Although it doesn’t rain often in Los Angeles,
when it does, it pours. In less than 20 days a
year, LA averages about 15 inches of rain. And
the major riverine artery of LA, the Los Angeles
River, is one of the fastest and steepest flowing
rivers in an urban environment. The LA River
watershed drops more than 7,000 feet in a little
over 40 miles, from its highest point in the San
Gabriel Mountains to the river’s outlet in Long
Beach. Over the 51 miles of the river’s course,
it falls 795 feet whereas the mighty Mississippi
River falls just 605 feet over its more than 2,000
mile course. This means that, in a big storm, water is moving quickly and voluminously through
our cities.
The flow of the LA River is accentuated by the
fact that is has been channelized and lined with
concrete. What’s more– the surrounding cities
are equipped with gutters and storm drain systems that direct all urban runoff straight into the
river. The storm water, of course, picks up all the
nasty pollutants in our streets, industrial facilities, and gutters before catching a ride straight to
the Pacific Ocean.
A couple weeks ago, LA experienced its first
real rain event of the season. While we welcome
the precipitation in what seems like a drying
climate, we also cringe at the pollution caused
during each year’s “first flush”. After months of
accumulation during the dry season, the first rain
of the season can be the nastiest for our water
quality.
First Flush,
First at the
Scene of the
Crime
An LA Waterkeeper Blog