Evolution of a foredune and backshore river complex on a high-energy, drift-aligned beach Derek K. Heathfield, Ian J. Walker ⁎ Coastal Erosion and Dune Dynamics (CEDD) Laboratory, Department of Geography, University of Victoria, Victoria, BC, Canada abstract article info Article history: Received 25 February 2015 Received in revised form 6 August 2015 Accepted 7 August 2015 Available online 9 August 2015 Keywords: Coastal erosion Foredune River Bluff LiDAR Wave-dominated Drift-aligned This paper examines the multi-decadal evolution of a foredune and backshore river complex on a wave- dominated, drift-aligned coast at Wickaninnish Bay on southwestern Vancouver Island, British Columbia, Canada. Local shoreline positions are generally prograding seaward as fast as +1.46 m a -1 in response to rapid regional tectonic uplift and positive onshore sediment budgets. The northern end of the foredune system has extended rapidly alongshore in response to net northward littoral drift. Despite these net accretional responses, the beach–dune system experiences relatively frequent (return interval ~1.53 years) erosive events when total water levels exceed a local erosional threshold elevation of 5.5 m above regional chart datum. Geomorphic recovery of the beach–dune system from erosive events is usually rapid (i.e., within a year) by way of high onshore sand transport and aeolian delivery to the upper beach. This response is complicated locally, however, by the influence of a backshore river that alters spatial–temporal patterns of both intertidal and supratidal erosion and deposition. Historic landscape changes and rates of shoreline positional change are derived from several years of aerial pho- tography (1973, 1996, 2007, 2009, 2012) using the USGS Digital Shoreline Analysis System (DSAS). Significant volumetric changes are also estimated from aerial LiDAR-derived DEMs in 2005, 2009 and 2012, and related morphodynamics are interpreted using a statistically constrained geomorphic change detection method. Results suggest that supratidal bar development, overwash deposition and aeolian deposition on a low-lying supratidal platform, combined with alongshore extension of the foredune complex, is forcing Sandhill Creek to migrate northward in the direction of beach drift. In response, the river actively erodes (-1.24 m a -1 ) a bluff system landward of the channel, which generates substantial sediment volumes (-0.137 m 3 m -2 a -1 ) that feed a large intertidal braided channel and delta system. These local responses provide context for a conceptual model of the evolution of a wave-dominated, drift-aligned beach–foredune system that interacts with a backshore river. This model may provide useful information to local park managers as erosion and sedimentation hazards threaten visitor safety and park infrastructure. © 2015 Elsevier B.V. All rights reserved. 1. Introduction The morphodynamics and longer-term evolution of wave- dominated coasts are shaped dominantly by erosion, deposition, and transport of sediment via high-energy wave processes and wave- generated currents (Davidson-Arnott, 2011). Coastal geomorphology in wave-dominated environments is often characterized by elongate shore-parallel sedimentary forms including longshore bars, beaches, beach ridges, and foredunes (e.g., Wright, 1977; Short and Hesp, 1982; Hesp, 2002). On such wave-dominated coasts, process-response morphodynamics typically depend on the magnitude and timing of wave energy with other forcing mechanisms such as tides, surge, and/ or wind energy that control nearshore and onshore sediment transport and supply. Davies (1980) distinguishes drift-aligned coasts as those that are oriented obliquely to an incident wave approach that generates strong, alongshore sediment transport gradients. In contrast, swash- aligned coasts are oriented essentially parallel to the incident wave approach and have negligible net alongshore transport rates. On drift- aligned coasts, beach–dune morphology is the net result of alongshore alignment of beach and barrier deposits and elongate swash bars and levees that can weld to the beach and, in turn, provide an onshore sediment source for shore parallel foredune growth and establishment (Sherman and Bauer, 1993; Anthony and Blivi, 1999). Foredune development is common on high-energy coasts with high onshore sediment supply and competent winds (Short and Hesp, 1982; Hesp, 2002). Foredune morphology can vary in complexity, height, and volume depending on a number of variables such as: i) sand supply; ii) vegetation type and density; iii) rates of aeolian deposition and/or erosion; iv) shoreline movement state (i.e. progradation or retrograda- tion); v) frequency and magnitude of other environmental forcing Geomorphology 248 (2015) 440–451 ⁎ Corresponding author at: Coastal Erosion and Dune Dynamics (CEDD) Laboratory, Department of Geography, University of Victoria, Victoria, BC V8W 34R, Canada. E-mail address: ijwalker@uvic.ca (I.J. Walker). http://dx.doi.org/10.1016/j.geomorph.2015.08.006 0169-555X/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph