Update on the McKillop Slideby Rochelle Rodgers |
A couple of small shakers on the Hayward Fault this October and the impending rainy season are enough to alert us that we can never take for granted our fault-ridden landscape. Streams flow from our hills to the Bay. Our soil soaks up water. Landslides can happen. |
One landslide began in May 2006 on McKillop Rd. After hanging on for more than six months, a home slid down the hillside on the day before Thanksgiving that year. Several other properties were damaged from the movement of the steep hill which bottoms out at Sausal Creek. Lawsuits, geological studies, and major street repairs followed. In January 2007, the city of Oakland sued EBMUD, trying to establish a connection between the landslide and EBMUD’s 164 million-gallon Central Reservoir. Elizabeth Bialik, Manager of Engineering Services for EBMUD, is a civil engineer. She said the reservoir is underlined with a pervious layer of sand and gravel, and has a system of drainage pipes. In 2007, EBMUD placed piezometers to monitor leaks. Bill Adams, an attorney representing the city in the lawsuit, said that Oakland settled against EBMUD earlier this year in part because piezometer test results showed that the catchment system is working as it was designed, and water leaks are not entering the hillside. Bialik said EBMUD‘s 2008 stability analysis concluded that the reservoir will be safe in an earthquake on the Hayward Fault registering 7.25 on the Richter scale. In addition, she said all California dams are entrusted to the California Division of Safety of Dams (DSOD). For years, Edward Goehring wrote about Oakland geography, including flood and earthquake safety, for the now disbanded Dimond Safety Group (groups.google.com/group/dimondpublicsafetycouncil). Goehring says that the McKillop hillside has been subjected to landslides for thousands of years. One of the biggest of modern times was in the 1930s, when 14 homes on McKillop Rd. were destroyed and a deep basin carved below the collapsed side of the street. Wood Park is there now, built on top of engineered fill placed in the landslide basin. When the hill collapsed in 2006, the entire hillside moved to Sausal Creek in what geologists call a “search for its angle-of repose.” The move pushed part of the creek up to ground level, and a portion of land was lost on Hickory St. bordering the creek. This fall, the Flood Control District of Alameda County shored up that area as a temporary measure for the winter. On the top of the hill, McKillop was excavated, and a retaining wall put underground to stabilize against further hillside movement. But not everyone is sanguine that all is safe whether the hillside from soil saturation or neighborhoods in the vicinity of the reservoir. Adams said monitors confirm the steep hillside is weak, still subject to movement, and that there is a correlation between that movement and rain-saturated soil. Goehring said that in earthquakes, something called “sloshing” occurs where water in a reservoir washes side to side. A major earthquake could cause water mains downhill to break, causing more flooding. Pat Haggarty is a member of the Commonplace Neighborhood Watch representing his neighborhood, which is 75 feet under the toe of the reservoir. He said that if the dam were to fail, his street could become a major river. A case study of the McKillop Slide by neighbor Andrew Alden is at geology.about.com/od/naturalhazardsclimate/ig/oaklandlandslide. Alden’s comments in a December 2010 blog at oaklandgeology.wordpress.com, reflect what some people feel about the danger. “Oakland is a fine town unless it rains too much. Then we have to worry about all the water.” |
