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1.
Weichselian geomorphological and fluvial evolution has been recorded in the valley fill of the Reusel, a small tributary of the lower Maas river. It has been studied by means of borehole sections. A first deep incision into the substratum occurred during the Early Weichselian-Lower Pleniglacial. This was followed by aggradation, at first by a braided river, at a later date by a meandering river, dating respectively from the Lower and Middle Pleniglacial. The Upper Pleniglacial aggradation again points to a braided river system. The end of the Pleniglacial is characterized by aeolian infilling of the valley and decreasing carrying capacity of the river.  相似文献   

2.
The actively deformed foreland of eastern Qilian Shan (mountains) contains well‐preserved geomorphic features such as erosion surfaces, river terraces and tectonically uplifted alluvial fans, providing suitable archives for research on regional tectonic activities and palaeoclimatic changes. These geomorphic surfaces are well dated by using a combination of magnetostratigraphy, electron spin resonance, thermoluminescence, infra‐red stimulated luminescence, radiocarbon dating, and correlation with the well‐established loess–palaeosol sequences of China. Our results show that the erosion surface formed about 1·4 Ma ago, and the age of river terraces is 1·24 Ma, 820–860 ka, 780 ka, 420–440 ka, 230–250 ka, 140 ka, 60 ka and 10 ka, respectively. Valley incision rates of c. 0·09–0·25 m ka?1 have been identified. The repetitive stratigraphic and geomorphic pattern of these terraces indicates the fluvial sedimentation–incision cycles are tightly associated with the 100‐ka glacial–interglacial climatic cycles. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

3.
Although river confluences have received geomorphic attention in recent years it is difficult to upscale these studies, so confluence‐dominated reaches are commonly presumed to be either: (1) braided; or (2) meandering and characterized by laterally migrating channels. If the geomorphology of a confluence zone is to be considered over longer timescales, changes in river style need to be taken into account. This paper uses a combination of remote sensing techniques (LiDAR, GPR, ER), borehole survey and chronometric dating to test this differentiation in the confluence‐zone of a medium‐sized, mixed‐load, temperate river system (Trent, UK), which on the basis of planform evidence appears to conform to the meandering model. However, the analysis of ‘confluence sediment body stratigraphy’ demonstrates that the confluence does not correspond with a simple meander migration model and chronostratigraphic data suggests it has undergone two major transformations. Firstly, from a high‐energy braid‐plain confluence in the Lateglacial (25–13 K yrs cal BP), to a lower‐energy braided confluence in the early to middle Holocene (early Holocene‐2.4 kyr BP), which created a compound terrace. Second, incision into this terrace, creating a single‐channel confluence (2.4–0.5 kyr cal BP) with a high sinuosity south bank tributary (the River Soar). The confluence sediment‐body stratigraphy is characterized by a basal suite of Late Pleistocene gravels bisected by younger channel fills, which grade into the intervening levee and overbank sediments. The best explanation for the confluence sediment body stratigraphy encountered is that frequent switching (soft‐avulsions sensu Edmonds et al., 2011) of the tributary are responsible for the downstream movement of the channel confluence (at an average rate of approximately 0.5 m per year) dissecting and reworking older braid‐plain sediments. The late Holocene evolution of the confluence can be seen as a variant of the incisional‐frequent channel reorganization (avulsion) model with sequential downstream migration of the reattachment point. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

4.
Effective river management strategies require an understanding of how fluvial processes vary both spatially and temporally. Here, we examine the natural range of variability in the Conejos River Valley, southern Colorado, through documentation of terrace morphostratigraphic and sedimentological characteristics as well as through investigation of sediment contributions from headwaters, hillslopes and tributary streams. Additionally, soil development and radiocarbon ages, together with local and regional paleoclimate reconstructions, were used to infer the range of processes acting in this system. Since de‐glaciation, the Conejos River has fluctuated between episodes of bedrock strath formation, aggradation and vertical incision. Morphostratigraphic relationships, soil development and radiocarbon ages enable us to propose a chronology for periods of alluvial deposition (around 8·9–7·6 ka, 5·5 ka and from 3·5 to 1·1 ka), separated by intervals of fluvial incision. We infer potential forcing mechanisms by utilizing multiple working hypotheses. Specifically, we discuss the potential for increases in sediment supply during periods of (1) para‐glacial adjustment, (2) climatic cooling, (3) increased frequency of climate change and (4) increased fire frequency or severity. We also consider the effects of changes in stream discharge and extreme storm occurrence. We conclude that combinations of these processes, operating at different times, have contributed to sediment mobilization since de‐glaciation. Stream and landform morphology also varies longitudinally due to the influence of remnant glacial topography. In particular, valley bottom overdeepening at tributary junctions has resulted in incision and strath formation into unlithified glacial deposits (i.e. fill‐cut terraces) rather than bedrock in some reaches. Overall, the Conejos fluvial system has varied significantly both temporally and spatially since de‐glaciation and appears to be sensitive to changes in sediment supply related to Holocene scale climate fluctuations. This natural range of variability must therefore be a key consideration in any future stream management policies. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

5.
Geomorphological analyses of the morphology, lithostratigraphy and chronology of Holocene alluvial fills in a 2·75 km long piedmont reach of the wandering gravel‐bed River South Tyne at Lambley in Northumberland, northern England, have identified spatial and temporal patterns of late Holocene channel and floodplain development and elucidated the relationship between reach‐ and subreach‐scale channel transformation and terrace formation. Five terraced alluvial fills have been dated to periods sometime between c. 1400 BC –AD 1100, AD 1100–1300, AD 1300–1700, AD 1700–1850 and from AD 1850 to the present. Palaeochannel morphology and lithofacies architecture of alluvial deposits indicate that the past 3000 years has been characterized by episodic channel and floodplain change associated with development and subsequent recovery of subreach‐scale zones of instability which have been fixed in neither time nor space. Cartographic and photographic evidence spanning the past 130 years suggests channel transformation can be accomplished in as little as 50 years. The localized and episodic nature of fluvial adjustment at Lambley points to the operation of subreach‐scale controls of coarse sediment transfers. These include downstream propagation of sediment waves, as well as internal controls imposed by differing valley floor morphology, gradient and boundary materials. However, the preservation of correlated terrace levels indicates that major phases of floodplain construction and entrenchment have been superimposed over locally complex patterns of sediment transfer. Reach‐scale lateral and vertical channel adjustments at Lambley appear to be closely related to climatically driven changes in flood frequency and magnitude, with clusters of extreme floods being particularly important for accomplishing entrenchment and reconfiguring the pattern of localized instability zones. Confinement of flood flows by valley entrenchment, and contamination of catchment river courses by metal‐rich fine sediments following recent historic mining operations, have combined to render the South Tyne at Lambley increasingly sensitive to changes in flood regimes over the past 1000 years. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

6.
Determining sediment transfer times is key to understanding source-to-sink dynamics and the transmission of environmental signals through the fluvial system. Previous work on the Bolivian Altiplano applied the in situ cosmogenic 14C-10Be-chronometer to river sands and proposed sediment storage times of ~10–20 kyr in four catchments southeast of Lake Titicaca. However, the fidelity of those results hinges upon isotopic steady-state within sediment supplied from the source area. With the aim of independently quantifying sediment storage times and testing the 14C-10Be steady-state assumption, we dated sediment storage units within one of the previously investigated catchments using radiocarbon dating, cosmogenic 10Be-26Al isochron burial dating, and 10Be-26Al depth-profile dating. Palaeosurfaces appear to preserve remnants of a former fluvial system, which has undergone drainage reversal, reduction in catchment area, and local isostatic uplift since ~2.8 Ma. From alluvium mantling the palaeosurfaces we gained a deposition age of ~580 ka, while lower down fluvial terraces yielded ≤34 ka, and floodplains ~3–1 ka. Owing to restricted channel connectivity with the terraces and palaeosurfaces, the main source of channel sediment is via reworking of the late Holocene floodplain. Yet modelling a set of feasible scenarios reveals that floodplain storage and burial depth are incompatible with the 14C-10Be disequilibrium measured in the channel. Instead we propose that the 14C-10Be offset results from: (i) non-uniform erosion whereby deep gullies supply hillslope-derived debris; and/or (ii) holocene landscape transience associated with climate or human impact. The reliability of the 14C-10Be chronometer vitally depends upon careful evaluation of sources of isotopic disequilibrium in a wide range of depositional and erosional landforms in the landscape. © 2018 John Wiley & Sons, Ltd.  相似文献   

7.
Terraces and floodplains are important indicators of near‐channel sediment dynamics, serving as potential sediment sources and sinks. Increasing availability of high resolution topography data over large areas calls for development of semi‐automated techniques for identification and measurement of these features. In this study we introduce a novel tool that accommodates user‐defined parameters including, a local‐relief threshold selected by a variable‐size moving window, minimum area threshold, and maximum distance from the channel to identify and map discrete terrace and floodplain surfaces. Each of the parameters can easily be calibrated for a given watershed or reach. Subsequently, the tool automatically measures planform area, absolute elevation, and height relative to the local river channel for each terrace polygon. We validate the tool in two locations where terrace maps were previously developed via manual digitization from lidar and extensive field mapping campaigns. The tool is also tested on six different types of rivers to provide examples of starting selection parameters, and to test effectiveness of the tool across a wide range of landscapes. Generally, the tool provides a high quality draft map of terrace and floodplain surfaces across the wide range of environmental conditions for which it has been tested. We find that the tool functions best in catchments where the terraces are spatially extensive, with distinct differences between the terrace and floodplain. The most challenging environments for semi‐automated terrace and floodplain mapping include steep catchments with dense riparian vegetation, and very small terraces (~10 m2 in areal extent). We then apply the tool to map terraces and floodplains in the Root River watershed, southeastern Minnesota and generate exceedance plots for terrace heights. These plots provide a first pass analysis to indicate the tributaries and reaches of the river where terraces constitute a significant source of sediment. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

8.
Changes in floodplain sediment dynamics have profound effects on riverine habitats and riparian biodiversity. Depopulation due to socio‐economic changes in the Dragonja catchment (91 km2) in southwestern Slovenia resulted in the abandonment of agricultural fields, followed by natural reforestation since 1945. This profoundly changed the water and sediment supply to the streams, as well as floodplain sediment deposition. This paper presents a reconstruction of the development of the Dragonja floodplain due to these land use changes during the last 60 years. The reconstruction is based on dating of floodplain sediments using 137Cs profiles, measurement of actual sedimentation rates using artificial grass sedimentation mats, and linking this information to the present‐day hydrological behaviour of the river. The sedimentation mats showed that floodplain sedimentation was restricted to peak flows of considerable magnitude. Due to the reforestation, the return period of such high flows increased from 0·31 year in the period 1960–1985 to 0·81 year between 1986 and 2003, with commensurate changes in sedimentation rates. At the 1·5 m river terrace (formed about 60 years ago), 137Cs‐based sedimentation rates (1960–1986) were roughly twice the rates inferred from the artificial grass mats (2001–2003). This finding matches the increase in the return period for larger peak events during the 1986–2003 period, which caused fewer major inundations at this level. Conversely, sedimentation rates determined for the lowest terrace at 0·5 m were similar for both techniques (and periods) because the return periods of the peak events responsible for sediment deposition at this lower level did not change much over the period 1986–2003. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

9.
Physically‐based modelling of rivers has advanced in recent decades by developing separate approaches for representing single‐thread and multi‐thread channels. This paper reports on a new morphodynamic model developed with the goal of simulating river and floodplain co‐evolution within a general framework suitable for investigating diverse fluvial styles. Simulations illustrate the potential for representing meandering, braided and anabranching channels using this model. Moreover, by adopting relatively simple parameterizations of many processes, this work provides insight into what may constitute sufficient (minimal) model complexity, and highlights uncertainties that should be addressed by future research. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

10.
There is limited knowledge about the preservation of aggradation phases in Quaternary fluvial records. Previous numerical modelling of erosion and deposition in Late Quaternary Allier River (France) generated the prediction that this river has reach-specific fluvial dynamics related to climate-driven tributary sediment-flux dynamics. To test this prediction, new optically stimulated luminescence (OSL) samples were collected of the Late Quaternary Fx terrace at five locations along a stretch of 60 km. OSL dates of both quartz and feldspar sand grains indicate that all relatively basalt-poor sediments display significantly different ages for each reach (ranging from 36.3 ± 2.0 to 21.1 ± 2.3 ka). The more basalt-rich terrace body consistently yields ages in the range 21.1 ± 1.7 to 16.1 ± 1.5 ka, suggesting contemporaneous aggradation along the whole studied Allier reach during this interval. Our own new OSL date of a Tartaret eruption around 16.8 ± 2.5 ka also fits this time window, suggesting a direct link with volcanic activity. However, there are many more dated volcanic events that coincide with the older basalt-poor units, making it less likely that a direct link between terrace-sediment basalt content and volcanic activity exists. The timings of the dated depositional events in MIS 3 and 2 all match with simulated climate drivers and published landscape erosion rates. Counterintuitively, the volcanic Chaîne des Puys area supplied more sediment during the cold and dry Last Glacial Maximum. Basalt content in the Allier terrace sediments reflects climate-related sediment-flux dynamics upstream. The scarcity of older basalt-poor sediment bodies from MIS 4 and 3 in the Fx terrace suggests that less sediment was supplied and/or the intermittent erosional phases in the Allier were very effective at removing them. We hypothesize that this observation of predominant preservation of the last aggradation phase could be a common phenomenon in most climate-driven terraces. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

11.
Numerical models have not yet systematically been used to predict properties of fluvial terrace records in order to guide fieldwork and sampling. This paper explores the potential of the longitudinal profile model FLUVER2 to predict testable field properties of the relatively well‐studied, Late Quaternary Allier system in France. For the Allier terraces an overlapping 14C and U‐series chronology as well as a record of 10Be erosion rates exist. The FLUVER2 modelling exercise is focused on the last 50 ka of the upper Allier reach because for this location and period the constraints of the available dating techniques are tightest. A systematic calibration based on terrace occurrence and thicknesses was done using three internal parameters related to (1) the sediment erodibility; (2) the sediment transport distance; and (3) the sediment supply derived from the surrounding landscape. As external model inputs, the best available, reconstructed, tectonic, climatic and base‐level data were used. Calibrated model outputs demonstrate a plausible match with the existing fluvial record. Validation of model output was done by comparing the modelled and measured timing of aggradation and incision phases for the three locations. The modelled range of landscape erosion rates showed a reasonably good match with existing erosion rate estimates derived from 10Be measurements of fluvial sands. The quasi‐validated model simulation was subsequently used to make new testable predictions about the timing and location of aggradation and erosion phases for three locations along the Allier river. The validated simulations predict that along the Allier, reach‐specific dynamics of incision and aggradation, related to the variations in sediment supply by major tributaries, cause relevant differences in the local fluvial terrace stratigraphy. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

12.
The Bellinger River catchment in the New England Fold Belt on the mid‐north coast of New South Wales is characterized by an assemblage of stepped late Quaternary alluvial units. Late Pleistocene terraces were formed by large, more competent rivers that eroded almost entire valley floors; however, a decline in discharge prior to the Holocene has resulted in the abandonment of these deposits as elevated terraces or residual alluvium, onlapped by contemporary floodplains. Intrinsic controls on floodplain formation appear to be superimposed over an early–mid‐Holocene climatic signature. A fluvially active period, known as the Nambucca Phase, from 10 to 4·5 ka, eroded Late Pleistocene terraces. Two floodplain surfaces, one higher than the other, both started to accrete vertically from 4 ka but with some valley locations remaining vulnerable to episodes of erosion, resulting in substantial units of even younger basal alluvium. The high floodplain is dominated by horizontally laminated, vertically accreted sequences, while the low floodplain, which overlaps in age, is characterized by pronounced cut‐and‐fill stratigraphy. Terraces and floodplains in partly confined settings can have similar elevations but be polycyclic, with very different basal ages. In such landscapes the classical assumption that individual terrace or floodplain profiles along a valley represent periods of coeval formation is shown to be frequently invalid. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

13.
The relative chronology of landscape evolution across the unglaciated Appalachian plateaus of Kentucky and Tennessee is well documented. For more than a century, geomorphologists have carefully mapped and correlated upland erosional surfaces inset by wide‐valley straths and smaller terraces. Constraining the timing of river incision into the Appalachian uplands was difficult in the past due to unsuitable dating methods and poorly preserved surface materials. Today, burial dating using the differential decay of cosmogenic 26Al and 10Be in clastic cave sediments reveals more than five million years of landscape evolution preserved underground. Multilevel caves linked hydrologically to the incision history of the Cumberland River contain in situ sediments equivalent to fluvial deposits found scattered across the Eastern Highland Rim erosional surface. Cave sediments correlate with: (1) thick Lafayette‐type gravels on the Eastern Highland Rim deposited between c. 5·7 and c. 3·5 Ma; (2) initial incision of the Cumberland River into the Eastern Highland Rim after c. 3·5 Ma; (3) formation of the Parker strath between c. 3·5 Ma and c. 2·0 Ma; (4) incision into the Parker strath at c. 2 Ma; (5) formation of a major terrace between c. 2·0 Ma and c. 1·5 Ma; (6) shorter cycles of accelerated incision and base level stability beginning at c. 1·5 Ma; and (7) regional aggradation at c. 0·85 Ma. Initial incision into the Appalachian uplands is interpreted as a response to eustasy at 3·2–3·1 Ma. Incision of the Parker strath is interpreted as a response to eustasy at 2·5–2·4 Ma. A third incision event at c. 1·5 Ma corresponds with glacial reorganization of the Ohio River basin. Widespread aggradation of cave passages at c. 0·85 Ma is interpreted as the beginning of intense glacial–interglacial cycling associated with global climate change. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

14.
Abstract A multidisciplinary study was conducted on the section of the Siwalik Group sediments, approximately 5000 m thick, exposed along the Karnali River. Analysis of facies, clay mineralogy and neodymium isotope compositions revealed significant changes in the sedimentary record, allowing discussion of their tectonic or climatic origin. Two major changes within the sedimentary fill were detected: the change from a meandering to a braided river system at ca 9.5 Ma and the change from a deep sandy braided to a shallow sandy braided river system at ca 6.5 Ma. The 9.5‐Ma change in fluvial style is contemporaneous with an abrupt increase of ?Nd(0) values following a ?Nd(0) minimum. This evolution indicates a change in source material and erosion of Lesser Himalayan rocks within the Karnali catchment basin between 13 and 10 Ma. The tectonic activity along the Ramgarh thrust caused this local exhumation. By changing the proximity and morphology of relief, the forward propagation of the basal detachment to the main boundary thrust was responsible for the high gradient and sediment load required for the development of the braided river system. The change from a deep sandy braided to a shallow sandy braided river system at approximately 6.5 Ma was contemporaneous with a change in clay mineralogy towards smectite‐/kaolinite‐dominant assemblages. As no source rock change and no burial effect are detected at that time, the change in clay mineralogy is interpreted as resulting from differences in environmental conditions. The facies analysis shows abruptly and frequently increasing discharges by 6.5 Ma, and could be linked to an increase in seasonality, induced by intensification of the monsoon climate. The major fluvial changes deciphered along the Karnali section have been recognized from central to western Nepal, although they are diachronous. The change in clay mineralogy towards smectite‐/kaolinite‐rich assemblages and the slight decrease of ?Nd(0) have also been detected in the Bengal Fan sedimentary record, showing the extent and importance of the two major events recorded along the Karnali section.  相似文献   

15.
Field studies suggest that a cohesive floodplain is a necessary condition for meandering in contrast to braided rivers. However, it is only partly understood how the balance between floodplain construction by overbank deposition and removal by bank erosion and chutes leads to meandering. This is needed because only then does a dynamic equilibrium exist and channels maintain meandering with low width–depth ratios. Our objective is to understand how different styles of floodplain formation such as overbank deposition and lateral accretion cause narrower channels and prevent chute cutoffs that lead to meandering. In this study we present two experiments with a self‐forming channel in identical conditions, but to one we added cohesive silt at the upstream boundary. The effect of cohesive silt on bank stability was tested in auxiliary bank erosion experiments and showed that an increase in silt reduced erosion rates by a factor of 2. The experiment without silt developed to a braided river by continuous and extensive shifting of multiple channels. In contrast, in the meandering river silt deposits increased bank stability of the cohesive floodplain and resulted in a reduction of chute cutoffs and increased sinuosity by continuous lateral migration of a single channel. Overbank flow led to deposition of the silt and two styles of cohesive floodplain were observed: first, overbank vertical‐accretion of silt, e.g. levee, overbank sedimentation or splays; and second, lateral point bar accretion with silt on the scrolls and in the swales. The first style led to a reduction in bank erosion, while the second style reduced excavation of chutes. We conclude that sedimentation of fine cohesive material on the floodplain by discharge exceeding bankfull is a necessary condition for meandering. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

16.
Cosmogenic 26Al, 10Be, and 14C dating of fluvial fill terraces in steep canyons of the Colorado Front Range provides a temporal framework for analysing episodic aggradation and incision. Results from Boulder Canyon show that terrace heights above the modern channel (grade) can be divided into: (1) Bull Lake (≳100 ka; 20–15 m above grade); (2) Pinedale (32–10 ka; 15–4 m above grade); and (3) Holocene age (<4 m above grade). No pre‐Bull Lake deposits are preserved along Boulder Canyon, and only three small remnants >15 m above grade record Bull Lake deposition. Well‐preserved terraces of Pinedale age suggest that the range of terrace height above grade reflects short‐term fluctuations in the river profile during periods of rapidly changing stream load and power. Net river incision apparently occurred during transitions to interglacial periods. Soil development and stratigraphic position, along with limited cosmogenic and 14C dating, suggest that ∼130 ka terraces in Boulder Canyon correlate with the Louviers Alluvium, and that 32 to 10 ka fills in the canyon correlate with the Broadway Alluvium on the adjacent High Plains. Late Pleistocene incision rates (∼0·15 m ka−1) along Boulder Canyon exceed pre‐late Pleistocene incision rates, and are higher than middle to late Pleistocene incision rates (∼0·04 m ka−1) on the High Plains. This study provides an example of how modern geochronologic techniques allow us to understand better rivers that drain glaciated catchments. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

17.
This paper presents a field investigation on river channel storage of fine sediments in an unglaciated braided river, the Bès River, located in a mountainous region in the southern French Prealps. Braided rivers transport a very large quantity of bedload and suspended sediment load because they are generally located in the vicinity of highly erosive hillslopes. Consequently, these rivers play an important role because they supply and control the sediment load of the entire downstream fluvial network. Field measurements and aerial photograph analyses were considered together to evaluate the variability of fine sediment quantity stored in a 2·5‐km‐long river reach. This study found very large quantities of fine sediment stored in this reach: 1100 t per unit depth (1 dm). Given that this reach accounts for 17% of the braided channel surface area of the river basin, the quantities of fine sediment stored in the river network were found to be approximately 80% of the mean annual suspended sediment yields (SSYs) (66 200 t year?1), comparable to the SSYs at the flood event scale: from 1000 t to 12 000 t depending on the flood event magnitude. These results could explain the clockwise hysteretic relationships between suspended sediment concentrations and discharges for 80% of floods. This pattern is associated with the rapid availability of the fine sediments stored in the river channel. This study shows the need to focus on not only the mechanisms of fine sediment production from hillslope erosion but also the spatiotemporal dynamics of fine sediment transfer in braided rivers. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

18.
Depositional environments along the tidal river downstream of Óbidos have been proposed as important sinks for up to one third of the sediment discharge from the Amazon River. However, the morphology of the intertidal floodplain and the dynamics of sediment exchange along this reach have yet to be described. River-bank surveys in five regions along the Amazon tidal river reveal a distinct transition in bank morphology between the upper, central and lower reaches of the tidal river. The upper tidal-river floodplain is defined by prominent natural levees that control the transfer of water and sediment between the mainstem Amazon River and its floodplain. Greater tidal influence in the central tidal river suppresses levee development, and tidal currents increase sediment transport into the distal parts of the floodplain. In the lower tidal river, the floodplain morphology closely resembles marine intertidal environments (e.g. mud flats, salt marshes), with dendritic tidal channels incising elevated vegetated flats. Theory, morphology and geochronology suggest that the dynamics of sediment delivery to the intertidal floodplain of the Amazon tidal river vary along its length due to the relative influence and coupling of fluvial and tidal dynamics. © 2018 John Wiley & Sons, Ltd.  相似文献   

19.
This paper describes and analyses a hillslope–channel slope failure event that occurred at Wet Swine Gill, Lake District, northern England. This comprised a hillslope slide (180 m3, c. 203 ± 36 t), which coupled with the adjacent stream, resulting in a channelized debris flow and fluvial flood. The timing of the event is constrained between January and March 2002. The hillslope failure occurred in response to a rainfall/snowmelt trigger, on ground recently disturbed by a heather moorland fire and modified by artificial drainage. Slide and flow dynamics are estimated using reconstructed velocity and discharge values along the sediment transfer path. There is a rapid downstream reduction in both maximum velocity, from 9·8 to 1·3 m s?1; and maximum discharge, ranging from 33·5 to 2·4 m3 s?1. A volumetric sediment budget quantified a high degree of coupling between the hillslope and immediate channel (～92%: 167 m3), but virtually all of the sediment was retained in the first‐order tributary channel. Approximately 44% (81 m3) of the slide volume was retained in the run‐up deposit, and termination of the debris flow prior to the main river meant that the remainder did not discharge into the fluvial system downstream. These results suggest poor transmission of sediment to the main river at the time of the event, but importantly an increase in available material for post‐event sediment transfer processes within the small upland tributary. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

20.
1 INTRODUCTION The construction of more than 75,000 dams and reservoirs on rivers in the United States (Graf, 1999) has resulted in alteration of the hydrology, geometry, and sediment flow in many of the river channels downstream of dams. Additionally, hydrologic and geomorphic impacts lead to changes in the physical habitat affecting both the flora and fauna of the riparian and aquatic environments. Legislation for protection of endangered species as well as heightened interest in ma…  相似文献   

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