Miseners - Long Beach, Nova Scotia
Introduction
Miseners -Long Beach is situated between Chezzetcook and Petpeswick Inlets, 22 km east of Dartmouth (site map). It is an example of a high gravel barrier which is only overwashed during extreme storms such as in 1996 by Hurricane Hortense or when long period storm waves coincide with high tide.
Plan Map:
Following Hurricane Juan a survey was completed along the highest portion (crest) of the entire barrier beach. A comparison of barrier crest position before and after the hurricane suggests it migrated less than 3 m landward.
Prior to hurricane Juan the beach crest of Miseners-Long Beach was less than 4.6 m and all of it was overwashed by waves during Juan. A longshore profile of the barrier beach crest is drawn to illustrate the location and magnitude of crestal scouring by wave overwash.To understand this graph pretend you are standing offshore looking toward Miseners -Long Beach. The upper blue line represents the top of the beach before Hurricane Juan and the bold black line shows the top of the beach after the hurricane.The beach crest was lowered by 0.3 to 0.9 m.
Longshore Profile:
The greatest reductions in crest elevation were at A, B and C which also were sites of large scale wave overwash during hurricane Hortense in 1996 and the storm of February 1998.These sites are transition zones which subdivide the barrier into zones of differing stability and dynamics and mark areas where greater instability is predicted for the future. The jagged nature of the barrier crest profile indicates it was dissected by discrete flows of wave overwash rather than extensive sheet overwash usually observed across the lower gravel barriers.
Looking along Miseners-Long beach showing a well defined ridge along the barrier crest which is thought to have formed as the storm waned. Long period waves were able to extend to the crest and deposit the pebble cobble clasts, but did not have the power to overwash the crest. The presence of this ridge illustrates the resilience of these beaches which begin to rebuild immediately after the storm.
Cross-shore profile:
Surveys were completed at three lines across Miseners-Long Beach to better understand how the beach changed across its width. Shown below is an example from Line 2 where the crest was lowered by 0.7 m and it migrated 1.5 m landward. The lowering of the beach crest to less than 3.5 m elevation puts it into a more dynamic zone subject to change by all storms which coincide with high tide rather than before when it was only affected by the largest storms. Surveys of the crest since the storm of February 1998 showed a general trend of a narrowing and lowering of the crest. Beach width was increased by 2 m because of the transfer of sediment to the backshore during hurricane Juan.
Views toward the west at cross shore line 2 (marked by pink flags and metal post -arrow) before hurricane Juan.
Views toward the west at cross shore line 2 (marked by pink flags and metal post -arrow) after hurricane Juan.
A comparison of the photos confirm the rounding of the beach crest and the increased landward transfer of sediment which buried the vegetation and built up the backshore slope. Also notice in b) the loss of sand from the lower intertidal zone and the trees in the backshore are leaning more.
Cross-shore profile:
A survey of line 2 on November 4, 2003 revealed well defined beach cusps had formed across the upper beach slope and the lower intertidal and subtidal zones had been deeply scoured since July - presumably during hurricane Juan. Breaking waves just offshore on November 4 suggested the scoured sand now existed farther seaward.
Longshore Profile:
Since October 6 crest recovery in elevation was less than 20 cm. The largest change in crest elevation was at "B" where 54 to 72 cm of accretion took place and at "C" where the washover channel was infilled by nearly 100 cm. Waves had overwashed much of the crest since Hurricane Juan, possibly in December 2003 resulting in slight crestal lowering and landward retreat of up to 2.5 m (at west end). Snow and ice fringing the top edge of the barrier prevented further retreat during a major storm in early March 2004.
Cross-shore Profile:
Since November 2003 the crest of the barrier beach at Line 2 was reworked by waves. The two small ridges observed in November were merged into one and the upper back barrier slope was built up as the crest was pushed landward by 2.3 m. By April 2004 a swash ridge was moved upslope (possibly early March) against a deposit of snow and ice which prevented further crest rebuilding and/or wave overwash
Ground Views at Survey Line 3:
The best evidence of wave overwash after hurricane Juan is the increased burial of the backshore vegetation at Line 3. Photo (a) was taken on October 6, 2003 (b) on April 1, 2004. It is assumed the wave overwash took place in December 2003 however residents describe high waves during early March 2004 when much of the barrier was fringed by snow and ice. Line 3 is located just east of "B" at 156 m on the crest profile shown above where the crest had recovered slightly since October 2003.