More is coming.

Maybe not more mammoth waves, such as the 25-footers that hit the Wedge this week, but more of the mammoth havoc that came with them.

Ocean water pouring into streets and houses in Seal Beach – this isn’t the last time homeowners will see that. Cliffs carved out of the sand at Newport – beachgoers should get used to it. Sand washed out from under walkways at Aliso Beach in Laguna – maybe it’s time to move those walkways.

Rising seas made this week’s hurricane-generated swell more damaging than it might have been, say, 50 years ago. Experts believe future storms will do the same or worse.

And for one of Southern California’s key resources – the beach – that’s bad news.

With ocean water eating away the sand on one side, and with man-made development blocking the sand from making its natural retreat on the other, the beach is shrinking.

Evidence of that trend was easy to see this week.

Huge chunks of beach went missing from the Wedge, the bodysurfing mecca that saw the biggest waves from the huge southern swell. And at Aliso Beach in Laguna, the disappearance of sand revealed pilings from a pier torn down a generation ago.

But the storm only revealed what might be a longer-term trend, one in which local beaches no longer can replenish themselves naturally.

Even as the sand is being squeezed away from the beach by the rising ocean, man-made dams in upstream rivers and creeks are holding back sediment that would otherwise put some new sand back. Also, channelized rivers and streams throughout Southern California lock in dirt, another natural beach replenishment. Sand mining in river basins saps additional supply.

Governments have come up with few solutions. Keep the sand in place, using structures like the jetties in Newport Beach and other spots, or haul sand in and dump it on the shoreline.

“Our answer is to engineer our way out of an engineer-caused problem,” said David Revell, chief scientist at Revell Coastal, an environmental consulting firm. “The only long-term solution is to slowly start moving back.”

This week’s storm broke from usual seasonal patterns.

Normally, heavier storms strike in winter and suck sand off the beach, depositing it in underwater sandbars 30 to 50 yards offshore. That leaves many winter beaches bare, narrow and rocky.

In summer, wave action gradually pushes the sand back to shore, buffering and building up beaches.

What, exactly, will happen with the sand swept off beaches this week isn’t known.

“At first, with these heavy, high-energy waves, (the sand) kind of goes into suspension. You have to wait a couple days to see where it settles out. I’m suspecting that it didn’t get pulled too far offshore,” said Susan Brodeur, a senior coastal engineer with Orange County Parks.

In recent years, governments have started worrying that natural cycles aren’t able to fully replenish the beach.

“In some places, we’ve built right down to where the dunes would be, and you impede the ability of the system to repair itself after a storm. So the system is less resilient now,” said Dave Hubbard, a coastal researcher at UC Santa Barbara.

Intentionally or not, offsite sand has long enlarged Southern California beaches.

The wide, sandy beaches of the Santa Monica Bay, for instance, were built between the 1950s and 1970s by sand displaced from various construction projects, such as the Hyperion Sewage Treatment Plant and the inlets at Marina del Rey.

Those deep beaches, though not necessarily natural, became the cultural norm, helping to foster Southern California’s image as haven of the endless summer.

At the same time, Southern California’s climate went through a period that spurred natural beach formation.

A long-term weather pattern called the Pacific Decadal Oscillation in the mid-20th century led to gentle wave and storm conditions that built up beaches across Southern California.

Those beaches, of course, have been irresistible. People built (and build) houses, parking lots, paths and businesses virtually onto the sand. Changing that – pulling businesses and homes away from the sand – is financially and culturally untenable.

But it’s not a recipe for healthy beaches going forward.

Seawalls may protect property, but they speed the elimination of the beach. As seas rise, the waves crash against seawalls and sandy expanses disappear.

Rising seas and coastal development aren’t the only factors hurting Southern California beaches.

The beaches’ one ally – sediment from upland mountains and rivers – cannot reach the ocean because of dams.

Dams can range in size from 200-foot-tall behemoths like the Matilija Dam in Ventura County to small debris basins at the fringes of Orange and Los Angeles counties. The basins prevent sediment from flowing into and clogging concrete flood control channels that are prevalent across Southern California.

Gary Griggs, director of the Institute of Marine Sciences at UC Santa Cruz, estimates that half of upland sediment never reaches the ocean in Southern California. And with 70 percent to 90 percent of sand on the beaches in California coming from streams and rivers, that’s a big cut.

About 500 dams statewide have held back about 200 million cubic yards of sediment. In Southern California, about 28 dams and 150 debris basins are holding back 5 million cubic yards of per year.

And seawalls, he said, aren’t helping.

“What we will gradually do is drown those beaches, flood those beaches,” Griggs said.

“Beaches will be getting narrower,” he added. “They can’t move inland.”

Contact the writer: aorlowski@ocregister.com or 562-310-7684