Home » After the L.A. fires stop burning, the flood risk looms – Jobsmaa.com

After the L.A. fires stop burning, the flood risk looms – Jobsmaa.com

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Unprecedented Firestorm It will eventually blow over much of Southern California, with the help of some much-needed rain. But emergency and public works workers won't have much time to rest: Any rain that follows the fire will bring the risk of mudslides and debris flows that will test the limits of the region's infrastructure.

Wildfires strip mountain slopes of vegetation as their intense heat burns the surface soil. Even modest amounts of precipitation in such altered landscapes can trigger significant runoff, which moves quickly downstream, grinding and collecting soil and debris into a fast-moving mix.

Depending on how much sediment, rock, and wood is attached, these events are called mudslides or debris flows. They are extremely dangerous to both property and people, and the danger can last for years until the vegetation regrows and the soil recovers.

After a series of deadly and damaging wildfires in the 1930s, Southern California invested heavily in infrastructure to contain such flows, particularly large dams and small debris basins designed to trap soil and debris hazards. mountains. More than 150 debris basins have been built across Southern California, where they serve as the first line of defense for communities below the Santa Monica and San Gabriel mountains, where the Palisade and Eden fires burned.

But this infrastructure does not provide absolute security. Smaller debris basins are prone to precession.

Another winter fire followed by rain, The Thomas Fire — which began in December 2017 in the Santa Ynez Mountains above Ventura and Santa Barbara counties — making some of California's Deadly flood in a century. Water, soil, boulders, brush, and debris from the canyons of the Santa Ynez Mountains overtook debris basins and traveled several miles, destroying parts of the town of Montecito and blocking Highway 101. The floods killed 23 people and destroyed 400 buildings.

Maintaining debris basins — specifically, sweeping accumulated sediment so they have enough capacity for the next storm — is critical to avoiding such tragedies. Cleaning debris basins between storms is more difficult and expensive due to soil concentration, but it can be especially important. Recent research from UC Irvine The cumulative effect of back-to-back storms shows that debris basins may have overtaken.

We were delighted to see it Gov. Gavin Newsom's executive order Calling on government agencies to prepare for landslide and debris flow hazards. Removing debris from burn zones can help reduce the amount of material that can contribute to debris flows, and clearing debris and flood channels can increase the ability of these structures to protect communities. But policymakers must provide the necessary funding to repeatedly clean up flood control infrastructure throughout the year, quickly update flood hazard maps to accurately reflect the severity of burns in watersheds, communicate hazards to nearby residents and businesses, and evacuate whenever they are deemed necessary.

Climate change is intensifying California's fire and flood cycles, putting more people at risk and putting more strain on infrastructure designed for a different climate and much smaller population. As the risk of wildfires has grown, the risk of post-fire landslides and debris flows has become more urgent and profound. It calls for immediate arrangements and public cooperation to save lives and protect the environment.

Jeffrey Mount is a senior fellow at the Public Policy Institute of the Water Policy Center of California. Brett Saunders is a professor of civil and environmental engineering, urban planning, and public policy at UC Irvine.

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