CHAPTER 2 Geomorphology Britt Argow arrier beaches are found along 18% of North the present coast include reworking of this narrow and America’s coasts, mostly along the Atlantic and thin wedge during sea-level rise, and new sediment in- BGulf seaboards. These barrier islands and spits create troduced from glacial deposits at headlands. a quiet, sheltered environment in which unique and diverse lagoon, marsh, and tidal flats develop, known The coast of Maine has been and continues to be shaped collectively as the back-barrier. About 100 km of Maine’s by the forces of wind, waves and tides. Maine experiences roughly 5,600 km coast is protected by barriers (Kelley semidiurnal tides (two high tides and two low tides daily) 1987, Duffy et al. 1989). Relatively little research has along its 5,600 km coastline (Dickson 2003). The mean focused on the ecological, sedimentary and physical tidal range (the vertical difference between mean high processes that shape this coastal environment relative to tide and mean low tide) at Wells Inlet is 2.7 m, increasing its southern counterparts. Wells NERR includes perhaps to 2.9 m around full and new moons each month (Ch. 15, the largest and best studied estuarine and marsh system Fig. 15-4). Winds are seasonal, coming from the north in Maine, and is an important example of a northern and northeast during the colder months and primarily back-barrier system. from the south and southwest during the summer (Ch. 3, Fig. 3-4, Fig. 3-5). Waves generated by these winds vary Wells NERR is located at 43°19’N and 70°34’W in the seasonally in their direction of approach to the shoreline Wells Embayment on the Gulf of Maine. The Wells (Byrne and Ziegler 1997), and also in their height. The Embayment is defined by its arcuate coastline, and lies largest waves, which have the highest energy, approach offshore between the Kennebunk River and the Ogunquit from the northeast and are associated with Northeasters River inlets. The Embayment has an irregular seafloor and winter storms. These waves can be 7 meters in height dominated by bedrock outcrop and relict deposits of while offshore on the western continental shelf of the glacial sediments from the last major North American Gulf of Maine (GoMOOS), and will increase in height ice sheet. Geophysical technology allows us to visualize and steepness as they approach the shore. These waves the layers below the surface and glimpse the sediments are often responsible for massive erosion during a single of the seafloor (Kelley et al. 1988, Fig. 2-1, Fig. 2-2, Fig. storm event, and are a dramatic reminder of the power 14-2). Sand is only a thin cover on the nearshore in most of the sea. During most of the year, however, wave ap- places (Miller 1998). The dominant sources of sand for proach into the Wells Embayment is from the south and 15 Figure 2-1: Seismic reflection profile. Glacial deposition left morainal ridges on the inner shelf as the ice retrated. Subse- quent reworking produced a seafloor composed of sand and gravel with some boulders. The horizontal dotted line traces the border between glacial till and the bedrock below. Source Maine Geological Survey. southeast, and these calm-weather waves are smaller the northern end of a semi-continuous chain of barrier and less energetic (GoMOOS), yet due to their steady, islands and spits stretching southwest along the coast of constant action, they dominate coastal sedimentation Maine, New Hampshire, and Massachusetts to Cape processes on the open coast of the Wells NERR barrier Ann. and headlands. The Wells NERR barrier system itself is a long, low coastal Back-barrier environments generally experience reduced feature. Stretching a total of 4.7 km in a gently curving wave, storm and wind conditions relative to open coast- arc from its anchor points on Moody Point to the till that lines. The resulting lower-energy environment becomes a forms Drakes Island (Fig. 2-3), the barrier island stands sediment sink for sands and muds carried into the system only 2 - 4 m above mean sea level. Wells Beach barrier is via the ocean inlet or from rivers and streams draining heavily developed, and large sections of the beach have the upland. The evolution of this coastal system will be been stabilized by sea walls or revetments. Stabilization discussed in Chapter 14; here we focus on the physical protects property in the short term, but alters the natural characteristics and processes of the dominant ecosystems evolution of the barrier complex and prevents the island and environments of the back-barrier and surrounding from migrating landward in a regime of rising sea level uplands. by reducing overwash processes. The three or more rows of houses effectively stop the action of winds moving sediment from the beach into a dune system and onto the ARRieR EACHes B B back-barrier (Jacobson 1988). The development of Wells The barrier system at Wells NERR comprises two Beach has resulted in several changes to the shoreface, beaches: Wells Beach, south of Wells Inlet, and Drake’s discussed in more detail in Chapter 14. Island Beach and Laudholm Beach (a single system) to the north. Wells Beach is a barrier spit, anchored on the The beach runs 3.5 km north from Moody Point to Wells till and bedrock outcrops of Moody Point. The Drakes Inlet (Wells Beach), and 2.2 km from Wells inlet to the Island / Laudholm Beach, located between Wells Inlet Little River Inlet (Laudholm Beach). Both beaches and Little River Inlet, is a barrier island anchored on till. narrow to the south. Wells Beach is ≈ 250 meters wide The barrier and inlet complex of Wells NERR is near at low tide at the inlet, and gradually becomes narrower 16 Wells National Estuarine Research Reserve Figure 2-2: Side-scan sonar image of the seafloor, looking down on a 5 – 10 m high moraine in the Wells Embayment. Nearby sand and gravel deposits were once part of the moraine but have been removed by erosion. This technique is used in combination with seismic reflection profiles and bottom sampling to determine substrate type. Source Maine Geological Survey. until it tapers and disappears at Moody Point. Laudholm balance of northerly and southerly transport in the long Beach is more consistent in width and the narrowing is term (Belknap et al. 1995), best demonstrated by the more subtle, widening again at the northern jetty. Low- symmetry of the deposits that have built up on both sides tide beach width ranges from 140-200 meters over its of the jetties at Wells Inlet (Timson and Kale 1976). length. Major winter storms are largely responsible for the sea- The variation of beach width is a function of the domi- sonal variation in beach width observed at the barrier nant direction of wave approach from the southeast and beach fronting Wells NERR, as the large waves associated the resulting transport of sediment in a northerly direc- with winter storms have so much energy that they do not tion along the shoreface. These waves also move sediment expend it all crashing on the beach, and therefore carry onshore, building up and widening the beach over the sediment offshore as well as up the beach face. During summer months. The north-south shoreline asymmetry especially large storms, overwash may occur in lower (or is milder than one might expect, however, because of less-protected) sections of the barrier spit system. In a the influence of Northeaster storms which move large natural setting this same process moves sediment from quantities of sediment in a southerly direction along the beach onto the barrier island, raising the elevation the beach, as well as offshore. Currently there is a near of the island and helping it to maintain its position with Geomorphology 17 rising sea level. In lower and thinner sections of a barrier, today face a much higher rate of sea-level rise (about 25 or on barriers that have been stabilized, overwash will centimeters in the last century). Rates of sea-level rise are deposit sediment in the back-barrier environment when expected to keep accelerating, resulting in the inunda- it occurs. tion and loss of these salt marshes if they are not able to maintain their position relative to rising sea level. The barrier itself is made up of layers of sand and gravel. These sediments are re-worked deposits first brought to There are two major classifications of salt marsh ecosys- the area by glacial processes during the last major glacia- tems found in Wells NERR. Low marsh systems form tion of North America (Ch. 14). The barrier is anchored between mean tide level and mean high-water (generally in its present position along the coast by till and bedrock from 0.8 to 1.3 meters above sea level at Wells NERR), outcrops (Fig. 2-3). and are commonly defined in the field by their vegetation. They appear to be a near-monoculture, comprised almost Soils on the barrier are derived from the sands that exclusively of the halophyte (salt-tolerant) grass spe- dominate the stratigraphy of this feature, and are char- cies Smooth cordgrass (Spartina alterniflora). At Wells acterized as thin, sandy loam. NERR, low marsh ecosystems are restricted to narrow ribbons along tidal creeks and to slumped ramps along the main tidal channels. The high marsh, in contrast, in- SALT MARSHes habits broad, fairly level fields, and makes up the majority The extensive salt marshes of the Webhannet River and of the marsh system in the Webhannet estuary (Fig.