Unraveling the Impact: Exploring the Varied Landslide Effects Triggered by LA’s Recent Major Storm
In the recent string of storms, Southern California witnessed an unprecedented amount of rainfall, nearly approaching a record for the highest rainfall in a three-day period. While the impact of the rain was felt across a wide area, the majority of the damage, particularly landslides, occurred in specific hillside communities.
This raises the question: why didn’t the storms result in more widespread and catastrophic landslides throughout the region?
To delve into this inquiry, I reached out to the US Geological Survey, emphasizing several key points:
The total rainfall during the early February storms was remarkable, exceeding 9 inches in downtown Los Angeles over a five-day period, representing over 60% of the typical yearly precipitation.
Notably, the mountainous region north of Hollywood and Westwood, especially Bel-Air, experienced significant impact, with around 14 inches of rain causing a house in Beverly Glen to slide off its foundation.
Various locations, including Studio City, Tarzana, Baldwin Hills, and Hacienda Heights, also witnessed destructive landslides and mudflows.
The increased risk of landslides in areas with alterations to land and drainage systems was evident due to heavy rainfall during the storm.
According to Matt Thomas, a research hydrologist with the USGS’ landslide hazards program, most observed slides occurred in the built environment, where conditions like oversteepened slopes, poorly developed fill eroding beneath houses, and site-drainage issues heighten the risk of landslides.
Anticipated areas like Malibu Canyon and along Pacific Coast Highway reported mudflows, common occurrences during rainy weather due to rockslides and landslides.
Downtown LA Meeting 1970s Landslide Criteria Sparks Questions in Southern California
The criteria for widespread landslides in Southern California, established in the 1970s, include a minimum of 10 inches of seasonal rainfall and a minimum rainfall rate of at least one-quarter inch per hour.
Downtown Los Angeles met this threshold on February 4th, coinciding with the storm’s first major day. However, there’s a suggestion that these standards may need updating, considering that a higher rate of rainfall per hour could lead to more impactful landslides.
