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Drakes Island Beach, Wells
Background geology and characteristics
Annual and seasonal beach profile changes
Drakes Island is predominantly fronted by seawalls, except for the beach area adjacent to the jetties at the Webhannet River, which is fronted by relatively expansive dunes. Data available for DI1 were from 2001-2003 and 2005-2007. Annualized profile data for 2001-2002 showed dramatic accretion along the entire profile (Figure 122). It is possible that this is a remnant influence of the beach nourishment project that was completed in the winter of 2000 (Dickson, 2001). The 2003 profile indicates that the beach continued to prograde along its entire length. By 2005, the beach appears to have eroded slightly, starting at about 50 m from the pin, while the upper portion of the berm appears to have grown slightly. In 2006 the entire profile continued to accrete; this trend surprisingly continued in 2007. Overall there is little difference in the seasonal profile shapes, with the winter berm tending to be slightly higher than the summer (Figure 123). The standard deviation data (Figure 124a) indicate that the summer berm is relatively variable, with up to about 60 cm of vertical variation occurring. Winter data indicate that variability is on the order of 40 cm or less.
The beach at DI2 underwent similar accretion from 2001-2002, with the development of a substantial berm and volume of sediment in the offshore. In 2003, the beach appeared to be about the same, with slight erosion near the 50 m mark (Figure 125). By 2005, erosion was apparent in the upper and lower portions of the profile. In 2006, the lower portion of the profile, from 50 m seaward, underwent accretion. The upper portion of the profile also gained some volume. In 2007, almost the entire profile appears to have gained sediment. The seasonal differences at DI2 (Figure 126) appear to be more typical, with a slightly more developed berm associated with the summer profile, and more sediment located offshore in the winter profile. The summer profile envelope shows more variability in the elevation of the berm than the winter profile. Standard deviation data indicate slightly more variability in the berm elevation - on the order of 30 cm - while winter data show little variability along the entire profile (Figure 124b).
Annualized changes at DI3 were characterized by analysis from two different profile locations; DI3FS (front stake), at which data were collected from 2001 to 2003, and DI3BS (back stake), where data were collected from 2005-2007. The 2001 annualized profile at DI3FS exhibited a slight berm, which was lost by 2002, in addition to additional sediment loss along the rest of the profile (Figure 127). In 2003, the berm had receded farther, but accretion occurred along the remainder of the profile, starting at about 20 m from the pin. When data collection was continued at DI3BS in 2005, it appears that the beach underwent accretion in the successive years, through 2007 (Figure 128). The most accretion occurred at the profile's mid-point, at about the 70 m from the pin mark. Overall accretion between 2005-2007 reached about 0.5 m. Seasonal changes at DI3FS (Figure 129) indicated more prominent berm formations and sediment offshore in the winter profile rather than the summer profile. Seasonal data from DI3BS (Figure 130) generally showed the same characteristics, though a slightly more prominent berm (albeit small) was noted. Standard deviation data for all stakes were combined, and show that the profiles during summer and winter generally underwent little variability (20 cm or less) (Figure 124c).
The beach at DI4 appears to have had slightly more sediment on its upper portion, adjacent to the seawall/dune in 2001 than in 2002. Accretion occurred in 2002 along the lower portions of the profile, however, from about 20 m from the pin seaward (Figure 131). The 2003 mean profile showed continued accretion on the lower portion of the profile. It appears that the beach underwent erosive episodes between 2003 and 2005, with lowering of the overall profile elevation along its entire length. In 2006, the beach accreted back to approximately the 2003 profile levels. Seasonally, DI4 exhibited characteristics of a more sediment-rich summer beach profile, with the average beach elevation of the summer profile being approximately 0.2 m higher than the winter profile (Figure 132). Interestingly, the summer profile maximum envelope exhibits the ephemeral presence of a significant bar offshore, at the 80 m from the pin mark, a characteristic more typical of the winter profile. Standard deviation data for DI4 (Figure 124d) indicate significant offshore sediment variability during the summer (up to 60 cm of vertical variation, between 80-105 m from the mark) and the winter (near 60-70 cm) with the variability being farther offshore, near the 120 m mark.
It appears that the jetties along the Webhannet River help trap sediment that is migrating to the south, along Drakes Island Beach. This is occurring mostly in the winter months, and may be responsible for some of the reverse seasonal trends seen along the Drakes Island profiles.
Last updated on January 3, 2008
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