1,720,952 research outputs found
Flow patterns around longitudinal training dams
No full textWith the intention to reduce the negative effects of ongoing bed erosion, as well as to improve several other river functions such as protection against floods, provision of safe and efficient navigation and ecology, a ‘pilot project longitudinal training dams’ was initiated. The training dams have recently been implemented in the Waal between Tiel and Sind Andries. In this project, river groynes have been completely removed and replaced by dams that lie parallel to the river bank. With help of the longitudinal training dams, a two-channel river system is created in which the river is divided into a main and side channel. The dams are placed in a continuous manner with openings in between that are relatively small compared to the dam length. At the beginning and end of the dam an inlet and outlet region is situated, as shown in Fig. 1. The combination of inlet and openings allows for water and sediment to be divided between the main and the side channel. Both inlet and openings are constructed with the help of a porous rock-layer. The crest heights can be altered by adding or removing stones. This is expected to influence the amount of water and sediment entering the side channel and can therefore be used as a regulation tool. A.J.F. Hoitink, T.V. de Ruijsscher, T.J. Geertsema, B. Makaske, J. Wallinga, J.H.J. Candel, J. Poelman (Eds.) NCR days 2017, Febr. 1-3, 2017. Book of abstracts, NCR publication 41-2017.Rivers, Ports, Waterways and Dredging EngineeringHydraulic Structures and Flood RiskEnvironmental Fluid Mechanic
Self-organizing avulsions in an endorheic dryland river system
No full textAccepted author manuscriptApplied Geolog
Luminescence at the end of the tunnelling - Investigating charge transfer mechanisms and luminescence dating methods for feldspar minerals
No full textThis thesis comprises analyses of mineral physics with an application in geology and archeology. The thesis contributes to the development of feldspar luminescence dating methods in order to extend the applicable age range of feldspar luminescence dating in the Quaternary (last 2.6 Ma). The research is divided into three parts: 1) Understanding feldspar luminescence by advancing the physical model that describes optical charge transfer mechanisms in natural feldspars; 2) Validating the recently developed method of post-IR IRSL dating and testing post-IR IRSL laboratory protocols used for dating; and 3) Investigating the bleaching behaviour of post-IR IRSL signals. The results presented in the thesis add to the understanding of the luminescence processes in feldspar minerals and to the applicability of feldspar post-IR IRSL dating. The charge transfer processes that give rise to luminescence in feldspar are complex and difficult to define, but the experiments presented here have yielded valuable additions to understanding these mechanisms. The current state-of-the-art of feldspar luminescence dating methods enables extension of the age range on which luminescence dating yields reliable ages up to ~500 ka.FAMEApplied Science
Causes of long-term bed degradation in rivers: Setup of research
No full textThe main objective of this research is to improve our understanding of the relative contribution of the causes of long-term bed degradation in Rhine and other degrading rivers. That is, the research is intended to quantify past channel adjustment processes, mainly bed degradation and bed surface coarsening over time and space, and to predict future trends, in bed elevation and bed surface texture, resulting from past interventions. A.J.F. Hoitink, T.V. de Ruijsscher, T.J. Geertsema, B. Makaske, J. Wallinga, J.H.J. Candel, J. Poelman (Eds.) NCR days 2017, Febr. 1-3, 2017. Book of abstracts, NCR publication 41-2017.Rivers, Ports, Waterways and Dredging Engineerin
Luminescence dating of Netherlands’ sediments
No full textOver the last decades luminescence dating techniques have been developed that allow earth scientists to determine the time of deposition of sediments. In this contribution we review: 1) the development of the methodology; 2) tests of the reliability of luminescence dating on Netherlands’ sediments; and 3) geological applications of the method in the Netherlands. Our review shows that optically stimulated luminescence dating of quartz grains using the single aliquot regenerative dose method yields results in agreement with independent age control for deposits ranging in age from a few years up to 125 ka. Optical dating of quartz has successfully been applied to sediments from a wide range of depositional environments such as coastal dunes, cover sands, fluvial channel deposits, colluvial deposits and fimic soils. These results demonstrate that optical dating is a powerful tool to explore the natural archive of the Netherlands’ subsurface.Civil Engineering and Geoscience
Shining a light on the past
No full textInvisible to the naked eye, pinpricks of light from minerals reveal how long they have been hidden inside a brick. Researchers at Delft University of Technology have ways of detecting the light, but their dating method yields results that don¿t tally with those of archeologists
Closing secondary channels in large sand-bed braided rivers
No full textLarge braided rivers have many beneficial roles, from provision of water for agriculture and means of transport to various ecosystem services. However, they are geomorphologically active, which results in problems with bank erosion and navigability. Some of the largest rivers may have bank line shifts of hundreds of meters per year (Baki and Gan, 2012). This leads to loss of homes and good agricultural land, destruction of infrastructure and flood protection works. River training measures are used to combat these problems and reclaim lost land. Conventional structures, mostly developed in smaller watercourses, are problematic in very large and unpredictable braided rivers, due to their required size, cost, inflexibility and environmental disturbance (Nakagawa et al., 2013). More adaptable, cheaper (local materials) and less disturbing measures are required. One promising possibility is the use of recurrent measures (such as bandals) to close aggressive secondary channels (Mosselman, 2006). Coupled with a prediction model for planform changes and erosion (such as Klaassen et al., 1993), this can be a very flexible and efficient way to protect nearby land against bank erosion, start land reclamation or improve navigability. A.J.F. Hoitink, T.V. de Ruijsscher, T.J. Geertsema, B. Makaske, J. Wallinga, J.H.J. Candel, J. Poelman (Eds.) NCR days 2017, Febr. 1-3, 2017. Book of abstracts, NCR publication 41-2017.Rivers, Ports, Waterways and Dredging Engineerin
Bank erosion processes in waterways
No full textWaterways serve for several functions besides transporting goods and people. The ecological importance of navigable rivers has taken much attention during recent decades bringing efforts to improve these natural corridors for fauna and flora (Boeters et al., 1997). Following the policy of the European Water Framework Directive (WFD), many Dutch river reaches have been recently restored through the removal of bank protections in search for better riparian habitats (Florsheim et al., 2009), but they also result exposed to erosive forces. Large uncertainties generally surround the prediction of erosion rates (e.g. Samadi et al., 2009) due to complex flow characteristics in the near-bank region, variable soil properties, etc. A better understanding of bank erosion processes is then of interest to predict erosion rates and improve the design of future interventions. A.J.F. Hoitink, T.V. de Ruijsscher, T.J. Geertsema, B. Makaske, J. Wallinga, J.H.J. Candel, J. Poelman (Eds.) NCR days 2017, Febr. 1-3, 2017. Book of abstracts, NCR publication 41-2017.Rivers, Ports, Waterways and Dredging EngineeringEnvironmental Fluid Mechanic
Optically stimulated luminescence signals under various stimulation modes assuming first-order kinetics
Full text linkWe present mathematical descriptions of optically stimulated luminescence (OSL) signals under linearly, hyperbolically, exponentially, and reciprocally increasing stimulation intensity for a one-trap one-recombination-center model assuming charge transfer governed by first-order kinetics. Depending on the stimulation mode, the OSL signal can be monotonically increasing, monotonically decreasing, show a peak shape, or be constant. The shape of the OSL signal is controlled by a stimulation-rate parameter (governed by the stimulation mode) and a decay-rate parameter that is proportional to the photoionization cross section. We demonstrate that the luminescence signal as a function of time under exponentially increasing-optical stimulation (EM-OSL) shows the same evolution in time as the luminescence signal under hyperbolically increasing-thermal stimulation (HM-TL). This similarity allows a new interpretation of the I?t versus In?t plot, where I is the optically stimulated luminescence intensity and t is the time. For a phosphor with several optically active traps, the OSL signal will contain several components. We show that the mathematical descriptions of the OSL signals under all stimulation modes can be related to the description of the OSL signal derived with continuous-wave (CW) stimulation. These so-called pseudo-OSL signals are helpful in a visualization of the various components in the OSL signal, where different pseudo-OSL transformations can be used to amplify different aspects. We demonstrate that the stimulation mode or pseudo-OSL transformation used has no effect on the overlap of the different OSL components. This implies that for the separation of multiple OSL components there is, in principle, no preference for a specific stimulation mode or pseudo-OSL transformation. Finally, we present a transformation related to hyperbolically modulated OSL which does facilitate separation of OSL components and may be of use for determining component specific photoionization cross sections or trapped-charge concentrations.Radiation, Radionuclides and ReactorsApplied Science
The effect of transverse bed slope and sediment mobility on bend sorting
No full textLateral sorting (= bend sorting) is observed in natural meanders, where the inner and outer bend are fairly fine and coarse, respectively (e.g. Julien and Anthony, 2002; Clayton and Pitlick, 2007). This is caused by the mass differences between grains on a transverse slope, leading to coarser grains being dragged down net more than finer grains (Ikeda et al., 1987). The slope of the transverse bed influences the degree of bend sorting greatly. Also vertical sorting occurs. Grainflows at the lee side of dunes result in a net fining upward trend (Kleinhans, 2005). The degree of vertical sorting depends on flow velocity and sediment mixture characteristics. Most previous studies focused on the development of the transverse slope using small ranges of uniform sediment, so spatial sorting was absent. Yet, it was argued that there is a feedback mechanism between bend sorting and the transverse slope (Ikeda et al., 1987). So, it is of key importance to attain better understanding of how sorting in river bends comes about, which can improve current numerical models. It is the objective of this study to examine experimentally the effect of transverse bed slope and sediment mobility on spatial sorting of bed load in a meander. A.J.F. Hoitink, T.V. de Ruijsscher, T.J. Geertsema, B. Makaske, J. Wallinga, J.H.J. Candel, J. Poelman (Eds.) NCR days 2017, Febr. 1-3, 2017. Book of abstracts, NCR publication 41-2017.Environmental Fluid Mechanic
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