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© Anthony Dunn

SGMA Planning Tools

Guidance for including nature in Groundwater Sustainability Plans

Groundwater Thresholds for Ecosystems: A Guide for Practitioners

This publication presents a practicable approach for protecting groundwater dependent ecosystems (GDEs) during groundwater allocation decisions and project planning and provides guidance on quantifying groundwater conditions that are protective of GDEs. Quantitative groundwater thresholds and objectives are intended to protect GDEs when evaluating new water project proposals (e.g., new wells, water transfers, etc.), developing regional and local water management plans, or meeting legal requirements such as the Endangered Species Act. This document highlights five steps to quantify what groundwater levels are needed to avoid adverse impacts from groundwater use on GDEs.


Mapping Indicators of GDEs in California

Groundwater Dependent Ecosystems (GDEs) are found in almost all groundwater basins in California. This spatial database maps the location of seeps and springs, wetlands, and vegetation that are indicators of GDEs. The Nature Conservancy partnered with the California Department of Water Resources and the Department of Fish and Wildlife to compile this information. You may view or download the data on vegetative indicators of GDEs through an online mapping tool.

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Big Springs Creek with vegetation
© Erika Nortemann

GDE Guidance Document for GSPs

The Sustainable Groundwater Management Act (SGMA) requires that GDEs be identified and considered in groundwater sustainability plans (GSPs). Modeled after DWR’s Guidance Documents, Groundwater Dependent Ecosystems under SGMA: Guidance for Preparing Groundwater Sustainability Plans provides a process for local agencies to identify and consider GDEs as a beneficial use and user of groundwater. This guidance was developed by The Nature Conservancy using best available science and expert review from local water agencies, state agencies, academics, technical consultants, and NGOs. It provides a step-by-step methodology as part of the overall planning process established by SGMA.

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Consumnes Preserve Egrets
© The Nature Conservancy (Mary Ann Griggs)

GDE Rooting Depth Database

Groundwater dependent vegetation includes riparian vegetation, wetlands, and purely terrestrial ecosystems like valley oak woodlands. The vegetation relies on the availability of groundwater within the rooting depth of the plants. Water uptake can be from within the saturated zone as well as the capillary fringe, which can extend inches to feet above the water table for sandy to more clayey soils, respectively.

Plant rooting depth information can provide a useful insight on what groundwater levels may be needed to sustain GDEs.  This species-specific rooting depth database of California groundwater-dependent plants provides a reference point for understanding whether GDEs are hydrologically connected to groundwater.

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Oak tree roots
© The Nature Conservancy (Laura Riege)

Arundo ET Literature Review

SGMA requires the inclusion of projects that will achieve the sustainability goal of the basin. Removal of the invasive, non-native plant Arundo donax (Arundo) along riparian corridors is a potential water savings strategy providing co-benefits for groundwater sustainability as well as native ecosystem restoration. Arundo is a fast growing, densely vegetated reed that has purportedly high-water consumption (i.e., transpiration). The Nature Conservancy provides a brief literature review of annual evapotranspiration (ET) rates for Arundo. 

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Arundo removal at The Nature Conservancy property along the Santa Clara River, Ventura County, CA
© The Nature Conservancy

GDE Pulse

Remotely sensed satellite data can provide a cost effective alternative to routinely monitor GDEs statewide. The GDE Pulse web app developed by The Nature Conservancy provides users easy access to satellite data to view long term temporal trends of vegetation metrics. These vegetation metrics serve as an indicator of vegetation health for Groundwater Dependent Ecosystems (GDEs). In addition, the GDE Pulse web app provides long-term temporal trends of groundwater depth and regional precipitation data. This provides users with a platform to infer relationships between groundwater levels, precipitation, and GDE vegetation metrics to monitor and sustainably manage groundwater and GDEs.

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