Comparing Futures for the Sacramento-San Joaquin Delta, University of California Press, Berkeley, CA, February 2010.

Suddeth, R., J. Mount, and J. Lund (2010), “Levee decisions and sustainability for the Sacramento San Joaquin Delta“, San Francisco Estuary and Watershed Science, Volume 8, No. 2, 23pp, August.

Gross, E., M. MacWilliams and W. J. Kimmerer (2010), “Three-dimensional modeling of tidal hydrodynamics in the San Francisco Estuary,” San Francisco Estuary and Watershed Science, 7(2).

Letter to Joseph Grindstaff, CALFED Director; Clifford Dahm, CALFED Lead Scientist December 2009, on Improved modeling capabilities needed for the Bay-Delta planning efforts, signed by 24 modelers from 14 different agencies, universities, and consulting firms.

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