Tesi sul tema "Aggradation"

Arroyos are entrenched channels characterized by near-vertical walls of alluvium and flat channel bottoms. Historic channel entrenchment in the southwest United States during the late AD 1800s and early 1900s has stimulated extensive research on these dynamic fluvial systems. The near-synchronous episodes of arroyo entrenchment and aggradation in Kanab Creek and other drainages in southern Utah during the last ~1 Ka has led many researches to argue that hydroclimatic forcings drive arroyo processes. These hypotheses remain largely untested, and there remains considerable uncertainty regarding the timing of these events and the specific mechanisms responsible for arroyo formations. Previous work established an alluvial chronology for the kanab canyon reach of Kanab creek, but it remained unclear if arroyo events in this reach were continuous with those downstream or synchronous with events in the disconnected arroyo in the upper basin. Using deailed sedimentologic and stratigraphic descriptions coupled with AMS radiocarbon and optically stimulated luminescence (OSL) dating, a new chronostratigraphic record of arroyo entrenchment and aggradation for kanab creek is produced in this study. Results suggest at least five periods of fluvial aggradation and episodic arroyo entrenchment during the middle-to late-Holocene, with aggradation occuring from ~6.2 to 3.67 ka (Qfl), ~3.2 to 2.5 ka (Qf2), ~2.2 to `.45 ka (Qf3), 1.4 to 0.8 ka (Qf4), and 0.75 to 0.14 ka (Qf5). This record is compared to regional alluvial and paleoclimate records to explore potential allogenic and autogenic forcing mechanisms. Rapid transitions from exceptional drought to pluvial periods are quasi-synchronous with regional arroyo entrenchment over the last ~1.5 Ka, but the lack of clear correlations amongst the regional alluvial records and between paleoclimate records beyond 1.5 Ka suggests that internal geomorphic thresholds are important controls on the timing of entrenchment in individual catchments. Previous research on arroyo dynamics has largely focused on the timing of entrenchment. The few studies that have investigated the processes related to aggradation have used historic observations, and not the stratigraphic record of arroyo deposits. In this study, the alluvial records from three reaches of Kanab Creek are combined to test models of the processes and geometric patterns of paleoarroyo aggradation. Results indicate that aggradation initially propagates upstream and then transitions to synchronous vertical aggradation along the entire channel profile as arroyos approach complete filling.

This study documents the stage adjustments in the Lower White River between 1931 and 2012 at four rated gaging stations along the trunk stem of the river. The study reach extends from Calico Rock, Arkansas, to the confluence of the White River with the Mississippi River north of Arkansas City, a distance of about 509 km. The specific gage approach was used to track hydrological response in the study reach. In order to approach spatial homogeneity across the four gaging locations along the study reach, input discharges were normalized to multiples of mean daily flow (MDF). Specific gage analysis tracks water surface elevation changes for fixed discharge conditions over time. Three discharges were analyzed at each station: low flow, mean flow, and high flow. The low flow specific gage trends are emphasized to highlight degradation and aggradation due to the sensitivity of specific stages at low flows to channel bed elevation changes. An `enhanced interpolation' technique was used to fill gaps in the specific stage time series in order to avoid errors derived from extrapolation of annual rating curves. The analysis shows decreasing trends in specific stage at Clarendon and DeValls Bluff at low flows, indicating net degradation. The gages at Newport and Calico Rock show increasing trends in specific stage over time at low flows, indicating aggradation downstream of Norfork and Bull Shoals reservoirs.

The trends of degradation and aggradation are measured in this study for the Lower Mississippi River. Historical riverbed elevation and stage data from the past hundred years were used from six gages in order to measure changes in riverbed gradation. It was found that using stage data to measure gradation changes is a superior method to using riverbed elevations, due to stage data’s reliability, length of record and daily measurements. Degradation in the Lower Mississippi River was seen during the

At the turn of the century, Kanab Creek incised 30-meters into its alluvium, leaving behind fluvial terraces and thick basin fill sediments exposed along arroyo walls. Research objectives were to determine the timing and causes of past valley-filling and arroyo-cutting episodes along a 20 km-long reach of Kanab Creek in southern Utah. Fluvial deposits were mapped at the 1:12,000 scale and sediments were described and dated using Optically Stimulated Luminescence (OSL) and radiocarbon dating. The Kanab Creek valley can be divided into a narrow, upper terraced reach and a broad lower basin fill reach near Kanab, Utah. The most prominent terrace in the upper reach is Quaternary alluvial terrace 4 (Qat4), followed by Qat3, Qat2/3, and Qat2 map units. These are composed of tabular-bedded, fine-grained sand, silt, and clay layers. The Qat2/3 map unit is a both a fill and fill-cut terrace underlain by Qa4, Qa3, and Qa2 alluvium and is used when the Qat3 fill-cut (fill-strath) terrace can not be differentiated from the Qat2 fill terrace due to their similar geomorphic position. The Qat3 fill-cut terrace upstream correlates to ~8 meters of aggradation downstream. The youngest terrace, Qat1, is a minor terrace, composed of coarse-grained channel facies. More recent channel and floodplain deposits were deposited over the last century following arroyo cutting. OSL and radiocarbon results suggest at least four cycles of fluvial cutting and filling: >6-3.5ka (Qa4), ~3->1ka (Qa3), 0.7-0.12ka (Qa2), and post-1880 AD (Qa1). Correlation to regional climate records suggests major periods of aggradation correlate to regionally cooler and wetter climatic intervals. Periods of arroyo cutting occurred at >6ka, ~3ka, 1-0.7ka, and during historic arroyo cutting (1882-1914 AD), and correlate to regionally warmer, drier intervals. These periods of aggradation and incision are roughly contemporaneous with regional drainages, except for the large aggradation seen in Kanab Creek 6-3.5ka (Qa4). Analysis of terrace longitudinal profiles indicates Qat4 has the lowest concavity suggesting that Qat4 aggraded during a period of greater sediment supply and/or reduced flood regime. Although OSL samples exhibited some degree of incomplete zeroing, calculated ages using a minimum age model are consistent with radiocarbon results.

This study uses the storm surge sediment beds deposited by Hurricanes Audrey (1957), Carla (1961), Rita (2005) and Ike (2008) to investigate spatial and temporal changes in sedimentation rates on the McFaddin National Wildlife Refuge in Southeast Texas. Fourteen sediment cores were collected along a transect extending from 90 to 1230 meters inland from the Gulf Coast. Storm-surge-deposited sediment beds were identified by texture, organic content, carbonate content, the presence of marine microfossils, and Cesium-137 dating. The hurricane-derived sediment beds are marker horizons that facilitate assessment of marsh sedimentation rates from nearshore to inland locations as well as over decadal to annual timescales. Near the shore, on a Hurricane Ike washover fan, where hurricane-derived sedimentation has increased elevation by up to 0.68 m since 2005, there was no measurable marsh sedimentation in the period 2008-2014. Farther inland, at lower elevations, sedimentation for the period 2008-2014 averaged 0.36 cm per year. The reduction in sedimentation in the period 2008-2014 on the nearshore part of the marsh is likely due to reduced flooding in response to increased elevation from hurricane storm surge sediment deposition. These results provide valuable knowledge about the sedimentary response of coastal marshes subject to storm surge deposition and useful guidance to public policy aimed at combating the effects of sea level rise on coastal marshes along the Gulf of Mexico.

The aim of this research is to assess hazards and risks associated with flooding in the city of Juárez, northern México, where there is a flood threat from active alluvial fans from mountains to the southwest and from the Rio Grande (Bravo River) to the northwest forming the northeast border of the city. Aims of this Ph.D. were addressed processing a digital elevation model (DEM) of the study area in a GIS platform to define the several alluvial fans, and thus to examine their history and palaeohydrology. Three OSL dates in the youngest parts of the fans show ages ranging from 74 - 31 ka. However, the fans were subsequently incised, broadly correlating with later Pleistocene to Holocene processes upstream, published in literature, in New México. These changes are not obviously linked to glacial-interglacial cycles, and there is indication of local controls of interplay of climate and topography, for which this work is a preliminary study. The flood threat to Juárez was addressed by using a classification of the uneven topography of the eroded alluvial fans, plus the Bravo River flood plain, into basins and subbasins. Field and laboratory work was used to define litho-facies of soils and rocks, location of structures such as, topographic and hydrologic apex and drainage system in the fans. The data were then used in association with published information on the parameters of the basins and sub-basins provided in published documents from the Mexican authorities to make flood models of the area, using standard models of HEC-HMS and HEC-RAS methods widely applied in semi-arid regions. The result was estimation of the ability of existing flood defences to resist high-flow floods that may be expected in upcoming decades. The modelling predicts that only a small number of the existing defences will hold in a catastrophic 1:100-year flood, and that substantial parts of the city are in considerable danger. Such results are important in relation to the expanded and dense population in Juárez, which is concentrated mostly on the most active part of the flooding system, the Colorado Fan, which is the subject of a focussed secondary study of vulnerability mapping. The map reveals that areas of the city of low socioeconomic development are under the greatest threat. Therefore there is a need for reconsideration of the city's flood planning, and remediation, plus the application of enforcements of areas which should not be built on, because of the threats.

An Alpine Fault Earthquake has the potential to cause significant disruption across the Southern Alps of the South Island New Zealand. In particular, South Island river systems may be chronically disturbed by the addition of large volumes of sediment sourced from coseismic landsliding. The Taramakau River is no exception to this; located north of Otira, in the South Island of New Zealand, it is exposed to natural hazards resulting from an earthquake on the Alpine Fault, the trace of which crosses the river within the study reach. The effects of an Alpine Fault Earthquake (AFE) have been extensively studied, however, little attention has been paid to the effects of such an event on the Taramakau River as addressed herein. Three research methods were utilised to better understand the implications of an Alpine Fault Earthquake on the Taramakau River: (1) hydraulic and landslide data analyses, (2) aerial photograph interpretation and (3) micro-scale modelling. Data provided by the National Institute of Water and Atmospheric Research were reworked, establishing relationships between hydraulic parameters for the Taramakau River. Estimates of landslide volume were compared with data from the Poerua landslide dam, a historic New Zealand natural event, to indicate how landslide sediment may be reworked through the Taramakau valley. Aerial photographs were compared with current satellite images of the area, highlighting trends of avulsion and areas at risk of flooding. Micro-scale model experiments indicated how a braided fluvial system may respond to dextral strike-slip and thrust displacement and an increase in sediment load from coseismic landslides. An Alpine Fault Earthquake will generate a maximum credible volume of approximately 3.0 x 108 m3 of landslide material in the Taramakau catchment. Approximately 15% of this volume will be deposited on the Taramakau study area floodplain within nine years of the next Alpine Fault Earthquake. This amounts to 4.4 x 107 m3 of sediment input, causing an average of 0.5 m of aggradation across the river floodplains within the study area. An average aggradation of 0.5 m will likely increase the stream height of a one-in-100 year flood with a flow rate of 3200 m3/s from seven metres to 7.5 m overtopping the road and rail bridges that cross the Taramakau River within the study area – if they have survived the earthquake. Since 1943 the Taramakau River has shifted 500 m away from State Highway 73 near Inchbonnie, moving 430 m closer to the road and rail. Paleo channels recognised across the land surrounding Inchbonnie between the Taramakau River and Lake Brunner may be reoccupied after an earthquake on the Alpine Fault. Micro-scale modelling showed that the dominant response to dextral strike-slip and increased ‘landslide’ sediment addition was up- and downstream aggradation separated by a localised zone of degradation over the fault trace. Following an Alpine Fault Earthquake the Taramakau River will be disturbed by the initial surface rupture along the fault trace, closely followed by coseismic landsliding. Landslide material will migrate down the Taramakau valley and onto the floodplain. Aggradation will raise the elevation of the river bed promoting channel avulsion with consequent flooding and sediment deposition particularly on low lying farmland near Inchbonnie. To manage the damage of these hazards, systematically raising the low lying sections of road and rail may be implemented, strengthening (or pre-planning the replacement of) the bridges is recommended and actively involving the community in critical decision making should minimise the risks of AFE induced fluvial hazards. The response of the Taramakau River relative to an Alpine Fault Earthquake might be worse, or less severe or significantly different in some way, to that assumed herein.

Coastal marshes and wetlands are vital natural resources that offer habitats for plants and animals, serve as ecological filtration for soil and water pollutants, and act as protection for coastlines. Fishing, both commercial and sport, has a large economic impact in the study area – the Gulf Coast between Galveston Bay, TX and Oak Grove, LA. The objective of this research was to determine the contribution of Hurricane Ike storm surge sedimentation to long-term marsh aggradation in Texas and Louisiana coastal marshes. The research hypothesized that Hurricane Ike’s storm surge deposit would be equal to decades and possibly even a century’s worth of the average annual non-storm sedimentation. A quantitative field study was performed. The storm surge deposit was examined in a series of 15 transects covering approximately 180 km east of Hurricane Ike’s landfall. Nine of the 15 transects were re-surveyed a year after the initial measurement to assess preservation of the deposit. The results demonstrate that Hurricane Ike contributed between 10 to 135 years’ worth of sediment to coastal marshes along the coasts of Texas and Louisiana, and the sediment deposits have been preserved for over two years.

The Permo-Triassic lower Beaufort Group fluvial deposits extend over 100s of kilometres within the Karoo Basin, South Africa. A detailed study of the depositional architecture and stacking patterns of sand bodies within a 900 m thick succession has enabled interpretation of the controls on ancient river channel and overbank processes. Facies include very fine- to medium-grained sandstone, intra-formational conglomerate, mudstone and palaeosols. Channel-belts are dominated by upper flow regime structures, consistent with a flashy to ephemeral fluvial system. The overbank deposits comprise splays interbedded with purple, green and grey mudstone; these floodplain colour changes signify water table fluctuations. A hierarchy of channel-related elements has been established that recognises beds, bedsets, storeys, channel-belts, complexes and complex sets. Each channel-belt may be single- or multi-storey, whereby one storey represents the complete cut and fill cycle of a single migrating river, comprising bar accretion elements and channel-abandonment fill. The abandonment fill elements often consist of heterolithic plugs of climbing ripple-laminated very fine-grained sandstone, or interbedded claystone with siltstone. The Beaufort channel-belts preserve either lateral- or downstream-accretion patterns, or a combination. Each belt has either a lenticular or tabular geometry, recognisable by an erosional base overlain by intra-formational conglomerate lag and barform deposits. Genetically related channel-belts cluster to form complexes, of which two broad styles have been identified: Type A) laterally and vertically stacked channel-belts, and Type B) sub-vertically stacked channel-belts. There is evidence of localised clustering of sub-vertically stacked channel-belts adjacent to extensive overbank mudstone deposits. The apparent lack of a well-defined ‘container’ surface with mappable margins, suggests that this stacked channel-belt architecture represents an avulsion complex rather than a palaeovalley-fill. The lateral and stratigraphic variability in fluvial-overbank architecture is interpreted as the interplay of several controls. Allogenic forcing factors include, tectonic subsidence that influences accommodation, sediment supply, and high frequency climate cycles associated with the flashy discharge regime and expressed in the mudrock colour changes and distribution of palaeosols. The depositional river style, variability in channel-belt stacking patterns and compensational stacking of some channel-belt/splay complexes is interpreted to be the result of autogenic channel avulsion, supported by an absence of significant erosion. The relative merits of basin-axial trunk river and distributive fluvial system (DFS) models are assessed from detailed architectural and stratigraphic outcrop studies.

Widespread Lake Bonneville sediments have been modified by river aggradation and degradation associated with Holocene fluctuations in the Great Salt Lake. Exposures of exceptionally abundant and well-preserved molluscan deposits in the Bear River Valley, Utah, allow detailed paleoenvironmental reconstruction of Holocene environments. The exposed basal unit consists of largely unfossiliferous deltaic silts and clays deposited during Lake Bonneville time ( roughly 11,000 - 13,000 yr B. P.). An unconformity representing at least 2000 yr separates the deltaic material from overlying highly fossiliferous stream sands. Eight species of molluscs, comprising a single community, occupied this low energy stream environment at 7690 ± 270 14C yr B. P. A second unconformity separates these sands from a dark brown silt unit deposited by a river-associated environment, most likely an over-bank marsh, at 2420 ± 135 14C yr B. P. Nine species of molluscs, comprising 3 communities, were present in this environment. Analysis of size-frequency distributions, percentage of pelecypod valves, preservation, and orientation of the shells that were present in each environment suggests that the 7690 ± 270 14c yr B. P. fossil assemblage has been only slightly altered by biostratinomic processes. The younger assemblage has also been altered, with the size-frequency curves of the smallest gastropods displaying normal distributions. Geomorphic and stratigraphic data from the Malad River show that water levels in the Great Salt Lake twice rose and fell significantly during the Holocene epoch. The oldest rise, to an altitude of at least 1288 m, occurred before 7690 ± 270 yr B. P., perhaps in response to a worldwide period of climatic cooling. This high-stand was followed by a fall of lake level roughly corresponding to the classic Hypsithermal Interval, about 7000 - 5000 yr B. P. A second rise occurred by 2420 ± 135 yr B. P., when the Great Salt Lake rose to approximately 1286 m. During this second rise, the Malad River overflowed its levees and later, as the Great Salt Lake receded for a second time, the river was captured by a headward-cutting tributary of the Bear River. The regional distribution of the fossiliferous deposits was controlled by the time at which capture occurred. Capture of the Malad channel by the Bear River occurred after the last fossiliferous sediments were deposited; thus no fossils are found downstream from the point of capture.

Several fringing coral reefs in Moreton Bay, Southeast Queensland, some 300 km south of the Great Barrier Reef (GBR), are set in a relatively high latitude, estuarine environment that is considered marginal for coral growth. Previous work indicated that these marginal reefs, as with many fringing reefs of the inner GBR, ceased accreting in the mid-Holocene. This research presents for the first time data from the subsurface profile of the mid-Holocene fossil reef at Wellington Point comprising U/Th dates of in situ and framework corals, and trace element analysis from the age constrained carbonate fragments. Based on trace element proxies the palaeo-water quality during reef accretion was reconstructed. Results demonstrate that the reef initiated more than 7,000 yr BP during the post glacial transgression, and the initiation progressed to the west as sea level rose. In situ micro-atolls indicate that sea level was at least 1 m above present mean sea level by 6,680 years ago. The reef remained in "catch-up" mode, with a seaward sloping upper surface, until it stopped aggrading abruptly at ca 6,000 yr BP; no lateral progradation occurred. Changes in sediment composition encountered in the cores suggest that after the laterite substrate was covered by the reef, most of the sediment was produced by the carbonate factory with minimal terrigenous influence. Rare earth element, Y and Ba proxies indicate that water quality during reef accretion was similar to oceanic waters, considered suitable for coral growth. A slight decline in water quality on the basis of increased Ba in the later stages of growth may be related to increased riverine input and partial closing up of the bay due to either tidal delta progradation, climatic change and/or slight sea level fall. The age data suggest that termination of reef growth coincided with a slight lowering of sea level, activation of ENSO and consequent increase in seasonality, lowering of temperatures and the constrictions to oceanic flushing. At the cessation of reef accretion the environmental conditions in the western Moreton Bay were changing from open marine to estuarine. The living coral community appears to be similar to the fossil community, but without the branching Acropora spp. that were more common in the fossil reef. In this marginal setting coral growth periods do not always correspond to periods of reef accretion due to insufficient coral abundance. Due to several environmental constraints modern coral growth is insufficient for reef growth. Based on these findings Moreton Bay may be unsuitable as a long term coral refuge for most species currently living in the GBR.

Charwell Basin is a 6 km-wide structural depression situated at the boundary between the axial ranges and faulted and folded Marlborough Fault Zone of north-eastern South Island, New Zealand. The basin contains the piedmont reach of the Charwell River, and a series of late Quaternary loess-mantled alluvial terraces and terrace remnants that have been uplifted and translocated from their sediment source due to strike-slip motion along the Hope Fault which bounds the basin to its immediate north. The aim of this study was to provide an interdisciplinary, integrated and holistic analysis of late Quaternary landscape evolution and environmental change in Charwell Basin using terrain analysis, loess stratigraphy, soil chemistry and paleoecological data. The study contributes new understanding of New Zealand landscape and ecosystem responses to regional and global climatic change extending to Marine Isotope Stage (MIS) 6, and shows that climatically-forced shifts in biogeomorphic processes play a significant role in lowland landscape evolution. Morphometric analysis of alluvial terraces and terrace remnants of increasing age demonstrated geomorphic evolution through time, with a decrease in extent of original planar terrace tread morphology and an increase in frequency of steeper slopes and convexo-concave land elements. Paleotopographic analysis of a >150 ka terrace mantled by up to three loess sheets revealed multiple episodes of alluvial aggradation and degradation and, subsequent to river abandonment, gully incision prior to and coeval with loess accumulation. Spatial heterogeneity in loess sheet preservation showed a complex history of loess accumulation and erosion. A critical profile curvature range of -0.005 to -0.014 (d2z/dx2, m-1) for loess erosion derived from a model parameterised in different ways successfully predicted loess occurrence on adjacent slope elements, but incorrectly predicted loess occurrence on an older terrace remnant from which all loess has been eroded. Future analyses incorporating planform curvature, regolith erosivity and other landform parameters may improve identification of thresholds controlling loess occurrence in Charwell Basin and in other South Island landscapes. A loess chronostratigraphic framework was developed for, and pedogenic phases identified in, the three loess sheets mantling the >150 ka terrace. Except for one age, infrared-stimulated luminescence dates from both an upbuilding interfluve loess exposure and colluvial gully infill underestimated loess age with respect to the widespread Kawakawa/Oruanui Tephra (KOT; 27,097 ± 957 cal. yr BP), highlighting the need for improvements in the methodology. Onset of loess sheet 1 accumulation started at ca. 50 ka, with a break at ca. 27 ka corresponding to the extended Last Glacial Maximum (eLGM) interstadial identified elsewhere in New Zealand. Loess accumulation through MIS 3 indicates a regional loess flux, and that glaciation was not a necessary condition for loess generation in South Island. Loess accumulation and local alluvial aggradation are decoupled: the youngest aggradation event only covers ~12 kyr of the period of loess sheet 1 accumulation. Older local aggradation episodes could not be the source because their associated terraces are mantled by loess sheet 1. In the absence of numerical ages, the timing of L2 and L3 accumulation is inferred on the basis of an offshore clastic sediment record. The upbuilding phase of loess sheet 2 occurred in late MIS 5a/MIS 4, and loess sheet 3 accumulated in two phases in MIS 5b and late MIS 6. Biogenic silica data were used to reconstruct broad shifts in vegetation and changes in gully soil saturation status. During interglacial/interstadial periods (MIS 1, early MIS 3, MIS 5) Nothofagus¬-dominated forest covered the area in association with Microlaena spp grasses. Lowering of treeline altitude during glacial/stadial periods (MIS 2, MIS 3, MIS 5b, late MIS 6) led to reduction in forest cover and a mosaic of shrubs and Chionochloa spp, Festuca spp and Poa spp tussock grasses. Comparison of interfluve and gully records showed spatial heterogeneity in vegetation cover possibly related to environmental gradients of exposure or soil moisture. A post-KOT peak in gully tree phytoliths corresponds to the eLGM interstadial, and a shift to grass-dominated vegetation occurred during the LGM sensu stricto. Diatoms indicated the site became considerably wetter from ca. 36 ka, with peak wetness at ca. 30, 25 and 21 ka, possibly due to reduced evapotranspiration and/or increased precipitation from a combination of strengthened westerly winds and increased cloudiness, or strengthened southerly flow and increased precipitation. Human influence after ca. 750 yr BP led to re-establishment of grassland in the area, which deposited phytoliths mixed to 30 cm depth in the soil. A coupled gully colluvial infilling/vegetation record showed that sediment flux during the late Pleistocene was ~0.0019 m3 m-1 yr-1 under a shrubland/grassland mosaic, and Holocene sediment flux was ~0.0034 m3 m-1 yr-1 under forest. This increase of 60% through the last glacial-interglacial transition resulted from increased bioturbation and down-slope soil transport via root growth and treethrow, which formed a biomantle as evidenced by slope redistribution of the KOT. These results contrast with sediment transport rates and processes hypothesised to occur contemporaneously in adjacent mountain catchments. This suggests that intraregional biogeomorphic processes can differ significantly depending on topography and geological substrate, with different landscapes responding in unique ways to the same climate shifts. Analysis of Quaternary terrestrial landscape evolution in non-glaciated mountainous and lowland areas must therefore consider spatial and temporal heterogeneity in sediment fluxes and underlying transport processes.

Charwell Basin is a 6 km-wide structural depression situated at the boundary between the axial ranges and faulted and folded Marlborough Fault Zone of north-eastern South Island, New Zealand. The basin contains the piedmont reach of the Charwell River, and a series of late Quaternary loess-mantled alluvial terraces and terrace remnants that have been uplifted and translocated from their sediment source due to strike-slip motion along the Hope Fault which bounds the basin to its immediate north. The aim of this study was to provide an interdisciplinary, integrated and holistic analysis of late Quaternary landscape evolution and environmental change in Charwell Basin using terrain analysis, loess stratigraphy, soil chemistry and paleoecological data. The study contributes new understanding of New Zealand landscape and ecosystem responses to regional and global climatic change extending to Marine Isotope Stage (MIS) 6, and shows that climatically-forced shifts in biogeomorphic processes play a significant role in lowland landscape evolution. Morphometric analysis of alluvial terraces and terrace remnants of increasing age demonstrated geomorphic evolution through time, with a decrease in extent of original planar terrace tread morphology and an increase in frequency of steeper slopes and convexo-concave land elements. Paleotopographic analysis of a >150 ka terrace mantled by up to three loess sheets revealed multiple episodes of alluvial aggradation and degradation and, subsequent to river abandonment, gully incision prior to and coeval with loess accumulation. Spatial heterogeneity in loess sheet preservation showed a complex history of loess accumulation and erosion. A critical profile curvature range of -0.005 to -0.014 (d²z/dx², m⁻¹) for loess erosion derived from a model parameterised in different ways successfully predicted loess occurrence on adjacent slope elements, but incorrectly predicted loess occurrence on an older terrace remnant from which all loess has been eroded. Future analyses incorporating planform curvature, regolith erosivity and other landform parameters may improve identification of thresholds controlling loess occurrence in Charwell Basin and in other South Island landscapes. A loess chronostratigraphic framework was developed for, and pedogenic phases identified in, the three loess sheets mantling the >150 ka terrace. Except for one age, infrared-stimulated luminescence dates from both an upbuilding interfluve loess exposure and colluvial gully infill underestimated loess age with respect to the widespread Kawakawa/Oruanui Tephra (KOT; 27,097 ± 957 cal. yr BP), highlighting the need for improvements in the methodology. Onset of loess sheet 1 accumulation started at ca. 50 ka, with a break at ca. 27 ka corresponding to the extended Last Glacial Maximum (eLGM) interstadial identified elsewhere in New Zealand. Loess accumulation through MIS 3 indicates a regional loess flux, and that glaciation was not a necessary condition for loess generation in South Island. Loess accumulation and local alluvial aggradation are decoupled: the youngest aggradation event only covers ~12 kyr of the period of loess sheet 1 accumulation. Older local aggradation episodes could not be the source because their associated terraces are mantled by loess sheet 1. In the absence of numerical ages, the timing of L2 and L3 accumulation is inferred on the basis of an offshore clastic sediment record. The upbuilding phase of loess sheet 2 occurred in late MIS 5a/MIS 4, and loess sheet 3 accumulated in two phases in MIS 5b and late MIS 6. Biogenic silica data were used to reconstruct broad shifts in vegetation and changes in gully soil saturation status. During interglacial/interstadial periods (MIS 1, early MIS 3, MIS 5) Nothofagus-dominated forest covered the area in association with Microlaena spp grasses. Lowering of treeline altitude during glacial/stadial periods (MIS 2, MIS 3, MIS 5b, late MIS 6) led to reduction in forest cover and a mosaic of shrubs and Chionochloa spp, Festuca spp and Poa spp tussock grasses. Comparison of interfluve and gully records showed spatial heterogeneity in vegetation cover possibly related to environmental gradients of exposure or soil moisture. A post-KOT peak in gully tree phytoliths corresponds to the eLGM interstadial, and a shift to grass-dominated vegetation occurred during the LGM sensu stricto. Diatoms indicated the site became considerably wetter from ca. 36 ka, with peak wetness at ca. 30, 25 and 21 ka, possibly due to reduced evapotranspiration and/or increased precipitation from a combination of strengthened westerly winds and increased cloudiness, or strengthened southerly flow and increased precipitation. Human influence after ca. 750 yr BP led to re-establishment of grassland in the area, which deposited phytoliths mixed to 30 cm depth in the soil. A coupled gully colluvial infilling/vegetation record showed that sediment flux during the late Pleistocene was ~0.0019 m³ m⁻¹ yr⁻¹ under a shrubland/grassland mosaic, and Holocene sediment flux was ~0.0034 m³ m⁻¹ yr⁻¹ under forest. This increase of 60% through the last glacial-interglacial transition resulted from increased bioturbation and down-slope soil transport via root growth and treethrow, which formed a biomantle as evidenced by slope redistribution of the KOT. These results contrast with sediment transport rates and processes hypothesised to occur contemporaneously in adjacent mountain catchments. This suggests that intraregional biogeomorphic processes can differ significantly depending on topography and geological substrate, with different landscapes responding in unique ways to the same climate shifts. Analysis of Quaternary terrestrial landscape evolution in non-glaciated mountainous and lowland areas must therefore consider spatial and temporal heterogeneity in sediment fluxes and underlying transport processes.

The present thesis is devoted to a particular topic regarding the fluvial sub-systems, namely the evaluation of the annual amount of sediment yield through a given cross-section of a river. This problem has been largely investigated in literature and the resulting models can be classify in different groups depending on the morphological characteristics they take into account and their complexity. In any case the large quantity of data required is always the main problem. With this work we want to find simple relationships that require the lesser number of data as possible, so we have made our evaluations at a basin-scale and assumed for the river the Local Uniform Flow hypothesis (LUF). Accordingly, each river reach is defined by its length, width, slope and bottom composition, while the watershed area is collapsed in its barycentre which coincides with the upstream end of the LUF reach. A basic state, called equilibrium and represented by a stationary rating curve (a monomial relation between the solid and the liquid discharge of Engelund-Hansen type) is first identified, with the purpose to evaluate the deviations of the real solid transport from the equilibrium value, deviations that depend on the time-scale considered. In particular we have developed three models, valid in three different time-scales. For the short-term analysis we use the 1-D deterministic solution of the harmonic river which provides the delay and attenuation of the perturbation of the solid transport with respect to the equilibrium condition. In other words we link the actual deviations of the solid transport recorded downstream with previous perturbations of the liquid discharge, happened upstream. For a pluri-annual time-scale we integrate the 1-D morphodynamic model to a zero-dimensional model. As the water and sediments inputs to the river are concentrated in its upstream end, the width of the entire river is assumed to be constant, while the slope and the grain-size composition are considered to be variable in time. The resulting mathematical model is implicit and non-linear, but at this time-scale we simplify it in order to find a simple and generic analytical solution for the pluri-annual morphological evolution of the river. Finally, for very long-term analysis we integrate numerically the exact 0-D morphodynamic model to predict the morphological reactions of a river at geological time-scale. In this case we schematize the river with two contiguous LUF channel, representing the highland and the lowland parts of the real watercourse respectively. In this way, this model can simulate the typical behaviour of natural rivers showing a grain-size segregation (fining) in the downstream direction, accompanied by smaller slopes, without the computational costs necessary for a complete one-dimensional model. Some comparisons and numerical applications have been made.
Questa tesi è dedicata ad un tema particolare che riguarda i sotto-sistemi fluviali, vale a dire la valutazione dell'importo annuo di produzione di sedimenti attraverso una determinata sezione fluviale. Questo problema è stato ampiamente studiato in letteratura e i modelli sviluppati possono essere classificati in diversi gruppi a seconda delle caratteristiche morfologiche di cui tengono conto e della loro complessità. In ogni caso, il problema principale è sempre la grande quantità di dati richiesti. Con questo lavoro vogliamo trovare delle semplici relazioni che richiedano il minor numero di dati possibile, per questo abbiamo sviluppato le nostre valutazioni ad una scala spaziale di bacino ed assunto per il fiume l'ipotesi flusso localmente uniforme (LUF). Di conseguenza ogni tratto fluviale è definito dalla sua lunghezza, dalla larghezza, dala pendenza e dalla composizione granulometrica del fondo, mentre l'estremità a monte del canale LUF coincide col baricentro del bacino in cui si assume sia concentrata l'intera area. Prima si identifica una condizione di base, chiamata di equilibrio e rappresentata da una curva stazionaria (una relazione monomia tra le portate solida e liquida di tipo Engelund-Hansen), con lo scopo di valutare le deviazioni del trasporto solido reale dal valore di equilibrio, deviazioni che dipendono dalla scala temporale considerata. In particolare abbiamo sviluppato tre modelli, validi per tre diverse scale temporali. Per l'analisi a breve termine usiamo la soluzione deterministica armonica 1-D del fiume, che fornisce il ritardo e l'attenuazione della perturbazione del trasporto solido rispetto alla condizione di equilibrio. In altre parole, colleghiamo le deviazioni effettive del trasporto solido registrate a valle con le precedenti perturbazioni della portata liquida avvenute a monte. Per una scala pluriannuale integriamo il modello morfodinamica 1-D ad un modello zero-dimensionale. Dato che gli ingressi di acqua e sedimenti al fiume sono concentrati alla sua estremità a monte, la larghezza dell'intero fiume è ipotizzata costante, mentre la pendenza e la composizione granulometrica sono considerate essere variabili nel tempo. Ne risulta un modello matematico implicito e non lineare, ma a questa scala temporale lo possiamo semplificare al fine di trovare una soluzione analitica semplice e generica per l'evoluzione morfologica pluriennale del fiume. Infine, per un'analisi a lungo termine integriamo numericamente il modello morfodinamico 0-D esatto per valutare le reazioni morfologiche di un fiume a scala temporale geologica. In questo caso si schematizza il fiume con due canali LUF contigui, che rappresentano rispettivamente il tratto montano e e il tratto di pianura del reale corso d'acqua. In questo modo, questo modello può simulare il comportamento tipico dei fiumi naturali mostrando una differenziazione granulometrica (affinamento) verso valle accompagnata da pendenze minori, senza i costi computazionali necessari per un modello unidimensionale completo. Sono stati fatti alcuni confronti e applicazioni numeriche.

Meandering channels constitute one of the fundamental components of tidal systems, as related tidal point bars are ubiquitous features in lagoonal or estuarine sedimentary successions. Nevertheless, a limited number of studies analyzed their morphodynamic evolution, together with their planimetric shape and morphometric characteristics. Their internal architecture and sedimentary facies distribution are relatively unexplored, and commonly investigated using facies models developed for fluvial meander bends. Focusing on differences, more than on similarities, between tidal and fluvial meanders, the present work aims at investigating the stratal architecture and sedimentary facies distribution of selected tidal point bars in the Venice Lagoon (Adriatic Sea, Italy). Three main issue were investigate by the present work: i) the role of low order tributaries in controlling the evolution of tidal meander bend; ii) the influence of salt marsh aggradation in shaping geometries of tidal point bars, iii) sedimentary process and morphodynamics changes acting on subtidal point bars. The morphodynamic evolution of tidal channels, and related sedimentary products, were analyzed using a multidisciplinary approach, which comprises the comparison of historical photos, the interpretation of high-resolution sub-bottom profiles, core logging analysis and 3D modelling. The main results stemmed out form the study sites highlight that: I) lateral tributaries can strongly influence the evolution of bends modifying local mechanisms of sediment and flow distribution; II); the migration of tidal point bars occurs under aggradational conditions both in intertidal and subtidal setting; III) subtidal bars evolve under the strong interaction between wave and tidal currents.
I canali meandriformi costituiscono una delle principali componenti dei sistemi tidali e, come le relative point bar, sono una caratteri ricorrenti all'interno delle successioni sedimentarie lagunari. Tuttavia, un numero limitato di studi hanno analizzato l’evoluzione morfodinamica e le caratteristiche morfometriche di canali meandriformi tidali. La loro architettura interna e la distribuzione delle facies sedimentarie sono relativamente inesplorate, e comunemente investigate utilizzando i modelli di facies sviluppati per i meandri fluviali. Concentrandosi sulle differenze, più che sulle similitudini, tra i meandri tidali e fluviali, questo lavoro si propone di investigare le architetture stratali e la distribuzione delle facies sedimentarie delle point bar selezionate nella della Laguna di Venezia (Mare Adriatico, Italia). In questo lavoro vengono affrontate tre problematiche principali: i) il ruolo dei tributari di ordine inferiore nell'evoluzione dei meandri tidali; ii) l’influenza dell'aggradazione delle barene nella modellazione delle geometrie delle point bar tidali; iii) i processi sedimentari e le variazioni morfodinamiche agenti sulle point bar subtidali. L’evoluzione morfodinamica dei canali tidali, e i relativi prodotti sedimentari, sono stati analizzati utilizzando un approccio multidisciplinare, che comprende la comparazione di foto storiche, l’interpretazione di profili sub-bottom ad alta risoluzione, log di carote e modellazione 3D. I risultati principali ottenuti dai tre siti in esame evidenziano che: I) gli affluenti laterali possono influenzare fortemente l’evoluzione dei meandri, modificando i meccanismi locali di distribuzione dei flussi e dei sedimenti; II) la migrazione delle point bar tidali avviene in contesti aggradazionali, sia in ambienti intertidali che subtidali; III) le barre subtidali evolvono sotto l’influenza della forte interazione tra correnti da onde e di marea.

Tidal channels play a key role in the evolution of coastal environments and commonly dominate tidal landscapes. These channels commonly show a clear meandering pattern which shapes the architectural geometries of sedimentary successions accumulated in tidal coastal realms. Nevertheless, a limited number of studies analysed the morphodynamic evolution of tidal meanders and the related point bar sedimentary bodies, whose internal architecture and sedimentary facies distribution remain still poorly explored, as highlighted by their scarce documentation in the rock record. The capability of reading the signature of tidal processes in sedimentary successions represents a powerful tool for paleo-environmental reconstructions. Detecting tidal channel deposits will contribute to studies on Holocene deposits and ancient rocks, with implications spanning from adaptation of natural systems to anthropic pressure to subsurface exploration for georesources. The present work aims at improving our understanding of the relationship between the evolution of tidal meander bends and the related sedimentary products, through the investigation of different research issues (RI), including: i) the influence of vertical aggradation and substrate compaction in shaping geometries of tidal point bars (RI1); ii) the reconstruction of three-dimensional architecture of tidal point bars, through a numerical modelling approach, developed under different aggradational conditions and planform transformation styles (RI2); iii) the relationship between mechanisms of bar growth and internal facies arrangements (RI3); and iv) the analysis of piracy-controlled geometries of point bar bodies (RI4). These research issues have been carried out in different tidal settings, including microtidal (Venice Lagoon, Italy – RI1, 2, and 4) and macrotidal (Bay of Mont Saint Michel, France – RI3) environments; both in modern (RI1, 2, 3, and 4) and ancient record (Eocene deposits of the Tremp-Graus Basin, Spain – RI4). A multidisciplinary approach has been adopted for modern examples, with different methodologies encompassing remote sensing techniques (i.e. historical aerial photos and LiDAR topographic time-series analysis), geomorphological field observations, sedimentary core analysis, and 3D forward stratigraphic modelling. The analysis of the ancient case study examples relies on classical outcrop sedimentology approach, which included line-drawing of photomosaics, bed-by-bed logging, and collection of paleo-flow measurements. The main results from this work highlighted that: I) geometries of tidal point bars can vary following aggradational conditions of surrounding overbank areas, along with changes in local accommodation space and channel discharge. These are, in turn, influenced by differential substrate compaction and channel network evolution; II) 3D geometries of point bars developed by slowly migrating tidal channels under aggradational conditions, differ from tabular bodies envisaged by traditional point bar models. Indeed, their geometries are shaped by the planform and vertical shift of channel bends; III) tidal meanders can expand alternating accretionary stages along seaward and landward side of point bars. In this contest, large amounts of mud-rich deposits are stored in their axial zone, where rhythmic tidal deposition is better recorded; IV) occurrence of densely-drained tidal networks prevents channel bends to freely meander and causes interaction with adjacent channels triggering piracies. These piracies cause premature deactivation of sinuous channels and hinder the development of laterally extensive point bar bodies.

The intermontane Ipswich Basin, which is situated 30km south-west of Brisbane, contains coal measures formed in the Late Triassic Epoch following a barren non-depositional period. Coal, tuff, and basalt were deposited along with fluvial dominated sediments. The Ipswich Coal Measures mark the resumption of deposition in eastern Australia after the coal hiatus associated with a series of intense tectonic activity in Gondwanaland during the Permo-Triassic interval. A transtensional tectonic movement at the end of the Middle Triassic deformed the Toogalawah Group before extension led to the formation of the Carnian Ipswich Coal Measures in the east. The Ipswich Coal Measures comprise the Brassall and Kholo Subgroups. The Blackstone Formation, which forms the upper unit of the Brassall Subgroup, contains seven major coal seams. The lower unit of the Brassall Subgroup, the Tivoli Formation, consists of sixteen stratigraphically significant coal seams. The typical thickness of the Blackstone Formation is 240m and the Tivoli Formation is about 500m. The coal seams of the Ipswich Basin differ considerably from those of other continental Triassic basins. However, the coal geology has previously attracted little academic attention and the remaining exposures of the Ipswich coalfield are rapidly disappearing now that mining has ceased. The primary aim of this project was to study the patterns of coal sedimentation and the response of coal seam characteristics to changing depositional environments. The coal accumulated as a peat-mire in an alluvial plain with meandering channel systems. Two types of peat-mire expansion occurred in the basin. Peat-mire aggradation, which is a replacement of water body by the peatmire, was initiated by tectonic subsidence. This type of peat-mire expansion is known as terrestrialisation. It formed thick but laterally limited coal seams in the basin. Whereas, peat-mire progradation was related to paludification and produced widespread coal accumulation in the basin. The coal seams were separated into three main groups based on the mean seam thickness and aerial distribution of one-meter and four-meter thickness contour intervals. Group 1 seams within the one-meter thickness interval are up to 15,000m2 in area, and seams within the four-meter interval have an aerial extent of up to 10,000m2. Group 1A contains the oldest seam with numerous intraseam clastic bands and shows a very high thickness to area ratio, which indicates high subsidence rates. Group 1B seams have moderately high thickness to area ratios. The lower clastic influx and slower subsidence rates favoured peat-mire aggradation. The Group 1A seam is relatively more widespread in aerial extent than seams from Group 1B. Group 1C seams have low mean thicknesses and small areas, suggesting short-lived peat-mires as a result of high clastic influx. Group 2 seams arebetween 15,000 and 35,000m2 in area within the one-meter interval, and between 5,000 and 10,000m2 within the four-meter interval. They have moderately high area to thickness ratios, indicating that peat-mire expansion occurred due to progressively shallower accommodation and a rising groundwater table. Group 3 seams, which have aerial extents from 35,000 to 45,000m2 within the one-meter thickness contour interval and from 10,000 to 25,000m2 within the four-meter interval, show high aerial extent to thickness ratios. They were deposited in quiet depositional environments that favoured prolonged existence of peat-mires. Group 3 seams are all relatively young whereas most Group 1 seams are relatively old seams. All the major fault systems, F1, F2 and F3, trend northwest-southeast. Apart from the West Ipswich Fault (F3), the F1 and F2 systems are broad Palaeozoic basement structures and thus they may not have had a direct influence on the formation of the much younger coal measures. However, the sedimentation patterns appear to relate to these major fault systems. Depocentres of earlier seams in the Tivoli Formation were restricted to the northern part of the basin, marked by the F1 system. A major depocentre shift occurred before the end of the deposition of the Tivoli Formation as a result of subsidence in the south that conformed to the F2 system configuration. The Blackstone Formation depocentres shifted to the east (Depocentre 1) and west (Depocentre 2) simultaneously. This depocentre shift was associated with the flexural subsidence produced by the rejuvenation of the West Ipswich Fault. Coal accumulation mainly occurred in Depocentre 1. Two types of seam splitting occurred in the Ipswich Basin. Sedimentary splitting or autosedimentation was produced by frequent influx of clastic sediments. The fluvial dominant depositional environments created the random distribution of small seam splits. However, the coincidence of seam splits and depocentres found in some of the seams suggests tectonic splitting. Furthermore, the progressive splitting pattern, which displays seam splits overlapping, was associated with continued basin subsidence. The tectonic splitting pattern is more dominant in the Ipswich Basin. Alternating bright bands shown in the brightness profiles are a result of oscillating water cover in the peat-mire. Moderate groundwater level, which was maintained during the development of the peat, reduced the possibility of salinisation and drowning of the peat swamp. On the other hand, a slow continuous rise of the groundwater table, that kept pace with the vertical growth of peat, prevented excessive oxidation of peat. Ipswich coal is bright due to its high vitrinite content. The cutinite content is also high because the dominant flora was pteridosperms of Dicroidium assemblage containing waxy and thick cuticles. Petrographic study revealed that the depositional environment was telmatic with bog forest formed under ombrotrophic to mesotrophic hydrological conditions. The high preservation of woody or structured macerals such as telovitrinite and semifusinite indicates that coal is autochthonous. The high mineral matter content in coal is possibly due to the frequent influx of clastic and volcanic sediments. The Ipswich Basin is part of a much larger Triassic basin extending to Nymboida in New South Wales. Little is known of the coal as it lacks exposures. It is apparently thin to absent except in places like Ipswich and Nymboida. This study suggests that the dominant control on depocentres of thick coal at Ipswich has been the tectonism. Fluvial incursions and volcanism were superimposed on this.

The intermontane Ipswich Basin, which is situated 30km south-west of Brisbane, contains coal measures formed in the Late Triassic Epoch following a barren non-depositional period. Coal, tuff, and basalt were deposited along with fluvial dominated sediments. The Ipswich Coal Measures mark the resumption of deposition in eastern Australia after the coal hiatus associated with a series of intense tectonic activity in Gondwanaland during the Permo-Triassic interval. A transtensional tectonic movement at the end of the Middle Triassic deformed the Toogalawah Group before extension led to the formation of the Carnian Ipswich Coal Measures in the east. The Ipswich Coal Measures comprise the Brassall and Kholo Subgroups. The Blackstone Formation, which forms the upper unit of the Brassall Subgroup, contains seven major coal seams. The lower unit of the Brassall Subgroup, the Tivoli Formation, consists of sixteen stratigraphically significant coal seams. The typical thickness of the Blackstone Formation is 240m and the Tivoli Formation is about 500m. The coal seams of the Ipswich Basin differ considerably from those of other continental Triassic basins. However, the coal geology has previously attracted little academic attention and the remaining exposures of the Ipswich coalfield are rapidly disappearing now that mining has ceased. The primary aim of this project was to study the patterns of coal sedimentation and the response of coal seam characteristics to changing depositional environments. The coal accumulated as a peat-mire in an alluvial plain with meandering channel systems. Two types of peat-mire expansion occurred in the basin. Peat-mire aggradation, which is a replacement of water body by the peatmire, was initiated by tectonic subsidence. This type of peat-mire expansion is known as terrestrialisation. It formed thick but laterally limited coal seams in the basin. Whereas, peat-mire progradation was related to paludification and produced widespread coal accumulation in the basin. The coal seams were separated into three main groups based on the mean seam thickness and aerial distribution of one-meter and four-meter thickness contour intervals. Group 1 seams within the one-meter thickness interval are up to 15,000m2 in area, and seams within the four-meter interval have an aerial extent of up to 10,000m2. Group 1A contains the oldest seam with numerous intraseam clastic bands and shows a very high thickness to area ratio, which indicates high subsidence rates. Group 1B seams have moderately high thickness to area ratios. The lower clastic influx and slower subsidence rates favoured peat-mire aggradation. The Group 1A seam is relatively more widespread in aerial extent than seams from Group 1B. Group 1C seams have low mean thicknesses and small areas, suggesting short-lived peat-mires as a result of high clastic influx. Group 2 seams arebetween 15,000 and 35,000m2 in area within the one-meter interval, and between 5,000 and 10,000m2 within the four-meter interval. They have moderately high area to thickness ratios, indicating that peat-mire expansion occurred due to progressively shallower accommodation and a rising groundwater table. Group 3 seams, which have aerial extents from 35,000 to 45,000m2 within the one-meter thickness contour interval and from 10,000 to 25,000m2 within the four-meter interval, show high aerial extent to thickness ratios. They were deposited in quiet depositional environments that favoured prolonged existence of peat-mires. Group 3 seams are all relatively young whereas most Group 1 seams are relatively old seams. All the major fault systems, F1, F2 and F3, trend northwest-southeast. Apart from the West Ipswich Fault (F3), the F1 and F2 systems are broad Palaeozoic basement structures and thus they may not have had a direct influence on the formation of the much younger coal measures. However, the sedimentation patterns appear to relate to these major fault systems. Depocentres of earlier seams in the Tivoli Formation were restricted to the northern part of the basin, marked by the F1 system. A major depocentre shift occurred before the end of the deposition of the Tivoli Formation as a result of subsidence in the south that conformed to the F2 system configuration. The Blackstone Formation depocentres shifted to the east (Depocentre 1) and west (Depocentre 2) simultaneously. This depocentre shift was associated with the flexural subsidence produced by the rejuvenation of the West Ipswich Fault. Coal accumulation mainly occurred in Depocentre 1. Two types of seam splitting occurred in the Ipswich Basin. Sedimentary splitting or autosedimentation was produced by frequent influx of clastic sediments. The fluvial dominant depositional environments created the random distribution of small seam splits. However, the coincidence of seam splits and depocentres found in some of the seams suggests tectonic splitting. Furthermore, the progressive splitting pattern, which displays seam splits overlapping, was associated with continued basin subsidence. The tectonic splitting pattern is more dominant in the Ipswich Basin. Alternating bright bands shown in the brightness profiles are a result of oscillating water cover in the peat-mire. Moderate groundwater level, which was maintained during the development of the peat, reduced the possibility of salinisation and drowning of the peat swamp. On the other hand, a slow continuous rise of the groundwater table, that kept pace with the vertical growth of peat, prevented excessive oxidation of peat. Ipswich coal is bright due to its high vitrinite content. The cutinite content is also high because the dominant flora was pteridosperms of Dicroidium assemblage containing waxy and thick cuticles. Petrographic study revealed that the depositional environment was telmatic with bog forest formed under ombrotrophic to mesotrophic hydrological conditions. The high preservation of woody or structured macerals such as telovitrinite and semifusinite indicates that coal is autochthonous. The high mineral matter content in coal is possibly due to the frequent influx of clastic and volcanic sediments. The Ipswich Basin is part of a much larger Triassic basin extending to Nymboida in New South Wales. Little is known of the coal as it lacks exposures. It is apparently thin to absent except in places like Ipswich and Nymboida. This study suggests that the dominant control on depocentres of thick coal at Ipswich has been the tectonism. Fluvial incursions and volcanism were superimposed on this.

碩士
國立交通大學
土木工程研究所
82
The purpose of this study is to develop a numerical model based on multimode characteristics method for fully coupled simulation of water and sediment movement in mobile-bed alluvial channels with nonuniform bed materials. According to multimode characteristics method, the characteristics equations and tota- -lly differential compatible equations of the numerical model could be obtained by consolidating water continuity and momen- -tum equations, sediment continuity equation and bed material sorting equtaions. The model contains explicit scheme, spatial reachback scheme, temporl reachback scheme and implicit scheme for solving flow depth, velocity, bed elevation, and bed-mate- -rial size fraction at each time step. The multimode scheme has the advantages of releasing Courant constraint and of effectively dealing with the problem of large differences in celerities among water-surface waves, bed-mate- -rial sorting waves. The multimode scheme is based on Lagrangian concept. The unknows could be computed from one time step to another by solving the compatible equations along the corres- ponding characteristics curves. When there are more then three governing equations, the eignvalues can only be solved numeri- -cally. The concept of buffer reach was adopted in this study to improve the stabilty and accuracy in numerical simulation affected by the upstream boundary condition. The simulation results for aggradation based on experimen- -tal data of Soni et al.(1980) and Yen et al.(1987) show that the proposed model can reasonably predict the evolution of bed elevation. Through the numerical simulation, the effect of boun- -dary condition on simulation results was examined. Furthermore, an assessment of model applicability was made through the analy- -sis of models stabilty, accuracy, and sensitivity.

碩士
國立中興大學
土木工程學系
89
The evolution of the river bed profile is related to the mechanism of sediment transport, including the interaction of flow and sediment. Therefore, the estimation of the sediment transport rate is very important for the watershed management, the clearance of reservoir sedimentation, and the soil and water conservation. In this study, a series of laboratory experiment is performed to investigate the transport characteristics of non-uniform gravel for steep channels in Taiwan. Both the particle size distribution and flow discharge were fixed, and four different initial slopes (2~5%) were selected to investigate the sorting phenomenon during the overloading and under-loading experiments. The data collection for the complicated evolution phenomenon of the natural rivers is difficult. The laboratory experiments and the numerical simulation conducted in this study can offer useful information for the future modeling of river evolution.

碩士
國立交通大學
土木工程系所
105
Unlike the achievement of bed material load estimation in laws of physics and numerical models in river channels in Taiwan, wash load estimation is rarely mentioned. Lacking of fundamental data in the past, wash load has been generally assumed as composed of 70% to 90% suspend load in the river, there are no clear standard of specified particle size and division method in different river,so overestimation or underestimation of sediment transport occurs frequently with inaccurate wash load proportion. This study aims at developing a relationship of the proportion of wash load with the influential factors including the hydraulic, geometrical, sediment, rainfall and physiographical factors. The empirical formula of wash load is established by using the regression analysis with data collected from the lower Chou-Shui River Reach. CCHE1D, a one dimensional mobile-bed model developed by the Center for Computational Hydroscience and Engineering, was applied to simulate the effect of river deposition-erosion with the influence of the proportion of wash load by different inflow sediment concentrations established by general empirical method and river empirical formula (the empirical formula of wash load by river condition) and rainfall empirical formula (the empirical formula of wash load by river, rainfall, physiographical condition.) This study used CCHE1D to simulate bed variation of Chou-Shui River Reach for 2008 to 2015, the standard error of bed variation between the application of rainfall empirical formula and the observed values is 0.63m, which is superior to the result of 0.76m and 0.89m while applying river empirical formula and general empirical method. In summary, the rainfall empirical formula of wash load is innovative and available for lower Chou-Shui River Reach and further application.

碩士
國立交通大學
土木工程學系
84
This study, based on the coupled nonuniform-sediment multimode characteristics model developed by Li (1992), Chen (1994), and Tsang (1995), conducts simulations under the condition of alternating aggradation and degradation of the channel beds. The model used previously has a shortcoming of failing to meet the law of mass conservation due to the sudden change of hydraulic conditions. To avoid this shortcoming, the numerical method adopted in this study compute the eigen-values and eigen-vectors along the propagation of the characteristic waves. This model is also extended to consider the cases with irregular cross- sections in natural rivers. To enhance the stability of the model, a modification was made to handle the upstream and the downstream boundary conditions. Moreover, the computation of transporting nonuniform sediment of different sizes was done to reflect the effects of the hiding factor and the exposure factor.Experimental data based on the laboratory studies of Yen et al. (1987 & 1990) were used to test the accuracy and the applicability of the model. According to the experiments, the model was used to investigate the bed elevation change and the bed material gradation under a sequence of equilibrium, overloading, underloading and clean water degradation stages. An assessment then was made through the analysis and comparison between the experimental data and the simulation results, which show a satisfactory prediction of this model.

The Nyl River and its floodplain are situated on the eastern foothills of the Waterberg mountain range in the Limpopo Province of South Africa. Tributaries flowing out of the Waterberg range display unusual downstream changes, as they approach and converge with the Nylsvlei (or Nyl floodplain). Tributary channels decrease in size downstream until, eventually, they disappear altogether forming unchannellized floodouts. On one such floodout, on the farm Driefontein, an actively aggrading piedmont has formed adjacent to the famous Wonderkrater peat mound, known for its pollen record dating back ~45,000 years. Sediments from the aggrading piedmont interlace with Wonderkrater’s peat layers, suggesting that as the piedmont aggrades so too does the peat mound. This setting presents a unique opportunity to study active aggradational processes, and their products, on hillslope deposits and floodout environments. This study aims to describe the geomorphology and nature of depositional processes along the length of the piedmont adjacent to the Wonderkrater peat mound. Cross-sections, drainage channels and vegetation indices based on topographic maps, orthophotographs and hyperspectral images, were created using ArcGIS in order to describe and determine the surface morphology and hydrology of the Driefontein piedmont in detail. Surface soil samples were collected in order to determine particle size distribution, which were in turn compared to vegetation indices and changes in slope elevation. Further grain samples were collected from depth for age dating using Optically Stimulated Luminescence (OSL), as well as to determine grain size distribution in relation to surface sediments and other fluvial environments. Hyperspectral indices were found to correlate to surface grain size distribution, demonstrating that the presence of vegetation acts as a retaining mechanism for particles along hillslopes where incline should be too steep to support fine-grained sedimentary material. Surface sediments were found to demonstrate the characteristics of an alluvial floodout system, affected greatly by the presence of vegetation and slope inclination. Sub-surface samples were characteristic of a colluvial setting, suggesting that pediment retreat and basin fill, coupled with evidential climatic changes, were dominant controls on the pediment’s morphological and aggradational mechanisms. OSL age results estimated the sediments to be between 37.33 and 58.66 ka old. As a result of its unique sedimentary characteristics, a new type of ‘slow creep fan’ class was established in order to describe the characteristics of the Driefontein piedmont.

Sediment delivery to a basin exerts a first-order control over sedimentation, and therefore study of sedimentary rocks can reveal information about the nature of sediment delivery in the past. This dissertation examines several aspects of this problem using experimental, outcrop, and subsurface data. Flume experiments were undertaken to test the combined effects of autogenic alluvial aggradation and forced regression on the development of fluviodeltaic stratigraphy. Alluvial aggradation occurred in response to steady relative sea-level fall, and eventually consumed the entire sediment budget as the river lengthened in response to forced regression. The Campanian Lower Castlegate Sandstone (Utah) was studied as a potential ancient analog resulting from similar autogenic behaviors as observed in the experiments. Extensive measurement of grain-size distributions and paleo-flow depths from outcrop were utilized to explore downstream changes in paleo-hydraulics of the ancient fluvial systems in the Lower Castlegate in response to extensive alluvial aggradation and consequent loss of sediment from transport. An interesting finding was the stratigraphic signature of backwater hydraulic conditions in the distal reaches of the Lower Castlegate paleo-rivers. Finally, a simple and novel inversion scheme was developed for estimating paleo-sediment flux from ancient shelf-margin successions. An advantage of the methodology is that it allows for both spatial and temporal reconstruction of paleo-sediment flux patterns. The inversion scheme was applied to shelf-margin successions in the Washakie-Sand Wash Basin of Wyoming, the New Jersey Atlantic margin, the North Slope of Alaska, and the Zambezi margin of East Africa using published subsurface datasets. The Neogene passive margins within the studied datasets were found to consistently deposit around one-third of their total sediment budget on the shelf-margin topset, and bypass two-thirds of their budget beyond the shelf edge. The implications of this finding on the flux of terrestrial-derived particulate organic carbon (POC) from rivers to the ocean were explored, and a long-term average flux of POC to deepwater storage was estimated. The sediment-flux inversion scheme was also applied to derive input parameters for stratigraphic modeling of the Ebro margin. The modeling results indicate that the autostratigraphic behavior of the margin may have been previously underestimated.
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