Granite Construction to perform CWA's Moosa Canyon Erosion Control project work

Granite Construction will be performing Moosa Canyon Erosion Control project activities under a contract from the San Diego County Water Authority.

The construction which will place engineered grouted and non-grouted riprap in the creek channel is expected to begin this month and to be complete during fall 2018. An April 12 San Diego CWA board vote approved a $1,235,889.40 contract to Granite Construction for the work.

“This needs to be addressed to prevent further erosion,” CWA senior engineer Mike Conner said.

The Moosa Canyon erosion control project will protect the CWA’s Second Aqueduct by preventing stream bank erosion, preventing head cuts from moving upstream and installing half-ton riprap.

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 water changes direction. A structural analysis of the internal water forces conducted in 2015 indicated that those forces were not a concern at the time, but the CWA was concerned that future storms could cause additional erosion and threaten the suitability of the pipelines at the creek crossing.

“A two-phased approach was implemented to protect the pipeline from future erosion and damage,” Conner said.

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 concrete blocks protected the Water Authority pipeline,” Conner said.

In June 2016 the CWA board authorized a $279,620 professional services contract with Michael Baker International for the design of pipeline protection and for construction phase design support services. The design incorporates the interim repair improvements into a long-term erosion control solution. The CWA board approved the project, along with the environmental Mitigated Negative Declaration and the Mitigation Monitoring and Reporting Program, in April 2017.

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 were prerequisites to advertising the project for bid. The project was advertised for bids, Feb. 14. A pre-bid meeting was held Feb. 20. The bid deadline was March 13, and six firms responded. The Granite Construction bid of $1,235,889.40 was the lowest with L.H. Woods, providing the second-lowest bid at $1,244,000.00. CWA staff reviewed the two low bids and determined that the Granite Construction proposal included all work specified in the bid package.