Lower Yolo Tidal Marsh Restoration Project

Fall/Winter 2013 Ecesis, Volume 23, Issue 3

Introduction

Looking south down the Yolo Bypass from over Interstate 80 during a flood event in April 2012. Photo courtesy Curt Schmutte, Curt Schmutte Consulting

Looking south down the Yolo Bypass from over Interstate 80 during a flood event in April 2012. Photo courtesy Curt Schmutte, Curt Schmutte Consulting

The State and Federal Contractors Water Agency (SFCWA) is undertaking the Lower Yolo Restoration project (Project) in collaboration with California Department of Water Resources and U.S. Bureau of Reclamation. The cooperative project is intended to reduce costs and help restore 8,000 acres of habitat as required by Biological Opinions issued by the U.S. Fish and Wildlife Service and National Marine Fisheries Service for continued operation of the State Water Project and federal Central Valley Project. SFCWA is a joint powers authority comprising public agencies that receive water from the State Water Project or Central Valley Project.

Regulatory Context

The Lower Yolo Restoration Project is part of a larger regional habitat restoration effort that has been in development for many years. Since the mid-1990s, state agencies, federal agencies, and stakeholders have worked to develop and implement a long-term program for improving the Sacramento-San Joaquin Delta’s ecosystem health. A primary venue for that effort was the CALFED Bay-Delta Program (CALFED), which was approved in 2000 to achieve four interrelated objectives: levee system integrity, ecosystem restoration, water supply reliability, and improved water quality. 

Subsequent to CALFED, the Delta Vision plan was created by then-Governor Arnold Schwarzenegger to “develop a durable vision for sustainable management of the Delta” so that the Delta can support environmental and economic functions important to the people of the state of California. The Delta Vision Strategic Plan was issued in 2007 and contains recommended strategies and actions which include: restoring tidal and riparian habitats and increasing frequency of floodplain inundation, improving migratory corridors, addressing invasive species, relocating export diversions and implementing conveyance improvements, revising flow standards and operating criteria, and improving water quality. Many of these actions are now being pursued through the proposed Bay Delta Conservation Plan (BDCP). 

Nearing completion of its planning phase, the BDCP is being prepared by a group of local water agencies, environmental and conservation organizations, state and federal agencies, and other interest groups in compliance with the federal Endangered Species Act and the California Natural Communities Conservation Planning Act. When complete, the BDCP will provide the basis for issuing endangered species permits for the operation of the State Water Project and Central Valley Project over the following 50 years. The heart of the BDCP is a long-term conservation strategy that sets forth actions needed for a healthy Delta, building upon the framework established through the CALFED and Delta Vision processes. The draft biological goals and objectives in the BDCP call for substantial commitments to restore natural habitats, including up to 65,000 acres of tidal wetland and associated estuarine and upland habitats distributed across the Delta; up to 10,000 acres of seasonally inundated floodplain habitat along major channels; and enhancement of floodplain in the Yolo Bypass.

Location

The Lower Yolo Project site is located at the southern end of the Yolo Bypass floodway directly to the north of Liberty Island and near the north end of the Cache Slough complex. The Yolo Bypass is a levee-protected, 59,000-acre floodplain west of the lower Sacramento River. The 41-mile-long bypass routes Sacramento River floodwaters away from heavily developed urban and suburban areas and onto minimally developed farmland. Land uses within the Yolo Bypass are managed to facilitate flood flow conveyance. Land uses within the Bypass consist of the state-owned Yolo Wildlife Area (16,700 acres) and privately owned agricultural lands, all of which are subject to flood flow conveyance easements that restrict development. The bypass is predominantly used for annual agricultural crops and some grazing. The Yolo Wildlife Area is managed for emergent wetland vegetation. Bordering the Yolo Bypass on the east is the Sacramento Deep Water Ship Channel. 

The Project site contains a ranch compound in the northwest corner of the property (including small seasonal residences, barns, other outbuildings, and corrals) and irrigated pasture on the remainder of the site. The topography of the Project site is primarily flat, with an almost imperceptible slope descending from the northwest to the southeast. Much of the site is at elevations above modern mean higher high tide (+6.5 ft. NAVD881), with elevations ranging between +6.5 to +15 ft. NAVD88. Approximately one-quarter of the site topography is within intertidal elevation ranges of +2 to +6.5 ft. NAVD88. Many areas within the site are currently pastures that have been graded to drain to agricultural drainage ditches. Before being diked off for agriculture in the early 1900s, the Project site likely contained a matrix of grasslands, seasonal wetlands, perennial open water backwater lake features, and tidal marsh. The Project site is now primarily used for seasonal cattle grazing except during the rainy season, when it provides flood conveyance capabilities as part of the Yolo Bypass. To prevent tidal flooding, the hydrology of the site is intensively managed through a series of levees, flood/drainage ditches, tide gates, flap gates, and other associated infrastructure.

Goals and Objectives

The overall Lower Yolo property, which is owned by Westlands Water District, is approximately 3,423 acres, of which approximately 2,134 acres will be restored, enhanced and/or preserved aquatic and terrestrial species habitat. The highlight of the project is restoration of approximately 1,672 acres of tidal freshwater marsh habitat. 

The goals and objectives of the project are to:

  • Enhance regional foodweb productivity and export to Cache Slough complex in support of delta smelt (Hypomesus transpacificus) recovery
  • Provide rearing habitats for out-migrating salmonids
  • Provide rearing, breeding, and refuge habitats for a broad range of aquatic and wetland-dependent species that utilize or depend upon the combination of Delta aquatic and terrestrial habitats
  • Suitable habitat for establishment of diverse native plant communities including rare plants
  • Minimize potential for colonization by Brazilian waterweed (Egeria densa)
  • Preserve existing topographic variability to allow for habitat succession and resilience against future climate change

Because of its location at the Sacramento-San Joaquin Delta margin, the Project site provides an opportunity to restore extensive wetland-upland transitional habitats, and can accommodate sea level rise for many decades as marsh expands landward.

Design and Construction

Utilizing historical ecological information recently developed by the San Francisco Estuary Institute, the Project seeks to utilize the site’s unique position on the landscape. According to the Institute, the Project site historically held a uniquely rich location at the intersection of the Putah Creek alluvial fan, historic Yolo Basin floodway, and north Delta tidal marshes. The proposed Project seeks to partially restore some of these ecological functions in the current, highly altered landscape and restore as much of the historic hydroperiod diversity as possible. This includes reconnecting the historic lake features with surrounding natural tidal waterways and removing obstructions to tidal inundation to allow seasonal and tidal waters to drain slowly through the marsh plains. 

The proposed Project also seeks to maximize ecological productivity by enhancing resiliency, diversity, and regional integration. Utilizing the existing topography and irrigated pasture infrastructure at the site, the proposed Project would increase hydraulic residence time through increased surface flow complexity and discharge distance to receiving waters. These Project features would maximize resiliency in the face of sea level rise and regional stressors such as changes in tides, floods, salinity mixing, and invasive species. Depending on the seasonal and regional hydrology, water would come from daily tidal exchange or from seasonal inundation during flood events in the Yolo Bypass.

Specific actions associated with the proposed Project include: restoring approximately 1,672 acres of tidal marsh, including 4 acres of tidal channels and swales; enhancing approximately 28 acres of tidal marsh habitat and 49 acres of riparian habitat; removing agricultural irrigation from approximately 385 acres surrounding the restored wetlands (fringe tidal wetlands); and relocating and installing several water control structures and some irrigation and drainage ditches. Approximately 58,000 cubic yards of soil will be excavated from the restoration area and stockpiled on existing agricultural fields in the northwest corner of the property, behind restricted-height levees.

Tidal restoration and enhancement would be accomplished by eliminating or moving existing water control infrastructure elements or installing new elements, excavating notches in existing internal and perimeter berms, and creating new tidal channels and swales to connect restoration and enhancement areas to existing tidal waters adjacent to the site. High tides would be temporarily captured behind existing berms that are part of the irrigated pasture landscape that now exists on the Project site. Water will discharge from the site though the existing irrigated pasture ditch network via overland flow, and through swales that will be cut to drain the deepest parts the existing landscape. Depth of the swales will vary in order to vary the hydroperiod within the associated drainage area and test different residency time hypotheses. Removing irrigation control structures will greatly reduce the potential for fish stranding. In addition, grazing will be restricted within the restoration footprint through the seasonal use of exclusion fencing.

Surrounding the restored wetlands will be an additional 385 acres of transitional uplands on which agricultural irrigation will be discontinued. Seasonal cattle grazing will be utilized within this wetland buffer zone as a vegetation management tool. To ensure that irrigation and drainage needs of the remainder of the site and of adjacent properties are maintained, the one tide gate will be relocated. Areas on the property that are outside of the Project footprint will remain in their current condition and continue to support agricultural operations following Project implementation. 

The final Environmental Impact Report for the project has been certified and regulatory permits for project construction are currently being reviewed by the relevant public resource agencies. Construction is scheduled for the summer of 2014. — by Carl Jensen, Landscape Architect, ICF International