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m and 3.7 m respectively. A cross section of the high ridge at SVI 009, the highest
ridge surveyed, is shown in Figure 4.25.
4) There are low lying areas on the island transect profile between 500 and 600 m, at
1,600 m and at the boundary between ridge sets K and G. These low elevation areas
correspond to low-lying, water-logged sloughs visible on the aerial photographs of
the island (Figure 4.23).
5) Ridges within set F have an average elevation of 3.5 m.
6) Ridges within set E have an average elevation of 1.6 m.
7) With some exceptions, ridge height increases from north to south on the island, as
indicated in Figure 4.26. This implies an increase in wave energy in more recent
years.
8) The average elevation of the swales between the ridges ranges from 0.9 m (set K) to
1.5 m (set F). The swales within sets E and G have average elevations of 0.95 m and
1.0 m respectively.
The relationship of these features to sea-level change will be discussed in chapter 5.
GPR Transect Results
The ground penetrating radar (GPR) transects were set up to cross the majority of the
beach ridge sets on the central portion of the island. The location of the GPR transect, which
was also along Road 4, is shown in Figure 4.23. Figure 4.27 shows the results of the GPR
survey conducted using the MALA 100 MHz unshielded antenna unit with a 1 m antenna
separation. The GPR profile was conducted along the same transect as the topographic profile.
The left (south) side of the profile is the Gulf shoreline of St. Vincent Island while the right
(north) side is the bay. The profile was conducted from south to north along the same line as the
topographic profile. Cross-bedded units have been identified on the profiles and their trend has
been demarcated by blue lines. The GPR survey enabled penetration to approximately 15 m
subsurface, providing an image of the internal structure of the strandplain. The profile shown in
Figure 4.27 has been divided into ridge sets. The average depth of penetration was 8 – 12 m.
All ridges within sets E, F and G, show seaward dipping subsurface features that extend to
approximately 4 to 5 m and then taper off at the base of the shoreface. The low angle reflectors
at about 8 m likely represent the contact between Pleistocene sand and the overlying Holocene
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