Freshwater Coastal Sand Dune - Burlington Beach
What are coastal sand dunes?
Coastal sand dunes are simply piles of sand. Sand dunes are present on shorelines where fine sediment is transported landward by a combination of wind and waves, and stabilized with vegetation such as native dune grass. Primary dunes (or fore dunes) are situated nearest to the water and are affected most significantly by waves and blowing sand.
Dunes can help protect coastal property from the destructive forces of damaging waves and wind, but human activities have had severe impacts on coastal sand dunes.
How do coastal sand dunes form?
Dunes are formed when wind and waves transport sand onto the beach. The ultimate source of the sand is often glacial till that resides offshore, or is eroded from nearby cliffs by waves and transported along the shoreline by longshore drift. (To learn more about Longshore Drift, visit The Beach Strip - A Natural Barrier - GC64GQW) Rivers can also transport sand to the coast from inland deposits. Waves wash this sand up on the beach, and also remove it during storms.
One beach can vary quite substantially with the seasons. During the winter, stronger waves pick up more sand (but leave behind larger sediment), causing the beach to be steeper and coarser. In summer, gentle waves transport sand onshore and the beach takes on a shallower slope with finer sand.
The shape and size of dunes formed depends on the shape of the beach. On a shallow-sloped beach, the energy of waves is dissipated and the suspended grains of sand are deposited, resulting in greater dune potential. Steeper beaches do not dissipate this energy as well, and sand is more frequently washed back out to sea. Consequently, dunes on steeper beaches are smaller.
Once sand has been deposited on a beach, it is transported by the wind. When the prevailing wind direction is onshore, the sand gradually migrates landward from the water’s edge.
Sand Movement
Creep
Sand that creeps, is sand that rolls along the surface of the beach, never losing contact. At this point, the wind is just enough to push or roll the sand. This is called creep or reptation. Here the forces exerted by the fluid on the particle are only enough to roll the particle around the point of contact with the surface.
Saltation
Once the wind reaches a certain speed, (termed the impact threshold), the drag and lift forces exerted by the wind are enough to lift some particles from the surface. These particles are accelerated through the air, and pulled downward by gravity, causing them to jump along the surface. As the particle moves, it will bump into other particles, which help to repeat this process. If the particle disintegrate on impact, or ejects a much finer sediment from the surface to cause it to be airborn, then we refer to it as, saltation bombardment, which is responsible for most of the dust in dust storms.
Suspension
This process of sand movement, generally affects small particles ('small' means ~70 micrometres). Winds can carry this much smaller particle for a much longer time, and the pull of gravity is often less affective. The smaller the particle, the less important the downward pull of gravity, and the longer the particle is likely to stay in suspension.
It is important to note that sand dunes undergo a continual cycle of erosion (breaking down) and accretion (building up) with the wind and waves. When structures are built so close to a beach as to prevent this natural fluctuation, overall erosion of the beach and loss of dunes can occur. This leaves a shoreline much more vulnerable to damage from storms.
Why are coastal sand dunes important?
Coastal sand dunes form a natural barrier against wind and waves, protecting inland areas from damage due to storms. They also provide habitat for plants and animals, including rare and endangered species. The structure of sand dunes depends largely on stabilizing vegetation such as native dune grass. Without it, the sand would simply blow away, as it does in areas that have been degraded by trampling and invasive species. Sand dunes, as a component of sandy beaches, are also popular recreation areas.
What threatens coastal sand dunes?
Coastal sand dune systems are highly vulnerable to disturbance by trampling. Pedestrians and motor vehicles can compact the sand and crush vegetation; for example, native dune grass dies when its roots are crushed. Without the stabilizing vegetation, the sand is blown away and dunes disappear. This can leave the shoreline more prone to damage from storm surges.
Logging Requirements
To log this EarthCache, visit all four waypoints provided, answer the following questions, and submit your answers to the CO listed at the top of the cache page. The intent of this EarthCache, like all EarthCaches, is to take you to a new location, and Help you develop an awareness and appreciation of this unique environment. I hope this cache does that for you.
Burlington Beach: A Natural Treasure - Waypoint 1 (Posted Coordinates)
1) The beach and dunes at Burlington Beach are recognized as what type of beach? _________ __________
A Beach and Dune Ecosystem (Waypoint 2)
2) How deep are the sand and gravel deposits on the beach? __________
3) Why are sand dunes important? _______________________________
Observational Questions
4) Visit all reference points and additional waypoints: What is being done to mitigate the environmental impacts of foot traffic on the the sand dune.
5) Standing on the beach, and pathway through the sand dune, provide your observations of sand movement (creep, saltation, suspension), as well as the windspeed and wind direction during your visit. Wind speed and wind direction can be found using the website here. If you have your own anemometer, you are of course welcome to use that. Alternately, you may choose to make an estimation of the wind speed, using the Beaufort Wind Estimation Scale, found below.
6) Given the time of year, what do you think is currently happening to the sand dune? Erosion (breaking down) or Accretion (building up)
7) Measure the width of the beach to determine how far the sand has to travel, from the water's edge to be deposited on the dune?
