Higher and more frequent flows that inundate wetlands for extended periods during the fall and winter months reconnect habitats that benefit native fish and birds.
The Measure
Restore land-water connections to increase hydrologic connectivity and seasonal floodplain inundation.
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Expectations
- Increase hydrologic surface water connectivity
- Increase the frequency of seasonal inundation
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Performance Metrics
- Acres of areas hydrologically connected to fluvial and tidally influenced waterways
- Acres of nontidal floodplains that inundate at least every two years
Yolo Bypass Salmonid Habitat Restoration and Fish Passage Project
Also known as the Big Notch Project, this project improves fish passage and increases floodplain fisheries rearing habitat in Yolo Bypass and the lower Sacramento River basin. This project broke ground in June 2022 and is expected to be completed in late 2023. It will help meet the inundation and connectivity acreage targets of this performance metric.
Since the 1800s, 91% of historical wetland habitat in California has been lost, including 95% of the Central Valley floodplain. In the Sacramento-San Joaquin Delta, most of these wetlands and floodplains have been drained and converted to agricultural land use. Although most of the natural wetlands no longer remain, some agricultural land, floodways, and floodplains can provide similar functions, including increased aquatic food production and transfer of nutrients to the ecosystem. However, for these functions to be maintained or restored, areas must be hydrologically connected via surface water and inundated by water for at least part of the year.
Restoring land-water connections to provide the biological benefits of floodplain inundation requires two components: 1) surface water connectivity for water to flow onto land; and 2) sufficient flow of water to inundate these connected areas.
This performance measure tracks the area of land hydrologically connected to Delta waterways and how much of this area becomes inundated during a two-year interval. Performance Measure 4.2a tracks Yolo Bypass inundation frequency and duration. These two performance metrics both track inundation, highlighting the importance of water connecting to land for native species population health.
1 Area that is inundated on a two-year recurrence frequency and is connected via surface water to the fluvial river or tidal system.
2 There is no depth threshold for the inundation analysis, as inundation occurs at any depth. While depth of inundation is important for ecological processes, the available data do not include depth measurements.
Each chapter of the Delta plan includes strategies to achieve the goals of the plan. These strategies are general guidance on achieving the objective laid out in the plan and in the Delta Reform Act of 2009. Associated with these strategies are recommendations. The recommendations describe more specific and implementable actions to support the achievement of Delta Plan strategies. Strategies and recommendations may also have associated performance measures. Delta Plan performance measures track progress in achieving desired outcomes for the Delta Plan. Below are the strategies and recommendations associated with this performance measure.
Strategy
- Restore Ecosystem Function
Recommendations
N/A
Metric
Acres within the Delta and Suisun Marsh that are:
- Hydrologically connected to fluvial and tidally influenced waterways.
- A nontidal floodplain1 area that inundates2 at least once every two years.
Baseline
As of 2018:
- An estimated 75,000 acres of land are physically connected to the fluvial river and tidal system.
- Approximately 15,000 acres of the connected land were inundated at a two-year interval, calculated as a long-term average for 1985-2018.
Target
By 2050:
- Additional 51,000 acres are added to the 75,000-acre baseline that is physically connected to the fluvial river and tidal system, for a total of 126,000 acres.
- At least an additional 19,000 acres of nontidal floodplain area is inundated on a two-year recurrence interval, for a total of 34,000 acres.
To provide a short-term assessment of progress toward the inundation and connectivity targets, intermediate milestones are set for evaluation every decade. The following interim milestones are established on an assumed linear progression toward the 2050 target date.
| Metric | Baseline (Acres) |
2030 Total Area (Baseline Acres Plus Net Increase) |
2040 Total Area (Baseline Acres Plus Net Increase) | 2050 Total Area (Baseline Acres Plus Net Increase) |
| Hydrologic Tidal and Fluvial Connectivity | 75,000 | 92,000 | 109,000 | 126,000 |
| Nontidal Inundation | 15,000 | 21,400 | 27,700 | 34,000 |
Although linear progression is presumed for setting interim milestones, many management and environmental uncertainties exist, such as climate change and frequency of drought in implementing restoration projects and achieving the target acres of inundation and connectivity. Interim assessments of the performance measure will consider the existing state of the restoration in the Delta and disclose conditions impacting the rate of restoration interim progress.
Methods
Connectivity: Review the Delta Stewardship Council covered actions portal annually for on-the-ground projects that restore surface water connectivity (such as levee breach, levee notch, weir modification, and tidal marsh restoration) and certified as covered actions consistent with the Delta Plan. Covered actions’ project descriptions and supporting documentation provide details on project restoration activities and acres of land opened for hydrologic connectivity.
Inundation: Use the Global Surface Water Explorer from the European Commission Joint Research Center (JRC) to calculate water surface areas inundating the connected land (water extent, duration, and seasonality derived from remote sensing data).
Data Sources
Landsat Dynamic Surface Water Extent
National Aeronautics and Space Administration (NASA) and Indian Space