Building a Healthier San Gabriel River Watershed Day 1

September 17, 2008 § 3 Comments

 I’m attending the “Building a Healthier San Gabriel River Watershed” conference in El Monte today and tomorrow.  Thanks to the Los Angeles and San Gabriel Rivers Watershed Council for hosting.  For me, today’s stand-out presentation was by Eric Stein of Southern California Coastal Water Research Project (SCCRWP, affectionately called “skwurp.”)  Stein, with others, is the author of a report called Historical ecology and landscape change of the San Gabriel River and floodplain which is available on SCCWRP’s website as Technical Report No. 499 (a 17MB PDF file.)  Jessica referred to this report in an earlier blog about L.A.’s historic streams.

Stein’s team compiled various historic San Gabriel River sources.  Primary sources included coastal resources mapping (1850s-1880s), Disenos – Spanish Land Grant maps (1830s-1860s), Irrigation maps (1880s), soil survey maps (early 1900’s) and early aerial photos – as well as secondary sources including the early County Flood Control District Interviews (that Jessica fondly blogged about here and here.)  From these, the team was able to map the changing historical configurations of the San Gabriel River.

In early accounts, the San Gabriel River was a tributary of the Los Angeles River.  Their confluence was where the Rio Hondo meets the L.A. River today.  In heavy rains in 1867 the San Gabriel River shifted out of its bed and moved to more-or-less its present course, emptying into the Pacific Ocean at Seal Beach.  Initially the new San Gabriel River course was simply called “the new river.”  Over time, the new river came to be called the San Gabriel and the old San Gabriel was re-named the Rio Hondo.

This shifting behaviour is not unusual for Southern California Rivers, which tend to move around the relatively flat alluvial plain.  The shifting courses of the L.A. River are mapped in Gumprecht’s book.  Our rivers have many mouths, many distributaries.  Indeed, Stein makes the case (as the Watershed Council does) that the San Gabriel and Los Angeles Rivers are historically inseparable.  They’re one overlapping and intermingling system.

Stein further states that the very dynamic local San Gabriel River system consisted of large continuous zones of floodplain – a large swampy area with sloughs, lakes and wetlands dotting the landscape.  These would sometimes dry up leaving vast seasonal alkali flats.  Stein characterized the main drivers of changes to the landscape (that is: near total loss of historic wetlands) as including: transportation (initially railroads followed by impermeable automobile roads), extraction of groundwater, and construction of flood control infrastructure.

The report has lots of excellent color maps that tell the story well.  I will try to get some of these and blog them here soon. The free conference continues tomorrow from 10am to 4:30pm.  Sorry for not blogging this sooner, but if you’re interested in the San Gabriel River, come on down and join us at the Grace Black Auditorium at 3130 N. Tyler Ave in El Monte, CA 91731.

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