- School of Geographical Sciences & Urban Planning and
School of Earth & Space Exploration
5th floor, Coor Hall, Arizona State University
P.O. Box 875302, Tempe, AZ 85287-5302
Ian J Walker
University of California, Santa Barbara, Geography, Faculty Member
- Geography, Geomorphology, Spatial Statistics, Aeolian Geomorphology, Coastal Dunes, Climate Change and coastal zones, and 19 moreCoastal Erosion, Conservation and Restoration, Sediment transport, Holocene relative sea-level change, Quaternary Sedimentology and Geomorphology, Aeolian sedimentology, Coastal Sand Dunes, Sand and sand dunes, Ecology of Sand Dunes, Education, Climate Change, Climate variability, Coastal Geomorphology, Sandy Beaches, Climate impacts on shorelines and dunes, Dune Restoration, Terrestrial Laser Scanning (TLS), Unmanned Aerial Vehicle (UAV), and Holocene sea level changeedit
- I am a geomorphologist with expertise in sediment transport and erosion processes. I specialize in aeolian (windblown... moreI am a geomorphologist with expertise in sediment transport and erosion processes. I specialize in aeolian (windblown) and coastal systems, beaches and sand dunes, flow dynamics over complex terrain, coastal erosion, assessing climatic or land use change impacts in the coastal zone, and restoration of coastal dunes. I also study relative sea level changes and Holocene landscape evolution. My research involves a combination of field experiments to quantify sediment transport and erosion, high-resolution land surveying with terrestrial laser scanning (TLS) and unmanned aerial systems (UAS), and spatial stats for geomorphic change detection. I am currently a Professor at Arizona State University in the Schools of Geographic Sciences & Urban Planning and Earth & Space Exploration.edit
Abstract Wind is a highly capable geological agent on many sandy beaches above, and sometimes below, the high-tide limit where sand can become dry and mobilised by aeolian (wind-blown) processes. This chapter reviews current understanding... more
Abstract Wind is a highly capable geological agent on many sandy beaches above, and sometimes below, the high-tide limit where sand can become dry and mobilised by aeolian (wind-blown) processes. This chapter reviews current understanding of the measurement and modelling of aeolian sand transport over beaches. The fundamentals of boundary layer airflow dynamics and aeolian sand transport are explained and key aeolian transport models are classified and critiqued with respect to their application on beaches. In particular, a suite of key environmental controls that affect aeolian sand transport on beaches are reviewed, namely wind climate, beach morphology: width, slope and fetch, moisture, salt and biological crusts, roughness elements and vegetation. For each, influences on aeolian sand transport mechanics and modelling are discussed and implications for back beach morphodynamics are explored. This chapter focuses primarily on empirical field and wind-tunnel research findings and identifies key advances and current challenges for aeolian research in coastal settings.
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Descriptions of the Cordilleran Ice Sheet retreat after the last glacial maximum have included short-lived readvances occurring during the Older and Younger Dryas stadial periods and into the Holocene, but identification of these events... more
Descriptions of the Cordilleran Ice Sheet retreat after the last glacial maximum have included short-lived readvances occurring during the Older and Younger Dryas stadial periods and into the Holocene, but identification of these events has been largely limited to southwest and central British Columbia and northwest Washington State. We present evidence of a late Pleistocene readvance of Cordilleran ice occurring on the central coast of British Columbia on Calvert Island, between northern Vancouver Island and Haida Gwaii. Evidence is provided by sedimentological and paleoecological information contained in a sedimentary sequence combined with geomorphic mapping of glacial features in the region. Results indicate that a cold climate existed between 15.1 and 14.3 cal ka BP and that ice advanced to, and then retreated from, the western edge of the island between 14.2 and 13.8 cal ka BP. These data provide the first evidence of a major fluctuation in the retreating ice sheet margin in t...
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The archipelago of Haida Gwaii, formerly known as the Queen Charlotte Islands, is one of the most dynamic geomorphic environments in Canada. Climatic and geophysical forces have combined to shape the unique landscape of the archipelago.... more
The archipelago of Haida Gwaii, formerly known as the Queen Charlotte Islands, is one of the most dynamic geomorphic environments in Canada. Climatic and geophysical forces have combined to shape the unique landscape of the archipelago. Strong cyclonic storms from the Pacific Ocean are frequent and are accompanied by heavy rainfall. The two strongest earthquakes in Canadian history happened on the Queen Charlotte Fault just west of the archipelago in the Pacific Ocean. Coastal landscapes on the west coast are rugged and rocky, whereas the north and east coasts are formed in thick glacial sediments that are being rapidly eroded by waves. The mountainous spine that runs the length of Haida Gwaii is susceptible to landslides and other mass wasting processes. Slope failures are the primary agent of natural disturbance in these mountains and occur at rates that are among the highest in Canada. They are triggered by heavy rainfall, forestry activities, and earthquakes.
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Research Interests: Geology, Geomorphology, Sedimentology, Coastal Management, Coastal Processes, and 12 moreRestoration Ecology, Coastal Geomorphology, Coastal Dunes, Aeolian Geomorphology, Restoration, Coastal Zone Management, Sandy Beaches, Beach Morphodynamics, Sediment, Sand dunes, Sediment budget, and Sand Dune Ecology
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Research Interests: Environmental Science, Geology, Oceanography, Coastal Management, Climate Change, and 15 moreCoastal Processes, Climatology, Climate variability, Coastal Dunes, Coastal Erosion, Multidisciplinary, El Niño, Shoreline Management Planning, Sea level rise, Coastal Vulnerability, Wave and Storm Surge Modelling, Coastal Flood Hazards, El Nino-Southern Oscillation, Pacific Decadal Oscilation, and Pacific Decadal Oscillation
Temporal and spatial scale of aeolian flux on a vegetated foredune during a high energy event R. Davidson‐Arnott, B.O. Bauer, I.J. Walker, P.A. Hesp, J. Ollerhead, C. Chapman In the past two decades the advent of high frequency acoustic... more
Temporal and spatial scale of aeolian flux on a vegetated foredune during a high energy event R. Davidson‐Arnott, B.O. Bauer, I.J. Walker, P.A. Hesp, J. Ollerhead, C. Chapman In the past two decades the advent of high frequency acoustic and piezo‐electric sensors has advanced our understanding of the temporal pattern of aeolian transport on beaches primarily at a single point above the bed. Recently, the deployment of laser particle counters has permitted the collection of data from a vertical array making it possible to examine temporal fluctuations in the vertical concentration profile. A vertical array of Wenglor laser particle counters deployed on the crest of a large, vegetated foredune on the north coast of Prince Edward Island yielded 1Hz data during a storm event in May, 2010 on transport intensity (grain counts) measured at six levels above the sand surface (between 1.4 cm and 47.2 cm) with coincident measurements of 3D wind vectors. Additional particle counters were deploy...
Airflow dynamics over dunes differ significantly from those over flat terrain due to topographically generated pressure fields that cause deviations in flow behavior (e.g., streamline compression, expansion and/or curvature, flow... more
Airflow dynamics over dunes differ significantly from those over flat terrain due to topographically generated pressure fields that cause deviations in flow behavior (e.g., streamline compression, expansion and/or curvature, flow separation and/or reversal). Recent research using ultrasonic anemometry, modeling of computational fluid dynamics (CFD), wind tunnel simulations, and detailed field experiments have enhanced our understanding of boundary layer flow over dunes and, thus, advanced recent efforts to model the interactions between dune geomorphology, airflow dynamics, and sand transport. This chapter reviews principally the fundamentals of airflow over and in the lee of transverse dunes and discusses several key advances and limitations in measurement and modeling of flow dynamics. Although progress in our understanding has been made mostly via study of transverse desert dunes, due to their relatively simple shape and surface roughness characteristics (i.e., no vegetation), research advances from other dune settings (e.g., coastal foredunes) are also reviewed briefly. Though covered more extensively in other chapters, implications for sediment transport and dune morphodynamics are also discussed. Areas for further research are identified based on gaps in knowledge on the implications of flow dynamics for mesoscale (i.e., landform to landscape scale) dune sediment budgets, migration and morphological evolution.
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This chapter provides a companion chapter to Hesp (2012) in which the initiation, dynamics, morphology, and evolution of the principal coastal dune types are examined. Those dune types are foredunes, blowouts, parabolic dunes, and... more
This chapter provides a companion chapter to Hesp (2012) in which the initiation, dynamics, morphology, and evolution of the principal coastal dune types are examined. Those dune types are foredunes, blowouts, parabolic dunes, and transgressive dune fields. This chapter presents an accompanying overview of those dunes in the form of a photoessay which attempts to show the morpho-ecological diversity of, and within the various dune types. The initiation, morphological types and stages, and evolutionary patterns of the various dune types are examined, and the photographs and diagrams attempt to provide a visual explanation of some of the diverse range of dune types, ages, and stages possible.
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33 Measurements of lee-side airflow response from an extensive array of meteorological instruments 34 combined with smoke and flow streamer visualization is used to examine the development and 35 morphodynamic significance of the lee-side... more
33 Measurements of lee-side airflow response from an extensive array of meteorological instruments 34 combined with smoke and flow streamer visualization is used to examine the development and 35 morphodynamic significance of the lee-side separation vortex over closely spaced transverse dune 36 ridges. A differential deflection mechanism is presented that explains the three-dimensional pattern 37 of lee-side airflow structure for a variety of incident flow angles. These flow patterns produce 38 reversed, along-dune and deflected surface sand transport in the lee that result in a net ‘lateral 39 diversion’ of sand mass transport over one dune wavelength for incident angles as small as 10° 40 from crest-transverse (i.e., 80° from the crest line). This lateral displacement in fluid mass transport 41 increases markedly with incident flow angle, when expressed as the absolute value of the total 42 deflection in degrees. Reversed flow and multidirectional sand transport occur for incident...
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: Sand dunes are large coastal features typically formed when windblown sand is trapped and stabilized by vegetation. Located between the back beach and inland features, they are an essential component of the coastal sediment budget and a... more
: Sand dunes are large coastal features typically formed when windblown sand is trapped and stabilized by vegetation. Located between the back beach and inland features, they are an essential component of the coastal sediment budget and a primary control on the backshore ecosystem. In this role, coastal dunes provide essential ecosystem services, including habitat for endangered species such as piping plovers,sites of high tourism value, groundwater recharge zones, and protection of coastal infrastructure and properties from wave erosion and storm surge flooding.
Research Interests: Environmental Science, Coastal Management, Coastal Engineering, Coastal Processes, Coastal Geomorphology, and 9 moreCoastal Dunes, Impact of climate change on sea level rise, Coastal Erosion, Groundwater recharge, Sea level rise, Integrated Coastal Zone Management, Sand dunes, Storm surge, and Sand Dune Stabilization
Uncrewed aerial systems (UAS) provide an effective method to examine geomorphic and vegetation change in restored coastal dune ecosystems. Coupling structure-from-motion (SfM) photogrammetry with RGB orthomosaic imagery allows researchers... more
Uncrewed aerial systems (UAS) provide an effective method to examine geomorphic and vegetation change in restored coastal dune ecosystems. Coupling structure-from-motion (SfM) photogrammetry with RGB orthomosaic imagery allows researchers to characterize spatial-temporal geomorphic responses associated with differences in vegetation cover. Such approaches provide quantitative data on landscape morphodynamics and sediment erosion and deposition responses that allow scientists and land managers to assess the efficacy of dynamic restoration efforts and, in turn, make informed decisions for future restoration projects. Two different restored coastal foredune sites in Humboldt County, California were monitored between 2016–20 with UAS (quadcopter and fixed-wing), kite aerial photogrammetry (KAP), and terrestrial laser scanning (TLS) platforms. We compared our KAP- and UAS-SfM elevation models to concurrently collected TLS bare earth models for five of our fifteen collections. The goal of...
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Research Interests: Human Geography, Geology, Geomorphology, Methods, Mapping, and 6 morePlanetary, Maps, Volcano, Santorini, Submarine, and Submarine Pipeline
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ABSTRACT The purpose of this study was to quantify relationships between season, sediment availability, sediment transport pathways, and beach/foredune morphology at Greenwich Dunes, PEI. This was done for periods ranging from a few days... more
ABSTRACT The purpose of this study was to quantify relationships between season, sediment availability, sediment transport pathways, and beach/foredune morphology at Greenwich Dunes, PEI. This was done for periods ranging from a few days to multiple decades using erosion pins, bedframe measurements, annual surveys, and digital photogrammetry using historical aerial photographs. The relative significance of seasonal/annual processes versus response of the foredune system to broader geomorphic controls (e.g. relative sea level rise, storms, etc.) was also assessed. The data show that there are clear seasonal differences in the patterns of sand supply from the beach to the foredune at Greenwich and that there are differences in sediment supply to the foredune between the east and west reaches of the study area, resulting in ongoing differences in foredunemorphology. They also demonstrate thatmodels that incorporatewind climate alone, or evenmodels that include other factors like beach moisture, would not be able to predict the amount of sediment movement from the beach to the foredune in this environment unless there were some way to parameterize system morphology, especially the presence or absence of a dune ramp. Finally, the data suggest that the foredune can migrate landward while maintaining its form via transfers of sediment from the stoss slope, over the crest, and onto the lee slope. Although the rate of foredune development or recovery after disturbance changes over time due to morphological feedback, the overall decadal evolution of the foredune system at Greenwich is consistent with, and supports, the Davidson-Arnott (2005) conceptual model of dune transgression under rising sea level.
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... VII International Conference on Aeolian Research, 5 - 9 July, Santa Rosa, Argentina. Item not available from this archive. ... URI: http://repository.edgehill.ac.uk/id/eprint/3904. Archive staff only. ... 2010 Edge Hill University, St... more
... VII International Conference on Aeolian Research, 5 - 9 July, Santa Rosa, Argentina. Item not available from this archive. ... URI: http://repository.edgehill.ac.uk/id/eprint/3904. Archive staff only. ... 2010 Edge Hill University, St Helens Road, Ormskirk, Lancashire, L39 4QP, UK. ...
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The morphodynamics of partially to fully vegetated foredunes had been little studied up until the 1980's (eg HSU, 1977; HESP, 1983), and since then, a few other studies have been conducted (eg RASMUSSEN, 1989; ARENS,... more
The morphodynamics of partially to fully vegetated foredunes had been little studied up until the 1980's (eg HSU, 1977; HESP, 1983), and since then, a few other studies have been conducted (eg RASMUSSEN, 1989; ARENS, 1996; ARENS et al., 1995; DAVIDSON-...
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Airflow dynamics over beach-foredune systems can be complex. Although a great deal is known about the effects of topographic forcing and vegetation cover on wind-field modification, the role of large woody debris (LWD) as a roughness... more
Airflow dynamics over beach-foredune systems can be complex. Although a great deal is known about the effects of topographic forcing and vegetation cover on wind-field modification, the role of large woody debris (LWD) as a roughness element and modifier of boundary layer flow is relatively understudied. Individual pieces of LWD are non-porous elements that impose bluff body effects and induce secondary flow circulation that varies with size, density, and arrangement. Large assemblages of LWD are common on beaches near forested watersheds and collectively have a degree of porosity that increases aerodynamic roughness in ways that are not fully understood. A field study on a mesotidal sandy beach with a scarped foredune (Calvert Island, British Columbia, Canada) shows that LWD influences flow patterns and turbulence levels. Overall mean and fluctuating energy decline as flow transitions across LWD, while mean energy is converted to turbulent energy. Such flow alterations have implications for sand transport pathways and resulting sedimentation patterns, primarily by inducing deposition within the LWD matrix.
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Climate change is increasingly affecting British Columbia’s landscapes, communities and economic activities. Future projections show that climate change will continue and suggest that direct and indirect impacts will become more... more
Climate change is increasingly affecting British Columbia’s landscapes, communities and economic activities. Future projections show that climate change will continue and suggest that direct and indirect impacts will become more pervasive. The following are some of the key risks and adaptation opportunities associated with climate change in BC: Many regions and sectors of British Columbia will experience increasing water shortages. Smaller glaciers, declining snowpack, shifts in timing and amount of precipitation, and prolonged drought will increasingly limit water supply during periods of peak demand. Competition amongst water uses will increase and have implications for transborder agreements. Ongoing adaptive measures include the incorporation of climate change impacts into some official water management plans, upgrades to reservoir capacity and various demand management initiatives. Hydroelectric power generation, especially during (increasing) peak energy demands in summer, is ...
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This paper compares and contrasts UAS-based Structure from Motion (SfM) and TLS survey methods as applied to evaluate the impacts of, and recovery from, the extreme El Niño 2015-16 on the seasonal geomorphic and sediment budget responses... more
This paper compares and contrasts UAS-based Structure from Motion (SfM) and TLS survey methods as applied to evaluate the impacts of, and recovery from, the extreme El Niño 2015-16 on the seasonal geomorphic and sediment budget responses of an embayed, high-energy beach-dune system on the central coast of British Columbia, Canada. TLS and UAS mapping campaigns over a two-year period provided seasonal bare-earth digital terrain models (DTMs) and orthophoto mosaics. Spatial-temporal change detection methods were used to quantify volumes of significant erosion and deposition within the beach-dune system. The frequency and magnitude of erosive events and aeolian activity were also estimated from oblique, time-lapse photography.
During the 2015-16 El Niño season, elevated water levels and storm waves eroded the foredune and lowered the beach surface by ~ 1m. Erosion was greatest in the middle of the beach with dune scarping of over 2m where wave energy was focused. Minor accretion occurred during the summer of 2016 on the upper beach, and ramp rebuilding was observed mostly from slumping and avalanching of existing dune sands. The following winter 2017 storm season led to minor erosion on the beach and extensive incipient dune development and sand ramp recovery fronting the foredune to an extent close to pre-El Niño elevations.
Comparison of change surfaces between methods revealed limitations in the SfM method, namely due to vegetation effects on DTM generation, which limit its ability to detect change in the coastal environment. The costs, time, logistics, and accuracy for both SfM and TLS survey methodologies for coastal geomorphic change detection analysis is also evaluated. Combined, the UAS and SfM workflow provides a competitive solution to more expensive and time-consuming survey methods, such as TLS and aerial LiDAR, but its utility and accuracy is highly dependent on research objectives and post-processing techniques.
During the 2015-16 El Niño season, elevated water levels and storm waves eroded the foredune and lowered the beach surface by ~ 1m. Erosion was greatest in the middle of the beach with dune scarping of over 2m where wave energy was focused. Minor accretion occurred during the summer of 2016 on the upper beach, and ramp rebuilding was observed mostly from slumping and avalanching of existing dune sands. The following winter 2017 storm season led to minor erosion on the beach and extensive incipient dune development and sand ramp recovery fronting the foredune to an extent close to pre-El Niño elevations.
Comparison of change surfaces between methods revealed limitations in the SfM method, namely due to vegetation effects on DTM generation, which limit its ability to detect change in the coastal environment. The costs, time, logistics, and accuracy for both SfM and TLS survey methodologies for coastal geomorphic change detection analysis is also evaluated. Combined, the UAS and SfM workflow provides a competitive solution to more expensive and time-consuming survey methods, such as TLS and aerial LiDAR, but its utility and accuracy is highly dependent on research objectives and post-processing techniques.