Surf vs. sand: U.S. beaches are washing out to sea. Can engineers save the shore without ruining the waves?

Science World, May 9, 2003 by Kim Y. Masibay

Surfing buffs have a word for the perfect wave--"tubular." A wave curls into a tube and surfers ride inside it toward shore. But the endless pounding of surf can really grind down a beach. "About 86 percent of U.S. shoreline is eroding [washing away]," says Chad Nelson, environmental director of the Surfrider Foundation.

The reasons are many: Damming rivers and building coastal structures cause some harm. And the U.S. Environmental Protection Agency thinks higher concentrations of greenhouse gases in the atmosphere is causing Earth's temperature to warm, which in turn could raise sea level a few feet in the next century. Bye-bye beaches?

Not if geologists or engineers can help it. But beach lovers are divided over how to best halt coastal erosion. Why? Because tactics that keep sand where sunbathers want it can also wipe out the wave action in the surf zone, the area between the outermost breakers and the shore. Can human ingenuity save the day?

SAND DAMS

Sand is always on the move. While wave action erodes the coastline in one place, the littoral drift (current running parallel to shore) eventually deposits the sand elsewhere. "When a beach erodes, the sand doesn't disappear," says coastal geologist Susan D. Halsey of the Stevens Institute of Technology in Hoboken, New Jersey. "It's just moved to other spots--either on shore or the seafloor."

The trouble is, most sunbathers and surfers don't want nature to move their beaches. So to make sand stay put, engineers use various but controversial methods. One example: They construct large stone structures called jetties perpendicular to the coastline to dam the sand flow along shore. While sand gathers on the up-current side of the jetty, the down-current side erodes. Although the sand-bars that form in the process can create good surf, "jetties can cause the thinning or even disappearance of beaches," Nelson says.

Another anti-erosion tactic: beach nourishment. Engineers have pumped sand ashore to raise and widen beaches from Florida to New Jersey. Dumping tons of sand creates more towel space, but surfers complain it often smothers the very beach shape that makes for good waves (see diagram, page 13).

SHORE BREAKERS

Waves form when wind blows on the surface of the ocean, thousands of miles from a beach. In fact, waves that reach California in summer arrive from storms generated as far as 8,000 kilometers (5,000 miles) to the south. As swells roll nearer to shore, friction (rubbing force) with the seabed slows them down. The distance between the waves' crests, or peaks, shortens, and the heights of waves increase. As water at the top of each wave overtakes the bottom, it topples forward and breaks.

What makes a wave break in a surfable way? "The exact conditions are subtle," Nelson says. "Usually it's a feature on the ocean floor, like a rocky reef or sandbar." When the bottom of a wave strikes a reef, the top of the wave pitches over--like when you trip and fall. If beach nourishment smoothes these features, good surfing waves are history.

FUTURE WAVE

The rocky reefs that create gnarly waves could yield a solution to coastal erosion for both sunbathers: and surfers. "Certain man-made structures create good surf spots," says avid surfer David Skelly, president of Skelly Engineering. The firm built an experimental 18-ton surfing reef 100 yards off a Los Angeles beach. The V-shape structure is made of 150 giant sandbags (or geotubes) and lies parallel to the shoreline in 15-foot-deep water. When waves hit the reef, they break. "When you change the surf, you change the way energy is delivered to the shoreline," Skelly says. "By forcing waves to break farther from shore, the reef can reduce beach erosion."

Skelly's artificial reef has generated such a swell of interest there are plans for two or more off the California coast. Surf's up?

DEBATE IT

Should engineers shore up sand at the expense of good surfing waves? Why or why not?

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Did You Know?

* Rivers carry grains of sediment from inland mountains and bluffs to the oceans. Those grains eventually wash up on beaches--unless, of course, dams or other structures trap the sediment first.

* Beach nourishment can turn a beach into an obstacle course for nesting sea turtles.

* Waves move energy, not water. Picture a seagull bobbing on windswept water. The bird remains more or less in one place as wave after wave passes beneath it.

Cross-Curricular Connection

Geography: Challenge students to research and create a map showing how U.S. coastlines have changed over the last 20 to 30 years.

Critical Thinking: No two beaches have the same exact needs: Tactics that help one beach might harm another. How should federal, state, and local authorities work together to manage beaches? Choose a beach and think of a plan.

Surf vs. Sand

Directions: Solve the clues below to complete this crossword puzzle.

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1. Sandbags: --.

2. Rubbing force: --.

3. A littoral drift is a current running -- to shore.

4. Large stone structures perpendicular to coastline used to dam sand flow: --