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Arroyo Seco Foundation

News of the Arroyo


New plan on Devil's Gate should be adopted: Editorial





<b>May 21, 2014</b> - The San Gabriel Valley lauds the work of the Sediment Working Group, whose recommendations have been adopted by the City of Pasadena for the management of Devil's Gate Dam in Hahamongna Watershed Park.




San Gabriel Valley Tribune


Atop Devil's Gate Dam in Pasadena, local residents protest Los Angeles County Public Works' project to dredge and clean sediment from the Hahamongna Watershed Park area. (Photo by Sarah Reingewirtz/Pasadena Star-News)

First, for millions of Los Angeles County residents in the shadow of our magnificently steep mountains it must be noted that dangers from flood, mud and boulders are real.

As ever, the best source for the lay reader on the geological facts at play here is John McPhee’s profound 1989 best-seller “The Control of Nature,” in which he explores all the ways the Army Corps of Engineers and similar government outfits across our continent have tried to harness the wild power of water from the Mississippi to our own seasonal streams in the far West.

In the book’s section on L.A. County Flood Control’s efforts, McPhee poetically begins: “In Los Angeles versus the San Gabriel Mountains, it is not always clear which side is losing.”

While we are quite used to it, sometimes it takes an Easterner such as McPhee to note how very odd it is that every single streambed in our region has been partially or fully paved in concrete and often broken up by debris basins in the post-1938-floods effort to save lives and property from devastation. The reason this has been necessary is the simple fact that the San Gabriels, tectonically young, rise as rapidly as any mountain range on Earth. That means when we do get rain, the torrents, and the boulders sometimes as big as Volkswagens that come with, are moving at extraordinary and quite deadly speed.

So the canyons all across the face of the mountains, from Sunland and Tujunga to Eaton to San Gabriel and on out east, have been channelized. If the engineers have not exactly fully controlled nature, they have made it pretty safe for 10 million people to live in what is essentially one gigantic flood plain, and we owe them much gratitude. But that doesn’t mean that, being human, they won’t try to overreach, or, having their hammer, see everything else as a nail.

After the Station Fire in 2009, which burned much of the watershed in the mountains above the Upper Arroyo Seco behind JPL, huge amounts of debris — rocks, mud and vegetation — flowed down into the basin behind Devil’s Gate Dam where La Canada Flintridge, Altadena and Pasadena meet. That means less room for water storage. And the debris that naturally gathers there hadn’t been removed since 1994. So the county proposed plans for removing over 2.4 million cubic yards of debris in order to keep the aging dam safer and free the area up for water storage. That’s a lot of dump-truck runs — tens of thousands of trips.

The problem is not only the noise and pollution of the trucks and the cost. In recent years, the area behind the dam has been transformed into Hahamongna Watershed Park, used by thousands of hikers, bikers, equestrians and Frisbee golfers ever day. Rather than take the county’s plan as gospel, citizen groups such as the Arroyo Seco Foundation and the Arroyos and Foothills Conservancy suggested that removing less sediment would mean less environmental impact and still keep the downstream world safe.

So bravo to the volunteer Sediment Working Group for proving that taking out just 1.1 million cubic yards would keep the region as safe and eliminate the need for weekend and holiday work. Don Bremner, Tim Brick, Gretchen Brickson, Nina Chomsky, Henreen Nunley and Seema Shah-Fairbank and advisors Norman H. Brooks and Mickey Long deserve applause for the plan, as does the Pasadena City Council for unanimously approving it. The county should follow the plan.




Arroyo Seco Foundation, 570 W. Avenue 26 #450, Los Angeles, CA 90065-1011
PO Box 91622, Pasadena, CA 91109-1622 (323) 405-7326