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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.
Groundwater flow modeling using iMOD for Barva and Colima aquifers in the central valley of Costa Rica : validation of a conceptual model using tracer data
A stationary numerical model of groundwater flow was developed using iMOD to better understand the recharge processes within Barva and Colima aquifers (BCS), located in the northwestern region of the Central Valley of Costa Rica. Lithological information was used to develop conceptual model representing the complexity of the system, defined as high transmissivities, low storage capacity, and steep hydraulic gradients. Due to the lack of more detailed lithological and hydrometric data to perform robust calibrations, the system was studied by analyzing water flux dynamics using the iMOD particle tracer and water balance tools. The validation process was done by comparing the results of each simulation with the potential recharge elevation (PRE) derived from the ages of existing noble gases (tritium/helium) at different wells and springs in the system. Tracer estimations indicate a groundwater age (GWA) ranging from 2.3 to 71 years. Based on the tracer information, two hypotheses of PRE were evaluated. The first scenario (H01), with a PRE between 1,500 to 2,500 m a.s.l., and a second one (H02), with a PRE between 1,300 to 1,500 m a.s.l. Results from H01 were the most reliable: 77% of the particles dropped in the PRE were captured by the Lower Colima aquifer, with a GWA ranging from 1 to 45 years. Although the results reflect the dynamic complex fluxes, more information is needed to understand the influence of surface water and recharge rates on groundwater levels in order to improve and calibrate the model as a reliable water management tool.
Liquefaction flow slides in large flumes
Liquefaction flow slides in sand have been investigated during an extensive experimental research programme during the period 1973–1977 on behalf of the design of the storm surge barrier in the Oosterschelde estuary. The programme included more than a hundred tests in large- and medium-sized flumes on submerged, loosely packed sand bodies. Each sand body had a horizontal surface and a very steep, supported slope as initial boundaries. Retrogressing liquefaction flow slides with high retrogression velocity and large retrogression distance occurred in several tests with very loosely packed sand. Retrogression velocities and distances in the other tests were just a fraction of those in first mentioned tests, although liquefaction occurred in some of them. The test set-up, measurements and results of the tests are described in this paper. An interpretation of the liquefaction flow slide process as a sequence of several interacting sub-processes is presented as well. Finally, tentative scaling rules are given and compared with observations.
Temperature buffering by groundwater in ecologically valuable lowland streams under current and future climate conditions
Groundwater seepage influences the temperature of streams and rivers by providing a relatively cool input in summer and warm input in winter. Because of this, groundwater seepage can be a determining factor in the provision of suitable water temperatures for aquatic biota. Climate warming affects stream and groundwater temperatures, and changes the thermal characteristics of streams leading to the potential disappearance of habitats. In this study the importance of groundwater for the temperature of two Dutch lowland streams and its possible role in mitigating the effects of climate change was determined by combining field measurements and a modelling experiment. Stream temperature measurements using fibre optic cables (FO-DTS) and sampling of 222Rn were done to map localized groundwater inflow. Several springs and seepage ‘hot-spots’ were located which buffered the water temperature in summer and winter. A stream temperature model was constructed and calibrated using the FO-DTS-measurements to quantify the energy fluxes acting on stream water. This way, the contribution to the stream thermal budget of direct solar radiation, air temperature and seepage were separated. The model was then used to simulate the effects of changes in shading, groundwater seepage and climate. Shading was shown to be an important control on summer temperature maxima. Groundwater seepage seemed to buffer the effect of climate warming, potentially making groundwater dominated streams more climate robust. Protecting groundwater resources in a changing climate is important for the survival of aquatic species in groundwater-fed systems, as groundwater seepage both sustains flow and buffers temperature extremes.
Voortgangsbericht KPP-project Versterking Onderzoek Waterveiligheid (no. 4)
Samen met enkele andere partijen doet Deltares voor Rijkswaterstaat onderzoek op het gebied van waterveiligheid. Dit gebeurt in het kader van het KPP-project Versterking Onderzoek Waterveiligheid, waarbij KPP staat voor kennis primaire processen. Rijkswaterstaat gebruikt de uitkomsten van het onderzoek om zijn primaire proces rondom waterveiligheid te verbeteren. Bij deze verbeteringen gaat het om kostenbesparingen bij aanleg, beheer en onderhoud, en ook om betere risicobeheersing en versterking van het imago van Rijkswaterstaat. Het merendeel van de projecten wordt in NKWK-kader uitgevoerd, dus samen met en met medefinanciering van andere partijen uit de sector, zoals STOWA, individuele waterschappen en TU Delft. Dit vierde voortgangsbericht brengt de werkzaamheden in beeld die we in 2018 hebben uitgevoerd. Daarbij geven we een inschatting van de meerwaarde van de projecten voor Rijkswaterstaat. Bij sommige projecten geeft Rijkswaterstaat ook zelf aan waarom het project van belang is.