Project Goal: There is a long term need to remove nearly half a million cubic yards of sediment from the pool of Swinburne Dam, located at the intersection of Unser Blvd and Irving Blvd. This will lower the elevation by about 15 feet, which is a bigger drop than the existing grade control structures at the outlets of the Main and West Branches of the Calabacillas Arroyo were built to accommodate. To prevent head-cutting and additional sediment transport in the arroyos, both the Main and West Branch grade control structures are being upgraded with 3,300 square yards of shotcrete and 9,000 cubic yards of grouted boulders. Work on the project began in December 2025 and is scheduled for completion in March of 2027.
March 2026 Construction Update: Existing soil cement removals are complete at both the Main and West Branch grade control structures. Excavation is still in progress on the Main Branch, while the West Branch is fully excavated and being prepared for concrete placement. A test panel of the shotcrete was placed on March 23rd, and shotcrete will be installed through April. Boulders are also being stockpiled onsite and will eventually be placed at the bottom of the grade control structures.
Grading and tamping at the West Branch
Excavation at the Main Branch
February 2026 Construction Update: Excavation and soil cement removals are in progress at both the Main and West Branch grade control structures to prepare for the placement of shotcrete. While most of the existing soil cement will remain in place, the downstream edges are being saw cut and removed to facilitate shotcrete tie in.
Aerial view of the West Branch grade control structure
Soil cement removal
[Updated 3/30/2026]