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ALTERNATIVE TO TRADITIONAL WAYS OF TREATING SHORELINE EROSION
In the United States national attention by major media has focused on America's "Threatened Coastlines". Misdirected engineering methods and efforts to control erosion of beaches have been proven to be wrong and counterproductive. "Armoring" the shore with structures such as sea walls or riprap is unavailing and unsightly. Expensive and temporary beach dredged nourishment is coming under increased attack for causing and increasing erosional damage. Corrective action requires a sound analysis of the ecology of natural beach formation. Mans' alteration of shorelines have created unnatural water currents, often remotely situated, which now divert the inbound littoral supply of sediment away from shore. Normally this sand would ensure a positive balance among factors preserving natural beach configurations.
Manmade artificial structures such as jetties also create disruptive currents. Proven environmentally and ecologically harmonious methods for controlling shoreline and bluff erosion and for restoring the natural environment are now available. Successful restoration of beaches and dune lands has resulted from patented low profile "Undercurrent Stabilizer" filtration systems in installations designed for specific sites. All countries with shoreline erosion need to review their present policies and make administrative changes to encourage such innovation via large scale planning and objectively monitored demonstration projects. Those who dictate policies of retreating from our coasts and express such views as letting nature take its' course are wrong. Nature is not the enemy and abandoning the seashore should never be considered as an option. In the United States and some other countries, streamlining permit procedures and a review of jurisdictional overlap is advocated to ensure a timely response to solving the current crisis.
In the United States national attention by major media has focused on America's "Threatened Coastlines". Misdirected engineering methods and efforts to control erosion of beaches have been proven to be wrong and counterproductive. "Armoring" the shore with structures such as sea walls or riprap is unavailing and unsightly.
Expensive and temporary beach dredged nourishment is coming under increased attack for causing and increasing erosional damage. Corrective action requires a sound analysis of the ecology of natural beach formation. Mans' alteration of shorelines have created unnatural water currents, often remotely situated, which now divert the inbound littoral supply of sediment away from shore.
Normally this sand would ensure a positive balance among factors preserving natural beach configurations. Manmade artificial structures such as jetties also create disruptive currents. Proven environmentally and ecologically harmonious methods for controlling shoreline and bluff erosion and for restoring the natural environment are now available. Successful restoration of beaches and dune lands has resulted from patented low profile Undercurrent Stabilizer filtration systems in installations designed for specific sites.
All countries with shoreline erosion need to review their present policies
and make administrative changes to encourage such innovation via large scale
planning and objectively monitored demonstration projects.
II. REVERSING BEACH EROSION IS THE ALTERNATIVE TO TRADITIONAL WAYS OF TREATING SHORELINE EROSION
Major news media have recognized the scope and national significance of "America's Threatened Coastline" (see e.g., Editorial Research Reports, 1984, or Newsweek, September 24, 1984). Immense losses in property values and in the recreational and aesthetic qualities of fine sand dunes and beaches have reached crisis proportions. Tragically, and all too commonly, beaches that once extended hundreds of feet in width and elevation have receded and disappeared into lakes and oceans. Unless countervailing efforts succeed, this trend is destined for continued destruction of our wondrous but finite heritage.
Paradoxically, our contemporary crisis in shore land eradication is not simply a natural process. The term "erosion" can mislead as it implies a slow and steady process of displacement of sedimentary materials. Indeed, at least one dictionary defines erosion as a "natural" process evoking an image of a relentless and ineluctable force, one which in examples such as the Grand Canyon is measured in geologic time ("The American Heritage Dictionary of the English Language", 1969). But relatively recent records up to around 1855 reveal a steady progression of expanded rather than contracted beaches (Dana, 1864; Door, 1971).
Excessive interest has been placed on a rising global oceanic high water table and its alleged effect on our shorelines. This is misleading, as evidenced by historical records indicating expanding and elevating coastlines created as a result of ice age melt ( Dana, Door, ibid.).
Our thesis is that beach, dune and bluff erosion have resulted primarily from fairly recent human interventions rather than from natural ecological and environmental factors. The importance of this is two fold. First, from a scientific and engineering point of view, it is critical that the natural ecology of beach formation be understood so that remedial efforts can lead to positive results. Second, from a public policy point of view, it is important that those victimized by counterproductive interventions in shoreline ecology not be castigated as culprits by those responsible for their protection.
The public interest in the reclamation and preservation of the coastal environment comes first but includes private property. It also goes beyond public recreational areas, important as these are. Beaches function as purification instruments safeguarding against pollution of water as well as waterfront. The chain of organic interdependence, ranging from micro-organisms to more complex fauna and flora, is also crucially benefitted by the filtration and percolation functions of our sandy beaches. A common interest must be recognized in the need for a concerted effort and awareness if a vital national resource is to be restored and preserved.
III. THE HEALTHY NATURAL BEACH AND ITS GROWTH
Although it seems the process of shoreline beach formation is generally well known, I will emphasize a neglected aspect. Wave action in its visible impact on cliff, dune and beach is commonly emphasized. Less visible and too little appreciated is the formation of currents accompanying distant underwater and near shore wave actions. Actually, waves generated by Southern Hemisphere storms have been recorded as traveling more than 5,000 miles before arriving on the California coast (Inman, 1982). Less dramatic subsurface currents and submerged wave pressures have equal significance for remote deposits or dislocations of sedimentary materials. This will bear upon our subsequent consideration of the influences of even distantly sited jetties, deepened channels, offshore dredging, etc., on shoreline erosion problems.
Beach areas are formed from sand, shell, coral and pebble deposits that are transported to them from their original upland or seabed source off by water, or hydro effects. The transport system primarily entails currents and waves generated by wind, gravity and other geophysical forces.
Rivers and streams venting into the ocean carry a vast quantity of material that contributes to perpetual nourishment of beaches. These streams flow through the land, picking up sediments that have been created by natural erosive processes. These sediments eventually reach the vents or mouths of the rivers and streams at the ocean front. As the river currents meet the littoral transport systems of the coasts, their power is lessened and the material they carry is deposited in the form of deltas. This process continually contributes to the shoaling in these areas. In many cases deepwater channels have been dredged for ships to navigate the area. The deltas and shoals that are formed become the eventual nourishment supply, or feeder, for the coastal beach areas. Those sand deposits and sediments transported into the deeper water form the life-supporting sandy bottoms and have now become the main natural source for protection and future nourishment for beach creation.
Prevailing winds influence the directions of littoral or near shore transport currents. Wind fetch, or the cumulative distance the wind has for building up without interference, dictates the formula for the wind's power feed. Another factor is called "constant direction measured in time". The longer the wind blows in one direction, the bigger the wave energy it creates to drive toward shore. When larger waves approach the shore, they energize the currents, moving them parallel to the shore. This increased power allows the sediment transport system to move even larger volumes of materials and water along the paths that these currents follow.
Waves are unrelenting as they approach, increasing the amount and height of the water table at the shore. The increased height, weight, power and current that are assembled in the near shore areas are managed in a positive way by a healthy beach.
A natural beach typically consists of a plentiful sand supply source, deltas, sandbars that are not dredged, shallow offshore sandbars that are unbroken, and, most important of all, a wide, slowly tapering beach with healthy vegetation growing above the high tide and wave wash-up zone.
A healthy, well-balanced beach area can engage large storms with minimal damage. Indeed, turbulent waves actually contribute to beach maintenance by mobilizing the wet sea beds unconsolidated sediments and moving the sand from deep water bottoms into the near shore beach and dune system. The process entails three basic stages:
IV. CAUSES OF SHORELINE EROSION: NATURAL AND MAN-MADE
A healthy beach, although temporarily vulnerable to storm-driven destructive power, has a homeostatic rebuilding capability to restore its natural equilibrium. The increased supply of sedimentary materials disturbed and relocated from remote bottoms and made part of the littoral transport system nourishes the beach and provides protection from the permanent storm damage. Natural factors such as storms are not the main source of lasting beach erosion, although all too dramatically manifested in the short run and at particular sites.
Manmade interventions into the natural equilibrium of beach and sea are the prime source of our erosion problems, including the inability of altered beach profiles to handle storm turbulence. Recall the process whereby a natural and gradually elevated beach absorbs wave and current-driven energy. This is vital to our understanding of the unintended but deleterious consequence of artificial structures and dredged channels, unless these are installed or dug with adequate analyses or countermeasures due to their impacts upon alongshore processes, sand supplies, current and other factors, they will upset the fragile balance of a natural beach system. Unfortunately, such care has not been taken since shoreline beach and dune erosion is considered by many to be a natural condition or ongoing process.
Comparison of beach profiles before and after storms suggests erosion of the beach (above MSL [mean sea level] ) can amount to 5 to 24 cubic meters per kilometer (10,000 to 50,000 cubic yards per mile) of shoreline during storms having a recurrence interval of about once a year (DeWall, Pritchett, and Galvin, 1971; Shuyskiy, 1970). While impressive in aggregate, such sediment transport is minor compared to longshore transport of sediment. Longshore transport rates may be greater than 765,000 cubic meters (1 million cubic yards) per year (U.S. Corps of Engineers, Department of the Army, 1984).
Since the landward sides of the deepwater jetties are anchored to the shore, the alongshore currents that cannot climb over the dikes in their paths are diverted seaward. As the current meets the structure, changing directions, reducing the ability of the transport currents to deposit sand, absorbs some of the energy charge. Some of the transported sand is deposited on the side of the jetty meeting the current. The balance of the material still in flow is diverted seaward. This riptide or diverted current, blends with the wind-driven, powerfully energized waves, and increases their velocity at this stage to compound the scouring and eddying effects at their meeting point. Accurate measurement of such discharges of materials into deep water has yet to be fully documented. But the immense scope of this diverted sedimentary material plays a large role in the loss of bottom profile along our shrinking shores. This phenomenon best explains our eroding and disappearing beaches.
Currents that create "scouring" cause a deepening and channel effect, which further increases the erosion from adjacent channel edges and shorelines. Simply put, upland soils will tend to restore elevation differentials created by scouring by moving downhill toward the channel bottom. For illustration, consider an alongshore current flowing in a continuous direction for a period of time with a certain velocity. The current is flowing in a north to south direction, passing a pair of relatively close discharging channels, both having jetties. At the rate of flow, the material picked up in transport from the northerly channel will quickly arrive at the southerly channel. This means that the remaining flow time of scouring is discharging beyond and seaward of the southerly channel. The influence of such jetties and similar structures is authoritatively recognized (Office of the Chief of Engineers, 1969). Only the amount of displaced material varies. A misleading and unproven authoritative view is that once such material is discharged into 18 feet of water or more, it becomes a non-returnable item (Bascom, 1980; Komar 1976).
Some persist in downplaying the negative consequences of such structures. We often are told that a jetty maintains a total blockage of material and that the beach material simply will be held temporarily from reaching the other side of the channel. Then, they claim, as soon as the wind changes, it will proceed in the opposite direction. Partly this is correct, but too commonly left out of the analysis is the tremendous amount of sand lost to the offshore areas having been diverted away from the beaches prior to wind redirection. The gradual loss of huge beach areas over a period of time has become a serious concern to the people living along these shores. Bottom profile and beach loss happen so slowly in the beginning that many people remain unaware of the major causes responsible for the loss cycle. Understandably, they are unaware of seemingly remote structures as causal influences on their beach profile. The currents are invisible to the untrained eye, whereas the beach visibly deteriorates under the force of now unimpeded wave actions.
When the closing sea endangers houses, roads and other construction, owners are driven to action. The first thought is to build structures to withstand the onslaught of the waves. Typical efforts include diking the shorelines with revetments or seawalls or with rocks piled high enough so that even a "hundred year" or major storm cannot go over them. Others build groins to try to hold the sand from being swept away by the currents running along the shore.
It is almost a primeval instinct that man tries to defeat the sea by building higher, bigger, stronger barriers. But these structures in short order actually increase the current flows by becoming hardened parallel shoreline. Gone is the absorption effect of a gradually rising beach, which drains energy from the waves by percolation and friction. Instead, unimpeded waves strike upon a hardened surface with no absorption power. Unabsorbed wave energy is thereby reflected and converted to scouring power and increased velocity means more material in transport and an increased speed of the alongshore current between the two points of the shoreline in our example of jetty influences. The more area hardened between these two points, the greater the velocity of the current between the points. This supercharged current flows parallel to them and scours a channel in a sandy bottom. Such a deep channel, forming at the front face of such structures, causes sand on the adjoining beaches to be pulled or to run downhill into the trench scoured out by the increased velocity. That is why, at the end of sea walls and similar structures, you see cuts accentuated into the shore. As the bottom profile in front of such structures becomes deeper, reverse reflection occurs. Incoming waves that feed the alongshore current are no longer losing energy to an elevated beach profile, so they strike with more power and are all the more strongly reflected back to sea. This power that sweeps seaward tends to accentuate a flattening of any near shore bar areas and causes breaks in their formations. This, in turn, reduces the ability of the bottom profile to dampen the power of the incoming waves. Again, the powers of reflection and alongshore currents are further increased.
Groins were also installed along the shorelines with the thought of slowing and trapping sand that is flowing in the alongshore currents. Most groins were solid like a wall placed perpendicular to the shore with a fixed elevation above the sea. They, too, cross the currents with results similar to jetties. We find that the design of these structures also directs currents seaward and, where the structures are not properly tied into the shore, we find currents being diverted around the structures at both ends. Most times the seaward route is dominant. Again, as with the jetties, we find eddying, compressing, seaward diversion of materials, and a trench or scouring channel forming. This further increases the movement of sand away from the shores and a deepening of the profiles. Another type of groin, called permeable, is intended to slow rather than stop the currents. However, these structures alter the currents so that, in many cases, they eddy and scour alongside the groins eventually creating trenches running seaward and sometimes settling or toppling them. This type of structure often plays havoc with down drift properties because of design problems. A tradition of fixed height has caused most of the difficulties.
It was recently disclosed that the US Army Corp of Engineers Manuals recommended structures were improperly designed because of inaccurate laboratory tests ( U.S. Corps of Engineers, 1994). The report stated structures such as rock revetments and groins tend to accelerate down cutting and erosion, in fact, direct materials offshore to a greater degree. Is there a structural solution? Moreover, can such structures harmonize with the natural environment of dune and beach? My affirmative answer derives both from theory and practical experience with successful applications.
V. CONTROL AND RESTORATION: BEACH DEVELOPMENT THROUGH PATENTED UNDERCURRENT STABILIZERS
The use of geo-fabric filter media for the purpose of soil stabilization has been developed and improved over the years. Before the use of rough, stable fabrics made from petrochemicals, many forms of filters were tried such as treated papers, vegetable and animal fiber, fiberglass, and even woven metallic fibers. With the advent of the petrochemical filter fabrics in the 1960's, vast improvements have been made, especially in durability.
Geo-filters were originally used in the Netherlands to assist in holding back ocean waters from farmlands wrenched from the sea. The use of geo-textile filters has since been adapted for other uses around the world. During the last 35 years a new use of geo-fabrics has been under research and development by our company for control of beach erosion. The systems have been tested and improved in applications along the Great Lakes and oceans with astounding success. An equilibrium has been restored at numerous locations, reversing critical deterioration of shorelines with natural beach nourishment systems.
The use of patented "Undercurrent Stabilizer" systems is being employed to work with nature by utilizing her wave, current and tidal energy carrying sand to the beach area from offshore deposits. This natural process actually accomplished the same result as artificial beach nourishment but without disturbing the natural ecology of the ocean bottom. An additional benefit is that it does not require continual replenishment, cause an increase in the erosion rate or the harmful effects that offshore dredging and strip mining does to maintain the beach (U.S. Corps of Engineers, 1989).
When considering methods available for beach restoration, each area requires its own special design system. Basically all effective systems involve one form or another of low profile structures adjusted to water and storm levels. Construction materials can vary from site to site, depending on conditions and the desired approach and final result. The most common materials employed are the geo-filter fabrics using concrete filler.
Sand accretion is obtained by creating a gentle gravity resistance to the onshore and littoral currents. This accretion or elevated profile induces wave energy and currents to deposit more materials, further increasing the near shore supply. This is similar to the underwater part of a delta formation which absorb some wave energy rather than redirect all of it. Sand is commonly abundant in these wave-driven and longshore currents flowing along the shores. Only a certain amount is removable from these streams by any method. The balance flows onward with the currents until directions are reversed by natural means. Also, it is not true that the accretion of sand in one area permanently robs another. If filter systems were installed along an entire shoreline, the vast quantity of flowing sand would be minimally reduced if at all. US systems will encourage volumetric sand accretion, but they will not cause accelerated erosion. The reverse actually occurs with remarkable speed. A beach that has been elevated and widened by a filter system will in time accelerate accretion downstream. Like natural deltas, it will slow down the currents and waves allowing sedimentary materials in transport to be deposited. Original sand deposits are unbalanced until enough sand has accumulated to uniformly straighten beach formations and build up the back shore and dunes.
The damaging effects of major storms cannot be prevented by armoring our shorelines. We can, however, minimize their powers by widening our beaches and restoring our dunes. This can best be accomplished by the installation of a system of filters laid on the near shore coastline bottoms in low profile and following the natural grade of the land. US system's technology requires competent analysis and sophisticated design. An attenuated installation, for the sake of shortsighted economy, will not succeed. The total program of filter systems in most cases involves several steps in the process of elevating the beach. Each step generally includes a network of filters, the most visible of which, noted during construction, are the fabric core, tube like filters consisting of heavy duty polyester media filled with cement. A less visible but equally vital part of a system includes sheet filter media placed horizontally under the cement filled core, extending outward a designed distance and provided with perimeter anchorage. All materials in the configuration blend harmoniously with the natural environment.
Step 1 involves a series of cement-filled tube forms laid perpendicular to an approximate proposed beach line. The length of the stabilizers is established by design computation, with the landward set being tied into a toe protection system along an existing bluff line to protect against wave action cutting behind the system.
Step 2 begins with the development of dunes from dried sands being accreted during initial stages of buildup. Special mixtures of organic and geo-textiles are utilized to enhance a growing medium. Vegetation should also be planted as soon as possible to develop a network of roots to hold the dunes from further wind movement.
The final result of a properly designed program is a wide, flat, graded beach gradually succeeded by vegetated dunes having an appearance in every respect akin to that which nature created before the advent of man's damaging structural systems. In a recent engineering summary of a four year field evaluation of Undercurrent Stabilizers, it states that Undercurrent Stabilizers are effective in protecting, and even elevating, the beach it was intended to protect. Furthermore, they perform this function at no detriment, and have actually shown benefits, to adjacent down drift beaches.
The low profile cross-section of these structures and their placement along the bottoms mimics the desired natural slope of the beach and generates a fraction of the turbulence and scour that accompany other shore protection structures. They remain in place when facing liquefaction forces, preventing the landward migration of scour troughs during significant storm events.
Because of these findings, stabilizers should be defined separately, in and of themselves, as a unique type of shore protection structure. The results of this study indicates that Undercurrent Stabilizers should be recommended for shore protection needs over traditional methods, and their permitting requests treated fairly. They should also be considered for mitigation efforts, when needed to counteract the negative effects of larger or more damaging marine structures (David Schultz, P.E., 2000).
VI. IMPLICATIONS FOR CHANGES IN PUBLIC POLICY
It has been argued that erosion is just as natural as are valued beaches. Indeed it is human valuation which categorizes beach formation as desirable and erosion of beaches as undesirable. But this value-neutral aspect of natural processes has led to a perverse distortion of its implications for public policy. Thus some claim that erosion is a natural phenomenon and that persons with a property, or environmental aesthetic interest in beach conservation, must accept "nature's" destruction of their property, or of public recreational shorelands. Indeed, an underlying attitude among some personnel responsible for protecting this highly valued and threatened public and private resource blames shoreline property owners and recreational beach managers for their erosion problems.
The primary source of erosion problems on the scale of the past century is the product of projects permitted or constructed by public agencies such as jetties and channels. There may have been reasons for the slowness of our coming to understand non-natural, manmade causes of coastal erosion but it is now understood that structures, dredging and channels which change natural processes or interfere with currents divert sand from normal littoral transport and beach deposition. Public policy and administrative regulations need to be adapted to this improved understanding.
Beaches can and must be restored to their original configurations. Regulatory agencies need to change their permit procedures accordingly. First, we need to recognize the futility, not to say the wasted expenditures, of barrier constructions such as seawalls, groins, revetments and riprap. They are not only unavailing to their intended purpose but they remove rather than preserve beaches. Moreover, they are aesthetically incompatible with the natural qualities which give value to beaches and dunelands. It is discouraging to find that advice on counter-erosion measures currently circulated by responsible public agencies approves the use of materials such as automobile tires. The conversion of beaches into junkyards is scarcely in the public interest. We have witnessed iron rods protruding from concrete slabs called riprap used to line once beautiful beach areas. Such unsightly, dangerous and counterproductive materials and methods should not be permitted.
We must not only prohibit harmful and outmoded methods, but need to encourage and facilitate the now available technology in a systematic program of beach restoration. This is not special pleading; there is a general public interest at stake. The vast scope of the problem has gone beyond the possibility of a lasting piecemeal solution, and the problem itself derives from a set of multiple and interrelated phenomena. As noted, individual sites are influenced by remote installations which frequently have been structures built by or under the aegis of public authorities. Effective application of new techniques can best be obtained from a multi-pronged design for large-scale reclamation. The piers, jetties, and channels, as well as the immediate targets of planned beach restoration need to be engaged in their reciprocal relationships. This entails supportive worldwide public policy and innovative leadership.
"The American Heritage Dictionary of the English Language". Houghton-Mifflin, 1969.
Bascom, Willard, Waves and Beaches. New York: Anchor Press/Doubleday, 1980.
Dana, J.D., Textbook of Geology. Theodore Bliss & Co., London Cribner and Co., 1864.
Door, J.A., Jr., and Heitman, D.F., Geology of Michigan. University of Michigan Press, 1971.
Editorial Research Reports. "America's Threatened Coastlines", November 2, 1984.
Inman, D.L., "Near Shore Sedimentary Processes." McGraw-Hill Encyclopedia of Science of Technology. VI. 9, p. 46. 1982.
Komar, P.D. "Beach Processes and Sedimentation", Prentice Hall, Inc., 1976
Newsweek, "The Vanishing Coasts," September 24, 1984, pp. 74-76.
U.S. Corps of Engineers, Department of the Army, "Shore Protection Manual". Vol. 1, 1984.
Office of the Chief of Engineers, "Water Research Policies and Authorities: Prevention and Mitigation of Shore Damage Caused by Existing Federal Navigational Works." Regulation 1165-2-309. Department of the Army, Office of the Chief of Engineers, Washington, D.C., June 23, 1969.
U.S. Army Corp of Engineers, Jacksonville District South Atlantic Division, "Navigation Study for Canaveral Harbor, Florida, Final Feasibility Report and Environmental Impact Statement-81240", August 1990.
Coastal Engineering Consultants, Inc., "Stump Pass Inlet Management Plan", CEC File No. 89.170, December, 1991.
Burch, T.L., and Sherwood, C.R., "Historical Bathymetric Changes Near the Entrance to Grays Harbor Washington", PNL-8414/UC-000, prepared for US Army Corps of Engineers, Seattle District by Pacific Northwest Laboratory, Richland, Washington, 1992.
Schultz, D., "Analysis of Lake Michigan Monitoring Surveys, Norton Shores, Michigan", PE August 30, 2000.
U.S. Corps of Engineers, "Lakebed Downcutting and Its Effect On Shore Protection Structures", No. 02124 Abstract form for all GSA Meetings, Charles N. Johnson, U.S. Army Corps of Engineers, North Central Division, Chicago, IL, 1994.
U.S. Corps of Engineers, "Beach Restoration Hearing", Environment, Energy, and Natural Resources Subcommittee of the COMMITTEE ON GOVERNMENT OPERATIONS HOUSE OF REPRESENTATIVES, April 28, 1989.
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