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Fortunes Rocks Beach, Biddeford
Background geology and characteristics
Annual and seasonal beach profile changes
The beach profiles at Fortunes Rocks Beach start behind the frontal dune crest and also within seawalls. Beach profile data were collected at the Fortunes Rocks locations from 1999-2006. At FR1, annualized changes showed little distinct patterns of general accretion or erosion (Figure 80). The beach appeared to be stable from 1999-2001, with accretion from 2001-2002 resulting in the most volumetrically sediment-rich profile in 2002. From 2002-2003, the profile underwent some loss, especially from about 25 m offshore seaward. In 2004, the beach was at its leanest shape. By 2005, the profile was similar in shape to the profile from 2001, with slightly more sediment stored offshore. Some erosion of the upper portion of the profile occurred between 2005-2006. Seasonally, the beach at FR1 (Figure 81) shows a typical summer shape, with more sediment stored in the berm area than the winter profile. Standard deviation data (Figure 82a) indicate that the berm at FR1 is relatively stable, changing its position laterally little between summer and winter. The berm appears to be positioned at about 30 m from the mark, with vertical variability on the order of 40 cm.
It appears that data collected at FR2 are from two different marks - one was used from 1999-2002, and a second (behind the dune) from 2003-2006. The beach at FR2 accreted from 1999-2002, and this trend continued from 2003-2005 (Figure 83). In 2006, the dune appears to have been eroded slightly, and the berm appears to have lost much of its sediment volume. On a seasonal basis, FR2 (Figure 84) exhibited somewhat similar profile shapes, with slightly more volume of sediment in the berm in the summer profile. The profile envelopes are nearly identical, and the standard deviation values are quite similar as well. The berm, positioned between the 30-40 m marks, appears to vary vertically on the order of about 50 cm (Figure 82b).
The beach at FR3 showed steady accretion from 1999-2002, and a well developed berm in 2002. By 2003, the berm had been eroded (Figure 85). Erosion continued into 2004. In 2005, slight accretion occurred on the uppermost portion of the profile (between 0 to -2 m below the pin), with sediment loss from about 45 m from the pin seaward. In 2006, the dune appears to have accreted, while there was additional sediment loss in the middle portion (berm) and offshore portions of the profile. Seasonally, FR3 data (Figure 86) indicate a more developed berm during the winter rather than the summer, with more slightly more sediment stored offshore in the winter. The winter berm varied vertically by about 60 cm, and was located around the 25 m mark. The summer berm varied only around 40 cm. However, the summer data indicate large amounts of variation - on the order of 50-60 cm - over a large stretch of the profile in the offshore, between 55 and 120 m from the mark (Figure 82c). This may indicate that FR3 sees volumes of sediment pass offshore during the summer months as sediment is moved along the beach.
Data at FR4 indicate that the beach was stable from 1999-2001, then accreted from 2001-2005, with the most volume in the profile in 2005 (Figure 87). In 2006, the upper portion of the profile (from about -2 m below the pin and higher) lost sediment, while the remainder of the profile remained relatively stable. Overall, the profile gained sediment from 1999-2006. Seasonal data (Figure 88) indicate that the summer profile tends to hold more sediment along the dune and upper portion of the profile, with the winter profile having slightly more sediment volume in the offshore portion. Standard deviations (Figure 82d) indicate that there is more variability along the entire profile in the summer (up to 50 cm) than the winter. The berm at this profile is located much closer to the pin (10 m), as opposed to the other profiles along Fortunes Rocks Beach.
Profiles along Fortunes Rocks Beach indicate variability from year to year, but general stability over the time period of data collection. Seasonally, the profiles vary as expected.
Last updated on January 3, 2008
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