The Tijuana River flows throughout the U.S.-Mexico border region in San Diego. / File photo by Adriana Heldiz
The Tijuana River flows throughout the U.S.-Mexico border region in San Diego. / File photo by Adriana Heldiz

There’s so much sand and silt buildup where the Tijuana River empties into the United States that a kind of invisible dam already exists and average rain can flood the valley.

Now add a border wall across that river where trash, tires and other debris could pile against dozens of steel gates beneath a 30-foot bridge that are supposed to open when it rains. Now imagine a big storm caused an electrical failure and the gates are blocked with trash and won’t open. Where does the river go?

Proposed design of a border wall crossing the Tijuana River into San Diego.
Proposed design of a border wall crossing the Tijuana River into San Diego, 2020. / CBP

In this worst-case scenario, the river backs up against the wall, breaches its levees and overhead flood waters consume most of Tijuana’s Zona Norte and into downtown, lapping against the doors of the popular Cesar’s restaurant (and originator of the renowned salad), according to maps from a study commissioned by the EPA and published this month. That’s under smaller-scale flooding conditions, called a 50-year event which means there’s a 2 percent chance of a flood of that magnitude happening every year. 

“There’s an elevated risk of flooding (already) because the system hasn’t been managed correctly,” said Jochen Schubert, a hydrologist from Zeppelin Floods, the contractor EPA hired to model flood risks the new border wall poses to the region. 

Voice of San Diego reported that EPA hit a dead end trying to get Border Patrol to study all the ways this new wall across the Tijuana River could flood both nations, especially under worsening floods anticipated as the planet warms due to human-caused climate change. So the EPA studied it instead. 

After that story published, California Sen. Alex Padilla notified U.S. Secretary of Homeland Security Alejandro Mayorkas of the border wall’s potential impact on flooding during an April 18 Homeland Security and Governmental Affairs committee hearing

“You correctly describe the challenge of climate change and the fact that the frequency and severity of extreme weather events is only increasing,” Mayorkas said. “I’m not familiar with the particular situation you describe with respect to Tijuana. That’s something I will look into.”

Climate change isn’t the only factor affecting the magnitude of flooding. Apparently, nobody has been dredging the river valley for years of muck and sand drooling into the U.S. 

The river lives in a concrete channel on the Mexican side of the border but empties into a natural river basin in San Diego. That transition point is known by engineering nerds as the “energy dissipator” because, while the concrete channel acts like a chute, the river slows where it turns into natural plain. Sediment the river carries has been piling up there for years, Schubert said.

“As the flow comes down the channel, it hits this wall of sand and dirt, elevating the flow in the channel so it backs up into Tijuana and could increase the risk of the levee overtopping,” Schubert said. 

Heavy rains and flooding described in magnitudes of 100-year or 200-year events would be more catastrophic for Tijuana and San Ysidro if the gates failed to open. 

“If a power failure happens, each gate would have to be manually lifted. I’ve heard it could take eight hours to lift each gate – so it’d take a lot of manpower to open this structure,” Schubert said.

Flood hazards of border wall across Tijuana River modeled here by Zeppelin Floods for the EPA. / Zeppelin Floods
Flood hazards of border wall across Tijuana River modeled here by Zeppelin Floods for the EPA. / Zeppelin Floods

The Tijuana River typically flows only during the rainy winter season, emptying a 1,750 square-mile watershed into the Pacific Ocean. Not to mention, this river is one of the cross-border region’s biggest environmental catastrophes as sewage and trash from Mexico flow into the Pacific Ocean causing beach closures up and down the coast.

The researchers also suggest that some of the $330 million worth of federally funded sewage control projects closest to the border would probably be underwater. 

Border Patrol has declined to comment on their border wall project. It’s unclear what the final design will be. But they confirmed that preliminary construction began in November. 

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In Other News

  • Lake Mead, the trigger point for the rest of the drought-stricken Colorado River, will rise 20 feet following a mega wet winter. (Las Vegas Review-Journal)
  • Students at University of California-San Diego protested the institution’s fossil fuel use during a rally in an attempt to get the campus to commit to decarbonize by 2030, following comments the university chancellor made about electrifying the campus by that date. (KPBS)
  • California Republicans are upset about a proposed income-based fixed delivery charge that will wind up on bills from investor-owned utilities like San Diego Gas and Electric, arguing that charge should be rendered based on usage (which it is now) not on income. The new fixed charge came from state legislation passed last summer. (Union-Tribune)
  • San Diego County began dropping larvicide in local waterways to combat disease-carrying mosquitoes this month. It’s part of a routine treatment conducted since the early 2000s when West Nile virus was first detected in the U.S. San Diego hasn’t had a positive West Nile case since 2017. (NBC 7)
  • Six of San Diego’s key species are struggling to survive, according to a new report. (Union-Tribune) 
  • Harmless, gelatinous animals called Velella velellas (kin to the dangerous Portuguese man o’war) have been washing ashore in San Diego in a rare mass stranding. (Union-Tribune)
  • In other depressing San Diego animal news, the famous sea lion known for wandering San Diego’s freeways has been euthanized after contracting a progressive disease last year, according to SeaWorld San Diego. (CBS News)

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1 Comment

  1. so we finally have a way to stop the repeated sewage flows from Mexico through the river: build a wall IN the channel that will direct the flow right back into Tijuana. i bet it wouldn’t take long for ALL the sewage infrastructure to be in tip-top condition.

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