̽��ֱ�� of Cambridge - Saltmarsh

Salt marsh plants key to reducing coastal erosion and flooding

sc604 — Thu, 02 Oct 2014 10:07:00 +0000

̽��ֱ��effectiveness of salt marshes – wetlands which are flooded and drained by tides – in protecting coastal areas in times of severe weather has been quantified in a study by researchers from the ̽��ֱ�� of Cambridge.

In the largest laboratory experiment ever constructed to investigate this phenomenon, the researchers have shown that over a distance of 40 metres, the salt marsh reduced the height of large waves in deep water by 18%, making them an effective tool for reducing the risk of coastal erosion and flooding. Sixty percent of this reduction is due to the presence of marsh plants alone. ̽��ֱ��results are published in the journal Nature Geoscience.

One of the most noticeable effects of climate change is the increasing frequency and severity of storms, such as the series of storms which battered parts of south west England last winter. As the climate continues to warm and sea levels continue to rise, the effects of these storms could be devastating, putting these and other coastal communities worldwide at risk.

While the important role of salt marshes in protecting against coastal erosion is well-known, their effectiveness in mitigating the effects of extreme weather, when water levels are at their maximum and waves are at their highest, had not been understood or definitively quantified.

Recreating a salt marsh in a large wave tank and subjecting it to realistic storm conditions, the researchers found that it significantly ‘buffered’ the effects of the waves. Similar to wind blowing through a forest, the plants reduce the energy of the water as it flows through and around them. Even when the waves flattened and broke the marsh’s vegetation, the soil surface beneath remained stable and resistant to surface erosion.

Salt marshes are found throughout the world, particularly at middle to high latitudes. In addition to their role in protecting against coastal erosion and reducing flooding, they also act as nurseries and refuges for many species of marine animals, and protect water quality by filtering runoff.

Given increased rates of global sea level rise, there are concerns about losing salt marsh on many coasts, particularly where there is insufficient sediment and space to allow marshes to build upwards and landwards.

“While we have long known that salt marshes and other natural defences such as sand dunes or mudflats can help protect our coastlines, a lack of data on their effectiveness in extreme conditions has meant that they often are not included in flood risk assessments,” said Dr Iris Möller of Cambridge’s Department of Geography (Cambridge Coastal Research Unit), who led the research. “But we’ve shown that even in extreme conditions, salt marshes are a vital defence for our coastlines and protect against more frequent storms.”

̽��ֱ��researchers used large sections of salt marsh, cut from a natural marsh in northwestern Germany. ̽��ֱ��team then rebuilt the marsh in one of the world’s largest wave tanks, located in Hannover, and subjected it to water depths and types of waves that are typical in storm surge conditions. Even after the waves flattened the plants, the marsh was still an effective barrier against erosion, demonstrating the importance of natural flood defences alongside manufactured defences such as flood walls.

̽��ֱ��flooding which hit south west England last winter was the worst in nearly 20 years. A series of 12 major storms between December and February caused huge waves, strong winds and hide tides to pummel large parts of Cornwall, Devon and the southwest, causing millions of pounds worth of damage. Many homes and businesses were flooded multiple times, and major flooding in the Somerset Levels forced many families to evacuate their homes and many farmers to evacuate their livestock.

As part of the government’s attempts to mitigate the effects of future storms, salt marshes have been re-created in several locations around the UK coast: a large new salt marsh on the Somerset’s Steart peninsula was recently completed, and several more are planned for locations throughout the UK.

̽��ֱ��research was supported by the European Community’s 7th Framework Programme and a grant from ̽��ֱ��Isaac Newton Trust, Trinity College, Cambridge.

̽��ֱ��researchers are blogging about their work at thesaltmarshexperiment.wordpress.com.

Study finds that natural flood defences such as salt marshes can reduce the height of damaging waves in storm surge conditions by close to 20%.

Even in extreme conditions, salt marshes are a vital defence for our coastlines

Iris Möller

James Tempest

Storm on a rising tide, Orplands, Essex

̽��ֱ��text in this work is licensed under a Creative Commons Licence. If you use this content on your site please link back to this page. For image rights, please see the credits associated with each individual image.

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Climate change: can nature help us?

Anonymous — Wed, 08 May 2013 11:05:19 +0000

Flooding, landslides, crop failure, water shortages. Across the globe, the frequency with which humans are suffering the ill effects of climatic variability and extreme weather events is on the increase. Can natural environments be used effectively to help people adapt to the effects of climate change? ̽��ֱ��first systematic review of this question – facilitated by the Cambridge Conservation Initiative (CCI) Collaborative Fund for Conservation – finds much evidence of their effectiveness.

" ̽��ֱ��delays in international agreements on ways to reduce global greenhouse gas emissions mean that planning to counter the impacts of climate change is a necessity,” said Robert Munroe, Climate Change Officer at BirdLife International. “Governments of all countries should be making plans to protect us against these impacts.”

One adaptation option is to invest in costly, large-scale structures such as sea walls, irrigation systems and dams. But while their short-term impact is clear, these solutions lead to ever-increasing maintenance costs and often have negative impacts on local ecosystems and biodiversity.

“International policy makers are having to think about the different approaches they could take, but the problem is that they don’t have enough information to make informed decisions,” said Munroe.

“Hard-engineered sea walls have a limited life span, and we know that they change wave and tidal currents, often to the detriment of saltmarshes or mangroves that act as a natural buffer to storm surges and coastal erosion. Do we really want to lose these buffers and face increasing costs of sea wall maintenance?” asked Dr Iris Möller, Deputy Director of the Cambridge Coastal Research Unit in the Department of Geography.

“There’s anecdotal evidence from events like the 2004 Indian Ocean tsunami that villages surrounded by mangroves were significantly less affected by the tsunami than more exposed areas,” she added. ̽��ֱ��mangroves may have saved thousands of lives and properties by absorbing a large proportion of the energy in the waves.

But local anecdotal evidence is not enough to provide a reliable measurement of the effectiveness of an approach. Now a review has been completed of the effectiveness of natural approaches to buffering the effects of climate change. Termed Ecosystem-based approaches for Adaptation (EbA), this relatively new concept incorporates approaches that have been used for a long time to address climatic variability, but not necessarily in the context of adaptation to climate change.

“We wanted to understand what the research evidence tells us, in terms of the relative importance of ecosystems as opposed to hard-engineering solutions to the same problem,” said Dr Bhaskar Vira in the Department of Geography. Vira, Möller, Dr Tom Spencer (Director of the Cambridge Coastal Research Unit) and Dr Andreas Kontoleon (Department of Land Economy) worked with climate change policy expert Munroe at BirdLife and climate change expert Dr Nathalie Doswald at the United Nations Environment Programme World Conservation Monitoring Centre, as well as with the International Institute for Environment and Development in London. They looked at published studies from around the world in which a wide range of EbA had been assessed. ̽��ֱ��step-by-step detail of their systematic review method was published in Experimental Evidence in 2012, which will enable it to be replicated for consistency in future studies.

“ ̽��ֱ��systematic review is very specific: we sifted out the most relevant published studies and compiled evidence from them on the different interventions being used and how effective they have been,” said Vira. ̽��ֱ��team found that activities related to EbA have been used across the globe to address a broad range of climatic hazards and impacts.

Interventions include the sustainable management of wetlands and floodplains to act as floodwater reservoirs and provide important water stores for times of drought, and the conservation and restoration of forests and natural vegetation to stabilise slopes and regulate water flows, preventing flash floods and landslides due to increased rainfall. Most of the approaches were reported by the studies to be effective in reducing human vulnerability to the effects of climate change, climatic variability or natural hazards.

“ ̽��ֱ��results are providing general guidance on the circumstances in which an EbA may be useful,” said Vira. “There are cases where it isn’t necessarily going to be helpful – if you live in Gloucestershire and you’re about to get flooded, you can’t start planting trees, you have to use sandbags. These interventions take time, and there are limitations to their effectiveness.”

“It’s important to work towards fully informed decision-making between alternative adaptation approaches,” said Munroe. “Large-scale infrastructural solutions may tend to be pursued because the financial costs are clear and their short-term effectiveness at buffering hazards has been tested by engineers. But by constraining natural ecological cycles, they may increase social vulnerability in the medium to long term. We found some discussions on the comparison between ecosystem-based and other kinds of approaches to adaptation, which are valuable for policy makers.”

“We also realised there are some real knowledge gaps,” added Möller. “We need information on the costs as well as the benefits, and on whether monitoring systems have been put in place to assess the long-term effectiveness of these approaches. With respect to ecosystems as coastal protection, for example, we need to know exactly how much energy mangroves and marshes absorb and what we can do to maximise and maintain the effect.”

̽��ֱ��project collaborators recognise that the divide between scientific research and policy making must be bridged if governments are to make the best decisions for long-term adaptation to climate change. “Our partnership with NGO colleagues meant the project has both academic rigour and a built-in pathway to impact,” said Vira. ̽��ֱ��Collaborative Fund for Conservation, which was established with the generous support of the Arcadia Fund, was set up explicitly to foster these innovative partnerships.

̽��ֱ��team’s collective range of contacts has enabled them to disseminate their results and recommendations. Their presentations at the United Nations Climate Change Conference in Durban in December 2012, and the distribution of briefing papers and guidance documents, have drawn the attention of decision-makers at the highest levels to the possibilities of ecosystem-based approaches.

“A technical workshop on EbA, likely to involve 70 countries, was recently convened by the Climate Change Convention,” said Munroe. “Our work contributed to the momentum that resulted in this decision. It’s really exciting as it’s the first time the Convention has met to discuss this approach.”

“EbA is an important tool in the adaptation toolkit, which has often been ignored because the evidence base had not been made clear,” said Munroe. “Employing it alongside other adaptation options will result in much more sustainable responses to the effects of climate change in both developed and developing countries.”

Hard-engineered sea walls have a limited life span. Could saltmarshes and mangroves offer a different approach to buffering against storm surges and coastal erosion?

Do we really want to lose these buffers and face increasing costs of sea wall maintenance?

Iris Moller

Saltmarshes starting to be inundated by the tide at Abbots Hall, Cumbria, UK

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