Understanding the Risk
“URGENT ACTION IS NEEDED TO PROTECT LIFE AND PROPERTY IN MONTECITO”
–Dr. Matthias Jakob, Principal Geoscientist, BGC Engineering and author of Debris Flow Hazards and Related Phenomena
Santa Barbara County and Montecito experience debris flows on average every 20 years, but sometimes these flows occur more often than 20 year intervals. Montecito has recorded catastrophic debris flows in 1914, 1926, 1964, 1971, and 2018. Additional flows have occurred outside Montecito, including La Conchita in 2005 and and El Capitan Canyon in 2017. Pubugou, China had three catastrophic debris flows in four years from 2008 to 2011. Illgraben, Switzerland typically gets multiple debris flows every year. Montecito is actually built on debris flow.
Based on the studies summarized below, we know:
There is still much material in our mountains “ready to mobilize”
The greatest risk for debris flow occurs in the years following a massive fire before the land has revegetated. Forest Service personnel predict our hills will take 6 to 8 years to revegetate
The National Weather Service predicts 78% chance of El Niño this year, bringing more intense rains
KANE Geohazard Assessment
In partnership with Santa Barbara County Public Works Department, we consulted with infrastructure builders and geologists working around the world on a variety of cutting edge solutions including mapping, monitoring, and mitigation. We funded a world-class Geohazard company KANE GeoTech to help develop a “roadmap” of solutions. KANE conducted site investigations and engineering assessments and recommended the construction of a number of debris flow barriers to retain the material that is still available to mobilize from the canyons in Montecito.
LIDAR (Light Detection and Ranging) is a remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances) to the Earth. Thomas Dunne, Professor of Hydrology & Geomorphology at UCSB’s Bren School of Environmental Science & Management, used comparative LIDAR images from 2015 and 2018 to inform decision makers about the debris flow and mitigation efforts. Data was used to map and measure the volume of landslide and gully debris sources in the canyons; calculate the potential speed, discharge and force from flow depths and mudline elevations; and measure the volume of boulders scoured from the canyons. This information is critical to designing adequate mitigation measures.
Debris Flow Site Reconnaissance
BGC Engineering is the gold standard for geologic risk assessment. BGC completed a reconnaissance-level site visit to Montecito and adjacent watersheds in July 2018 to determine how much material could still come down and how much could be mitigared. Dr. Matthias Jakob of BGC wrote the worldwide bible of debris flow, Debris Flow Hazards and Related Phenomena. And Dr. Joseph Gartner of BGC, whom we are also working with, spent 12 years at the U.S. Geological Survey where he developed models for post fire debris flow probability and volume, and rainfall intensity-duration thresholds for post fire debris flow initiation.
"The Partnership provides great value to the community with their resources, broad thinking, thorough analysis, and willingness to support practical actions as well as scientific understanding of the long-term hazardous situation".
– Thomas Dunne
Professor of Hydrology & Geomorphology
UCSB Bren School of Environmental Science & Management