storm

Rain creating soil instability in Santa Cruz Mts burn zone

ByDavid Louie KGO logo

Saturday, October 15, 2016

Rain creating soil instability Santa Cruz Mts burn zone

At about 3,00 feet above sea level, Loma Prieta gets slammed by strong winds and heavy rainfall, neither of which is welcome in a burn zone where the soil is unstable.

SANTA CRUZ, Calif. (KGO) -- The nearly 4,500 acres that burned in the Loma Fire are at higher risk for flooding and mudslides.

At about 3,00 feet above sea level, Loma Prieta gets slammed by strong winds and heavy rainfall, neither of which is welcome in a burn zone where the soil is unstable.

There are early signs of potential trouble, but so far, this first storm has not produced any mudslides.

The scorched earth in the fire zone has created an impervious layer.

Cal Fire division Chief Ed Orre says it's like a waterproof skin that reduces the ability of rainfall to percolate into the soil. So that's why a team of seven people is working on a comprehensive study of hazards that lie ahead.

Rocks already are tumbling down hillsides and landing in roadways. This could be an early sign of soil instability with the potential for landslides or mudslides.

The fast-flowing runoff is being produced during a period of light rain. It may reflect that waterproof skin.

Foresters, geologists, hydrologists and wildlife experts are also part of the research team that will produce a report similar to one done after the Soberanes Fire in Monterey County.

To help with this study of risk assessment, Cal Fire is installing a portable weather station at Loma Prieta where climate data will be compiled at the burn site, such as temperature, humidity and rainfall - all factors that contribute to a possible mudslide.">

The Santa Clara County Office of Emergency services asked for the study. Two days ago, aerial study was done by helicopter. Satellite imagery will also be incorporated.

So for residents, it's a time to wait and see how much rain will fall and for how long. Storm systems are known to stall and dump large amounts of rain in a short time.

The watershed emergency response team has a couple more days of field research to do. It will help identify where to expect post-burn complications.

Be sure to download the ABC7 News App to track the rain with Live Doppler 7 HD as it moves into the Bay Area.

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