Knowledge Framework
Use Cases
- Reduce water demand during shortages — Implement restrictions, campaigns, and pricing measures to cut water consumption when supply is r...
- Allocate water between competing users — Distribute available water fairly between agriculture, cities, industry, and the environment when...
Decision Patterns
- Demand reduction programmes — Reduce water usage behaviourally
- Basin governance systems — Allocate water at basin scale
System Models
Allocation & governance models
Tool: MODFLOW / C2VSim groundwater models — Models groundwater sustainability under extraction limits
Overview
The Sustainable Groundwater Management Act (SGMA), signed into law in September 2014, is the most significant reform of California’s water governance in decades. It requires local agencies to develop and implement Groundwater Sustainability Plans (GSPs) to halt chronic over-extraction and achieve sustainability within 20 years.
California was the last western US state to regulate groundwater, despite the resource providing approximately 40% of the state’s water supply in normal years and up to 60% during drought. Decades of unregulated pumping caused severe aquifer depletion, land subsidence (up to 28 feet in some areas of the San Joaquin Valley), and impacts on rivers, wetlands, and drinking water wells.
SGMA requires avoidance of six “undesirable results”: chronic lowering of groundwater levels, significant and unreasonable reduction in groundwater storage, significant and unreasonable seawater intrusion, degraded water quality, land subsidence, and depletion of interconnected surface water.
Timeline & Location
2014: SGMA signed into law during a severe multi-year drought. 2017: Groundwater Sustainability Agencies (GSAs) formed for critically over-drafted basins. 2020: GSPs submitted for 21 critically over-drafted basins. 2022: GSPs submitted for medium- and high-priority basins. 2022–2024: DWR reviews and approves/rejects submitted plans (several Central Valley plans rejected as inadequate). 2040–2042: Deadline for critically over-drafted basins to achieve measurable sustainability. 2042: Deadline for all medium/high-priority basins.
Stakeholders
The California Department of Water Resources (DWR) provides technical assistance and reviews GSPs. The State Water Resources Control Board has backstop authority to impose management if local agencies fail.
260+ Groundwater Sustainability Agencies (GSAs) were formed by local governments, water districts, and county agencies. Implementation has been politically contentious, particularly in the San Joaquin Valley where achieving sustainability may require significant reductions in irrigated acreage. Agricultural interests, environmental groups, disadvantaged communities (whose domestic wells are threatened by dropping water tables), and tribal nations are key stakeholders with competing interests.
Digitalisation & Data
SGMA implementation relies heavily on groundwater monitoring and data:
Monitoring Networks
GSAs are required to establish monitoring networks tracking groundwater levels, quality, subsidence, and interconnected surface water. Many leverage existing USGS and DWR monitoring wells supplemented by new installations.
Remote Sensing for Subsidence
InSAR (Interferometric Synthetic Aperture Radar) satellite data is used to monitor land subsidence across the Central Valley, providing evidence of ongoing over-extraction impacts.
Water Accounting
New metering requirements and water budgets are being developed using satellite-based evapotranspiration estimates (e.g., OpenET) to quantify actual agricultural water use at field scale.
Hazards
Exogenous Hazards
Climate change reducing Sierra Nevada snowpack (California’s primary surface water storage mechanism). Increasing drought frequency and severity. Federal water supply restrictions to protect endangered species in the Sacramento-San Joaquin Delta.
Endogenous Hazards
Decades of unregulated groundwater pumping depleting aquifers. Political resistance from agricultural interests to pumping restrictions. Inequitable impacts on disadvantaged communities whose shallow domestic wells go dry first. Inadequate data on actual groundwater use in many basins.
Cost & Benefit
Cost: Implementation costs vary widely by basin, with estimates of $2–5 billion in total across all GSAs for monitoring, planning, projects, and administration over the 20-year implementation period. The economic cost of required agricultural land fallowing in the San Joaquin Valley is estimated at $5–7 billion in lost agricultural output.
Key Benefits: Long-term protection of an aquifer system that provides 40–60% of California’s water supply. Halting land subsidence that damages infrastructure (canals, roads, bridges). Protection of domestic drinking water wells in rural communities. Establishing a governance framework for sustainable groundwater management that can be adapted over time.
Resilience Principles Assessment
Assessment of meeting Principles of Resilient Infrastructure
Shared Responsibility (P5)
SGMA distributes responsibility to local agencies while retaining state backstop authority. It requires coordination among overlapping agencies within the same basin and between surface water and groundwater managers.
Adaptively Transforming (P6)
SGMA fundamentally transforms California from unregulated groundwater pumping to managed sustainability. The 20-year implementation timeline allows gradual adaptation, but the trajectory is transformative for agricultural communities dependent on groundwater.
Continuously Learning (P1)
GSPs must be updated every five years based on monitoring data and evolving understanding of basin conditions. DWR’s review process provides feedback loops. New remote sensing and data tools are continuously improving the evidence base.
Socially Engaged (P4)
SGMA requires GSAs to consider the interests of all beneficial uses and users, including disadvantaged communities. However, implementation has revealed tensions between agricultural water users and communities reliant on domestic wells.
Proactively Protected (P2)
SGMA establishes minimum thresholds for groundwater levels, subsidence, and water quality that must not be exceeded, providing proactive protection of the resource.
Environmentally Integrated (P3)
SGMA requires management of impacts on interconnected surface waters, linking groundwater management to river and wetland ecology. Managed aquifer recharge using floodwaters is an increasingly important sustainability tool.
Futures
The critical test of SGMA will come in the 2030s as GSAs implement pumping restrictions in critically over-drafted basins. The economic and social impacts on agricultural communities in the San Joaquin Valley will be significant. Climate change adaptation, managed aquifer recharge, and water markets will be key tools for implementation.