Revisiting the morphological method in two-dimensions to quantify bed-material transport in braided rivers     

Gilles Antoniazza  Maarten Bakker  Stuart N. Lane 《地球表面变化过程与地形》2019,44(11):2251-2267

Research in the 1990s showed that bed-material transport rates could be estimated at the reach scale in both one-dimension and, over small spatial scales (10s of m), in two-dimensions. The limit on the latter was the spatial scale over which it was possible to obtain distributed data on morphological change. Here, we revisit the morphological method given progress in both topographical data acquisition and hydraulic modelling. The bed-material transport needed to conserve mass is calculated in both one and two dimensions for a 1600 m × 300 m Alpine braided river “laboratory”. High-resolution topographical data were acquired by laser scanning to quantify Digital Elevation Models (DEMs), and morphological changes caused by the flushing of the water intake were derived from repeated surveys. Based on DEMs of differences, 1D bed-material transport rates were calculated using the morphological method. Then, a 2D hydraulic model was combined with a topographic correction to route sediment through the network of braided channels and to obtain a spatially variable estimate of transport in both downstream and cross-stream directions. Monte Carlo simulation was applied to the routing model parameters, allowing identification of the most probable parameter values needed to minimize negative transport. The results show that within-section spatial compensation of erosion and deposition using the 1D treatment leads to substantial local errors in transport rate estimates, to a degree related to braiding intensity. Even though the 2D application showed that a large proportion of the total transport was actually concentrated into one main channel during the studied low flow event, the proportion of transport in secondary anabranches is substantial when the river starts braiding. Investigations of the effects of DEM resolution, competent flow duration and survey frequency related to ‘travelling bedload’ and sequential erosion-deposition emphasized the critical importance of careful data collection in the application of the morphological method. © 2019 John Wiley & Sons, Ltd.  相似文献   

A New Operational Paradigm for Small‐Scale ASR in Saline Aquifers     

Marloes van Ginkel  Theo N. Olsthoorn  Mark Bakker 《Ground water》2014,52(5):685-693

A new operational paradigm is presented for small‐scale aquifer storage and recovery systems (ASR) in saline aquifers. Regular ASR is often not feasible for small‐scale storage in saline aquifers because fresh water floats to the top of the aquifer where it is unrecoverable. In the new paradigm, fresh water storage is combined with salt water extraction from below the fresh water cone. The salt water extraction counteracts the buoyancy due to the density difference between fresh water and salt water, thus preventing the fresh water from floating up. The proposed approach is applied to assess the feasibility of ASR for the seasonal storage of fresh water produced by desalination plants in tourist resorts along the Egyptian Red Sea coast. In these situations, the continuous extraction of salt water can be used for desalination purposes. An analytical Dupuit solution is presented for the steady flow of salt water toward a well with a volume of fresh water floating on top of the cone of depression. The required salt water discharge for the storage of a given volume of fresh water can be computed with the analytical solution. Numerical modeling is applied to determine how the stored fresh water can be recovered. Three recovery approaches are examined. Fresh water recovery rates on the order of 70% are achievable when salt water is extracted in high volumes, subsurface impermeable barriers are constructed at a distance from the well, or several fresh water recovery drains are used. The effect of ambient flow and interruptions of salt water pumping on the recovery efficiency are reported.  相似文献   

Raman spectroscopy of pure H2O and NaCl-H2O containing synthetic fluid inclusions in quartz—a study of polarization effects     

M. Baumgartner  R. J. Bakker 《Mineralogy and Petrology》2009,95(1-2):1-15

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Flow dynamics at the origin of thin clayey sand lacustrine turbidites: Examples from Lake Hazar,Turkey          下载免费PDF全文

Sophie Hage  Aurélia Hubert‐Ferrari  Laura Lamair  Ulaş Avşar  Meriam El Ouahabi  Maarten Van Daele  Frédéric Boulvain  Mohamed Ali Bahri  Alain Seret  Alain Plenevaux 《Sedimentology》2017,64(7):1929-1956

Turbidity currents and their deposits can be investigated using several methods, i.e. direct monitoring, physical and numerical modelling, sediment cores and outcrops. The present study focused on thin clayey sand turbidites found in Lake Hazar (Turkey) occurring in eleven clusters of closely spaced thin beds. Depositional processes and sources for three of those eleven clusters are studied at three coring sites. Bathymetrical data and seismic reflection profiles are used to understand the specific geomorphology of each site. X‐ray, thin sections and CT scan imagery combined with grain‐size, geochemical and mineralogical measurements on the cores allow characterization of the turbidites. Turbidites included in each cluster were produced by remobilization of surficial slope sediment, a process identified in very few studies worldwide. Three types of turbidites are distinguished and compared with deposits obtained in flume studies published in the literature. Type 1 is made of an ungraded clayey silt layer issued from a cohesive flow. Type 2 is composed of a partially graded clayey sand layer overlain by a mud cap, attributed to a transitional flow. Type 3 corresponds to a graded clayey sand layer overlain by a mud cap issued from a turbulence‐dominated flow. While the published experimental studies show that turbulence is damped by cohesion for low clay content, type 3 deposits of this study show evidence for a turbulence‐dominated mechanism despite their high clay content. This divergence may in part relate to input variables, such as water chemistry and clay mineralogy, that are not routinely considered in experimental studies. Furthermore, the large sedimentological variety observed in the turbidites from one coring site to another is related to the evolution of a sediment flow within a field‐scale basin made of a complex physiography that cannot be tackled by flume experiments.  相似文献   

500 years of trophic-state history of a hypertrophic Dutch dike-breach lake     

Emiliya P. Kirilova  Maarten van Hardenbroek  Oliver Heiri  Holger Cremer  André F. Lotter 《Journal of Paleolimnology》2010,43(4):829-842

We present a palaeolimnological study encompassing five centuries of trophic-state change of the dike-breach lake De Waay located on the Rhine-Meuse delta (the Netherlands). Diatom-inferred total phosphorus (TP) concentrations indicate hypertrophic epilimnetic conditions (>300 μg l⁻¹ TP) since the formation of the lake in the fifteenth century until the end of the eighteenth century. Cladocera data support the reconstructed trophic state and indicate turbid conditions in lake De Waay during this period. High inferred TP concentrations as well as the amount of Ti in the sediment reflect numerous flooding events. From the nineteenth century onwards reconstructed TP concentrations decreased to 40–150 μg l⁻¹ due to improvements in sewage and dike systems that considerably diminished direct river flooding and seepage-derived nutrients. As a consequence, the increased stability of littoral habitats led to an increased diversity of the Cladocera assemblages. The most significant decrease in TP concentrations to ~40 μg l⁻¹ occurred between about 1900 and 1930. This mesotrophic phase was a consequence of the isolation of the lake from catchment drainage and the introduction of a highly elaborate flood control during this period. However, since the mid twentieth century a eutrophication trend is preserved in the record, likely related to increased agricultural activity in the vicinity of the lake. Our results emphasize that land-use and trophic-state history must be taken into account when evaluating the ecological status of lakes for water management and protection actions, especially for lakes in landscapes that are strongly modified by human action.  相似文献   

Distinct patterns of interaction between vegetation and morphodynamics          下载免费PDF全文

Mijke van Oorschot  Maarten Kleinhans  Gertjan Geerling  Hans Middelkoop 《地球表面变化过程与地形》2016,41(6):791-808

Dynamic interaction between river morphodynamics and vegetation affects river channel patterns and populations of riparian species. A range of numerical models exists to investigate the interaction between vegetation and morphodynamics. However, many of these models oversimplify either the morphodynamics or the vegetation dynamics, which hampers the development of predictive models for river management. We have developed a model coupling advanced morphodynamics and dynamic vegetation, which is innovative because it includes dynamic ecological processes and progressing vegetation characteristics as opposed to commonly used static vegetation without growth and mortality. Our objective is to understand and quantify the effects of vegetation‐type dependent settling, growth and mortality on the river pattern and morphodynamics of a meandering river. We compared several dynamic vegetation scenarios with different functional trait sets to reference scenarios without vegetation and with static vegetation without growth and mortality. We find distinct differences in morphodynamics and river morphology. The default dynamic vegetation scenario, based on two Salicaceae species, shows an active meandering behaviour, while the static vegetation scenario develops into a static, vegetation‐dominated state. The diverse vegetation patterns in the dynamic scenario reduce lateral migration, increase meander migration rate and create a smoother floodplain compared to the static scenario. Dynamic vegetation results in typical vegetation patterns, vegetation age distribution and river patterns as observed in the field. We show a quantitative interaction between vegetation and morphodynamics, where increasing vegetation cover decreases sediment transport rates. Furthermore, differences in vegetation colonization, density and survival create distinct patterns in river morphology, showing that vegetation properties and dynamics drive the formation of different river morphologies. Our model demonstrates the high sensitivity of channel morphodynamics to various species traits, an understanding which is required for floodplain and stream restoration and more realistic modelling of long‐term river development. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Potential evidence of fossilised Neoproterozoic deep life: SEM observations on calcite veins from Oppaminda Creek,Arkaroola, South Australia     

Paul D. Bons  Michael Montenari  Ronald J. Bakker  Marlina A. Elburg 《International Journal of Earth Sciences》2009,98(2):327-343

Scanning electron microscopy revealed micron-sized globular and coccoid objects, associated with filaments and mucus-like patches in antitaxial fibrous calcite veins from Oppaminda Creek, Northern Flinders Ranges, South Australia. Chemically the objects only differ from their calcite (CaCO₃) matrix by a higher sulphur content. The ∼585 Ma veins formed at about 3–6 km below the surface. Fluid inclusions indicate a temperature of formation of about 60–80°C, and not exceeding 100°C. A non-biogenic origin of the objects is discussed, but considered unlikely. Instead, morphology, chemistry and size distribution all indicate that the objects are fossilised microbes that lived in the veins at the time and depth of vein formation.  相似文献   

Erodibility of soft freshwater sediments in Markermeer: the role of bioturbation by meiobenthic fauna     

Miguel Angel de Lucas Pardo  Marieke Bakker  Thijs van Kessel  Francesco Cozzoli  Johan Christian Winterwerp 《Ocean Dynamics》2013,63(9-10):1137-1150

The Markermeer is a large and shallow man-made freshwater lake in the Netherlands, characterized by its high turbidity. As part of a study aiming to mitigate this high turbidity, we studied the water–bed exchange processes of the lake’s muddy bed. The upper centimeter’s–decimeter’s of the lake bed sediments mainly consists of soft anoxic mud. Recent measurements have proved the existence of a thin oxic layer on top of this soft anoxic mud. This oxic layer, which is much easier to be eroded than the anoxic mud, is believed to be related with Markermeer’s high-turbidity levels. Our hypothesis is that the thin oxic layer develops from the anoxic mud, enhanced by bioturbation. Actually, we will demonstrate that it is the bioturbated state of the bed that increases its erodability, and not the oxidation state of the sediments. In particular, we will refer to bioturbation caused by meiobenthic fauna. The objective of this study is therefore to determine the influence of the development of the thin oxic layer on the water–bed exchange processes, as well as to establish the role of bioturbation on those processes. This is done by quantifying the erosion rate as a function of bed shear stresses, and at different stages of the development of the oxic layer. Our experiments show that bioturbation increases the rate at which Markermeer sediments are eroded by almost an order of magnitude. The short-term fine sediment dynamics in Markermeer are found to be driven by the complex and highly dynamic interactions between physics, chemistry, and biology. Finally, the long-term fine sediment dynamics are driven by the erosion of the historical deposits in the lake’s bed, which is only possible after bioturbation, and which leads to an increase of the stock of sediments in the lake’s muddy bed.  相似文献   

River bifurcations and avulsion     

Maarten G. Kleinhans  Richard J. Hardy 《地球表面变化过程与地形》2013,38(3):317-318

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Challenges of an integrated water resource management for the Distrito Federal, Western Central Brazil: climate, land-use and water resources     

C. Lorz  G. Abbt-Braun  F. Bakker  P. Borges  H. B?rnick  L. Fortes  F. H. Frimmel  A. Gaffron  N. Hebben  R. H?fer  F. Makeschin  K. Neder  L. H. Roig  B. Steiniger  M. Strauch  D. Walde  H. Wei?  E. Worch  J. Wummel 《Environmental Earth Sciences》2012,65(5):1575-1586

Land-use/cover change (LUCC) and climate change are major controlling factors for water resources in the Distrito Federal in Western Central Brazil. Dynamic LUCC in the region has severe impacts on water resources, while climate changes during the last three decades is thought to have only moderate effects. LUCC affects water quantity mostly during base flow conditions. River basins with substantial expansion of agriculture since the end 1970s show a dramatic decrease of base flow discharge by 40?C70%, presumably due to irrigation. In contrast, the effects of urbanization on runoff are less distinct, since factors controlling runoff generation might be more variable. For water quality, we found urban areas to have a strong influence on the parameters CSB, NH₄ ⁺, and suspended solids. In addition, we assume emerging pollutants, e.g. organic (micro)pollutants, might play a major role in the future. The project IWAS-áGUA DF focuses on creating the scientific base to face these problems in frame of an IWRM concept for the region. Results of our study will be a contribution to an IRWM concept for the Distrito Federal and will help to maintain high standards in water supply for the region.  相似文献