Higgins Beach Management Plan
Sections 3.0 - 3.2


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3.0 Geologic Processes and Beach Resources

Higgins Beach is a small barrier spit attached to the mainland at its western end, and extending eastward into the mouth of the Spurwink River estuary. The barrier spit is approximately 1.0 kilometer (.62 miles) long. (Figure 1a shows the study area, and Figure 1b shows the larger area.)

3.1 The Higgins Beach Geologic Ecosystem

The beach spit ecosystem of Higgins Beach includes the following major environments: the dune system; the intertidal beach; the inlet and inlet sand bodies of the mouth of the Spurwink River estuary; and the salt-marsh tract just north of the barrier spit. The shoreface just seaward of the barrier spit must also be included as part of the beach ecosystem. Figure 2 identifies, by location and areal extent, the important sub-systems of the Higgins Beach ecosystem as a geologic entity - the environments are related in that they define a sand transport system. The sediment transport system entails a source of sediment, environments which indicate temporary storage or transport of sediment, and sediment "sinks" - areas of long-term sediment storage.

A review of historical charts, vertical aerial photographs, previous geologic data, and recent geologic observations of the system environments defines the elements of the geologic ecosystem and a depiction of how these environments interact with one another and their future trends.

3.2 Historical Shoreline Changes of the Higgins Beach Barrier Spit Ecosystem

Historical shoreline positions can be located with the use of historical navigation charts, vertical aerial photography surveys, and old lot surveys.

Historical charts define old mean high water lines, mean low water lines, and the location and general shape of intertidal sand bodies and coastal dune tracts.

Aerial photography can be utilized to define shoreline positions (the boundary between vegetated shore environments and unvegetated intertidal environments), the areal extent of intertidal sand bodies, and wave approach angles.

Historical lot surveys generally only provide historical mean high water lines.

3.2.1 Historical Chart Data

Two historical navigation charts cover the Higgins Beach shoreline and adjacent Richmond Island Harbor areas. These charts were compiled by the U.S. Coast Survey Office in 1851 and 1879.

The 1851 chart defines a historical shoreline position approximately 90 meters (295 feet) seaward of the present shoreline position. The other notable feature of the 1851 chart is that the channel of the Spurwink River was approximately 110 meters (361 feet) west of its present position (Figure 3).

The 1879 chart shows a similar configuration of coastal shoreline positions and intertidal environment locations, as does the 1851 chart. The changes noted over this period is the apparent shift landward of the beach shoreline by about 10 meters (33 feet) and a shift eastward of the spit end by almost 20 meters (66 feet). The shoreline changes over this period of time are interpreted to be caused by the net displacement of beach sand from the central portion of the beach to the spit end, extending the spit in an eastward direction. The growth of the spit also forced the inlet of the Spurwink River estuary to move in an eastward direction.

3.2.2 Historical Lot Surveys

An historical lot survey was obtained from a Higgins Beach resident. The shorefront lot survey included an approximate mean high water mark for the year 1939. The 1939 shoreline position on the lot survey indicated that the shoreline had receded from 38 to 45 meters (125 to 148 feet) from the 1879 shoreline position. The spit in 1939 was in the same approximate position as of 1879. A tidal channel, extending from the inlet to the marsh behind the spit, formed or migrated southward to effectively narrow the width of the spit to approximately one-half its width in 1879 (Figure 3).

3.2.3 Historical Vertical Aerial Photography

Subsequent to World War II, aerial photographic surveys of the State and Town of Scarborough have provided at least a six-year interval of photography of Higgins Beach. Vertical aerial photographs utilized by Nelson (1979) were reexamined for evidence of measurable shoreline changes of the Higgins Beach ecosystem. Aerial photographs of the Higgins Beach area were taken in the years of 1952, 1964, 1969, 1976, and 1977.

Development of shoreline cottages just after World War II was accompanied, along some areas of the beach, by the stabilization of the shoreline with the emplacement of seawalls. The history of shoreline recession since 1952, then, can only be traced in three sections along the length of the beach. These sections and their respective shoreline histories are:

- Houghton Street to Ashton Street: By 1952, the shoreline had receded back from its 1939 position to the seaward edge of Bayview Street, a distance of about 34 meters (110 feet), thereby exposing a natural bedrock ledge seawall. Extending from Pearl Street to Ashton Street, a short length of natural dune shoreline remains between the natural bedrock ledge (now behind a town-constructed seawall) and seawalls to the east.

Presently, the Higgins Beach system is separated entirely from its ancestral larger beach system by a ledge foreland. The supply of sand available to the system is now much less and confined mostly to the existing beach, dune and ebb-tidal delta sand-bodies.

In order to predict future shoreline changes at Higgins Beach, it is necessary to understand what causes the present recessional and erosional trends of the beach.

1. Natural Recession Processes

The beach is receding partially due to natural causes. There is no discernable source of new sand supply being delivered to the system, and the natural littoral and storm transport processes are removing sand from the beach to the offshore or into the Spurwink River.

2. Human Inducement of Erosion and Recession

Human activities on the beach have accelerated the natural loss of sand from the beach. The major contribution to the continual loss of sand to the beach is the seawalls constructed along a 1,700 foot length of Higgins Beach. These walls have been constructed historically to prevent property loss due to erosion and to protect structures, public streets and utilities from storm damage.

Seawalls accelerate beach erosion by:

Unregulated foot-traffic and general ignorance about the important role which sand dunes play in conservation of the beach resource and as a natural protective flood and storm wave barrier have resulted in the general degradation of sand dune areas on the beach, diminishing their capability to temporarily store sand and provide anything more than a token barrier to storm waves.

This portion of natural shoreline has receded continuously from 1939 to its present position. Presently, this shoreline lies 30 meters (100 feet) landward of the 1939 shore, and 10 meters (34 feet) behind the 1952 shoreline.

- Vesper Street to Champion Street: The shoreline section between Vesper and Champion Streets remained unstabilized by seawalls until the late 1960's. Shoreline recession between 1939 and 1952 amounted to about 23 meters (75 feet). Further recession occurred to 1964, followed by progradation (migration of the shore in a seaward direction) until 1968 when seawalls stabilized shoreline movements.
- The spit end of Higgins Beach has fluctuated in position since 1952. Generally, the spit has extended in an easterly direction (174 meters [570 feet] since 1939) and receded landward over the long-term. Long-term recession of the spit end has been punctuated by shorter-term (12-17 years) progradation, especially from 1952 to 1969. Maximum progradation occurred in 1969 when the shoreline was 50 meters (165 feet) seaward of today's position. The shore then receded to its present position.

Figure 3 illustrates the historical shoreline changes at Higgins Beach documented from past photographs and map records.

3.2.4 A Summary of Higgins Beach Shoreline Historical Changes

From the previous description of historical shoreline positions, the trends of these changes are summarized as:

  1. the Higgins Beach shoreline exhibits a history of long-term recession (landward migration) and spit extension in an easterly direction;
  2. short-term progradation of the spit shoreline and accelerated spit elongation occurred subsequent to the mid- to late 1940's when approximately one-third of the beach's shoreline was stabilized by seawalls; and
  3. spit shoreline recession commenced again after 1969 and has continued to the present. Geologic observations of present spit behavior indicate that the inlet may now be migrating westerly - shortening spit length.

3.2.5 Average Shoreline Recession Rates

A comparison of shoreline positions over time leads to a determination of average annual shoreline recession rates over the beaches documented history. Calculation of recession rates assists in the determination of possible cyclical beach changes and future shoreline positions.

The following average annual recession rates have been calculated over the known history of the Higgins Beach shoreline:

     1851-1879              --   .36 meters (1-2 feet) per year
     1879-1939              --   .7  meters (2.3 feet) per year
     1939-1952              --  2.6  meters (8-5 feet) per year
     1952-1977
     (western beach)*       --   .36 meters (1.2 feet) per year
     1952-1977
     (spit)*                --   .7  meters (2.3 feet) per vear

     *Includes period of shoreline progradation from 1952 to 1969 and a period of
     recession from 1969 to the present.

The recession rates for the period prior to 1939 and for the period after 1952 are from one-sixth to one-third slower than the rate which apparently occurred from 1939 to 1952.

The high rate of recession which took place between 1939 and 1952 might be attributable to several factors such as storm frequencies during that period, sea-level rise, or the rapid development of seawalls.

  1. Storms: Burton et al (1965) indicates that almost three times the number of damaging storms have occurred after 1952 as during the 1939 to 1952 period. Therefore, it appears unlikely that the high rate of shoreline recession from 1939 to 1952 was due to storms.
  2. Sea-Level Rise: Long- and short-term changes in sea level occur in the Gulf of Maine. Historical tide gauge data from Portland, Maine (Hicks and Crosby, 1974) indicate that sea level has been rising along the Maine coast since 1910. The long-term trend of the rise is of the magnitude of .22 cm/year. The long-term trend in sea-level is made up of short-term up and down fluctuations of the surface of the sea. Of note on the tide records are two periods of greater than normal sea-level rise - from about 1941 to 1957 and a period commencing about 1968 when absolute rises during those periods were approximately 16 cm. (6.3 inches) and 10 cm. (4 inches) respectively. These periods coincide with the 1939 to 1952 period of the 2.6 meter annual recession rate and the commencement of the spit recession after 1952 (a recession rate of 4.5 m/yr. to the present) (Figure 4).
  3. Seawall Construction: Seawall construction on Higgins Beach has taken place since the mid-1940's. Two periods of seawall construction are notable - the period from the forties to 1959 when approximately 50% of the present seawalls were built, and from 1967 to 1969 when the mid-section portion of the beach was stabilized.

3.2.6 Cause of Accelerated Recession Rates

Both a rise in sea level and shoreline stabilization appear to correlate with higher Higgins Beach recession rates. The data do not allow for a separate evaluation of each causal factor; but, theoretically, both factors would contribute to an increase in shoreline recession.

A short-term rapid increase in sea-level rise would allow waves to travel further landward than the previous period - shoreline recession would accelerate. The construction of seawalls would have prevented supplies of dune sand from entering the beach transport system, replacing sand lost during storm erosion periods on nearby, unstabilized portions of the beach.

Both factors, then, are concluded as the possible reasons for accelerated recession rates over the known history of Higgins Beach. Unfortunately, the recent past (1975 to 1980) is without sea-level rise data which are conclusive in trend, and complicated by the long-term effects of the large-magnitude 1978 storm to effectively conclude whether the lower recession rates or the higher ones prevail today.


References:

(1) Burton, I., R.W. Kates, J.R. Mather, and R.E. Snead, 1965. The shores of megalopolis: coastal occupance and human adjustment to flood hazard. Lab. Climatology, Pub. in Climatology, 18 (3) 603 pp.

(2) Hicks, S.D., and Crosby, J.E., 1974. Trends and variability of yearly mean sea level, 1893-1972: N.O.A.A. Technical Memo. NOS 13, Rockville, MD, 14 pp.

(3) Nelson, B., 1979. Shoreline changes and physiography of Maine's sandy coastal beaches: Unpub. MS Thesis, University of Maine at Orono, Dept. of Oceanography, 302 pp.


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Creation Date: October 30, 1997
Reproduced with Permission of Barry Timson and Arthur Lerman