Copernicus Downstream Service Supports Nature-Based Flood Defense: Use of Sentinel Earth Observation Satellites for Coastal Needs

This is a copy of the article published in Sea-Technology Magazine, which the authors have bought the rights to redistribute.With an uncertain future that includes climate change, sea level rise and increasing coastal populations, being able to make informed policy decisions in coastal zones will be critical for ensuring the well-being of citizens, the environment and the sustainability of economic activities. Earth observation (EO) can be used to efficiently and systematically provide the key information needed to make these decisions. However, getting access to the right EO in- formation can be a complicated and costly business, limiting availability. However, the launch in April 2014 of the first Sentinel satellite from Europe’s flagship EO program, Copernicus, represents a major advance in the availability of EO data, which has great potential to benefit numerous sectors involved in marine and coastal activities. We discuss some examples of applications being developed and give an example of a new service which intends to support nature-based flood defense schemes.The research leading to these results has received funding from the European Union Seventh Framework Program (FP7/2007-2013) under grant agreement n° 607131. All views presented are those of the authors. The EU is not liable for any use that may be made of the information contained herein.PDF, 5 pages, 20.4 M

Algal-Induced Biogeomorphic Feedbacks Lay the Groundwork for Coastal Wetland Development

Ecosystem establishment under adverse geophysical conditions is often studied within the “windows of opportunity” framework, identifying disturbance-free periods (e.g., calm wave climate) where species can overcome establishment thresholds. However, the role of biogeophysical interactions in this framework is less well understood. The establishment of saltmarsh vegetation on tidal flats, for example, is limited by abiotic factors such as hydrodynamics, sediment stability and drainage. On tidal flats, raised sediment ridges colonized by algal mats (Vaucheria sp.) appear to accomodate high densities of plant seedlings. Such ridges were previously found to have higher sediment strength than substratum without algae. Here, we investigate whether these measurements can be explained by geophysical factors only, or that biological (Vaucheria-induced) processes influence tidal marsh establishment by forming stabilized bedforms. We performed two experiments under controlled mesocosm conditions, to test the hypotheses that (a) Vaucheria grows better on elevated topographic relief, that (b) the binding force of their algal filaments increases sediment strength, and that (c) Vaucheria consequently creates elevated topographic relief that further facilitates algal growth. Our experimental results confirm the existence of this algal-induced biogeomorphic feedback cycle. These findings imply that benthic algae like Vaucheria may contribute significantly to tidal marsh formation by creating elevated and stabilized substratum. This suggests biogeophysical feedbacks can “widen” the windows of opportunity for further ecosystem establishment. Our results could be useful for the design of managed realignment projects aimed at restoring the unique ecosystem services of coastal wetlands, such as habitat biodiversity, carbon sequestration potential and nature-based flood defense

The importance of marshes providing soil stabilization to resist fast-flow erosion in case of a dike breach

Salt marshes provide valuable ecosystem services including coastal protection by reducing wave loading on dikes and seawalls. If the topsoil is erosion resistant to fast-flowing water, it may also reduce breach depth if a dike fails. In this experiment, we quantified the topsoil erosion resistance from marshes and bare tidal flats with different soil types to understand the extent to which they can help reduce breach depth. Intact soil samples were collected from 11 locations in the Netherlands at different tidal elevations and then exposed for 3 h to 2.3 m/s currents. To the samples that remained stable after flow exposure, an artificial crack was made to test their stability following soil disturbance. All samples from the tidal flats were completely eroded, regardless of sediment type. In contrast, all samples from well-established marsh plateaus were stable as long as no disturbances were made, including those with sandy subsoils. After creating artificial cracks, samples with a thin cohesive top layer on top of sandy subsoil collapsed, while marshes with silty subsoils remained stable. Pioneer marshes on sandy substrate without a cohesive top layer were the only vegetated soils that completely eroded. The lower erosion of marshes with either sandy or silty soils compared to bare tidal flats was best explained by the presence of a top layer with belowground biomass, high organic content, high water content, and low bulk density. When analyzing the erodibility of marshes only, fine root density was the best predictor of erosion resistance. This study demonstrates the importance of preserving, restoring, or creating salt marshes, to obtain a topsoil that is erosion resistant under fast-flowing water, which helps reduce breach dimensions if a dike fails. The probability of topsoil erosion in established marshes with sandy subsoil is higher than in silty marshes. A silty layer of cohesive sediment on top of the sand provides extra erosion resistance as long as it does not break. Pioneer marshes that have not developed a cohesive top layer are erosion sensitive, especially in sandy soils. For future marsh creations, using fine-grained sediments or a mixture of sand with silt or clay is recommended

Am I Safe? Copernicus downstream service is zooming in on coastal flood risk

FAST project poster for the EUROPEAN STAND of the GEO WEEK EXHIBITION (Washington DC, October 2017

D.3.6 – Sediment dynamics and stability

The objective of the FAST project is to develop a Copernicus downstream service based on (Sentinel) satellite data and in situ data to assess the function of wetlands in reducing flood risk and erosion. This requires an assessment of the erodibility and stability of foreshores, as well as knowledge on how saltmarshes function and develop, in order to predict their future status, and hence their flood defence value over longer time-scales. While detailed results on sediment and marsh dynamics are presented in particularly Deliverable 5.2, this Deliverable 3.6 serves to lists publication output of the project related to the study of vertical and lateral sediment dynamics of foreshores and marsh range changes and their drivers. The potential for implementation of products and services related to sediment dynamics and stability in the Copernicus downstream service is discussed