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Onderzoek naar effecten aanwezigheid van TGG in dijken van de Perkpolder : eindrapportage
Thermisch Gereinigde Grond is grond die verhit is om organische verontreinigingen te verwijderen. Na reiniging kan TGG worden toegepast als ophoogmateriaal. In de Perkpolder is TGG toegepast in de kern van enkele dijkvakken. In een (verkennend en aanvullend) onderzoek zijn boringen in de TGG uitgevoerd, is de TGG bemonsterd en gekarakteriseerd. Dat is ook gedaan voor de grond en het grond- en oppervlaktewater in de directe omgeving van de TGG. Tijdens het verkennend onderzoek heeft de opdrachtgever ‘handgeboorde’ monsters genomen uit de TGG en vier emmers met resterende TGG beschikbaar gesteld. De resultaten namen de zorgen met betrekking tot de geotechnische eigenschappen niet weg en daarom is een aanvullend onderzoek uitgevoerd.
Coastal and port engineering in developing countries, 7th conference : proceedings of the international COPEDEC-VII (Dubai, U.A.E., 24-28 February 2008)
Gezocht: een rivierloods - Om de toekomst van onze rivieren
Bij Adaptive Delta Planning gaat het om de vraag hoe beslissingen te nemen over de inrichting en het beheer van deltagebieden. Het gaat daarbij om ruimtelijk beleid en het beheer van het natuurlijk systeem, maar vooral om de aanleg en het beheer van infrastructuur die leven in deze zeer dynamische milieus op de grens van land en zee mogelijk maakt. Beslissingen over dergelijke infrastructuur zijn beslissingen over hoe een land er eeuwen later bij ligt. En het zijn beslissingen over interventies in een natuurlijk systeem, waarin je niets kunt doen zonder dat het systeem daarop reageert. Samengevat staat Adaptive Delta Planning voor: anticiperen op toekomstige ontwikkelingen, voorkomen dat we daarbij zodanig afwentelen dat we er later spijt van krijgen, en voorkomen dat we vastlopen (lock-in).
Assessment of system effects of large-scale implementation of offshore wind in the southern North Sea
The possible upscaling in offshore wind for 2030 and even more so for 2050 in the southern North Sea is likely to have an impact on its functioning in very fundamental ways. Large-scale extraction of wind energy from the lower part of the atmosphere may affect local wind patterns, wave generation, tidal amplitudes, stratification of the water column, dynamics of suspended particles and bedload transport of sediment. Furthermore the infrastructure will provide extra hard substrate, not only on the bed (in the form of scour protection) but also providing attachment opportunities for biota in the upper layers of the water column. Such changes to the physical functioning of the North Sea may have far-reaching consequences for the ecological functioning, such as changes to the total amount and the timing of primary production, food availability of filter feeders and higher trophic levels, and habitat suitability for many species. In this report the potentially most important effects of the possible upscaling in offshore wind in the southern North Sea and the most important knowledge gaps have been identified.
Flow division dynamics in the Mekong Delta : application of a 1D-2D coupled model
The Mekong Delta constitutes a complicated multi-channel estuarine system, exchanging water with a delta-wide irrigation system. A 1D–2DH coupled numerical domain is calibrated and validated for water level and discharge during the dry season. This approach benefits from the simplicity of a 1D network within the estuarine and irrigation systems, while maintaining the interaction with the spatial tidal dynamics of the 2DH coastal domain. First, the role of the irrigation system on tidal dynamics is quantified; then, tidal propagation, freshwater budget, and the effect of offshore subtidal water level on discharge division are investigated. The results show that the complex irrigation system, in a friction-like manner, reduces the tidal amplitude up to 25%. The channels aggregate to 1% of the total water volume in the delta, while accommodating up to 10% of the tidal prism. Tidal amplitude reduces upstream, while subtidal water level is highly sensitive to upstream discharge, spring–neap cycles, and wind-generated oshore surge. Although cumulative discharge division within the estuarine network is consistent, temporal discharge division can be significantly sensitive to offshore wind-surge. During the dry season, it can reverse the expected subtidal discharge division within the time-scale of a few days and potentially influence salt intrusion.
De geschiedenis van het hydraulica laboratorium
Het boekje brengt meer dan een halve eeuw geschiedenis van de Wageningse hydraulica in beeld.
The shadow price of irrigation water in major groundwater depleting countries
In many semi‐arid regions with irrigation, the depletion rate of groundwater resources has increased substantially during the last decades. A possible reason for this is that the price that users pay for their water does not reflect its scarcity and value. An alternative way to assess the perceived value of water is calculating its shadow price, which is defined here as the marginal value produced, and relates to the efficiency gain from current reallocation. Here, we determine the shadow price of water used for irrigation for the most important groundwater depleting countries and for four staple crops and one cash crop. To quantify the shadow price, the relation between the output and water input is represented using production functions. We use globally available panel data on country‐specific crop yields and prices together with crop‐specific water consumption, calculated with the global hydrological model PCR‐GLOBWB, to parameterize the production function by country and crop with econometric analyses. Our results show that the variation of shadow prices for staple crops within several countries is high, indicating economically inefficient use of water resources, including non‐renewable groundwater. We also analyse the effects of re‐allocating irrigation water between crops, showing that changes in water allocation could either lead to an increase in the economic efficiency of water use or large reductions in irrigation water consumption. Our study thus provides a hydroeconomic basis to stimulate sustainable use of finite groundwater resources globally.
Paleo-hydrogeological reconstruction of the fresh-saline groundwater distribution in the Vietnamese Mekong Delta since the late Pleistocene
Present-day distribution of fresh-saline groundwater is highly heterogeneous in the Mekong Delta (MKD). Close to the coastline, fresh groundwater is found in aquifers up to 500 m below ground surface. To gain better insight into the fresh-saline groundwater evolution since the late Pleistocene, we simulated long-term groundwater flow and salt transport in a two-dimensional NW-SW cross-section over the MKD. To fully consider the regression and transgression phases of sea-level changes over the past 60 ka, variable-density groundwater flow and salt transport was simulated with SEAWAT to reproduce characteristics of the present-day distribution of freshsaline groundwater and its age. We simulated nine scenarios to evaluate the most important factors controlling freshening and salinization processes of the MKD groundwater system. We compared the final model stage with present day observations of groundwater salinity and age. New hydrological insights for the region: The sedimentation and erosion processes, related to sea-level changes over the last 60 ka, were important drivers of the fresh-saline distribution in the present MKD. The two-dimensional model indicates that most fresh groundwater in the MKD was recharged 60–12 ka before present, when the sea-level was at its lowest and the top sedimentary layers had a relatively high permeability. Due to deposition of a clayey top layer during the Holocene, at present, groundwater recharge of the deeper MKD groundwater system is very limited.
Long-term population dynamics of dreissenid mussels (Dreissena polymorpha and D. rostriformis) : a cross-system analysis
Dreissenid mussels (including the zebra mussel Dreissena polymorpha and the quagga mussel D. rostriformis) are among the world’s most notorious invasive species, with large and widespread ecological and economic effects. However, their long-term population dynamics are poorly known, even though these dynamics are critical to determining impacts and effective management. We gathered and analyzed 67 long-term (>10 yr) data sets on dreissenid populations from lakes and rivers across Europe and North America. We addressed five questions: (1) How do Dreissena populations change through time? (2) Specifically, do Dreissena populations decline substantially after an initial outbreak phase? (3) Do different measures of population performance (biomass or density of settled animals, veliger density, recruitment of young) follow the same patterns through time? (4) How do the numbers or biomass of zebra mussels or of both species combined change after the quagga mussel arrives? (5) How does body size change over time? We also considered whether current data on long-term dynamics of Dreissena populations are adequate for science and management. Individual Dreissena populations showed a wide range of temporal dynamics, but we could detect only two general patterns that applied across many populations: (1) Populations of both species increased rapidly in the first 1–2 yr after appearance, and (2) quagga mussels appeared later than zebra mussels and usually quickly caused large declines in zebra mussel populations. We found little evidence that combined Dreissena populations declined over the long term. Different measures of population performance were not congruent; the temporal dynamics of one life stage or population attribute cannot generally be accurately inferred from the dynamics of another. We found no consistent patterns in the long-term dynamics of body size. The long-term dynamics of Dreissena populations probably are driven by the ecological characteristics (e.g., predation, nutrient inputs, water temperature) and their temporal changes at individual sites rather than following a generalized time course that applies across many sites. Existing long-term data sets on dreissenid populations, although clearly valuable, are inadequate to meet research and management needs. Data sets could be improved by standardizing sampling designs and methods, routinely collecting more variables, and increasing support.