A drone provides a view of a section of the California Aqueduct within the California State Water Project, located near John R. Teerink Pumping Plant, which convey California Aqueduct water between Buena Vista and John R. Teerink Pumping Plants within Kern County. Photo taken March 28, 2019. Ken James / California Department of Water Resources, FOR EDITORIAL USE ONLY

CA WATER COMMISSION: Addressing California Aqueduct subsidence; State Water Project Operations and Maintenance

At the November meeeting of the California Water Commission, Commissioners were briefed on subsidence issues with the California Aqueduct and current construction and maintenance projects underway for the State Water Project.


Dan Whisman, Program Manager of the Department of Water Resource’s California Aqueduct Subsidence Program (or CASP) who gave a brief background and update on the efforts being undertaken in response to subsidence of the California Aqueduct in the San Joaquin Valley.

The California Aqueduct is the main artery of the State Water Project; it begins in the Delta and has multiple terminations in Riverside, Los Angeles, and Santa Barbara counties.  The aqueduct supplies water for residential, municipal, and industrial use to 27 million Californians, as well as provides water to irrigate 750,000 acres of farmland, mostly in the San Joaquin Valley.

During the 2012 to 2016 drought, the California Aqueduct experienced up to 3 feet of subsidence in some areas in the San Joaquin Valley; the subsidence is projected to continue if no action is taken.

The damage

The map shows the subsided areas in red that have occurred along the 222 miles of the California Aqueduct that lies between San Luis Reservoir in the north and the Edmonston Pumping Plant at the base of the Tehachapi Mountains to the south.

The California Aqueduct Subsidence Study of 2017 and the California Aqueduct Subsidence Supplement of 2019 determined that the subsidence of the California Aqueduct is in response to deep groundwater pumping.  Just during the four years of the drought, over 2 feet of subsidence occurred in some locations, which has reduced the design flow capacity of the aqueduct up to 33% and consequently, the California Aqueduct has suffered a reduction of operational flexibility and operational efficiency.

The chart on the slide at the lower left shows the reduction in flow capacity of the pools of the California Aqueduct in the San Joaquin Valley.  The blue lines indicate the original design flow capacity in cubic feet per second and the red lines indicate the flow reductions due to subsidence in various pools.  Mr. Whisman pointed out that pools 20 and 21 have a design flow capacity reduction of 33%.

The diagram on the slide on the upper right shows a cross-section of the California Aqueduct canal in the original design condition above and a subsided cross-section below.  Subsidence causes multiple adverse impacts, including decreased flow capacity, decreased operational efficiency, decreased system reliability, increased maintenance, and operations.

In addition to the subsidence of the canal lining, other features and appurtenances of the Aqueduct are also subsiding.  The photos on the slide show a check or gate structure designed to control flow between the canal pools of the California Aqueduct.  The photo on the left shows the beam supporting the gates that have subsided to the point it is restricting flow in the canal; the photo on the right shows the gate arm resting in the water where it is becoming corroded.

The Check 17 photo on the left shows the support for the gate arms underwater due to the subsidence of the check structure; note the corrosion.  The photo on the right shows the gate arms of check 20 supported above the water as designed.

Subsidence also damages the canal liner and embankment as shown in the picture.

Takeaways from the subsidence study

Key takeaways from the California Aqueduct subsidence study and recent experience in operating the California Aqueduct include:

  • a need to restore design flow capacity
  • a need to restore key operational flexibility
  • a need to strengthen the infrastructure resilience
  • a need to improve operational efficiency
  • supplemental funding for this effort is warranted and is being pursued to augment traditional funding sources to address these needs.

Addressing the cause of the subsidence

The 2014 Sustainable Groundwater Management Act has created a new framework for groundwater management that has led to the formation of local Groundwater Sustainability Agencies responsible for managing groundwater basins.

This allows the CASP to engage with GSAs in an effort to ensure the goals established in their groundwater sustainability plans will avoid future subsidence to the California Aqueduct,” said Mr. Whisman.

Next steps

There are two projects within the California Aqueduct Subsidence Program that are focused on different aspects of subsidence:

The rehabilitation project is engaged in near term activities over the next five years to maintain water deliveries to contractors.  The projects include raising 35 miles of the California Aqueduct, reconstructing check structure 17 at the downstream end of pool 17, raising bridges and relocating crossing infrastructure, and raising turnout structures.

The recovery project is addressing long-term subsidence and is developing a recovery plan, including an alternative study to implement enduring repairs to the California Aqueduct.

We are developing the plan in a time of changing regulatory, energy, environmental, cultural, and climate influences that have emerged since the initial construction of the California Aqueduct,” said Mr. Whisman.  “We are approaching the process with resilience, sustainability, and multiple benefits in mind and that the California Aqueduct meet these changes.  In consideration of the needs of the millions who rely on the California Aqueduct, stakeholder engagement is a cornerstone of our planning process.  Stakeholder outreach will begin in early 2021.”


Behzad Soltanzadeh, Assistant Division Chief Division of Operations & Maintenance with the State Water Project next briefed the Commission on the status of the major State Water Project investigative, construction, and refurbishment efforts for 2020.

The Division of Operations and Maintenance within the Department of Water Resources is the caretaker of the assets within the State Water Project.  There are five main field divisions that stretch from Oroville all the way down to Southern California, as well as two support groups in Sacramento, Centralized Operations and Engineering Support.

Mr. Soltanzadeh noted that every year, they go through a budgeting process which includes assigning priorities to 300 to 400 projects.  They consider the risk, the resources available, and the risk to the operational viability of the State Water Project, and generally select about 200 projects to be done in any given year.  Most of the projects are multiyear, multiphase projects, and take many years to complete.

State Water Project Fire & Life Safety Modernization

This project was triggered by a fire in the Thermalito Powerhouse on Thanksgiving Day in 2012 in which the plant sustained major damage.  The Thermalito plant is one of the few plants with a bypass so the Department was able to continue water deliveries while work was underway to restore operations at the plant.  The incident also triggered a system-wide update of fire detection and suppression systems, HVAC systems, emergency response communications, and other issues to make sure all the facilities are up to date.

The project started with the Oroville Field Division, and at this time, the fire suppression and fire notification systems have been updated and the project is mostly complete.  They have nearly completed the design process for the San Luis Division and are working towards construction.  They are working on the initial design phases for the San Joaquin Field Division.  Mr. Soltanzadeh noted that as they go to the next phase of the project, they are incorporating the lessons learned into the construction of future phases to ensure efficiency and ease of construction.

California Aqueduct Canal Liner and Embankment Repairs

Mr. Soltanzadeh noted that the canal is about 700 miles long, and while the California Aqueduct Subsidence Program is addressing the subsided areas, there are other parts of the aqueduct that need to be maintained.  As part of the conditions assessment program, the full length of the aqueduct is inspected each year.  Any problem areas such as cracks or leaks are documented, the repairs are prioritized, and targeted construction contracts are issued based on a priority and risk assessment.

In 2021, 35 to 45 sites have been identified.  Some of the repairs may take multiple years.  Some of the repairs are in the water and will require divers and special equipment, and some work is needed on the embankment.

We are not doing any embankment raise or anything like that,” said Mr. Soltanzadeh.  “This is just natural condition assessment repairs, and it is ensuring that the California Aqueduct is resilient and we are preserving the operational reliability of the aqueduct.”

State Water Project Pipeline Assessment

The State Water Project has a number of pipelines; most are located in Northern California in the Delta Field Division, there are some in the Coastal Aqueduct in the San Joaquin Field Division, and a large portion in Southern California in the Southern Field Division.  Traditionally, assessing the condition of the pipelines required dewatering the pipelines to go inside and inspect the pipeline.  However, new technologies have come online in the last 3 to 4 years that allow the same type of assessments almost the water in the pipeline and minimum impact on the operation of the pipeline.

It requires for provisions to be installed in the pipeline for the deployment and retrieval of these items, but they are very critical in identifying if we have any leaks on the pipeline and based on that, the integrity of the pipeline and also use that information to inform priorities on which pipelines we’re going to take on and what contracts we’re going to take on,” said Mr. Soltanzadeh.

Southern Field Division East Branch Maintenance Outage

One of the projects that maximized many of the condition assessments that had been done is the Southern Field Division East Branch Maintenance Outage.  There were repairs that needed to be done as well as the regulatory requirement of exercising the gates on some of the dams, so they worked to coordinate the projects to do them all under one outage and minimize the unavailability of the State Water Project.

This particular project was in the San Bernardino area and the Devil Canyon Power Plant. During the outage, they worked on the San Bernardino Tunnel and Intake Tower; the Devil Canyon Powerplant Penstock; worked on the Devil Canyon 2nd Afterbay, and the Santa Ana Valley Pipeline.   They also performed the regulatory requirements of operating the gates on the dam which had to be witnessed by the Division of Safety of Dams.  All tasks were accomplished within that planned outage.

South Bay Aqueduct Reliability Improvement Project

With the South Bay Aqueduct Reliability Improvement Project, they are working with Santa Clara, Alameda, and Zone 7.  Anderson Reservoir, one of the reservoirs that supply water to their customers, has seismic issues and is being drained in order to make seismic retrofits.  This means that for a period of time, those contractors will be single-sourced out of the South Bay Aqueduct.

They are going to be single-sourced in February of 2021, so we’re taking an outage on and starting in December into January of about 6 to 7 weeks to do some preemptive and proactive measures to install some seals and to do some repairs that increase the reliability and the level of service on this pipeline,” said Mr. Soltanzadeh.  “We’ve coordinated this with those three contractors and also we’ve done the preparatory work to be able to get the contract out and the water contract and be ready for that outage that is upcoming.”

California Aqueduct Radial Gate Maintenance and Repairs

There are about 250 gate structures and radial gates along the aqueduct and on the gated spillways of the 26 dams of the State Water Project. These gates are used to control the flow of the water and to isolate pools in the aqueduct when maintenance or repairs are needed.  About 5 to 10 of them are refurbished in any given year.

It’s a big job to improve the structural capability of these gates,” said Mr. Soltanzadeh. “We do corrosion repairs, we do welding repairs, and we blast and coat them for future protection.  This is important for the reliability and operational availability of the SWP.”

Cedar Springs Dam Spillway Under Drain Repairs and Access Road Improvements

There were a number of projects triggered by the Oroville Spillway incident and the lessons learned from that.  One of those is the Cedar Dam project in San Bernardino County.  The dam stores 75,000 acre-feet of water.

An access road was installed to facilitate future inspections, the underdrains of the spillway were cleaned, and the collector drains were replaced.  The project is for the most part complete with the exception of some minor work that will be completed in the next year.

Pyramid Dam Gated and Emergency Spillway Investigations

Pyramid Dam, located in Los Angeles County, has two spillways: an unlined emergency spillway and a gated spillway.  The project included exploratory drilling on both the emergency spillway and the gated spillway to inform future risk and engineering analysis.  As the terrain is very steep, it was difficult work requiring a helicopter with rope access.

Right now we have collected the data that is going to inform the engineering analysis and risk analysis that will determine what the next steps are,” said Mr. Soltanzadeh.  “What we found based on the preliminary result is that the chute of the concrete lining of the gated spillway is much thicker than what we thought and the erodible rock on the emergency spillway is much shallower than we thought, so that is some good news, but we still have to go through the risk analysis and engineering analysis.  We’re working in coordination with both the FERC and DSOD which are the regulators of this dam, so there are going to be future phases of this project upcoming.”

Bethany Dams Restoration and Rodent Burrow Prevention Project

Bethany Dam is located in the Delta Field Division 10 miles northwest of Tracy.  It has sustained a lot of rodent damage with ground squirrels so they have been coordinating with the Division of Safety of Dams to do the needed repairs.  There were a lot of challenges to this project, mainly due to the environmental permitting and three protected species that are in the area.

The permits have now been acquired and they have approval from the Division of Safety of Dams, so construction is scheduled to start in the spring of 2021.

Castaic Dam Outlet Tower Bridge Seismic Retrofit

Castaic Dam is located in Los Angeles County downstream of Pyramid Dam and is the terminus of the West Branch of the California Aqueduct.  This project involves retrofitting the bridge to prevent collapse for the 50th percentile maximum credible earthquake.  The project is expected to begin in the spring of 2021 and completed in 2022.

The spillway of the dam is also being assessed and there will be future construction activities and modernization of the instrumentation of this dam in the future.

Thermalito Restoration Project

After the fire at the Thermalito Pumping Plant in 2012, the facility has gone through an extensive construction project to replace the electrical, mechanical, and other features.  This project has now been completed and has been turned over to the Oroville Field Division, the custodian of the plant, in September of this year.

This is one of the major accomplishments and concludes our reporting of the project,” said Mr. Soltanzadeh.  “It’s one of the most modernized plants that we have on the State Water Project.”

Edmonston East Motor Generator Failure

The Edmonston Pumping Plant is one of the largest pumping plants on the State Water Project.  It is located south of Bakersfield at the foot of the Grapevine and it lifts the water 2000 feet over the Tehachapis.  The plant is unique in that the pumps are so large, there are two generators that are used to “soft start’ the main pumps.  These generators are approximately 50 years old and have been in service without a major overhaul; without these, the main pumps cannot be started so this is a major single point of failure on the State Water Project, Mr. Soltanzadeh said.

There was a failure earlier this year, so they refined the maintenance plans.  The repairs were made in two months.

One of the innovative things that we did, instead of removing the entire generator which historically has been done and put on the top floor of the plant to do the repair, we did the repair in place by sliding some of the components to the side to be able to achieve that,” said Mr. Soltanzadeh.  “We documented that for future use.  We are going through a process of identifying and purchasing a lot of the long lead items of these motor-generators to ensure that in the future, we enhance the operational availability of the plant and we don’t sacrifice any water deliveries.”

SWP Switchyard Instrument Transformer Modernization

The State Water Project has 30 pumping and generating plants, each one with a switchyard (or substation) that isolates the pumping and generating plants from the utility and isolates the utility from the pumping and generating plants.  The equipment is approximately 50 years old and is beyond the design life.

In February of 2020, there was a failure in the switchyard at the Banks Pumping Plant, which was quickly repaired.  As a result, they refined their testing, monitoring, and surveillance of the switchyards, as well as looking at the other switchyards in the system to identify similar components that are vulnerable to failure and are in the process of replacing those.

SWP Control, Protection, And Regulatory Compliance Asset Replacement

A lot of the assets, such as the pumps, motors, generators, turbines, and gates are controlled remotely through the pumping and generating plants, area control centers, or through centralized operations in Sacramento.  This requires communication infrastructure, control infrastructure, and electronics, as well as regulatory compliance assets aspects of these that are monitored and regulated by the federal government.

We get audited periodically on these components,” said Mr. Soltanzadeh.  “These electronic components have basically a life of 15 to 20 years, so in order to make sure that we don’t have obsolescence within our SWP and we meet the regulatory requirements and also ensure that we maintain the reliability of the SWP, we constantly go through projects and construction contracts to test and replace these, so these items are not only protected by also are up to date and we have sufficient spare parts and support for these.”

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