DELTA STEWARDSHIP COUNCIL: West False River Salinity Barrier Project

The Department of Water Resources is working on a final EIR to install the barrier two times over ten years as needed

California is highly prone to droughts, and droughts are expected to increase in frequency as climate change impacts intensify.  In times of severe drought, the amount of water stored in the upstream reservoirs may not be enough to hold back the saltwater that pushes into the Delta along with the tide from the San Francisco Bay. If the saltwater intrudes into the central Delta, it can hinder the ability to extract freshwater from the Delta for municipal use, cause Delta water to become unfit for farming, and impact aquatic habitat.

This drone photograph shows the completed temporary emergency drought barrier for the West False River in the Delta in Contra Costa County. The 750-foot-wide rock barrier will help deter the tidal push of saltwater from San Francisco Bay into the central Delta. Photo taken July 13, 2021 by Jonathan Wong / DWR

To combat severe drought conditions in 2015 and 2021-22, the Department of Water Resources constructed a temporary barrier in the West False River in the Central Delta.

These previous barriers were built as an emergency response under the Governor’s emergency drought orders.  Given the success of the barrier in reducing the intrusion of saltwater into the Delta, the Department of Water Resources circulated an environmental impact report (EIR) last year that would cover two installations of the barrier over a period of ten years.  The EIR is anticipated to be finalized this fall.

At the May meeting of the Delta Stewardship Council, Robert Trang, supervising engineer with the Department of Water Resources, updated the Council on the project.

How saltwater enters the Delta

The graphic shows how water moves in and out of the central Delta.  The Sacramento River provides most of the Delta’s inflows from upstream reservoirs and natural inflows.   The Sacramento River flows from the north into the central Delta, where it meets the San Joaquin River from the south, joins with the rivers from the east, and flows out west towards the San Francisco Bay and, ultimately, the ocean.

The Delta is a tidal environment, so tides can push the saltwater into the Central Delta, which is why the arrow points both ways.

During a normal or above normal water year, there is enough freshwater to keep the salinity at bay and protect the beneficial uses of Delta water.

The figure on the left shows the salinity in the Central Delta during a normal or above-normal water year; the figure on the right shows the Central Delta during severe drought conditions.

Under drought conditions, the tidal influence is the same, but the freshwater inflows into the Delta from upstream reservoirs and natural flows are insufficient to push the saltwater out.  So the saltwater can intrude into the central Delta, where it can negatively impact Delta agriculture, the environment, water supplies for municipalities that draw from the Delta, and the ability to export water from the Delta.   And once there, the saltwater can only get flushed out by high inflows into the Delta, which depends on Mother Nature.

Controlling salts in the Delta is a complex undertaking; there are a lot of interconnected waterways, so isolating an area is challenging.  In 2009, DWR’s modeling support branch analyzed the use of temporary rock barriers to identify which option best protected the central Delta from salinity intrusion.  While Sutter Slough and West False River single rock barrier location ranked amongst the top options, the West False River location was the most consistent in achieving salinity reduction.

The proposed project

The project proposes installing the rock barrier twice over the next ten years as needed to respond to severe drought conditions.  The Department would install it on April 1 and remove it by November 30 in the same year or the following year.  Mr. Trang said that the ten-year timeframe was chosen because the Department could assess the project impacts of two barrier installations more accurately, and it is consistent with other federal permitting durations.

“We know that drought is unpredictable, and it’s cyclical in the state of California, so we felt like a 10-year period will kind of give us the coverage to deploy the barrier if needed,” he said.

Mr. Trang said the Department would only construct the barrier under dire hydrologic conditions due to severe drought.  “It is a last resort … We’re planning for the worst and hoping for the best as far as what Mother Nature would deliver.”

Consistency with the Delta Plan

Jeff Henderson, the Council’s Deputy Executive Officer for Planning & Performance, said that the project is a covered action as defined under the Delta Reform Act, so the Department will be required to submit a certification of consistency with the Delta Plan.  He noted that potentially seven Delta Plan policies apply to the project.

Construction crews work into the night on the temporary emergency drought barrier in the West False River in the Sacramento-San Joaquin Delta in Contra Costa county. Photo taken June 7, 2021.  Kelly M Grow / California Department of Water Resources

Mr. Trang said the Department anticipates submitting the certification of consistency with the Delta Plan sometime during the fall once the final EIR is completed.  However, he noted that the project may change based on comments received.

“The proposed project is consistent with the coequal goals of protecting the Delta ecosystem and ensuring water supply reliability,” said Mr. Trang.  “By increasing the resiliency in the central Delta, it helps protect water quality, aquatic habitat, and water delivery.  This strengthens our ability to resist variability in the compounding impacts of severe drought by protecting the beneficial uses of water.”

“Installing the drought barrier at West False River is our best option to adaptively manage the system considering the dire circumstances,” he continued.  “It is a project that we don’t want to build, but we just want to be proactive in planning for it if we need to do so.”

Monitoring the impacts of the barrier

During the discussion period, Councilmember Lee asked what monitoring was being done to look at the impacts of the barrier.  Mr. Trang said that HABs and predation were being studied.  Mr. McQuirk pointed out that it’s difficult to differentiate between drought impacts and drought barrier impacts because all these things worsen during drought.  “It’s very difficult for us to untangle the difference between a drought effect and a drought barrier effect, but we have spent substantial resources, and we’ve hired USGS to help us with these efforts.  So we are working to get at that.”

This drone photograph shows construction crews working on the temporary emergency drought barrier for the West False River in the Sacramento-San Joaquin Delta in Contra Costa County. Andrew Innerarity / DWR

As for fish migration, there is a question as to whether the effect is good or bad.  “It’s not a preferred migratory pathway for salmonids; it’s also not the direction that we want fish like Delta smelt to go,” said Jacob McQuirk, principal engineer for DWR.  “So there’s a theory out there that having this channel blocked off is good for salmonids and Delta smelt.  We don’t have enough science to back that up, but that is a hypothesis out there.”

Dr. Laurel Larsen, Delta Lead Scientist, noted that after the barrier was installed in 2015, the Council funded studies of the ecological impacts.  “The main adverse finding was an expansion of invasive aquatic weeds within the Franks Tract.  I did see an update on that study when I attended the CWEMF meeting last month.  That study suggested that when the drought barriers are in place, you get the tidal energy that’s redirected over to the north.  It does still enter the Franks track at lower salinity.  And there appears to be almost a jet effect where there’s a clear pathway that’s free of invasive aquatic weeds that’s aligned with that tidal energy.  But really, that expansion of aquatic weeds was noted as the most salient adverse impact.”

What about a permanent solution?

If the drought barrier is so beneficial, Councilmember Lee asked why the Department is not considering a permanent barrier at that location.

Mr. McQuirk said that building a permanent structure required much more planning and design, would cost hundreds of millions of dollars, and take many years to permit, so it’s not possible to do that quickly.  He also noted that it isn’t known if a permanent structure would be something that’s appropriate there.

The Franks Tract Futures project used a collaborative planning process with multiple stakeholders to produce the final design.

But what about a nature-based solution?  Dr. Larsen pointed out that a collaborative planning process was conducted for Franks Tract, which resulted in a design for a wetland in the northwest part of Franks Tract that the model suggested would also be very effective at directing salinity away from this part of the Delta.  “So I wanted to put that out there as something else that could potentially be very effective during dry years.  I can’t speak to its efficacy relative to the barrier during extreme drought; I think it’s probably not as good.  But perhaps having that in place could change the frequency with which a drought barrier would be needed.”

Mr. McQuirk agreed that restoration of Franks Tract is an option.  “It works every day, so you’re getting some salinity management benefits day in and day out by restoring Franks Tract.  So it’s not something that we have to put in to get benefits. … but the drawback is, really, how will we fund this?  This project is over a billion dollars.  So this is really the charge for everybody.  How will we get the federal government to loosen up their purse strings and try to invest in something like Franks Tract?  Because it is a good project but a billion-dollar project.”

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