Analysis of coastal dune dynamics, shoreline position, and large woody debris at Wickaninnish Bay, Pacific Rim National Park, British Columbia

Abstract

Large woody debris (LWD) and colonizing vegetation alter the sediment budgets and stability of coastal dune systems. In British Columbia, LWD on beaches consists largely of historical escape logs from the coastal logging industry. In areas with strong wind regimes and high sand supply, LWD can trap appreciable amounts of windblown sand in the backshore, which can enhance foredune development and stabilization (roles typically played by vegetation) on stable or prograding shorelines. This additional store of sediment provides an important buffer that reduces erosion of established foredunes and backshore ecosystems. This study examines trends in LWD and vegetation coverage and associated geomorphic changes within the Long Beach unit of Pacific Rim National Park Reserve derived from aerial photography since the early 1970s. Over this time LWD has been reworked seasonally to interannually and, at Wickaninnish Bay, has declined in areal coverage by 61%. Despite this decline, LWD is found extensively within established foredunes and swales in the study area. In combination with vegetation colonization, this has promoted shoreline advance rates as rapid as 1.5 m·a -1 . At Schooner Cove and Wickaninnish Beach, vegetation colonization is occurring rapidly and has reduced active sand surfaces of large, transgressive dunes landward of the foredune by~28% over the 34 year observation period. This may reflect both park protection initiatives (i.e., reduced foot and vehicular traffic) and a warming and wetter climate regime on the British Columbia coast over the study period and suggests increasing future stabilization of dune systems in the area.Résumé : D'importants débris de bois et une végétation colonisatrice altèrent les bilans sédimentaires et la stabilité des systèmes de dunes littorales. En Colombie-Britannique, ces importants débris de bois sont en général constitués de billots éga-rés provenant de l'industrie forestière de la côte. Là où les vents sont très forts et que beaucoup de sable est disponible, les débris peuvent piéger de grandes quantités de sable soufflé par le vent dans l'arrière-plage, ce qui peut encourager le déve-loppement et la stabilisation d'avant-dunes (des rôles habituellement réservés à la végétation) sur des littoraux stables ou d'accrétion. Cette réserve additionnelle de sédiments fournit un tampon important qui réduit l'érosion des avant-dunes et des écosystèmes d'arrière-plage établis. La présente étude examine les importants débris de bois et la couverture végétale ainsi que les changements géomorphologiques connexes à l'intérieur de l'unité Long Beach de la Réserve de parc national du Canada Pacifc Rim à partir de photographies aériennes depuis le début des années 1970. Durant cette période, les importants débris de bois ont été travaillés selon les saisons et les années et, à la baie Wickaninnish, leur superficie a été réduite de 61 %. Malgré cette diminution, les débris de bois se retrouvent un peu partout dans les avant-dunes et les bassières établies du secteur à l'étude. Jumelés à ...

The influence of coarse woody debris on gravel beach geomorphology

“…In sandy environments it appears that CWD is of greater importance in the development of dunes through interrupting air flow across the beach and therefore inducing deposition of sediment being transported by aeolian processes (Walker and Barrie, 2006;Eamer and Walker, 2010;Heathfield andWalker, 2011). Carter (1988) described two types of depositional features related to the accumulation of debris; ephemeral and embryo foredunes.…”

“…Small lines of broken vegetation (or wrack lines) have been shown to increase the roughness of beach surfaces, thereby enhancing drag and encouraging aeolian sand deposition (Jackson et al, 2004;Nordstrom et al, 2006bNordstrom et al, , 2011; however, these accumulations are generally only temporary features on those fetch-limited beaches studied. Where CWD is composed of large logs sourced from the timber industry, such on the west coast of Canada, it can initiate incipient foredune development (Walker and Barrie, 2006;Eamer and Walker, 2010;Heathfield and Walker, 2011). Research has also focussed on the accumulation of anthropogenic rubbish and its distribution on the coast (Garrity and Levings, 1993;Convey et al, 2002;Claereboudt, 2004), and driftwood has been used to estimate sea ice conditions in the Arctic (Häggblom, 1982), but there has been little attention given to how accumulations of CWD impact on beach morphology.…”

“…This is especially the case in areas where high rates of erosion and steep forested catchments provide an ample supply of woody debris to the coast such as in western North America (e.g. Terich and Milne, 1977;Walker and Barrie, 2006;Heathfield and Walker, 2011) and New Zealand. In this study the gravel beaches of the lower part of the North Island of New Zealand are investigated to ascertain the role of CWD in determining beach morphology.…”

Quantifying spatial and temporal trends in beach–dune volumetric changes using spatial statistics

“…The dune complex is located toward the southern end of a 10 km-long embayed beach within Wickaninnish Bay, which has a southwest aspect to the Pacific Ocean, a mesotidal range (spring tide rangẽ 4.2 m), and is exposed to energetic wave conditions (average winter significant wave height of 2.47 m and period 12.07 s). Beaches in the area are wide, dissipative and backed by 1 to 5 m high vegetated foredunes that are prograding at a rate of approximately 0.2 m a −1 (Heathfield and Walker, 2011) in response to regression of relative sea level in response to crustal uplift along the Cascadia subduction zone (Mazzotti et al, 2008). The foredunes are backed by one of the largest active transgressive dune complexes on Vancouver Island.…”

Ecoengineering with Ecohydrology: Successes and failures in estuarine restoration

“…Nevertheless, considerable attention to the design and cost of both passive Ecohydrology natural recruitment and active Ecoengineering placement schemes in river systems Kail and Hering, 2005;Manners and Doyle, 2008) is now also being employed for estuarine and coastal restoration planning (e.g., Heathfield and Walker, 2011). While providing beneficial services in terms of wind-driven wave erosion mediation and ecological functions using tree debris (e.g.…”