You Asked, We Answered: Your Top Stormwater Questions
You Asked, We Answered: Your Top Stormwater Questions Image

The new year began with a train of atmospheric storms barreling straight for California and a whole lot of rain falling here in Los Angeles. To give you a sense of the magnitude of one of the most powerful storms, over a 24-hour period between January 9-10, the Hollywood Reservoir received an eye-popping five inches of rainfall. That’s more than 1/3 of the rainfall LA receives in a normal rainy season (from October to April) falling in a single day! Wow!

 

With all the recent storms, we’ve seen a lot of questions from residents about stormwater. Where does it flow once it leaves my street? Why can’t we capture more of it? Is the drought over? As is often the case with complex issues, stormwater management is more complicated than it looks. Read on for answers to your top five stormwater questions:

 

We’ve received more than 10 inches of rain over the last few months. LA’s drought is over, right?

 

Unfortunately, LA’s drought is not over quite yet. 

 

Remember that in a normal rainy season, Los Angeles is supposed to receive just under 15 inches of rain. Over the last decade, LA has received less than normal rainfall totals for seven of those 10 years, which means we’ve been operating at a big deficit for a long time. Unfortunately, one wet year isn’t going to make up for those many dry years. 

 

Like everyone here in California, we look forward to the final numbers on how much of a positive impact the recent rains and snow had on California’s drought, and we are hoping that it did put a significant dent in the drought. In the meantime, we encourage all residents to continue conserving water. 

 

Why is the LA River channeled? Why doesn’t LA have natural rivers and creeks like other parts of the US?

 

Back in the early 1900s, Los Angeles did have natural creeks, streams and rivers. However, in 1938 massive storms and the resulting flooding caused loss of life and millions of dollars worth of property damage. Officials decided to channelize (i.e. pave over) LA’s waterways to reduce property damage from future storms.

 

As a result, LA has more than a thousand miles of open channels and storm drains that all work to remove stormwater from neighborhoods and divert it quickly away from property and into the LA River and Ballona Creek and reduce the flooding risk.

 

I’m seeing reports of trash along the beaches and notices to stay out of the ocean for 72 hours after a storm. Why are our beaches so polluted?

 

While the channelization of the LA River and other local waterways here in LA did solve LA’s flooding problem in the mid-1900s, the concreting of local waterways combined with the urbanization of LA that began in the mid-20th century and continues to this day, created other problems. LA’s impervious environment (think paved streets, alleys, parking lots, housing) now contributes to the problem of urban pollution in our waterways and ultimately on our local beaches. 

 

When it rains in LA, all that rainfall flows off LA’s streets and into regional storm drains. Along the way, it picks up any trash and pollutants (litter, motor oil, dog waste, pesticides) left on our streets and in our neighborhoods. That toxic urban runoff flows untreated to both Santa Monica and San Pedro Bays, triggering 72-hour notices to stay out of the ocean by the LA County Health Department. The negative impact to the quality of ocean water can sicken and harm ocean goers and marine life. 

 

Why can’t we capture and use the rainwater that is flowing down the LA River?

 

The sheer volume of the rainwater flow from a major storm is a challenge to capturing and retaining stormwater. On a rainy day here in LA, more than a 100 million gallons of water can flow through our regional storm drain system and during atmospheric river-type storm events, that volume can reach tens of billions of gallons of water. The bottom line is that we don’t have anywhere to put that much water when it comes as fast as it did earlier this month.

 

Another challenge is Los Angeles’ topography. Back east, the Mississippi River drops 1,475 feet in elevation over 376 miles. Water from the Mississippi’s headwaters takes three months to reach the Gulf of Mexico. In contrast, the LA River drops 780 feet in just 52 miles. That quick drop in elevation means that rainwater falling where the LA River begins in the Santa Susana Mountains reaches San Pedro Bay in mere days. The channelization of the LA River makes that water flow even faster. The speed of the water flowing in the LA River during a big storm can top out at a whopping 45 mph.

 

As a region we need to do more to capture and retain rainwater. A growing recognition by residents and officials to view stormwater as an asset and not a liability is what propelled the passage of Proposition O back in 2004, which resulted in the building of dozens of stormwater capture projects. That mindset also helped Measure W (LA County’s Safe Clean Water Initiative) pass in 2018.

 

The City of LA has multiple Safe Clean Water Program-funded regional stormwater capture projects in the design and construction phase. And, the City of LA continues to actively seek funding for stormwater capture projects. One day those projects will capture hundreds of millions of gallons of water that will be able to be used to offset LA’s dependence on imported water. However, because of the complex and complicated nature of stormwater capture and treatment, it will take another decade to see those projects built and operational.

 

Can you tell me more about Measure W and the Safe Clean Water Program? Where can I learn more about this program?  

 

Made possible with the passage of Measure W by LA County voters in 2018, the Safe Clean Water Program creates a comprehensive, regional plan to address how we capture stormwater and reduce our region’s reliance on imported water. It is a multi-pronged program that offers annual funding for both large-scale regional projects and smaller municipal-based projects.  

 

All Safe Clean Water Program projects must include nature-based solutions, which help to achieve the multi-beneficial goals of capturing, cleaning, and storing stormwater. This captured stormwater can then either be used to offset potable water demands, infiltrated into underground aquifers or treated and released back into LA’s local rivers, creeks or lakes. Successful projects also provide community enhancements such as the rehabilitation of public parks, streets, alleys, and/or trails.

 

If you’d like to learn more about LA’s Safe Clean Water Program, we invite you to learn more by visiting LA City’s Safe Clean Water Program webpage.

 

Do you have a stormwater related question that isn’t answered here? Send your question to lastormwater@lacity.org.

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