What Makes a Beach?
By “Awake!” correspondent in Guatemala
TO MULTITUDES the thought of spending a day of pleasant recreation down at the edge of the ocean is most inviting. It can mean much fun—swimming, sunning, playing games and associating with friends and loved ones in the fresh open air, with the soothing sound of surf in the background. Particularly in the summertime the beach holds a powerful attraction.
Around the world beaches line thousands of miles of coastline bordering the oceans, seas and lakes. They constitute natural playgrounds that come to be thought of as changeless, long lasting, almost permanent. But to observant persons who visit the same beach year after year, definite changes are apparent. The quantity of sand on the beach may fluctuate. In some instances radical changes for better or worse can be noticed.
As we enjoy the attractions of the beach and take note of its gradual transformations, perhaps some questions pop into mind. Where does all the sand come from? Why do some beaches become eroded, others practically disappear? Why are some pleasant stretches almost denuded of sand in wintertime, only to regain the supply during the summer months? The answers to those questions may well surprise us, especially if, like most people, we have been inclined to take the beaches very much for granted.
Not All the Same
If one has not traveled far afield and visited other parts of the world it is easy to conclude that all beaches are about the same. Indeed, there are great variations—in color, in sand quality, in slope of the beach, and so on. For example, in volcanic areas the beach will most often consist of coarse black sand deriving from the lava. In other regions the sands may be most colorful, being composed of offshore coral that has been ground fine. Still other beaches may be a glistening white, for they are formed of broken seashells that are ground to powder.
The majority of beaches, however, have sand comprised of small rounded quartz crystals along with fine particles of many different rock types. This sand comes principally from inland areas, having been washed down to the sea by river and stream. It may range all the way from very coarse to very fine.
It is that coarseness or fineness of the sand, by the way, that will, to a large extent, determine the characteristics of the beach. If the sand on a beach is fairly coarse, then the slope of the beach will be relatively steep. Such coarse sand grains do not become tightly packed because of their very nature.
On the other hand, fine sand forms an entirely different kind of beach. The beach slope will be more gradual, the water offshore will continue shallow for a greater distance, and for this reason the waves will break farther out also. And fine sand packs down quite solidly, so that automobiles can be safely driven on it. An outstanding example is Daytona Beach, Florida, in the United States.
Governed by Laws
But where does all the sand come from, anyway? Were you not under the impression that it resulted from the pounding of surf constantly breaking down the coastal rocks? That may be involved, but it accounts for only a small percentage of the total sand on the beaches. For the vast majority of the world’s beaches the answer is quite different. Not until the last twenty years or so have men begun to gain a clearer understanding of the forces acting on beaches and the resulting effects.
As the ordinary weathering processes decompose rock formations, often far inland, the streams and rivers carry varying amounts of sediment to be deposited at the river’s mouth. The finer silts and clays are soon washed out to sea, leaving behind large quantities of sand in the river deltas. But then, how does that sand get to where the beaches are formed? To understand this transfer we must examine some of the forces that act on a beach.
Waves that are generated by the wind far out at sea eventually expend their energy on the shoreline. However, they do not always strike the beach head on, that is, the waves are not always parallel to the coastline. For this reason the energy of the oncoming waves is divided into two parts. The major part is directed perpendicularly to the beach and dissipates in the breaking surf. The second part, much less in total energy, is directed in a current parallel to the beach and confined between the dry land and the line of the breaking surf. This current could be likened to an actual river, having as one “bank” the edge of the dry beach, the other “bank” being the offshore line along which the surf first begins to break.
This river may flow upcoast or downcoast, depending on the direction of the incoming waves. This coastal “river” is quite like its cousins that flow through the land in that it is capable of carrying large amounts of sediment. The sediment carried by the coastal “river,” of course, is the sand that makes up the beach past which it is flowing.
The sand borne along by these coastal “rivers” may involve large quantities—in some areas millions of tons of sand per year. This would amount to many railroad cars of sand moving down the coast every day of the year. The quantity, however, varies from one region to another, but we can clearly see how the sand brought down to the ocean by the rivers and streams comes to be distributed along the coastlines.
While this process of sand transportation goes forward continuously, still another process is under way. This process is one that changes the appearance of the beach itself from one season to another. In most parts of the world the incoming waves are smaller and gentler during the summer months, larger and more powerful during the wintertime. The gentler waves tend to push the sand up on the beach, whereas the stormy waves of winter drag the sand from the beach and deposit it in long mounds parallel to the beach. We call these mounds sandbars. When summer’s gentler waves return, the sandbars tend to disappear as the sand is once more pushed up on the beach.
Were all the sands brought down to the ocean by the rivers to remain on the beaches, we would eventually have large, sandy beaches all around our continents. But, as it turns out, vast amounts of sand are lost offshore each year beyond the point where waves can affect them.
Man Upsets the Equilibrium
The hand of man, particularly during this twentieth century, has in many places affected the natural equilibrium. Construction of harbors and breakwaters has often wrought great changes on the nearby coastlines. Among other effects one can note the buildup of sand on one side of a harbor, expensive dredging operations within the harbor itself, and erosion of the beach on the opposite side. True, this is but one of the costs of progress as man sees it, but there is yet another problem that is coming to have more far-reaching complications.
Flood control, water conservation and hydroelectric power installations have resulted in construction of more and more dams in all parts of the world. These dams greatly reduce the sediment-carrying capacity of rivers and streams, thus seriously cutting down the supply of sand destined for beach building. When the river deltas no longer supply sufficient quantities of sand, the beaches immediately downcoast begin to erode. The fine balance between gain and loss of sand has been upset.
Bringing sand in from other areas and dumping it on a depleted beach can only be a temporary measure, for the process of erosion will continue to wash the sand out to sea. The cost of artificial replacement of sand could become prohibitive.
Another method of beach maintenance involves the construction of shoreline structures, most commonly the long narrow type built at right angles to the shore and projecting out into the surf. These “groins,” as they are called, may be formed of large rocks or woodwork. The idea is to trap sand as it is carried past the beach so as to avoid further erosion.
Beach erosion is indeed a mounting problem, especially in the world’s thickly populated areas. Beach property, valued in the millions of dollars, is becoming seriously endangered. Short-lived humans, with their very limited view of the future, have gone ahead with plans for producing immediate gain, financial or otherwise—plans that boomerang on them with unexpectedly disastrous results. Thus while large segments of population are at last gaining extra time for recreation, more and more of the natural recreation areas along the earth’s coastlines are disappearing.
The making of a truly beautiful and natural beach is beyond the ingenuity of man. In contrast, God’s creative and maintenance forces have for long centuries kept the beaches of the world places of refreshment and relaxation.