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Managing Delta Salinity in Time of Drought

August 2014

An unforgiving challenge facing those who manage the Delta’s water supply is keeping high salinity levels at bay – or at least, in the Bay. Doing so means continuously flushing the Delta’s waterways with a healthy supply of fresh water emanating from various Northern California watersheds, something that’s in short supply given California’s persistent drought conditions.

To learn more about the drought and its potentially detrimental effects on Delta agriculture, the fish and wildlife that live in the estuary, and the water supply required for human use, the Delta Stewardship Council hosted a panel of water managers at its July 25, 2104 meeting to discuss the challenges of managing salinity conditions whenever fresh water is scarce. Included were:

John Leahigh, principal engineer, Department of Water Resources (DWR) – State Water Project Operations
Mark Gowdy, senior water resources control engineer, State Water Resources Control Board’s (SWRCB) Division of Water Rights
Cindy Garcia, chief, Department of Water Resources (DWR) – Municipal Water Quality Investigations Program
John Herrick, counsel and manager, South Delta Water Agency

John Leahigh used a PowerPoint presentation to explain the basics of how the State Water Project (SWP) and the Central Valley Project (CWP) currently operate to maintain the appropriate salinity levels in the Delta.

“We store fresh water in our respective State and federal reservoirs in the winter and spring,” said Leahigh. “That’s our opportunity to store that water so that we can release it later in the summer and the fall to meet beneficial uses in the system.”

Leahigh told the Council members that the SWRCB has set criteria dictating how much of the natural flows need to pass through the upstream reservoirs to provide Delta inflow and salinity management. He said the SWRCB has three types of flow criteria; those for fish and wildlife, those for municipal and industrial (human) use, and criteria for agricultural purposes.

“It’s a big tug of war between the salts and the fresh water,” said Leahigh. “On the salt side of things, that’s driven by the tides, which are out of our control. We only manage on the fresh water side of it.”

DWR has three fresh water tools at its disposal for salinity management. They are:

• Releases from the upstream reservoirs
• Opening and closing the Delta Cross Channel Gates located near Walnut Grove, CA
• The amount of water exported from the Delta

Leahigh says his agency adjusts each of these tools depending on how far and how fast the salinity is intruding into the Delta.

“The salts tend to creep in more prominently during spring tides and the most extreme tides occurring each month. These are predictable because they can be measured by the movement of heavenly bodies like the moon,” said Leahigh. “But, meteorological events are less predictable. A storm event and the associated winds have a bearing on tidal changes. And the State and federal projects need to respond to these events.”

Which tools are used depends on how fast the agencies need to respond. For instance, Leahigh says water released from the Shasta Dam takes five days to travel to the Delta, whereas water released from the Oroville Dam takes three days.

If a more rapid response is necessary, he says they may simply adjust the amount of water exported from the Delta. “We can generally affect the salinity levels within a day by reducing the exports, thereby leaving more fresh water in the system.”

Using the Cross Channel Gates is a difficult decision he says because of the legal constraints imposed by water project Biological Opinions that focus on the habitat requirements for endangered fish in the Delta. Leahigh says normally it’s better for salinity control purposes to have the gates open. But that, he says, conflicts with fish migration periods, which is why regulations and a court order require gate closures.

“There is a cost to keeping the gates closed,” said Leahigh. “The fresh water flows become less efficient to meet the SWRCB criteria, which in turn requires either additional flows from the upstream reservoirs or less exports to compensate for the closure of the gates.”

Add to the equation a persistent drought resulting in less available fresh water and the entire exercise becomes more problematic.

The result, Leahigh says, was DWR petitioning the SWRCB to modify its spring Delta flow criteria to lessen the need for reservoir releases thereby saving water for releases later in the year. DWR also proposed installing two emergency drought barriers to stem the tide of salt water intrusion. Fortunately, February and March experienced above average rainfall allowing DWR to “limp along” without the barriers – something Leahigh says may not continue next year.

“Reservoir storage levels will likely be lower going into 2015 than they were going into 2014,” said Leahigh. “That means we will once again consider adjusting the Delta criteria and installing the drought barriers as a last resort.”

Mark Gowdy, an SWRCB engineer, also used a PowerPoint presentation that offered specifics about salinity and how it damages crops. “The problem is not just about the sodium chloride (table salt). It’s also about the other dissolved ions found in the water including calcium and magnesium.”

Gowdy says the SWRCB has been focused on the southern Delta where they check for compliance with existing SWRCB criteria by reviewing electrical conductivity measurements. The issue in the southern Delta is on how salinity affects crops, particularly in the way salty water stresses plants.

“As a plant extracts water, it leaves whatever salts are in the water behind through osmosis,” said Gowdy. “But, as the salinity levels increase in the soil around the plant’s roots, the plant has to exert more energy to repel the salts. This takes away energy for the plant to grow and ultimately affects yield.”

The SWRCB also enlisted the help of Dr. Glenn Hoffman, a retired U.S. Dept. of Agriculture salinity expert, says Gowdy. Dr. Hoffman studied the effects on crops occurring in the southern Delta and devised a “Steady State Yield Impact Modeling Approach” to help the SWRCB with review of its salinity objectives. He used dried beans as his “canary in the coal mine” to base his recommendations because of the crop’s salinity sensitivity.

Other details of the modeling approach can be found on page 68 of Dr. Hoffman’s report Salt Tolerance of Crops in the Southern Sacramento-San Joaquin Delta, which became part of the SWRCB’s Bay-Delta Plan Update for salinity objectives.

Cindy Garcia, who monitors water quality for municipal use, then offered her thoughts on how the drought’s persistence is affecting water deliveries to customers south of the Delta. She says her southern Delta monitoring stations are noting higher concentrations of bromide (a component of salinity). Bromide, a naturally occurring chemical compound typically present in seawater, can be converted to toxic byproducts when water is treated for household use.

“With the drought, and without that extra fresh water coming from the upstream reservoirs to push that salt water out, you see salinity intrusion at our southern Delta pumps,” said Garcia. “This is of particular concern to the South Bay customers who get their water in a matter of hours after leaving the pumps. The South Bay Aqueduct managers require constant data from us so they can react quickly if the salinity levels become too high. They may have to take fresh water from Lake Del Valle or switch to groundwater sources.”

Finally, John Herrick, general manager of the South Delta Water Agency, offered some comments from an “in-Delta” perspective. He told the Council members that his primary salinity concern is that the salt coming into his region has nowhere to go.

“There isn’t any mechanism that flushes the salts out of our area,” said Herrick. “There’s some upstream storage dedicated to dilute it, but there’s nothing to get it out of the area.”

Herrick believes there is a solution to the issue, but admits that some may find it contentious, especially during the drought conditions.

“Water diverted from the State and federal pumps and put it into the San Luis Reservoir could actually be released back into our area to maintain fresh water quality,” said Herrick. “Now that’s very controversial and nobody wants to do that. But, I believe it’s appropriate because of the drought situation we find ourselves in. In order to meet fresh water quality standards last year and this year, we rolled the dice that natural flows would take care of that – and we lost.”

You can view the entire hour-long discussion, by clicking here and then selecting Agenda Item 10.

Coequal goals

The Delta Stewardship Council was created in legislation to achieve the state mandated coequal goals for the Delta. "'Coequal goals' means the two goals of providing a more reliable water supply for California and protecting, restoring, and enhancing the Delta ecosystem. The coequal goals shall be achieved in a manner that protects and enhances the unique cultural, recreational, natural resource, and agricultural values of the Delta as an evolving place." (CA Water Code §85054)