Donald L. Forbes

FLUME STUDY OF SILT TRANSPORTATION AND DEPOSITION

A small recirculating laboratory flume was used to study the transportation and deposition of coarse silt (Do0 = 0.045 mm) under conditions of approximate transport equilibrium. Nineteen runs were made with a range of Froude numbers between 0.07 and 1.23 and with total sediment con- centrations as high as 393,000 mg/l. Depths of flow (as much as 10 cm or one half of channel width) were adjusted by means of a sidewall correction for subsequent calculations of Reynolds number, Froude number, and stream power. Ripple bed forms in the lower regime of flow developed at Froude numbers less than 0.75 approximately. Plane bed and standing wave or antidune bed forms developed at Froude numbers in excess of 1.0. Flat symmetrical ripples, irregular low ripples, and plane bed forms characterized the transition between the lower and upper regimes of flow. The transition occurred at a stream power value of approximately 2 g.cm.-1.s-1. There was, however, some overlap in the stability fields of the several types of bed forms. Lenticular, tabular, and irregular units of crosslamination were deposited, in addition to parallel (plane) lamination, in the lower regime of flow. Parallel (plane) lamination, undulose lamination, and thin units of cross-lamination were deposited in the transitional regime. The upper regime of flow was cha- racterized primarily by parallel and undulose lamination. The cross-laminated units deposited by ripple migration in the low- er regime of flow had an average length of about 0.7 x the ripple wave length and an average maximum thickness of 0.8 x ripple height. The silt behaved essentially as a cohesionless material.

Physical basis of coastal adaptation on tropical small islands

Small tropical islands are widely recognized as having high exposure and vulnerability to climate change and other natural hazards. Ocean warming and acidification, changing storm patterns and intensity, and accelerated sea-level rise pose challenges that compound the intrinsic vulnerability of small, remote, island communities. Sustainable development requires robust guidance on the risks associated with natural hazards and climate change, including the potential for island coasts and reefs to keep pace with rising sea levels. Here we review these issues with special attention to their implications for climate-change vulnerability, adaptation, and disaster risk reduction in various island settings. We present new projections for 2010–2100 local sea-level rise (SLR) at 18 island sites, incorporating crustal motion and gravitational fingerprinting, for a range of Intergovernmental Panel on Climate Change global projections and a semi-empirical model. Projected 90-year SLR for the upper limit A1FI scenario with enhanced glacier drawdown ranges from 0.56 to 1.01xa0m for islands with a measured range of vertical motion from −0.29 to +0.10xa0m. We classify tropical small islands into four broad groups comprising continental fragments, volcanic islands, near-atolls and atolls, and high carbonate islands including raised atolls. Because exposure to coastal forcing and hazards varies with island form, this provides a framework for consideration of vulnerability and adaptation strategies. Nevertheless, appropriate measures to adjust for climate change and to mitigate disaster risk depend on a place-based understanding of island landscapes and of processes operating in the coastal biophysical system of individual islands.

The Gathering Storm: managing adaptation to environmental change in coastal communities and small islands

Small island communities are inherently coastal communities, sharing many of the attributes and challenges faced by cities, towns and villages situated on the shores of larger islands and continents. In the context of rapidly changing climates, all coastal communities are challenged by their exposure to changing sea levels, to increasingly frequent and severe storms, and to the cumulative effects of higher storm surges. Across the globe, small island developing states, and small islands in larger states, are part of a distinctive set of stakeholders threatened, not only by climate change but also by shifting social, economic, and cultural conditions. C-Change is a collaborative International Community–University Research Alliance (ICURA) project whose goal is to assist participating coastal communities in Canada and the Caribbean region to share experiences and tools that aid adaptation to changes in their physical environment, including sea-level rise and the increasing frequency of extreme weather events associated with climate change. C-Change researchers have been working with eight partner communities to identify threats, vulnerabilities, and risks, to improve understanding of the ramifications of climate change to local conditions and local assets, and to increase capacity for planning for adaptation to their changing world. This paper reports on the knowledge gained and shared and the challenges to date in this ongoing collaboration between science and society.

Understanding and managing global change in small islands

Climate variability and change, associated changes in sea level, ocean acidification and surface warming, extreme events such as tropical cyclones and tsunamis, and the quality and quantity of freshwater resources are among the major environmental issues related to the sustainable development of small islands, including small island developing states (SIDS). In addition to natural change and hazards, principal sources of stress on small islands include changing social, demographic, economic, cultural, and governance conditions and maladaptive local development initiatives. As global pressures increase, including those related to climate change, the ability to cope with the adverse consequences of complex change may be compromised increasingly by limits to adaptive capacity, unsustainable development practices, institutional barriers, and other governance challenges. Island communities are social-ecological systems and their resilience in the face of uncertain futures (environmental, economic, and others) and surprises (extreme events) is a key element of sustainability (Kates et al. 2000; Adger 2006; Adger et al. 2005). Small island developing states and small islands within larger states are physical, ecological, and social entities with distinctive attributes related to their insularity, remoteness, size, geographic setting, climate, culture, governance, and economy (e.g. Pelling and Uitto 2001; Mimura et al. 2007; Hay 2013; Forbes et al. 2013). Yet despite the sense of separation that attends the experience of small islands, global change in a variety of forms impinges directly or indirectly on the environment and sustainability of these island communities. As a group, they pose some of the most striking challenges to sustainability science. Low-lying island states, such as the Maldives and Tuvalu, face pressing concerns about the limits to habitability under accelerated sea-level rise, the result of a warming global climate. Ocean warming and acidification pose threats to the conservation of reef corals and the stability and resilience of coral reefs under rising sea level (IPCC 2007). Together with concerns about freshwater resources, these environmental threats exacerbate challenges related to small size and remoteness, demographic pressures, small markets and limited economic opportunities, high per-capita infrastructure costs, reliance on external finance, limited technical capacity (including capacity for disaster response, recovery, and risk reduction), and cultural transformation through processes such as J. E. Hay (&) N. Mimura Institute for Global Change Adaptation Science (ICAS), Ibaraki University, Environment Research Laboratory Building, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan e-mail: johnhay@ihug.co.nz

Evolution and Morphodynamics of a Prograded Beach‐Ridge Foreland, Northern Baffin Island, Canadian Arctic Archipelago

Abstract Landward retreat (marine transgression) is a common response of coastal systems to rising relative sea level. However, given sufficient sediment supply, the coast may advance seaward. The latter response of gravel barriers has been recorded in parts of southeastern and northwestern Canada, where seaward‐rising sets of beach ridges are observed in areas of Holocene RSL rise. Cape Charles Yorke, northern Baffin Island, is a 5 km long gravel foreland characterized by seaward‐rising beach‐ridge crest elevations. The prograded morphology of the Cape Charles Yorke foreland is a prime example of coastal response to a combination of rising RSL and abundant sediment supply, an unusual and little‐documented pattern in the Canadian Arctic. The main gravel supply to Cape Charles Yorke is likely from eroding bedrock and raised marine deposits southwest of the foreland. Although not the dominant sediment source, the Cape Charles Yorke delta contributed to the formation of the foreland by sheltering it from easterly storm waves and providing an anchor point for the prograding ridges. The truncation of relict ridges by the modern shoreline suggests a recent regime shift from continuous deposition to predominant erosion. The cause and timing of this shift are unknown but could result from a recent dwindling in sediment supply, increased accommodation space, increased wave energy, and/or an accelerated rise of relative sea level.