What Happens to Alamitos Bay If the Peninsula Is Weakened?

Here is a question Long Beach should answer before the next major coastal emergency:

What happens to Alamitos Bay if the Peninsula’s protective capacity is substantially reduced?

Let me make clear what I am – and am not – saying.

I am not claiming that erosion of the Peninsula will cause Alamitos Bay, Naples, Treasure Island or Marina Pacifica to flood.

I am saying we should use professional coastal and hydrodynamic modeling to determine whether severe changes to the Peninsula could alter wave and water conditions elsewhere in the bay.

That distinction is critical.

The Peninsula separates Alamitos Bay from the Pacific Ocean. The city describes Alamitos Bay as a naturally protected bay augmented by offshore breakwaters.

Behind the Peninsula are neighborhoods and facilities whose daily lives depend upon those comparatively protected waters.

Naples and Treasure Island contain homes, streets, bridges, canals, seawalls, docks, utilities and drainage infrastructure immediately adjacent to the water.

If severe erosion substantially changed the Peninsula, how much – if at all – would wave energy entering Alamitos Bay change during an extreme storm?

I don’t know.

That is precisely the point.

It should be modeled, not guessed.

Long Beach already knows that its southeastern coastal communities have flood vulnerabilities. The city’s Climate Action Plan states that low-lying areas including Belmont Shore, Naples and the Peninsula already experience coastal flooding, particularly when high tides and rain occur together. It projects increasing exposure as sea levels rise.

What we do not have, based upon the material I have reviewed, is an engineering determination that severe Peninsula erosion would cause flooding elsewhere in the bay.

Let’s find out.

Consider the Naples bridges.

In an extreme coastal emergency, boats, pieces of docks, lumber and other floating material could potentially move through waterways. Debris can obstruct passages, and scour can threaten structures.

A bridge does not have to collapse to create an emergency.

A closure can be enough.

If an important crossing becomes unsafe, emergency response and evacuation become more difficult.

Every waterfront community should have more than one viable evacuation route, and Long Beach should know in advance which bridges and roadways could become bottlenecks under worsening coastal conditions.

Now consider Marine Stadium and Mother’s Beach.

These areas normally enjoy substantially different conditions from the open oceanfront.

What would happen if the Peninsula were substantially altered?

Would there be any meaningful change in wave penetration?

Would there be increased currents?

Would there be no significant change at all?

Those are questions for coastal modeling.

The same applies to Colorado Lagoon, where coastal waters, tidal systems, drainage and low-lying land interact.

Rather than publish frightening predictions, let’s obtain credible answers.

The city has another opportunity to learn more through its Alamitos Bay Entrance Channel Dredging Project. The project is intended to restore navigable depths in the entrance channel while using dredged sand to widen and stabilize Peninsula Beach. The city identifies safer access to Alamitos Bay and support for Naples, Marine Stadium, Spinnaker Bay and Alamitos Bay Marina among the project’s benefits.

That demonstrates how interconnected this coastal system already is.

So let’s study it as a system.

Model the Peninsula at its present beach width and elevation.

Then model it after substantial erosion.

What happens if the berm becomes significantly lower?

What happens if portions of the beach lose large quantities of sand?

How do different tides, wave heights and swell directions change the result?

Then examine potential effects on Naples, Treasure Island, Marine Stadium, Mother’s Beach, the marinas, PCH and critical bridges.

Perhaps the modeling will demonstrate that these areas remain adequately protected under even severe Peninsula-erosion scenarios.

That would be reassuring.

Perhaps it will reveal vulnerabilities we did not appreciate.

That would be valuable, too, because vulnerabilities identified beforehand can be addressed.

What is unacceptable is simply assuming that tomorrow’s conditions will resemble yesterday’s.

We don’t need speculation.

We need measurements.

We don’t need predictions presented as facts.

We need engineering.

And we need the answers before the next major coastal emergency arrives.

Hayes is a longtime Long Beach resident, an academic research specialist, and credentialed educator of architecture and engineering.