David Leveson (1973)
1.1. THE COASTAL DILEMMA
The history of development in coastal North Carolina is unlike other human endeavors due to the high-energy and dynamic character of the coastal system. The evolutionary formation of the North Carolina coastal system has taken place during the past 10,000 years and continues today as a work in progress. More importantly, change is the only constant within the coastal system and this change happens at rates that defy conventional human perception and development patterns on more stable and inland terrains.
In 1975, Bellis et al. used the demise of Batt’s Island in Albemarle Sound to demonstrate ongoing estuarine shoreline erosion in direct response to the intimately coupled processes of wave action and rising sea level. This island, which occurred about 0.75 miles offshore of Drummond Point at the entrance to Yeopim River, first appeared on the 1657 Comberford map (Cumming, 1938) as Hariots Island. The island subsequently became the home of Captain Nathaniel Batts, the first Virginian to settle in the Albemarle region and the Governor of “Roan-oak”. The island is referred to as Batts Grave on the 1733 Moseley and 1770 Collet maps (Cumming, 1966) (Figs. 1-1-1A, 1B). In 1749 the island consisted of 40 acres occupied by houses and orchards (Powell, 1968). Bellis et al. (1975) estimated that the island was about 10 acres in size on a 1849 U.S. Coast and Geodetic Survey bathymetric survey map. By the early 1970s a lone cypress skeleton marked the total demise of the island (Fig. 1-1-1C) and by the early 1990s only a red buoy marker reflected the presence of shallow shoals (Fig. 1-1-1D).
Native Americans inhabited North Carolina prior to 10,000 years ago. However, today little record of their occupancy of the coastal zone exists. Even the record of the first European settlement on the north end of Roanoke Island in 1584-85 has been obliterated by the dynamic processes of shoreline recession. The processes of change continue to take their toll today as every nor’easter and hurricane place their mark upon the shifting sands of time. If the rapid rates of coastal evolution presently taking place within our coastal system continue, no great remnants from our present coastal civilization will survive into antiquity. This is our coastal heritage.
*** FIGURE 1-1-1 HERE ***
BAT’S GRAVE
Geologists are generally perceived as dealing only with millions of years of geologic time. Yes, when considering earth history, geologists do think in terms of millions, and even billions of years. However, when considering modern earth processes such as earthquakes, volcanic eruptions, and riverine floods the time scales shift to hours, days, years, decades, and centuries. Likewise, in considering high-energy coastal systems, geologic time is synonymous with time as experienced during a trip to the beach, a unique winter, an individual life span, or even a few generations. Thus, modern coastal processes result in geologic events that range in human time frames from individual storm events to the rise and fall of specific civilizations. At this scale, geologic time is human time!
1.2. THE ESTUARINE SHORELINE
Wherever calm, flat estuarine water intersects the irregular land surface, there is a shoreline. However, rarely is the estuarine water surface horizontal. Rather it fluctuates slightly in response to both astronomical and wind tides and severely during storm tides. These changes in water level cause the shoreline to move up and down and produce a shore zone that extends over some area determined by the geometry of the adjacent land surface. If the land is dominated by low slopes, such as occur in the outer portions of coastal North Carolina, the shore zone tends to be very broad forming vast areas of marsh and swamp forest. Wherever the land has steeper slopes, such as dominate the inner portions of the North Carolina coastal zone, the shore zone is narrow and characterized by sediment and rock banks.
In addition, the shore zone is an environment of highly variable physical energy conditions ranging from dead calm water to the extreme wave and storm-tide conditions associated with major storm events. As a result, the shore zone is like a great energy transfer station where physical energy of waves, tides, and currents in the water is transferred to the land through work processes that accomplish the erosion, transport, and deposition of sediments. The amount work accomplished within an estuarine shore zone depends upon the topography and composition (i.e., shoreline type), as well as the source, amount, and duration of energy expended. Each new input of energy (i.e., storm event) causes shorelines to change and evolve through time. This is the function of a shoreline-—to absorb the physical energy occurring at the contact between sea and land. Thus, storm events that input major amounts of energy can result in significant shoreline modification. Whereas, little happens on calm summer days.
Sand beaches are not only important habitats for specific types of organisims, but they are extremely efficient energy absorbing sponges of wave energy. A sand beach will form on a given shoreline if three general conditions are met. There must be adequate wave energy, a low sloping ramp for the beach to perch upon at the shoreline, and an adequate supply of sand available for waves to build a beach. Most sand for mainland estuarine shoreline beaches within North Carolina is derived directly from the erosion of the adjacent sediment bank. If no sand exists in the sediment bank, there is no sand beach. Or, if the eroding sediment bank is hardened, the sand beach often disappears--unless there are cooperative neighbors that won’t modifiy their eroding banks.
Wherever water level and associated waves intersect the land, waves will erode a shoreline that consists of a wave-cut cliff and a wave-cut terrace eroded directly into the sediment or rock that comprises the shoreline. If the material is unconsolidated sand and wave energy is high, the recession rates will be severe. Whereas, if the shoreline material is hard rock, the erosion rates will be slow or negligible.
As energy input, character of land, or sea level change through time, the shoreline responds with dramatic evolutionary changes. Herein lies the dilemma. Rates of change along the North Carolina estuarine shorelines occur in time frames of days and years, in severe contrast to the expectations of permanence and economic values placed upon waterfront properties. Raleigh style approaches to development are not possible in a high-energy coastal system. For long-term success for both society and the estuarine ecosystem, use and development of coastal resources must recognize and be done in harmony with the energy and processes of the natural system.
1.3. CONCLUSION
Thus, shoreline erosion is an ongoing natural process within the North Carolina estuarine system resulting from the short- and long-term coastal evolution. While various methods are available to combat erosion and land loss, none are permanent solutions, and all have significant environmental trade offs. Recognizing and understanding the complex causes and dynamic processes involved in shoreline erosion is the first step towards minimizing the impact of erosion and managing our shoreline resources and economic investments. Ultimately, to both preserve our coastal estuarine resources and maximize human utilization, long-term management solutions to the problems of estuarine shoreline erosion problems must be in harmony with the dynamics of the total coastal system.