Drought coincident with aeolian activity in a Great Lakes coastal dune setting during the Algoma Phase (3.1–2.4 ka), southwest Michigan

Aeolian studies of Lake Michigan’s coastal dunes have yet to elucidate what factors control their episodic activity over the past 5000 years. High lake levels exposing sand along with increased storminess is generally accepted for high perched dunes. This hypothesis, however, remains poorly tested for low perched dunes along the southeast Lake Michigan coastline. Here, small lakes in the lee of dune complexes contain aeolian sand and various biological proxies. Age and sedimentation rate models from Gilligan Lake cores guide analysis of aeolian sand, charcoal, pollen, and diatoms at high resolution (1 cm [10.4 yr/cm]) during the high-water Algoma Phase (3.1–2.4 ka) of the upper Great Lakes. The diatoms record a transition from a deep, more acidic lake to a shallower, more alkaline lake with fewer wetlands. This transition is accompanied by a stepped increase in the amount of aeolian sand. There is a weak correlation (R² 0.5, p < 0.01) between increasing abundances of charcoal chunks and sand. Peaks of sand follow peaks in charcoal threads and sheets, suggesting fire played a role in removing vegetation, presaging the landscape for increases in storminess. Arboreal pollen records a transition from a mesic forest Fagus-Acer-Quercus-Abies assemblage suggestive of moister conditions to one richer in mesic hardwoods tolerant of drier conditions. Together, the environmental proxy data record a shallowing lake concomitant with increasing aeolian sand, suggesting that drought-like conditions along the coastline conditioned the landscape for renewed aeolian activity. Once initiated, increased storminess and shoreline erosion maintained dune activity through increased sediment supply.     

Foredune dynamics at a Lake Michigan site during rising and high lake levels

On Great Lakes dunes, the link between foredune dynamics and coastal processes is seen in dune responses to changing lake levels. This paper investigates foredune dynamics during a recent period of rising and high lake levels. The study location was an active foredune in P.J. Hoffmaster State Park on the east coast of Lake Michigan, where field data were collected from 2000 through the final destruction of the foredune by wave removal in November 2019. Foredune dynamics were studied with erosion pins, direct observations, photographs, mapping, and on-site wind measurements. Regional climate and lake-level data were obtained from established data collection programs. The response of the foredune to rising lake levels was compared to several models of foredune behavior. During the study, the Lake Michigan-Huron level rose 1.89 m from January 2013 to July 2020. After an early transitional period, foredune activity was characterized by scarp retreat (4–19 m per year) and dune narrowing from 2014 to 2019. When the foredune completely disappeared in November 2019, erosion/scarping began on the next landward dune. The foredune activity fits Olson’s (1958) model for foredune growth and erosion through lake-level cycles. The foredune migration predicted by the revised Davidson-Arnott (2021) model of foredune response to relative water level rise did not occur, most likely because the rate of lake-level rise was too high. The six years of foredune narrowing before wave erosion started affecting the next landward dune represent a time-lag in Lake Michigan dune history models of increased dune activity during high lake-level stands.     

Stratigraphic and sedimentologic investigation of collapse features in the Mount Baldy Dune in the Indiana Dunes National Park

Mount Baldy dune is one of the largest active eolian dunes along the southern shore of Lake Michigan and a famous tourist attraction within the Indiana Dunes National Park. It is an anthropogenically disturbed landform where restoration efforts include native beach-grass plantings and restricted foot traffic. In July 2013, a 6-year-old boy was buried more than 3 m below the dune stoss surface after falling into a hole, or “collapse feature.” While previous work indicated that holes formed through the decay of buried oak trees (Quercus spp.), neither the origin of this hole in relation to the dune’s stratigraphy nor its significance as a potential geological hazard were understood. Groundpenetrating radar, sediment cores, and radiocarbon and optically stimulated luminescence dates were collected to define sedimentary packages and facies, and interpret the dune’s depositional history. The data show that an alongshore migrating coastal dune field stabilized ∼3000 ya atop backbarrier lagoonal deposits. Modern Mount Baldy evolved as sands were mobilized and transported onshore over the relict dune field, triggered by ongoing downdrift coastal erosion related to the development of the Michigan City Harbor. The internal architecture of the dune reveals how the topography of the forested landscape, now buried beneath the modern dune form, contributes to variations in the thickness of the upper dune package, controlling the relation of buried and decayed trees to the surface of the stoss slope. The data on sand thicknesses, were used with maps and aerial photographs to create a geohazard map of the dune.     

Maximum-Limiting Ages of Lake Michigan Coastal Dunes: Their Correlation With Holocene Lake Level History

Coastal geomorphology along the Great Lakes has long been linked with lake-level history. Some of the most spectacular landforms along the eastern shore of Lake Michigan are high-relief dunes that mantle lake terraces. It has been assumed that these dunes developed during the Nipissing high stand of ancestral Lake Michigan. This hypothesis was tested through stratigraphic analyses and radiocarbon dating of buried soils at four sites between Manistee and Grand Haven, Michigan.At each site, thick deposits of eolian sand overlie late-Pleistocene lacustrine sands. Moderately developed Spodosols (Entic Haplorthods) formed in the uppermost part of the lake sediments are buried by thick dune sand at three sites. At the fourth locality, a similar soil occurs in a very thin (1.3 m) unit of eolian sand buried deep within a dune. These soils indicate long-term (∼ 4,000 years) stability of the lake deposits following subaerial exposure. Radiocarbon dating of charcoal in the buried sola indicates massive dune construction began between 4,900 and 4,500 cal. yr B.P. at the Nordhouse Dunes site, between 4,300 and 3,900 cal. yr B.P. at the Jackson and Nugent Quarries, and between 3,300 to 2,900 cal. yr B.P. at Rosy Mound. Given these ages, it can be concluded that dune building at one site occurred during the Nipissing high stand but that the other dunes developed later. Although lake levels generally fell after the Nipissing, it appears that dune construction may have resulted from small increases in lake level and destabilization of lake-terrace bluffs.     

Wetland vegetation response to record-high Lake Ontario water levels

Lake Ontario water levels were the highest in recorded history in 2017 and 2019, resulting in significant impacts to shoreline properties and observable (but not previously quantified) changes in coastal wetland vegetation. In this study, we assessed differences in coverage of five plant community guilds (submerged aquatic vegetation, Typha, meadow marsh, shrub, and upland) along the shoreline elevation gradient from 12 Lake Ontario coastal wetlands surveyed from 2009 to 2019. This time period included a span of relatively stable water levels (2009–2016), followed by the two high-water years. In general, we found that extreme high water levels led to a decrease in vegetation coverage, most notably at the lower extent of the elevation ranges for the meadow marsh, shrub, and upland vegetation guilds. We also found a modest increase in Typha coverage at the upper extent of its elevation range in 2019, indicating that Typha advanced into the meadow marsh zone during the study period. These findings can be used to calibrate and validate predictive models that inform adaptive management of the new outflow regulation plan for Lake Ontario and can aid in modelling the dynamics of wetland vegetation in relation to predicted changes in Great Lakes water levels due to climate change.     

Waxing and waning slacks: The changing ecohydrology of interdunal wetlands/slacks in a Lake Michigan coastal dune complex during rising Lake Michigan-Huron levels

Since 2016 we have studied the largest interdunal wetlands/slack lying within a deflated parabolic dune east of Lake Michigan. Geologic cross-sections show ∼ 15 m of sand and gravel beneath the dunes, creating an aquifer hydraulically connecting Lake Michigan-Huron (MH) with the water table/shallow groundwater influencing the slack. Lake Michigan-Huron (MH) water levels have risen ∼ 1 m from 2016 to 2020, increasing water levels within and around the slack ∼ 1 m. Color-infrared images and vegetation quadrat sampling show water appearing, then significantly expanding with the main slack and upland/dune vegetation transitioning to wetland vegetation in response to this rise. Monitoring well data show slack water levels rise in spring as Lake MH rises. Levels drop as the growing season begins while Lake MH continues to rise through summer. Short-term slack water level increases occur due to local rain events, but significant water level declines follow due to evapotranspiration. Slack water levels begin to rise again in late summer and into fall as the end of the growing season arrives, evapotranspiration decreases, and heavier, more frequent rain events occur. Together, these factors push slack water levels to their highest point of the year while Lake MH levels are decreasing. In late fall–winter, slack water levels drop in concert with Lake MH levels. Climate change effects, increased transpiration from higher temperatures, summer drought, and greater variability in lake level fluctuations, may make it more difficult to maintain wet growing conditions for hydrophytic vegetation. Hence, climate change poses risks to the existence of this imperiled ecosystem.     

Ground-penetrating radar stratigraphy and depositional model for evolving Late Holocene aeolian dunes on the Lake Huron coast,Ontario

One of the largest (36 km²) Late Holocene systems anywhere in Ontario lies in Pinery Provincial Park on the southeast coast of Lake Huron and postdates a 12‐km‐long beach barrier system left by Lake Nipissing some 5000 years ago. Dunes lie parallel to the lake shoreline, oblique to the dominant west–northwest wind. Linear dunes in the north of the field regardless of age are stable and of moderate height (< 10 m) having grown in situ from foredunes on emergent beach ridges. Southwards however, the same dunes evolve into wider, higher (up to 20 m) parabolic forms with large blow outs. This change in form from north to south appears to have been a persistent evolutionary trend over the past 5000 years. Some 5 km of high resolution radar profiles identifies the changing internal stratigraphy of dunes as they evolve in shape. Linear dunes are composed of a ‘vertical aggradation sequence’ (VAS) that records initial formation of a foredune on top of shore-parallel beach ridges, and upwards growth of the dune by sand trapped by vegetation. Southwards over some 12 km, dunes grow in height and assume a parabolic form expressed on radar profiles by a lowermost VAS overlain by cross-bedded sand comprising a landward accretion sequence (LAS) recording landward migration. A depositional model relates the change in dune shape and stratigraphy to southward increasing sand supply within a large persistent littoral cell in Lake Huron.     

Effects of wind patterns and changing wind velocities on aeolian drift potential along the Lake Michigan shore

Climate influences the amount of wind energy available to transport sand in coastal dune complexes. Wind data from meteorological stations were used to calculate aeolian sand drift potential along the Lake Michigan shore and surrounding region. Data from 11 nearshore stations were used to identify 83 potential aeolian transport events during 2015. All events were associated with the passage of cyclones and anticyclones with the strongest pressure gradients occurring when the lake was between high- and low-pressure centers. There are statistically significant correlations between the positions of cyclones and anticyclones and the orientation of the shores with onshore drift potential. There is enough variability in cyclone and anticyclone tracks to drive aeolian activity on the north, east and south coasts, not all of which can be explained by the regional “prevailing” winds. Wind data from seven airports were used to examine changes in regional drift potential since 1948. Total drift potential decreased over this time, including a decrease of approximately 40% over the period 1961–2019. Trends in directional drift potential are less clear and appear to indicate a decrease in the proportion of onshore drift potential for the east and north shores and an increase for the south shore. This decrease in the ability of winds along Lake Michigan shores to transport sand should contribute to a stabilization of the coastal dunes. Shifts in the tracks of cyclones and anticyclones associated with climate change are anticipated to shift the relative amounts of aeolian activity associated with shores of different orientations.     

Sedimentary in-filling of an urban Great Lakes waterfront embayment and implications for threshold-driven shoreline morphodynamics,Montrose Beach,SW Lake Michigan

This paper addresses subaqueous and subaerial patterns of geomorphic change across Montrose Beach, an urban embayment along Chicago’s engineered SW Lake Michigan coastline. Our goal was to better characterize the urban littoral zone, its sediment-transport processes, and associated shoreline morphodynamics (from the early 1950s to present). Succinct beach geomorphic responses to decadal base-level changes (i.e., regression during lake-level fall and transgression during lake-level rise) occurred once a morphologic threshold in the subaqueous portion of the system had been crossed. Despite continuous sand trapping, nearshore elevations were initially not conducive to promoting expansion of the subaerial beach environment, regardless of water-level condition. Rapid beach expansion after 1990 (by a factor of four in <25 years) was facilitated by prior decades of nearshore accretion. Shoreline morphodynamic trajectories and degree of coupling to nearshore sedimentary processes are important considerations for developing long-term beach-management strategies. Rapid cross-shore movements of the shoreline in response to oscillatory base levels are expected to persist at Montrose and other urban beaches of similar design (and nearshore conditions). This has important implications for managing urban lakefront ecosystems, including coastal dunes and shore-bird habitats. Few datasets have thus far quantified time-variant and threshold-driven patterns of beach geomorphic development along engineered coastlines. Such insights should help coastal managers better understand littoral sediment interconnectivity across the urban lakefront and anticipate future geomorphic trajectories of beach environments with anticipated decadal-scale oscillatory patterns in lake level.     

Urban pocket-beach morphodynamics along the wave-dominated southwest coast of Lake Michigan: An analysis of shoreline and sand volumetric changes

Many of the world’s beaches are embayed, but while a large body of work addresses the geomorphology of pocket beaches in oceanic settings, little is known about urban analogs, especially within the Great Lakes of North America. Groins and jetties shelter these systems from direct interaction with littoral processes, which elsewhere can influence how changes in lake level, winter-ice cover, and wave climate impact beach evolution. We address the direct controls of these forcing parameters on beach morphodynamics over a 33-yr period at North Point Beach, which is confined to an engineered ‘container’ along Lake Michigan’s wave-dominated SW margin. Analysis of near-annual beach change suggests lake-level change is the dominant geomorphic driver over inter-annual to decadal timeframes, with winter ice playing a secondary role. Pocket-beach shoreline positions were found to be unreliable indicators of sand volumetric changes. Lake-level rise facilitated shoreline retreat and overwash-induced beach accretion while high lake levels created the accommodation for additional sands to enter the embayment. This is important for coastal managers to consider when developing mitigation strategies for ongoing lake-level fluctuations and anticipated regional climate impacts. This foundational assessment has implications for embayed beaches of the greater Chicago coastal margin (n > 20), where many other site-specific variables (e.g., groin orientations and shoreline aspect) may factor into nearshore and onshore beach morphodynamics. Continued research into urban pocket beaches of the Great Lakes stands to offer useful information on the impacts of littoral fragmentation on coastal sediment routing during different lake-level phases and degrees of littoral interconnectivity.     

Using LiDAR to reconstruct the history of a coastal environment influenced by legacy mining

LiDAR (light detection and ranging) data can be used to create fine digital elevation and bathymetric models (DEMs). Here we examine natural coastal erosion in Grand Traverse Bay, Michigan, a part of Keweenaw Bay in Lake Superior, and discuss how a variety of geological features (submersed river bed and channels associated with the Houghton Low; Nipissing dunes) interact with long-term sediment accumulation patterns. The geological features also modify migrating tailings from a legacy mining site. The combination of LiDAR derived images and aerial photographs allowed us to reconstruct the historical movement of tailings along the coastline. A total of 22.8 million metric tonnes (Mt) of stamp sand were discharged into the coastal environment off Gay, MI. Over a span of 80 years, beaches to the southwest of Gay have progressively received 7.0 Mt (30.7%) of the mass eroded from the original pile, whereas 11.1 Mt (48.7%) have moved into the bay. The total amount accumulated along the beaches now greatly exceeds the mass remaining on the original tailings pile (3.7 Mt; 16.2%). Bathymetric differences between two LiDAR surveys (2008 and 2010) were also used to estimate the mass, and to track the movement of migrating underwater stamp sand bars. These bars are moving southwesterly towards Buffalo Reef, creating a threat to the lake trout and lake whitefish breeding ground.     

Microplastic pollutants in the coastal dunes of Lake Erie and Lake Ontario

Microplastic particles, often studied as aquatic pollutants, have been recovered from coastal dunes along the shores of Lake Ontario and Lake Erie in New York and Pennsylvania. Surface and shallow sub-surface sand samples were collected from coastal dunes in 1 m² areas from 5 locations along Lake Erie: Sunset Bay, Dunkirk Harbor, Point Gratiot, and Canadaway Creek in New York and Presque Isle State Park Beach #11 in Pennsylvania. Samples were also collected from coastal dunes on Lake Ontario at Sandy Island Beach State Park, NY. Abundances, shapes, sizes, textures, and degradation of microplastics were characterized. Twenty-one of 26 samples yielded a variety of microplastics: pellets, fragments, and fibers. Larger microplastics (5.0–1.0 mm) were dominated by spheroidal and disk-shaped pellets with fewer fragments. Smaller microplastics (≤1.0 mm) were predominantly fibers and small fragments. Some microplastic particles exhibited evidence of degradation and weathering as a consequence of transport and exposure to the elements. The presence of microplastics in coastal dunes is attributable to aeolian transport from the adjacent beach.     

Characterizing the cultural ecosystem services of coastal sand dunes

Coastal sand dunes provide an array of important benefits that are supported by coastal geomorphic processes and location-specific ecosystems, including direct and indirect economic benefits to humans. Coastal sand dune ecosystems are ecologically important, but their specific values and uses are little studied, poorly understood, and underappreciated. Michigan, USA, is home to the largest land area of freshwater coastal sand dunes in the world. This study used an online survey that allowed participants to record the types of activities in which they engaged during visits and respond to questions about the importance of the cultural ecosystem services of coastal sand dunes. The survey captured the responses of 3610 individuals, a majority of whom rated scenic beauty, protection for future generations, protection of a unique ecosystem, and outdoor recreation as extremely important or very important. The survey results provide some preliminary insights into the role of cultural ecosystem services of coastal sand dunes in providing and sustaining benefits for humans and how these benefits and values are perceived by the public. These insights have important implications for policy makers responsible for coastal zone management in the Great Lakes region and in other areas characterized by coastal sand dunes ecosystems.     

Stratigraphy,age, and flora of the Southport forest bed,Southeastern Wisconsin

A mid-Holocene buried organic layer 10 to 60 cm thick is present along the Lake Michigan shoreline in southeastern Wisconsin. Named the Southport forest bed for its location in Kenosha County, the unit has yielded abundant wood specimens, including large logs, branches, twigs, stumps, and root material. Roots of truncated in situ oak (Quercus) and elm (Ulmus) trees extend into the underlying till of the late Wisconsin Oak Creek Formation. Nearshore lacustrine sand above the organic layer contains abundant driftwood, overlain by 2 to 3 m of cross-bedded dune sand. More than 50 wood samples have been identified; the assemblage is that of a mixed hardwood forest dominated by oak (Quercus) and hickory (Carya), which account for about 60% of the assemblage. Although the site has been mostly concealed for many years, it was beautifully exposed in the 1960s and early 1970s, when it was initially studied by Phil Sander, who discovered the site and documented it with field notes and numerous photographs. Here we report several new (unpublished) radiocarbon dates and details of the stratigraphy and arboreal flora. Radiocarbon dates suggest that the Southport forest probably lived for 900–1000 ¹⁴C years, possibly longer, reaching its climax at about 5300 B.P. The site is of particular importance because of its proximity to the Nipissing shoreline and provides a significant point on the Nipissing transgression time curve. The unusually large number of identified specimens affords an accurate evaluation of the warm and relatively dry climate that characterized the southern Great Lakes region during the mid-Holocene.     

Delineating spatial distribution and thickness of unconsolidated sand along the southwest Lake Michigan shoreline using TEM and ERT geophysical methods

Erosion and accretion of various magnitudes occur along the southwest Lake Michigan shoreline. These processes are triggered by natural events and human activities, which affect the distribution and thickness of sand on the nearshore lake bottom. Significant erosion along the Illinois coastline has highlighted the need for a large-scale means of acquiring spatially rich data to build models of sand distribution along the entire shoreline. Thus, we implemented a high-resolution airborne transient electromagnetic (TEM) method, coupled with a ground-based electrical resistivity tomography (ERT) method to determine the sand distribution and thickness along the shore from the beach to ~1 km into the lake. From Kenosha, Wisconsin, to Chicago, Illinois, we acquired 1049 line-km of TEM data, and 13.43 line-km of ERT data. Our results indicated a distinct, uneven distribution and thickness of the unconsolidated sand unit covering the southwestern Lake Michigan shoreline. The unconsolidated sand unit was found to range in thickness from 0 to ~12 m. This unconsolidated sand unit was shown to be thickest (4.5 to ~10 m) in the northern part of the study site. In southern Wisconsin and Chicago, the sand layer beneath the water column was found to be very thin, ≤1 m. We propose, based on our analysis, that lake-bed conditions and wind direction are the main factors that limit southward littoral transport. Our data suggest that the current state of the shoreline is relatively analogous to how it has always behaved; however, anthropogenic disturbance has exacerbated the natural patterns of erosion and accretion.     

Using photographic measurement and gigapixel panoramas to study changes in a Lake Michigan sand dune

Detailed measurements of changes in aeolian landscapes help researchers better understand aeolian processes and monitor the effects of climate change in these systems. This study focuses on a photographic method to measure sand surface changes. It introduces custom erosion pins (photoscale pins) designed to allow proper scaling of measurements taken from digital images or high resolution (gigapixel) panoramas. Furthermore, this study discusses errors associated with measuring photoscale pins photographically. Resolution errors arise when marking object boundaries on digital images. These typically affect measurement precision, but even so, differences between repeated measurements of the same pin average 0.58 mm. Perspective errors arise when pins are tilted relative to the camera’s line of sight and introduce bias, affecting measurement accuracy. Photographic measurement can allow remote surveillance, reduce site disturbance, increase the frequency of observation, and reduce measurement error compared to manual measurement of erosion pins. A study of sand movement in a dune complex on the southeastern shoreline of Lake Michigan provides an example of the method’s application. Photoscale pin measurements that bracket a wind event associated with Hurricane Sandy show average surface elevation changes of 3.97 cm/pin. Regional wind data, pin measurements, and surface changes recorded in gigapixel panoramas suggest that vegetation baffling, recirculation eddies, and topographic steering played roles in sand deposition and erosion at the site. Photographic measurement of erosion pins can complement wind instrumentation and other tools as aeolian research increasingly incorporates multiple techniques to study surface changes in greater detail both in time and space.     

Dynamics of beach-ridge formation along a migrating strandplain with implications for paleo-environmental assessment,Illinois Beach State Park,southwestern Lake Michigan

This paper provides insights into shoreline morphodynamics and ridge-plain physiographic compartmentalization along the migrating Zion Beach-ridge Plain, a mainland-attached strand along the high-energy, wave-dominated SW coast of Lake Michigan. Results of UAS-based topographic monitoring during the recent decadal lake-level high (2018–2020) captured the earliest phase of the ridge-formation process along several beach sites. This process-based study of net-erosional (i.e., littoral updrift) and net-accretionary (i.e., littoral downdrift) parts of the system offers much-needed context for assessing relict strand architectures. Embayed beach-ridge plains of the Laurentian Great Lakes have long served as paleo-environmental archives. They form from water-level changes and can be used to interpret isostacy. The preservation of beach ridges here is facilitated by unidirectional infilling. Much less is known about how nearshore littoral processes impact unconfined strand systems and whether useful paleoenvironmental information absent within embayed system analogs might be elucidated from their complex architecture. We herewith promote a model of punctuated development. Major episodes of shoreline transgression are manifested as continuous ridgelines of topographic prominence that, along the northern, erosive strand, truncate older ridges and are onlapped by younger ones. These major discontinuities reflect environmental changes greater in magnitude than decadal water-level oscillations observed to have formed ridgelines in recent decades. The temporal offset across the most lakeward of these major erosional strandlines is on the order of 1 kyrs and it formed between 1.8 ka and 0.9 ka, based on available C-14 ages, coincidental with a regional shift in dominant storm-wind pattern to one promoting higher-energy littoral dynamics.     

Water level fluctuation and sediment–water nutrient exchange in Great Lakes coastal wetlands

The influence of water level fluctuation on sediment–water nutrient exchange in coastal wetlands of Lakes Michigan and Huron was investigated using controlled, laboratory experiments. At each wetland, sediment cores were collected from 5 locations along a transect perpendicular to the shoreline, desiccated for 8 weeks, and then re-wetted with original site water for 24 h to simulate water level fluctuation. Soluble reactive phosphorus release declined exponentially along transects, with highest release rates from sediments collected at the ordinary high water mark (OHWM), and lowest rates from sediments underlying water > 0.25 m in depth. Nitrate exchange showed no obvious pattern in the Lake Michigan wetlands but nitrate was lost at all locations in the Lake Huron wetlands, suggesting denitrification. Ammonium was released at all sites, but with no obvious pattern along transects. Sulfate release was low at the OHWM locations and increased in a lakeward direction, plateauing by the 0.25 m water depth.     

Mapping Stamp Sand Dynamics: Gay,Michigan

Monitoring coastal change is vital because a high percentage of the world's population lives in close proximity to coastal areas. This paper examines a portion of Lake Superior's shoreline where coastal landscape has been shaped by the introduction of 25 billion kg of stamp sand from the copper industry and subsequent dynamics associated with longshore currents. Shoreline areal change from this movement is documented through comparison of archival and current air photos. A series of historical air photo mosaics were processed with a Geographic Information System (GIS). Sets of spatially registered, temporal map polygons were developed to illustrate and allow measurement of the areas of erosion and deposition, relevant to shoreline planning and measurement. Measurements indicate that the length of shoreline affected by the stamp sand increased by 2.4 km during a 59-year period. Measurements of area indicate a decrease of 8 ha in the same amount of time. Breadth of the stamp sand shows discernable decline of 630 m width at the original deposit area at the north near Gay, Michigan, and increase of 410 m width 1,500 m southward along the coast. The methodology and results are relevant to a diversity of linear and areal landscape considerations along shorelines (property rights, planning, conservation, etc.).     

Combined effects of coastal forest and sea embankment on reducing the washout region of houses in the Great East Japan tsunami

Coastal vegetation is widely recognized for its ability to reduce tsunami damage; however, coastal forests in large areas of the Tohoku and Kanto districts of Japan were destroyed by the Great East Japan tsunami on 11 March 2011. To elucidate the tsunami-mitigating effect of a coastal forest during a destructive tsunami, the combined effects of sea embankment and coastal forest were analyzed using post-tsunami survey data of the damage and a nonlinear long wave equation model that includes the breaking or washout condition of trees. The numerical simulations estimated that a 600-m-long coastal forest reduced the washout region of houses due to a 10-m-high tsunami at the coast by approximately 100 m, and the reduction achieved by a sea wall of approximately 5.4–6.4 m in height was approximately 560–1520 m. The height of a sea embankment or wall with sand dunes greatly affects the breaking condition of trees behind it by changing the tsunami flux overflowing the sea wall and the sand dune. For the combination of a sea embankment and a coastal forest during a destructive tsunami, the tsunami mitigation function of the coastal forest has an optimum value when the fluid force on the trees is strong but not strong enough to break the trees under the condition at which the tsunami overflows the sea embankment. At the investigated site, the effect of the coastal forest was larger than that of the sea embankment under optimal conditions. Thus, a coastal forest on a sand dune should be designed as a mitigation measure behind a sea embankment and optimally designed to protect the houses that are not protected from a tsunami by the sea embankment alone.