Post-tropical Storm Noel struck Atlantic Canada on November 3-4, 2007. Wave impacts were greatest along Atlantic coast of Nova Scotia from Port Joli to just east of Clam Bay.
The area of gale to storm force southerly and southwesterly winds was at least an order of magnitude larger in Noel than Hurricane Juan in 2003, and extended along most of the Atlantic coast of Nova Scotia. Sustained wind speeds offshore peaked at 70 knots during Noel and 82 knots during Juan. The direction of waves was just west of south when their heights peaked and the duration of waves higher than 8 m was 6 hours.
Key parameters which differentiate Noel from previous tropical storms such as Hurricane Juan include: lower water level; less wind intensity, longer duration of high intensity waves; larger area of storm and greater wave setup of ocean, specific wave orientation; and larger extent of coastline impacted. Similarities with Juan include: timing, both occurred in the fall and in the night, Noel generated similar size waves and struck the same segment of the Atlantic coast of Nova Scotia.
If Noel had occurred in the previous week when spring tides were 40-50 cm higher, in all probability the intensity of coastal damage would have been comparable to Juan, and would have extended over much of the Atlantic Coast of Nova Scotia.
The Atlantic coast of Nova Scotia has been retreating landward for thousands of years because of sea level rise. Storms such as Noel cause one small step in that natural process which varies in magnitude depending on the condition of specific shores. For the eight beaches investigated Noel maintained the rapid breakdown and landward migration of Cherry Hill and Cow Bay, left parts of Lawrencetown and Martinique more susceptible to rapid change, continued the slow migration of Hirtles and Miseners-Long beaches, had less impact on Conrads Beach which is in a building phase. The backshore habitat at Hirtles Beach was dramatically transformed from freshwater to saltwater and at Crescent Beach, dune erosion from Noel triggered a management decision to further armour it with rock and constrain its natural movement.
At all beaches investigated, the seaward dune crest or storm ridge was lowered by 0.4 to 1.4 m and pushed landward by 5 to 8 m. Where water reached the lagoon the shores were extended as much as 10 m. Dunes were eroded back by 1 to 7 m and narrow channels up to 20 m long were cut through the dunes where water flow was concentrated.
Waves overwashed all shores less than 4.4 m elevation and water flooded up to a distance of 84 m across the backshore. Where backshores were higher, wave run-up extended to elevations of 6 m across vegetated sand dunes and possibly as high as 12 m across smooth bedrock shores. The minimal regional building guidelines in Halifax Regional Municipality are 20 m distance and 2.5 m above ordinary high tide level which is an elevation of 3.2 m. In select locations, the guideline for building setback has been increased to 60 m distance from ordinary high water. Given the elevations and distances that water reached on shore during Post -tropical Storm Noel, a further review of existing and proposed coastal building guidelines is warranted.
The foreshore zone across all sand, and mixed sand and gravel, barrier beaches examined in 2008 had recovered typical seasonal sand accumulations. Along central Crescent Beach the foreshore zone was built higher than usual, based on 30 years of record, but the upper beach remained lower than in 2003. The only rebuilding of the backshore were isolated, aeolian sand drifts along parts of Conrads, Cherry Hill and Martinique Beaches and the creation of extensive washover deposits which infilled much of the lagoon and tidal creek east of Cooper Island at Cherry Hill Beach. This low wave washover area continued to expand eastward along Cherry Hill Beach.
Both gravel barrier beaches examined experienced at least some wave reworking and rebuilding of their crest and backshore but they had not built to pre -Noel levels by May 2008. Waves reached maximum elevations of 4.2 m, toward the eastern portion of Miseners-Long Beach and crest erosion occurred along the western and eastern parts of the beach.
The highest part of Cow Bay Beach, at line 3a, was eroded back and along the beach crest two low areas continued to expand making them potential sites of future breaching. The seaward part of the eastern breach was submerged at high tide but the landward portion was built just high enough to prevent flooding during normal high tides. At the western breach, sand accumulation was merging with flood deposits previously built in Cow Bay Lake forming a large sand flat.
All channels cut through the three beaches during Post-tropical storm were widened by 8 to 24 m. Hirtles and Lawrencetown beaches were infilled with sufficient sediment to prevent continued overwash into the backshore. Waves washed through the channel cut through Martinique Beach more frequently, forming a large washover fan 0.8 to1.0 m thick which extended the estuarine shore 20 m northward.
Despite rebuilding along all beaches studied, those with channels cut during Post-tropical storm Noel remained just above high tide level and remaine extremely vulnerable to re-breaching during future high water storm events.