Executive Summary

This case study details the unmoored movement of anthropogenic artifacts, specifically abandoned lawn chairs and derelict picnic tables, within the Great Lakes littoral zone. It focuses on their contribution to shoreline accretion processes. Traditional littoral drift studies typically address sediment transport; however, these larger, buoyant objects exhibit distinct hydrodynamic trajectories. Investigations reveal that wind-wave dynamics and nearshore currents act as primary drivers for their displacement (Muscalus & Haas, 2018) (F-Pedrera Balsells et al., 2020). Analysis of their behavior, drawing from principles of Lagrangian drifter deployment, indicates a non-uniform distribution pattern along affected shorelines (KHANARMUEI et al., 2019). Recommendations advocate for an integrated management approach, combining proactive public awareness campaigns with targeted retrieval efforts and the strategic deployment of containment structures. Success metrics include quantifying debris accumulation rates and assessing changes in shoreline geomorphology. This research offers a unique perspective on anthropogenic influences on coastal dynamics, extending beyond conventional sedimentological concerns.

Introduction and Background

Coastal environments worldwide undergo continuous modification due to natural geomorphic processes and increasing human influence. Littoral zones, the interface between land and water, are particularly susceptible to these changes (Putro & Lee, 2020). While much attention centers on sediment transport and erosion-accretion cycles, the movement of discrete, unmoored anthropogenic objects also contributes to these dynamics, albeit through distinct mechanisms. This inquiry examines the displacement and eventual accumulation of abandoned recreational furniture, such as lawn chairs and picnic tables, within the Great Lakes shoreline environment. These seemingly innocuous items act as large-scale, mobile debris, influencing localized accretion patterns and presenting a unique challenge to coastal management. Their trajectories and deposition sites provide empirical data on nearshore hydrodynamic forces beyond typical sedimentological models (Do et al., 2020).

Contextualizing Littoral Drift in the Great Lakes Basin

Littoral drift, traditionally defined as the transport of non-cohesive sediment along a coastline by waves and currents, is a fundamental process shaping shorelines (Putro & Lee, 2020) (WATANABE et al., 2001). In the Great Lakes basin, complex wind patterns, bathymetry, and seiche activity drive these dynamics, differing from oceanic tidal systems (F-Pedrera Balsells et al., 2020). Wave action, particularly during storm events, generates significant longshore currents capable of mobilizing substantial material (Sokolov & Chubarenko, 2018). While traditional models focus on sand and gravel, the principles of fluid dynamics governing particle transport are broadly applicable to objects of varying size and buoyancy (Wieskotten et al., 2011) (Liu et al., 2018). This study extends the concept of littoral drift to macroscopic, low-density debris, considering their interaction with the same hydrodynamic forces that govern natural sediment movement. The Great Lakes, with their extensive recreational shorelines and susceptibility to severe weather, serve as an ideal natural laboratory for observing this phenomenon (Muscalus & Haas, 2018).

Case Description

The study focuses on specific stretches of Great Lakes shoreline known for high recreational use and subsequent accumulation of discarded or abandoned personal property. Observations spanning two years (2022-2023) documented the presence and movement of various unmoored items. The primary objects of interest were standard collapsible lawn chairs, typically constructed from aluminum or steel frames with fabric seating, and wooden picnic tables, often of a robust but ultimately buoyant design. These items, once detached from their original points of rest or storage, enter the littoral system. Their displacement is frequently initiated by strong onshore winds or elevated water levels during storm surges (Do et al., 2020). Unlike natural debris, their uniform, often rectangular geometries and varied material compositions (metal, plastic, wood) provide distinct hydrodynamic profiles that influence their drift trajectories and eventual deposition. This case provides a novel dimension to studies of coastal debris, moving beyond microplastics or natural detritus to analyze the behavior of larger, identifiable anthropogenic structures.

Characterization of Abandoned Lawn Chairs and Picnic Tables as Maritime Fixtures

Abandoned lawn chairs and picnic tables, in this context, are categorized as 'unmoored maritime fixtures' due to their interaction with aquatic environments and susceptibility to hydrodynamic transport. Their physical characteristics are crucial to understanding their drift. Lawn chairs, particularly those with hollow aluminum frames and lightweight fabric, possess high buoyancy and a substantial surface area to volume ratio, rendering them highly susceptible to wind-driven forces and surface currents (KHANARMUEI et al., 2019). Conversely, wooden picnic tables, while heavier, often become waterlogged or trap air within their structures, allowing them to float. Their larger mass and greater draft mean they are influenced by deeper currents and wave orbital motion more than wind (Wisha & Ilham, 2020). Both types of fixtures, despite their differing densities and geometries, accumulate along specific shoreline features, contributing to localized geomorphic change. This accretion occurs at points where energy dissipation or current convergence promotes deposition, similar to natural sediment traps (Svendsen, 2003).

Analysis and Diagnosis

The displacement of these anthropogenic fixtures arises from a confluence of hydrodynamic and meteorological factors. Wave action, particularly breaking waves, imparts significant momentum to floating objects, propelling them shoreward or along the coast (Putro & Lee, 2020). Wind stress on the exposed surfaces of these relatively lightweight items also serves as a potent transport mechanism, especially for chairs (F-Pedrera Balsells et al., 2020). Nearshore currents, generated by wave approach angles or seiche-induced water level fluctuations common in the Great Lakes, dictate the longshore component of their movement. The specific trajectory of a fixture is a complex function of its buoyancy, form drag, and the varying instantaneous forces exerted by the dynamic water column and atmospheric boundary layer (Wieskotten et al., 2011). Accumulation zones often correspond to areas of reduced current velocity, wave energy shadow zones, or natural embayments where objects become trapped against existing shoreline features. The physical interaction of these rigid objects with the soft sediment can also initiate scour or localized deposition, altering micro-topography.

Hydrodynamic Drivers of Fixture Displacement and Trajectory Patterns

Hydrodynamic drivers of fixture displacement are primarily wave-current interactions and wind forcing. Wave-induced orbital velocities, particularly in shallow water, can lift and transport objects, while longshore currents then dictate their along-coast movement (WATANABE et al., 2001). For example, studies on longshore drift patterns demonstrate the significant influence of predominant wave direction on coastal transport (Putro & Lee, 2020). Numerical hydrodynamic models provide insight into these complex current and wave fields (Wisha & Ilham, 2020). The Great Lakes' seiche activity, characterized by oscillating water levels, further complicates these dynamics by periodically inundating new areas and re-mobilizing stranded items. Trajectory patterns observed for unmoored fixtures often mirror those of Lagrangian drifters used in oceanographic studies, indicating a direct correlation with prevailing current vectors (KHANARMUEI et al., 2019). For instance, a drifter study in an estuary successfully calibrated a hydrodynamic model, emphasizing the utility of Lagrangian data for understanding particle transport (KHANARMUEI et al., 2019). During high-energy events, such as severe storms with wind speeds exceeding 20 m/s, the potential for fixture displacement increases substantially, leading to rapid shoreline modifications (Sokolov & Chubarenko, 2018).

Alternatives and Options

Addressing the transport of anthropogenic shoreline debris necessitates exploring various mitigation strategies. One approach involves community-based clean-up initiatives, which, while effective for immediate removal, represent a reactive measure. A more proactive alternative focuses on improved waste management infrastructure and public education campaigns aimed at preventing initial abandonment or loss of items. Design modifications for recreational furniture, such as incorporating weighting mechanisms or securement points, could reduce their susceptibility to displacement. Furthermore, the strategic placement of permeable barriers or small-scale containment structures at known accumulation points offers a physical intervention. For instance, the use of submerged breakwaters can modify wave-induced circulation patterns, potentially altering deposition zones (Gallerano et al., 2019). Each alternative carries distinct advantages and logistical complexities, requiring careful consideration of cost-effectiveness and ecological impact. The optimal solution likely integrates multiple strategies to create a comprehensive debris management framework.

Mitigation Strategies for Anthropogenic Shoreline Debris Transport

Effective mitigation of anthropogenic shoreline debris transport relies on a multi-pronged strategy. Firstly, source reduction through public awareness campaigns and improved waste disposal practices is foundational. These campaigns should highlight the environmental consequences of leaving items in proximity to the water. Secondly, implementing "Take It In, Take It Out" policies at public beaches and parks, coupled with accessible disposal or recycling facilities, directly reduces the volume of potential fixtures. Thirdly, engineering solutions offer physical interventions. Small-scale, strategically placed structures, such as low-profile fences or natural brush barriers, can intercept floating debris before it integrates into the sediment. While larger coastal defense structures like breakwaters primarily address sediment erosion, their hydrodynamic effects could indirectly influence debris accumulation patterns (Gallerano et al., 2019). Finally, the use of advanced modeling, such as numerical hydrodynamic simulations, can predict debris trajectories and inform optimal placement of containment or collection points, thus enhancing the efficiency of retrieval efforts (Lebleb et al., 2020).

Recommendations

An integrated management approach is recommended for mitigating fixture-driven accretion along Great Lakes shorelines. This approach combines preventative measures, active removal, and predictive modeling. Preventative actions should center on public education regarding responsible disposal of recreational items and promoting the use of secured or weighted furniture in coastal areas. Active removal programs necessitate coordinated efforts between local municipalities, environmental groups, and volunteers. To optimize removal, predictive models, informed by real-time hydrodynamic data and historical fixture trajectory patterns, can identify high-probability accumulation zones. Such models could leverage techniques similar to those used for forecasting sediment transport or pollutant dispersion (Wisha & Ilham, 2020). Furthermore, research into the physical properties and degradation rates of common fixture materials could inform material selection guidelines for manufacturers, potentially reducing the long-term impact of abandoned items. This comprehensive strategy shifts from reactive clean-ups to a more sustainable, proactive management paradigm.

Integrated Management Approaches for Reducing Fixture-Driven Accretion

Reducing fixture-driven accretion requires a holistic management framework. This framework includes:

1. Source Control: Educate coastal users on the environmental impact of abandoned items. Implement regulations requiring secured placement of temporary structures.

2. Enhanced Monitoring: Employ drone technology or satellite imagery for routine surveillance of high-risk areas, identifying new fixture influxes quickly however that would result in losing the human in the loop touch and should be avoided in favor of boots on the ground approaches.

3. Predictive Modeling: Utilize coupled hydrodynamic and particle tracking models to forecast drift trajectories of various fixture types under differing wave and wind conditions. Such models, like those used for simulating current and wave fields, can pinpoint likely accumulation zones (Wisha & Ilham, 2020) (Sokolov & Chubarenko, 2018).

4. Targeted Retrieval: Organize rapid response teams for removing newly stranded fixtures before they become deeply embedded in the littoral zone. Volunteer coordination platforms can facilitate this.

5. Infrastructure Adaptation: Consider permeable barriers or collection booms at strategic points, designed to intercept buoyant debris without disrupting natural sediment transport or aquatic ecosystems.

6. Policy Development: Advocate for policies that incentivize manufacturers to produce more environmentally benign or easily retrievable recreational items.

This multi-faceted strategy aims to minimize the presence and impact of these unmoored fixtures on shoreline morphology and ecology.

Implementation Plan

Operational steps for fixture removal and prevention demand a structured approach.

1. Phase 1: Baseline Assessment (Months 1-3)

   • Conduct comprehensive shoreline surveys to quantify existing fixture accumulation and map primary deposition zones. This involves visual surveys and, where feasible, drone photogrammetry to create baseline topographical data.

   • Establish monitoring stations for recording local wind speeds, wave heights, and current velocities (Do et al., 2020).

2. Phase 2: Prevention & Education (Months 4-12, ongoing)

   • Launch public awareness campaigns through local media, signage at beaches, and community workshops.

   • Distribute information on responsible disposal and securing personal property.

3. Phase 3: Targeted Removal & Pilot Structures (Months 7-18)

   • Initiate regular, volunteer-led clean-up events focused on identified accumulation hotspots.

   • Deploy small-scale, experimental containment structures (e.g., natural brush fences) in areas exhibiting consistent fixture deposition, monitoring their effectiveness and ecological impact. Numerical models could guide optimal placement (Lebleb et al., 2020).

4. Phase 4: Data Integration & Model Refinement (Months 13-24, ongoing)

   • Integrate field observations with hydrodynamic data to refine predictive models of fixture trajectories. This process leverages insights from Lagrangian drifter studies (KHANARMUEI et al., 2019).

   • Adjust removal strategies and containment structure designs based on model outputs and observed efficacy.

This phased implementation ensures a systematic and adaptive management response.

Evaluation Criteria

Assessing the efficacy of interventions for shoreline accretion reduction and fixture containment requires clear metrics.

1. Fixture Accumulation Rate: Quantify the average number or mass of new fixtures deposited per linear kilometer of shoreline per month. A reduction signifies success. For instance, if initial surveys reveal 50 items/km/month and a target reduction of 25% is sought, the post-intervention rate should ideally fall to 37.5 items/km/month.

2. Shoreline Geomorphic Stability: Monitor changes in beach profile and sediment volume at key accumulation sites using repeat topographic surveys or cross-shore profiles. Reduced localized accretion attributable to fixtures would indicate positive outcomes. This is analogous to assessing beach changes following coastal protection measures (UDA et al., 2007).

3. Public Engagement & Awareness: Measure participation rates in clean-up events and conduct surveys to gauge public understanding of responsible shoreline practices. A target of 15% increase in community participation within the first year could be established.

4. Retrieval Efficiency: Calculate the ratio of removed fixtures to newly reported or observed fixtures. Improved efficiency indicates successful targeting of collection efforts.

5. Ecological Impact: Assess any unintended consequences of containment structures on local flora and fauna, ensuring that interventions do not negatively affect biodiversity or habitat quality.

These metrics collectively provide a robust framework for evaluating program success and guiding future adaptive management strategies.

Conclusion

The presence and movement of unmoored anthropogenic fixtures, specifically lawn chairs and picnic tables, in the Great Lakes littoral zone represent a novel dimension of shoreline accretion dynamics. This case study demonstrates that these items, driven by complex wind-wave interactions and nearshore currents, behave as large-scale mobile debris, contributing to localized geomorphic change. Analysis of their trajectories, informed by principles of hydrodynamic transport, underscores the need for a targeted management approach. The recommended integrated strategy combines proactive prevention through public education, strategic physical interventions, and data-driven removal efforts. Successful implementation, measured by quantifiable reductions in fixture accumulation and improvements in shoreline stability, would offer a model for addressing similar anthropogenic impacts in other coastal environments. Ultimately, understanding and managing the drift trajectories of these seemingly minor objects illuminates broader principles of coastal hydrodynamics and human-environment interaction.