Silver Sands (Cow Bay) Beach, Nova Scotia

Silver Sands or Cow Bay Beach as it is also known, is located just east of Dartmouth (map). The 1 km long barrier beach fronts a small estuary Cow Bay Lake which is connected to the ocean through an inlet at the west end of the beach. Three cross-shore lines, marked 1, 2, 3a, and a line along the crest or top of the barrier were surveyed to document beach changes resulting from Hurricane Juan (air photo 92350-13, July 25, 1992, courtesy Nova Scotia Geomatics).

Aerial photo of Silver Sands beach, July, 1992

Aerial photo of Silver Sands beach, July, 1992

Silver Sands Beach is representative of low gravel barrier beaches (less than 4 m elevation) which are easily overwashed by waves during major storms such as hurricanes or when less intense storms coincide with high tide. Waves scour the beach slope and roll the highest portion (crest) of the beach onto the lower backshore. Where waves transport sediment as far as the lake or lagoon the backshore can be extended landward as individual lobes called washover fans, shown on the air photo.

View of Silver Sands Beach from the parking area at the east end of the beach, November 7, 2002 illustrating how waves overwash the barrier during storms. The landward extent of overwash is shown by the line of melted snow on the backshore. Waves reached Cow Bay Lake along the central part of the beach as shown by the absence of snow.

View of Silver Sands Beach from the parking area at the east end of the beach, November 7, 2002 illustrating how waves overwash the barrier during storms. The landward extent of overwash is shown by the line of melted snow on the backshore. Waves reached Cow Bay Lake along the central part of the beach as shown by the absence of snow.

Pre- Hurricane Juan June 15, 2003

Pre- Hurricane Juan June 15, 2003

Post Hurricane Juan October 7, 2003 Views of Silver Sands Beach a) before and b) after Hurricane Juan from same location as photo above. A comparison of the two photos reveals that waves washing over the barrier smoothed and flattened the top or crest of the barrier. The backshore was built up and much of the vegetation observed in June was buried by sediment. Tree damage, especially to the conifers, is visible along the lake shore.

Post Hurricane Juan October 7, 2003

Views of Silver Sands Beach a) before and b) after Hurricane Juan from same location as photo above. A comparison of the two photos reveals that waves washing over the barrier smoothed and flattened the top or crest of the barrier. The backshore was built up and much of the vegetation observed in June was buried by sediment. Tree damage, especially to the conifers, is visible along the lake shore.

Plan Map:

Survey lines along the top and back of the barrier beach are compared to previous surveys to determine how far Silver Sands Beach was pushed landward during Hurricane Juan. The beach crest was pushed 2.2 to 23.6 m landward. The beach crest moved farthest landward at the central portion near line 2, just west of line 3a and adjacent to the inlet at the far western end. The position of the lake shore along the barrier beach only shifted landward by 1 to 5 m as the backshore was built up by sediment carried landward by wave overwash.

Survey lines along the top and back of the barrier beach are compared to previous surveys to determine how far Silver Sands Beach was pushed landward during Hurricane Juan. The beach crest was pushed 2.2 to 23.6 m landward. The beach crest moved farthest landward at the central portion near line 2, just west of line 3a and adjacent to the inlet at the far western end. The position of the lake shore along the barrier beach only shifted landward by 1 to 5 m as the backshore was built up by sediment carried landward by wave overwash.

Longshore Profile:

A survey along the barrier beach crest from the base of the hill at the east end to the inlet is drawn to show how much the beach crest was lowered during Hurricane Juan. To understand this graph pretend you are standing offshore looking toward Silver Sands Beach. The upper two lines represent the top of the beach before Hurricane Juan struck and the bold black line shows the top of the beach after the hurricane. The crest was lowered by 0.6 m along the east end, 0.7 to 1.1 m along the central portion, and maintained a similar elevation near the inlet. The deepest cuts in the barrier of more than 1 m were at A and B which mark transition zones which subdivide the barrier beach into three longshore segments. Both sites now are commonly flooded at high tide and site B is where tree stumps were exposed (shown in next section).

A survey along the barrier beach crest from the base of the hill at the east end to the inlet is drawn to show how much the beach crest was lowered during Hurricane Juan. To understand this graph pretend you are standing offshore looking toward Silver Sands Beach. The upper two lines represent the top of the beach before Hurricane Juan struck and the bold black line shows the top of the beach after the hurricane. The crest was lowered by 0.6 m along the east end, 0.7 to 1.1 m along the central portion, and maintained a similar elevation near the inlet. The deepest cuts in the barrier of more than 1 m were at A and B which mark transition zones which subdivide the barrier beach into three longshore segments. Both sites now are commonly flooded at high tide and site B is where tree stumps were exposed (shown in next section).

The following views of Silver Sands beach just west of cross-beach line 3a a) before and b) after Hurricane Juan showing the where the largest landward thrust of the beach occurred. The beach crest was smeared landward over top of the low vegetated backshore and old beach ridges. Arrows mark the same location for reference.

The following views of Silver Sands beach just west of cross-beach line 3a a) before and b) after Hurricane Juan showing the where the largest landward thrust of the beach occurred. The beach crest was smeared landward over top of the low vegetated backshore and old beach ridges. Arrows mark the same location for reference.

When the beach was pushed landward just west of Line 3a, a large number of tree trunks became exposed in the intertidal zone. Since the trees must grow above sea level these trunks mark a former shoreline built when sea level was lower. Sea level has been rising along Atlantic Nova Scotia at 30-40 cm /century therefore these trees are estimated to be several hundred years old. A sample from one tree was sent to the radio-carbon laboratory of the Geological Survey of Canada, Ottawa for age determination.

When the beach was pushed landward just west of Line 3a, a large number of tree trunks became exposed in the intertidal zone. Since the trees must grow above sea level these trunks mark a former shoreline built when sea level was lower. Sea level has been rising along Atlantic Nova Scotia at 30-40 cm /century therefore these trees are estimated to be several hundred years old. A sample from one tree was sent to the radio-carbon laboratory of the Geological Survey of Canada, Ottawa for age determination.

Cross-shore profile:

Surveys were completed at three lines across Silver Sands Beach to better understand how the beach has changed across its width. Shown here is an example from Line 2 where the highest point on the barrier shifted 14 m landward as a result of the hurricane. The lagoon shore was built up and extended 1 to 2 m into the lake. The distance a backshore migrates depends on the severity of wave overwash and the depth of the backshore water body. If the water is shallow, it is easier to fill it with sediment and extend the backshore landward.

Cross-shore Survey of Line 2, the black bold line represents beach after hurricane Juan

Cross-shore Survey of Line 2, the black bold line represents beach after hurricane Juan

Although slightly different views looking east at cross-shore line 2 these photos illustrate a) a normal beach profile sloping seaward and landward from the crest (where person is standing) before the hurricane compared with just after the storm b) when the profile has been flattened which allows more extensive wave overwash as marked by the line of seaweed. For reference arrows mark the same concrete pillar in each photo.

Although slightly different views looking east at cross-shore line 2 these photos illustrate a) a normal beach profile sloping seaward and landward from the crest (where person is standing) before the hurricane compared with just after the storm b) when the profile has been flattened which allows more extensive wave overwash as marked by the line of seaweed. For reference arrows mark the same concrete pillar in each photo.



Post Storm Recovery: After One Month

Cross-shore profile:

By November 3, 2003 the beach slope was further eroded and sediment was transported upslope to rebuild the barrier beach crest 0.5 m higher, and 3 m seaward of the pre-hurricane Juan crest location (grey line). It is anticipated that this crest is temporary and it is in the process of building farther landward.

By November 3, 2003 the beach slope was further eroded and sediment was transported upslope to rebuild the barrier beach crest 0.5 m higher, and 3 m seaward of the pre-hurricane Juan crest location (grey line). It is anticipated that this crest is temporary and it is in the process of building farther landward.



Post Storm Recovery: After Six Months Longshore Profile:

By April 2004 the barrier crest at Cow Bay had been rebuilt to nearly pre-Juan elevations of 3 to 3.6 m except at 'A' and 'B' where the two washover channels cut during Hurricane Juan became better defined by recurved ridges extending into the lagoon along each side.

By April 2004 the barrier crest at Cow Bay had been rebuilt to nearly pre-Juan elevations of 3 to 3.6 m except at "A" and "B" where the two washover channels cut during Hurricane Juan became better defined by recurved ridges extending into the lagoon along each side.

Cross-shore Profile:

Within six months the barrier crest at Line 2 was rebuilt to 2.74 m which was 0.3 m less than the elevation recorded in 2002. The crest was built from sediment eroded from the beach slope and transported upslope. The new crest had migrated a net distance of 11m landward from where it existed before the hurricane despite initially being pushed 14 m landward right after the hurricane. It was built on the backshore slope which had been extended during Hurricane Juan.

Within six months the barrier crest at Line 2 was rebuilt to 2.74 m which was 0.3 m less than the elevation recorded in 2002. The crest was built from sediment eroded from the beach slope and transported upslope. The new crest had migrated a net distance of 11m landward from where it existed before the hurricane despite initially being pushed 14 m landward right after the hurricane. It was built on the backshore slope which had been extended during Hurricane Juan.

Beach Survey Line 2:

Ground view taken on April 5 2004 provides a visual comparison with the photos above showing the change in relative position of the dance hall foundation where sediment was scoured downward by more than 0.7m and the beach migrated 11m landward.

Ground view taken on April 5 2004 provides a visual comparison with the photos above showing the change in relative position of the dance hall foundation where sediment was scoured downward by more than 0.7m and the beach migrated 11m landward.