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Update on Mudslides from Last Winter

Post Date:11/17/2017 4:00 PM
Following periods of heavy rainfall last winter, four mudslides occurred in the Sausalito area – three within City limits and one just outside City limits on land belonging to the National Park Service. All four mudslide sites were immediately stabilized, and preparations are underway for additional work to prevent future slides. Below is an update on the status of the four sites.

Mudslide at 47 and 49 Marin
On Saturday January 7, 2017, a slide occurred in the rear yards of 47 and 49 Marin Avenue. At the top of their rear yard slopes, these properties adjoin a parcel owned by Pacific Gas & Electric that fronts Rodeo Avenue. To temporarily stabilize the site last winter (and after the City secured permission from the property owners), a contractor for the City placed plastic tarps anchored with sandbags and ropes over the slide area, and a rigid plastic stormwater diversion pipe was installed to redirect drainage. The City, PG&E, and the other property owners are in discussions regarding permanent stabilization of this site. 

Bridgeway Mudslide
On the evening of Sunday, January 21, a slide occurred on the west side of southbound Bridgeway, between Nevada and Olive streets. Debris from the slide obstructed the sidewalk, bike lane, and a portion of roadway. In the immediate aftermath of the slide, debris was removed from the roadway and temporary K-rail barriers were installed. When weather permitted, the K-rails and additional debris were removed and the sidewalk reopened. The City also installed a temporary storm drain pipe at the top of the slope to convey water from the adjoining properties to the City's drainage system.

City consultant Miller-Pacific Engineering Group is expected to recommend additional soil removal and a small structural retaining wall to protect against future mudslides at this site. Budget permitting, construction will begin as early as spring 2018. The City has been informed that its debris removal costs in response to this mudslide will be reimbursed by the Federal Emergency Management Agency (FEMA). 

Mudslide at San Carlos and Caledonia
A February 7 mudslide at the intersection of San Carlos Avenue and Caledonia Street affected the City's sanitary sewer system and the yards and storm drainage facilities of private property. The slide also knocked a pine tree into secondary electrical distribution wires owned by PG&E. Once PG&E responded, City staff were able to clear debris, make a temporary reconnection of the City's sanitary sewer main, and reroute storm drainage piping to the toe of the slope. The site was then covered with plastic tarps anchored with sandbags and rope. The toe of the slide was fitted with temporary K-rail debris barriers, pending completion of more permanent repairs. The cost to repair the public sanitary sewer main and the costs of debris removal for the slide were approved for reimbursement by FEMA.

City consultant Miller-Pacific Engineering Group assessed the site and is in the process of identifying and recommending alternatives for permanent stabilization. Following the completion of Miller-Pacific's investigation and topographic survey, this site was again protected with plastic tarps secured by sandbags and ropes. It is anticipated that a public storm drain segment will be constructed in the public right-of-way to convey stormwater to the street rather than allowing it to be dispersed along the slope. Budget permitting, construction is expected to begin as early as spring 2018.

Alexander Avenue Mudslide
Also during the morning of February 7, a mudslide developed on the west side of Alexander Avenue, just south of City limits on National Park Service property. The slide ultimately resulted in debris resting against a previously-constructed debris fence in the side and rear yard of a residence at 1 Alexander Avenue in Sausalito and closure of Alexander Avenue to motor vehicles for an extended period of time. During the closure, debris was cleared, loose material remaining on the slide surface was removed, the exposed rock was covered with plastic tarps secured by sandbags, and temporary debris barriers were placed. The incident was responded to and work performed by the Golden Gate Bridge, Highway and Transportation District, with the approval of the National Park Service.

Since then, the Bridge District has retained Earth Focus Geological Services, Inc. to identify and evaluate alternatives for more permanent stabilization of the slide site. On that basis, the Bridge District expects within the next few weeks to issue a Request for Qualifications and Proposals for the consultant services necessary for environmental compliance and design of more permanent slope stabilization of the slide. The Bridge District has confirmed eligibility for federal assistance for the work and is working with FEMA and other agencies on the appropriate applications and procedures. The Bridge District continues to monitor the area and expects to retain a contractor to install new coverings on the slope for the rainy season of 2017-18.

For further information on the status of mudslides from last winter, please contact Jonathon Goldman, Director of Public Works, at (415) 289-4176 or jgoldman@sausalito.gov.
 
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