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92 126.96.36.199 Sand Dunes Associated with Bedrock and Thin Till
Sand dunes along the majority of the Atlantic Shore are comprised of relict beach deposits and are receiving very limited inputs of modem sediment. These dune systems can be divided into several categories according to their morphological setting, bay head barriers, bay mouth barriers, with or without islands attached, and beaches. Further categorization can be made depending the substrate of the barrier (see Fig.4.9)
Bay Head Barriers:
Bay head barriers with multiple ridges exist at only two locations on the Atlantic Shore, Summerville beach and Risser's beach. These two systems occupy similar positions across small bays created by river mouths, at the head of much larger bays. They are also relatively short and wide compared to most systems along this coast, and have been the focus of much recreational activity . Summerville has an unusual profile in that it consists of a few low, wide ridges backed by a high centre ridge of eroded dunes (Fig.4.20). The embankment of the railway line, which once ran the length of the barrier to the bridge at the far end, is responsible for the strange profile of the back of the highest ridge, with its flattened section and steepened slopes. The dunes adjacent to the old railway are unnaturally high, due to sand accumulation around a fence that once existed
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along the ridge, and the frequent blowouts in this ridge are the result of a well used trail along the fence (Bowen et al.,1975). The barrier is now a Provincial Park, and since people were prevented from camping on the dunes and from driving trailers on to the dunes via the old railway bed, the system has become well vegetated and is prograding (Bowen et al., 1975; Taylor et al., 1985). Although Risser's beach has most likely received material from drumlins to the southwest, as is suggested by the red colour of the beach, its morphology and the sand deposition at the western end indicate that longshore transport is from the east, therefore restricting sediment input from the drumlins (Fig.4.21). Risser's beach is a provincial park, with a campground and day use area. A breakwater at the far end, originally built during the 1940s and replaced a few years ago, is successfully trapping sand, as is the sand fencing along the foredune. The existence of sand fencing suggests that the foredunes were once in a degraded condition, however they are now well vegetated and accumulating sand, with the exception of an area of erosion along the ramp at the distal end. Backing the foredune ridge are several steep ridges and forest vegetation. Much of the centre area of the barrier at the land end is occupied by park facilities. The rest of the area is forested, with a salt marsh along the landward shore of the barrier .
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Bay Mouth Barriers (sand):
Bay mouth barriers, consisting entirely of sand are more rare, but are found at Cape Sable Island. Crescent, and Martinique. The dune morphology on these barriers is the same as on those formed of coarse clastic material, with a single ridge, a steep seaward slope and a gentle lee slope, Like the other systems, the sand barriers are usually also attached to islands at some point along their length Crescent is a true tombolo, connecting Bush Island of the LaHave Island, to the mainland, and has a paved road running the length of the barrier The dunes of this system are very badly eroded, with high dunes, over 2 m, remaining only at the southern end of the barrier (Fig. 4.31). A large salt marsh also occurs at the southern end, directly behind the largest dunes. The remaining dune ridge is very broken. with boulders filling the gaps (Fig. 4.32). A wooden retaining wall protects the windward face of the dunes, creating a strange ramp profile. Despite numerous attempts to repair the system, the barrier is becoming narrower as beach and dune material is transferred to the marsh behind, The first known repair work was done in 1905 following a winter storm, and since then the barrier has been reinforced with car bodies, posts, rocks, trees, and a seawall (Bowen et al. 1975), Crescent beach would have failed and retreated before now if not for the anchoring effect of the road. It is a popular recreation area, and is the only place in the province that cars were observed driving and parking on the beach. The speed limit, twenty-five km/h, was imposed when attempts to keep
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vehicles of the beach failed in the early 1970s (Bowen et al., 1975). Martinique beach is another that is threatening to fail (Fig. 4.33). The eastern end of the barrier, attached to Flying Point Island, has been breached and rebuilt, and an estimated 9 m of dune was lost of the front of the ridge between 1976 and 1981 (Taylor et al., 1985). The barrier consists of one dune ridge that is widest at the western end, and gets narrower and steeper towards the east. The highest dunes, also the most eroded and narrowest, occur just to the east of a rocky shoal, approximately 2 km along the beach. This shoal appears to be I holding the barrier in place, and once the beach moves landward of the influence of the shoal, the centre of the barrier will stretch, narrow and eventually separate from Flying Point Island. During the winter of 1991-1992, the most vulnerable area of the dunes, that just east of the shoal, was eroded by wave action along both the front and along the back. Snow fencing along the front of this area had accumulated sand in the past, but much of the fence and the sand were removed I during the winter. Martinique has been a provincial park since 1971, vehicle tracks across the dunes are now well vegetated, and the only area where sand removal occurred for local use, at the western end, has recovered.
Figure 7.3 Sand Dunes which are currently, or are likely to become, or have been degraded (see Table 7.1).
Also close up of South Shore from Figure 7.3
Summary of the Condition of the Sand Dunes Table 7.1 & key to Table 7.1.
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7.3.1 Currently Disturbed by Human Activity
The majority of the systems which are currently severely disturbed by human activity are being primarily damaged by vehicle traffic. The one I ; exception is Mavillette, where pedestrian disturbance is the greatest problem, and is exacerbating the damage created by vehicle traffic. The high old dunes at Carters Beach are being destroyed by vehicles driving over them and by foot traffic, as is happening at South West Port Mouton, which is also being seriously eroded by wave action. The dunes at Glace Bay are thinly vegetated, most likely due to the unstable nature of the sand dunes, which are a popular area for walking and riding off-highway vehicles. This system can be likened to the description of Dominion in 1974 as a remnant of a much larger dune system with frequent blowouts and washovers (Bowen et al. , 1975). The recovery of the Dominion dunes under the care of the Provincial Parks, suggests that the same can be done for Glace Bay. On the other systems of this group vehicle traffic, and foot traffic, as mentioned before is the biggest problem, destroying the vegetation cover and initiating erosion. The dunes on Crescent Beach are being threatened by both human activity and natural processes. Human activity has, and is, damaging the dunes, while rising sea level is forcing the barrier to retreat, although it is being held by the paved road along the back of the dunes and the wooden retaining wall along their seaward side ....
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Other common forms of dune protection utilized in provincial parks, and at some other dune sites, include parking lots, sand fencing, and piping plover protection. By identifying specific parking areas and providing beach access from these areas, visitors are prevented from parking anywhere along the dunes and crossing to the beach at random, a practice which results in numerous trails across the dunes, possibly resulting in multiple areas of erosion. Sand fencing fills two roles. Its primary purpose is to increase sand deposition, however it also affectively prevents people from crossing fenced areas (i.e. Fig. 5.7 and 7.2). The sand fencing on the high dunes at Summerville, for example, is collecting little sand, but is reducing further erosion by stopping people from walking on these sensitive areas. Isolating areas of the beach and dune for the piping plover , an endangered species in the Maritimes, by roping them off and by posting signs prohibiting entry, also protects the dunes in the area (Fig. 7.1). Plovers usually nest between late April and early August, allowing. dune protection during most of the busiest recreational season (Farrier et al., 1991). Poison ivy, common on Pomquet, Merigomish and Mahoneys, is also- affective in keeping people off the sand dunes, however its introduction would not be recommended for this purpose. Through use of these techniques, badly damaged dune systems such as Lawrencetown, Dominion, and Melmerby have regained their integrity .It should re noted, however, that all these systems are in areas of adequate sediment supply, and that the same methods may not be so successful in areas with little new sediment input.