I have a soft spot for Sharknado the movie
. It's just pure, campy fun, especially for meteorologists from Los Angeles.* I also like that it highlights the relationship between our storm drains and the ocean.
Los Angeles is not as threatened by rising sea levels as other cities because most of the city lies well above projected sea level rise. We're also mostly safe from tsunamis
(except at a few low-lying spots.)
The real danger is underground, from seawater intrusion
The LA region gets about one third of our water from aquifers fed by rain that falls in the basin and is squeezed out of the sky by the mountain ranges that surround the basin.
The aquifer is subject to seawater intrusion along the coast and in estuaries further inland.
|Seawater intrusion happens underground|
In the wild west days, anyone could sink a well and pump groundwater in the LA basin. This drew the sea water ever inland. Furthermore, some parts of LA subsided, as the Central Valley is sinking today, from groundwater over pumping. This was unsustainable.
By the 1960s, the LA region became an adjudicated basin; people agreed who got to pump groundwater and how much. All pumping has to be publicly logged.
LA also created a ring of barrier injection wells whereby fresh water is pumped into the ground to push the underground toe of seawater back out towards the sea.
|Pumping groundwater out draws seawater inland. Injecting freshwater along the coast pushes the seawater back towards the sea.|
We used to do it with imported water from the Colorado River or the California Aqueduct. Now, we do it with sewage water recycled to drinking water quality at great expense in energy and dollars. This protects our freshwater supply. I had previously thought the main danger as sea level rises is that we will need more to put more (scarce/expensive) freshwater into the aquifer to push back the sea.
The Sea Beneath Us
brought my attention to a very real horror story:
In a nutshell, as a warming climate raises sea levels, the sea won’t only move inland, flooding low-lying land near the shore; it may also push water up from beneath our feet. That’s because for those of us living near the shore, a sea lurks in the ground—a saltwater water table. On top of that salt water floats a layer of lighter fresh water. As the salt water rises with rising seas, [UC Berkeley professor Kristina] Hill and others think, it will push the fresh water upward. In low-lying areas, that water may emerge from the ground.
The result, Hill explained, will be that in places like Oakland, flooding will occur not just at the shoreline, but inland in areas once considered safe from sea level rise, including the Oakland Coliseum and Jones Avenue, where Hill and her students now stood, more than a mile from San Leandro Bay. In fact, she added, rising groundwater menaces nearly the entire band of low-lying land around San Francisco Bay, as well as many other coastal parts of the U.S.
Most of us (including me, until I read this article) don't pay much attention to the small difference between the specific gravity (weight) of fresh vs seawater
. That 2.5-4% difference in density turns out to matter quite a bit. If freshwater cannot percolate down through the heavier seawater, then it has no where to go but up.
In the Boulder, Colorado floods of 2013, homes in low-lying places above clay soils had water come up through their foundations and their drains. The rainwater could not continue to flow downhill on the surface or percolate down through the soil. If there is enough water and hydrologic pressure, the water will go up. It came up for days and even weeks as the water flowed downhill underground and got trapped.
Heaven or High Water
explains a similar phenomena, Miami's "Sunny Day Flooding." Building sea walls against rising seas won't help when the water is moving underground.
Since Miami is built on limestone, which soaks up water like a sponge, walls are not very useful. In Miami, sea water will just go under a wall, like a salty ghost. It will come up through the pipes and seep up around the manholes. It will soak into the sand and find its way into caves and get under the water table and push the ground water up. So while walls might keep the clogs of Holland dry, they cannot offer similar protection to the stilettos of Miami Beach.
The horror story gets even worse. The seawater doesn't just retreat with the tide, it leaves salt in the soil. Rewet it with rainwater from above and you've made more salt water. Pour more rainwater on top, and the water has no where to flow underground. It has to come up to the surface.
In the sequel, an atmospheric river strikes the region with intense rain and wind. Wind-driven waves pound the shore and push the seawater inland both on the surface and underground. Suppose we're successful in capturing much of the rain in the aquifer instead of letting it flood our streets and flowing out to sea.
The rain water flows slowly downhill underground until it reaches an impenetrable salty layer. Then the horror movie begins:
In East Oakland, on a residential street in front of a small park, Kristina Hill stopped and got out of her vehicle. She walked to the center of the street as a gaggle of graduate students emerged from their cars and gathered around her. It was midday, early September, the bright, hot sun directly overhead. Hill, a professor of urban and environmental design at UC Berkeley, had chosen the spot because when it rains heavily, water gushes up from storm drains here, forming filthy brown ponds. “That will happen more and more,” Hill said. Then she proceeded to describe a peculiar, almost apocalyptic future.
Water will leach inside homes, she said, through basement cracks. Toilets may become chronically backed up. Raw sewage may seep through manholes. Brackish water will corrode sewer and water pipes and inundate building foundations. And most hazardous of all, water percolating upward may flow through contaminants buried in the soil, spreading them underground and eventually releasing them into people’s homes. The coup de grace will be the earthquakes, which, when they strike, may liquefy the entire toxic mess, pushing it toward the surface.
Residents of Boulder, Colorado lived this nightmare. To solve the problem, cities dug through the clay layers to give water a way to flow down that did not inundate homes and infrastructure from above or below. Years later, those homes still suffer with elevated levels of bacteria and mold in their walls and foundations.
People who live along the beaches in California are similarly vulnerable. Instead of building sea walls like Holland or excavating clay soils like Colorado, we need to push back the underground toe of seawater with as much fresh water underground as we can.
We've built a largely impermeable city where the rainwater flows along the surface and out towards the sea. Low-lying areas already flood in the current scenario. Moreover, rain water on the surface does nothing to help push the seawater out.
The more rainwater we can get to soak into the ground, the less (expensive!) water we need to pump into the injection wells. That will save us all money. It will also prevent rainwater from flushing out into the sea, laden with dog poop and motor oil.
Collecting rainwater and letting it soak into the ground should be a win-win for both the people who live along the shore and the millions of people who rely on the aquifer. It would also be a win for the marine life that would appreciate us not dumping trash, bacteria and pollution into the bay.
Recognizing that this is both a local and regional problem, the state had committed $3.1M to help our local governments deal with this local pollution hotspot
The Herondo Drain outfall is the largest storm drain in the South Bay Beach Cities and typically receives an “F” grade during rain events on the Heal the Bay Beach Report Card due to high bacteria levels, resulting in beach closures.
The Hermosa Beach Greenbelt Infiltration Project is the highest priority project identified in the Beach Cities Enhanced Watershed Management Program (EWMP). The project will capture and infiltrate storm water runoff that otherwise flows through the Herondo Drain into Santa Monica Bay. Water quality grades for the Herondo Storm Drain are expected to improve to an “A” grade as a result of the project.
The proposed location for the project is under the greenbelt between Herondo and Second Street. When complete, the project will be contained completely underground and will include the installation of California-friendly plant habitat along the greenbelt.
Here's the map of the watershed and storm drain system that feeds into the troubled storm drain
|A map of the various South Bay sewers that feed into the Herondo venue drain, which lets out at Hermosa’s southern border. Rendering by Geosyntec|
Here's a USGS map from 1963 with elevations of the area. The greenbelt follows the old streetcar right of way a couple of blocks from the beach, north of Herondo (the straight street ending at the north side of the harbor and the border of the cities of Hermosa Beach and Redondo Beach). The map shows the elevation of the greenbelt and park area as 30', but sea level has risen since then.
|1963 USGS map of the area with elevation contours and benchmarks.|
Notice that the park and greenbelt sit on top of former oil wells. Imagine what interesting hydrocarbons would percolate up with the groundwater if it can't flow downwards due to encroaching seawater.
The Hermosa Beach staff plan
would have screened the trash out of the water from the storm drain, sent the "first flush" of rainwater, which tends to have the heaviest pollutant and bacterial load, to the sewage plant; filtered the remaining rainwater, and then spread it under the greenbelt in a network of pipes.
The entire system would have been built underground and been invisible except for a few maintenance access points.
The rainwater would have served the dual purpose of pushing back against the seawater and watering the landscaping in the greenbelt. This would have saved the city money in landscaping water and the neighborhood from the horror of watching water and a chemical and bacteria soup percolate up through the ground.
Roughly 100% of the current vegetation is non-native invasive species such as ice plant, mustard, and (highly flammable!) eucalyptus trees. The abandoned plan would have replaced the vegetation with California natives or drought-tolerant non-invasive species that required little or no additional water.
|A peaceful place to jog and walk, but think how much nicer it would look with native plants. Can you see the yellow mustard blooming amidst the ice plant? The invasive and flammable eucalyptus tree?|
|There is even some turf grass if you are playing environmental faux pas bingo.|
If the state and a coalition of city governments were willing to pay millions to make your home safer and give you free relandscaping with water, you'd think the neighborhood would support it.
You'd think wrong. In fact, the opposite happened
“It looks like we're heading in the right direction to try to get everybody working together rather than having two separate groups to put as much pressure as we can on the City Council to do the right thing, to get it out of the residential area,” said Ira Ellman, who along with Jessica Guheen and Gina DeRosa, facilitated the Sunday meeting.
“It's literally in my backyard,” said DeRosa, about South Park. “But there are more big picture concerns.”
“The more I learn about this, the more I honestly think this is not the right project for Hermosa Beach,” said Guheen, who helped spearhead a 10-year renovation of South Park.
At the study session, the consensus from the crowd was that the “project is important, but the location is wrong.”
Concerns included the removal of a third of the trees on the greenbelt; liquefaction; moving utilities that line the greenbelt; pollutants in the soil; street closures and traffic during construction; odor and noise coming from the system after completed; structural integrity of homes; as well as lawsuits on other projects against Tetra Tech, the project contractor.
Check out this USGS geologic map of the area
. Not only was the neighborhood built on top of the site of former oil wells, but it's built on Qds=loose dune and drift sand. Yup, those homes you see adjacent to the green belt in the photos above sit on loose sand and they claim this infiltration project will cause ground liquefaction. The horse is already out of the barn on that one.
On March 26, 2019, the Hermosa Beach city council caved
. They cancelled the entire project, jeopardizing the state funding and trashing years of planning. HB doesn't want the infiltration project anywhere within their city boundaries.
By saying no to infiltration projects, they will continue to use more landscaping water in the short-term. In the longer-term, HB will have to find the money to build a network of injection wells and pay for the water to put in them on their own.
Redondo Beach is looking at some sites a few blocks away where the project can be built. Redondo Beach has a history of welcoming infiltration projects such as the NRB library
and the one next to Aviation Blvd
. This would mean more time spent planning another project from the ground up and possibly the loss of state matching funds.
Construction is always painful, but the result will be a cleaner bay and healthier landscape. It will also protect the neighborhood near the beach as much as possible from sea level rise. We really need this project.
* ~20 years ago, I went to a mixer for first time attendees of the American Meteorological Society's annual meeting. Our names and locations were printed on our badges. Mine said Los Angeles. All evening long, I heard,
"Florida? Hurricanes! Cool!"
"Oklahoma? Tornadoes! Awesome!"
"Los Angeles? I'm so sorry!"