Evaluation of Portuguese Bend Landslide
The city geologist has issued an opinion letter regarding development within the city's Landslide Moratorium Area. In summary, the city geologist has opined that:
- From a geologic and geotechnical perspective, the city should continue to prohibit construction on vacant lots within the entire landslide moratorium area
- From a geologic and geotechnical perspective, it is not detrimental to the landslide moratorium area to continue to allow existing residences to add minor square footage and improvements to their existing homes and, thus, a cumulative maximum of 1,200 square feet of additions (habitable plus non-habitable) should be established
- The above rules should be the same for the entire Landslide Moratorium Area (red area and blue area)
The city's geotechnical consultant's opinion letter has been given to a peer panel of 3 geotechnical professionals, who have extensive knowledge of the Portuguese Bend Landslide, to review. The peer panel is made up of Mark Mclarty, a certified engineering geologist; Scott Kerwin, a certified engineering geologist; and Glenn Tofani, a civil and geotechnical engineer. The peer panel's assessment of the city geologist's was issued on May 31, 2007. View a copy of the Peer Review Assessment Letter. In summary, the peer panel agrees with Zeiser Kling's conclusions, although the panel's analysis of the issues is somewhat different from Zeiser Kling's analysis. The Zeiser Kling report and the peer panel's assessment of the Zeiser Kling report will be presented to the City Council at its upcoming June 5, 2007 meeting. In addition, staff will be recommending that the City Council implement the city's geotechnical consultant's recommendations.
Provided below is some background information that explains the circumstances that have led the city to evaluate the status of the Portuguese Bend landslide and the city's codes that address grading and construction within the city's landslide moratorium area. In addition, there is a summary of the City Council actions that have been taken thus far on this matter, including the holding of a public workshop on the matter. At the conclusion of the text is a list of related documents that you can access for more detailed information. Furthermore, if you wish to subscribe to a list serve group that will enable you to receive periodic information about this topic as it becomes available, you may do so at the bottom of this page.
Area in Red & Area in Blue
The city's Landslide Moratorium Ordinance (Municipal Code Chapter 15.20) establishes 2 separate areas within the overall landslide moratorium area, each with differing restrictions. Almost all the mapped landslide moratorium area is referred to as the area "outlined in red" (the "Red Area"). In the Red Area, new development on vacant lots is prohibited. There is also a small area on the eastern side of the moratorium area described as the area "outlined in blue" (the "Blue Area"). Most of the Blue Area consists of the eastern portion (37 lots) of the Seaview tract, which is affected by the Klondike Canyon landslide. Unlike the Red Area, the owners of properties in the Blue Area are currently allowed, subject to certain conditions, to develop residential buildings and accessory structures on vacant lots, build pools/spas, and perform grading.
Klondike Canyon Landslide Movement (Blue Area)
Following the heavy rains that occurred in the 2004-05 rainy season, city staff noticed new street cracks in the Seaview tract near the intersection of Dauntless Drive and Exultant Drive in May 2005. As a result, the area was periodically monitored for signs of additional cracking. In a report to city staff dated October 25, 2005, the city's geologist noted that the tension cracks on Dauntless Drive are indicative of landslide movement. As a result, city staff placed an item on the City Council's November 15, 2005 agenda to consider eliminating the more lenient restrictions of the Blue Area and revoking permits for projects that had been approved in the Blue Area but not built. The City Council ended up adopting Urgency Ordinance Number 427U (PDF), which placed a 60-day moratorium on the issuance of permits in the Blue Area to allow the city geologist to prepare a report on the observed street cracking. On December 20, 2005, the City Council adopted Urgency Ordinance Number 432U (PDF) extending the temporary moratorium an additional 66 days to March 21, 2006 to allow the city geologist additional time to complete his report.
On March 14, 2006, the city geologist submitted his report on the more recent movement related to the Klondike Canyon landslide. In general, the report concluded that the Klondike Canyon landslide experienced accelerated movement just prior to June 2005 due to the record rainfall during the winter of 2004-05 and increased drag from the accelerated movement of the abutting Portuguese Bend landslide. Although the city geologist also concluded that the Klondike Canyon landslide is not capable of catastrophic failure at this time, he did conclude that it should be considered an active landslide with the potential for continued slow movement and occasional increased acceleration. On March 21, 2006, the City Council accepted the city geologist's report and adopted Urgency Ordinance Number 438U (PDF), extending the temporary moratorium an additional 30 days to April 20, 2006. The City Council also directed staff to prepare an analysis on the differences between the red and blue areas within the Landslide Moratorium Area. Staff presented a follow-up Staff Report to the City Council on April 4, 2006, at which time, the City Council directed staff to prepare an ordinance that would apply the same standards to the Moratorium area outlined in blue that are applied to the area outlined in red, revoke all pending permits that are impacted by these changes, and set a date for a public workshop within 60 days to discuss the scientific distinctions that can be drawn between the red and blue areas and areas located outside the Landslide Moratorium Area.
On April 18, 2006, the City Council adopted Urgency Ordinance Number 439U (PDF) which extended the temporary moratorium to June 30, 2006 on the issuing of any permits for the construction of additions or new structures in the Blue Area and expanded the temporary moratorium to apply to additions to existing homes in the Red Area. This temporary moratorium also applied to projects that had received planning approval but had not received a building permit or begun construction. In addition, the City Council agreed to conduct a public workshop on June 3, 2006 to discuss the geologic distinctions that can be drawn among the various portions of the Landslide Moratorium area. On June 20, 2006, the City Council adopted Urgency Ordinance Number 440U (PDF) which extended the temporary moratorium on new construction in the landslide area to October 25, 2006 and re-scheduled the public Landslide Moratorium Ordinance workshop to Saturday, October 7, 2006.
The City Council conducted a public workshop at Miraleste Intermediate School on Saturday, October 7, 2006 to discuss the history, land use controls, significant observations and existing data related to the Portuguese Bend landslide complex. View the Landslide Moratorium Workshop Agenda or watch a video of the workshop. On October 7, 2006, the City Council adopted Urgency Ordinance Number 448U (PDF) which extended the temporary moratorium on new construction in the landslide area to January 23, 2007 to allow the city's geologic experts to prepare additional work to address the inquiries of the City Council. On January 16, 2007, staff reported to the City Council that the city geologist had been tasked with preparing a geologic opinion on the various issues that need to be sorted out by the City Council and that said opinion paper would be given to a group of 3 geologists for peer review. Therefore, on January 22, 2007, the City Council adopted Urgency Ordinance Number 452U (PDF) which extended the temporary moratorium on new construction in the landslide area to April 23, 2007 to allow said peer review to occur. On April 17, 2007, the City Council adopted Urgency Ordinance Number 457U (PDF) which extended the temporary moratorium on new construction in the landslide area to June 22, 2007 to allow additional time for the geologic opinion paper to be prepared and the peer review to be conducted.
Abalone Cove Landslide Movement (Red Area)
In July 2006, a resident in the Abalone Cove landslide area notified city staff about recent movement in the Abalone Cove landslide area. In response, the city geologist went out to observe the reported signs of landslide movement. Specifically, the city geologist inspected the Wayfarers chapel, residences at 20 and 28 Narcissa Drive, and street portions of Narcissa Drive, Palos Verdes Drive South, Figtree Road, and Cinnamon Lane. The city geologist submitted his report to the city on August 4, 2006, which concluded that the horizontal movement recorded by the city's GPS survey observations in 2005 is consistent with the movement he observed on his site visits. The city geologist recommended that the frequency of GPS observations be increased so that if there is a change in the current distress regime, additional steps can be taken.
Abbott Associates Presentations
- City Council Staff Report - April 17, 2007 (PDF)
- City Council Staff Report - January 16, 2007 (PDF)
- City Council Staff Report - October 7, 2006 (PDF)
- City Council Staff Report - June 20, 2006 (PDF)
- City Council Staff Report - April 18, 2006 (PDF)
- City Council Staff Report - April 4, 2006 (PDF)
- City Council Staff Report - April 4, 2006 (PDF)
- City Council Staff Report - March 21, 2006 (PDF)
- City Council Staff Report - December 20, 2005 (PDF)
- City Council Staff Report - November 15, 2005 (PDF)
- ACLAD Presentation by Robert Douglas (PPT)
- City Geologist Report on Abalone Cove Landslide - August 1, 2006 (PDF)
- City Geologist Report on Klondike Canyon Landslide - March 14, 2006 (PDF)
- Landslide Aerial Approximate Movement 1994 to 2006 (PDF)
- Landslide Area Approximate Movement prepared by GeoKinetics (PDF)
- Landslide Area Map (PDF)
- Landslide Moratorium Workshop (PDF)
- Landslide Workshop Presentation by Zeiser Kling (PPT)
- Red Area vs. Blue Area Development Standards Table (PDF)