Groundwater and Stream Interaction in California's Central Valley: Insights for Sustainable Groundwater Management Completed June 2014 Updated and Released February 2016 Prepared by: Prepared for: Funded by: A Note to Readers This report was undertaken to provide technical information on the state of streams and groundwater resources in the Central Valley. The findings of this report were used to support the need for what is now known as the Sustainable Groundwater Management Act (SGMA). The intent was to illustrate the physical inter-relationship between the surface and groundwater resources and the potential impacts that groundwater pumping has had and is currently having on our rivers and streams to demonstrate the need for sustainable groundwater management. Based on the scale of the data used in this study, the findings contained herein should not be used as a definitive source in determining whether a particular stream or river reach should or should not be considered as an interconnected surface water for SGMA purposes. Further study at a finer scale would be necessary for such a determination. Suggested Citation The Nature Conservancy. 2014. Groundwater and Stream Interaction in California's Central Valley: Insights for Sustainable Groundwater Management. Table of Contents Section 1 Introduction and Background .......................................................................................... 1 1.1 Goals and Objectives ................................................................................................................ 3 Section 2 C2VSim Model ................................................................................................................ 5 2.1 Model Background and Capabilities ........................................................................................ 5 2.2 Hydrologic Model Platform Selection ...................................................................................... 6 2.3 Revisions Made to the C2VSim Model ..................................................................................... 7 2.3.1 Initial Conditions Update ......................................................................................................... 7 2.3.2 Stream-Bed Conductance Update............................................................................................ 7 2.3.3 Surface Water Supply Data Update ......................................................................................... 8 2.3.4 Small Watershed Parameters Update...................................................................................... 8 2.4 C2VSim Model Update Results ................................................................................................ 8 Section 3 Historical Simulation ..................................................................................................... 10 3.1 Modeling Approach and Assumptions ................................................................................... 11 3.2 Modeling Results .................................................................................................................... 12 3.2.1 Land Use ................................................................................................................................. 12 3.2.2 Surface Water Supply ............................................................................................................. 13 3.2.3 Groundwater Pumping ........................................................................................................... 15 3.2.4 Groundwater Budget and Change in Groundwater Storage ................................................. 19 3.2.5 Groundwater Levels ............................................................................................................... 25 3.2.6 Groundwater Flows to Streams ............................................................................................. 26 Section 4 Baseline for Management Scenario Simulations ............................................................ 29 4.1 Modeling Approach and Assumptions ................................................................................... 29 4.2 Modeling Results .................................................................................................................... 29 4.2.1 Groundwater Budget and Change in Groundwater Storage ................................................. 29 4.2.2 Groundwater Levels ............................................................................................................... 34 4.2.3 Groundwater Flows to Streams ............................................................................................. 35 Section 5 Water Management Scenarios ...................................................................................... 37 5.1 Scenario 1: Groundwater Substitution .................................................................................. 37 5.1.1 Modeling Approach and Assumptions ................................................................................... 37 5.1.2 Results .................................................................................................................................... 38 5.2 Scenario 2: Increased Agricultural Demand ........................................................................... 41 5.2.1 Modeling Approach and Assumptions ................................................................................... 41 5.2.2 Results .................................................................................................................................... 42 5.3 Scenario 3: Increased Irrigation Efficiency ............................................................................. 44 5.3.1 Modeling Approach and Assumptions ................................................................................... 45 5.3.2 Results .................................................................................................................................... 45 Section 6 Conclusions .................................................................................................................. 49 Tables .......................................................................................................................................51 Figures .......................................................................................................................................55 Works Cited ……………………………………………………………………………………………………………………………………126 December 2014 i List of Tables Table 1 - C2VSim Model Features ............................................................................................................... 52 Table 2 - Simulation Year and Water Year Type Mapping for the EC BL and Scenarios ............................. 53 List of Figures Figure 1 - C2VSim Model Origins (IWFM) ................................................................................................... 56 Figure 2 - C2VSim model Grid ..................................................................................................................... 57 Figure 3 - C2VSim model Hydrologic Period ............................................................................................... 58 Figure 4 - Comparison of Observed and Simulated Groundwater Levels - Sacramento Valley.................. 58 Figure 5 - Comparison of Observed and Simulated Groundwater Levels - Sacramento Valley.................. 59 Figure 6 - Comparison of Observed and Simulated Groundwater Levels - Sacramento Valley.................. 59 Figure 7 - Comparison of Observed and Simulated Groundwater Levels - San Joaquin Basin ................... 60 Figure 8 - Comparison of Observed and Simulated Groundwater Levels - San Joaquin Basin ................... 60 Figure 9 - Comparison of Observed and Simulated Groundwater Levels - San Joaquin Basin ................... 61 Figure 10 - Comparison of Observed and Simulated Groundwater Levels - Tulare Basin .......................... 61 Figure 11 - Comparison of Observed and Simulated Groundwater Levels - Tulare Basin .......................... 62 Figure 12 - Comparison of Observed and Simulated Groundwater Levels - Tulare Basin .......................... 62 Figure 13 - Comparison of Observed and Simulated Groundwater Flows to Streams - Stony Creek ........ 63 Figure 14 - Comparison of Observed and Simulated Groundwater Flows to Streams - Tuolumne River .. 63 Figure 15 - Comparison of Observed and Simulated Groundwater Flows to Streams - Merced River ...... 64 Figure 16 - Comparison of Observed and Simulated Groundwater Flows to Streams - Kings River .......... 64 Figure 17 - The Central Valley’s Lost Wetlands - Source: (Hannak, et al., 2011) ........................................ 65 Figure 18 - Sacramento River Unimpaired Runoff and Sacramento Valley Water Year Hydrologic Classification from 1922 to 2009 ....................................................................................................... 66 Figure 19 - San Joaquin River Unimpaired Runoff and San Joaquin Valley Water Year Hydrologic Classification from 1922 to 2009 ....................................................................................................... 66 Figure 20 - Hydrologic Regions of the Central Valley .................................................................................. 67 Figure 21 - Historic Land Use vs. Water Supplies in the Sacramento Valley .............................................. 68 Figure 22 - Historic Cropping