BAY DELTA SCIENCE CONFERENCE: Restoration in the Cache Slough Complex: The Yolo Flyway Farms Restoration Project

The Yolo Flyway Farms Restoration Project involves restoring and enhancing approximately 278 acres of tidal freshwater wetlands at the southern end of the Yolo Bypass within the Cache Slough Complex. The Project seeks to partially restore historical ecological functions in this highly altered regional landscape.

The Project will involve minimal excavation of approximately 65,000 cubic yards of soil to provide access to emergent marsh and floodplain habitats connected to the adjoining tidal system by breaching existing agricultural berms and creating an interior tidal channel network. The excavated material will be placed on existing upland areas on the project site. Following excavation, the site will be planted with salvaged emergent marsh vegetation.

At the Bay Delta Science Conference, Director and Ecohydrologist Chris Campbell with CBEC Eco Engineering gave a presentation on the goals and status of the project.  This project was initially conceived as a component of the Lower Yolo Restoration project, and has been in the works for approximately eight years.  This project will be the first one implemented under the public-private partnership agreement with the Department of Water Resources.

The red star on the map is the location of the Yolo Flyway Farms project at the north end of the Cache Slough Complex planning area which is outlined in yellow.  The Cache Slough Complex is at the intersection of the Yolo Bypass and the Delta.  This project is part of the effort to implement the goals of the 2008 Delta smelt biological opinion to restore tidal habitat as well as the 2009 salmonid biological opinion to restore and improve salmonid rearing habitat within the Yolo Bypass.

The project goals and objectives are to enhance regional food web productivity and export to Cache Slough Complex in support of delta smelt recovery; provide rearing habitats for out-migrating salmonids; provide rearing, breeding, and refuge habitats for a broad range of other aquatic and wetland-dependent species; provide suitable habitat for establishment of diverse native plant communities including rare plants; minimize potential for colonization by Egeria; and preserve existing topographic variability to allow for habitat succession and climate change resilience.

On the slide, the graphic on the left shows the historical ecology of the Delta and the location of the restoration site, which is at the intersection of the historic tidal marsh and seasonal wetlands.  The graphic on the right is a map of the project and vicinity, with the Yolo Flyway Farms in yellow and the Lower Yolo Restoration Project outlined in black.

What this graphic shows is at the turn of the century and in the early 1900s, the site really did support tules, tidal marsh, seasonal wetlands, uplands, and open water habitat,” he said.  “However, that’s been largely influenced by land reclamation and the implementation of flood control infrastructure.”

The Lower Flyway Farms is in the heart of the Yolo Bypass which is a significant feature of the Sacramento Valley flood control system.  The Yolo Bypass conveys floodwaters from the Sacramento River overtopping of the Fremont Weir, and less frequently from the Sacramento Weir.  There are also the west side tributaries that contribute flow and inundate the Yolo Bypass more frequently; those flows move down the Toe Drain and then intersect with the Yolo Flyway Farms Restoration Project.

There are system improvements underway to provide additional flood conveyance and levee setbacks within the system.  There is a fish passage facility for adult salmon currently under construction to move salmon that enter the bypass out of the system and back to the river.  As part of that 2009 biological opinion, there’s a floodplain study that is looking at the introduction of a new gated facility at Fremont Weir that would introduce more frequent flows into the bypass, as well as introduce juvenile salmon into the system so they can take advantage of the floodplain, and by taking advantage of that floodplain, they will also be taking advantage of the restoration sites.

There are also other restoration projects in the region that are in various forms of development.  The Yolo Flyway Farms Restoration Project was once linked to the Lower Yolo Project, and south of that is the Terry parcel at the north end of Liberty Island; all three projects are largely in the upper intertidal elevation range.  The Lookout Slough project is relatively new project; it’s a multi-objective project in the intertidal elevation range and will support Delta smelt and salmonid habitat and also has flood system benefits.  Further downstream is Prospect Island which DWR is advancing the design on and Little Egbert Tract is a multi-objective project with significant flood system benefits that is in the feasibility stage.

The topography of the site is that much of the land elevations within  Lower Flyway Farms is in the upper intertidal and supertidal elevations, so the site is at a unique elevation for providing for restoration of tidal marsh habitat and rearing habitat for salmonids, as well as providing for sea level rise accommodation in the upland areas.  The soil has a lot of minerals; it is at the intersection of the Putah Creek Alluvial Fan and the historic Yolo Basin that received floodwaters from the Sacramento River.

Presently, the site is largely mapped in some form of either perennial or seasonal wetland (lower, left).  It is currently used for grazing for cattle six months out of the year during the agricultural season.  The flood irrigation regime to some degree supports what works on the landscape in terms of the degraded seasonal and perennial wetland habitats that are out there that the site will take advantage of, he said.

There are several wildlife easements in the vicinity of the project site, largely to support waterfowl (upper, right).  Those are largely disconnected, they are not tidally connected to the toe drain, and are largely inundated only by the larger floods that are moving down the Yolo Bypass.

The map on the right side shows the project footprint.  The project will restore 359 acres with an 80 acre parcel that is for ag preservation.  The grading activities will move 60,000-65,000 cubic yards of material, so there is a relatively small stockpile area.

A key element of the project is breaching to the Toe Drain which runs along the east side of the project and provides the tidal connectivity to the Cache Slough Complex.

The idea is to have a northern inlet that we breach to the Toe Drain as well as a southern inlet,” Mr. Campbell said.  “Then in the interior, the idea is to partially degrade selectively some of the interior agricultural berms that isolate various field units.  Not fully degrade them, but partially degrade some of them to provide a bit more complexity in terms of the flow regime and connectivity throughout the site.  In addition to the tidal marsh component, there’s also going to be other enhancement of either open water or riparian as a key consideration during the design was that there is a pretty healthy riparian corridor along that Toe Drain berm.”

He presented a drawing of the north inlet, noting that it was located where it is because its connecting to the lowest ground on the site.

What we’re trying to do is a minimal amount of earth moving as possible to maximize the resiliency of the site in terms of its future evolution, so we’re connecting in here at this north end,” he said.  “We’re having to remove some trees, but we’re also preserving some of the more significant trees along the Toe Drain berm.”

At the southern connection, there is a subtidal channel that is deep enough so that it doesn’t recolonize with tules.

What this channel does is it allows connectivity to the site interior,” he said.  “So we’re creating connectivity from the north to the south and vice versa to get to this western central section of the tract.  There is also a spur in the vicinity not shown on the graphic, so when the Lower Yolo Ranch project advances, there is the opportunity in the future to connect up to that project as well and create a more integrated system at the lower end of the Yolo Bypass.”

Since the project is located in the Yolo Bypass, one of the critical things to think about is flood control and the project’s impacts on the flood control system.  He noted that the areas in orange show the slight increases in water surface elevation and the cooler colors show slight reductions in surface elevation.

We can have localized impacts on the system but we can’t have system-wide impacts,” Mr. Campbell said.  “We have some small increases locally upstream of the stockpile because we’re piling a minimal amount of dirt.  If we did significantly more earth moving in the system, we would have adverse impacts on flood control, and this is a system that is currently deficient, and so we’re planning for the present day; we can’t necessarily plan for all the things that are yet to come where we’ll be gaining back freeboard.”

Mr. Campbell then showed a short animation that showed tidal conditions followed by a small flood pulse coming down the Yolo Bypass.  He pointed out that there are areas in the north, central, and south end that are holding on to water longer, and other higher slightly supertidal elevations that are more frequently wetting and drying on a daily basis.

We’re working with the land elevations that are out there, so they are very much in that upper intertidal or supertidal elevation,” he said.  “We’re not doing any significant mass skim grading on that site to enhance that now.  We’ll get what we need in terms of marsh habitat as this site continues to evolve over time.”

He then showed another small animation that showed how water flowed across the project.  “What this shows is that through these two connections, we have water and fish that could be entering onto the site, and given the way that the agricultural berms have been partially degraded, it creates quite a bit of flow complexity on the site,” Mr. Campbell said.  “Then we have Yolo Lower Ranch Project, so we’ll be looking at what we can do hopefully in the next year about how we can integrate these two sites in terms of degrading the permanent berm between the two properties.”

Several permits were secured and finalized in 2018, and most notably, this is one of two restoration projects that were selected under the 2016 DWR Habitat Restoration RFP, and will actually be the first one implemented under the public-private partnership agreement, he said.

The project is now under construction.


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