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Human versus natural mud fluxes in the Scheldt Estuary : are they significant and if so, how can they be optimised?
The mud dynamics of the Scheldt estuary is governed by the interplay between tidal flow, freshwater discharge, marine and fluvial mud supply and local sources and sinks. A question is how large human impacts are on these mud dynamics. Using a process-based mud transport model of the Scheldt estuary, these impacts have been quantified by evaluating different scenarios representative for present or alternative maintenance dredging procedures. The results show that although the ‘human’ fluxes caused by maintenance dredging are typically small compared to natural gross fluxes, they are very significant compared to natural residual fluxes, notably in the narrower section of the estuary near Antwerp. Here more than half of the available mud is ‘second-hand’, i.e. it has been dredged from and released back into the estuary at least once. This implies that an optimization of the dredging and release cycles, including the smart selection of release locations, offers the perspective of smaller human impacts, possibly even at lower costs. A down-estuary shift of release locations would be favourable. Also, locations closer tidal flats may contribute to interrupting the vicious circle between dredged mud dispersion and maintenance dredging by enhancing the accretion rate of these flats. However, the surface area of these flats has to be substantial to provide more than just a short-term solution.
A smooth Scheldt
The Western Scheldt is the seaward part of the Scheldt estuary with a pronounced multichannel morphology and extensive intertidal flats. Observations of the bathymetry and aerial photographs of the intertidal and supra-tidal environments over the last 60 years reveal distinct transformations of the morphology on various spatial scales. The overall change is from an irregular distribution of intertidal flats with branching channels and shallow areas towards smooth tidal flats in between the main channels. A decline in the number of small tidal channels – ebb- and flood chutes and channels that connect the main ebb- and flood channels, is observed throughout the Western Scheldt. The large number of small tidal flats have merged into a limited number of bigger entities, and the jagged edges of the flats have given way to almost straight water lines. The surface area of the intertidal flats that is covered with mega-ripple fields has decreased. Mechanisms that account for the changes on all scales throughout the Western Scheldt have not been recognized. So far intrinsic pattern development and/or the closure of branching tidal basins are recognized as candidates to explain the changes.
From stakeholder to shareholder : organising stakeholder commitment for the Schelde Estuary of the future
The Scheldt Estuary provides the stage for a broad range of stakeholders and (conflicting) interests. These diverging interests led to complex decision-making on estuarine policy and management. The EU Interreg project ‘Estuaries on the MOVE’ (EMOVE) aims to bring stakeholders together and organize bottom-up commitment for a sustainable Scheldt Estuary of the future, by turning them into shareholders, implying ‘ownership’ of a particular development or project. Crucial in the approach were: 1) generating a shared understanding on the physical and ecological functioning of estuary and the different perspectives stakeholders have on the estuary and 2) collectively formulating projects and organizing coalitions. The result of the approach was both successful and promising. Five different projects were formulated – ranging from a change in polder regime (‘growing land’) to a cross-border nature reserve, environmental-friendly sediment disposal techniques, silt agriculture and governance opportunities. The applied methodology of bottom-up project formulation, combined with Group Decision Modelling provided a fruitful ground for measures towards a sustainable Scheldt Estuary that have sufficient support to come to implementation and also important generic lessons for organizing stakeholder commitment in sensitive decision-making environments like estuaries.
Scheldt Estuary physics and integrated management : special session of the 36th IAHR World Congress (28 June - 3 July 2015, Delft and The Hague, the Netherlands)
The 36th IAHR world congress was organized in the Netherlands. This was an excellent opportunity to present the state of knowledge on the Scheldt estuary and special sessions were organized on Monday June 29th. No less than 17 papers and extended abstracts were submitted and accepted for a presentation.
Bodemdaling door grondwateronttrekking in het Westland en omgeving
In de driehoek Den Haag - Rotterdam - Hoek van Holland, en met name in het Westland, wordt de afgelopen 30 jaar steeds meer grondwater onttrokken uit het eerste watervoerende pakket. De grondwateronttrekking zorgt voor stijghoogteverlaging. Zoals bekend uit andere delen van de wereld kan onttrekking en stijghoogteverlaging aanzienlijke bodemdaling veroorzaken, vooral als er onder of boven het watervoerende pakket waaruit onttrokken wordt veel klei of veen aanwezig is. In het Westland en omgeving is veel klei en veen aanwezig in de Holocene afzettingen tussen het eerste watervoerende pakket en het maaiveld. Voor beleidsontwikkeling is het voor de provincie Zuid-Holland en andere overheden belangrijk om inzicht te krijgen in de bodemdaling die door de toenemende grondwateronttrekking in het gebied is veroorzaakt, en mogelijk nog kan worden veroorzaakt in de toekomst. In deze studie is hier onderzoek naar gedaan.
Seafloor classification in a sand wave environment on the Dutch Continental Shelf using multibeam echosounder backscatter data
High resolution maps of sandy seafloors are valuable to understand seafloor dynamics, plan engineering projects, and create detailed benthic habitat maps. This paper presents multibeam echosounder backscatter classification results of the Brown Bank area of the North Sea. We apply the Bayesian classification method in a megaripple and sand wave area with significant slopes. Prior to the classification, corrections are implemented to account for the slopes. This includes corrections on the backscatter value and its corresponding incident angle. A trade-off in classification resolutions is found. A higher geo-acoustic resolution is obtained at the price of losing spatial resolution, however, the Bayesian classification method remains robust with respect to these trade-off decisions. The classification results are compared to grab sample particle size analysis and classified video footage. In non-distinctive sedimentary environments, the acoustic classes are not attributed to only the mean grain size of the grab samples but to the full spectrum of the grain sizes. Finally, we show the Bayesian classification results can be used to characterize the sedimentary composition of megaripples. Coarser sediments were found in the troughs and on the crests, finer sediments on the stoss slopes and a mixture of sediments on the lee slopes.
Morphodynamic acceleration techniques for multi-timescale predictions of complex sandy interventions
Thirty one percent of the world’s coastline consists of sandy beaches and dunes that form a natural defense protecting the hinterland from flooding. A common measure to mitigate erosion along sandy beaches is the implementation of sand nourishments. The design and acceptance of such a mitigating measure require information on the expected evolution at time scales from storms to decades. Process-based morphodynamic models are increasingly applied, together with morphodynamic acceleration techniques, to obtain detailed information on this wide scale of ranges. This study shows that techniques for the acceleration of the morphological evolution can have a significant impact on the simulated evolution and dispersion of sandy interventions. A calibrated Delft3D model of the Sand Engine mega-nourishment is applied to compare different acceleration techniques, focusing on accuracy and computational times. Results show that acceleration techniques using representative (schematized) wave conditions are not capable of accurately reproducing the morphological response in the first two years. The best reproduction of the morphological behavior of the first five years is obtained by the brute force simulations. Applying input filtering and a compression factor provides similar accuracy yet with a factor five gain in computational cost. An attractive method for the medium to long time scales, which further reduces computational costs, is a method that uses representative wave conditions based on gross longshore transports, while showing similar results as the benchmark simulation. Erosional behavior is captured well in all considered techniques with variations in volumes of about 1 million m3 after three decades. The spatio-temporal variability of the predicted alongshore and cross-shore distribution of the morphological evolution however have a strong dependency on the selected acceleration technique. A new technique, called ’brute force merged’, which incorporates the full variability of the wave climate, provides the optimal combination of phenomenological accuracy and computational efficiency (a factor of 20 faster than the benchmark brute force technique) at both the short and medium to long time scales. This approach, which combines realistic time series and the mormerge technique, provides an attractive and flexible method to efficiently predict the evolution of complex sandy interventions at time scales from hours to decades.
Finding the essential : improving conservation monitoring across scales
To account for progress towards conservation targets, monitoring systems should capture not only information on biodiversity but also knowledge on the dynamics of ecological processes and the related effects on human well-being. Protected areas represent complex social-ecological systems with strong human-nature interactions. They are able to provide relevant information about how global and local scale drivers (e.g., climate change, land use change) impact biodiversity and ecosystem services. Here we develop a framework that uses an ecosystem-focused approach to support managers in identifying essential variables in an integrated and scalable approach. We advocate that this approach can complement current essential variable developments, by allowing conservation managers to draw on system-level knowledge and theory of biodiversity and ecosystems to identify locally important variables that meet the local or sub-global needs for conservation data. This requires the development of system narratives and causal diagrams that pinpoints the social-ecological variables that represent the state and drivers of the different components, and their relationships. We describe a scalable framework that builds on system based narratives to describe all system components, the models used to represent them and the data needed. Considering the global distribution of protected areas, with an investment in standards, transparency, and on active data mobilisation strategies for essential variables, these have the potential to be the backbone of global biodiversity monitoring, benefiting countries, biodiversity observation networks and the global biodiversity community.
Global 5km resolution estimates of secondary evaporation including irrigation through satellite data assimilation
A portion of globally generated surface and groundwater resources evaporates from wetlands, waterbodies and irrigated areas. This secondary evaporation of “blue” water directly affects the remaining water resources available for ecosystems and human use. At the global scale, a lack of detailed water balance studies and direct observations limits our understanding of the magnitude and spatial and temporal distribution of secondary evaporation. Here, we propose a methodology to assimilate satellite-derived information into the landscape hydrological model W3 at an unprecedented 0.05∘, or ca. 5 km resolution globally.
Application of hydrological forecast verification information
Verification studies and systems often focus solely on the exercise of verifying forecasts and not on the application of verification information. This chapter discusses the potential for application of hydrological forecast verification information to improve decision-making in and around the forecast process. Decisionmakers include model developers and system designers, forecasters, forecast consumers, and forecast administrators. Each of these has an important role in decisions about forecasts and/or the application of forecasts that may be improved through use of forecast verification. For each, we describe the role, the actions that could be taken to improve forecasts or their application, the context and constraints of those actions, and needs for verification information. Consistent with other studies and assessments on forecast verification, we identify the need for a routine forecast verification system to archive data, plan for operations, measure forecast performance, and group forecasts according to application. Further, we call on forecast agencies and forecast consumers to use forecast verification as a routine part of their operations in order to continually improve services and to engage others to use forecast verification to improve decision-making.