City of Sunnyvale – Storm Drain Rehabilitation Project
Public Works
In 2023, Brannon Corporation completed the rehabilitation of a 60″ storm drain outfall structure located in the Stevens Creek Channel, which involved significant ecological sensitivity including protected species and habitats (red legged frog and western pond turtles.) Within the ecologically sensitive zone, Brannon implemented dewatering and flow bypass via cofferdam, removed the broken pieces of existing flap gate, pipe, and concrete, and subsequently rehabilitated and stabilized the 60-inch outfall pipe and the channel downstream from it.
      • PROBLEM: Several sections of the existing 60″ corrugated metal pipe, including a flap gate, separated from the storm pipe exiting the creek embankment. The creek bank surrounding the outfall structure and the protective cement sack riprap had been undermined. The rehabilitation was necessary to assure storm water conveyance and mitigate system failure.
      • SOLUTION: Storm drain outfall rehabilitation work to assure storm water conveyance and mitigate system failure.
      • TRANSFORMATION: Brannon rehabilitated the storm drain outfall, as well as restored the creek channel and disturbed areas by revegetating with harvested native plantings (cottonwood stakes and willows.). Brannon achieved a successful project outcome while protecting sensitive species and habitats by implementing the following actions, amongst others: installation of temporary coffer dam, installation of flow-through plugs/bypass system to divert water flow in 60-inch storm drain pipe around work area, installation of dewatering systems and installation of temporary sediment basin, tree removal, channel excavation, installation of outfall protection and pipe bedding stabilization, dewatering and flow bypass via cofferdam to divert flow within the channel, dewatering systems installation of temporary sediment basin, testing for contaminants and proper disposal of removed groundwater, erosion control measures including hydroseed, and revegetation with native plantings via installation of willow and cottonwood stakes, sourcing cuttings from local source, excavating, sorting, stockpiling, inspecting, blending, live poles and planting tubes, topsoil segregation and placement and import or off-haul of surplus materials, hauling, placing, and completing work to the targeted lines and grades, watering and maintaining revegetated plants and areas for a period of 90 days, monitoring survival of willow and cotton wood poles and replacement of poles during establishment phase.