CWA approves Moosa Canyon erosion control project

The San Diego County Water Authority approved the Moosa Canyon erosion control project.

The SDCWA board action April 27 also approved the project's environmental Mitigated Negative Declaration and the Mitigation Monitoring and Reporting Program. The project will protect the CWA's Second Aqueduct by preventing stream bank erosion, preventing head cuts from moving upstream, and installing half-ton riprap.

"We are working towards getting that work done before the next rainy season," said CWA Water Planning Committee chair David Cherashore, who is one of the City of San Diego's representatives on the CWA board.

The CWA's Second Aqueduct includes Pipelines 3, 4, and 5. The pipelines transport water through steep terrain and cross under Camino Del Rey in Bonsall. Moosa Creek is a riparian environment with dense vegetation, and in 2013 CWA staff observed that a portion of Pipeline 4 was exposed in Moosa Creek due to creek bed erosion. The location coincides with a horizontal bend in the pipeline where the pipeline crown is visible.

The exposed bend in Pipeline 4 is subject to internal water force, or thrust, as the water changes direction although a structural analysis of the internal water forces indicated that those forces are not currently a concern. The CWA is concerned that future storms could cause additional erosion and threaten the suitability of the pipelines at the creek crossing.

During 2016 CWA staff installed interim erosion control measures to restore cover over the pipeline and stabilize the area prior to the next wet season. "The improvements are performing as intended," said CWA senior water resources specialist Don Chadwick.

In June 2016, the CWA board authorized a $279,630 professional services contract with Michael Baker International, Inc., for the design of pipeline protection. That 30-month contract includes design services, bidding services, and construction phase design support services.

The CWA held a public hearing on the draft environmental Mitigated Negative Declaration for the Moosa Canyon erosion control project Feb. 23, and the hearing did not produce any opposition to the draft MND. The MND cites less than significant impacts for all environmental categories other than riparian habitat, and a combination of on-site restoration and off-site acquisition will reduce that impact to less than significant.

A revision to the draft MND describes changed site conditions due to erosion from the storm in late February. That change did not create any new significant impacts or the need for additional mitigation measures, although it has not yet been determined whether the changed conditions will extend the construction schedule or increase the cost of the project.

During the 30-day public comment period from Feb. 6 to March 8 two written comment letters were received. The letters from the Native American Heritage Commission and the County of San Diego focused on flood control and traffic. The comment letters and responses are included in the final MND.

Prior to construction, the project will still require temporary right-of-way agreements, a U.S. Army Corps of Engineers letter allowing the project, and a streambed alteration agreement with the California Department of Fish and Wildlife. Once the requirements to proceed are met, the CWA will advertise the project for bid. The actual construction is expected to begin in fall 2017 and take approximately 40 workdays.