The Central Dredging Association (CEDA) is committe to environmentally responsible management of dredging activities and this paper – produced by the CEDA Environment Commission – seeks to raise awareness, to help the dredging community prepare for the consequences of climate change, and to understand how dredging can contribute to adaptation measures.
Introduction
Climate change is now a fact. It is also now widely accepted that human activities are playing a role in the increase of greenhouse gas emissions that have accelerated global warming during the last century, although the significance of the human contribution is still a matter of debate. The related effects include sea level rise, an increase in seawater surface temperature and changes in (seasonal) precipitation and hence river flow. Climate change research moves rapidly and there is still a great deal of uncertainty: some new estimates project faster rates of sea level rise than those reported by IPCC in 2007 whilst other (satellite) data suggest that rates of sea level rise may be slowing.
In addition to trends for an ongoing rise in global temperature and associated sea level rise, it is anticipated that there will be an increase in the frequency of extreme events like storms, surges, floods and droughts. Climate change effects are expected to increase in the coming decades.
Low-lying coastal areas worldwide face a large-scale increase in population density, urbanization, changes in land use and land subsidence. These increasing pressures make the coastal zones and deltas especially vulnerable to the impacts of climate change, not only flooding and erosion, but also implications for ecosystems. Adaptation strategies are therefore absolutely necessary to reduce the consequences of climate change by improving resilience and reducing vulnerability. Dredging will often be an important element in the adaptation ‘toolkit’.
The dredging community needs to be aware of the projected changes and the type of adaptations likely to be required. The dredging community comprises not only the dredging industry (contractors, manufacturers) but also port and water authorities, policy makers, regulators, consultants and stakeholder groups. Mitigation measures designed to reduce the contribution of the dredging sector to greenhouse gas (carbon dioxide) emissions (for example, the use of alternative fuels and materials) whilst clearly important, are outside the scope of this paper.
This position paper firstly highlights the main implications of climate change for dredging, and discusses potential preparatory and adaptation measures in general terms. It then elaborates on specific climate change issues and adaptation requirements or options in relation to three typical environments in which dredging takes place: open coasts; seaports, estuaries and access channels and inland waters.
Potential climate change implications for the dredging community
Dredging activities mostly take place in rivers, canals, estuaries, ports and coastal areas. The morphology of these areas is influenced by sediment supply, currents, waves, winds, water levels and tidal range. Changes in these conditions due to global warming may induce changes in erosion and sedimentation patterns, with potential consequences for both inland and offshore dredging requirements. Adaptation measures might relate to dredging volumes or locations, the type or number of dredging tools, or new dredging methodologies and technologies.
In the short-term, actions such as raising awareness, additional data collection and monitoring, risk assessments, scientific support to help understand and judge the effectiveness of proposed adaptations and planning will be critical elements of climate change preparation. In the longer-term, decisions on more concrete measures will be needed – for example, the physical modification of infrastructure or changes in working practices.
Responding to climate change will involve a wide range of stakeholders if the optimal options in all aspects are to be identified and if inflexible or irreversible ‘regrets’ measures are to be avoided. Uncertainty about the impacts of climate change and the occurrence of extreme events means that solutions have to be flexible and regulatory regimes also need to be able to accommodate such flexible approaches.
The design of new projects, particularly those with a design life extending to decades, needs to accommodate the uncertainties inherent in many climate change projections or design parameters. This is likely to result in an increased requirement for flexibility in a climate proof design.
In some cases, an increased frequency of extreme events may mean that more reactive dredging is needed than is currently done; in other cases proactive dredging may be more appropriate to deal with the implications of long-term seasonal changes in flow.
Adaptation measures should be sustainable, not only in environmental terms but also with regard to economics, flood risk management and other societal interests. Measures which use the dynamics of the natural system as the starting point for the design, and which make optimal use of natural processes, will usually be amongst the most sustainable. Careful planning to identify and deliver the most sustainable option in the site specific context will be essential.
Sustainable solutions may involve more conventional dredging (for example, where greater quantities of beach nourishment material are required) or they may involve less (such as where higher water levels mean that less dredging is needed). In some cases the most sustainable option may not involve conventional dredging practice at all (for example, as a result of changes in flood defence policies). The dredging community needs to be prepared to seek new and innovative solutions. Climate change will provide new opportunities, but it will also pose challenges.
The potential implications of climate change for the dredging community are discussed in more detail in the following sections for three interconnecting environments: open coasts; seaports, estuaries, and access channels; and inland waters.
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