9 results
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2. Prediction of Transient Bed Profiles in an Aggrading Stream Using ANN
- Author
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Das, Arindom, Kumar, Virender, Maji, Soumen, Bhattacharjee, Ratnajit, editor, Neog, Debanga Raj, editor, Mopuri, Konda Reddy, editor, and Vipparthi, Santosh Kumar, editor
- Published
- 2023
- Full Text
- View/download PDF
3. Alluvial fan response to Alpine Fault earthquakes on the Westland piedmont, Whataroa, Aotearoa‐New Zealand.
- Author
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Almond, Peter C., Berryman, Kelvin, Villamor, Pilar, Read, Stuart, Alloway, Brent V., and Tonkin, Philip
- Subjects
ALLUVIAL fans ,CHI-chi Earthquake, Taiwan, 1999 ,EARTHQUAKES ,AGRICULTURE ,RIPARIAN areas ,CARBON isotopes ,LANDSLIDES - Abstract
We examined the stratigraphy of alluvial fans formed at the steep range front of the Southern Alps at Te Taho, on the north bank of the Whataroa River in central West Coast, South Island, New Zealand. The range front coincides with the Alpine Fault, an Australian‐Pacific plate boundary fault, which produces regular earthquakes. Our study of range front fans revealed aggradation at 100‐ to 300‐year intervals. Radiocarbon ages and soil residence times (SRTs) estimated by a quantitative profile development index allowed us to elucidate the characteristics of four episodes of aggradation since 1000 CE. We postulate a repeating mode of fan behaviour (fan response cycle [FRC]) linked to earthquake cycles via earthquake‐triggered landslides. FRCs are characterised by short response time (aggradation followed by incision) and a long phase when channels are entrenched and fan surfaces are stable (persistence time). Currently, the Te Taho and Whataroa River fans are in the latter phase. The four episodes of fan building we determined from an OxCal sequence model correlate to Alpine Fault earthquakes (or other subsidiary events) and support prior landscape evolution studies indicating ≥M7.5 earthquakes as the main driver of episodic sedimentation. Our findings are consistent with other historic non‐earthquake events on the West Coast but indicate faster responses than other earthquake sites in New Zealand and elsewhere where rainfall and stream gradients (the basis for stream power) are lower. Judging from the thickness of fan deposits and the short response times, we conclude that pastoral farming (current land‐use) on the fans and probably across much of the Whataroa River fan would be impossible for several decades after a major earthquake. The sustainability of regional tourism and agriculture is at risk, more so because of the vulnerability of the single through road in the region (State Highway 6). [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
4. Sea-level changes and paleoenvironmental responses in a coastal Florida salt marsh over the last three centuries
- Author
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Seitz, Carina, Kenney, William F., Patterson-Boyarski, Brittany, Curtis, Jason H., Vélez, María I., Glodzik, Katie, Escobar, Jaime, and Brenner, Mark
- Published
- 2023
- Full Text
- View/download PDF
5. Alluvial fan aggradation in low relief, humid‐temperate landscapes, Uwharrie National Forest, North Carolina Piedmont.
- Author
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Opalka, Catherine E., Eppes, Martha‐Cary, Bobyarchick, Andy R., and Spatz, Andrew A.
- Subjects
ALLUVIAL fans ,FOREST reserves ,SOIL profiles ,AGGRADATION & degradation ,SEDIMENTATION & deposition ,DIGITAL elevation models - Abstract
We describe the soils, stratigraphy, distribution and ages of alluvial fans in the North Carolina Piedmont to understand factors contributing to their formation in this low relief, humid‐temperate setting. We find that those contributing factors (i.e., contributing source basin area and rock type; and climate) parallel, but do not precisely mimic those of arid and semi‐arid climate fans. Digital elevation model (DEM) and field observations revealed that about 25% of 209 mapped basin outlets contain alluvial fans. Fans are all < 0.01 km2 in area, with a contributing basin area threshold of ~0.1km2 above which fans are not commonly observed. Fans issuing from basins underlain by more easily weatherable and erodible argillites are generally larger than those that contain more resistant rhyolites. Radiocarbon dates of fan sediments are dominantly late Holocene (13 ages < 3000 ka; two ages between 7000–10,000 ka), with notably no late‐Pleistocene aged fans. We thus infer that fan aggradation is predicated on watershed characteristics – and climates – that favor high sediment supply to discharge ratios. Detailed soil and sediment descriptions from pits located on 15 fans reveal that approximately half exhibit cumulic over‐thickened soil profiles forming dominantly in sheetflood deposits, providing evidence of ongoing, relatively slow deposition. Low iron ratios measured from those fan soils suggests recycling of more developed soils from basin hillslopes. Occasional matrix‐supported debris flow deposits in some fans provide evidence of much less common, rapid (0.5–1 m) fan accumulation. While acknowledging a paucity of detailed climate records in the Piedmont precludes identifying precise mechanistic relationships, our mapping, soils and sedimentologic data suggest that climates favoring modest hillslope erosion without extreme runoff lead to periods of fan aggradation in this transport‐limited landscape. Overall, this work documents significant rock‐type modulated, climate‐driven Holocene landscape evolution in the south‐eastern US Piedmont predating legacy sediment erosion and deposition that has gone largely underappreciated. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
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6. Evolution of the Upper Reaches of Fluvial Systems within the Area of the East European Plain Glaciated during MIS 6.
- Author
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Panin, Andrey, Borisova, Olga, Belyaev, Vladimir, Belyaev, Yuri, Eremenko, Ekaterina, Fuzeina, Yulia, Sheremetskaya, Elena, and Sidorchuk, Aleksey
- Subjects
FLUVIAL geomorphology ,WATERSHEDS ,PLAINS ,EROSION ,HOLOCENE Epoch ,GLACIATION - Abstract
The headwaters of fluvial systems on the East European Plain between the boundaries of the Marine Isotope Stage 2 (MIS 2) and MIS 6 glaciations evolved during the last 150,000 years. At least three main events of high surface runoff caused intensive erosion: at the end of MIS 6, at the end of MIS 2 and in the Middle Holocene. Erosion developed in the territory with variable resistance of geological substrate, from hard-to-erode tills to weak sandy deposits. All erosional features in moraines formed in the pre-Holocene time. Even relatively large forms, such as balkas (small dry valleys), have not yet reached concave longitudinal profiles. A general tendency of their development was deepening. Short episodes of incision occurring during climatic events with increased water flow alternated with long periods of stabilization. Sand-covered areas are most favorable for linear erosion. The gullies formed in the Middle Holocene developed concave longitudinal profiles. The diversity of catchment areas, initial slope inclinations and sediment properties causing their resistance to erosion led to greater differences in the relief features and evolution of the upper reaches of the fluvial systems within the MIS 6 glaciation area compared to the more uniform landscape conditions in the extraglacial regions. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
7. Celerity and Height of Aggradation Fronts in Gravel-Bed Laboratory Channel.
- Author
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Zanchi, Barbara and Radice, Alessio
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FROUDE number ,BED load ,WATER supply ,SEDIMENT transport ,GRAVEL - Abstract
We present the results of laboratory experiments specifically designed to quantify the height and migration rate of an aggrading gravel front. The experiments were performed in sediment feed mode with constant water and sediment supply. Particular care was put into the experimental procedure and the methods to determine the quantities of interest to ensure reproducibility of the results. The celerity and height of an aggradation front were modeled as functions of the Froude number of the flow for the initial bed profile and of a load ratio defined as the ratio of the sediment feed rate to the transport capacity of the flow for the initial bed. The two control parameters (Froude number and load ratio) also determined the translational or dispersive nature of a sediment front. Two predictors were provided to estimate the dimensionless height and celerity of an aggradation front. The former was an increasing function of the load ratio and a decreasing function of the Froude number, and the latter was roughly proportional to the squared Froude number and had no evident relationship with the load ratio. The present results are of interest for scholars and practitioners needing to determine the key properties of swift gravel fronts as those developing, for example, during flash floods. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
8. Late-Holocene evolution of the Northern Bay of Cádiz from geomorphological, stratigraphic and archaeological data
- Author
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Claudia Caporizzo, L. Lagóstena, Gaia Mattei, A. Higueras-Milena, P. P. C. Aucelli, J.A. Ruiz, C. Martín-Puertas, C. Alonso, F.J. Gracia, L. Barbero, J.A. López-Ramírez, and I. Galán-Ruffoni
- Subjects
010506 paleontology ,geography ,geography.geographical_feature_category ,Fluvial ,Estuary ,010502 geochemistry & geophysics ,01 natural sciences ,law.invention ,Aggradation ,law ,Salt marsh ,Sedimentary rock ,Physical geography ,Radiocarbon dating ,Bay ,Holocene ,Geology ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
The present paper deals with the historical evolution of the northern Bay of Cadiz (SW Spain) between the last eustatic maximum (6.5 ka BP) and the present day, by means of a series of independent proxies. The zone is constituted by the tidal estuary of the Guadalete River, filled with saltmarsh sediments during the late Holocene, due to the sheltering of the zone by a confining outer sandy barrier. The northern border of the Bay records an urban settlement of Phoenician Age (first millennium BC), Dona Blanca. A detailed survey was made in the contact between the Phoenician city and the saltmarshes in order to detect other possible urban structures related to the morphological and sedimentary evolution of this environment during historical times. Two campaigns with GPR Stream-X array were carried out as well as aerial imaging and topographic survey with UAV. In parallel, a total of 8 boreholes were made in different parts of the saltmarshes, including radiocarbon dating of selected samples for estimating sedimentation rates in the saltmarshes. Results obtained by georadar prospection and UAV survey revealed the presence of a second urban settlement on the marginal sedimentary plain, very probably installed upon a sandy fluvial island of the Guadelete River. The urban remains, of Punic Age, are partly covered by clay sediments due to the subsequent evolution of these saltmarshes, where sedimentation rates of up to nearly 2.4 mm/yr have been estimated for environments close to fluvial and/or tidal channels and hence more affected by sediment aggradation during flooding episodes. In recent times, river regulation by dams and the artificial desiccation and cropping of the saltmarshes have interrupted the natural trend of the area towards sedimentary silting up.
- Published
- 2021
9. Mapping of major river terraces and assessment of their characteristics in Upper Pindar River Basin, Uttarakhand: A geospatial approach
- Author
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Ajay Kumar Taloor, Senjuti Nandy, and Girish Chandra Kothyari
- Subjects
Pharmacology ,geography ,geography.geographical_feature_category ,Sequence of terrace development ,Landform ,Drainage basin ,Structural basin ,River terraces ,Tectonic uplift ,Archaeology ,Terrace (geology) ,Aggradation ,Tributary ,Geography. Anthropology. Recreation ,Glacial and fluvio-glacial processes ,Physical geography ,Local processes ,CC1-960 ,Geology ,Cut and fill type - Abstract
In the present paper, an attempt has been made to trace out the major terraces and analyse their characteristics in the Upper Pindar valley of the Uttarakhand state. The study is based on digital elevation model (DEM), satellite data-based terrain characterisation with field and ground truth investigations. The results are derived from the data, which shows the preservation of river terraces along the trunk and tributary streams of the Pindar River. The terraces are formed because of the combined effect of local structural, geological, lithological, and tectonic control along with the climatic influence on landform development. Among the eight surveyed terraces, seven are cut and fill type and influenced by climate, tributaries, formed by both glacial and fluvio-glacial processes, whereas the rest terrace is developed because of tectonic uplift and creates a strath type. The terrace of Upthar and T3 of Langari has gone through the past tectonic events operated within this region. The analysis through cross-section profiles also exhibits the fact that the Upper Pindar basin has experienced a maximum of three stages of terrace development during different phases of the Holocene period and Late Pleistocene period. The alternative river aggradation, degradation, local landsliding, and a sudden increase in sediment flux caused by the monsoonal surge, tectonic uplift, and rapid incision in three separate times are the prime factors that are responsible for the generation of maximum three-tiered terrace landform in the study area. The sequence of terrace development reveals that the trunk of the Pindar River creates the highest number of terraces followed by the tributary rivers, which are generated in the later phase. The three phases of river aggradation in 33.5 ka, 17.5–13 ka, and 8–3.6 ka separated by a deep incision of different timescale are remarkable in this area, mainly around Langri and Khati, which creates the ordering of a maximum of three levels of terrace development. The results concluded that the dominance of local processes plays a vital role in the formation and characterization of river terraces in the Upper Pindar valley. The present study gives a detailed idea of the valley development and the result can also be used as an identification of suitable areas for human interactions with the environment.
- Published
- 2021
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