Groundwater Dependent Ecosystems

Groundwater is a hidden resource, occurring almost everywhere beneath the land surface. Groundwater is critically important to Californians, supplying 40% of the state’s water supply in normal years and much more in dry years.

Groundwater also plays a vital role for nature. Where groundwater reaches the surface, it can provide a reliable source of water for wildlife, which is especially important in places where surface waters are seasonally scarce. For some plant species, groundwater serves as the only source of water year-round. It can also replenish rivers and streams that would otherwise run dry in late summer, making it possible for iconic species like steelhead and salmon to survive.

Groundwater dependent ecosystems, or GDEs, are ecological communities of species that depend on groundwater for survival. These ecosystems support a diverse array of plants and animals, including many rare and endangered species here in California. GDEs were largely unstudied in the state until 2010 when Conservancy scientists comprehensively catalogued and mapped these unique ecosystems. The resulting study revealed that all 515 of California’s groundwater basins harbor GDEs.

In 2014, California enacted the Sustainable Groundwater Management Act (SGMA), landmark legislation that established a framework for sustainable management of groundwater basins. Although California was the last state to pass comprehensive groundwater legislation, it is the only state to specifically recognize GDEs – and the needs of nature – in its groundwater law.

Under SGMA, delivering groundwater for human uses is not enough; local groundwater sustainability agencies are also tasked with identifying and considering GDEs in their Groundwater Sustainability Plans. To assist agencies with their planning process, the Conservancy and partners at California Department of Water Resources and California Department of Fish and Wildlife updated the 2010 GDE study to provide a current statewide map of seeps and springs, wetlands, and vegetation that are likely to depend on groundwater.  

Since many groundwater sustainability agencies are con­sidering GDEs for the first time, the Conservancy created a step-by-step guide using the best available science to help them set thresholds to sustainably manage groundwater. With partners in the Fox Canyon Groundwater Management Agency in Ventura County, the Conservancy is testing and refining these tools with local practitioners through the development of one of the first groundwater sustainability plans in the state. Fox Canyon will then provide a blueprint for other agencies on how to incorporate nature in thier plans.

Visit the Conservancy's Groundwater Resource Hub for all resources on how to manage groundwater dependent ecosystems under SGMA.