Lawrencetown Beach, Nova Scotia
Introduction
Lawrencetown Beach is a 1.9 km long mixed sand and gravel barrier beach which fronts Lawrencetown Lake, 12 km east of Dartmouth (map). It is a popular recreational beach and a provincial park. A highway extends along the length of the backshore.
Aerial photo of Lawrencetown Beach with location of cross-shore survey lines
Cross-shore profile:
Surveys were completed along two parts of Lawrencetown Beach, one in the west near the park buildings where the duneline reaches nearly 6 m elevation (Lines 303 to 305) and a second at the eastern end where the duneline is less than 4.5 m and backed by numerous excavation hollows (Lines M, 306 to 309).
Waves from Hurricane Juan dumped significant amounts of beach sand and cobble on the highway at the west end of the beach, damaged boardwalks and spread cobbles and debris across the duneline to maximum elevations of 5.4 m
At the east end of Lawrencetown Beach water level ponded to 1.95 m at one of the houses (arrow) and flotsam debris lines varied from 2.3 to 4.9 m in elevation.
View of upper beach and dunes at the western end of Lawrencetown Beach (a) July 2001.
b) Sept 29, 2003; only the foundation of the boardwalk survived Hurricane Juan. The duneline was cut back a maximum of 5.5 m and the upper beach was scoured resulting in the loss of a cobble deposit developed since the storm of February 1998
Changes observed at survey line 304 were representative of others at this end of the beach. Cobble was swept up into the dunes; the base of the duneline was cut back 0.8 m and cut down vertically by 0.8 m.
View of a path cut by people walking from the upper boardwalk to the beach.
Waves during hurricane Juan were funnelled upslope, carved out the duneline and undermined the upper boardwalk. Where a path or dune scarp did not exist prior to the hurricane, waves swept up the duneslope flattening and cutting vegetation and depositing cobbles and debris and caused little damage to boardwalks.
At the eastern end of Lawrencetown Beach waves completely removed the seaward ridge/duneline at line 309 which had been eroding since 1998.
View of the eastern part of Lawrencetown Beach at Line 307 a) in Aug 2001 showing the lush dune grass and the initiation of a path at the duneline.
b) post -hurricane Juan after waves widened the path into a large washover channel (in front of person) and transported large amounts of coarse clasts onto the backshore.
At other locations, e.g. line 306, where the duneline was higher (4.5 m) and the beach slope was covered by pebble cobble boulder material, the waves extended up and over the crest. Water flowing down the backslope scoured hollows several metre deep and flooded the former sediment excavation pits. Despite the absence of change across the beach face, the scouring of the backslope has left a more narrow beach ridge vulnerable to upper beach collapse and/or lowering during future storms.
Post Storm Recovery: after one month (Line 304)
Cross-shore profile:
After one month the lower beach slope was cut back 8m landward and scoured downward by 0.5 m as sediment was transported upslope to form two pebble cobble swash ridges. The highest of the two ridges was built at the same location as the pre-Juan ridge but it was not yet as high. Little beach recovery was observed above upper ridge since Juan struck in September 2003.
Post Storm Recovery: after six months (Line 304)
Cross-shore profile:
Between November 2003 and April 2004 pebble cobble continued to be moved by waves upslope to the base of the dunes as in 2002 (see photo above). The cobble formed a single ridge 1.1m higher than the post Juan surface and higher than the ridge which existed before hurricane Juan. At the eastern end of Lawrencetown Beach a swash ridge was developed along the upper beach slope but it was much smaller than the gravel ridge at Line 304 and the western end of the beach.
Line 304: Ground views looking west (a) on October 2, 2003 and (b) March 31, 2004 showing the switch from a surface cover of sand to pebble cobble across the upper beach. Snow from "White Juan" February 2004 protected the base of the dunes from further retreat.