Progress through Persistence at San Gabriel and Santa Anita
Persistence is a core value at Ames Construction, and our teams showcased this value at the San Gabriel and Santa Anita Reservoirs in California in 2023. Crews made progress in post-fire emergency sediment removal projects despite record water levels and a tropical storm.
Both projects were triggered by the 2020 Bobcat Fire in Los Angeles County. With a lack of vegetation in the watershed after the fire, heavy rains have carried debris into the reservoirs, reducing their capacity.
Persevering at San Gabriel
Ames is excavating and transporting 4 million cubic yards of sediment to drying beds at San Gabriel. At the drying beds, crews work the material to optimum conditions. The material is then transported to a permanent fill site via a 2-mile-long conveyor belt that gains 800 feet in elevation.
Ames removed 700,000 cubic yards of material in 2022, the project’s first season. Between the end of the 2022 season and the start of the 2023 season, the area received more than 50 inches of rain, leading to record water levels and inflows. Ames and Los Angeles County officials responded by identifying which activities would be priorities for 2023, and the project team devised a plan for a successful season despite the late start and difficult field conditions.
With the seasonal scope revised down, work began in earnest in mid-June. Crews rebuilt the access ramp that washed away during the offseason and installed multiple river crossings despite high flow rates.
By mid-August, the project was on pace to exceed the season’s revised goal. Then Tropical Storm Hilary delivered 6 inches of rain in less than 12 hours.
Crews had worked overnight on pre-rain preparations, which limited some of the storm’s impact. But the rainfall damaged the access ramp, destroyed all of the crossings Ames had built, washed away some of the sediment in the drying bed area, and refilled part of the reservoir. The area being excavated was submerged in 5-10 feet of water.
Within days, crews rebuilt the ramp and had the conveyer up and running. Despite the season’s challenges, the project finished strong, removing 470,000 cubic yards of sediment, which was on the high end of the revised seasonal goal.
“Through determination, the team adapted and overcame Tropical Storm Hilary,” says San Gabriel Project Manager Chris Sandez. “Everyone was committed to making the most of the season, regardless of the number of challenges we faced.”
Belting and excavation operations will begin again in full force by June 2024. The project’s final two season will also include repairs related to scour discovered within the existing main outlet tunnel during inspections in 2022. The tunnel is 800 feet long and sits more than 90 feet below the access point.
Ames will also construct three new debris basins within the current fill site. These basins will require more than 200,000 pounds of rebar, 1,700 cubic yards of concrete, and the in-place construction of three, 20-feet-tall concrete intake towers.
Clearing hurdles at Santa Anita
West of the San Gabriel Dam, Ames is removing more than half a million cubic yards of built-up sediment and debris from the reservoir behind the 96-year-old Santa Anita Dam.
The Santa Anita project team faced the same challenges in 2023 as San Gabriel. From the time of the project bid to the first working day on the project, rainfall washed nearly 220,000 additional cubic yards of sediment into the reservoir and wiped out sections of a mile-long portal access road.
After reconstructing the access road, Ames installed conveyor belts from the reservoir to the sediment placement site. All sediment must be conveyed through an existing tunnel, which was covered by 30 feet of sediment before the extreme weather. With the new sediment deposits, Ames crews excavated nearly 60 feet deep to reach the tunnel.
The project team was preparing to begin conveying sediment when Tropical Storm Hilary hit. Despite the setback, the team was able to move more than 101,000 cubic yards of sediment by early November.
Caution! Peregrine falcons nesting
The Santa Anita Reservoir is home to a peregrine falcon nest, and if the nest is active, work each season may be restricted until June 1.
Nest activity occurred later than usual in 2023 because of the wet weather. To keep the project moving, Los Angeles County provided a full-time biologist to monitor the nest during construction activities.
Ames proceeded with caution to minimize disturbances, ceasing operations if the biologist noted any abnormal activity. The nest’s three chicks fledged by July 20 without incident.
