Groundwater
Development of the original Butte Basin Groundwater Model (BBGM) began in 1992 by Hydrologic Consultants, Inc. under the direction and funding of the Butte Basin Water Users Association. With the establishment of the Butte County Department of Water and Resource Conservation (Department) in 1999, model development and updates were led by the Department often through state grant funding. During 2003 to 2008, Camp, Dresser, and McKee (CDM) conducted a significant update to the model, changing the modeling code to Integrated Water Flow Model (IWFM) v.2.4.1, revising the hydro stratigraphy from three layers to nine layers based on the Department of Water Resources Northern Region Office geologic cross sections, and expanding the model domain into the foothill area to directly incorporate potential recharge areas. The model was recalibrated and used to run a base case and 50% surface water curtailment scenario. This version of the BBGM is referred to as BBGM-2008. Documentation is available further on this page.
Davids Engineering, Inc. and Department staff, supported by local Butte County funding, updated the BBGM for the 2016 Water Inventory and Analysis Update. This version retained the same model domain, grid, sub-regions, and stream network as the BBGM-2008. The BBGM-2016 version updated the model code to IWFM-2015 and version 2015.0.36 of the IWFM Demand Calculator (IDC) using v. 4.0 of the root zone component (DWR 2015). It maintained a daily time step with some daily input (i.e. precipitation, stream inflow), some monthly input data (i.e. surface water diversions) and some annual input data (i.e. land use). The BBGM-2016 model time period was 1970 to 2014.
Between late 2018 and mid-2020, Davids Engineering, Inc. and Woodard and Curran updated the BBGM (version BBGM-2020) to support the development of Groundwater Sustainability Plans (GSPs) in the Vina, Butte, and Wyandotte Creek Sub basins. This model update utilized IWFM-2015.0.961, extended the time series inputs through water year 2018, and calibrated aquifer and stream parameters based on observed groundwater levels and stream flows. Several additional refinements were made including the assignment of recoverable losses from irrigation conveyances to model elements, implementation of root zone vertical hydraulic conductivity values specific to rice and wetlands, and refinements to seepage estimates for Thermalito Afterbay. In addition, to support the development of GSPs for sub-basins within the model domain, four baseline model scenarios simulating 50 years of hydrology were developed representing (1) current conditions, (2) future development without climate change, (3) future development with projected climate change at 2030, and (4) future development with projected climate change at 2070. Results from these scenarios are included in each respective GSP available on the DWR SGMA Portal.
Although the BBGM-2020 model structure is the same in many ways as the 2008 CDM version, major differences include additional crop types to better represent ponded crops (i.e. rice and wetlands), recalibrated soil parameters, and elemental land use. A major change in the rootzone v.4.0 code is a representation of land use on the elemental scale rather than the sub-region scale and direct representation of flooding fields for ponded crops (i.e. rice and wetlands). These changes to the BBGM are described in more detail in the Model documentation included on this page.