CVHM-D

CVHM-D (Central Valley Hydrologic Model - Delta)

Criterion	Explanation
General Description	Simulates groundwater flow in the Sacramento-San Joaquin Delta.
Model Domain	Groundwater and water balance in the unsaturated zone in the Delta.
Developer	CH2M HILL, with assistance from the USGS.
Hardware computing requirements	The code has been used on UNIX-based computers and personal computers running various forms of the Microsoft Windows operating system.
Code language	FORTRAN
Original application	CVHM-D is a modification of CVHM (MODFLOW) to simulate Delta groundwater conditions to determine effects of Cal Water Fix. It was modified to better represent Delta hydrology by HydroFocus. Stream, slough, and canal networks were digitized from USGS maps and included in CVHM-D. Also, drains and stratigraphy were more realistically represented. CVHM-D is a local scale model of the Delta Region that simulates hydrological processes in the Delta at a finer grid-cell spacing of 0.25 mi (compared with CVHM resolution of 1 mi). It uses the MODFLOW‐2005 groundwater flow model code combined with FMP. The model was used to evaluate the following potential impacts of the Bay Delta Conservation Plan (BDCP) in the Delta: Groundwater impacts due to construction and dewatering occurring in the near term. Groundwater impacts due to the long-term operation of the conveyance facilities
Public/proprietary and cost	The MODFLOW source code is readily available for free.
Physically or empirically based	Physically based.
Mathematical methods used	The physical parameter values of the modeled groundwater system were left unchanged from CVHM. Refinements include a finer discretization of the original model grid, and the subdivision of what was a single WBS in the CVHM representing the central Delta, into 23 individual WBSs, each roughly representing the main Delta islands. Topography was refined using Digital Elevation Model (DEM) data based on 2007 LiDAR mapping by DWR, and Suisun Bay bathymetry is included in CVHM-D. Climate (precipitation, ET) data are the same as in CVHM derived using PRISM, but they are re-sampled over 1/16^th square mile grid cells for greater resolution. CVHM was run initially to assign transient groundwater levels to the GHBs on the northern and southern boundaries of CVHM-D. This ensured that the CVHM information was transferred to the refined scale CVHM‐D. Three boundary conditions are used in the model: Prescribed-flux: surface and/or groundwater is specified Head-dependent flux: GW flux is internally computed across the boundary using an appropriate governing flow equation No-flow: Where GW can flow parallel to the boundary but not across it
Input data requirements	Files in the program are organized based on BDCP alternatives. No Action files contain: Model array files No Action Alternative (with climate change) – 24 input files and 38 output files No Action/Existing Conditions - 24 input files and 38 output files Alternative 1 Operation Files contain: Model array files Input and output files for Alternatives 1A, 1B, 1C operation runs – 24 input files and 37 to 40 output files Construction Dewatering Files contain: Model array files Input and output files for Alternatives 1A, 1B, 1C, 2A, and 4 construction dewatering runs
Outputs	The output folder contains the output files for the transient simulations of each alternative: Existing Conditions/No Action No Action Alternative (with climate change) Alternative 1A – Construction dewatering Alternative 1A – Operation Alternative 1B – Construction Dewatering Alternative 1B – Lined canal operation Alternative 1B – Unlined canal operation Alternative 1C – Construction Dewatering Alternative 1C – Lined canal operation Alternative 1C – Unlined canal operation Alternative 2A – Construction dewatering Alternative 4 – Construction dewatering
Pre-processing and post-processing tools	Multiple pre-and post-processing programs can be used with MODFLOW. These include Visual MODFLOW (Waterloo Hydrogeologic), Groundwater Vistas (Rockware), USGS Model Muse and Model Viewer.
Representation of uncertainty	Uncertainty can be evaluated using sensitivity analysis for key parameters.
Prevalence	The model's only known use was for the BDCP process.
Ease of use for public entities	There are no barriers to public use of the model.
Ease of obtaining information and availability of technical support	There is no active support of the model.
Source code availability	The MODFLOW source code is available for modification if needed at: https://water.usgs.gov/ogw/modflow/MODFLOW.html#related
Status of model development	Fully developed and ready for use.
Challenges for integration	Challenges include the following: Difficulties associated with integrating in time and space with surface water models. CVHM-D is not calibrated and more work is needed to better represent Delta subsurface conditions. Any surface water or groundwater features occurring at a smaller scale than one-quarter mile cannot be simulated.

References

Draft Environmental Impact Report / Environmental Impact Statement for the Bay Delta Conservation Plan: Appendix 7A. Available online at:
http://baydeltaconservationplan.com/Libraries/Dynamic_Document_Library/Public_Draft_BDCP_EIR-EIS_Appendix_7A_-_Groundwater_Model_Documentation.sflb.ashx