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Mile and Half Mile Beaches at Reid State Park
Introduction and Significance
Mile Beach is located between two rocky promontories: Griffith Head (Outer Head) in the east and Todds Point (Little River Ledges) in the west (Figure 2). A continuous and high natural frontal dune protects a salt marsh and estuarine channels in the back barrier environment (Figure 3). Southwest of Mile Beach is Half Mile Beach (Figure 4). This shorter beach is a true barrier spit that constricts the opening of the Little River and its extensive salt marsh (Figure 5).
Both beaches have similar sand characteristics. Compared to many Maine beaches, Mile Beach has coarser sand and has a rich orange-pink hue due to an abundance of feldspar minerals. Some sand grains are composed of dark-red mineral grains of garnet. Garnets have a higher specific gravity (density) than quartz or feldspar sand grains and can be selectively sorted by waves into red bands or patches on the beach.
The beaches at Reid State Park have classic seasonal changes to the beach profiles with the formation of a broad berm in the summer and a low, convex up profile in the winter (Figure 6). Most of the seasonal shifting of sand is probably involved in the formation of an offshore sand bar in the winter. The edge of the berm is often curved and beach cusps, made by wave action, often persist for days to weeks (Figure 7). Interaction of waves with the rocky headlands at either end of Mile Beach is probably responsible for the formation of ephemeral beach cusps.
Access, facilities, dates of operation, directions, fees for admission, etc. for Reid State Park.
Topographic map: Boothbay Harbor 7.5' quadrangle, scale 1:24,000, U.S. Geological Survey. Available for purchase from the Maine Geological Survey web site. This quadrangle may be available at other Maine locations.
National Ocean Service nautical charts: No. 13295 Kennebec and Sheepscot River Entrances, scale 1:15,000. No. 13293 Damariscotta, Sheepscot, and Kennebec Rivers, scale 1:40,000. Available from National Ocean Service.
Mile and Half Mile Beaches are located in an interesting geological setting. Many coastal barrier beaches and dunes in Maine are located adjacent to rivers that supplied sand to the sea. Fluvial sand is primarily derived from river-bank erosion of glacial deposits. At the coast, sand is reworked and concentrated along the shoreline by marine processes (waves, currents, tides) into coastal beaches and sand dunes. Routinely reworked by wind and waves, sand has accumulated into dunes over thousands of years. While the beaches at Reid State Park are near two rivers: the Sheepscot and Kennebec, it is unlikely that modern rivers supply sand that makes up these beaches.
The Sheepscot River channel is very deep and muddy and does not carry sand this far to sea (Belknap and others, 1986). The Kennebec River is very sandy, but studies of sand transport near the river mouth (FitzGerald and others, 1989; Fenster and FitzGerald, 1996; Fenster and others, 2001) suggest that river sand is most likely accumulated on Pond Island Shoal and Popham Beach on the west side of the river mouth. This leaves the offshore as the most likely source of beach sand at Reid State Park.
Another interesting consequence of the elevation of the sea is how salt water enters the back-barrier salt marshes. The Little River has a classic tidal inlet with the full ebb and flow during a 3 m (10 ft) tide. The salt marsh and lagoon (Figure 2 and Figure 11) behind Mile Beach has an inlet controlled by a bedrock sill. The ledge here confines the lateral movement of the channel to a narrow opening (beneath a bridge in the park; Figure 12). The bedrock also limits the exchange of salt water during the lower part of the tidal cycle. In many ways, the rock sill acts as a dam. About 2000 years ago sea level was probably low enough to prevent the tides from entering the lagoon (Nelson and Fink, 1980). Prior to that time the back barrier environment was probably a fresh water marsh with a small stream that drained to the sea over the bedrock sill. As a result of this controlling bedrock sill, the oldest salt marsh in the park is behind Half Mile Beach and Todds Point.
Coastal Barrier Resources System
The Groundhog Day Storm of 1976 caused extensive coastal flooding at Reid State Park. Morrill and others (1979) measured flooding as high as 2.7 m (8.7 feet) above the predicted high tide. This flooding was the result of both wind pushing coastal water onto the shore and wave runup due to large surf. Such an event may have caused sand to be washed off the beach profile and up into the sand dunes and possibly over the frontal dune ridge. Storm flooding results in deposition of sand in the dunes called washover. Repeated storm sedimentation helps maintain the dune elevation as sea level gradually rises.
Before the park was established, World War II Navy fighter pilots trained by firing rockets at floating targets just offshore of Mile Beach. From 1944 to 1946 planes from Brunswick Naval Air Station flew over the ocean, beach, dunes, and marsh and fired 3- and 5-inch diameter practice ordnance (Hoey, 1997a, b, c) at a barge moored just off the beach as they approached land. The exceptionally large dune (Figure 2 and Figure 3) within the frontal dune ridge was built as a "back stop" for aviator target practice.
In 1976 erosion exposed metal ordnance at the southwest end of Mile Beach (Nelson and Fink, 1980). During subsequent periods of beach profile erosion, such as in the January and February 1978 blizzards, ordnance probably settled to greater depths below the beach.
Grain size sorting
Walk along either beach and observe changes in the size of grains of sand. Walk up and down the beach profile and pick up a sample of sand from the berm near the dune edge, beach face, and low-tide terrace (if the tide is low). Compare these to see where the coarsest sand grains are. Note which places the coarsest and finest grains come from. These grains are sorted by wave action on the low-tide terrace and beach face. Both wind and waves transport sand on the berm and next to the dune. Close to the dune the influence of waves decreases and the relative importance of wind increases in transporting sand. Wind-blown sand tends to be quite fine-grained and well sorted.
Keep the beach face sample in your hand and carry it along on your walk. Compare sand samples from the beach face as you go and search for a coarsening or fining trend. In general, grains tend to become finer in a "down drift" direction. That is, grains become smaller in the direction of sand movement. Are you walking up drift or down drift?
Fine sand will move along the beach more quickly than coarse sand so there will be some selective sorting by waves and the alongshore current. Observe the size and angle of waves washing ashore. Estimate their height and period (count the seconds between crests arriving ashore or breaking). At a later time, compare what you observed with data recorded by buoys offshore. In the future you will have a better idea of the size of the surf down at the beach based on readings at wave-rider buoys you can access on the internet from home or the classroom.
Beach cusp measurement and berm width
From time to time the berm on Mile Beach is scalloped into rhythmic beach cusps (Figure 7). This irregular shape consists of horns and cusps that protrude and recede from the average berm crest. Sometimes there can be more than one berm on the beach profile due to changes in the tidal range from a large (spring) range to a small (neap) range which allows more than one set of beach cusps to be temporarily preserved. As the tides change over a month, a larger range and different wave conditions will rework the cusps into a linear berm or another cuspate berm. Figure 3 shows a relict cuspate topography in the berm; this relief can be seen in the undulations of the sand fence.
Walk along the berm and look for variations in the edge and top of the berm. Is the berm crest linear or curved? Are there fresh or old cusps cut into the berm? Is there more than one berm? As you walk the beach notice how the berm width changes. Which end of Mile Beach has the biggest berm (and hence best beach blanket space)?
Measure the wavelength of the cusps by counting the paces from crest to crest. Are the crests all the same distance apart? Record the distance (number of paces) of several crests and calculate the average wavelength. Chances are the next visit to the beach the cusps will be a different size or perhaps not even present. As you walk the length of the beach does the cusp wavelength change? Does it increase or decrease up drift or down drift?
References, Additional Resources, and Further Reading
Barnhardt, W. A., Belknap, D. F., Kelley, A. R., Kelley, J. T., and Dickson, S. M., 1996, Surficial geology of the Maine inner continental shelf; Cape Elizabeth to Pemaquid Point, Maine: Maine Geological Survey (Department of Conservation), Geologic Map 96-9, Scale 1:100,000.
Barnhardt, W. A., Belknap, D. F., and Kelley, J. T., 1997, Stratigraphic evolution of the inner continental shelf in response to late Quaternary relative sea-level change, northwestern Gulf of Maine: Geological Society of America, Bulletin, v. 109, p. 612-630.
Belknap, D. F., Shipp, R. C., and Kelley, J. T., 1986, Depositional setting and Quaternary stratigraphy of the Sheepscot Estuary, Maine: a preliminary report: Geographie Physique et Quaternaire, v. XL, no. 1, p. 55-69.
Belknap, D. F., Shipp, R. C., Kelley, J. T., and Schnitker, D., 1989, Depositional sequence modeling of late quaternary geologic history, west-central Maine coast: Studies in Maine Geology, Volume 5 - Quaternary geology, Maine Geological Survey, p. 29-45.
Buynevich, I. V., and FitzGerald, D. M., 1999, Structural controls on the development of a coarse sandy barrier, Reid State Park, Maine: Coastal Sediments '99.
Buynevich, I. V. and FitzGerald, D. M., 2000. The coastal geology of Popham and Reid Beaches, in Yates, M. G., Lux, D. R., and Kelley, J. T. (editors), Guidebook for field trips in coastal and east-central Maine: New England Intercollegiate Geological Conference, 92nd Annual Meeting, Dept. of Geological Sciences, Univ. of Maine, Orono, p. 226-237.
Dickson, S. M., 2001, Beach and dune geology aerial photos: Open-file maps on a photo base with interpreted geology and legend, Maine Geological Survey, 1:4,800 scale. Catalog Numbers: 01-459 Half Mile Beach, Little River; 01-460 Half Mile Beach, Reid State Park; 01-461 Mile Beach, Reid State Park; 01-462 Griffith Head, Reid State Park.
Dickson, S. M., 1999, The role of storm-generated combined flows in shoreface and inner continental shelf sediment erosion, transport, and deposition: Ph.D. dissertation, School of Marine Sciences, University of Maine, 321 p., 1 plate.
Fenster, M. S., and FitzGerald, D. M., 1996, Morphodynamics, stratigraphy, and sediment transport patterns of the Kennebec River estuary, Maine, USA: Sedimentary Geology, v. 107, p. 99-120.
Fenster, M. S., FitzGerald, D. M., Kelley, J. T., Belknap, D. F., Buynevich, I. V., and Dickson, S. M., 2001, Net ebb sediment transport in a rock-bound, mesotidal estuary during spring-freshet conditions: Kennebec River estuary, Maine: Geological Society of America, Bulletin, v. 113, p. 1522-1531.
FitzGerald, D. M., Buynevich, I. V., Fenster, M. S., and McKinlay, P. A., 2000, Sand circulation at the mouth of a rock-bound, tide-dominated estuary: Sedimentary Geology, v. 131, p. 25-49.
FitzGerald, D. M., and Fink, L. K., Jr., 1987, Sediment dynamics along an indented coast; Popham Beach-Kennebec River, Maine, in Kraus, N. C. (editor), Coastal Sediments '87: American Society of Civil Engineers, New York, New York, p. 2047-2061.
FitzGerald, D. M., Lincoln, J. M., Fink, L. K., Jr., and Caldwell, D. W., 1989, Morphodynamics of tidal inlet systems in Maine, in Tucker, R. D., and Marvinney, R. G. (editors), Studies in Maine Geology, Volume 5 - Quaternary Geology: Maine Geological Survey , p. 67-96.
Fink, L. K., Jr., and Nelson, B. W., 1980, The morphological record of dynamic processes active in Maine's swash-aligned beach systems (abstract): Geological Society of America, Abstracts with Programs, v. 12, no. 2, p. 35.
Hoey, D., 1997a, Explosives cleanup to close state park: Portland Press Herald, November 21, 1997.
Hoey, D., 1997b, Warhead cleanup at state park delayed: Portland Press Herald, August 21, 1997.
Hoey, D., 1997c, State Park ordnance cleanup "a success": Portland Press Herald, December 9, 1997.
Kelley, J. T., Dickson, S. M., Belknap, D. F., 1996, Maine's history of sea-level changes: Maine Geological Survey, Fact Sheet.
Komar, P. D., 1998, Beach processes and sedimentation, second ed.: Prentice Hall, Upper Saddle River, New Jersey, 544p.
Nelson, B. W., 1979, Shoreline changes and physiography of Maine's sandy coastal beaches: M.S. thesis, University of Maine, Orono, 302 p.
Nelson, B. W., and Fink, L. K., Jr., 1980, Geological and botanical features of sand beach systems in Maine: Maine Sea Grant Publications, Bulletin 14, 163 p. (originally published by Maine State Planning Office, Critical Areas Program, Planning Report 54).
Morrill, R. A., 1977, Maine coastal flood of February 2, 1976: U. S. Geological Survey, Open-File Report 77-0533, 40 p.
Morrill, R. A., Chin, E. H., Richardson, W. S., 1979, Maine coastal storm and flood of February 2, 1976: U. S. Geological Survey, Professional Paper 1087, 20 p.
Smith, C. L., and Ruter, B. D., 1996, Morphodynamics of a reflective sand beach, Reid State Park, Maine (abstract): Geological Society of America, Northeastern Section, 31st Annual Meeting, Abstracts with Programs, v. 28, no. 3, p. 100.
Sullivan, J. J., IV, 1998, Alongshore variation in erosion and deposition on a reflective sand beach, Reid State Park, Maine (abstract): Geological Society of America, Northeastern Section, 33rd Annual Meeting, Abstracts with Programs, v. 30, no. 1, p. 77.
Trudeau, P. N., 1979, Ecology of barrier beaches in south-central Maine (Popham Beach State Park, Reid State Park, and Small Point Beach): Ph.D. dissertation, University of Massachusetts, Amherst, Massachusetts, 412 p.
Trudeau, P., Godfrey, P. J., and Timson, B. S., 1977, Beach vegetation and oceanic processes study of Popham State Park beach, Reid State Park beach, and Small Point beach: Maine Department of Conservation and U. S. Department of Agriculture, Soil Conservation Service, Resource Conservation and Development Project, 144 p.
Site by Stephen M. Dickson
Originally published on the web as the April 2002 Site of the Month.
Last updated on April 19, 2012
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