This presentation is part of the Supporting Sediment Transport organized session.
A littoral cell is a conceptual sediment compartment that defines the supply, longshore transport, and deposition of sand and gravel along the coast in the Great Lakes. Within a littoral cell, there is typically an updrift supply area that features a long-term erosion trend, a net direction of longshore sediment transport (LST), and historically a downdrift depositional area that features a positive sediment budget and accretion trend. Understanding the sediment dynamics in littoral cells and the role of these natural physical processes have on protecting coastal ecosystems, beaches, and infrastructure is critical to developing equitable and sustainable long-term adaptation strategies to natural hazards and climate change.
The presentation will provide examples of littoral cell boundaries and sub-cell boundaries, which occur when artificial barriers are constructed that reduce the natural flow of sediments in the nearshore. New sources of sediment from shore erosion and riverine systems will be reviewed, including anthropogenic influence. The role of lake levels and storms in re-distributing sediment in the cells will be highlighted, along with potential impacts of climate change. Finally, characteristics of depositional sinks in littoral cells and examples will be highlighted.
This presentation is part of the Supporting Sediment Transport organized session.
Coastal erosion and the impacts associated with it such as infrastructure damage and habitat loss are ubiquitous issues throughout the Great Lakes region. During periods of high lake level, these issues are at the forefront of management concerns within coastal communities. While decades of coastal change research have been conducted throughout the Great Lakes region and our scientific understanding of the driving processes of coastal erosion continues to grow, we generally lack the ability to accurately predict future coastal changes. This stems primarily from the challenge in predicting future lake levels, which are inherently tied to weather patterns that cannot be reliably forecasted beyond 6 months. While an understanding of the predictive limitations helps to set realistic expectations for coastal managers, it does not provide meaningful planning assistance which is requisite for working towards coastal resilience. To address this, our recent research has focused on developing simple methods for predicting the likelihood of beach recovery following high lake levels at coastal sites along the Great Lakes. The foundation of our approach is to utilize publicly available datasets, such as NOAA lake level data and the USACE Wave Information Studies hindcast wave data, and simple to collect beach and nearshore morphology data that can be generated either by research teams or community scientists. With these data, we utilize fundamental morphodynamic relationships to predict the active zone of coastal sediment transport under past and present wave and water level conditions. The likelihood of sediment transport can then be estimated for varying morphodynamics conditions (e.g., erosive, accretionary) and compared to present morphology to infer whether beach recovery is probable for a site. Case studies along the eastern coast of Lake Michigan were used to develop and evaluate this approach and revealed that moderately erosive conditions that preferentially pull sand lakeward are the most dominant morphodynamic condition. Accretionary conditions that lead to beach recovery occur less frequently (generally less than 25% of the time) and only operate on a narrow portion of the nearshore, within 100 m of the shoreline. These results mechanistically explain why shoreline armoring leads to the loss of beach area and minimizes beach recovery as armoring drives sand lakeward of the zone where accretionary waves operate. This approach provides coastal managers with a probabilistic tool for predicting future coastal change and is currently being scaled up and operationalized throughout the State of Michigan.
This presentation is part of the Supporting Sediment Transport organized session.
This presentation will cover some recent examples of work around the Great Lakes that prioritizes more sensitive and contextual approaches to sediment management that aim to work with coastal forms and processes to protect, enhance, and leverage the ecological and cultural values that make coastal landscapes valuable. These approaches address the tendency for coastal management decisions to “improve” toward the most efficient and transferrable possible outcomes as opposed to the most strategic and contextually sensitive. Coastal management features and initiatives should instead be understood as an extension of the cultural attitudes of a particular place in response to a set of coastal conditions or challenges specific to that place. Otherwise, coastal management, understood as a universal and transferrable collection of efficiency-motivated strategies, threatens to sacrifice the local conditions that make places special to residents and visitors. This one-size-fits-all motivation also closely aligns with the prevalent funding mechanisms that prioritize large capital projects designed and scaled to address a worst-case modeled scenario. While often providing the protection planned, these strategies are large, expensive, and often lack monitoring or adaptation funding needed to both demonstrate efficacy or respond to unplanned conditions. By way of example, this presentation will look at a collection of projects that have attempted to prioritize more strategic and adaptive practices of coastal management, particularly in relationship to existing coastal processes such as sediment transport, and including practices understood as “natural and nature-based approaches”. Additionally, it hopes to set the stage for a larger conversation about the challenges to such approaches and how they can be addressed. Underpinning all of this is a simple assumption that coastal landscapes are not just important things, but what makes them important is the relationships these places engender. Coastal management is not something done to protect something else, but instead is part of the important thing itself and would benefit from acknowledging its place as a cultural and ecological project – a project that has the ability to reinforce and celebrate what we all love about coastal landscapes and what makes them different from one another.
This presentation is part of the Supporting Sediment Transport organized session.
Given what we now understand about the dynamism of Great Lakes coasts, we ask: “How could the policies governing management of these coasts empower communities to think and act in a way that maintains the ecological health of the coastal zone?” Through a comprehensive review of federal, state and local policies governing coastal management in the Great Lakes States, we have evaluated the matrix of protections across states. While this review has revealed gaps in protections, contradictory intents, inherent conflicts between the public trust and private property rights, and tensions between state and local rule, we also have discovered model policies. This presentation will briefly summarize the matrix of policies that govern shoreline protections, dredging and coastal placement, coastal wetlands and beach nourishment highlighting model policies and opportunities for their expansion as urgency grows to increase climate resiliency for people and nature.
This presentation is part of the Supporting Sediment Transport organized session.
Because of a confluence of development pressures and irrepressible physical dynamics, growing numbers of Great Lakes shoreland properties and structures, built on shifting sandy shores, are at heightened risk of loss from coastal storm surge, inundation, erosion, and shoreline recession—a phenomenon akin to sea level rise on ocean coasts. In response, property owners often install (or seek to install) extensive hardened shoreline armoring structures like seawalls and revetments to arrest those erosional processes. Those structures, however, substantially impair, if not ultimately destroy, natural coastal beaches and other shoreland resources, as well as accelerate erosion of neighboring shoreland properties. The clash of imperatives to protect shoreland properties versus conserving coastal resources signifies a wicked dilemma that Great Lakes coastal states and communities cannot avoid: armor or withdraw? More precisely, should a state or locality allow the continued armoring of Great Lakes shorelines in an attempt to fix in place shoreland properties, at great and ongoing private and public expense, and ultimately risk the loss of public trust resources? Or alternatively should it allow—and should it compel shoreland property owners to allow—natural processes to proceed, even though doing so will result in the natural conversion of privately owned shorelands into state-owned submerged bottomlands sooner than would otherwise occur? In many places, states and communities cannot hope to simultaneously protect both the beach and the beach house along naturally receding Great Lakes shorelines; they must choose which interest to prioritize first, recognizing the cost of doing so by losing the other. Given that conundrum, this presentation will provide a survey overview of the institutional arrangements that shape federal, state, and local management of Great Lakes coastal shorelands; key planning methods and policy options that states and localities can employ to reconcile competing demands between development pressures, public and private investments, property rights, and natural systems; and legal doctrines that authorize and constrain state and local actions, including especially the public trust doctrine. The presentation will also briefly identify and consider litigation that will likely arise given growing pressures to armor and—potentially—enhanced natural shoreline protection efforts that states and localities might undertake in response, along with the potential adjudication of those claims.
This panel is part of the Supporting Sediment Transport organized session.
When Great Lakes’ shorelines are able to function naturally and dynamically, they can provide multiple ecosystem benefits to the Great Lakes Basin and surrounding communities – including protection from the impacts of storms, fluctuating water levels and eroding lands – benefits that are increasingly important with changes in climate. Longshore sediment transport refers to the cumulative movement of sand, gravel, and cobble (i.e. coarse sediments) along the shoreline by the combined action of shore-parallel currents, wind, and waves. This mobilization of new sand and gravel from naturally occurring coastal erosion provides nearshore sediment-dependent protective features such as beaches, barrier bars, and dunes with the materials they need to persist and rebuild. These natural features host critical coastal habitat, provide the protected conditions that support wetlands and embayments, and provide flood protection and attenuation to surrounding properties and communities. Without these raw materials, these protective natural features and their associated wetlands disappear, impacting resiliency for coastal communities and ecosystems, as well as recreational opportunities.
Shoreline hardening is the primary method of addressing erosion on Great Lakes shorelines currently used by landowners and coastal managers. Hardening shorelines decreases the amount of sediment flowing along our shores, changes the hydrodynamics, and often increases the degree of erosion experienced by adjacent and down drift properties. Property owners who are experiencing more erosion from reduced sediment availability due to updrift shoreline hardening, find themselves in a position of either hardening their shoreline too, or losing their property investment due to increased erosion.
Join us for a moderated discussion with our session presenters, experts on the many facets of coastal management, to consider how we might come together to address this complex and challenging problem and what questions we still need to answer before we can count on resilient Great Lakes shorelines.
