The Semeniuk Slough Maintenance Dredging Project, a cooperative project led by the City of Newport Beach (City) with support by Caltrans, proposes to restore flood conveyance capacity in Semeniuk Slough and the State-owned storm drain box culvert that drains into the south end of the slough to restore the channel within the slough to its original depth of three feet below the Mean Lower Low Water. This depth will match that of the recently restored downstream section at the Santa Ana Marsh by the U.S. Army Corps of Engineers.
The construction work will be performed “in-the-dry” by construction of a temporary sheet pile cofferdam across the channel at the north end and then dewatering the channel. Water pumped out during the dewatering operation will be discharged within a silt curtain enclosure adjacent to the cofferdam. The silt curtain will intercept and contain sediment so any accumulation can be removed at the end of the project. The sheet piling will be completely removed at the conclusion of all dredging work.
Conventional land-based equipment consisting of excavators, blades, and front-end loaders will be used by the City’s contractor to remove approximately 8,500 cubic yards of sediment within the main body of the slough. An additional 2,000 cubic yards of sediment will be removed by the City’s contractor from the storm drainage ditch immediately south of the slough channel and a portion of the Caltrans storm drain.
Sediment deposits within the 14-foot-wide by 5-foot-high box culvert will be removed by Caltrans using a small, low-height, remotely controlled excavator that is specially designed for such work. The excavator will temporarily stockpile material near the entrance to the culvert. All excavated material will be hauled inland and disposed of immediately at an approved and selected disposal site. A temporary 800-foot-long gravel roadway will be placed in the culvert drainage ditch and south end of the Semeniuk Slough channel bed to allow an off-highway truck to haul the sediment from the culvert opening to the highway truck loading area. Approximately 1,000 tons of gravel will be imported and placed in a 15-foot wide, 18-inch thick roadbed section. All gravel will be removed from the channel bed and hauled away after the culvert cleaning operation is complete.
Non-native vegetation will be removed along the east bank of Semeniuk Slough at five locations to provide equipment access. Access points will be selected where non-native plants and non-native vegetation currently exist.
The California Coastal Commission determined that a coastal develop permit is not required for this project and issued the City a De Minimis Waiver on March 10, 2016.
Pursuant to the Contract Specifications, the contractor will have 180 consecutive calendar days to complete project tasks.
For questions about this project, please contact Robert Stein at firstname.lastname@example.org.
Semeniuk Slough Maintenance Project UPDATES
October 25, 2016
The City awards the Semeniuk Slough Maintenance Project to Innovative Construction Solutions. Bob Stein (949-644-3322) is the project manager for the City.
December 27, 2016
The contractor begins mobilization on-site.
January 9, 2017
The contractor begins the installation of the cofferdam near the tennis courts by first creating a gravel road partially across the slough.
January 13, 2017
The contractor completed installation of the cofferdam. The cofferdam includes a spillway that is constructed at a lower elevation. This elevation is 18 inches below street level to allow flood flows to exit the slough without flooding of the adjacent neighborhood.
January 16, 2017
The contractor installed three pumps and completed dewatering of the slough.
January 19, 2017
The contractor modified the dewatering system to allow pumping of some low areas in the slough and to capture flow existing the Newport Shore’s stormdrains.
January 21, 2017
The contractor decided to maintain the pumps in operation during the storm predicted for Sunday.
January 22, 2017, 7 pm
The contractor confirmed that the system is performing well. Water has risen in the slough but is still below the spillway elevation.