Profiles in Sand

Beach Profiles or Transects


Beaches and dunes are in constant motion, continually changing shape and shifting position in response to winds, waves, tides, relative sea level, and human activities.

The most significant changes occur seasonally and following storms. During summer, beaches are generally higher and sandier than they are in winter. During the winter, the ‘missing’ sand moves from the beach to nearshore areas to form sandbars. This happens as a result of changing wave shape due to more intense storm activity. During spring and early summer, or following a storm, the sand in the nearshore region moves back toward -- and eventually attaches to -- the beach. Once on the beach, the finer sand grains are moved by wind action to form higher, wider sand dunes. These seasonal and storm-related interactions and changes in the form, volume, and position of beaches, dunes, and nearshore areas produce what is known as ‘dynamic equilibrium’ (Figure A, below).

Beach and dune profiling is one way to obtain information about seasonal and storm-induced beach and dune shapes. Comparing season-to-season profiles and profiles taken before and after a significant storm clearly illustrates the important changes taking place along the shoreline and how quickly coastal landforms change.

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Beach profile animation SUMMER / WINTER

Beach profile animation Storm effects


NOAA ADVANCED GLOSSARY

Barrier Island Environments

There are numerous distinct environments found within any particular barrier island. Although one or more of these environments may be present for any given barrier island, the overall scheme appear

s both consistent and predictable. Taken in sequential order, and beginning from open ocean to the outermost reaches of the back-barrier, these environments are as follows: nearshore, beach, dune, washover fan, marsh, tidal flat, and the adjacent estuary/lagoon.

Beach
The beach, or visible portion of the profile, is the most familiar of the barrier island environments, and in many respects is the most important because it affords protection from wave attack to the landward upland environments (where development is typically located). The beach extends from the shoreline landward, and often includes numerous changes in topography such as sand dunes, sea walls, or other man made structures. A beach is typically divided into the seaward sloping foreshore and the nearly horizontal backshore.

The foreshore is considered to be that area where the last vestiges of waves rush up and back. This constitutes what is referred to as the swash zone, although such wave action can often cover an entire foreshore. This area is also the zone of the intertidal portion of the beach and may range in width depending upon slope or gradient.

The backshore is generally dry except during the occurrence of severe storms and their associated storm tides. Under normal conditions, the backshore is subjected only to wind action that blows the dry sand landward, creating dunes. Opportunistic dune or beach vegetation may occupy this portion of the beach.

Storms can cause a beach to erode, and can result in a uniformly seaward-sloping beach. This typically occurs during the winter months. During the calmer summer months, the beach gradually accumulates sediment as the result of currents, produced by low waves that return sand landward to the foreshore, or emergent, portion of the profile. If there is long-term erosion of a beach, it may be due to a variety of phenomena, including storms, high rates of sea level rise, interruptions in the longshore transport system along the beach, or inappropriate construction practices along the shoreline area that function to interrupt the longshore movement of sand.

SHORELINE STRUCTURES

See student experiments at SWASHBUCKLERS

Hard Solutions / Coastal Construction

Swash Bucklers

Start here for animation on Coastal Changes

We are now experimenting on how human interaction can affect natural coastal changes



Several engineering solutions are used for coastal protection and beach restoration. In the past, construction of hard structures, hard solutions such as groins and sea walls, jettys and breakwaters have been used with varying degrees of success. Some solutions have been successful, some require expensive ongoing maintenance and others have caused even more problems. Another method of coastal protection is to artificially nourish the beaches by transporting sand from another location to restore a beach. Once again, this method has varying levels of success.

Students are attempting to answer "Hard Solution" questions regarding beach and coastal erosion. They "wonder" WHAT and HOW "hard solutions" to beach erosion are supposed to work.

Developing testable predictions ...... defining independent and dependent variables...

IF IV

Then DV

Students developed a myriad of possible solutions...




If you increase the resistance to beach swash, then the landward beach erosion will...... (hmmmmmmm?... increase? ...decrease?... stay the same?)


Groins and Longshore Drift

Groins, usually made of timber, rock or concrete, are built perpendicular to a beach and into the water to trap sand. On beaches where waves arrive at right angles to the shore, a series of groins can trap sand, creating a series of small beaches







On beaches where waves arrive at an angle to the shore and the beach is affected by longshore drifting, a different situation arises. As the water and sand move by, the first groin will trap sand meanwhile starving the beach of sand (and other groin) further along the shore. Groins can be designed to allow some sand to spill around the structure and minimize downstream erosion.

Groins are not successful in all circumstances contributing to further erosion. A careful analysis of wave approach and currents should precede any decision to install a groin, and the structures should be carefully designed for the specific location.






Seawalls



Seawalls may be constructed of timber, rock, steel or concrete and are placed at the back of a beach. Although seawalls can protect the land directly behind, they can also accelerate erosion at the end of the wall and/or cause erosion of the beach in front of the seawall. When waves hit the wall and retreat, the wave action scours sand from the beach back into the water. Ultimately, the beach becomes lower and flatter, creating a condition where waves become larger, which increases the scouring action and the beach is eventually lost.
Artificial beach nourishment (replenishment) is the depositing of sand from elsewhere to replenish eroded beaches. Sand may be trucked in or dredged and pumped from offshore. But it is not as easy as it sounds. The nourishing sand must be as coarse as the sand that is currently on the beach. If the nourishing sand is of a finer grain, the sand will be easily swept away by normal wave action. On beaches where sand has been lost through longshore drifting it is likely that nourishing sand will also be lost. Sometimes in this scenario, groins are constructed to trap drifting sand.

It is important to remember that coastal erosion is a natural process and does not always have a negative outcome. It is the natural erosion process which gets sand on beaches in the first place, but if interference occurs with natural erosion and deposition patterns, undesired outcomes requiring further action can occur.


So what is the solution? Or has nature found its own solutions and we have just ignored them?


What do you think?