In 2014, the State of California adopted historic legislation to help manage its groundwater, the Sustainable Groundwater Management Act (SGMA). According to the act, local agencies must develop and implement Groundwater Sustainability Plans (GSPs) for managing and using groundwater without causing "undesirable results," including groundwater-level declines, groundwater-storage reductions, seawater intrusion, water-quality degradation, land subsidence, and interconnected surface-water depletions.
The California Department of Water Resources (DWR), the lead agency assisting local and regional Groundwater Sustainability Agencies (GSAs) in achieving groundwater sustainability, has engaged the U.S. Geological Survey (USGS) to conduct a broad range of technical activities to support both GSAs and DWR.
The USGS uses data collection, modeling tools, and scientific analysis to help water resource managers plan for, and assess, hydrologic issues that can cause "undesirable results" associated with groundwater use. This information helps managers understand trends and investigate and predict effects of different groundwater management strategies.
According to SGMA, local agencies must develop and implement Groundwater Sustainability Plans (GSPs) for managing and using groundwater. Each GSP must consider the following sustainability indicators:
Measurements of water levels in wells are fundamental indicators of the status of groundwater. These measurements are critical to meaningful evaluations of the quantity and movement of groundwater.
Extensive groundwater withdrawals from aquifer systems have caused land subsidence throughout California. Land subsidence can damage structures, such as wells, buildings, and highways, and creates problems in the design and operation of facilities for drainage, flood protection, and water conveyance. Groundwater-level and land-subsidence monitoring are important to mitigating subsidence and managing future effects.
Seawater intrusion associated with lowering of groundwater levels is an important issue in many of California's coastal groundwater basins. Quantifying the rate and extent of seawater intrusion involves understanding the aquifer–ocean interconnection and distinguishing among multiple sources of saline water.
Changes in groundwater storage can be estimated by using direct measurements, such as measuring groundwater levels, and indirect measurements, such as remote sensing, coupled with modeling tools.
Groundwater and surface water are interconnected resources. Much of the flow in streams, and the water in lakes and wetlands, is sustained by the discharge of groundwater, particularly during dry periods. Coordinated measurement and modeling of surface and groundwater conditions are needed to estimate surface-water changes that result from groundwater development.
Determining changes in groundwater quality over time involves systematic monitoring of constituents of concern, coupled with understanding of the dynamics of the groundwater-flow system.
A hydrologic model is a simplified conceptual and computer model used to simulate and predict the movement and use of water. It takes into account various or all components of the landscape, aquifer system, and water cycle and provides a framework to organize data, knowledge, and understanding of hydrologic systems. Models can provide insights that water-resource managers need to plan effectively for future water demands and to answer scientific and management questions.
Groundwater-level monitoring is a fundamental way of gaining an understanding of a groundwater basin, determining directions of groundwater movement and trends in groundwater storage, and evaluating progress toward meeting water resource management goals. DWR advises that, in order to be SGMA compliant, each GSP must include a sufficient monitoring network to provide data needed to demonstrate progress toward achievement of a plan's sustainability goal.