November, March shutdowns set in CWA's 2020-2021 Aqueduct Operating Plan

The San Diego County Water Authority has an annual Aqueduct Operating Plan, and the SDCWA’s 2020-2021 plan was presented at the Thursday, July 23, CWA board meeting as a non-voting item. The 2020-2021 plan includes shutdowns due to planned maintenance, and Fallbrook Public Utility District and Rainbow Municipal Water District turnouts will be impacted by a November shutdown to Pipelines 1 and 2 and a March 2021 shutdown to Pipeline 5.

The shutdown of Pipelines 1 and 2 will allow for the removal of the bulkheads which were installed as part of the relining and other rehabilitation of the First Aqueduct pipelines. The Pipeline 5 shutdown will allow for a warranty inspection along with the installation of turbine train isolation valves.

The aqueduct operating plan is used as a planning element to optimize the delivery, treatment and storage of water in the CWA’s service area by facilitating coordination and communication among the CWA, its member agencies and the Metropolitan Water District of Southern California.

The AOP includes a summary of scheduled shutdowns or outages which impact delivery of treated or untreated water, pump station operating schedules, member agency major maintenance information and the production and consumption of energy for CWA hydroelectric facilities, pump stations and the CWA’s treatment plant.

The plan utilizes information obtained from member agencies, historical delivery data, aqueduct constraints and shutdown plans. A shutdown is defined as a temporary closure of a large portion with regional effects while an outage is defined as a more localized portion closure and impact.

Currently five CWA pipelines carry water along the San Diego Aqueduct from MWD’s Lake Skinner facility in Temecula. The First Aqueduct consists of Pipelines 1 and 2 and the Second Aqueduct has Pipelines 3, 4 and 5. Pipelines 1, 2, and 4 convey treated water while Pipelines 3 and 5 deliver untreated supply. The aqueduct system has a treated water capacity of 650 cubic feet per second and an untreated water capacity of 780 cubic feet per second.

The First Aqueduct pipelines are the oldest in the CWA’s system. Construction on Pipeline 1 began in 1945 and water was first delivered in 1947. Pipeline 2 was constructed between 1952 and 1954 and brought online in 1954. Both are primarily reinforced concrete pipes with welded steel pipe being utilized in high-pressure siphons.

The First Aqueduct also includes 10 flow control facilities which were built between 1954 and 1987; some of those flow control facilities connect to both pipelines while others connect to only one. The northern portion of the First Aqueduct runs from the delivery point, where the CWA takes water from MWD 6 miles south of the San Diego County line, to Hubbard Hill in Escondido.

The southern portion of the First Aqueduct delivers water from Hubbard Hill to the San Vicente Reservoir in Lakeside.

An inspection of the steel pipelines in the First Aqueduct revealed deterioration of the original pipe lining, which created corrosion damage. In December 2018, the CWA board approved a contract to rehabilitate a portion of the First Aqueduct.

The project will rehabilitate 3 miles of steel pipe lining through 12 access portals and will also rehabilitate 60 pipeline and valve access structures by installing new piping, valves, access hatches and ladders. The lining will be removed and replaced from the inside to minimize excavation and community impacts.

Construction began in 2019, and Pipelines 1 and 2 were taken out of service alternatively to rehabilitate both. The work schedule allows construction to occur during extended aqueduct shutdowns, and the rehabilitation is expected to be complete in spring 2021.

The shutdown of Pipelines 1 and 2 is expected to begin Nov. 1 and last through Nov. 10. Total treated water capacity will be reduced by 180 cubic fee per second during the shutdown. Fourteen CWA member agency turnouts will be impacted including two providing water to Rainbow and one supplying FPUD.

In May 2018, the CWA board awarded a contract to J.F. Shea Construction Inc. for the relining of Pipeline 5. The project relined two sections of the 96-inch pipeline: a 10,000-foot segment from the delivery point to Sage Road and a 2,300-foot portion just north of the Twin Oaks Valley Treatment Plant. The work was completed in 2019, and J.F. Shea posted a faithful performance bond which guaranteed completion of the work and which will remain in force for the construction’s two-year warranty period.

The shutdown from March 8, through March 17, 2021, will allow for a warranty inspection. The isolation points will be at the Red Mountain and the Twin Oaks Diversion areas. Pipeline 3 will be reconfigured before the shutdown to maintain untreated water deliveries of up to 280 cubic feet per second.

Joe Naiman can be reached by email at [email protected].