Altamira Canyon Creek Restoration Project

Project Background

In 2015, due to approximately two decades of severe erosion of the embankments of Altamira Canyon Creek resulting from high storm flows within the creek itself and adjacent drainages, the property owner of 25 Sweetbay Road installed gabion baskets along the eastern bank of Altamira Canyon Creek and along the northern bank of an unnamed drainage. The purpose of installing these structures was to prevent further loss of property and protect the animals in the equestrian facilities immediately abutting the drainages. These rock-filled, wire mesh baskets, along with concrete footings, armored the eroding eastern bank and served to protect the bank from further high flow events. The gabions were installed without proper permits from the United States Army Corps of Engineers (USACE), California Department of Fish and Wildlife (CDFW), and Los Angeles Regional Water Quality Control Board (LARWQCB). Subsequently, after site visits by the USACE and LARWQCB, a notice of violation for failure to obtain a Section 401 Water Quality Certification was issued. The property owner was directed to conduct required biological and engineering studies to support the regulatory permitting process.

Project Location

The Project Site is located in the gated Portuguese Bend neighborhood, north of Palos Verdes Drive South, on the south side of Sweetbay Road, southeast of the intersection with Narcissa Drive, and east of Cinnamon Lane. The section of Altamira Canyon Creek that comprises the Project Site is located along the common boundary between the two properties at 25 and 26 Sweetbay Road. The natural embankments of Altamira Canyon Creek are incised and show moderate slopes to near vertical conditions, with heights of 10 to 20 feet. Portions of the embankments within the Project Site have been modified with protection consisting of concrete and gabion walls. The slope that ascends on the west side of Altamira Canyon Creek is generally at a grade slightly steeper than 2:1 and exhibits a surface slump.

Project Characteristics

In response to the notice of violation, the Project would involve the following:

  • Most of the existing gabion baskets and foundation, grout, and grouted stones that were installed as part of the existing creek embankment protection would be removed. Approximately 100 linear feet of the existing gabion wall and foundations would be removed.
  • Exposed channel bank would be restored to a 2:1 slope.
  • Any channel protection within the Project Site would be removed and restored.
  • Any surface slumps within the Project Site would be repaired.
  • A section of the slope would be reinforced with erosion control mats (i.e., Enkamats[1]) and riprap and earthen fill over the riprap.
  • Areas along the slope would undergo habitat restoration, while other areas within the creek channel would be left in place. The habitat restoration would be implemented in accordance with the Habitat Mitigation and Monitoring Plan (HMMP) specifically prepared for the Project.

The area within Altamira Canyon Creek and the embankments that would be disturbed would be limited to approximately 4,192 square feet and would involve approximately 748 cubic yards of earthen cut, approximately 195 cubic yards of gabion removal, approximately 92 cubic yards of earthen fill, and approximately 679 cubic yards of rock riprap fill.

Please click here to view the Notice of Intent, and here to view the MND and all associated attachments. The last day to provide comments on the Initial Study/MND is February 24, 2023 at 4:30pm.

[1]       Enkamat is an open three-dimensional synthetic mat, consisting of randomly placed filaments of plyamide and nylon. Application of Enkamats is ideal for protection of slopes and embankments against hydraulic loadings and erosion by rainfall and wind and establishment of vegetation on steep weathered slopes.