The Coast in Motion

By Elizabeth King

Focus Question

How does the coast change? What causes these changes? What effect do man-made structures have on the beach?

Activity Synopsis

Basic coastal processes and resulting geomorphology of a “typical” beach and barrier island along the Atlantic Coast of the U.S., especially in SC, are modeled to demonstrate the dynamic nature of the coast. This activity can be done in the classroom as well as on a beach.

Time Frame

1 or 2 50-minute class periods

Student Key Terms

  • longshore current
  • spit
  • sandbar
  • scarp
  • surf zone
  • maritime forest
  • salt marsh
  • dune
  • berm
  • profile
  • hurricane
  • storm surge
  • inlet
  • ridge and runnel
  • groin
  • seawall
  • revetment
  • swash
  • backwash
  • littoral drift

Objectives

The learner will be able to:

  • understand basic coastal processes and geomorphology
  • model the dynamic nature of the coast
  • model the effects that man-made structures have on the beach

Fifth Grade Standards Addressed

Science Standards

IA5a; IA6a; IIIA1j

Background

Key Points

Key Points will give you the main information you should know to teach the activity.

  • The beach is dynamic in nature, and is constantly changing.
  • Longshore current provides the force for the most change to our coastline, by moving great amounts of sand offshore and depositing them at opposite ends of individual barrier islands.
  • Winds, waves, currents, tides and storms are all natural forces that continually change the beach. Human impacts such as seawalls, revetments, and groins also change the topography of the beach.

Detailed Information

Detailed Information gives more in-depth background to increase your own knowledge, in case you want to expand upon the activity or you are asked detailed questions by students.

Wintertime is a wonderful time to walk on the beach, the section of barrier island closest to the ocean. Summer crowds have thinned, and shells are abundant. There is something about the beach that lures us back visit after visit. The beauty and spaciousness attract us, but there is another aspect on the interface between land and sea that we find intriguing: the beach is constantly changing.

A continual force working along our coast is the longshore current. This current or mass movement of water (also known as littoral drift) generally flows from north to south along the face of the beach. Littoral drift is the force that carries you down the beach, away from your towel and sunscreen, as you swim in the surf. Just as it carries you, this current moves tons of sand each year. In fact, so much sand is transported along the front of the beach that geologists call this phenomenon a “river of sand.” The longshore current tends to erode the north end and build up the south end of barrier islands, a process that occurs daily little by little.

If you live near the beach you can watch it change seasonally. The larger waves and stronger winds of winter carve sand away and give the beach a steep slope; often a little sandy cliff will appear in the midsection of the beach. This profile is called a “winter beach.” Much of the sand removed during the winter is stored just offshore in the form of a sand bar. During the summer, climate patterns change and strong winds calm. Waves reaching the beach are gentler and push the sand back onto the front of the beach. The slope becomes more gradual as the beach flattens out. The profile is now called a “summer beach.”

A force that may bring instantaneous change to a barrier island is a big storm or hurricane. The large waves associated with big storms can flatten yards of grass and cover relatively stable dunes. The effects of a storm are magnified when the storm coincides with a spring tide, a period of particularly high and low tides. Hurricanes are usually accompanied by a storm surge, a large mound of water that may wash over sections of a barrier island. Sometimes the surge carries sand and other debris as far inland as the maritime forest or marsh behind the island. Occasionally the storm surge will focus on a narrow section of the island, cutting a new inlet at that point.

Wind, waves, currents, tides, and storms are some of the natural forces that are continually changing the face of the beach. It is this active landscape that we find so alluring at the beach; there is something different to see each day.

Procedures

Materials

For Classroom

  • Large shallow tray such as a wave table or child’s swimming pool
  • Enough sand to make a sizeable pile (at least 1 5-gallon bucket full)
  • Variety of objects (shells, coins, straws, sticks, gravel, etc.), either from the beach or classroom, to represent buildings, seawalls, jetties, groins, etc.
  • Optional - map of SC coast- NOAA nautical charts and/or topographic maps work well
  • Optional – directional compass

For Beach

  • No materials are necessary for modeling on the beach since there is an unlimited amount of sand! Objects found on the beach such as shells and dried grass stalks can be used to represent buildings, groins, and seawalls.
  • Optional – map of SC coast – NOAA nautical charts and/or topographic maps work well
  • Optional – directional compass

Procedure

  1. Divide the students into teams (Map Team A, Map Team B, Longshore Current Team, Seasonal Change Team, Hurricane/Storm Team, Development Team, Coastal Engineering Team A, and Coastal Engineering Team B). Each team will be responsible for one aspect of the modeling. Depending on the number of students, team size may vary and teams can be expanded or combined.
  2. Gather students around the work area (wave table or swimming pool). Sand should be smooth and flat to begin with.
  3. On the beach, students can form an oval. Ultimately, they will need to kneel in the sand. As they model, especially on the beach, hands will get sandy. It is extremely important on the beach that students do not stand up and brush off sand so that it blows into someone’s eyes!
  4. Map Team A - Ask students on the Map Team to “draw” the aerial view of the outline of a barrier island in the sand. Maps may be used as a reference and are helpful to get a preliminary outline. Students should decide which direction represents north, east, etc. (a compass may be used to determine true orientation) in relation to their barrier island. For Atlantic Coast beaches, the long axis of the island generally runs north and south. See Appendix A.
  5. Map Team B – Students on this team should next add appropriate topography to the model. They can draw on their own experiences: is a SC beach mountainous or flat? (flat) Where do you see “bumps” on barrier island? (dunes) Is there a steep drop-off at the water’s edge or can you wade into the water for some distance? (shallow slope) Or examine a topographic map to determine actual elevation. Note: for this model, the vertical scale will be somewhat exaggerated in order to see various features. The resulting basic barrier island model should look like an elongate oval mound. The classic “drumstick” barrier island shape can also be incorporated. Additional features include dunes, ridges and runnels, and sand bars. Students should mark the water line on the model. A good portion of the active beach is actually underwater!
  6. Longshore CurrentTeam – The next step is to model some common coastal processes. The longshore current is a wave-generated current that transports many tons of sand along the beach. It exists in the surf zone or area of breaking waves. Ask students if they have ever played in the waves at the beach and suddenly noticed that they had drifted from their starting point. Of course, if the longshore current transports them, certainly the sand is transported as well.

Since the longshore current is wave generated, the angle of the approaching waves determines the directions of the longshore current on the beach (Appendix A). Typically waves seen breaking on East Coast beaches are created by wind blowing across the water’s surface far out at sea. The predominant wind direction drives the wave direction, which in turn determines the longshore current direction. The prevailing winds in the Atlantic are northeasterly so waves tend to approach the beaches from the northeast. In general, the dominant trend on SC beaches is a north to south flowing longshore current. It should be noted that one could observe a south to north longshore current when the wind direction does change.

  1. Students (on longshore current team) can line up along the side of the island determined to be the east or ocean side. Beginning with the northernmost student, she or he should push a handful of sand up the slope of the model at an angle and drag it straight back down the slope (as seen in Appendix A). The next student in line should take the “sand packet” and repeat the motion, passing the sand to the next student. Meanwhile, the first student should continue to move the sand so that sand is moved continually. The last student in line at the south end of the island will receive the sand and push is around the tip of the island to form the sand spit. After a few passes of sand, pause the activity and allow students to examine the results. Some obvious changes might include sand loss at the north end of the model and sand gain at the south end. This is in fact a common trend on East Coast barrier islands.
  2. Seasonal Change Team – This team models the high-energy (larger) winter waves and the low-energy (smaller) summer waves (Appendix B). The team should line up along the ocean side of the model. All together, students should take their hands and reach up the beach face and scoop away some sand, pulling it toward the ocean side. Repeat this several times until a second ridge of sand is built parallel to the island model. This smaller ridge represents an offshore sandbar. The removal of sand from the beach face may have carved a scarp or ledge into the beach or even the dune. This often occurs during winter Nor’easter storms. The beach has narrowed and aside from the scarp the slope has become flatter. The next step is to model the summer waves. To do this the students should push the sand from the sandbar back to the beach. They can continue until the entire bar is wielded back onto the beach. This new profile represents the summer beach. In most cases a sandbar remains off the beach but is decreased in size during the summer months.
  3. Hurricane/Storm Team – Another major influence on the geomorphology of barrier islands is the occasional large storm or hurricane. The Storm Team can take position along both the east and west sides of the model. Since a storm surge or bulge of high water usually accompanies hurricanes, barrier islands are often breached or washed over. When a storm surge does wash over an island it can carry an immense amount of sand and deposit it in the maritime forest, salt marsh, or beyond. As the water from the storm surge retreats, it can cut deep gouges through the island to the extent that new inlets may be formed. Students can model this process by pushing sand from the ocean side of the model to the students across from them. Those on the inland side can continue the process and pull the sand across the model to “deposit” it on the west side. New inlets or breaches in the island can also be created in this major rearrangement of the topography of the model.
  4. Development Team – This team can use the objects to create a developed barrier island. Ask students to predict and then demonstrate what could happen to buildings at the erosional, north end of the island or what could occur during a storm surge.
  5. Coastal Engineering Team A – Use straws, sticks, pencils, or piles of gravel to represent groins, shore-perpendicular structures used to trap sand. With groins in place, ask students to predict what will happen to the sand transported by the longshore current. (Appendix C: the sand is deposited on the updrift side of the groin and carved away from the downdrift side). Although groins strap sand, the current continues to flow and picks up sand on the downdrift side of the groin. Groins can even impact other beaches o the south and lead to additional problems for downdrift beach communities. Many geologists and coastal zone managers believe that groins are more detrimental to the beach system than they are helpful.
  6. Coastal Engineering Team B – This team can simulate change associated with a seawall or revetment. These structures are built parallel to the beach and are intended to protect development on the landward side of the structure. Use pencils, sticks, or straws to build a seawall or gravel to build a revetment. Sand may be piled up on the west side of the seawall and houses added if desired. Waves often carve away the sand at the base of the seawall. Students can model this by pulling sand away. Eventually when enough sand is removed, the wall becomes unstable.

Assessment

Have the students draw a diagram of the barrier island that they just created in the sand and also of the beach profile. Tell them to label all wave action, current directions, beach structures, and man made structures that relate to the island. Diagrams should be very similar to Appendix A, B, and C.

Rubric (out of 12 points):

Label longshore current (2 points)

Label swash and backwash (1 point each)

Draw barrier island like drumstick model (2 points)

Label dune (1 point)

Label scarp (1 point)

Label berm (1 point)

Label ridge and runnel (1 point each)

Draw and label sand bar (1 point)

Draw groin with build up of sand on one side (1point)

Members of the COASTeam Aquatic Workshops development team include: Katrina Bryan, Jennifer Jolly Clair, Stacia Fletcher, Kevin Kurtz, Carmelina Livingston, Leslie Sautter, and Stephen Schabel.

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From COASTeam Aquatic Workshops: Oceans (grade 5); a joint effort between the COASTeam Program at the College of Charleston and the South Carolina Aquarium – funded by the SC Sea Grant Consortium.

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Appendix A

Appendix B

Appendix C