San Francisco, CA
Located at Crissy Beach in San Francisco,CA, this project involved a large Caltrans storm water outfall pipe that conveys rainfall and run-off from Doyle Drive to the Bay. The outfall pipe was replaced, enlarged, and extended in order to alleviate on-going flooding issues related to sand accretion along the beach.
The existing outfall was installed across Crissy Field and terminated at the shoreline of the Bay. Sand accumulation from tides had been causing the pipe to plug frequently, requiring costly excavation and clearing. Enlarging the pipe and extending it into the Bay was the solution to the problem. The existing 42-in HDPE pipe (high density polyethylene pipe) was expanded to 54-in and the new discharge point extended almost 500 feet out into the Bay in deeper water.
The two biggest challenges of the project were the environmental sensitivity of a construction site inside a National Park and the rigorous in-water and shoreline timeline of 10-weeks.
Construction occurred in three distinct stages: 1-beach, 2-intertidal, and 3-offshore. Each stage was characterized by different conditions, all subject to unique methods of construction. To take on the timeline challenge, Power found opportunities to overlap stages and gain efficiency. The ability to execute on this type of schedule had much to do with Power’s 30 years of experience with marine and civil construction near, on, and under water.
The environmental challenge was addressed using a rigorous checks and balances system to carry out meticulous protective measures every step of the way. A fabric and mat system was designed to keep heavy construction equipment off the beach and to protect native vegetation. Marine mammal, terrestrial, and acoustic monitors were onsite at all times keeping a close eye on the project boundaries. A rough water turbidity curtain was deployed around the in-water construction within the tidal zone to contain turbid water from sheet pile installation and dredge spoils. Turbidity testing was necessary every two hours to ensure turbidity was indeed contained and surrounding waters were unaffected. A high volume air bubble curtain, which is considered cutting edge technology, was utilized to protect marine life from noise generated by the hydraulic impact and vibratory hammers. The project was permitted and successfully completed with a zero take allowance for fish, bird, or marine mammal casualties. Throughout the project there were zero safety or hazardous environmental incidents in the Bay.
Power’s 100-ton derrick barge, 20-ton derrick barge, material barges, and ADC certified dive crews were essential for the dredging, shoring, pile driving and underwater construction necessary to accomplish this work.
This project was completed two months ahead of the contract schedule, prior to all work window deadlines, and within budget.
“Although our project was carefully designed and planned it was in a terrestrial and environmentally sensitive marine area and was also under a very tight construction window. This was of great concern to us. Power had to adhere to some very strict project specifications and permit conditions. Power’s communication with their client in the form of Bidder Inquiries, RFI during construction, problem solving skills, and expertise significantly aided in a high risk project to be completed with minimal issues and ahead of schedule. Their communication with us throughout the project was invaluable.”
—Peter Aguilera, P.E., CalTrans Project Engineer