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Een realistische kijk op zeewierproductie in de Noordzee
Dit memo is bedoeld om op basis van de huidige stand van kennis een inschatting te geven van de orde van grootte van het mogelijke ruimtebeslag van zeewierproductie binnen toekomstige windparken. Vooralsnog wordt uitgegaan van productie van zeewier zonder bemesting. In dit memo willen wij verduidelijken dat 14.000 km2 zeewierproductie op de Noordzee geen realistische opdracht is zonder rekening te houden met innovaties in productiesysteem en oog voor effecten op het ecosysteem functioneren. Ten eerste is binnen windparken slechts een deel van de ruimte daadwerkelijk beschikbaar voor medegebruik. Ten tweede is het niet realistisch aan te nemen dat een kwart van het NCP gebruikt kan worden voor zeewierproductie zonder de draagkracht van de Noordzee zowel voor zeewier als voor andere componenten van het ecosysteem te overschrijden. Zowel voor de zeewiersector zelf, als voor een verantwoord, duurzaam gebruik van het ecosysteem is het goed om de verschillende randvoorwaarden zo vroeg mogelijk in beeld te hebben.
Grain size fractionation by process-driven sorting in sandy to muddy deltas
Modern and ancient analogues are often consulted by geologists to help understand subsurface systems. While modern analogues provide information on the areal relationship between facies, ancient systems provide detailed data on the vertical facies variations, typically along a two-dimensional outcrop. Combining data from modern and ancient systems effectively requires translating areal morphology, which is often still evolving, to the related sediments preserved in three dimensions. Process-based models simulate both depositional processes while preserving stratigraphy. These models can be employed to unravel the relationship between sediment supply and preserved deposits in natural systems and to help integrate field data. Four synthetic deltas were modelled using different sediment supply compositions, from coarse to very fine sand systems. The resultant sedimentary deposits are classified into architectural elements, and the grain size composition of each architectural element is studied over time. Facies that are extensive in their horizontal dimensions are often less abundant in three-dimensional preserved deposits. Between deltas, grain size composition of a specific architectural element type (e.g. mouth bars) are more similar than their corresponding sediment supply compositions. This is due to selective deposition of grain size classes across each architectural element type. This selective deposition causes overrepresentation of the same range of grain sizes, even for systems with different sediment supply compositions. When a particular supply composition does not contain enough of the overrepresented grain size class for a particular architectural element, that element will be under-supplied and constitute a smaller proportion of the overall delta deposits. It is imperative to account for over-representation of grain size classes in particular architectural elements when estimating palaeo-sediment supply, delta architecture and morphology from field data. Even when data availability/accessibility does not allow the inclusion of distal deposits in field studies, process-based simulations can contribute valuable information on sediment sorting patterns in three dimensions.
Initiation of backward erosion piping in uniform sands
The process of backward erosion piping poses a threat to dams and dikes on foundations of nonplastic sands and silts. The available models for design and predictions focus predominantly on the progression of the pipe. However, sand boils in the field will occur as a result of the initiation of sand transport. Although criteria are available for predicting sand boiling and heaving in columns, there is no model describing the initiation of piping in situations where the exit flow is not uniform, as is the case in most backward erosion experiments and situations in the field. This study compared laboratory experiments in which the process of initiation leads directly to failure with analytical and numerical groundwater flow calculations and heave criteria. The aim was to develop a model for the onset of pipe formation. It emerged that the sand bed needs to be fluidised over a distance of at least 20 times the grain diameter from the toe of the structure for a pipe to initiate. The proposed model explains the scale effects of grain size and configuration on a critical gradient. This approach clarifies the processes governing pipe initiation and progression and it can be used to establish a conservative estimate of the critical head in uniform sands, which is essential for laboratory work on this topic and for the appraisal of sand boils in practice.
Developments in modelling of backward erosion piping
One of the failure mechanisms that can affect the safety of a dyke or another water-retaining structure is backward erosion piping, a phenomenon that results in the formation of shallow pipes at the interface of a sandy or silty foundation and a cohesive cover layer. The models available for predicting the critical head at which the pipe progresses to the upstream side have been validated and adapted on the basis of experiments with two-dimensional (2D) configurations. However, the experimental base for backward erosion in three-dimensional (3D) configurations in which the flow concentrates towards one point, a situation that is commonly encountered in the field, is limited. This paper presents additional 3D configuration experiments at two scales with a range of sand types. The critical gradients, the formed pipes and the erosion mechanism were analysed for the available experiments, indicating that the erosion mechanism is more complex than previously assumed, as both erosion at the tip of the pipe (primary erosion) and in the pipe (secondary erosion) are relevant. In addition, a 3D configuration was found to result in significantly lower critical gradients than those predicted by an accepted calculation model calibrated on the basis of 2D experiments, a finding that is essential for the application of the model in the field.
32nd Symposium on the Application of Geophysics to Engineering and Environmental Problems 2019 - SAGEEP 2019 : electrical methods I : short abstracts (Portland, Oregon, 17-21 March 2019)
PVC membrane detection using ERT : modeling and laboratory experiments
PVC membranes are applied in the subsurface in infrastructural works, for example to prevent groundwater leakage. When the structure has to be adapted to changing conditions, the position of the PVC membrane needs to be known to reduce the risk of damage during the reconstruction works. So far, no “off-the-shelf” method is available to detect the position of the membrane with sufficient accuracy (0.1-0.2 m). Deltares is developing a method for the Ministry of Infrastructure, Rijkswaterstaat based on Electrical Resistivity Tomography (ERT).
Nighttime cooling of an urban pond
One of the processes by which open water cools the air during hot summer days is by storing the heat and increasing its own temperature. This heat is then released at night. The aim of this paper is to analyze this cooling process by quantifying the magnitude of turbulent, latent and sensible, heat fluxes in comparison to radiative and ground fluxes. A detailed vertical temperature profile was measured in an urban pond (∼70 cm deep with surface area of 3,627 m2) in Delft (NL) using Distributed Temperature Sensing for a period of one month. The results show that, from the total of 2.7 MJm−2 of heat released by the pond on an average summer night, 43% of the thermal energy is emitted as longwave radiation, 39% as latent energy, and only 11% as sensible heat. An additional 0.10–0.32 MJm−2 is transferred into the bottom of the lake. Temperature distribution and cooling of the water profile is influenced by weather conditions during the preceding day. This paper provides an insight into a behavioral pattern of an urban pond at night. The results can shed some light into the potential of urban bodies to increase the air temperature of their surroundings at night.
Amplification and deformation of tidal wave in the Upper Scheldt Estuary
The records of HW and LW in the most upper part of the Scheldt Estuary since 1971 have been analysed together with the daily river discharge. The tidal range, the hydraulic head and the ratio between the rising tide period to falling tide period have been determined for investigating the tidal amplification, the water surface slope along the river and the tidal asymmetry. The purpose of the investigation is to find out if a regime shift to high turbidity and strong tidal amplification is developing in the system. The results of the analysis show that both the hydraulic head and the tidal amplification have increased over time. The tide in this part of the estuary is flood-dominant, but the flood-dominancy is decreasing in time. These developments of the tide can be plausibly explained by a decrease of the river width followed by gradual deepening in the river. The most upper part of the Scheldt Estuary still behaves normally as a not too muddy system. No decisive answer can be given whether or not a regime shift towards a high-turbid system with strong tidal amplification may develop. How the system will develop depends on the change in capacity of pumping mud towards the upper reaches of the estuary. The increasing tidal amplitude can enhance this capacity although the flood-dominance itself is decreasing. Further study is recommended to better specify the potential danger of a regime shift to high-turbid system.
Effects of wave orbital velocity parameterization on nearshore sediment transport and decadal morphodynamics
Nearshore morphological modelling is challenging due to complex feedback between hydrodynamics, sediment transport and morphology bridging scales from seconds to years. Such modelling is, however, needed to assess long-term effects of changing climates on coastal environments, for example. Due to computational efficiency, the sediment transport driven by currents and waves often requires a parameterization of wave orbital velocities. A frequently used parameterization of skewness-only was found to overfeed the coast unrealistically on a timescale of years-decades. To improve this, we implemented a recently developed parameterization accounting for skewness and asymmetry in a morphodynamic model (Delft3D). The objective was to compare the effects of parameterizations on long-term coastal morphodynamics. We performed simulations with default and calibrated sediment transport settings, for idealized coastlines, and compared the results with measured data from analogue natural systems. The skewness-asymmetry parameterization was found to predict overall stable coastlines within the measured envelope with wave-related calibration factors within a factor of 2. In contrast, the original parameterization required stronger calibration, which further affected the alongshore transport rates, and yet predicted erosion in deeper areas and unrealistic accretion near the shoreline. The skewness-asymmetry parameterization opens up the possibility of more realistic long-term morphological modelling of complex coastal systems.
Can the implementation of the Water-Energy-Food Nexus support economic growth in the Mediterranean region? : the current status and the way forward
Water resources is a crucial environmental good for the function of the human societies and the ecosystems. Moreover, water is an important input for the economy and an indispensable factor for economic growth. Especially in regions that are facing water scarcity, the adoption of water management policies and approaches fostering the sustainable use of resources while promoting economic growth becomes an emerging issue. The Mediterranean region is one of the most vulnerable regions regarding the availability of water resources due to climate change and human activities. The Water-Energy-Food (WEF) Nexus offers an integrated approach analyzing the synergies and trade-offs between the different sectors in order to maximize the efficiency of using the resources, whereas adapting optimum policies and institutional arrangements. The Mediterranean is a region where we observe a large spectrum of issues emanating from water pollution and natural resource degradation to water scarcity, large amounts of food loss and waste and increasing demand for energy and food. Agricultural practices, urban development, demand management for water, and protection of ecosystems, particularly aquatic ecosystems, are areas of particular intervention available to the decision-makers in enhancing availability of water for the various water using sectors. In this context, the current policy note paper aims to address a major issue: how can the implementation of the WEF Nexus support the economic growth in the Mediterranean? Based on the outcome of an experts and stakeholders regional workshop, this paper presents the current status, including the opportunities and the practices of applying the WEF Nexus in the Mediterranean and draws specific recommendations for the way forward. Regarding the later, the strengthening of WEF Nexus in the Mediterranean requires a set of interventions to strengthen the institutional capacities, to enhance the finance mechanisms, to support the intra-regional dialogue as well, to enhance data collection and management, as well as to implement economic instruments and integrated economic approaches to measure the impact of Nexus into economy and employment.