Thursday, July 19, 2018

Banking Rain for Sunny Days

Did you get the memo? Climate change will make rain less predictable and more intense in southern California. It's not clear if the total amount of rain will decrease along the coast. Rain will decrease in the Colorado River Basin, from which we import some of our water. For the sake of our water supply, we need to change how we handle water runoff.

Gregory Rachel, a firefighter and surfer, wrote a good primer on the why and how of water harvesting, with a photo of the Los Cerritos Channel Sub Basin 4 Stormwater Capture Project.

Joe Mozingo wrote A behind-the-scenes battle to divert L.A.'s storm water from going to waste for the LA Times and illustrated it with a picture of the huge Paseo del Rio at San Gabriel Coast Basin spreading grounds.

In 2016, he reported that only 65 billion gallons of rainwater is captured and stored in aquifers. Another 164 billion gallons goes out to sea.  I'm not sure if that 65 billion includes the water captured by smaller-scale "rain gardens" in homes and parks, such as this one that captures all the water on the parcel of the North Redondo Beach Branch Library.  I wrote about it in 2016.

The "local supplies" that provides ~40% of the water used in the LA area comes from wells or reservoirs stocked by water that fell as rain in our area (instead of water imported from the Colorado River or Northern California via long canals.) It does not count the rain that fell in your garden and soaked into the ground because that isn't metered/measured.

It's pretty clear that the Colorado River Basin is drying up and climate change is a major contributor. I'll write about regional competition and cooperation of cities and states in the Colorado River Compact later.

The supply from the California State Water Project that moves water from the Sacramento Delta to central and southern California is also endangered. It's threatened in the north by sea level rise and increased diversions that increase the salinity (salt) in the water supply.  Insane over-pumping of well-water by farmers in the Central Valley have caused the ground to sink as much as a foot per year in some areas, buckling and breaking the canals.  Currently, the peak capacity of the water canals to SoCal has been decreased by 20% because of the buckling.  Add to this that the canals must cross earthquake country and were built when we had much less experience in how to engineer for earthquake safety.  The California "Water Fix" is a political football and you can get whiplash from watching it.  That sounds like another blog post.

Long story short, we need to improve the things that are completely within our control.  That means we should build our neighborhoods with the intent of soaking as much rain water in the ground as we can.  It can be as simple as putting in gravel in the lowest spot in your garden so it doesn't flow off your property.  It can be giant basins that can harvest 200 million gallons from one storm and put it in the ground.   Or it can be something in between.

I'll end with pictures of a neighborhood-scale rainwater capture project in North Redondo Beach.  Thousands of people pass it every day on Aviation Boulevard and have no idea what it is.  This aerial view does not show you how hilly this area is.  Some of the streets are 15-20% grade!

Low-lying area in 90278
Some low-lying homes used to flood repeatedly.  Rather than rebuild these flood-prone homes, the homes were purchased for alternative uses.  The plot in the red box was bought by the city of Redondo Beach and turned into a parkette.  It also functions as a spreading ground to soak up the water that flows into it from surrounding areas.  After a heavy rain, it may be too soggy, or even covered in water, for kids to play in.  In that case, the park is temporarily closed off with cones until it dries up, typically in a few days.

The blue box was mysterious until I saw a workman doing maintenance there.  We had a fantastic conversation where he taught me what they do behind the chain link fence and I explained to him our best understanding of what climate change will do to our area.

The concrete channel in the blue box collects the rainwater that comes out of the storm drains (and flows off the surrounding land like the parkette.)  The "first flush" of stormwater, about 1/4" is sent to the sewage treatment plant for cleaning.  The rest of the water is sent downstream.

[LA has separate storm drains and sewage systems, aka "sanitary sewers."  Many older cities, notably Chicago, have just one system and raw sewage can be spilled when the sewage treatment plants cannot handle the rainwater volume.]

Water capture at local minima
Rainwater after the first flush is much cleaner.  It is sent slightly further downhill to a spreading ground where the water can slowly infiltrate into the shallow aquifer.  The grounds are blocked off from street view with a tall, solid fence, but an adjacent triangular permeable garden/parkette is visible from Aviation Boulevard.

Spreading grounds for rainwater
I've written earlier about how LA is ringed by hundreds of injection wells where fresh water (often reclaimed) is sent into the shallow aquifer to block sea water intrusion into the larger aquifer that we depend on.  The more rain we can get into the ground, the less fresh water we need to pump into the ground. 

Sea level rise from climate change increases the danger of salt water intrusion.  We'll need to put more fresh water into the ground along the coast to stave it off.

If we are to survive and thrive as a city/metro region in the face of climate change, we need to do smart things at the regional, local and personal levels.  Take a look around your neighborhood.  What is your city doing?  What are you personally doing?

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