CVHM-D

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:

1. Groundwater impacts due to construction and dewatering occurring in the near term.
2. 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:

1. Prescribed-flux: surface and/or groundwater is specified
2. Head-dependent flux: GW flux is internally computed across the boundary using an appropriate governing flow equation
3. 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.