January 23, 2010

California Torrential Rains

This morning a news bulletin talked about the massive rain fall in Southern California and mentioned that the debris basins were full. You might wonder, what the heck are debris basins? They are the football field-sized man-made holes at the base of the San Gabriel mountains which were dug to catch the massive boulders and debris that are sloughed off the mountains during torrential rains. I wrote about this here when I recommended John McPhee's book which has a vivid description of the phenomena LA is experiencing now. Fortunately it appears that this year, LA has been spared the worst of it.

Cannon said the mountains ended up getting less rain than forecasters had predicted, and that helped tremendously. The most powerful cells from the storms veered away from the Station fire burn area, she said.

...But Spencer and Schmidt cautioned that the preparations won't be enough if heavier rains soak the mountains.

"We want to prevent a sense of complacency," Schmidt said Friday. "It's not like crying wolf. It wasn't worse, because the rainfall intensity and its duration was not as high as forecasted. If we had gotten what was forecasted, it would have been a lot worse."

From October 2003:
Listening to the news this morning about the incredible wildfires in Southern California reminded me of my very favorite John McPhee book: In Control Of Nature . In this book, McPhee talks about three natural disasters: volcanic eruptions, floods and landslides, and how modern day humans have tried to constrain their impact. The section on landslides is an excellent primer on the reasons the fires in Southern California are so bad and how the consequences of the fires can mean massive mudslides.

The landscape in Southern California has been created to be one of the most flamable in the world and the ecosystem is shaped by earthquakes, wind, fire and water. The worst of the fire season in California is always in October and in Southern California are conjoined with the Santa Ana winds (hot and dry) that help the fires move and grow. The latest studies show that urban growth is now exacerbating the fire danger.

McPhee's story shows how the fires in autumn can be combined with torrential rains in the winter (the 100 year rains) to create huge mudslides, enough so that in the foothills of the San Gabriel Mountains are found huge football field sized man-made holes designed to catch the boulders that are sloughed off the mountains. The interaction between the vegetation, the fires, the soil and the rain is quite fascinating. And how although men are constantly attempting to tame nature, this is not always something we do well or wisely. This is one book that I definitely recommend.

Posted by Mary at January 23, 2010 08:32 AM | Science | Technorati links |