Imagine lounging on your deck, a book on your lap and a cocktail in your hand. Just steps away, turquoise waters slip gently up onto the coral-grain sand. Overhead palms rustle and pelicans flap their long wings. There is a gentle breeze blowing and all of a sudden you notice a shadow in the water offshore, causing a distinct color difference between masses of water. At first you think it is a cloud over head that is causing the shadow. But you then observe that the sky is clear above you. I experienced this scenario and when I saw the shadow I had to find out what was going on in the waters off the beach. So I launched my 15 foot skiff and motored out to what appeared to be the color changes in the water, about 300 yards (3 football fields) offshore.
What the shadow turned out to be was a stretch of surface seawater that was murky brown with muddy sediments in contrast to the surrounding seawater that was sky blue in color. This murky water spread up and down parallel with the coast and was about 100 yards across with blue water on the inner and outer surface waters surrounding the “plume”. I could not tell how long the plume of sediment water was but it stretched parallel to the coast as far as I could see in both directions. I could only describe it as a “river of sand” in the waters off my beach in Belize.
Now imagine a beautiful Belizean Beach Resort with guest rooms and condominiums, a fine restaurant and all the finest amenities. This resort is not only popular because of its accommodations, service, and restaurant, but also because of its beautiful beach. But picture the waves on the beach breaking at the roots of palm trees which use to form a barrier between the building infrastructure of the resort and a long expanse of sandy beach leading to the clear turquoise waters of the Caribbean Sea. And not only is the beach area scarred by the baring of palm tree roots but sand bags litter the tree line to try and keep the sand erosion from proceeding any further up on land and possibly felling the trees. Not a pretty picture for the resort goer wanting to sun bathe on the beach and take a leisurely swim. There’s nothing to bathe on except waves and water!
What we are talking about are the geomorphic dynamics that control beach build-up (accretion) and beach loss (erosion). A beach is defined as the location along a shoreline where the sediment is in motion, being moved by waves, tides, and currents. The beach is often bounded on the upland side by a cliff, dune, or vegetation. Beaches are very dynamic environments, with coastlines that can change daily, making them challenging places to manage. And they are very much controlled by the sand budget which is affected by the offshore movement of sand in longshore currents – representing what I referred to above as the river of sand.
On a mega-scale, exposed coasts are typical of many western Atlantic Ocean and Caribbean Sea coast lines. These important environments protect the mainland from storm events and wave action, while providing a vital ecosystem for many species. Features such as sand dunes, maritime forests, inlets, lagoons, back-barrier marshes, and vegetation constitute these fragile coastal systems. Depending upon the specific environment these coastlines are classified into coastal compartments according to distinct geomorphic settings including spits, headlands, wave-dominated coasts and mixed energy shores. Without intervention, these coast lands maintain a state of dynamic equilibrium between sediment exchange, wave energy, and sea-level rise. Human activities may interfere with this balance, causing costly damage, both economically and environmentally.
On a micro-scale, this past winter I had the opportunity to collect a photographic record of spit formation with an inlet and sediment dispersal along-shore to observe the changing sand budget related to an artificial structure that protruded out into the water from shore. Small coastal plain inlets generally have arcuate ebb deltas transected by a radially distributed pattern of channels. This arrangement permits an efficient flow of sediment across the inlet with little disturbance to the sediment budget of the adjacent shorelines. But when this lateral sediment flow encounters objects that are perpendicular to the shoreline this flow is diverted into nearby shores causing sand accretion and the further down-drift shore experiences erosion. This phenomenon was demonstrated over a 3 month photographic record on the coast of Riversdale in Belize. Again on a micro scale, around the protruding point/dock structure sand accumulated just beyond spit development, held in check by the physical structure of this protrusion. The proximal beach showed significant build-up of sand and grew significantly. About a mile down the beach (south in the direction of the prevailing currents) the beach eroded to the base of the tree line, starved of sand.
On a global scale, people are increasingly becoming concerned about the scientific projection of rising sea level that could occur over the 21st century. More than 50% of the world’s population lives within 100 miles of a sea coast and could potentially be vulnerable to higher sea levels. And much of the effects of higher sea levels can be worsened by beach erosion along the coast, especially erosion affected by human development. In obtaining a better understanding for coastal dynamics related to beach erosion, however, sustainable development strategies can be advanced that will slow erosional processes, guard against sea level rise and protect human infrastructure in the coastal zone.
As described above, coastal erosion is a growing problem in Belize and is beginning to exert a significant impact on the economy of local communities as well as the entire country. The coast, its cays, reefs, shallow waters, beaches, mangrove swamps, lagoons, estuaries, and riparian waterways protect the upland areas of Belize and all the human communities that inhabit these areas. These ecosystem regions will become especially important as sea level continues to rise and storm intensity and number increase. For example, this observer has noted major areas of beach erosion along the Placencia Peninsula that are occurring not necessarily from natural processes but rather from man-made influences in the coastal zone. Beach zone clearing and break wall building are inhibiting the natural alongshore movement of materials that would otherwise maintain a healthy beach along these shores. The basic state of affairs comes down to a situation of public awareness and understanding for how these natural systems work and how humans must integrate their activities within the natural workings of nature to not disrupt normal processes such as beach erosion and accretion.
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