Variation of Beach Morphology along the Saco Bay Littoral Cell

Results

Alongshore variations (from south to north) of different shoreline characteristics (e.g., coastline orientation, net erosion or accretion, etc.) along the Saco Bay shoreline are presented in Figures 9-23. The Saco Bay shoreline was divided into four different regions based on morphologic and littoral characteristics, as shown in Table 5A and illustrated on Figure 1. Regions were further subdivided into compartments, and labeled alphabetically (Table 5B). All distances are referenced to zero (0) being the southern end of Hills Beach, near the entrance to The Pool. Results are generally presented in relation to the different regions (and their compartments) described.

Coastline Orientation

Mean orientations for each region and compartment are presented in Table 5. Coastline orientation varies from 100-175^o from true north (TN) within region 1, from 135-190^o in region 2, from 115-270^o in region 3, and from 115-200^o in region 4 (Figure 6). A graph illustrating the percent occurrence of coastline orientations (every 10 degrees) shows that approximately 23% of the entire bay shoreline is oriented between 211-220^o (corresponding with region 3), with a secondary peak of 12% at 171-180^o (Figure 7).

Figure 6

Figure 7

Sea Level Rise (1962-1995)

Figure 8

The average annual rate of sea-level rise for the Portland tide gauge's overall record (1912-2001) was 1.9 mm/yr (Figure 8A). The average annual rate of sea-level rise during the study period (1962-1995) was slightly lower at 1.1 mm/yr (Figure 8B).

Estimated Net Erosion and Accretion (1962-1995)

varition of erosion and accretion along Saco Bay

Figure 9

Figure 9 illustrates the patterns of net erosion and accretion along Saco Bay from 1962-1995. The Saco Bay shoreline in general is relatively stable to accretive, however several pockets of distinct erosion exist in the Camp Ellis area (7,800-12,800 ft). The areas of largest net accretion are located in region 1 (1,000-2,000 ft, and 4,000-6,000 ft), and region 3 (23,500-25,600 ft and 37,000-42,600 ft). The highest net accretion was over 300 ft (~5,800-6,000 ft), nearest the southern jetty of the Saco River.

Region 1 (Hills Beach): Accretion and segments of little shoreline change dominate the shoreline south of the Saco River (Figure 9). This region was divided into three distinct compartments. Compartment 1A stretches from The Pool (0 ft) northwestwards approximately 2,000 ft to Surf Avenue. The southernmost portion of compartment 1A (0-800 ft, north to near Sky Harbor Drive) is rocky headland. The beach from here northward to near Surf Avenue (2,000 ft) exhibits high net accretion. Compartment 1B encompasses the central portion of Hills Beach (2,000-4,000 ft, the narrowest part of the island near 4,000 ft), and is generally stable, with a small pocket of slight net erosion (~ -50 ft) near Surf Avenue (2,000 ft). Pockets of high net accretion (>100 ft) are located within compartment 1C (4,100-6,000 ft) with the largest net accretion (~300 ft) occurring adjacent to the southern Saco River jetty.

Region 2 (Camp Ellis Beach, Ferry Beach, Bay View, and Kinney Shores): The shoreline in this region has undergone the highest net erosion along Saco Bay based on data used for this study (Figure 9). The majority of erosion is concentrated within a 5,000 ft compartment (2A) north of the Saco River (7,700-12,700 ft), stretching roughly from Bay Avenue in Camp Ellis to near Pond Avenue in Ferry Beach. High erosion (up to 100 ft) is concentrated in a 1,000-foot stretch directly adjacent to the jetty, from Bay Avenue north to Lower Beach Avenue, while net erosion is generally on the order of -20 to -40 ft from 1,400-5,000 ft north of the jetty, from Sunrise Avenue in Camp Ellis to approximately 1,000 ft north of Pond Avenue in Ferry Beach, near Long Pond. A small pocket of generally stable shoreline extends from Lower Beach Avenue to Sunrise Avenue (8,700-9,200 ft) in Camp Ellis.

A zero crossing occurs near 12,800 ft (5,000 ft north of the jetty), in Ferry Beach. This designates the southern extent of compartment 2B. Accretion generally extends from north of Long Pond to Outlook Avenue in Kinney Shores (near 17,000 ft), with intermittent pockets of erosion and accretion adjacent to Goosefare Brook (17,000-18,700 ft).

Region 3 (Ocean Park, Old Orchard Beach, Surfside, Grand Beach, Pine Point): The shoreline along region 3 is relatively stable to highly accretive, with only several small pockets of net erosion, generally 20 ft or less. Net accretion is generally 60 ft or less from 19,500-23,000 ft, generally from Goosefare Brook north to near Odessa Avenue in Ocean Park, and 25,500-36,400 ft, from Fernald Street in Old Orchard Beach northeast to near Little River Road in Grand Beach. Highest net accretion (>60 ft) occurs from 23,100-25,400, from Odessa Avenue in Ocean Park to Fernald Street in Old Orchard Beach, and from 36,500-42,300 ft, near Little River Road northeast to the southern Scarborough River jetty.

Region 4 (Western Beach): Western Beach underwent accretion over the 33-year study period. The majority of accretion has been concentrated along compartment 4B, nearer to Prouts Neck, while areas of less accretion are near the Scarborough River.

Shoreline Type, Dry Beach Width, and Total Landward Width

Figure 10

Figure 10 illustrates the variation of dry beach and total widths along the Saco Bay shoreline. Mean values for dry beach widths and total widths for Saco Bay as a whole, and for each region, are presented in Table 6. Region 4, Western Beach, has been excluded since no dry beach width data has been collected to date, and there are no habitable structures along this region. In terms of dry beach widths, for the overall bay, shorelines comprised of a combination of dune/seawall or seawall/dune are fronted by the widest dry beaches; surprisingly, the dry beach widths in dune-only shorelines are the thinnest. In terms of total widths (from the HWL to the first habitable structure), it seems that shorelines fronted by dunes are the widest.

Region 1 (Hills Beach): The Hills Beach shoreline is comprised of seawalls, rock outcrops, or vegetated dunes. Bedrock coastline dominates the southernmost portion, while the central section, from north of Surf Avenue to the narrowest part of the island (approximately 2,900-4,200 ft) is fronted by seawalls. The south-central and northern portions of region 1 are comprised of vegetated dune, and correspond with the widest distances to habitable structures. Distances from the seaward edge of dunes/structures appear largest in front of vegetated dunes, and smallest in front of the artificially stabilized stretches of shoreline along Hills Beach.

Region 2 (Camp Ellis Beach, Ferry Beach, Bay View, and Kinney Shores): Seawalls stabilize the first 2,000 ft of compartment 2A (Camp Ellis). Intermittent stretches of vegetated dune and vegetated dune backed by seawall extend from Beacon Avenue in Camp Ellis north to south of Stowe Avenue in Ferry Beach (9,600-13,800 ft). Vegetated dune and seawall combinations comprise the southern shoreline of compartment 2B (13,900-15,200 ft, Stowe Avenue north to Bay View Avenue). Naturally vegetated dune stretches from 15,300-16,900 (Bay View Avenue to Outlook Avenue). A mix of vegetated dune and seawall, seawall and vegetated dune, and only seawall completes the stretch of shoreline from 17,000-18,700 ft from Outlook Avenue north to Goosefare Brook. Vegetated dune segments of the shoreline are generally wider than stretches of shoreline stabilized with seawalls.

Region 3 (Ocean Park, Old Orchard Beach, Surfside, Grand Beach, Pine Point): The majority of region 3 shoreline includes a seawall in combination with a dune, although the northernmost stretch from near Grandview Avenue in Surfside north to the southern Scarborough River jetty (32,800-42,600) is fronted by vegetated dune only (compartments 3B and C). The widest distances from dune to habitable structure along the entire Saco Bay shoreline exist within compartment 3C, at the northern end of this region. Vegetated dune backed by a seawall is the most common shoreline type, although several stretches of seawall backed by vegetated dune, and seawall only are apparent.

Region 4 (Western Beach): Western Beach fronts a golf course and therefore supports very few structures or seawalls. Vegetated dune is the dominant shoreline type within compartments 4A and 4B.

Alongshore Variation of Beach Profile Shapes

Several distinct variations exist among beach profile shapes along the Saco Bay shoreline. In general, low profile elevations and relatively steep slopes dominate the southern portion of the bay (region 1 and part of region 2), from the entrance to The Pool in Hills Beach north to Long Pond in Ferry Beach (0-12,700 ft). Profiles tend to flatten and attain higher elevations from compartment 2B northward, past Goosefare Brook, to the south-central portion of Old Orchard Beach (compartment 3B). Here, profile elevations decrease dramatically, and profile slopes flatten substantially. Northwards, within compartment 3C, profiles appear to shallow seaward, but increase in overall elevation. Alongshore variations in beach profile shapes are presented in three-dimensional line and color interpolated plots in Figure 11A and 11B for the entire Saco Bay. In addition, similar plots have been created illustrating variations within the compartments of each region (Figures 12-15).

Region 1 (Hills Beach): Hills Beach profiles (Figures 11, 12) appear relatively steep, especially within the central compartment (1B), and attain maximum elevations of generally 15 ft or less. Profiles in compartments 1A and 1C are slightly flatter. Profile maximum elevations dip to near 12 ft within the northern part of compartment 1C.

Region 2 (Camp Ellis Beach, Ferry Beach, Bay View, and Kinney Shores): Region 2 (Figures 11, 13) exhibits a dramatic alongshore variation in beach profile shapes, in both slope and elevation. Profiles nearest the Saco Bay north jetty (compartment 2A) are extremely steep, and generally attain depths of -3 ft within 200 ft of the dune or seawall crest. Profile elevations are generally less than 15 ft in the immediate vicinity of the jetty (~2,000 ft north of the jetty). Within compartment 2B (from Fairhaven Avenue northwards), there is an increase in profile elevations and decrease in slope. Closest to Goosefare Brook, however, profiles tend to steepen.

Region 3 (Ocean Park, Old Orchard Beach, Surfside, Grand Beach, Pine Point): Profiles along the central to northern portions of Saco Bay (Figures 11, 14) achieve their highest elevations from Goosefare Brook northeast to near Fernald Street in Old Orchard Beach (compartment 3A), and the 2,000 ft closest to the Scarborough River southern jetty (compartment 3C, from the Avenue Five Extension northeast to the Scarborough River). Compartment 3B, the central stretch of the region, exhibits relatively low (generally 15 ft maximum elevation or less), flat profiles. These profiles appear highly uniform in overall shape and slope.

Region 4 (Western Beach): Profiles along Western Beach (Figures 11, 15) are relatively steep nearest the Scarborough River (compartment 4A), and substantially flatten farther away from the river, to the southeast (compartment 4B).

Mean Profile Shapes

Mean beach profiles were computed for each region and their respective compartments. Regional mean profiles are presented in Figure 16. Compartmental mean profiles are shown in Figures 17-20. All mean profiles were offset to 0 NAVD for ease of comparison. Mean profiles from the different regions exhibit very different shapes, from steep and somewhat reflective, to gently sloped and dissipative. The mean profile from region 1 exhibits the steepest slope and lowest maximum elevation, while region 3 is the most dissipative profile overall. The region 2 mean profile achieves the highest elevation, and exhibits a slope in between those of the other regions. The region 4 mean profile falls in between the mean shapes of regions 1 and 2.

Region 1 (Hills Beach): Region 1 profiles fall into compartments 1A, 1B, and 1C based on overall profile shapes (Figure 12). Mean profiles calculated for each compartment exhibit different features (Figure 17). Compartment 1A (0-2,000 ft), exhibits the best-developed dune along Hills Beach. Compartment 1B achieves the same maximum elevation (14 ft), but is much steeper in slope. The mean profile, representing beach conditions from the thinnest part of the island north to the southern jetty of the Saco River, reaches a relatively low maximum elevation (12 ft) and has the flattest overall slope.

Region 2 (Camp Ellis Beach, Ferry Beach, Bay View, and Kinney Shores): Distinct profile shapes are apparent between compartments 2A and 2B (Figure 13). Profiles from the north Saco River jetty northwards approximately 5,000 ft (to near Long Pond) are relatively steep and low. Profiles from compartment 2B are much higher and show much more variability in their dune shapes. Mean profiles for the compartments are similar in overall shape and slope; however, the 2A mean profile reaches an elevation of only 13 ft, and is slightly steeper than the mean profile from compartment 2B (Figure 18).

Region 3 (Ocean Park, Old Orchard Beach, Surfside, Grand Beach, Pine Point): The first profile compartment (3A) extends from Goosefare Brook northeast to near Fernald Avenue in Old Orchard Beach, and exhibits the best-developed dunes of the region, with maximum elevation near 18 ft (Figure 14). Profiles from compartments 3B and 3C are generally much lower in elevation and much flatter. Mean profiles from each compartment reflect this trend; the mean profile for compartment 3B is very low and flat. The profile from compartment 3C, although low, exhibits a flat, dissipative shape, yet exhibits a larger volume of sediment within the upper portion of the profile than 3B (Figure 19).

Region 4 (Western Beach): Mean profiles for compartments 4A and 4B exhibit substantial differences in terms of slope, elevation, and dune/beach topography (Figure 20). Compartment 4A, although it achieves a higher elevation (near +15 ft), is much steeper than compartment 4B.

Variation of Maximum Profile Elevations (MPE) in Reference to Base Flood Elevations (BFE)

Figure 21

Figure 21 illustrates the alongshore variation of maximum profile elevations in relation to base flood elevations from FEMA Flood Insurance Rate Maps. Elevation data from FIRM maps were converted from NGVD29 to NAVD88 using the Vertcon conversion utility (NAVD88 values are approximately 0.7 ft greater than NGVD29 values in this geographic area) in order to compare with maximum profile elevations. Elevation data clearly identifies areas that are at risk for flooding during storm events along the Saco Bay shoreline. Approximately 61% of the region 1 shoreline is below BFE, while 17% of region 3 and less than 4% of region 2 is below BFE. None of region 4 is below FEMA BFE values.

Region 1 (Hills Beach): Aside from the southernmost transect (near 0 ft), compartment 1A is above BFE. Profiles within compartment 1B are typically below BFE values (up to 6 ft), while elevations nearest the southern Saco River jetty (5,500-6,000 ft) are at or above BFE values.

Region 2 (Camp Ellis Beach, Ferry Beach, Bay View, and Kinney Shores): Profiles along the Camp Ellis Beach shoreline from the jetty north to near Island View Avenue (7,700-10,200 ft) exhibit MPE values that are slightly higher than BFE, except near Bay (7,700 ft) and Riverside Avenues (8,300 ft), where MPE values are about 1 ft below BFE. From Riverside Avenue northwards for approximately 1,000-ft, MPE values range from 1-2 ft above BFE. From Island View Avenue in Camp Ellis northwards to Goosefare Brook, MPE values are generally 2-6 feet higher than BFE values. Highest MPE values are from 9,800-12,800 ft within compartment 2A. Within compartment 2B, MPE values are typically 2-3 ft or greater than MPE values.

Region 3 (Ocean Park, Old Orchard Beach, Surfside, Grand Beach, Pine Point): MPE values within compartment 3A are 2-8 ft above BFE values (from Goosefare Brook northeast to near Fernald Avenue, 19,700-25,500 ft). Within compartment 3B, MPE values tend to follow the overall alongshore trend of BFE values, remaining at or several feet above BFE (north of Fernald Avenue northwards into Surfside). Values fall below BFE at the seawalled portion of Old Orchard Beach (26,300-27,200 ft). From 30,500 to 34,500 ft, MPE values are generally at or below BFE values. A transect near 33,600 ft is over 2 ft below BFE, corresponding with the former location of the Little River inlet. Compartment 3C profiles are generally 1-5 ft above BFE values along the remainder of the region 3 shoreline northeastwards to the Scarborough River jetty.

Region 4 (Western Beach): MPE values are well above BFE values along the entire Western Beach shoreline. Within compartment 4A, MPE values are typically 3-7 ft above BFE, while in compartment 4B, elevations are 3-6 ft above BFE.

Variation of Overall Beach Profile Slopes

Figure 22

Region 1 (Hills Beach): Profile slopes range from 0.019 at the southern end of Hills Beach, to 0.193 north of Surf Avenue (near 2,300 ft), with a mean value of 0.071 (Figure 22). Lowest slopes (<0.100) are concentrated in within compartment 1A (0-1,600 ft) and central to north-central portions of compartments 1B and 1C (2,600-5,500 ft). Steepest slopes occur just south and north of Surf Avenue (1,700-2,500 ft), and from Pleasant Avenue to the southern Saco River jetty (5,600-6,000 ft), while the mean value for the region is 0.072.

Region 2 (Camp Ellis Beach, Ferry Beach, Bay View, and Kinney Shores): In general, the steepest slope values along the entire Saco Bay shoreline are found in region 2. These are concentrated within compartment 2A. Slope values decrease accordingly with distance from the northern jetty, ranging from 0.237 near Pearl Avenue (8,000 ft) near the northern jetty, to 0.060 near Sylvain Avenue in Ferry Beach (10,700 ft). Slope values steepen from 0.06 near Sylvain Avenue to 0.09 near Pond Avenue (11,700 ft), followed by a subsequent flattening of slope values from 0.09 to 0.05 from Pond Avenue north to just north of Bay View Avenue (11,800-15,600 ft). Slopes stabilize to near 0.050 within Bay View and Kinney Shores (15,600-18,700 ft). The mean value for the region is 0.080.

Region 3 (Ocean Park, Old Orchard Beach, Surfside, Grand Beach, Pine Point): In contrast with region 2, this region exhibits the lowest slope values along Saco Bay. Slopes range from 0.025 to near 0.080 at the Scarborough River jetty and approximately 0.010 at the eastern end of Western Beach. The region has a mean value of 0.040. Values remain constant at 0.050 from Goosefare Brook north to Fernald Avenue (19,700-25,500 ft), with slightly steeper slopes (~0.060) nearest Goosefare Brook. In Old Orchard Beach, from Fernald Avenue north to Brisson Street (25,500-28,500 ft), slopes flatten slightly to ~0.040 and remain relatively constant. From Brisson Street north to Grand View Avenue in Surfside (28,600-32,000 ft), slopes steadily decrease to values near ~0.025, then remain constant to Parcher Avenue (32,100-33,700). There is a slight increase in slope values to 0.030 near Parcher Avenue, then slope values remain near 0.030 through Surfside and Grand Beach to Oak Street, near 38,100 ft. Slopes increase to ~0.050 in Pine Point, near Dunefield Road (40,400 ft), with a small segment of shoreline with increased slope values between Dunefield Road and Avenue Five Extension, then decrease to 0.050 from Avenue Five Extension east along Pillsbury Drive. Along Pillsbury, slopes abruptly increase to a maximum value of 0.080 at 41,600 ft, then decrease to 0.050 nearest the Scarborough River jetty.

Region 4 (Western Beach): Along Western Beach, profile slopes range from near 0.100 adjacent to the Scarborough River, to less than 0.010 at the beach's eastern extent.

Estimated Net Volume Changes (1962-1995)

Figure 23

As a whole, beach profiles along the Saco Bay shoreline appear to have undergone a positive net gain in sediment volume from 1962 to 1995 (Figure 23). This trend is also apparent for individual regions. Region 3 underwent the largest net volume gain, on the order of 1,266,450 yd³, while region 2 gained the least (approximately 27,800 yd³). Negative volume change (erosion) is generally concentrated within the Camp Ellis and Ferry Beach segments of region 2, from the northern Saco River jetty north to near Long Pond in Ferry Beach (7,700-12,800 ft). Table 7 summarizes the net volume changes for each region, and the smaller compartments defined within each region.

Region 1 (Hills Beach): Region 1 supports three separate compartments based on volumetric changes (Table 7). The southern compartment (entrance to The Pool north to near Surf Avenue), has a high net volume change on the order of 76,600 yd³, while the central compartment (Surf Avenue north to the thinnest point of the island near 4,100 ft), is more stable, with a net volume change of near 18,700 yd³ over the 33 year period. The northern compartment underwent the most accretion, with a net volume change of approximately 136,900 yd³.

Region 2 (Camp Ellis Beach, Ferry Beach, Bay View, and Kinney Shores): Two distinctly different net volume change patterns exist within this region. From Bay Avenue in Camp Ellis to north of Pond Avenue in Ferry Beach (7,700-12,700 ft), the compartment has a net volume change of approximately -55,400 yd³, while the northern compartment, stretching from north of Pond Avenue to Goosefare Brook, has a net positive change near 83,200 yd³, including a small segment of net negative volume change nearest to Goosefare Brook. The first 2,500 ft north of the Saco River jetty (7,700-10,200 ft) had a net loss of -37,400 yd³, or approximately two-thirds of the loss within the southern compartment.

Region 3 (Ocean Park, Old Orchard Beach, Surfside, Grand Beach, Pine Point): This region is highly accretive, with an overall net volume change of 1,266,450 yd³. Several distinct compartments of high positive net volume change exist, along with several segments of little or almost no volume change. Segments of shoreline with little volumetric changes extend from Goosefare Brook northeast to near Tioga Avenue in Ocean Park (19,700-21,500 ft), and in Surfside, from Rosewood Street northeast to north of Parcher Avenue (31,700-34,200 ft). The largest positive volume changes occur from Ocean Park northeast to Parcher Avenue in Old Orchard Beach (21,500-31,700 ft), and from Little River Road in Grand Beach northeast to Pillsbury Drive in Pine Point (35,800-42,300 ft), combining for a net positive volume change of approximately 1,063,100 yd³.

Region 4 (Western Beach): Net volume changes along Western Beach are also largely positive, with a change of approximately 141,200 yd³, the majority of which is concentrated along the easternmost portion of the beach (44,900-46,900 ft).

Contents Introduction Historical Background Methods Results Discussion Recommendations Conclusions Additional Study and Research References Appendix A

Last updated on January 9, 2006.