Minako American Corp. to rehabilitate Diamond Valley Lake wave attenuator

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Minako American Corp. has been given the Metropolitan Water District of Southern California contract to rehabilitate the wave attenuator at Diamond Valley Lake.

MWD’s Oct. 13 board meeting included the approval of a $276,373 contract with Minako, which is based in Gardena. The MWD board also found that the work on an existing facility is categorically exempt from California Environmental Quality Act review.

Diamond Valley Lake includes the east marina which has public access for boat launches and rentals. Wind can generate waves on the lake which can be a challenge in launch areas, and the waves can also create the risk of property damage. In 2006, MWD constructed a floating wave attenuator to reduce the impact of wind-generated waves. The reduction of waves traveling across the lake focused on protecting boat ramp operations. The wave attenuator is approximately 1,300 feet away from the boat ramp and is held in place with a system of anchors and cables.

The wave attenuator is 800 feet in length and 8 feet wide. It has a depth of 8 feet and also has a metal skirt system which extends down below the waterline. The 16 reinforced concrete box segments are connected with post-tensioned cables running throughout the attenuator’s length.

Because the wave attenuators are now 14 years old and have operated in a harsh environment, they have incurred significant damage including cracked concrete sections with exposed reinforcing bars. Some of the post-tensioned cables are broken and no longer connect the concrete box segments, which makes the system non-rigid and structurally inefficient. The wave attenuator has a lessened ability to dampen waves during periods of high winds and waves.

Further deterioration may prevent visitors from safely maneuvering and berthing boats at the docking facilities. In April, the rehabilitation of the wave attenuator was included in MWD’s two-year capital investment plan. The rehabilitation work will replace 900 feet of cable tendons which link the 16 reinforced box segments, reinforce the polyurethane spacers which separate and buffet the reinforced box segments and replace the damaged concrete. During the study phase of the project, MWD staff considered replacing the existing wave attenuator with a new attenuator, but that process would have taken more than two years to complete and a functional attenuator is required for continued recreation. In the future, MWD staff will evaluate a long-term solution which considers updated attenuator designs and expansion of the attenuator system to accommodate potential future improvements to the marina.

The advertisement for bid on the contract to rehabilitate the wave attenuator was issued July 9. Two firms responded by the Sept. 1 deadline. The Minako proposal, which includes subcontractor work by Dywidag Systems International, had the lower bid. The $276,373 bid amount was under the engineer’s estimate of $348,000.

The $440,000 budget for the rehabilitation of the wave attenuator also includes $65,000 for submittal review, technical support during construction, responding to requests for information and preparation of record drawings, $38,000 for contract administration and project management, $28,000 for construction inspection and $32,627 for contingencies. An additional $175,000 has already been spent for design, bid preparation and other activities so the total estimated project cost is $615,000.

The construction is expected to be complete in June 2021.

Joe Naiman can be reached by email at jnaiman@reedermedia.com.