Articoli di riviste: "Aggradation"

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Nikic, Zoran, Ratko Ristic, Nenad Maric, Vukasin Milcanovic, Sinisa Polovina e Ivan Malusevic. "Function of check dam aggradation in local water supply of mountainous areas". Bulletin of the Faculty of Forestry, n. 120 (2019): 117–30. http://dx.doi.org/10.2298/gsf1920117n.

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Check dams are built to control erosion processes and torrential floods. In Serbia, legally binding documents, VOS (2002) and PPRS (2010), provide the concept for the water supply of the population and industry by regional systems for which water is provided by building high dams and formation of reservoirs. With this concept, it is often not possible to meet the needs of local communities in mountainous areas. In order to contribute to solving the water supply problems of these mostly poor villages, research was conducted on the possibility of using check dam aggradation groundwater for this purpose. Field investigations and analysis of project documentation for numerous check dams and aggradations in Serbia were carried out. Potential quantities and quality of groundwater in the aggradations were analyzed as a resource for the water supply of the population. The results of the research indicate very favorable possibilities of the aggradations for the accumulation of groundwater in the form of unconfined or phreatic aquifer with a free water table, in quantities that can be used for water supply. It was stated that: 1) under favorable conditions, with check dams on watercourses with constant flow and large-scale aggradations, there is a possibility of accumulating sufficient quantities of groundwater as a resource for water supply, 2) improving the quality of infiltrated waters by the process of filtration through intergranular porous media of the aggradation, and reaching the level of water supply quality, and 3) favorable economic parameters for opening the source at the aggradation, compared to other types of water sources. The possibility that check dams, in addition to their traditional role, could be used for local water supply facilities was also highlighted.

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Johnson, Peggy A., Richard D. Hey, Michael W. Horst e Amanda J. Hess. "Aggradation at Bridges". Journal of Hydraulic Engineering 127, n. 2 (febbraio 2001): 154–57. http://dx.doi.org/10.1061/(asce)0733-9429(2001)127:2(154).

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Alappat, Linto, Palaniandy Seralathan, Anil Shukla, Kyth Thrivikramji e Ashok Singhvi. "Chronology of red dune aggradations of South India and its Palaeo-environmental significance". Geochronometria 40, n. 4 (1 dicembre 2013): 274–82. http://dx.doi.org/10.2478/s13386-013-0118-5.

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Abstract Red sand dunes occur in the coastal plains of south east and west of Tamil Nadu, India between the coordinates of 8°00′ to 9°30′ N; 77°18′ to 79° 00′ E. OSL dating of these sands indicated aggradations between ∼16-9 ka and ∼9-3 ka in the west and east coasts respectively. Dating results from inland red dunes at the foothills of Western Ghats show a break in deposition at ∼6 ka and aggradation since ∼2 ka. The sand aggradations in the west coast occurred during the transition period when SW monsoon in the area was reestablishing. The dunes attained their stability by 9 ka. In the coastal region, the aggradations were controlled by sea level changes and a local recycling of earlier dunes (in the east coast). In the inland areas, the dune building was controlled by sand supply from fluvial sources.

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Treat, Claire C., e Miriam C. Jones. "Near-surface permafrost aggradation in Northern Hemisphere peatlands shows regional and global trends during the past 6000 years". Holocene 28, n. 6 (19 gennaio 2018): 998–1010. http://dx.doi.org/10.1177/0959683617752858.

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The history of permafrost aggradation and thaw in northern peatlands can serve as an indicator of regional climatic history in regions where records are sparse. We infer regional trends in the timing of permafrost aggradation and thaw in North American and Eurasian peatland ecosystems based on plant macrofossils and peat properties using existing peat core records from more than 250 cores. Results indicate that permafrost was continuously present in peatlands during the last 6000 years in some present-day continuous permafrost zones and formed after 6000 BP in peatlands in the isolated to discontinuous permafrost regions. Rates of permafrost aggradation in peatlands generally increased after 3000 BP and were greatest between 750 and 0 BP, corresponding with neoglacial cooling and the Little Ice Age (LIA), respectively. Peak periods of permafrost thaw occurred after 250 BP, when permafrost aggradation in peatlands reached its maximum extent and as temperatures began warming after the LIA, suggesting that permafrost thaw is likely to continue in the future. The broader correlation of permafrost aggradation in peatlands with known climatic trends and other proxies such as pollen records suggests that this record can be a valuable addition to regional climate reconstructions.

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Humlum, Ole. "Holocene permafrost aggradation in Svalbard". Geological Society, London, Special Publications 242, n. 1 (2005): 119–29. http://dx.doi.org/10.1144/gsl.sp.2005.242.01.11.

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Vandermaelen, Nathan, Koen Beerten, François Clapuyt, Marcus Christl e Veerle Vanacker. "Constraining the aggradation mode of Pleistocene river deposits based on cosmogenic radionuclide depth profiling and numerical modelling". Geochronology 4, n. 2 (15 dicembre 2022): 713–30. http://dx.doi.org/10.5194/gchron-4-713-2022.

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Abstract. Pleistocene braided-river deposits commonly represent long periods of non-deposition or erosion that are interrupted by rapid and short aggradation phases. When dating these sedimentary sequences with in situ-produced cosmic radionuclides (CRNs), simple concentration depth profiling approaches often fall short, as they assume that the alluvial sedimentary sequence has been deposited with a constant and rapid aggradation rate and been exposed to cosmic radiations afterwards. Numerical modelling of the evolution of CRNs in alluvial sequences permits one to account for aggradation, non-deposition and erosion phases and can simulate which scenarios of aggradation and preservation most likely represent the river dynamics. In this study, such a model was developed and applied to a Middle Pleistocene gravel sheet (Zutendaal gravels) exposed in NE Belgium. The model parameters were optimised to the observed 10Be and 26Al concentrations of 17 sediment samples taken over a depth interval of 7 m that constitutes the top of a gravel sheet up to 20 m thick. In the studied sedimentary sequence, (at least) three individual aggradation phases that were interrupted by non-deposition or erosion can be distinguished, each interruption lasting ∼ 40 kyr. The age for the onset of aggradation of the upper 7 m of the gravel sheet was further constrained to 654-62+218 ka. This age, within error limits, does not invalidate previous correlations of the gravel sheet with the Cromerian Glacial B and Marine Isotope Stage (MIS) 16. The deposition of the entire gravel sheet likely represents more than one climatic cycle and demonstrates the importance of accounting for the depositional modes of braided rivers when applying in situ cosmogenic radionuclide techniques.

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Pelletier, J. D. "The linkage between hillslope vegetation changes and late-Quaternary fluvial-system aggradation in the Mojave Desert revisited". Earth Surface Dynamics Discussions 2, n. 1 (24 marzo 2014): 181–213. http://dx.doi.org/10.5194/esurfd-2-181-2014.

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Abstract. Valley-floor-channel and alluvial-fan deposits and terraces in the southwestern US record multiple episodes of late Quaternary fluvial aggradation and incision. Perhaps the most well constrained of these episodes took place from the latest Pleistocene to the present in the Mojave Desert. One hypothesis for this episode, i.e. the paleo-vegetation change hypothesis (PVCH), posits that a reduction in hillslope vegetation cover associated with the transition from Pleistocene woodlands to Holocene desert scrub generated a pulse of sediment that triggered a primary phase of aggradation downstream, followed by channel incision, terrace abandonment, and initiation of a secondary phase of aggradation further downstream. A second hypothesis, i.e. the extreme-storm hypothesis, attributes episodes of aggradation and incision to changes in the frequency and/or intensity of extreme storms. In the past decade a growing number of studies has advocated the extreme-storm hypothesis and challenged the PVCH on the basis of inconsistencies in both timing and process. Here I show that in eight out of nine sites where the timing of fluvial-system aggradation in the Mojave Desert is reasonably well constrained, measured ages of primary aggradation and/or incision are consistent with the predictions of the PVCH if the time-transgressive nature of paleo-vegetation changes with elevation is fully taken into account. I also present an alternative process model for PVCH that is more consistent with available data and produces sediment pulses primarily via an increase in drainage density (i.e. a transformation of hillslopes into low-order channels) rather than solely via an increase in sediment yield from hillslopes. This paper further documents the likely important role of changes in upland vegetation cover and drainage density in driving fluvial-system response during semiarid-to-arid climatic changes.

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Pelletier, J. D. "The linkages among hillslope-vegetation changes, elevation, and the timing of late-Quaternary fluvial-system aggradation in the Mojave Desert revisited". Earth Surface Dynamics 2, n. 2 (21 agosto 2014): 455–68. http://dx.doi.org/10.5194/esurf-2-455-2014.

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Abstract. Valley-floor-channel and alluvial-fan deposits and terraces in the southwestern US record multiple episodes of late-Quaternary fluvial-system aggradation and incision. Perhaps the most well-constrained of these episodes took place from the latest Pleistocene to the present in the Mojave Desert. One hypothesis for this episode – i.e., the paleovegetation-change hypothesis (PVCH) – posits that a reduction in hillslope vegetation cover associated with the transition from Pleistocene woodlands to Holocene desert scrub generated a pulse of sediment that triggered a primary phase of aggradation downstream, followed by channel incision, terrace abandonment, and initiation of a secondary phase of aggradation further downstream. A second hypothesis – i.e., the extreme-storm hypothesis – attributes episodes of aggradation and incision to changes in the frequency and/or intensity of extreme storms. In the past decade a growing number of studies has advocated the extreme-storm hypothesis and challenged the PVCH on the basis of inconsistencies in both timing and process. Here I show that in eight out of nine sites where the timing of fluvial-system aggradation in the Mojave Desert is reasonably well constrained, measured ages of primary aggradation are consistent with the predictions of the PVCH if the time-transgressive nature of paleovegetation changes with elevation is fully taken into account. I also present an alternative process model for PVCH that is more consistent with available data and produces sediment pulses primarily via an increase in drainage density (i.e., a transformation of hillslopes into low-order channels) rather than solely via an increase in sediment yield from hillslopes. This paper further documents the likely important role of changes in upland vegetation cover and drainage density in driving fluvial-system response during semiarid-to-arid climatic changes.

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Tamang, Sagar Kumar, Wenjun Song, Xing Fang, Jose Vasconcelos e J. Brian Anderson. "Framework for quantifying flow and sediment yield to diagnose and solve the aggradation problem of an ungauged catchment". Proceedings of the International Association of Hydrological Sciences 379 (5 giugno 2018): 131–38. http://dx.doi.org/10.5194/piahs-379-131-2018.

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Abstract. Estimating sediment deposition in a stream, a standard procedure for dealing with aggradation problem is complicated in an ungauged catchment due to the absence of necessary flow data. A serious aggradation problem within an ungauged catchment in Alabama, USA, blocked the conveyance of a bridge, reducing the clearance under the bridge from several feet to a couple of inches. A study of historical aerial imageries showed deforestation in the catchment by a significant amount over a period consistent with the first identification of the problem. To further diagnose the aggradation problem, due to the lack of any gauging stations, local rainfall, flow, and sediment measurements were attempted. However, due to the difficulty of installing an area-velocity sensor in an actively aggrading stream, the parameter transfer process for a hydrologic model was adopted to understand/estimate streamflow. Simulated discharge combined with erosion parameters of MUSLE (modified universal soil loss equation) helped in the estimation of sediment yield of the catchment. Sediment yield for the catchment showed a significant increase in recent years. A two-dimensional hydraulic model was developed at the bridge site to examine potential engineering strategies to wash sediments off and mitigate further aggradation. This study is to quantify the increase of sediment yield in an ungauged catchment due to land cover changes and other contributing factors and develop strategies and recommendations for preventing future aggradation in the vicinity of the bridge.

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Hereford, Richard. "Modern Alluvial History of the Paria Rver Drainage Basin, Southern Utah". Quaternary Research 25, n. 3 (maggio 1986): 293–311. http://dx.doi.org/10.1016/0033-5894(86)90003-7.

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Stream channels in the Paria River basin were eroded and partially refilled between 1883 and 1980. Basin-wide erosion began in 1883; channels were fully entrenched and widened by 1890. This erosion occurred during the well-documented period of arroyo cutting in the Southwest. Photographs of the Paria River channel taken between 1918 and 1940 show that the channel did not have a floodplain and remained wide and deep until the early 1940s. A thin bar (<50 cm), now reworked and locally preserved, was deposited at that time. Basin-wide aggradation, which began in the early 1940s, developed floodplains by vertical accretion. The floodplain alluvium, 1.3–3 m thick. consists of two units recognizable throughout the studied area. An older unit was deposited during a time of low flow and sediment yield whereas the younger unit was deposited during times of high flow, sediment yield, and precipitation. Tree-ring dating suggests that the older unit was deposited between the early 1940s and 1956, and the younger between 1956 and 1980. The units are not time transgressive, suggesting that deposition by knickpoint recession was not an important process. High peak-flood discharges were associated with crosion and low flood discharges with aggradation. The erosional or aggradational mode of the streams was determined principally by peak-flood discharge, which in turn was controlled by precipitation.

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Johnson, Bradley G., Martha Cary Eppes, John A. Diemer, Gonzalo Jiménez-Moreno e Anthony L. Layzell. "Post-glacial landscape response to climate variability in the southeastern San Juan Mountains of Colorado, USA". Quaternary Research 76, n. 3 (novembre 2011): 352–62. http://dx.doi.org/10.1016/j.yqres.2011.08.006.

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AbstractGeomorphic mapping in the upper Conejos River Valley of the San Juan Mountains has shown that three distinct periods of aggradation have occurred since the end of the last glacial maximum (LGM). The first occurred during the Pleistocene–Holocene transition (~ 12.5–9.5 ka) and is interpreted as paraglacial landscape response to deglaciation after the LGM. Evidence of the second period of aggradation is limited but indicates a small pulse of sedimentation at ~ 5.5 ka. A third, more broadly identifiable period of sedimentation occurred in the late Holocene (~ 2.2–1 ka). The latest two periods of aggradation are concurrent with increases in the frequency of climate change in the region suggesting that Holocene alpine and sub-alpine landscapes respond more to rapid changes in climate than to large singular climatic swings. Soil development and radiocarbon dating indicate that hillslopes were stable during the Holocene even while aggradation was occurring in valley bottoms. Thus, we can conclude that erosion does not occur equally throughout the landscape but is focused upslope of headwater streams, along tributary channels, or on ridge tops. This is in contrast to some models which assume equal erosion in headwater basins.

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12

Notebaert, B., G. Houbrechts, G. Verstraeten, N. Broothaerts, J. Haeckx, M. Reynders, G. Govers, F. Petit e J. Poesen. "Fluvial architecture of Belgian river systems in contrasting environments: implications for reconstructing the sedimentation history". Netherlands Journal of Geosciences - Geologie en Mijnbouw 90, n. 1 (agosto 2011): 31–50. http://dx.doi.org/10.1017/s0016774600000652.

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AbstractAccurate dating is necessary to get insight in the temporal variations in sediment deposition in floodplains. The interpretation of such dates is however dependent on the fluvial architecture of the floodplain. In this study we discuss the fluvial architecture of three contrasting Belgian catchments (Dijle, Geul and Amblève catchment) and how this influences the dating possibilities of net floodplain sediment storage. Although vertical aggradation occurred in all three floodplains during the last part of the Holocene, they differ in the importance of lateral accretion and vertical aggradation during the entire Holocene. Holocene floodplain aggradation is the dominant process in the Dijle catchment. Lateral reworking of the floodplain sediments by river meandering was limited to a part of the floodplain, resulting in stacked point bar deposits. The fluvial architecture allows identifying vertical aggradation without erosional hiatuses. Results show that trends in vertical floodplain aggradation in the Dijle catchment are mainly related to land use changes. In the other two catchments, lateral reworking was the dominant process, and channel lag and point bar deposits occur over the entire floodplain width. Here, tracers were used to date the sediment dynamics: lead from metal mining in the Geul and iron slag from ironworks in the Amblève catchment. These methods allow the identification of two or three discrete periods, but their spatial extent and variations is identified in a continuous way. The fluvial architecture and the limitation in dating with tracers hampered the identification of dominant environmental changes for sediment dynamics in both catchments. Dating methods which provide only discrete point information, like radiocarbon or OSL dating, are best suited for fluvial systems which contain continuous aggradation profiles. Spatially more continuous dating methods, e.g. through the use of tracers, allow to reconstruct past surfaces and allow to reconstruct reworked parts of the floodplain. As such they allow a better reconstruction of past sedimentation rates in systems with important lateral reworking.

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Yen, Chin‐lien, Shou‐young Chang e Hong‐Yuan Lee. "Aggradation‐Degradation Process in Alluvial Channels". Journal of Hydraulic Engineering 118, n. 12 (dicembre 1992): 1651–69. http://dx.doi.org/10.1061/(asce)0733-9429(1992)118:12(1651).

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Weninger, J. M., e J. H. McAndrews. "Late Holocene aggradation in the lower Humber River valley, Toronto, Ontario". Canadian Journal of Earth Sciences 26, n. 9 (1 settembre 1989): 1842–49. http://dx.doi.org/10.1139/e89-157.

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Alluvial fills are common in the lower reaches of rivers along the western shore of Lake Ontario. The Humber River floodplain at Toronto is underlain by a 2.5 km long wedge of alluvium that thins upstream from Lake Ontario. Floodplain sediments were studied for their lithology, 14C age, and fossil pollen. On the levees, grey clay is overlain by oxidized silt and sand. Sediment cores from two flood ponds grade upward from gravel, sand, and silt, to silty marl, mineral peat, and clay, to heterogeneous silt and sand. Base-level (Lake Ontario) rise directly controlled aggradation between 6500 and 1800 years ago, after which time base level no longer directly controlled aggradation because levees had emerged alongside the channel and reduced the supply of sediment to the floodplain. For the past 150 years, upstream forest clearance and urbanization increased sediment input to the floodplain, broadened the levees, and filled the flood ponds.Average flood-pond aggradation rates were estimated from seven 14C dates; these rates declined from 65 cm/100 years between 6500 and 3800 years ago, to 47 cm/100 years between 3800 and 3400 years ago, to 26 cm/100 years between 3400 and 1800 years ago. These rates reflect contemporaneous lake-level rise. Between 1800 and 150 years ago, the average aggradation rate declined below the estimated rate of lake-level rise to 14 cm/100 years. Since then, the average aggradation rate has increased tenfold to 140 cm/100 years, surpassing the historic rate of lake-level rise of 23 cm/100 years. Fossil pollen from the flood ponds reflects local flood plain and regional upland vegetation during the past 4000 years.

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Mehl, A. E., e M. A. Zárate. "Late Glacial-Holocene climatic transition record at the Argentinian Andean piedmont between 33–34° S". Climate of the Past Discussions 9, n. 5 (31 ottobre 2013): 6125–60. http://dx.doi.org/10.5194/cpd-9-6125-2013.

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Abstract. The Arroyo La Estacada (~33°28' S, 69°02' W), eastern Andean piedmont of Argentina, cuts through an extensive piedmont aggradational unit composed of a dominant late Pleistocene–early Holocene (LP–EH) alluvial sequence including several paleosols. The arroyo sedimentary record exhibits a paleosol developed affecting the topmost part of likely Lateglacial aeolian deposits aggraded into a floodplain environment by the end of the late Pleistocene. The paleosol shows variable grade of development in the outcrops along the arroyo probably in relation to fluvial valley paleotopography. Organic matter humification, carbonate accumulation and redox processes were the dominant processes associated with paleosol formation. By the early Holocene, when the formation of the paleosol ended, alluvial aggradation renewed and a higher frequency of flooding events could have affected the arroyo's floodplain environment. A period of relative landscape stability in the Arroyo La Estacada basin is inferred from the paleosol developed by the LP–EH transition in response to a climatic amelioration in the Andes cordillera piedmont after the Late Glacial arid conditions. The renewal of early Holocene alluvial aggradation was probably influenced by the South American Monsoon and resulted in a change in the sedimentary dynamics of the arroyo. The analyzed Late Glacial-Holocene alluvial record of the Andean piedmont constitutes a suitable record of the LP–EH climatic transition at the extra Andean region of Argentina. It is in agreement with regional paleoclimatic evidence along the southern tip of the South American continent, where other sedimentary sequences record similar late Quaternary paleoenvironmental changes over both fluvial and interfluvial areas.

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Melo, Rafael Roney Camara de, e José Roberto Gonçalves de Azevedo. "Dynamics of sedimentary Capibaribe River bed after deepening dredging". RBRH 21, n. 4 (24 ottobre 2016): 871–81. http://dx.doi.org/10.1590/2318-0331.01161603.

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ABSTRACT The growth of urban centers in the country are increasingly dependent on the adoption of new mobility options, and before this need was developed and initiated a project to build a river corridor passenger in a part of the Capibaribe River in the city of Recife-PE. For the implementation of a navigation channel deepening are needed dredging to define a geometry of the bed of the river compatible with the needs of ships that will traverse the channel. The monitoring of dredging is done with the constant bathymetric surveys where the information volumes of dredged sediments are removed, aiming to also check the temporal behavior of deposition and erosion processes. In this context, the work aimed to evaluate the geometry of the Capibaribe river bed after the deepening dredging, using data from bathymetric surveys at different times for making longitudinal and transverse profiles, and create digital models of depth to extract information about the deposition/aggradation or erosion/removing sediments and their respective volumes. Early Profile Capibaribe river showed mild slope and heterogeneity in the bottom of the form, especially after kilometer five, with trends of deposition/aggradation downstream of the confluence region with tax arising from the weir Apipucos and upstream of the winding sections in local enlargement of the cross section, and the amount of the fork located at kilometer nine. The scenarios after the dredging to deepen indicate places with predominance of erosion and other sedimentation processes. They compared the longitudinal and transverse profiles of two areas located in western shipping channel, one with 350 meters and over 1000 meters, where it was found that the area 1 to erosion/sediment removal exceeded sedimentation/aggradation, indicating the occurrence of dredging the interval between the two surveys linked to the natural processes. In the study area 2 the sedimentation/aggradation exceeded the removal/erosion, with a volume equivalent to 1 cm thickness. The aggradation occur homogeneously in the navigation channel, while erosion was located on the banks, more intensely on the right bank of the river.

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Lauer, Tobias, Matthias Krbetschek, Manfred Frechen, Sumiko Tsukamoto, Christian Hoselmann e Michael Weidenfeller. "Infrared radiofluorescence (IR-RF) dating of middle pleistocene fluvial archives of the Heidelberg Basin (Southwest Germany)". Geochronometria 38, n. 1 (1 marzo 2011): 23–33. http://dx.doi.org/10.2478/s13386-011-0006-9.

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AbstractThe infrared radiofluorescence (IR-RF) dating technique was applied to eight fluvial samples that were collected from two sediment cores at the Heidelberg Basin located near Viernheim and Ludwigshafen in southwest Germany. Based on the IR-RF derived ages of the samples it was possible to establish a chronological framework for the Mid-Pleistocene fluvial deposits of the Heidelberg Basin. The results allow us to distinguish between four main periods of aggradation. The lowermost sample taken from 100 m core depth lead to an IR-RF age of 643 ± 28 ka pointing to a Cromerian period of aggradation (OIS 17–16). For the Elsterian it is now possible to distinguish between two aggradation periods, one occurring during the Lower Elsterian period (OIS 15) and a second during the Upper Elsterian period (OIS 12–11). For the so called Upper interlayer (or “Oberer Zwischenhorizont” — a layer of organic-rich and finer-grained deposits), the IR-RF results point to a deposition age of around 300 ka, with samples taken directly on top and out of this layer yielding IR-RF ages of 288 ± 19 ka and 302 ± 19 ka, respectively. Hence, the measured IR-RF ages clearly point to a deposition during the Lower Saalian period (OIS 9–8) whereas earlier studies assumed a Cromerian age for the sediments of the Upper Interlayer based on pollen records and also mollusc fauna. The new IR-RF dataset indicates that significant hiatuses are present within the fluvial sediment successions. In particular the Eemian and Upper Saalian deposits are missing in this part of the northern Upper Rhine Graben, as the 300 ka deposits are directly overlain by Weichselian fluvial sediments. It is obvious that time periods of increased fluvial aggradation were interrupted by time periods of almost no aggradation or erosion which should have been mainly triggered by phases of increased and decreased subsidence of the Heidelberg Basin.

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Zhang, Hou, e R. Kahawita. "Nonlinear Model For Aggradation in Alluvial Channels". Journal of Hydraulic Engineering 113, n. 3 (marzo 1987): 353–68. http://dx.doi.org/10.1061/(asce)0733-9429(1987)113:3(353).

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Cui, Yantao, Chris Paola e Gary Parker. "Numerical simulation of aggradation and downstream fining". Journal of Hydraulic Research 34, n. 2 (marzo 1996): 185–204. http://dx.doi.org/10.1080/00221689609498496.

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Slootman, Arnoud, e Matthieu J. B. Cartigny. "Cyclic steps: Review and aggradation-based classification". Earth-Science Reviews 201 (febbraio 2020): 102949. http://dx.doi.org/10.1016/j.earscirev.2019.102949.

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Rice, Stephen P. "Tributary connectivity, confluence aggradation and network biodiversity". Geomorphology 277 (gennaio 2017): 6–16. http://dx.doi.org/10.1016/j.geomorph.2016.03.027.

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Ulanowicz, Robert E., Sven Erik Jørgensen e Brian D. Fath. "Exergy, information and aggradation: An ecosystems reconciliation". Ecological Modelling 198, n. 3-4 (ottobre 2006): 520–24. http://dx.doi.org/10.1016/j.ecolmodel.2006.06.004.

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Sándor, Andrea, e Tímea Kiss. "Floodplain aggradation caused by the high magnitude flood of 2006 in the lower Tisza region, Hungary". Journal of Environmental Geography 1, n. 1-2 (1 gennaio 2008): 31–39. http://dx.doi.org/10.14232/jengeo-2008-43855.

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The area of floodplains in the Carpathian Basin was dramatically reduced as a result of river regulation works in the 19th century. Therefore, the accumulation processes were limited to the narrower floodplains. The aims of the presented study are to determine the rate of accumulation caused by a single flood event on the active, narrow floodplain of the Lower Tisza and to evaluate the relations between the aggradation, flow velocity during the peak of the flood and the canopy. The uncultivated lands in the study area cause increased roughness which decreased the velocity of the flood, influencing the rate of aggradation. The highest flow velocity was measured on points where the flood entered to the floodplain and at the foot of the levee. These points were characterised by thick (over 50 mm) and coarse sandy sediment. In the inner parts of the floodplain flood conductivity zones were formed, where the vegetational roughness was small. In the inner parts of the floodplain the rate of aggradation was influenced by the geomorphology and the vegetation density of the area.

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Radice, Alessio, e Stefanía Unigarro Villota. "Propagation of aggrading sediment fronts in a laboratory flume". E3S Web of Conferences 40 (2018): 05055. http://dx.doi.org/10.1051/e3sconf/20184005055.

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Channel bed aggradation due to sediment overloading was studied experimentally. A series of aggradation tests, with uniform lightweight sediment, were performed to observe the hydro-morphologic response of a laboratory flume to bed-load sediment transport and nonequilibrium upstream sediment feeding. The hydro-dynamic and the sediment feeding rates were kept constant in time. The temporal evolution of the longitudinal profiles of the stream bed and of the water surface was measured by imaging methods. The experimental data were used to (i) provide a phenomenological description of the aggradation process, recognizing different morphologic features superimposed on one another and (ii) characterize the height and velocity of propagation of aggrading sediment fronts. The front heights increased with increasing sediment supply, while the front celerity decreased. The celerity values were compared to a few predictors available in the literature. The literature formulae return celerity values scattered over almost two orders of magnitude, and present conflicting trends (a predicted celerity may either increase or decrease for increasing sediment feeding rate), thus stimulating further research on the topic.

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von Suchodoletz, Hans, e Dominik Faust. "Late Quaternary fluvial dynamics and landscape evolution at the lower Shulaveris Ghele River (southern Caucasus)". Quaternary Research 89, n. 1 (24 ottobre 2017): 254–69. http://dx.doi.org/10.1017/qua.2017.80.

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AbstractThe southern Caucasus was intensively settled through the Neolithic period to present. Studies of late Quaternary fluvial dynamics and landscape development at the lower Shulaveris Ghele River in southeastern Georgia aid understanding of the Quaternary history of this region. Our studies show that following river aggradation to form a fan-shaped alluvial surface during the late Pleistocene, fluvial sedimentation shifted west, leaving a fan surface subject only to local fluvial and colluvial processes as well as late Neolithic settlement. At about 6 ka, the river avulsed to the east and eroded some late Neolithic settlements occupying the eastern portion of the fan. The avulsion was followed by 3 distinct episodes of aggradation at about 6 ka, 3–2 ka, and since 1.0 ka. No such aggradation is evident in the early Holocene. Regional Holocene fluvial activity in this area was apparently influenced by vegetation dynamics, possibly controlled by regional climatic and/or anthropogenic factors, and significantly differs from the eastern Mediterranean region. All late Neolithic settlements were originally built far from an active river, possibly indicating late Neolithic water management systems.

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26

Wu, Chia-Yu, e Joann Mossa. "Decadal-Scale Variations of Thalweg Morphology and Riffle–Pool Sequences in Response to Flow Regulation in the Lowermost Mississippi River". Water 11, n. 6 (5 giugno 2019): 1175. http://dx.doi.org/10.3390/w11061175.

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The lowermost Mississippi River (LMR) is one of the largest deltaic systems in North America and one of the heavily human-manipulated fluvial river systems. Historic hydrographic surveys from the mid-1900s to the early 2010s were used to document the thalweg morphology adjustments, as well as the riffle–pool sequences. Extensive aggradation was observed during 1950s to 1960s, as the Atchafalaya River was enlarging before the completion of the Old River Control Structure (ORCS). Following the completion of the ORCS, reductions in sediment input to the LMR resulted in net degradation of the thalweg profile patterns since the mid-1960s except for the 1992–2004 period. Different flood events that supplied sediment might be the cause of upstream aggradation from 1963–1975 and net aggradation along the entire reach from 1992–2004. Furthermore, the change pattern of thalweg profiles appear to be controlled by backwater effects, as well as the Bonnet Carré spillway opening. Results from riffle–pool sequences reveal that the averaging Ws ratios (length to channel width) are 6–7, similar to numerous previous studies. Temporal variations of the same riffles and pools reveal that aggradation and degradation might be heavily controlled by similar factors to the thalweg variations (i.e., sediment supply, backwater effects). In sum, this study examines decadal-scale geomorphic responses in a low-lying large river system subject to different human interventions, as well as natural flood events. Future management strategies of this and similar river systems should consider recent riverbed changes in dredging, sediment management, and river engineering.

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27

Poggetti, Emilio, Corrado Cencetti, Pierluigi De Rosa, Andrea Fredduzzi e Felipe Raphael Rivelli. "Sediment Supply and Hydrogeological Hazard in the Quebrada De Humahuaca (Province of Jujuy, Northwestern Argentina)—Rio Huasamayo and Tilcara Area". Geosciences 9, n. 11 (16 novembre 2019): 483. http://dx.doi.org/10.3390/geosciences9110483.

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This paper describes the hydrogeological hazard in a reach of Quebrada de Humahuaca, (Upper Valley of Rio Grande de Jujuy, in the Argentine Andes), elected a World Heritage Site by UNESCO in 2003. Along the Quebrada, the Rio Huasamayo, flowing into the Rio Grande, formed a large alluvial fan where the village of Tilcara was built. The final reach of Rio Huasamayo is an artificial channel, embanked by unconsolidated material removed from the riverbed. The village is located in an area at a lower elevation with respect to the riverbed, still in aggradation; so it is affected by an evident hydrogeological hazard. The main cause of the riverbed aggradation is the enormous sediment supply from the slopes of the Rio Huasamayo basin. The aim of the paper is to estimate the soil loss on the slopes and the consequent sediment supply to the main stream, identifying the areas of the basin mostly affected by erosion processes that cause the aggradation of the Rio Huasamayo riverbed. In this case, due to the lack of hydrometeorological stations (monitoring rainfalls, temperature, flow rates, etc.), soil loss and sediment supply to the main stream cannot be estimated through the application of commonly used models in the literature (e.g., USLE, RUSLE, USPED). Here the Gavrilovic method (EPM) was applied in combination with the data of the CORINE Project, allowing the estimation of the volume of material exiting from the catchment. So the main supplying areas (sub-basins of the Rio Huasamayo) can be identified where focused interventions for the control of solid transport could be realized, to mitigate the process of riverbed aggradation.

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28

Szafraniec, Joanna Ewa, e Wojciech Dobiński. "Deglaciation Rate of Selected Nunataks in Spitsbergen, Svalbard—Potential for Permafrost Expansion above the Glacial Environment". Geosciences 10, n. 5 (25 maggio 2020): 202. http://dx.doi.org/10.3390/geosciences10050202.

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Spitsbergen has recently experienced a continuous deglaciation process, linked to both glacier front retreat and lowering of the glacier surface. This process is accompanied by permafrost aggradation from the top of the slopes down to the glacier. Here, the authors determine the rate of permafrost expansion in this type of vertical profile. To this end, seven nunataks across the island were analysed using Landsat satellite imagery, a high-resolution digital elevation model (ArcticDEM), and geoinformation software. Over the last 24–31 years, new nunataks gradually emerged from the ice cover at an average linear rate of 0.06 m a−1 per degree of increment of the slope of the terrain at an average altitude of approximately 640 m a.s.l. The analysis showed that the maximum rate of permafrost expansion down the slope was positively correlated with the average nunatak elevation, reaching a value of approximately 10,000 m2 a−1. In cold climates, with a mean annual air temperature (MAAT) below 0 °C, newly exposed land is occupied by active periglacial environments, causing permafrost aggradation. Therefore, both glacial and periglacial environments are changing over time concomitantly, with permafrost aggradation occurring along and around the glacier, wherever the MAAT is negative.

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29

Oetelaar, Gerald A. "River of Change: a Model for the Development of Terraces Along the Bow River, Alberta". Hydrological and Flood Reconstructions 56, n. 2-3 (7 ottobre 2004): 155–69. http://dx.doi.org/10.7202/009102ar.

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Abstract Researchers working in the Bow River valley have identified a minimum of four alluvial terraces, the upper two of which have been designated as paired terraces. Over the past 35 years, they have attempted to correlate these alluvial landforms and to generate models for the development of the terraces along the section of the Bow River between Calgary and the Rocky Mountains. In this study, Mazama ash and an early Holocene paleosol are used to correlate the terrace suites examined by previous researchers and to generate a model which accounts for the development of the upper two sets of paired terraces. These paired terraces reflect major episodes of aggradation and degradation that result from changes in independent variables such as climate and uplift. The initial episode of aggradation, dating from the late Pleistocene, is the result of paraglacial processes in a sparsely vegetated, yet saturated environment. Following a brief episode of degradation at the end of the Younger Dryas, the second episode of aggradation, dating from 9000 to 5000 BP, is caused by increased sediment load and lowered stream power during the Hypsithermal.

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30

Reddy, Dontireddy Venkat, Vuddaraju Singaraju, Rakesh Mishra, Devender Kumar, Puthusserry Joseph Thomas, Karra Kameshwa Rao e Ashok Kumar Singhvi. "Luminescence chronology of the inland sand dunes from SE India". Quaternary Research 80, n. 2 (settembre 2013): 265–73. http://dx.doi.org/10.1016/j.yqres.2013.06.003.

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Records of past climate changes have been preserved variously on the earth's surface. Sand dunes are one such prominent imprint, and it is suggested that their presence is an indicator of periods of transition from arid to less arid phases. We report inland sand dunes from Andhra Pradesh (SE India) spread over an area of ~ 500 km2, ~ 75 km inland from the east coast. The dune sands are examined to understand their provenance, transportation, timing of sand aggradation and their relationship to past climates. The dune distribution, grain morphology and the grain-size studies on sands suggest an aeolian origin. Physiography of the study area, heavy mineral assemblage, and abundance of quartz in the parent rocks indicate that the dune sands are largely derived from first-order streams emanating from hills in the region and from weathering of the Nellore schist belt. It appears that the geomorphology and wind direction pattern both facilitated and restricted the dune aggradation and preservation to a limited area. OSL dating of 47 dune samples ranged from the present to ~ 50 ka, thereby suggesting a long duration of sand-dune aggradation and/or reworking history.

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31

Carver, Daniel P., e Jared M. Beeton. "Holocene landscape evolution and geoarcheology of low-order streams in the Rio Grande basin, San Juan Mountains, Colorado, USA". Quaternary Research 82, n. 2 (settembre 2014): 331–41. http://dx.doi.org/10.1016/j.yqres.2014.05.006.

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AbstractThis geoarcheological study investigates soil stratigraphy and geochronology of alluvial deposits to determine Holocene landscape evolution within the Hot Creek, La Jara Creek, and Alamosa River drainage basins in the San Juan Mountains of Colorado. Geomorphic mapping and radiocarbon dating indicate synchronicity in patterns of erosion, deposition, and stability between drainage basins. In all three basins, the maximum age of mapped alluvial terraces and fans is ~ 3300 cal yr BP. A depositional period seen at both Hot Creek and the Alamosa River begins ~ 3300 to 3200 cal yr BP. Based on soil development, short periods of stability followed by alluvial fan aggradation occur in the Alamosa River basin ~ 2200 cal yr BP. A period of landscape stability at Hot Creek before ~ 1100 cal yr BP is followed by a period of rapid aggradation within all three drainages between ~ 1100 and 850 cal yr BP. A final aggradation event occurred between ~ 630 and 520 cal yr BP at La Jara Creek. These patterns of landscape evolution over the past ~ 3300 yr provide the framework for an archeological model that predicts the potential for buried and surficial cultural materials in the research area.

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32

Qiao, Li, e Jian Feng Sheng. "Environmental Analysis on Insulation Resistance Reduction Case". Applied Mechanics and Materials 483 (dicembre 2013): 257–61. http://dx.doi.org/10.4028/www.scientific.net/amm.483.257.

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An insulation resistance reduction case was studied in this paper. An electrical component composed with metal panel, screw and insulation panel occurred flashover after 2-year service. Environment assessment, dust analysis and material analysis were done to find the reduction reason. The result shows that the reduction is caused by conductive dust aggraded on insulation panel surface; the aged surface of insulation material is favor for the conductive dust aggradation; humid air and high-hygroscopic dust accelerate this aggradation. It is suggested to improve the hydrophobicity and anti-aging property of insulation materials as well as increase the creepage for avoiding the kind of failure.

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33

Panin, Andrey, Olga Borisova, Evgeny Konstantinov, Yury Belyaev, Ekaterina Eremenko, Andrey Zakharov e Aleksey Sidorchuk. "The Late Quaternary Evolution of the Upper Reaches of Fluvial Systems in the Southern East European Plain". Quaternary 3, n. 4 (13 novembre 2020): 31. http://dx.doi.org/10.3390/quat3040031.

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Networks of dry valleys (or balkas) and hollows in the upper reaches of fluvial basins in extraglacial areas in the Penultimate Glaciation (Marine Isotope Stage 6—MIS 6) regions of the East European Plain demonstrate clear incision/aggradation rhythms corresponding to global glacial/interglacial climate cycles. The first phase of each incision/aggradation rhythm began after the global glacial maximum and was characterized by a cool and humid climate, permafrost and sparse vegetation, when high surface runoff and active linear erosion formed a dense network of gullies. The second phase occurred at the glacial–interglacial transition and the subsequent interglacial period with its warm and humid climate and dense vegetation. This phase was distinguished by the partial filling of fluvial forms with slopewash deposits, the transformation of gullies into dry valleys (balkas) and the subsequent stabilization of fluvial forms marked by the formation of mature soils on the sides and bottoms of balkas. The third phase of the rapid accumulation of balkas developed during the cold and dry part of the next glacial epoch, resulting in the balkas becoming shallow hollows filled in with sediments. The last full incision/aggradation rhythm occurred in the late MIS 6 to mid-MIS 2. The erosion network formed during the late MIS 6 was almost completely filled by mid-MIS 2, and its manifestation in the modern topography is limited to a network of shallow hollows in the upper parts of the fluvial systems. The modern (incomplete) incision/aggradation rhythm began in the late MIS 2 and caused the formation of the modern erosion landscape in the upper reaches of fluvial systems. This rhythm is now in the stabilization phase, and the main accumulation phase of this rhythm is still far in the future.

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34

Chao, Yi-Chiung, Chi-Wen Chen, Hsin-Chi Li e Yung-Ming Chen. "Riverbed Migrations in Western Taiwan under Climate Change". Water 10, n. 11 (12 novembre 2018): 1631. http://dx.doi.org/10.3390/w10111631.

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In recent years, extreme weather phenomena have occurred worldwide, resulting in many catastrophic disasters. Under the impact of climate change, the frequency of extreme rainfall events in Taiwan will increase, according to a report on climate change in Taiwan. This study analyzed riverbed migrations, such as degradation and aggradation, caused by extreme rainfall events under climate change for the Choshui River, Taiwan. We used the CCHE1D model to simulate changes in flow discharge and riverbed caused by typhoon events for the base period (1979–2003) and the end of the 21st century (2075–2099) according to the climate change scenario of representative concentration pathways 8.5 (RCP8.5) and dynamical downscaling of rainfall data in Taiwan. According to the results on flow discharge, at the end of the 21st century, the average peak flow during extreme rainfall events will increase by 20% relative to the base period, but the time required to reach the peak will be 8 h shorter than that in the base period. In terms of the results of degradation and aggradation of the riverbed, at the end of the 21st century, the amount of aggradation will increase by 33% over that of the base period. In the future, upstream sediment will be blocked by the Chichi weir, increasing the severity of scouring downstream. In addition, due to the increased peak flow discharge in the future, the scouring of the pier may be more serious than it is currently. More detailed 2D or 3D hydrological models are necessary in future works, which could adequately address the erosive phenomena created by bridge piers. Our results indicate that not only will flood disasters occur within a shorter time duration, but the catchment will also face more severe degradation and aggradation in the future.

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35

Ribberink, J. S., e J. T. M. Van Der Sande. "Aggradation in rivers due to overloading - analytical approaches". Journal of Hydraulic Research 23, n. 3 (maggio 1985): 273–83. http://dx.doi.org/10.1080/00221688509499355.

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36

Akram Gill, Mohammad. "Nonlinear solution of aggradation and degradation in channels". Journal of Hydraulic Research 25, n. 5 (ottobre 1987): 537–47. http://dx.doi.org/10.1080/00221688709499254.

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37

Lee, Hong-Yuan, e Wei-Sheng Yu. "Nonlinear Solution Of Aggradation And Degradation In Channels". Journal of Hydraulic Research 26, n. 4 (agosto 1988): 497–98. http://dx.doi.org/10.1080/00221688809499208.

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38

Daniels, J. Michael. "Floodplain aggradation and pedogenesis in a semiarid environment". Geomorphology 56, n. 3-4 (dicembre 2003): 225–42. http://dx.doi.org/10.1016/s0169-555x(03)00153-3.

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39

Petts, G. E., e M. C. Thoms. "Channel aggradation below Chew Valley Lake, Somerset, U.K." CATENA 13, n. 3 (settembre 1986): 305–20. http://dx.doi.org/10.1016/0341-8162(86)90005-6.

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40

Eliot, I. G., e D. J. Clarke. "Semi-diurnal variation in beachface aggradation and degradation". Marine Geology 79, n. 1-2 (febbraio 1988): 1–22. http://dx.doi.org/10.1016/0025-3227(88)90153-3.

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41

McCarthy, T. S., I. G. Stanistreet, B. Cairncross, W. N. Ellery, K. Ellery, R. Oelofse e T. S. A. Grobicki. "Incremental aggradation on the Okavango Delta-fan, Botswana". Geomorphology 1, n. 3 (settembre 1988): 267–78. http://dx.doi.org/10.1016/0169-555x(88)90017-7.

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42

Persico, Lyman, e Grant Meyer. "Holocene beaver damming, fluvial geomorphology, and climate in Yellowstone National Park, Wyoming". Quaternary Research 71, n. 3 (maggio 2009): 340–53. http://dx.doi.org/10.1016/j.yqres.2008.09.007.

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AbstractWe use beaver-pond deposits and geomorphic characteristics of small streams to assess long-term effects of beavers and climate change on Holocene fluvial activity in northern Yellowstone National Park. Although beaver damming has been considered a viable mechanism for major aggradation of mountain stream valleys, this has not been previously tested with stratigraphic and geochronologic data. Thirty-nine radiocarbon ages on beaver-pond deposits fall primarily within the last 4000 yr, but gaps in dated beaver occupation from ~ 2200–1800 and 950–750 cal yr BP correspond with severe droughts that likely caused low to ephemeral discharges in smaller streams, as in modern severe drought. Maximum channel gradient for reaches with Holocene beaver-pond deposits decreases with increasing basin area, implying that stream power limits beaver damming and pond sediment preservation. In northern Yellowstone, the patchy distribution and cumulative thickness of mostly < 2 m of beaver-pond deposits indicate that net aggradation forced by beaver damming is small, but beaver-enhanced aggradation in some glacial scour depressions is greater. Although 20th-century beaver loss and dam abandonment caused significant local channel incision, most downcutting along alluvial reaches of the study streams is unrelated to beaver dam abandonment or predates historic beaver extirpation.

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43

Townsend, Kirk F., Michelle S. Nelson, Tammy M. Rittenour e Joel L. Pederson. "Anatomy and evolution of a dynamic arroyo system, Kanab Creek, southern Utah, USA". GSA Bulletin 131, n. 11-12 (2 maggio 2019): 2094–109. http://dx.doi.org/10.1130/b35195.1.

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Abstract Many alluvial valleys in the American Southwest are entrenched within continuous arroyos, and stratigraphic evidence indicates that these fluvial systems experienced repeated periods of entrenchment and aggradation during the mid- to late-Holocene. Previous research suggests arroyo dynamics were regionally quasi-synchronous, implying that they were driven by allogenic forcing due to hydroclimatic fluctuations. However, several of these interpretations rely on records with limited age control and include distal correlations across the American Southwest. While hydroclimatic variability must exert some role, autogenic mechanisms related to catchment-specific geomorphic thresholds are hypothesized to partially control the timing of arroyo dynamics. If driven by autogenic processes, episodes of arroyo cutting and filling may not be regionally contemporaneous. Recent improvements in dating methods permit more detailed reconstructions of the timing and evolution of arroyo dynamics, allowing for a more nuanced assessment of these competing hypotheses. Here we present a uniquely large and focused chronostratigraphic data set from two alluvial reaches of Kanab Creek, located in the Grand Staircase region of southern Utah. Episodes of prehistoric arroyo cutting and filling are reconstructed from 27 sites through recognition of soils and buttressed unconformities in the arroyo-wall stratigraphy, and age control derived from 54 optically stimulated luminescence (OSL) ages and 50 radiocarbon ages. Our chronostratigraphic data set indicates five periods of channel aggradation occurred since ca. 6.0 ka, with each interrupted by an episode of arroyo entrenchment. Repeated aggradation to a similar channel elevation suggests attainment of a threshold profile, and comparison of the pre-entrenchment longitudinal profile with the modern arroyo channel demonstrates that changes between end-member entrenched and aggraded states are expressed in channel concavity and slope. We propose that arroyo dynamics are partially driven by sediment supply and the rate of channel aggradation, and that these systems must approach complete re-filling before they become sensitive to incision. Entrenchment itself appears to be associated with rapid transitions from pronounced decadal-scale aridity to pluvial (wetter) periods. Not all such hydroclimatic fluctuations are associated with arroyo entrenchment, which highlights the importance of threshold controls on the behavior of these systems. The collective period of “dynamic instability” characterized by epicycles of arroyo entrenchment and aggradation did not initiate until the mid-Holocene, when a climatic shift toward warmer and drier conditions likely increased fine-grained sediment supply to the fluvial system.

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44

S. Kale, Vishwas. "Mid to late Quaternary Fluvial activity in allochthonous river systems of the Maharashtra Plateau, India: A review and new observations". Journal of Palaeosciences 70, n. (1-2) (10 settembre 2021): 289–304. http://dx.doi.org/10.54991/jop.2021.20.

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The Maharashtra Plateau dominantly displays an erosional landscape and the Quaternary alluvial deposits in the valleys are remarkably limited in areal extent and thickness. The only exceptions are the infilled basins/valleys downstream of bedrock gorges with knickpoints. Earlier studies have inferred a good correspondence between the major changes in the monsoon regime and the fluvial activity (aggradation and incision/excavation) on the regional–scale during the last ~103 –105 years. However, geomorphic evidence suggests that some of the mid to late Quaternary aggradational events may not be directly related to known climatic events and the fluvial activity in some of the tributaries did not correspond with the recognized regional behavioural pattern. Basin–specific tectonic activity as well as alterations in the isohyetal pattern in the rainshadow zone appear to be the plausible reasons for the observed variations in the fluvial responses. The relationship between Quaternary climate changes and the fluvial activity, even in this area of uniform lithology, appears to be a complex one.

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45

Gilbert, Graham L., Stefanie Cable, Christine Thiel, Hanne H. Christiansen e Bo Elberling. "Cryostratigraphy, sedimentology, and the late Quaternary evolution of the Zackenberg River delta, northeast Greenland". Cryosphere 11, n. 3 (30 maggio 2017): 1265–82. http://dx.doi.org/10.5194/tc-11-1265-2017.

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Abstract. The Zackenberg River delta is located in northeast Greenland (74°30′ N, 20°30′ E) at the outlet of the Zackenberg fjord valley. The fjord-valley fill consists of a series of terraced deltaic deposits (ca. 2 km2) formed during relative sea-level (RSL) fall. We investigated the deposits using sedimentological and cryostratigraphic techniques together with optically stimulated luminescence (OSL) dating. We identify four facies associations in sections (4 to 22 m in height) exposed along the modern Zackenberg River and coast. Facies associations relate to (I) overriding glaciers, (II) retreating glaciers and quiescent glaciomarine conditions, (III) delta progradation in a fjord valley, and (IV) fluvial activity and niveo-aeolian processes. Pore, layered, and suspended cryofacies are identified in two 20 m deep ice-bonded sediment cores. The cryofacies distribution, together with low overall ground-ice content, indicates that permafrost is predominately epigenetic in these deposits. Fourteen OSL ages constrain the deposition of the cored deposits to between approximately 13 and 11 ka, immediately following deglaciation. The timing of permafrost aggradation was closely related to delta progradation and began following the subaerial exposure of the delta plain (ca. 11 ka). Our results reveal information concerning the interplay between deglaciation, RSL change, sedimentation, permafrost aggradation, and the timing of these events. These findings have implications for the timing and mode of permafrost aggradation in other fjord valleys in northeast Greenland.

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46

Candy, Ian, Stuart Black e Bruce W. Sellwood. "U-series isochron dating of immature and mature calcretes as a basis for constructing Quaternary landform chronologies for the Sorbas basin, southeast Spain". Quaternary Research 64, n. 1 (luglio 2005): 100–111. http://dx.doi.org/10.1016/j.yqres.2005.05.002.

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AbstractImmature and mature calcretes from an alluvial terrace sequence in the Sorbas basin, southeast Spain, were dated by the U-series isochron technique. The immature horizons consistently produced statistically reliable ages of high precision. The mature horizons typically produced statistically unreliable ages but, because of linear trends in the dataset and low errors associated with each data point, it was still possible to place a best-fit isochron through the dataset to produce an age with low associated uncertainties. It is, however, only possible to prove that these statistically unreliable ages have geochronological significance if multiple isochron ages are produced for a single site, and if these multiple ages are stratigraphically consistent. The geochronological significance of such ages can be further proven if at least one of the multiple ages is statistically reliable. By using this technique to date calcretes that have formed during terrace aggradation and at the terrace surface after terrace abandonment it is possible not only to date the timing of terrace aggradation but also to constrain the age at which the river switched from aggradation to incision. This approach, therefore, constrains the timing of changes in fluvial processes more reliably than any currently used geochronological procedure and is appropriate for dating terrace sequences in dryland regions worldwide, wherever calcrete horizons are present.

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47

Aricò, C., e T. Tucciarelli. "Diffusive Modeling of Aggradation and Degradation in Artificial Channels". Journal of Hydraulic Engineering 134, n. 8 (agosto 2008): 1079–88. http://dx.doi.org/10.1061/(asce)0733-9429(2008)134:8(1079).

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48

Bhallamudi, S. Murty, e M. Hanif Chaudhry. "Numerical Modeling of Aggradation and Degradation in Alluvial Channels". Journal of Hydraulic Engineering 117, n. 9 (settembre 1991): 1145–64. http://dx.doi.org/10.1061/(asce)0733-9429(1991)117:9(1145).

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49

Bradford, Scott F., e Nikolaos D. Katopodes. "Hydrodynamics of Turbid Underflows. II: Aggradation, Avulsion, and Channelization". Journal of Hydraulic Engineering 125, n. 10 (ottobre 1999): 1016–28. http://dx.doi.org/10.1061/(asce)0733-9429(1999)125:10(1016).

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50

Simms, Alexander R., John B. Anderson e Michael Blum. "Barrier-island aggradation via inlet migration: Mustang Island, Texas". Sedimentary Geology 187, n. 1-2 (maggio 2006): 105–25. http://dx.doi.org/10.1016/j.sedgeo.2005.12.023.

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