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Chapter 6: The Beach

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One night in the summer of 1983 while headed to Los Angeles in a cramped VW Beetle to start graduate school, I drove along a dusty dirt road in Northern California toward a beach campground known as Gold Bluffs. According to my tattered tour book, the campground offered views of coastal redwood trees and the Pacific Ocean, and since I had three weeks to spare before school started, I thought I would check it out.

The next morning I awoke to thunderous surf. Rolling out of my tent, I felt like I had stepped back into the Land of the Giants (Allen 1968). Mammoth redwood trees stood like sentinels on hundred-foot cliffs, guarding Earth, shrouded in a dense mist, seemingly frozen in time. At the base of the cliffs, several gigantic trees lay upended, tossed to their death on the beach below. They were no match for the wallop packed by the Pacific Ocean during a storm, a bitter war between land and sea waged across the millennia.

As I sat on a weathered picnic table eating Cheerios from the box—because that’s what you do when you’re camping—I heard a sound. Out of the gloomy mist and morning chill, beyond the breakers and a few sparse blades of kelp, I saw a gray whale surface and expel his lungs. It was an odd time of year for a gray whale to visit these parts. Typically, they roam the coast between November and May. But I guessed that this fellow was a loner—not unlike me on that morning—one of the old-school males who’d had enough of those ten-thousand-mile annual migrations. He rolled gently just outside the surf, feeding perhaps, or just enjoying a solitary moment in time, as I was. It was one of those instances when time stands still and everything in life is just the way it’s supposed to be. “Welcome to California,” I thought.

I visited Gold Bluffs Beach again in 2005 with my mom on her California journey to live with me after my father died. A few more giant trees had fallen, and a herd of elk grazed among colorful wildflowers. Otherwise, it was exactly as I remembered it. It was a special place to share with my mom. After all, she was the person who introduced me to the beach when I was just a few weeks old. As you can probably tell, the beach holds great meaning for me. I hope it does for you too.

In this chapter, we examine that strip of land along the rim of the world ocean, the beach. Because most of us have formed our deepest impressions of the ocean here, the beach makes a natural starting point for exploring the geology and chemistry of the ocean—subjects in our chapters ahead. 

6.1 What Is a Beach?

The term beach commonly refers to the loose bits and fragments of material along the shore of a body of water, including lakes, rivers, and the world ocean. These bits and fragments consist mostly of sediments, solid particles of various sizes fragmented from rocks. While we think of beaches as mostly sand, they may include any of the six major size classes of sediments as defined in a geological classification system known as the Udden-Wentworth scale. From smallest to largest, they include clay, silt, sand, pebbles, cobbles, and boulders (Udden 1914; Wentworth 1922). Many beaches exhibit the full range of sediment sizes, from clay to boulders.

Sediments also originate from biological and chemical processes. Fragments of shells, corals, and even calcified algae can be found on beaches. Sanibel Island on the west coast of Florida features beaches made almost entirely of intact or broken fragments of shells. Bahamian beaches accumulate ooids, light-colored ovals of calcium carbonate that resemble the hard mint candies known as Tic Tacs. Ooids originate from the precipitation of solids in supersaturated seawater. 

Beaches may host a wide variety of other materials, too—natural and manmade. Beaches in the state of Washington are often covered in driftwood and logs, castaways from the logging industry. The Skeleton Coast on the northern coast of Namibia accumulates the bones of whales, seals, and shipwrecks. And as you well know, debris from humans—especially plastics—can be found on every beach in the world, including those in Antarctica.

6.2 Anatomy of a Beach

Though beaches vary widely in their sediments, they generally exhibit a similar appearance—a common structure—with recognizable features. Identification of these different parts helps us appreciate the nature of beaches and better understand the processes that shape them. (Our discussion here generally follows Pilkey et al. 2004.)

When you enter from a parking lot or a cliff, you first encounter the back of the beach, a typically flat portion known as the backshore. At some locations (such as Oceano Dunes near Pismo Beach, California), you may walk over sand dunes prior to entering the backshore. The backshore is generally the most stable portion of the beach because it is only occasionally inundated by waves. 

The backshore may also contain accumulations of sand in the form of berms, which represent shelves of sand left by waves in a receding tide. Multiple berms may be present on a backshore, especially in the days following the highest tides (e.g., spring tides). During periods of high surf or seasonally extreme tides—popularly known as king tides—the backshore may be completely submerged on some beaches. Much of the debris found on the upper portion of the backshore is deposited during periods of high surf or unusually high tides. Large swaths of sand may be removed from the backshore during these times as well. Otherwise, if the sand on the backshore is untouched by waves or tides, winds may create accumulations of sand as beach dunes.

The lower portion of the beach is called the foreshore. The part that slopes toward the sea—alternately submerged and exposed during a tidal cycle and subject to daily wave action—is called the beach face. The backshore berm, or clifflike beach scarp, if present, marks the upper boundary of the foreshore, while the lower boundary of the foreshore ends at the location of sea level during low tide. Note that the width of the foreshore changes dynamically as a result of the action of waves and tides. The foreshore may grow during periods of high-energy waves and spring tides (when tidal range is greatest). Waves and high water levels push the berm toward the backshore. During periods of low-energy waves and neap tides (when tidal range is lowest), the foreshore shrinks as the berm migrates seaward. 

A common feature on the upper boundary of the foreshore is a line of seaweed and debris known as the wrack line (pronounced “rack”). Kelp wrack is common on Atlantic and Pacific coast beaches where kelp grows nearby. Ocean currents drag sargassum weed from the Sargasso Sea and deposit it (often in great quantities) on Florida beaches. In truth, any kind of dislodged seaweed and marine debris may be deposited on the beach face as the tide recedes. The location of the wrack line on any given day indicates the height of the highest tide at the beach. At times when the height of the highest tide is lower each succeeding day, you may observe several wrack lines, each corresponding to the height of the highest tide of the previous days. 

Beach cusps, a series of crescent- or scallop-shaped deposits of sand parallel to the beach, are another common feature on the upper beach face. Scientists remain uncertain as to the mechanisms that form beach cusps. A type of shore-parallel wave called an edge wave may play some role. However they form, beach cusps are fascinating to observe and a prominent feature on a beach face.

On some beaches the lower portion of the beach face may be flat and exposed during low tide. This is the low-tide terrace. I like to think of it as the ocean’s patio, albeit one with holes, bumps, and streams. The low-tide terrace represents the shallowest portion of the seafloor. If you’re standing on the low-tide terrace, you can truly say that you are walking on the seafloor. 

Sandbars often mark the seaward side of a low-tide terrace. Sandbars represent a “reservoir” of sand that forms when high-energy waves move sand offshore. Under low-energy conditions, the sandbar may be pushed toward the beach and build up the foreshore.

As the waves and tide recede and expose the low-tide terrace, water that has penetrated the sand will flow back into the ocean. Because the foreshore is sloped, the water may flow out of the sand as little streams. As these streams of water flow, they move sand, and, much like a river, they erode the sand and leave tell-tale signs of their flow. The tree-like, or dendritic, patterns left by water seeping out of the sand at low tide are called rills. Look for them the next time you’re at the beach at low tide. 

Often the low-tide terrace is separated from the foreshore by a runnel, a strip of shallow water parallel to the beach. A runnel most often appears in the summer, when small waves push sand toward the beach. Small fish, sea stars, conch shells, and other kinds of marine life may get trapped in these temporary pools. Look, but don’t take. A living creature plays a valuable role in the ocean ecosystem, something it can’t do sitting on a shelf collecting dust in your home.

Directly offshore of the low-tide terrace, you will encounter the area that many people travel to the beach to experience—the surf zone. It extends from the point where the waves begin to break to the edge of the beach. A current may be present here which flows parallel to the beach between the surf zone and the foreshore (see below). 

The region below the low-tide terrace and beyond is called the offshore. The term also refers to a direction—away from the shore. Winds blowing from the land toward the ocean—such as occurs during Santa Ana wind conditions in Southern California—are classified as offshore winds.

Finally, the region of the ocean from the low-tide terrace to the edge of the continental shelf is called the coastal ocean (or neritic zone). The coastal ocean includes all the waters above the continental shelf (discussed in Chapter 7). Beyond that, we’re in the open ocean, the deep blue sea, largely removed from any terrestrial influences.

6.3 The Origins of Beach Sand

The individual bits of materials on a beach are called grains, as in grains of sand. Individual grains generally consist of a single mineral, defined as solids of inorganic material with a unique chemical composition and crystalline structure. Rocks consist of aggregates of minerals and non-minerals according to Fullerton College emeritus geology professor Richard Lozinsky, aka “Doc Rock” (Lozinsky 2010). Thus, sand grains and their minerals come from rocks (as we shall see).

Close inspection of the grains of sand from a typical Southern California beach will show that the sand consists mostly of white or clear grains, identified as the mineral quartz; yellowish grains, identified as the mineral feldspar; and gray or black grains, identified as the mineral biotite. Identification of the minerals present in a sample of sand provides clues as to where the sand originated. They can also help detectives catch criminals, a field called forensic geology (e.g., Ruffell and McKinley 2008).

Three major types of rocks can be found on Earth: 

  • Igneous rocks, rocks originating from the solidification of magma (molten material below Earth’s surface) or lava (molten material extruded onto Earth’s surface)
  • Sedimentary rocks, rocks formed from the fragmentation and consolidation of other rocks
  • Metamorphic rocks, rocks modified by heat, pressure, and fluids

According to Best (1995), igneous-type rocks comprise nearly 65 percent of the rocks found in Earth’s continental crust and more than 95 percent of  rocks forming the seafloor. Sedimentary rocks make up about 8 percent of the volume of Earth’s continental crust and less than 2 percent of oceanic crust. Metamorphic rocks make up slightly more than 27 percent of Earth’s continental crust and a small percentage of oceanic crust. 

Earth’s rocks rarely remain the same. Any of these three rock types may be transformed into another. Geologists refer to these transformations of rock and the processes that cause them as the rock cycle. Plate tectonics plays a major role in the transformations of the rock cycle. But a number of processes on Earth’s surface also alter the properties of rocks, as we shall see.

6.4 From the Mountains to the Sea

Our search for the origins of beach sand begins in the most unlikely of places, the mountains. This is where many sediments begin their life. Geologists refer to the source material that produces sediments as the parent rock. The rock(s) from which sediments originate defines the sediments’ heritage—the properties inherited by the sediments from the parent rock. Just as your heritage may be defined by the genes and cultures of your parents, the heritage of a particular type of sediment comes from the characteristics of the rock that gave rise to it. Sediments have parents, and they inherit properties from those parents, just like us.

To understand how sediments move from the mountains to a beach, it’s useful to introduce the concept of a watershed, an interconnected region of waterways that drains water, dissolved materials, sediments, and debris to a common outlet. Watersheds drain water from higher elevations to lower elevations. Eventually, the water and any associated dissolved or solid materials come to rest in a lake, a manmade reservoir, or the ocean (e.g., Dobson and Beck 2022). 

Most watersheds are associated with rivers, and these may be supplemented by smaller creeks and streams, what are known as tributaries. A river’s watershed includes all the tributaries that feed water into the main artery of a river. In outline, a watershed may resemble a branched tree, where the smaller branches (i.e., creeks) merge into larger branches (i.e., the streams) and the larger branches connect to the main trunk (the main channel of the river). You might think of these pathways as being like capillaries that connect with veins that merge in the heart. All paths lead to the same place. The waters where the river begins are referred to as headwaters. At the other end, the common outlet of the watershed is called the mouth (e.g., Dobson and Beck 2022). 

As one example, the Santa Ana River Watershed—the largest watershed in Orange County, California—represents all the creeks, streams, and rivers that flow into the main body of the Santa Ana River, an area of 2,840 square miles (7,356 km2; SAWPA 2019). The headwaters of the Santa Ana waters lie near Mt. San Gorgonio, the highest peak in Southern California (the seventh highest in the lower 48 states). The mouth of the river—some 100 miles (161 km) downstream—opens between Newport Beach and Huntington Beach and empties into the Pacific Ocean.

The concept of a watershed is an important one for understanding how each of us plays an important role in protecting the ocean. Anything thrown or poured on the ground—even dozens of miles from the shore—represents a potential pollutant. With sufficient flows—which occur during heavy rainfall or rapid snowmelt—this material enters the watershed and flows to the ocean. As Long Beach oceanographer and Algalita founder Captain Charles Moore says, “The ocean is downhill from everywhere.” 

6.4.1 Weathering

We now return to the three most common minerals found in Southern California beaches—quartz, feldspar, and biotite. Based on what we just learned, we know that they must have come from a rock containing these minerals. As it turns out, we find these minerals in granite, a common igneous rock. Could granite from the mountains be the parent of beaches?

Next time you venture into your local mountains, look carefully at the foot of a rocky outcrop. You will see chunks of smaller rocks and sediments broken off from the main rock. These sediments formed as a result of weathering, the disintegration and alteration of rock at Earth’s surface. Geologists recognize three major types of weathering (e.g., Carroll 1970):

  • Physical (or mechanical) weathering, the breakdown of rocks by physical processes
  • Chemical weathering, the breakdown of rocks by chemical processes
  • Biological weathering, the breakdown of rocks by biological processes (some geologists lump this category with the other two because organisms can physically or chemically break down rocks)

Physical weathering refers to any process that bangs rocks together and breaks them apart or physically separates them through wrenching or brute force. Rockslides, the tumbling of rocks downhill, and earthquakes, the violent shaking of the ground (which also causes rockslides), are two examples. Heating and cooling of rocks—thermal expansion and thermal contraction, respectively,  that wrench and weaken rocks—is another. Moving water—rivers, waves, currents—and even strong winds can clang rocks against each other and cause them to fragment. And water that freezes and expands in the cracks of rocks causes a type of weathering called frost wedging.

Chemical weathering occurs as a result of dissolution (i.e., dissolving) of the more soluble parts of rocks, usually by water. Some rocks contain salts, which, of course, readily dissolve in water. In fact, dissolution of salts in rocks and drainage of the saltwater into a basin create hypersaline lakes. Rainfall, too, plays a role. Raindrops naturally dissolve carbon dioxide in the atmosphere. By the time they reach the ground, they are slightly acidic. The slightly acidic rainfall is responsible for the weathering of statues and tombstones, which makes them appear as if they have melted.

Biological weathering refers to the activities of organisms that contribute to the fragmentation of rocks. Lichens—a fascinating partnership between fungi and algae—secrete chemicals that accelerate rock decomposition. Trees are very good at wedging their roots between cracks and physically breaking rocks apart. Think about that next time you are skating down a sidewalk and come to an abrupt “ramp” caused by a tree root.

All of these weathering processes can produce prodigious amounts of sediment. Consider that more than 30,000 feet of sediments (more than 9 km)—nearly as deep as the Mariana Trench—fill the Los Angeles Basin at its deepest spot beneath Downey (Yerkes et al. 1965). That sediment came from the surrounding mountains. But how did it get there?

6.4.2 Sediment Transport

Scientists who study sediments—sedimentologists—refer to the movements of sediments over space and time as sediment transport. For the most part, sediment transport refers to motions of grains due to moving fluids, such as winds or moving water (e.g., rivers, currents, street runoff). But gravity-driven flows, such as those that occur when glaciers push sediments downhill, also contribute to the movements of sediments. 

When a moving fluid encounters a particle, it exerts a force on the particle. The force exerted by the fluid depends on a number of factors, such as:

  • the properties of the fluid (i.e., its density and viscosity)
  • the speed of the fluid and the nature of its flow (i.e., steady or turbulent)
  • the size, shape, density, saturation, and compaction of the particles
  • the shape of the surface on which the particle rests 
  • other factors

Now, like us, a particle can withstand a certain amount of flow without budging: we don’t get blown away every time the wind blows. However, there comes a point when the fluid motion is strong enough that the particle begins to rock and roll. The fluid speed at which a particle begins to move is called the threshold velocity.

Three definitions describe the motion of an individual particle in a moving fluid. The particle can tumble across a surface, generally (but not always) in the direction of fluid flow, a process called rolling. The particle can hop, that is, it can become temporarily suspended in the fluid and move forward before landing back on a surface, a process called saltation. Or the particle can “fly” within the fluid: it can move as part of the fluid, a process called suspension. In most environments, an individual particle will experience all three of these processes—rolling, saltation, and suspension—as the motions of a fluid generally vary with time and distance. (See Biju-Duval 2002 for a more extensive treatment of this topic.)

6.4.3 Sediments in Motion

Now, let’s stop and think about these simple concepts as they might apply to sediments, and especially to different size classes of sediments. Fluids such as water or air exert a force on objects immersed within them. Fluid velocity determines whether a given particle will roll, hop, or become suspended in the flow. The faster the fluid, the more likely a given particle will become suspended.

However, the likelihood of a particle taking off, so to speak, also depends on the size of the particle. Smaller particles move more easily than larger particles. Consider your own experience with house dust, which consists of particles in the silt and clay size fractions. A swift blow across a dusty surface quickly sends the dust into the air (i.e., the dust becomes suspended). Yet try this with a boulder, and you will likely become winded before the rock budges. Smaller particles—ones without a lot of mass to resist fluid motions—will move sooner and become suspended faster than larger particles. Put another way, we can say that smaller particles have lower threshold velocities than larger particles do. 

Given this, it should make sense to you that the threshold velocity of particles increases as the size of the particles increases. Specifically, clay-sized particles have lower threshold velocities than silt, sand, gravel, and boulder-sized particles, which have higher threshold velocities. From this, it should also make sense that clay-sized particles will move under a wide range of fluid velocities while boulder-sized particles will only move at the highest fluid velocities, a narrow range of fluid velocities. 

Of course, the type of fluid will make a difference, too. Eight hundred times denser than air, water packs a punch on anything in its path. If you’ve ever seen video of fast-moving water from a torrential rain, an overflowing river, or a tsunami, you’ve probably seen cars floating downstream. In places where flash floods occur, you should be familiar with the National Weather Service warning “turn around, don’t drown.” It takes only six inches of water to knock a person off of their feet and only a foot of water to levitate a small car. So while strong winds can make suspended sand feel like sandpaper on your bare legs, the wind, even at hurricane velocities, is not likely to move cars. But water moving at even moderate speeds can move boulders and larger objects.

If smaller particles move more easily, then it stands to reason that they also move more often and over greater distances than larger particles. Particles of clay, silt, and even sand will be carried by wind or moving water much more frequently and much farther than gravel and boulders. Trade winds can blow clay-sized particles clear across the Atlantic Ocean, from the Sahara Desert to Florida and Texas (e.g., Toon 2003; Goudie and Middleton 2006; Conway and John 2014). Particles of ash from volcanoes or large fires may be carried around the world (Carn et al. 2015; Peterson et al. 2018). So, too, water moves clay- and silt-sized sediments hundreds of miles or more. When rivers deliver clay and silt to the ocean, currents may distribute them far across ocean basins (e.g., Hedges et al. 1997).

6.4.4 Sorting of Sediments

As a result of transport by fluids, different size classes of sediments separate from each other. Larger particles stay close to their source while smaller particles move farther from their source. The size separation of sediments that results from their transport by moving fluids is called sorting. If you’ve ever sorted laundry—separating socks and undergarments from shirts and pants—you have some idea of what sorting means. Generally, high winds and strong currents sort sediments faster than light winds and weak currents. Alternatively, light winds and weak currents acting over long periods of time will also sort sediments. Your mom may sort laundry faster than you, but given time, your slow and steady pace achieves the same result.

Because winds and currents sort sediments, sedimentologists can learn a great deal by studying the degree of sorting in a given deposit of sediments, a characteristic called the grain size distribution. If the range of grain sizes in a deposit is narrow, that is, if the grain sizes are similar, the deposit is said to be well sorted. Alternatively, if a wide range of grain sizes is found in a deposit, we can say that the deposit is poorly sorted (e.g., Folk and Ward 1957). Can you think of why a sample might be well-sorted or poorly sorted? (Hint: It has to do with fluid motions.)

6.4.5 Modification of Sediment Grains

All this moving causes sediment grains to lose some of their original character. Sedimentologists use the term texture to refer to the size, shape, and arrangement of particles in sediments or sedimentary rocks. As particles slide, hop, and glide in a moving fluid, they jostle and bump into each other, a kind of sedimentary mosh pit. The collisions between particles slowly wear them down and smooth out their rough edges. Particles that were initially angular in shape take on a more rounded appearance. If you’ve ever walked in a dry riverbed or along the shore of a lake with a cobble beach, you may have noticed the flat and smooth rocks. That’s because these rocks have been modified by water as it flows over them and tumbles them against their fellow rocks. The action of the water works a lot like a rock tumbler, a device with a rotating drum used to polish rocks. Thankfully, nature does the same thing. How would we skip rocks across the surface of a lake if they weren’t round and smooth?

6.4.6 Where the River Meets the Sea

Finally, we return to the beach. Let’s review the journey of a grain of sand from the mountains to the beach:

  • Weathering and fragmentation of parent rock into sediments
  • Erosion and transport of sediments away from their parent rock
  • Modification of sediments as they roll, jump, and fly downstream
  • Deposition of sediments at a river’s mouth or transport out to sea

Each of these steps unfolds over timescales of days to decades. In Southern California, rain falls mainly in winter, so weathering, transport, and modification of sediments will be greater in winter. In late spring, the Santa Ana River dries up. In fact, most times of the year, all you’ll see is a dry riverbed. Little change in sediments or their properties will occur at these times. But when we get significant rainfall, such as happens in January–March, or during periods of El Niño, the river becomes a torrent. Higher flows mean a greater volume of sediment is transported and that the sediment will travel farther from its source. 

Satellite images following extreme rainfall show plumes of sediments being carried offshore (e.g., Nezlin et al. 2008; Holt et al. 2017). These images likely represent suspended silts and clays, the smaller and more easily suspended sediments. Sand-sized sediments tend to be deposited at the mouths of rivers. There the energy of the river diminishes as the river enters the ocean. Slowing below the threshold velocity of suspension, the sand settles onto the river bottom. These deposits of sand at the mouth of a river form deltas—a landform shaped like a paper fan, a bird’s foot, or other form. But deltas don’t always form, and sand doesn’t always pile up at the mouth of a river. Let’s see why.

6.5 Wave-Driven Sediment Transport

Ocean waves, the physical expression of energy moving through the ocean, transfer some of their energy to sediments as the waves break at the mouth of a river. If given sufficient energy by the moving water, the sand will roll, hop, or become suspended. And if the waves arrive at an angle relative to the river mouth—as opposed to straight on—a current of water—the longshore current—will be generated along the shore. This current—driven by the energy of the waves—can move sediments down the beach.

6.5.1  Longshore Transport

Once the river-transported grains of sand reach the ocean, they keep moving down the beach with the assistance of the energy provided by the wave-generated longshore current. This current moves sand (and even you!) down the beach if it’s strong enough. Have you ever gone into the water on a day with high surf and found yourself way down the beach a few minutes later? You’ve experienced the longshore current.

Unlike ocean currents, the longshore current operates only within the surf zone. As a wave approaches at an angle, one part of the wave reaches the beach before the rest, and the water temporarily “piles up.” Just like water flowing downhill owing to the force of gravity, the water piled up from the wave flows “downstream,” that is, in the direction opposite the incoming wave. The result is the longshore current.

Grains of sand within the longshore current generally move parallel to the beach. But because of the back-and-forth nature of waves, the suspended materials often take a zig-zag path down the beach. This wave-generated movement of sand grains and other materials is called longshore transport. 

Enormous volumes of sand may be transported along coastlines. Patsch and Griggs (2006) report that up to a million cubic yards of sand may move southward along the California coast annually. Considering that one cubic yard of sand weighs roughly 2,700 pounds—about the weight of a Kia Forte (Kia 2023)—that’s a million Kias worth of sediment traveling down our coast each year. That’s a lot of sand. Sedimentologists estimate that tens of thousands to possibly more than two million cubic yards of sand move southward along the US East Coast annually (e.g., van Gaalen et al. 2016).

The longshore transport of sediments by the longshore current has been eloquently referred to as a “river of sand” (Encyclopedia Britannica Films 1966). Just like a terrestrial river that moves sand from the mountains to the ocean, the river of sand (i.e., the longshore current) moves sand down the beach from the mouths of the rivers. This conceptual model of longshore transport proves useful for envisioning the transport of sediments along beaches, as we shall see.

6.5.2 Cross-Shore Transport

Waves also carry sediments back and forth across the beach, a process called cross-shore transport. When a wave strikes a beach, it transfers enough energy to the sand to cause the sand to become temporarily suspended. Once suspended, the sand flows with the motion of the water. As the wave slides up the beach, it carries sand with it. If the wave energy is high enough, the sand will remain in suspension and be carried back out toward the sea as the wave recedes from the shore. If the wave energy is low, the sand will be deposited at the point where the wave can no longer carry it. Simply put, high-energy waves move sand away from the beach and low-energy waves move sand onto the beach.

When big waves pound the shore, as they typically do in winter in Southern California, they remove sand from the beach face.  The excavated sand moves offshore. In the deeper water, where the waves’ energy is reduced, the sand settles and forms sandbars. When gentle waves caress the shore, as they typically do in summer in Southern California, they move sand from sandbars onto the beach. A sandbar acts as a reservoir of sand, at least on a temporary basis. 

It’s quite dramatic to see the changes that can occur on a beach. Beaches are ever changing, which is just another thing that makes them so darn interesting.

6.5.3 The Beach Profile

The movement of sand onto or away from the beach face by cross-shore transport alters the appearance of a beach, what is known as the beach profile. Like a profile of a person when viewed from the side, a beach profile refers to the changing slope of the beach from the backshore to the foreshore. 

Measurements of beach profiles provide a simple and useful means for tracking seasonal and other kinds of changes in beaches. First described in 1961 by University of Southern California marine geologist Kenneth O. Emery (1914–1998), the method requires only two 2-meter-long measuring sticks and a tape measure. By holding the sticks in a line perpendicular to the beach and separating them by a known distance, the slope of the beach can be determined by observing the marks on the beach-side stick where the top of the oceanside stick lines up with the horizon. Known as the Emery method, this tool for determining beach profiles has found wide adoption among beach managers, beach scientists, and students. (See Emery 1961.) If you take an oceanography field class, you’re very likely to encounter this technique in your studies.

6.5.4 Contributions from Beach Bluff Erosion

Recent research on some California beaches suggests that a percentage of their sand comes directly from the erosion of coastal bluffs, a type of rounded cliff found on coastlines. For example, bluff erosion contributes 31 percent of the sediments found on Laguna Beach (Patsch and Griggs 2007). Oceanside receives 80 percent of its sediments from the erosion of coastal bluffs (Young et al. 2010). Of course, many of these bluffs were created by sedimentary processes in times past. But recognition of beach bluff erosion adds a new wrinkle to the explanation of where sand comes from on our beaches.

6.5.5 Submarine Canyons

The final step in our journey from the mountains to the sea takes us to the resting place for sediments in the ocean. In many places along the coastline, the river of sand suddenly stops, as if the sediments have disappeared. In fact, as it turns out, sediments are drained from beaches by the presence of a submarine canyon, a steep-sided underwater valley whose shallow end—its head—comes close to shore. 

Sediments carried by the longshore current often accumulate where a landform—such as a headland—interrupts their flow. The sediments may eventually move around the landform, but if a submarine canyon is present, they will be deposited at the head of the canyon. Here gravity takes over. If the mass of deposited sediment grows too large, it may become unstable, at which point it will tumble down the canyon. Such underwater landslides are called turbidity currents and they are one of the forces that create submarine canyons. 

Submarine canyons can be found along all coastlines of the world. The Southern California Continental Borderland—roughly the coastal waters from Point Conception to the US-Mexican border—boasts 11 submarine canyons and 2 sea valleys (a similar feature) that drain sediments to basins (Normack et al. 2009). This includes the Newport submarine canyon, a branch of which lies less than 500 feet (150 m) from the Newport Beach pier (Felix and Gorsline 1971). Submarine canyons serve as a major sink for beach sediments and represent an important pathway for delivering sediments to deep basins (e.g., Sweet and Blum 2016). 

6.6 The Littoral Cell

The sand on a beach on any given day may be thought of as a reservoir, a place where something is stored. The size of this reservoir represents a balance between sources—processes that add to the reservoir—and sinks—processes that remove from the reservoir. Applying this idea, we may think of a beach as a reservoir of sand. Rivers and coastal erosion that bring sediments to the beach act as sources. Submarine canyons that remove sand from the beach are a sink. We can use this model to understand why some beaches grow in size, why some shrink, and why others seem to maintain a balance of sand over time.

The watershed-beach-submarine canyon system—the path of sand from the mountains to the seafloor—form a system known as a littoral cell (or coastal cell). The concept of a littoral cell originated from a desire to understand why sand disappears on some beaches. The littoral cell embodies the sources, transport path, and sinks that determine the size of a beach. 

The balance between sources and sinks in a littoral cell can be modeled in terms of a beach sand budget (e.g., Bowen and Inman 1966). This accounting of the sources and sinks helps beach managers evaluate strategies for maintaining an adequate reservoir of sand. We won’t go into the mathematics here, but understanding the basic idea that sources add sand to the beach and sinks take sand away will help you appreciate efforts to understand human impacts on beaches and efforts to preserve these critically important habitats.

6.7 Human Impacts on Beaches

The longshore and cross-shore transport of sand from rivers and the journey of sand from the mountains to the sea are eloquently documented in an Encyclopædia Britannica video classic, The Beach: A River of Sand (1966). The film—now more than 50 years old—also tells another story, a darker story, one that reveals the ways people have altered the natural functioning of beaches.

Beaches serve as the centerpiece of a trillion-dollar global tourist ocean economy (Brumbaugh and Patil 2017). In the US alone, beaches generate billions of dollars in revenue from tourists and beachgoers (e.g., Houston 2018). Municipalities in charge of maintaining beaches have a strong desire to make sure that the sand on the beach stays clean and stays put—no sand, no tourists, the thinking goes. 

Human activities can disrupt the natural flows of sand. In some cases, these activities lead to increases in the amount of sediments flowing downstream. In others, the supply of sand is diminished. Both have consequences for the coastal ecosystem and for human wealth, health, and safety.

6.7.1. State of the World’s Beaches

Using observations from satellites, researchers can now reasonably estimate the state of the world’s beaches and their changes over time. A recent study found that about a quarter of the world’s beaches are eroding, about a quarter are growing, and about half appear stable (Luijendijk et al. 2018). Whether that’s good news or bad news depends on where the beaches are located. 

More than two billion people and a third of the world’s “megacities” live in the coastal zone, defined as the area within 62 miles (100 km) of a coastline (Small and Nichols 2003). Compiling a global database on beaches using data from remote sensing platforms, researchers can identify “hotspots” where beaches are either losing sand or gaining sand (Luijendijk et al. 2018). Four of seven receding hotspots are in the United States. The world’s fastest-growing beach is in southwest Namibia, where an active beach diamond mining operation adds sand to the beach.

6.7.2 Too Much Sand?

Several human activities increase the downstream flow of sand to beaches. Mining, deforestation, agriculture, and road construction rank highest on the list. These activities result in an oversupply of sediments that clog urban and coastal waterways, generate dangerous debris flows, and damage coastal ecosystems. 

An overabundance of sediments has several negative consequences. Sediments can bury organisms, deliver toxins, reduce light penetration required for the growth of marine seaweeds and plants, and promote the growth of harmful bacteria (e.g., Granger et al. 2010; Mekonnen et al. 2015; Saunders et al. 2017; Lintern et al. 2018). However, these negative consequences can be reduced by restoring natural flows of sediments. 

6.7.3 Too Little Sand?

Manmade structures can block the natural flow of sand. Paving of land (reducing erosion), construction of dams, and building of coastal infrastructure to trap sediments upstream (e.g., groins, jetties, and seawalls) may impede the flow of sediments to a beach. Anything that reduces the natural weathering processes or that alters the downstream transport of sediments will reduce the delivery of sediments to the ocean. 

Beaches whose supply of sediments is shrinking experience beach starvation. In California, a study by the US Geological Survey revealed that 40 percent of beaches have experienced long-term erosion—over 120 years—and 66 percent exhibited severe short-term erosion—over 25 years (Hapke et al. 2009).

Starved beaches are more susceptible to extreme waves and more prone to flooding as a result of sea level rise, especially during times of king tides. When water moves closer to shore, coastal structures suffer damage by waves and intrusion of saltwater, which dissolves metals and corrodes machinery. People can no longer enjoy the beach because much of it is gone. Fewer beachgoers translates into economic losses for industries dependent on coastal tourism. Beach erosion can be deadly as well. In 2019, three people lost their lives when a coastal bluff collapsed  at Grandview Surf Beach in Encinitas, California (Xia 2019).

One cause of beach starvation is the damming of rivers. Used for flood control or to generate power, dams prevent the flow of sand to the beach. The sand becomes trapped behind the dam. Starved of its natural supply of sediments, the beach shrinks. In recent years, dam removal has been carried out to restore coastal sediments. The largest project ever attempted—removal of two dams on the Elwha River in the state of Washington—resulted in a release of 30 million tons of sediments into the watershed (Ritchie et al. 2018). Remarkably, after nearly a hundred years of beach and estuarine sediment starvation, a supply of sand was returned to the shoreline (Warrick et al. 2019). 

Other impediments along coastlines are structures built along shorelines. Groins, concrete and rock structures built perpendicular to the shore, act as a barrier to maintain sand on beaches. While groins effectively trap sand on their upstream side, they cause a deficit of sand on their downstream side. Coastal armoring—paving or hardening of bluffs and seawalls to block wave action—protect shorelines, at least temporarily. However, armoring reduces bluff erosion, cutting off a source of sand. Seawalls intensify wave energy and increase erosion adjacent to the seawall. The net effect of these efforts is to reduce flows of sand and disrupt natural beach processes (e.g., Pilkey and Cooper 2012).

6.7.4 Beach Nourishment

Another temporary measure is the feeding of beaches. Beach nourishment refers to the practice of adding sand directly to the beach from an external source. Sand may be dredged from channels or river mouths and piped to beaches or transported from local deserts. Whatever the source, beach nourishment can be costly and may have negative consequences for coastal ecosystems (e.g., Speybroeck et al. 2006; Elko et al., 2021). Like the giant man-eating plant in the film Little Shop of Horrors (Corman 1960), some beaches just can’t be fed enough.

To track beach nourishment efforts, the Program for the Study of Developed Shorelines at Western Carolina University in North Carolina maintains a public website (beachnourishment.wcu.edu). According to its database, more than 350 million cubic yards of sediment have been applied to 343 sites in California at a cost exceeding $281 million (2019 dollars). 

Orange County, California, recently completed a $19.5 million sand management project—dredging the Santa Ana River mouth and using the dredged material to replenish local beaches (Connelly 2016). Despite these efforts, beach nourishment in California has met only about half of the sand deficit (Patsch and Griggs 2007). Long-term beach erosion and cliff retreat remain problems on at least 40 percent of California beaches (Hapke et al. 2009).

In New Jersey, nearly a billion dollars has been spent on beach nourishment in the past three decades. The choice is one to maintain the beach (through nourishment) or rebuild coastal homes every decade or two. As one coastal manager justifies it, “We live on the shore. We love the beach. We need to maintain it. . . . Yes, it’s expensive, but it’s not the most expensive thing you can do for shore protection” (O’Neill 2015).

6.7.5 Sand Mining

Journalist and Los Angelino Vince Beiser calls sand “the most important solid substance on Earth.” You might think he’s joking until you realize that sand is part of just about everything we build. As marvelously portrayed in Beiser’s book, The World in a Grain: The Story of Sand and How It Transformed Civilization (2018), the world is running out of sand.

It turns out that sand is an essential ingredient of concrete, the stuff of which modern civilization is built. The other two ingredients are cement and gravel, but these are abundant. And though sand is also abundant, it turns out that only a special kind of sand works to make concrete. That sand is largely found on beaches. Desert sand has grains that are too smooth. Smooth grains in a concrete make it fall apart. Beach sand, on the other hand, has angular grains that lock together in the matrix of the cement. In essence, beach sand makes concrete hard. And the bulk of sand goes into construction. To build using concrete, you need sand. Lots and lots and lots of sand. 

Sand can only be obtained by mining it—sand mining—shoveling sand off beaches or sucking it off the seafloor. Not surprisingly, sand mining operations can be found on beaches and coastal waters all around the world. Unfortunately, sand mining operations often destroy the habitats where the sand is extracted. As you might guess, mining of sand from beaches accelerates beach erosion. It can also negatively impact sensitive nearshore habitats, such as coral reefs, mangrove forests, and seagrass beds (Beiser 2018). Environmental concerns led the state of California to shut down one of the longest-operating sand mining operations in the United States, the CEMEX Sand Mine in Marina, California (very near Cal State University, Monterey Bay). The plant, blamed for accelerating beach erosion, ended operations in December 2020 (Shalev 2020).

As sources for sand dwindle, people turn to illegal means to obtain it. Beiser describes what he calls the “sand mafia.” In parts of India, where the illegal sand economy is estimated at $2.3 billion annually, local residents describe torture and murder in the name of sand (Beiser 2018). Stealing and smuggling have become so prevalent that some countries have now banned exports of sand.

Experts believe that the only way to reduce environmental threats and violence is to implement some kind of “global sand governance system” (Torres et al. 2017). Better data on the global demand for sand will enable development of a global sand budget. And efforts must be taken to raise public awareness of the “sand crisis” to spur policymakers to take action. Regulations with sensitivity to local concerns and means for enforcement and monitoring will enable “the global community . . . to use sand more sustainably and avert a tragedy of the sand commons” (Torres et al. 2017).

6.7.6 Beach Diamond Mining

Though limited to one region of the world, beach diamond mining in southern Namibia, near South Africa, deserves mention. Diamond mining developed in 1908 when Zacharias Lewala, a Namibian railway worker who had worked previously in a diamond mine, recognized on the ground several kimberlite rocks, the kind of deep mantle rocks that contain diamonds. He showed them to his German boss, August Stauch (1878–1947), who staked a claim on the area and became a millionaire. For his part, Lewala’s name earned a place in the history books, but little else is known about the man (e.g., Badenhorst 2003).

Similar to alluvial mining, beach miners sift the sand for rock and diamonds, often using heavy machinery and giant sifters. Front loaders and shovels may be used where diamond-bearing material occurs. To gather the diamonds, workers use brooms and hand collection. Conditions for workers appear less harsh than in “blood diamond” regions, primarily because of strong agreements between the sole mining company, De Beers, and the Namibian government (Munier 2016). But the mines are nearing the end of their profitability—less than 15 years may remain—so alternative employment (including cutting and polishing of diamonds) and other possible industries (such as tourism) are being considered to offset unemployment as the diamonds dwindle.

6.7.7 Living Shorelines

Ultimately, best practices for protecting coastal habitats from upstream threats involves ecosystem-based management principles, which encompass the full range of interconnections between ocean, estuarine, wetland, freshwater, and land habitats. Sheaves (2009) refers to the connectivity between land and sea as “the coastal ecosystem mosaic.” 

One recent approach involves a kind of hybrid between constructed and natural landscapes. Known as living shorelines, this approach combines structural materials (natural and artificial) with natural vegetation and marine organisms to protect coastlines and preserve the ecological services that coastal habitats provide (e.g., Sutton-Grier et al. 2015). 

As the concept of living shorelines has matured and gained acceptance, coastal stakeholders have increasingly turned to its principles to ensure success of their projects (e.g., Bilkovic et al. 2017). Structures that reduce erosion upstream prevent those materials from moving downstream. Installation of permeable surfaces traps sediments and debris in place. Biological filters help remove nutrients and toxins and other harmful substances. While solutions based on incorporating natural processes into urban systems remain relatively new, their potential to solve a wide variety of environmental threats makes them promising, if not essential.

6.8 The Last Beach?

In their sobering book The Last Beach (2014), renowned coastal geologists Orrin Pilkey (b. 1934) and Andrew Cooper (b. 1962) spell out clearly the impacts of humans on beaches:

The hands of humans are very clearly on the beaches of the world. Many of our actions are fairly benign—we swim, fish, sunbathe, stroll, or just enjoy the view, the sea breezes, and the smells of the sea. But we also dump trash and discharge our waste pipes onto beaches. We rake them to “clean them up,” drive on them, and mine them for minerals, gravel, and sand. We bulldoze them to make “dunes” to protect houses, pump or truck sand around the beach to “improve” it, and build walls and breakwaters of various types to block waves and hold the sand in place.

Though progress has been made, many questions remain regarding the future of beaches and our efforts to maintain them for human and natural uses. As Vitousek and colleagues (2017) put it: “The science of the coastal zone is bursting at the seams with unanswered questions. . . . The future of the coastline will be what we engineer it to be.”

6.9 Chapter References

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