There is growing awareness that ‘nature-based solutions' (NbS) can help to protect us from climate change impacts while slowing further warming, supporting biodiversity and securing ecosystem servi...

https://royalsocietypublishing.org/doi/pdf/10.1098/rstb.2019.0120

Understanding the value and limits of nature-based solutions to climate change and other global challenges

United States. National Oceanic and Atmospheric Administration (Postdoctoral Fellowship Program)

Physically-based Assessment of Hurricane Surge Threat under Climate Change

There is great interest in the restoration and conservation of coastal habitats for protection from flooding and erosion. This is evidenced by the growing number of analyses and reviews of the effectiveness of habitats as natural defences and increasing funding world-wide for nature-based defences-i.e. restoration projects aimed at coastal protection; yet, there is no synthetic information on what kinds of projects are effective and cost effective for this purpose. This paper addresses two issues critical for designing restoration projects for coastal protection: (i) a synthesis of the costs and benefits of projects designed for coastal protection (nature-based defences) and (ii) analyses of the effectiveness of coastal habitats (natural defences) in reducing wave heights and the biophysical parameters that influence this effectiveness. We (i) analyse data from sixty-nine field measurements in coastal habitats globally and examine measures of effectiveness of mangroves, salt-marshes, coral reefs and seagrass/kelp beds for wave height reduction; (ii) synthesise the costs and coastal protection benefits of fifty-two nature-based defence projects and; (iii) estimate the benefits of each restoration project by combining information on restoration costs with data from nearby field measurements. The analyses of field measurements show that coastal habitats have significant potential for reducing wave heights that varies by habitat and site. In general, coral reefs and salt-marshes have the highest overall potential. Habitat effectiveness is influenced by: a) the ratios of wave height-to-water depth and habitat width-to-wavelength in coral reefs; and b) the ratio of vegetation height-to-water depth in salt-marshes. The comparison of costs of nature-based defence projects and engineering structures show that salt-marshes and mangroves can be two to five times cheaper than a submerged breakwater for wave heights up to half a metre and, within their limits, become more cost effective at greater depths. Nature-based defence projects also report benefits ranging from reductions in storm damage to reductions in coastal structure costs.

/pdf/the-effectiveness-costs-and-coastal-protection-benefits-of-55uyx68f5y.pdf

The Effectiveness, Costs and Coastal Protection Benefits of Natural and Nature-Based Defences.

We propose an ecomorphodynamic model which conceptualizes the chief land-forming processes operating on the intertwined, long-term evolution of marsh platforms and embedded tidal networks. The rapid network incision (previously addressed by the authors) is decoupled from the geomorphological dynamics of intertidal areas, governed by sediment erosion and deposition and crucially affected by the presence of vegetation. This allows us to investigate the response of tidal morphologies to different scenarios of sediment supply, colonization by halophytes, and changing sea level. Different morphological evolutionary regimes are shown to depend on marsh ecology. Marsh accretion rates, enhanced by vegetation growth, and the related platform elevations tend to decrease with distance from the creek, measured along suitably defined flow paths. The negative feedback between surface elevation and its inorganic accretion rate is reinforced by the relation between plant productivity and soil elevation in Spartina-dominated marshes and counteracted by positive feedbacks in multispecies-vegetated marshes. When evolving under constant sea level, unvegetated and Spartina-dominated marshes asymptotically tend to mean high water level (MHWL), different from multiple vegetation species marshes, which can make the evolutionary transition to upland. Equilibrium configurations below MHWL can be reached under constant rates of sea level rise, depending on sediment supply and vegetation productivity. Our analyses on marine regressions and transgressions show that when the system is in a supply-limited regime, network retreat and expansion (associated with regressions and transgressions, respectively) tend to be cyclic. Conversely, in a transport-limited regime, network reexpansion following a regression tends to take on a new configuration, showing a hysteretic behavior. Copyright 2007 by the American Geophysical Union.

Landscape evolution in tidal embayments: modeling the interplay of erosion, sedimentation, and vegetation dynamics

Nature-based solutions (NbS)-solutions to societal challenges that involve working with nature-have recently gained popularity as an integrated approach that can address climate change and biodiversity loss, while supporting sustainable development Although well-designed NbS can deliver multiple benefits for people and nature, much of the recent limelight has been on tree planting for carbon sequestration There are serious concerns that this is distracting from the need to rapidly phase out use of fossil fuels and protect existing intact ecosystems There are also concerns that the expansion of forestry framed as a climate change mitigation solution is coming at the cost of carbon rich and biodiverse native ecosystems and local resource rights Here, we discuss the promise and pitfalls of the NbS framing and its current political traction, and we present recommendations on how to get the message right We urge policymakers, practitioners and researchers to consider the synergies and trade-offs associated with NbS and to follow four guiding principles to enable NbS to provide sustainable benefits to society: (1) NbS are not a substitute for the rapid phase out of fossil fuels; (2) NbS involve a wide range of ecosystems on land and in the sea, not just forests; (3) NbS are implemented with the full engagement and consent of Indigenous Peoples and local communities in a way that respects their cultural and ecological rights; and (4) NbS should be explicitly designed to provide measurable benefits for biodiversity Only by following these guidelines will we design robust and resilient NbS that address the urgent challenges of climate change and biodiversity loss, sustaining nature and people together, now and into the future

https://onlinelibrary.wiley.com/doi/pdf/10.1111/gcb.15513

Getting the message right on nature-based solutions to climate change

https://repository.tudelft.nl/islandora/object/uuid%3Ae82fa129-094a-46b4-944d-b0ae7c1de284/datastream/OBJ/download

Nature-based flood protection: The efficiency of vegetated foreshores for reducing wave loads on coastal dikes

Global change amplifies coastal flood risks and motivates a paradigm shift towards nature-based coastal defence, where engineered structures are supplemented with coastal wetlands such as saltmarshes Although experiments and models indicate that such natural defences can attenuate storm waves, there is still limited field evidence on how much they add safety to engineered structures during severe storms Using well-documented historic data from the 1717 and 1953 flood disasters in Northwest Europe, we show that saltmarshes can reduce both the chance and impact of the breaching of engineered defences Historic lessons also reveal a key but unrecognized natural flood defence mechanism: saltmarshes lower flood magnitude by confining breach size when engineered defences have failed, which is shown to be highly effective even with long-term sea level rise These findings provide new insights into the mechanisms and benefits of nature-based mitigation of flood hazards, and should stimulate the development of novel safety designs that smartly harness different natural coastal defence functions

/pdf/historic-storms-and-the-hidden-value-of-coastal-wetlands-for-3porxfrchq.pdf

Historic storms and the hidden value of coastal wetlands for nature-based flood defence

One of the services provided by coastal ecosystems is wave attenuation by vegetation, and subsequent reduction of wave loads on flood defense structures. Therefore, stability of vegetation under wave forcing is an important factor to consider. This paper presents a model which determines the wave load that plant stems can withstand before they break or fold. This occurs when wave-induced bending stresses exceed the flexural strength of stems. Flexural strength was determined by means of three-point-bending tests, which were carried out for two common salt marsh species: Spartina anglica (common cord-grass) and Scirpus maritimus (sea club-rush), at different stages in the seasonal cycle. Plant stability is expressed in terms of a critical orbital velocity, which combines factors that contribute to stability: high flexural strength, large stem diameter, low vegetation height, high flexibility and a low drag coefficient. In order to include stem breakage in the computation of wave attenuation by vegetation, the stem breakage model was implemented in a wave energy balance. A model parameter was calibrated so that the predicted stem breakage corresponded with the wave-induced loss of biomass that occurred in the field. The stability of Spartina is significantly higher than that of Scirpus, because of its higher strength, shorter stems, and greater flexibility. The model is validated by applying wave flume tests of Elymus athericus (sea couch), which produced reasonable results with regards to the threshold of folding and overall stem breakage percentage, despite the high flexibility of this species. Application of the stem breakage model will lead to a more realistic assessment of the role of vegetation for coastal protection.

/pdf/stem-breakage-of-salt-marsh-vegetation-under-wave-forcing-a-265xw9mokz.pdf

Stem breakage of salt marsh vegetation under wave forcing: A field and model study

https://repository.tudelft.nl/islandora/object/uuid%3A266d4b68-21ed-4858-b67a-b4738290172f/datastream/OBJ/download

Vincent Vuik

Papers

Nature-based flood protection: The efficiency of vegetated foreshores for reducing wave loads on coastal dikes

Historic storms and the hidden value of coastal wetlands for nature-based flood defence

Stem breakage of salt marsh vegetation under wave forcing: A field and model study

Assessing safety of nature-based flood defenses: Dealing with extremes and uncertainties

Salt marshes for flood risk reduction: Quantifying long-term effectiveness and life-cycle costs