Map of the Cuyama Valley study area.
Currently, groundwater is the only source for domestic, agricultural and municipal water use in the Cuyama Valley groundwater basin in Santa Barbara County, California. Groundwater withdrawals, mainly to irrigate agricultural crops, have resulted in water-level declines of as much as 300 feet in the area since the 1940s. To plan for sustainable future use of the groundwater, the U.S. Geological Survey (USGS), in cooperation with the Santa Barbara County Water Agency have conducted research aimed at defining the quantity and quality of the groundwater supply, and are establishing tools to allow users to efficiently utilize the available groundwater resources.
Between 2008 and 2012, geologic, water-quality, hydrologic and geomechanical data were collected from selected sites throughout the Cuyama Valley groundwater basin to assess the water resources of the area.
In order to develop tools that will aid in water-resource management of the Cuyama Valley groundwater basin, a conceptual understanding of the geologic setting of the basin is needed.
Evaluation of the basin's geologic structure reveals that the valley is composed of groundwater sub-basins. Groundwater samples indicate that water does not move freely between these different formations, or between different geologic regions within the Cuyama Valley. Because of the differences in geology, hydrology, and water quality, there are unique management issues for each sub-basin, in addition to a need for a whole-basin-management approach.
Previous estimates of groundwater recharge (Singer and Swarinski, 1970) include estimates from the earliest periods of development in the area. The current study reevaluates these estimates and creates newer estimates from more recent time periods using new hydrologic data and modeling tools. These new estimates of the hydrologic budget, and projections of how it changes through time with continued development and climate variability, will help resource managers understand and manage for sustainability of water resources.
To plan for future use, it will be important to define the quantity and quality of the groundwater supply and establish tools to allow users to efficiently utilize the available groundwater resources. The geohydrologic and hydrologic models will be used to estimate the volume of water resources that have been depleted, still remain, and may be unusable owing to poor water quality. This study will provide a clearer picture of the limits of the groundwater resources, the connection between the supply and demand components of water use, and the potential availability of the water resources under current and alternative climatic and cultural water-use scenarios.
Existing climate, land-use, geologic (geologic maps, well logs, and geophysical logs), hydrologic (streamflow, water levels, and spring locations), water-quality, and geodetic data will be compiled and assembled into a Geographic Information System (GIS) using ARCINFO. Although much of the development of the GIS will occur early in the study the GIS will be used, updated, and revised throughout the study. Hydrologic and water-quality data will be compiled and integrated into a regional synthesis of water resources.
Land Use maps for 1992 from the national Land Cover Digital Data (U.S. Geological Survey, 1999)
Land use for 2000 from California Department of Water Resources, (2000).
Color photo image from U.S. Department of Agriculture, National Agriculture Imagery Program, 1 meter resolution, 2005.
Refining the geohydrologic framework of the valley, as well as developing new geologic and hydrologic models, will require the collection of depth-dependent or aquifer dependent geohydrologic and geochemical data. The existing monitoring network maintained by Santa Barbara County and the USGS will be enhanced during the study period and be used to collect temporal and spatial water-level and water-quality data. Streamflow data will be collected at selected streams to help determine the recharge characteristics of the valley. Geodetic data will be collected to determine if subsidence is occurring in the valley.
Maps showing locations of wells with selected hydrographs of historical groundwater levels. Groundwater levels show historical groundwater-level declines of up to 300 ft in the main parts of Cuyama valley to about 10 ft in the Ventucopa area.
Map shows preliminary Interferometric Synthethic Apeture Radar (InSAR) image of Cuyama Valley and related continuous GPS measurements at Cuyama Valley High School from the Plate Boundary Observatory site (PBO). The changes in color overlayed on the map indicate the relative amount of vertical movement of the land surface between August and March, 1997.
The above graph shows the northerly, easterly, and vertical movement of the PBO continuous GPS site near Cuyama Valley High School (CUHS). These data indicate lateral movement from tectonic forces of about 0.14 feet per year in a direction of 70 degrees West of North and a vertical displacement downward (land subsidence) of about 0.26 ft in nine years (0.03 feet per year) Selected seasonal and interannual InSAR images and the CORS site will be used to estimate monitor recent land subsidence. The CUHS site will also be used to reference the estimates of vertical deformation from InSAR images and will be used to compare measured and simulated subsidence from the hydrologic model. The data from the CUHS site combined with continuous groundwater level data from the Cuyama Valley High School water-supply well will also provide estimates of subsidence properties needed to simulate land subsidence with the valley-wide hydrologic model. (SOPAC web site image last accessed 10/06/2009).
The USGS has drilled and installed three multiple-well monitoring sites that will provide depth-specific data on groundwater levels, geophysical data on the alluvial deposits, hydrologic properties, water quality, and water chemistry from selected water bearing layers within the aquifer system of Cuyama Valley. The USGS Research Drilling operations provides detailed geologic, geophysical, and hydrologic information that cannot be obtained from conventional water-supply wells. The areal photo shows the multiple-well site along Kirschenmann Road in proximity to the Cuyama River and a nearby agricultural supply well where it can help us observe the possible interaction with groundwater recharge from flood flows and from pumpage for irrigation.
Multiple-well monitoring site at Kirschenmann Road drilled with Mud Rotary USGS Research Drilling Rig. Four wells installed at different depths to give depth-specific information about water levels, water quality, and water chemistry that are enclosed in a secure vault that will allow the observation of potential effects from groundwater pumpage for irrigation and potential recharge from flood flows along the adjacent Cuyama River near Cuyama, California.
Geohydrologic and hydrologic models will be developed as part of this study to more accurately assess and simulate the storage and flow of water in Cuyama Valley. A geohydrologic model will be developed to help understand the three-dimensional geohydrologic framework of the Cuyama Valley. The model will incorporate information from existing drillers and geophysical logs, cross sections, and geologic maps as well as new information from research drilling at new monitoring-well sites and well-bore flow logs collected for this study. A Basin Characterization Model (BCM) will be linked with the Cuyama Valley hydrologic-flow model (CUVHM) to simulate engaged runoff from the surrounding mountains as recharge. CUVHM will be used to simulate streamflow, land-use processes, and groundwater flow in the Cuyama Valley.
The Farm Process for MODFLOW-2005 (MF-FMP) allows the simulation, analysis, and management of all components of human and natural water use within one hydrologic model. It represents a complete hydrologic model that fully links the movement and use of groundwater, surface water, and imported water for water consumption of irrigated agriculture, but also of urban use, and of natural vegetation. Supply and demand components of water use are analyzed under demand-driven and supply-constrained conditions. From large to small scale settings, the MF-FMP has the unique set of capabilities to simulate and analyze historical, present, and future conditions. MF-FMP facilitates the analysis of agriculture where little data is available for pumpage, land use, or agricultural information. MF-FMP can also analyze the effects of agricultural demand and supply from multi-aquifer well pumpage, delayed recharge through thick unsaturated zones, or rejected recharge as additional runoff, and all six components of evaporation and transpiration.
The impact of water use can be simulated and analyzed for historical and future conditions, drought response alternatives, impact of surface-water rights appropriations or priorities, or operational management of various water sources. MF-FMP can estimate unknown historical pumpage. MF-FMP can help to forecast anticipated future water demand and constrained supply in response to climate change scenarios. In addition, MF-FMP can project further how future water demand and supply would change subject to potential policies or capital projects that try to mitigate or adapt to climate change.
The hydrologic model will be used to evaluate how selected water-use and climate scenarios affect the availability of ground water in the Cuyama Valley. Potential water-use scenarios include changes in cropping patterns, increased urbanization, and artificial recharge. The USGS will meet with water managers and other stakeholders to help define the water-use and climate scenarios that will be evaluated for this study. The assessment of these scenarios will provide the stakeholders with a clearer picture of the limits of the resources, the connection between the supply and demand components of water use, and the potential availability of the water resources under current and alternative climatic and cultural water-use scenarios.
Of particular importance will be using the hydrologic model to analyze changes in groundwater flow and groundwater storage in different hydrologic regions of the Cuyama Valley caused by current and projected groundwater use. The geohydrologic and hydrologic models will be used to estimate the volume of water resources that have been depleted, still remain, and may be unusable owing to poor water quality.
Hydrologic cycle--Data collected on the three-dimensional character of the aquifer flow and chemistry will help develop a greater understanding of the groundwater processes in the Cuyama Valley and evaluate the potential hydrologic effects of future groundwater withdrawals on different parts of the valley. The hydrologic cycle shown here demonstrates how precipitation (rain and snow) in the mountains recharges the aquifer system, moves down gradient through the aquifers, and then is pumped from long-screened supply wells.
Provide information for all levels of interest in the geology and water resources of Cuyama Valley
Provide documentation to the residents, public officials, and business leaders that describe the climatic, geologic, and hydrologic factors that affect the use, movement, quality, and availability of water resources in Cuyama Valley.
Prepared in cooperation with Santa Barbara County Water Agency
Project Chief, Research Hydrologist
U.S. Geological Survey
California Water Science Center
4165 Spruance Road, Suite 200
San Diego, CA 92101
Claudia C. Faunt, Ph.D., P.E.
U.S. Geological Survey
California Water Science Center
4165 Spruance Road, Suite 200
San Diego, CA 92101
Santa Barbara County Public Works Department
620 West Foster Road
Santa Maria, CA 93455