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Building with nature : restoring mangrove coast
Communities in Northern Java, Indonesia are suffering from coastal erosion affecting hundreds of kilometres of coastline. At the north coast of the province of Central Java in the district of Demak more than 3 kilometres of land including entire villages has already been swallowed up by the sea. The main causes of the problem are the removal of mangrove belts for aquaculture development, the construction of coastal infrastructure impacting sediment build-up from offshore sources, river canalisation and land subsidence caused by groundwater extraction. The Building with Nature (BwN) approach was introduced in Demak to address these root causes and mitigate their effects. The approach integrates mangrove and river restoration, small-scale engineering and sustainable land use. Permeable brushwood and bamboo structures have been built to dampen the waves and capture sediment. Once the near shore bed level had risen enough, mangrove seedlings will start to regenerate naturally. Local communities build and maintain these permeable structures through a Bio-rights approach. They are also trained to practice sustainable mixed mangrove-aquaculture, working with probiotics and local food sources. A strategy of learning-by-doing was adopted, where sharing the knowledge and the lessons learnt is supporting sound replication of the BwN approach through capacity building, knowledge exchange and embedding in policies and planning. A lesson learnt is that the land subsidence is more severe than expected which affects the net sedimentation rate behind the permeable structures and slows down the recolonization by mangroves. This lesson is communicated to the communities and policy makers.
Applying a numerical wave flume to predict wave overtopping
The hydraulic design of coastal structures like breakwaters and revetments is generally based on empirical formulations, physical model tests and a fair amount of expert judgement. Each of these techniques has his own accuracy and efficiency and the difference in these properties is quite large between the different methods. To provide an additional design tool, the Joint Industry Project (JIP) CoastalFOAM was started with the goal to further develop and apply a numerical wave flume to simulate the wave/structure interaction of permeable coastal structures.This study showed that a numerical wave flume could be useful in the design of hydraulic structures to determine the wave overtopping.
Hydraulic research for the new lock in Terneuzen
This paper discusses the main results of extensive scale model research done to assess the performance of the levelling system for the new lock in Terneuzen, in The Netherlands. The hydraulic design of the levelling system has a large influence on the resulting hydrodynamic forces acting on the vessel during levelling operations, and therefore on achievable passage times and operational windows. Different hydraulic designs for the new system were considered at different stages of the project and their performance is discussed here, focusing on the effect of density currents on the resulting hydrodynamic forces acting on the vessel. The results here presented show that density currents lead to the dominant forces and their effect must be considered when designing sea locks. Numerical models can be used to determine the main layout and dimensions of the levelling system, but the performance of the system including non-stationary flow, density currents and a vessel present in the lock chamber cannot yet be accurately assessed without performing physical scale model research.
Wood-induced backwater effects in lowland streams
Placement of wood in streams has become a common method to increase ecological value in river and stream restoration and is widely used in natural environments. Water managers, however, are often hesitant to introduce wood in channels that drain agricultural and urban areas because of backwater effect concerns. This study aims to better understand the dependence of wood-induced backwater effects on cross-sectional area reduction and on discharge variation. A newly developed, onedimensional stationary model demonstrates how a reduction in water level over the wood patch significantly increases directly after wood insertion. The water level drop is found to increase with discharge, up to a maximum level. If the discharge increases beyond this maximum, the water level drop reduces to a value that may represent the situation without wood. This reduction predominately depends on the obstruction ratio, calculated as the area covered by wood in the channel cross section divided by the total cross-sectional area. The model was calibrated with data from a field study in four lowland streams in the Netherlands. The field study showed that morphologic adjustments in the stream and reorientation of the woody material reduced the water level reduction over the patches in time. The backwater effects can thus be reduced by optimizing the location where wood patches are placed and by manipulating the obstruction ratio. The model can function as a generic tool to achieve a stream design with wood that optimizes the hydrological and ecological potential of streams.
Ecological impact of land reclamation on Jiangsu coast (China) : a novel ecotope assessment for Tongzhou Bay
China’s continuous and rapid economic growth has led to the reclamation of large sections of the intertidal mud coast in combination with port construction, such as that of the proposed Tongzhou Bay port on the Jiangsu coast. These reclamations threaten the local ecosystem services. An ecotope distribution map was created and a hydrodynamic numerical model of Tongzhou Bay was set up to quantify the impacts of reclamation on the ecosystem. Based on the field data and model results, several abiotic features were classified into 11 ecotopes and visualized in an ecotope map of the Tongzhou Bay ecosystem. Validation with spatial distributions of two threatened shorebird species (bar-tailed godwit and great knot) showed confirmation with the mid-range and low-range littoral zones (inundated from 40% to 100% of a tidal cycle), indicating the importance of the areas with these conditions to these populations. Overlaying the ecotope map with recent and proposed land reclamation schemes revealed a loss of ecotopes, composed of the high-range (42%), mid-range (48%), and low-range (38%) littoral habitats, corresponding to a 44%–45% loss of the most important ecotopes for bar-tailed godwit and great knot (mid-range and low-range littoral zones). These results confirm the applicability of the novel ecotope assessment approach in practice.
Improving the classification of flood tweets with contextual hydrological information in a multimodal neural network
While text classification can classify tweets, assessing whether a tweet is related to an ongoing flood event or not, based on its text, remains difficult. Inclusion of contextual hydrological information could improve the performance of such algorithms. Here, a multilingual multimodal neural network is designed that can effectively use both textual and hydrological information. The classification data was obtained from Twitter using flood-related keywords in English, French, Spanish and Indonesian. Subsequently, hydrological information was extracted from a global precipitation dataset based on the tweet’s timestamp and locations mentioned in its text. Three experiments were performed analyzing precision, recall and F1-scores while comparing a neural network that uses hydrological information against a neural network that does not. Results showed that F1-scores improved significantly across all experiments. Most notably, when optimizing for precision the neural network with hydrological information could achieve a precision of 0.91 while the neural network without hydrological information failed to effectively optimize. Moreover, this study shows that including hydrological information can assist in the translation of the classification algorithm to unseen languages.
Wave-tracking in the surf zone using coastal video imagery with deep neural networks
In this paper, we propose a series of procedures for coastal wave-tracking using coastal video imagery with deep neural networks. It consists of three stages: video enhancement, hydrodynamic scene separation and wave-tracking. First, a generative adversarial network, trained using paired raindrop and clean videos, is applied to remove image distortions by raindrops and to restore background information of coastal waves. Next, a hydrodynamic scene of propagated wave information is separated from surrounding environmental information in the enhanced coastal video imagery using a deep autoencoder network. Finally, propagating waves are tracked by registering consecutive images in the quality-enhanced and scene-separated coastal video imagery using a spatial transformer network. The instantaneous wave speed of each individual wave crest and breaker in the video domain is successfully estimated through learning the behavior of transformed and propagated waves in the surf zone using deep neural networks. Since it enables the acquisition of spatio-temporal information of the surf zone though the characterization of wave breakers inclusively wave run-up, we expect that the proposed framework with the deep neural networks leads to improve understanding of nearshore wave dynamics.
Milieuhygiënisch toetsingskader voor grootschalige bodemtoepassingen in diepe plassen : voorstel voor beoordeling van partijen grond en bagger
In 2010 is naar aanleiding van het advies van de Commissie Verheijen de ‘Handreiking voor het inrichten van diepe plassen’ opgesteld. Met de handreiking is invulling gegeven aan het proces van vormgeven van de herinrichting en is vanuit het omgaan met de zorgplicht een strenger milieuhygiënisch toetsingskader ontwikkeld. De handreiking wordt sindsdien gehanteerd bij nieuwe initiatieven. Aansluitend is in 2011 gestart met een onderzoeksprogramma diepe plassen, met als doel de mogelijkheden te verkennen om op basis van een deugdelijke (wetenschappelijke) analyse het milieuhygiënisch toetsingskader onderbouwd te kunnen verruimen. In de onderhavige rapportage zijn de resultaten hiervan beschreven en is een toetsingskader uitgewerkt met samenstellingswaarden voor in diepe plassen toe te passen grond en/of bagger.
Achtergrondbelasting fosfaat in de Maasregio
De doelstelling van deze studie is te bepalen of er een relevante bijdrage is van (semi)natuurlijke fosfaatbronnen (achtergrondbelasting) in het Maas stroomgebied. Indien dit het geval is, dan kan de waterkwaliteitsbeheerder dit meenemen bij het bepalen van de waterkwaliteitsdoelen. Op basis van de bronnenanalyse en gemeten concentraties in de vanggebieden zijn achtergrondconcentraties vastgesteld. De gehanteerde methode brengt de nodige onzekerheden met zich mee, maar is op dit moment met de huidige informatie de best beschikbare. Daarom bevelen we aan de berekende achtergrondconcentraties niet zonder meer te gebruiken voor het aanpassen van de KRW-doelen voor fosfaatconcentraties in oppervlaktewater. Voor de gebieden waar een flink hogere achtergrondgehalte is berekend dan het huidige KRW doel, adviseren we om verder te bestuderen of technische KRW doelaanpassing te verantwoorden is.
Nitraat in oppervlaktewater vanuit grondwater
Deze studie is een verkenning van wat we vanuit bestaande datasets en beschikbare modellen kunnen zeggen over de vraag: ‘Als er wordt voldaan aan de normen voor nitraat in grondwater, hebben we dan nog een probleem in de oppervlaktewateren?’. Hierbij wordt, als voorbeeld gekeken naar de oppervlaktewateren in het Maasstroomgebiedsdistrict, zowel naar landbouw- als natuurgebieden. Deze studie moet worden gezien als een eerste, ruwe verkenning van deze vraag. Hiervoor hebben we nationale modelinstrumenten en recente datasets ingezet om normoverschrijdingen in het oppervlaktewater te berekenen. Er zijn, naast de variant huidig beleid, vier varianten bekeken met berekeningen in het Landelijk KRW-Verkenner Model (LKM) en met de STROMON benadering van stofstromen. In deze vier varianten zijn de nitraatconcentraties in de bovenste meter van het grondwater gevarieerd: in de eerste variant zijn deze concentraties overal nul, in de tweede variant zijn ze nergens hoger dan 25 mg/l NO3 (afgeknot); in de derde variant zijn ze nergens hoger dan 50 mg/l NO3 (afgeknot) en in de vierde variant zijn de concentraties overal 50 mg/l (opgevuld).