@phdthesis{Mamede2008,
  author    = {Mamede, George Leite},
  title     = {Reservoir sedimentation in dryland catchments : modelling and management},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17047},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {Semi-arid environments are mainly characterized by scarce water resources and are usually subject to risks of water stress. In these regions, water supply for drinking and irrigation purposes depends strongly on storage in surface reservoirs and sediment deposition in these reservoirs affects adversely the water storage. In order to reproduce the complex behaviour of sediment deposition in reservoirs located in semi-arid environments and the effects of using sediment management techniques, a reservoir sedimentation model is developed and coupled within the WASA-SED model, which simulates rainfall-runoff processes and sediment transport at the hillslope and river network. The reservoir sedimentation model consists of two modelling approaches, which may be applied according to reservoir size and data availability. For reservoirs with information about their geometric features (reservoir topography, stage-area and stage-volume curves) and physical properties of sediment deposits, such as deposition thickness, grain size distribution of sediment deposits and sediment densities, a detailed modelling approach of reservoir sedimentation may be applied. For reservoirs without those characteristics, a simplified modelling approach is used. The detailed modelling approach of reservoir sedimentation enables the assessment of sediment deposition pattern in reservoirs and the evaluation of sediment release efficiency of sediment management techniques. It simulates sediment transport along the longitudinal profile of a reservoir. The reservoir is divided into cross sections to elaborate the sediment budget. The sediment transport component is calculated using a non-uniform sediment transport approach based on the concept of sediment carrying capacity. Four different sediment-transport equations can be selected for the simulations. The simplified modelling approach of reservoir sedimentation is suitable to simulate water and sediment transfer in dense reservoirs network. Nevertheless, it allows simulating neither sediment management techniques, nor spatial distribution of sedimentation. In this approach, the reservoirs are classified into small and strategic reservoirs according to their location and size. Strategic reservoirs are medium and large-sized reservoirs located on main rivers at the sub-basin's outlet or reservoirs of particular interest. The small reservoirs are located at tributary streams and represented in the model in an aggregate manner by grouping them into size classes according to their storage capacity. A cascade routing scheme is used to describe the upstream-downstream position of the reservoir classes. The water and sediment balances of small reservoirs are computed for one hypothetical representative reservoir of mean characteristics. Sediment trapping efficiency and effluent grain size distribution are estimated using the overflow rate concept. Three model applications are carried out within this research, as follows: • The detailed modelling approach of reservoir sedimentation is applied to the 92.2 Mm³ Barasona Reservoir, located in the foothills of the Central Pyrenees (Aragon, Spain). A two-stage calibration was performed to account for changes on the sediment deposition pattern caused by sediment management. The reservoir sedimentation model is then validated for another simulation period which confirms that the processes related to reservoir sedimentation are well represented by the model. • An application is carried out to the 933-km² Bengu{\^e} catchment, located in the semi-arid region of Northeast Brazil. The catchment is characterized by a dense reservoir network, covering almost 45\% of the catchment area, with a significant lack of data. Water and sediment balances of those reservoirs are computed using the simplified modelling approach. Three spatial configurations describing the cascade routing scheme are tested. • The reservoir sedimentation model is applied again to the Barasona reservoir to evaluate the sediment release efficiency of sediment management strategies. Cost analysis is presented to help in the choice of the most promising sediment management technique for that situation. Thus, the model enables the assessment of technical features of the sediment management strategies. Overall, simulation results are characterized by large uncertainties, partly due to low data availability and also due to uncertainties of the model structure to adequately represent the processes related to reservoir sedimentation.},
  language  = {de}
}
@phdthesis{Nguyen2014,
  author    = {Nguyen, Van Manh},
  title     = {Large-scale floodplain sediment dynamics in the Mekong Delta : present state and future prospects},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-72512},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 95},
  year      = {2014},
  abstract  = {The Mekong Delta (MD) sustains the livelihood and food security of millions of people in Vietnam and Cambodia. It is known as the "rice bowl" of South East Asia and has one of the world's most productive fisheries. Sediment dynamics play a major role for the high productivity of agriculture and fishery in the delta. However, the MD is threatened by climate change, sea level rise and unsustainable development activities in the Mekong Basin. But despite its importance and the expected threats, the understanding of the present and future sediment dynamics in the MD is very limited. This is a consequence of its large extent, the intricate system of rivers, channels and floodplains and the scarcity of observations. Thus this thesis aimed at (1) the quantification of suspended sediment dynamics and associated sediment-nutrient deposition in floodplains of the MD, and (2) assessed the impacts of likely future boundary changes on the sediment dynamics in the MD. The applied methodology combines field experiments and numerical simulation to quantify and predict the sediment dynamics in the entire delta in a spatially explicit manner. The experimental part consists of a comprehensive procedure to monitor quantity and spatial variability of sediment and associated nutrient deposition for large and complex river floodplains, including an uncertainty analysis. The measurement campaign applied 450 sediment mat traps in 19 floodplains over the MD for a complete flood season. The data also supports quantification of nutrient deposition in floodplains based on laboratory analysis of nutrient fractions of trapped sedimentation.The main findings are that the distribution of grain size and nutrient fractions of suspended sediment are homogeneous over the Vietnamese floodplains. But the sediment deposition within and between ring dike floodplains shows very high spatial variability due to a high level of human inference. The experimental findings provide the essential data for setting up and calibration of a large-scale sediment transport model for the MD. For the simulation studies a large scale hydrodynamic model was developed in order to quantify large-scale floodplain sediment dynamics. The complex river-channel-floodplain system of the MD is described by a quasi-2D model linking a hydrodynamic and a cohesive sediment transport model. The floodplains are described as quasi-2D presentations linked to rivers and channels modeled in 1D by using control structures. The model setup, based on the experimental findings, ignored erosion and re-suspension processes due to a very high degree of human interference during the flood season. A two-stage calibration with six objective functions was developed in order to calibrate both the hydrodynamic and sediment transport modules. The objective functions include hydraulic and sediment transport parameters in main rivers, channels and floodplains. The model results show, for the first time, the tempo-spatial distribution of sediment and associated nutrient deposition rates in the whole MD. The patterns of sediment transport and deposition are quantified for different sub-systems. The main factors influencing spatial sediment dynamics are the network of rivers, channels and dike-rings, sluice gate operations, magnitude of the floods and tidal influences. The superposition of these factors leads to high spatial variability of the sediment transport and deposition, in particular in the Vietnamese floodplains. Depending on the flood magnitude, annual sediment loads reaching the coast vary from 48\% to 60\% of the sediment load at Kratie, the upper boundary of the MD. Deposited sediment varies from 19\% to 23\% of the annual load at Kratie in Cambodian floodplains, and from 1\% to 6\% in the compartmented and diked floodplains in Vietnam. Annual deposited nutrients (N, P, K), which are associated to the sediment deposition, provide on average more than 50\% of mineral fertilizers typically applied for rice crops in non-flooded ring dike compartments in Vietnam. This large-scale quantification provides a basis for estimating the benefits of the annual Mekong floods for agriculture and fishery, for assessing the impacts of future changes on the delta system, and further studies on coastal deposition/erosion. For the estimation of future prospects a sensitivity-based approach is applied to assess the response of floodplain hydraulics and sediment dynamics to the changes in the delta boundaries including hydropower development, climate change in the Mekong River Basin and effective sea level rise. The developed sediment model is used to simulate the mean sediment transport and sediment deposition in the whole delta system for the baseline (2000-2010) and future (2050-2060) periods. For each driver we derive a plausible range of future changes and discretize it into five levels, resulting in altogether 216 possible factor combinations. Our results thus cover all plausible future pathways of sediment dynamics in the delta based on current knowledge. The uncertainty of the range of the resulting impacts can be decreased in case more information on these drivers becomes available. Our results indicate that the hydropower development dominates the changes in sediment dynamics of the Mekong Delta, while sea level rise has the smallest effect. The floodplains of Vietnamese Mekong Delta are much more sensitive to the changes compared to the other subsystems of the delta. In terms of median changes of the three combined drivers, the inundation extent is predicted to increase slightly, but the overall floodplain sedimentation would be reduced by approximately 40\%, while the sediment load to the Sea would diminish to half of the current rates. These findings provide new and valuable information on the possible impacts of future development on the delta, and indicate the most vulnerable areas. Thus, the presented results are a significant contribution to the ongoing international discussion on the hydropower development in the Mekong basin and its impact on the Mekong delta.},
  language  = {en}
}
@misc{AndersenEgholmFaurschouKnudsenetal.2015,
  author    = {Andersen, Jane Lund and Egholm, David L. and Faurschou Knudsen, Mads and Jansen, John D. and Nielsen, S. B.},
  title     = {The periglacial engine of mountain erosion},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {530},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-40965},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-409656},
  pages     = {16},
  year      = {2015},
  abstract  = {With accelerating climate cooling in the late Cenozoic, glacial and periglacial erosion became more widespread on the surface of the Earth. The resultant shift in erosion patterns significantly changed the large-scale morphology of many mountain ranges worldwide. Whereas the glacial fingerprint is easily distinguished by its characteristic fjords and U-shaped valleys, the periglacial fingerprint is more subtle but potentially prevails in some mid- to high-latitude landscapes. Previous models have advocated a frost-driven control on debris production at steep headwalls and glacial valley sides. Here we investigate the important role that periglacial processes also play in less steep parts of mountain landscapes. Understanding the influences of frost-driven processes in low-relief areas requires a focus on the consequences of an accreting soil mantle, which characterises such surfaces. We present a new model that quantifies two key physical processes: frost cracking and frost creep, as a function of both temperature and sediment thickness. Our results yield new insights into how climate and sediment transport properties combine to scale the intensity of periglacial processes. The thickness of the soil mantle strongly modulates the relation between climate and the intensity of mechanical weathering and sediment flux. Our results also point to an offset between the conditions that promote frost cracking and those that promote frost creep, indicating that a stable climate can provide optimal conditions for only one of those processes at a time. Finally, quantifying these relations also opens up the possibility of including periglacial processes in large-scale, long-term landscape evolution models, as demonstrated in a companion paper.},
  language  = {en}
}
@phdthesis{Kaempf2015,
  author    = {K{\"a}mpf, Lucas},
  title     = {Extreme events in geoarchives},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-85961},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xii, 94},
  year      = {2015},
  abstract  = {A main limitation in the field of flood hydrology is the short time period covered by instrumental flood time series, rarely exceeding more than 50 to 100 years. However, climate variability acts on short to millennial time scales and identifying causal linkages to extreme hydrological events requires longer datasets. To extend instrumental flood time series back in time, natural geoarchives are increasingly explored as flood recorders. Therefore, annually laminated (varved) lake sediments seem to be the most suitable archives since (i) lake basins act as natural sediment traps in the landscape continuously recording land surface processes including floods and (ii) individual flood events are preserved as detrital layers intercalated in the varved sediment sequence and can be dated with seasonal precision by varve counting. The main goal of this thesis is to improve the understanding about hydrological and sedimentological processes leading to the formation of detrital flood layers and therewith to contribute to an improved interpretation of lake sediments as natural flood archives. This goal was achieved in two ways: first, by comparing detrital layers in sediments of two dissimilar peri-Alpine lakes, Lago Maggiore in Northern Italy and Mondsee in Upper Austria, with local instrumental flood data and, second, by tracking detrital layer formation during floods by a combined hydro-sedimentary monitoring network at Lake Mondsee spanning from the rain fall to the deposition of detrital sediment at the lake floor. Successions of sub-millimetre to 17 mm thick detrital layers were detected in sub-recent lake sediments of the Pallanza Basin in the western part of Lago Maggiore (23 detrital layers) and Lake Mondsee (23 detrital layers) by combining microfacies and high-resolution micro X-ray fluorescence scanning techniques (µ-XRF). The detrital layer records were dated by detailed intra-basin correlation to a previously dated core sequence in Lago Maggiore and varve counting in Mondsee. The intra-basin correlation of detrital layers between five sediment cores in Lago Maggiore and 13 sediment cores in Mondsee allowed distinguishing river runoff events from local erosion. Moreover, characteristic spatial distribution patterns of detrital flood layers revealed different depositional processes in the two dissimilar lakes, underflows in Lago Maggiore as well as under- and interflows in Mondsee. Comparisons with runoff data of the main tributary streams, the Toce River at Lago Maggiore and the Griesler Ache at Mondsee, revealed empirical runoff thresholds above which the deposition of a detrital layer becomes likely. Whereas this threshold is the same for the whole Pallanza Basin in Lago Maggiore (600 m3s-1 daily runoff), it varies within Lake Mondsee. At proximal locations close to the river inflow detrital layer deposition requires floods exceeding a daily runoff of 40 m3s-1, whereas at a location 2 km more distal an hourly runoff of 80 m3s-1 and at least 2 days with runoff above 40 m3s-1 are necessary. A relation between the thickness of individual deposits and runoff amplitude of the triggering events is apparent for both lakes but is obviously further influenced by variable influx and lake internal distribution of detrital sediment. To investigate processes of flood layer formation in lake sediments, hydro-sedimentary dynamics in Lake Mondsee and its main tributary stream, Griesler Ache, were monitored from January 2011 to December 2013. Precipitation, discharge and turbidity were recorded continuously at the rivers outlet to the lake and compared to sediment fluxes trapped close to the lake bottom on a basis of three to twelve days and on a monthly basis in three different water depths at two locations in the lake basin, in a distance of 0.9 (proximal) and 2.8 km (distal) to the Griesler Ache inflow. Within the three-year observation period, 26 river floods of different amplitude (10-110 m3s-1) were recorded resulting in variable sediment fluxes to the lake (4-760 g m-2d-1). Vertical and lateral variations in flood-related sedimentation during the largest floods indicate that interflows are the main processes of lake internal sediment transport in Lake Mondsee. The comparison of hydrological and sedimentological data revealed (i) a rapid sedimentation within three days after the peak runoff in the proximal and within six to ten days in the distal lake basin, (ii) empirical runoff thresholds for triggering sediment flux at the lake floor increasing from the proximal (20 m3s-1) to the distal lake basin (30 m3s-1) and (iii) factors controlling the amount of detrital sediment deposition at a certain location in the lake basin. The total influx of detrital sediment is mainly driven by runoff amplitude, catchment sediment availability and episodic sediment input by local sediment sources. A further role plays the lake internal sediment distribution which is not the same for each event but is favoured by flood duration and the existence of a thermocline and, therewith, the season in which a flood occurred. In summary, the studies reveal a high sensitivity of lake sediments to flood events of different intensity. Certain runoff amplitudes are required to supply enough detrital material to form a visible detrital layer at the lake floor. Reasonable are positive feedback mechanisms between rainfall, runoff, erosion, fluvial sediment transport capacity and lake internal sediment distribution. Therefore, runoff thresholds for detrital layer formation are site-specific due to different lake-catchment characteristics. However, the studies also reveal that flood amplitude is not the only control for the amount of deposited sediment at a certain location in the lake basin even for the strongest flood events. The sediment deposition is rather influenced by a complex interaction of catchment and in-lake processes. This means that the coring location within a lake basin strongly determines the significance of a flood layer record. Moreover, the results show that while lake sediments provide ideal archives for reconstructing flood frequencies, the reconstruction of flood amplitudes is a more complex issue and requires detailed knowledge about relevant catchment and in-lake sediment transport and depositional processes.},
  language  = {en}
}
@misc{SkinnerCoulthardSchwanghartetal.2018,
  author    = {Skinner, Christopher J. and Coulthard, Tom J. and Schwanghart, Wolfgang and Van De Wiel, Marco J. and Hancock, Greg},
  title     = {Global sensitivity analysis of parameter uncertainty in landscape evolution models},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {1084},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-46801},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-468013},
  pages     = {4873 -- 4888},
  year      = {2018},
  abstract  = {The evaluation and verification of landscape evolution models (LEMs) has long been limited by a lack of suitable observational data and statistical measures which can fully capture the complexity of landscape changes. This lack of data limits the use of objective function based evaluation prolific in other modelling fields, and restricts the application of sensitivity analyses in the models and the consequent assessment of model uncertainties. To overcome this deficiency, a novel model function approach has been developed, with each model function representing an aspect of model behaviour, which allows for the application of sensitivity analyses. The model function approach is used to assess the relative sensitivity of the CAESAR-Lisflood LEM to a set of model parameters by applying the Morris method sensitivity analysis for two contrasting catchments. The test revealed that the model was most sensitive to the choice of the sediment transport formula for both catchments, and that each parameter influenced model behaviours differently, with model functions relating to internal geomorphic changes responding in a different way to those relating to the sediment yields from the catchment outlet. The model functions proved useful for providing a way of evaluating the sensitivity of LEMs in the absence of data and methods for an objective function approach.},
  language  = {en}
}
@article{BrookeWhittakerArmitageetal.2018,
  author    = {Brooke, Sam A. S. and Whittaker, Alexander C. and Armitage, John J. and Watkins, Stephen E. and D'Arcy, Mitchell},
  title     = {Quantifying sediment transport dynamics on alluvial fans from spatial and temporal changes in Grain Size, Death Valley, California},
  series = {Journal of geophysical research : Earth surface},
  volume    = {123},
  journal   = {Journal of geophysical research : Earth surface},
  number    = {8},
  publisher = {American Geophysical Union},
  address   = {Washington},
  issn      = {2169-9003},
  doi       = {10.1029/2018JF004622},
  pages     = {2039 -- 2067},
  year      = {2018},
  abstract  = {How information about sediment transport processes is transmitted to the sedimentary record remains a complex problem for the interpretation of fluvial stratigraphy. Alluvial fan deposits represent the condensed archive of sediment transport, which is at least partly controlled by tectonics and climate. For three coupled catchment-fan systems in northern Death Valley, California, we measure grain size across 12 well-preserved Holocene and late-Pleistocene surfaces, mapped in detail from field observations and remote sensing. Our results show that fan surfaces correlated to the late Pleistocene are, on average, 30-50\% coarser than active or Holocene fan surfaces. We adopt a self-similar form of grain size distribution based on the observed stability of the ratio between mean grain size and standard deviation downstream. Using statistical analysis, we show that fan surface grain size distributions are self-similar. We derive a relative mobility function using our self-similar grain size distributions, which describes the relative probability of a given grain size being transported. We show that the largest mobile grain sizes are between 20 and 35mm, a value that varies over time and is clearly lower in the Holocene than in the Pleistocene; a change we suggest is due to a drier climate in the Holocene. These results support recent findings that alluvial fan sedimentology can record past environmental change and that these landscapes are potentially sensitive to climatic change over a glacial-interglacial cycle. We demonstrate that the self-similarity methodology offers a means to explore changes in relative mobility of grain sizes from preserved fluvial deposits. Plain Language Summary A key challenge in Earth Science is understanding how landscapes respond to climate. It may be possible to observe measurable differences in certain landscapes settings such as alluvial fans in desert regions. Alluvial fans are believed to be effective recorders of climate, representing a cumulative store of material transported downstream by rainfall-sensitive river systems. In northern Death Valley, California, we measure at high resolution grain size on three alluvial fans with surfaces that date from the Holocene and the arid climate of today to the 20-40\% wetter late-Pleistocene epoch. We find that older late-Pleistocene surfaces are coarser on average than surfaces deposited during the modern and Holocene dry period, suggesting a changing sediment transport regime potentially in response to precipitation. We also show that measured grain size distributions within and between surfaces can be successfully normalized based on the decay in mean grain size and variance downstream, exhibiting a self-similar pattern. Finally, we employ a grain size relative mobility model using our field data to establish which grain sizes are likely to be in transport or locked in the substrate. This model predicts that during the wetter late-Pleistocene mobile grain sizes are up to 40\% larger than during the Holocene.},
  language  = {en}
}
@misc{WickertSchildgen2019,
  author    = {Wickert, Andrew D. and Schildgen, Taylor F.},
  title     = {Long-profile evolution of transport-limited gravel-bed rivers},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {680},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-42571},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-425718},
  pages     = {27},
  year      = {2019},
  abstract  = {Alluvial and transport-limited bedrock rivers constitute the majority of fluvial systems on Earth. Their long profiles hold clues to their present state and past evolution. We currently possess first-principles-based governing equations for flow, sediment transport, and channel morphodynamics in these systems, which we lack for detachment-limited bedrock rivers. Here we formally couple these equations for transport-limited gravel-bed river long-profile evolution. The result is a new predictive relationship whose functional form and parameters are grounded in theory and defined through experimental data. From this, we produce a power-law analytical solution and a finite-difference numerical solution to long-profile evolution. Steady-state channel concavity and steepness are diagnostic of external drivers: concavity decreases with increasing uplift rate, and steepness increases with an increasing sediment-to-water supply ratio. Constraining free parameters explains common observations of river form: to match observed channel concavities, gravel-sized sediments must weather and fine - typically rapidly - and valleys typically should widen gradually. To match the empirical square-root width-discharge scaling in equilibrium-width gravel-bed rivers, downstream fining must occur. The ability to assign a cause to such observations is the direct result of a deductive approach to developing equations for landscape evolution.},
  language  = {en}
}