This will have a moderating influence on future reinforcement works and their costs along these stretches.’ Wading birds ‘We can now distinguish between protective requirements of dike stretches with and without salt marshes. ‘The study provides data that allow us to estimate the reduction of wave height and run-up depending on the presence and characteristics of the salt marshes in front,’ comment Kornelis de Jong and Jan-Willem Nieuwenhuis, two co-authors from the water authority. This is an important conclusion for the local water authority. Our conclusion is therefore that in some locations, we will still depend on hard engineering solutions because these nature-based defences are not effective enough.’ Her long-term analysis showed that marshes expanded in areas where the adjacent tidal flats where higher (more than 0.5m above the average local sea level), while salt marshes retreated mainly where the mudflats in front of them were affected by erosion. ‘The areas where marshes are not developing are in turn the ones that would need more protection. Moderating influenceįurthermore, Marin-Diaz observed that in areas where the mud flat elevation is relatively low, salt marshes are absent. ‘This finding is not dependent on the wind direction of the storm, the exposure relative to the barrier islands, the grazing state of the marsh, or the vegetation type.’ The main drivers appeared to be the foreshore elevation and marsh width: higher foreshores and wider marshes provide more protection. ‘The key message is that compared to bare tidal flats, marshes were more effective in reducing run-up on the dikes,’ explains Marin-Diaz. The results show that salt marshes indeed reduce the wave run-up on dikes. The paper in the Journal of Applied Ecology is based on the observations and measurements during three storm seasons. Moreover, she analysed charts dating back some twenty years to study changes in the size of salt marshes. Next to the measurements she took herself, Marin-Diaz also received data on wind direction and strength from the Royal Dutch Meteorological Institute (KNMI). The impact of storms was assessed using wave loggers, but also by measuring the position of flood marks on the dikes. However, little data is available on what is really happening in the open air.’ ObservationsĪlong the coastline, Marin-Diaz has taken different measurements, such as elevation of the mud flats, the width of salt marshes, and the vegetation growing there. ‘Most of our knowledge about the protection these marshes provide is from models. The research area was situated along the Wadden Sea, a shallow zone between a range of barrier islands and the northern coast of the Netherlands consisting of tidal flats and wetlands. ‘After a storm we had to visit our research area to assess the impact of the waves,’ she explains. The results, which were published in the Journal of Applied Ecology on 10 May, help the water authority to quantify the protective effect of salt marshes.įor three years, ecologist Beatriz Marin-Diaz always had one eye on the weather forecast during the storm season. Scientists from the University of Groningen and the Royal Netherlands Institute for Sea Research (NIOZ), in collaboration with the local water authority, have monitored wave run-up during storms over a three-year period. This is especially important in low-lying countries like the Netherlands. Salt marshes provide multiple ecosystem services, one of those is protection of the coast against flooding. Some values are coded, in that case a decoded value is also provided.Image: These pictures show tidal marks after a storm on a stretch of dike with a salt marsh in front of it (left), or just a tidal mud flat. Each field within these hashes has a value and an descriptive label. It's an array of hashes with weather measurements. Language code (nl for Dutch, en for English) to be used for data labels.įunction name to be called on JSON data (JSONP). Latitude to search for nearest weatherstation (eg. Longitude to search for nearest weatherstation (eg. Shows historic measurements of nearest Dutch weatherstation for specified date and location.ĭata source is the Royal Netherlands Meteorological Institute, specifically:
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