by William Fleenor

The San Joaquin (left) and Sacramento (right) rivers meet near Antioch, an important location for X2 management during dry years. (Image credit: Carson Jeffres)

In 2008 a group from the Center for Watershed Sciences (including this author), joined by an economist from the Public Policy Institute, published findings that suggested that an alternative conveyance for Sacramento River water might improve ecological conditions in the Delta and improve reliability for Delta water exports [1, 2].

The original 2013 draft of the Bay Delta Conservation Plan (BDCP) (DEIR/EIS) included several alternatives using tunnels for Delta conveyance [3].  Long-term planning of this nature requires greatly simplified hydrodynamic models to simulate decades of data to estimate performance under a range of variable conditions.  These models also require manipulation to account for physical effects they don’t simulate (e.g., changes in habitat and sea-level rise conditions for which future management is unknown).

The manipulation involves simulating habitat changes and sea-level rise with other models that have far more physically accurate numerical computations, but which run too slowly to simulate details over many decades.  With results from the more accurate detailed models, a simple model can be calibrated to simulate a fuller range of conditions.

For the BDCP, the results of slow, more detailed 2- and 3-dimensional models (already imperfect) are incorporated into DWR DSM2, a faster 1-dimensional model, and run for a longer period, producing additional errors.  Results from DSM2 are then used to create an artificial neural network (ANN) for salinity intrusion used in the still-faster DWR CalSim II model to simulate the decades of planning for the DEIR/DEIS (more potential errors).  CalSim II is a monthly model that cannot resolve issues occurring on a shorter time scale (e.g., spring/neap tidal cycles, real-time flow changes, 14-day average compliance requirements, etc.).  Nearly all decisions made in the DEIR/DEIS were made using long-term averages of monthly averages of CalSim II results.

An earlier review of the DEIR/DEIS [4] pointed out this potential cascade of errors and recommended that the higher dimensional models be simulated for shorter periods of stressful conditions (e.g., drought) to corroborate the results.  The corroboration would help ensure that decisions made from the results were reasonable.

The final EIR/EIS [5] of the California Water Fix (FEIR/EIS) was released December, 2016 and still lacks such efforts to corroborate the results of the long-term simulations.

Here, I applied the 2-dimensional model, RMA2, to simulate Delta flows and salinity with and without the CWF for conditions of water year 2008, a dry year.  It is the same software used in CWF to provide input to modify DSM2 for habitat restoration.  It is the last year for which Clifton Court Forebay intake data have been made publicly available. (It would be easy to argue that not releasing Clifton Court Forebay operations data is a violation of California law (SB54).  These data are vital for detailed modeling of Delta flows and water quality.)

Figure 5-53 (Fig 1 below) in the FEIR/EIS summarizes results with a long-term average of ~3.5 MAF of water exported in dry and critical years with ~1 MAF of that through north Delta diversions (NDD).  Actual exports for water year 2008 were 3.43 MAF, which was similar to the long-term average and used for simulation with ~1 MAF taken from the new NDD intakes.

Figure 1 Figure 5-53 from the FEIR/EIS demonstrating exports in dry and critical water years

In the initial effort, I could not apply every operational restriction identified in the FERI/EIS, lacking time and money to re-write internal model code.  I honored first pulse constraints and sweeping velocity constraints past the NDD locations.  Beyond those, I applied the maximum volume of intake at the NDD locations to produce the maximum change throughout the Delta.  Using these criteria, the NDD volumes exceed 60% of total exports during the highest Sacramento River flows (6,000 of 11,000 cfs), but less than 30% during lower flow periods (Fig 2).

Figure 2. Modeled exports from NDD and south Delta pumps.

This modeling effort demonstrates that the work of the FEIR/EIS should hold true during low-flow drought periods, and I commend those involved with the modeling.  But I remain critical of their lack of providing detailed model corroboration.

One of the most watched Delta regulations is X2, the distance in kilometers from the Golden Gate Bridge of 2 psu (practical salinity unit) near the bottom along the path of the Sacramento River.  Since X2 is usually downstream of the confluence of the two rivers, and my analysis made no changes in net outflow, the only differences occur in fall and winter (Fig 3).  NDD exports only produced minor changes in X2 that could be easily managed.

Figure 3. Changes in X2 during water year 2008 by CWF and Base case

The key to salinity in Delta and export water is salinity in Franks Tract (FT).  Once salt gets into FT it is pulled to the pumps.  A graph of salinity changes in eastern FT helps explain when NDD affects Delta salinity (Fig 4), which includes the ratio of Total Exports to NDD.

Figure 4. Eastern Franks Tract EC changes along with Total Exports/NDD ratio.

Interestingly, salinity in Franks Tract falls during lower flow periods with CWF.  Only during the highest Sacramento River flows with NDD exports exceeding 50% of Total Exports does salinity in Franks Tract increase during CWF simulation.  The improvements during the lower flow periods result from a lower proportion of inflow into FT from False River and Dutch Slough, and a higher percentage of inflow from the Old River connection at the San Joaquin River (SJR) (supplied by water from the San Joaquin River and Sacramento River via the Delta cross channel).

The greater salinity near the end of January correlates with abrupt increases in the ratio of Total/NDD exports and the lack of Sacramento River water through the closed cross-channel gates.  However, for Total/NDD export ratios approaching 50% in May-June, salinity still falls with CWF.  A follow-up simulation capping the Total/NDD ratio to 50% shows that any increases in salinity can be managed.  Not shown is the simultaneous pulse of salinity up the San Joaquin River contributing to the January increase.  All these effects are manageable with proper insight and monitoring of the Delta.

For any given total export rate, any NDD export should reduce the negative net Old & Middle River flows (OMR) from through-delta pumping, and create more natural flow patterns through the Delta.  With proper monitoring and management, the negative OMR flows could likely be eliminated during critical times.  Creating a more natural flow pattern while reducing fish ‘salvage’ at the south Delta pumps and producing a system with improved reliability while maintaining Delta water quality goals would seem to benefit  all interests.

William Fleenor is an affiliate of the U.C. Davis Center for Watershed Sciences. His research focuses on the development and application of numerical hydrodynamic models for water management.

Further reading

[1] Lund, J., E. Hanak, Wm. E. Fleenor, R. Howitt, J. Mount, and P. Moyle, Comparing Futures for the Sacramento-San Joaquin Delta, Public Policy Institute of California, 2008, 241 pg

[2] Fleenor, W., E. Hanak, J. Lund, and J. Mount, “Delta Hydrodynamics and Water Quality with Future Conditions,” Appendix C to Comparing Futures for the Sacramento-San Joaquin Delta, Public Policy Institute of California, San Francisco, CA, July 2008.

[3] ICF International, 2013, Administrative Draft Environmental Impact Report/Environmental Impact Statement for the Bay Delta Conservation Plan, prepared for Califronia Department of Water Resources, U.S. Bureau of Reclamation, U.S. Fish and Wildlife Service, and National Marine Fisheries Service

[4] Mount, J., Wm. Fleenor, B. Gray, B. Herbold, and W. Kimmerer, 2013, Panel Review of the Draft Bay Delta Conservation Plan, prepared for The Nature Conservancy and American Rivers

[5] ICF International, 2016, Final Environmental Impact Report/Environmental Impact Statement for the Bay Delta Conservation Plan/California WaterFix, prepared for Califronia Department of Water Resources and U.S. Bureau of Reclamation