Sediment Supply (sediment + supply)

Distribution by Scientific Domains

Selected Abstracts

Climatic influence on the inter-annual variability of late-Holocene minerogenic sediment supply in a boreal forest catchment

Gunilla Petterson
Abstract Processes controlling sediment yield vary over a range of timescales, although most process-based observations are extremely short. Lake sediments, however, can be used to extend the observational timescale and are particularly useful when annually laminated (varved) sediment is present. The sediment record at Kassjön (N. Sweden) consists of ,6400 varves, each 0·5,1 mm thick. Image analysis was used to determine grey-scale variation and varve thickness from which annual minerogenic accumulation rate (MinAR) (mg cm,2 year,1) was inferred for the period 4486 BC , AD 1900. MinAR varies on annual to centennial scales and mainly reflects channel bank erosion by the inflow streams. The mineral input reflects the intensity of the spring run-off, which is dependent on the amount of snow accumulated during the winter, and hence MinAR is a long-term record of variability in past winter climate; other factors will be a variable response to catchment uplift, vegetation succession and pedogenesis. A major shift from low to high MinAR occurred ,250 BC, and peaks occurred around AD 250, 600, 1000, 1350 and 1650. Wavelet power spectrum analysis (confirmed by Fourier analyses) indicated significantly different periodicities throughout the period 4000 BC , AD 1700, including 275 years for the period 4000 BC , 2900 BC, 567 years for the period 2901 BC , 1201 BC, and 350 and 725 years for the period 1200 BC , AD 1700. The long-term, centennial scale variability (,350 years) may reflect solar forcing (cf the 385-year peak in tree-ring calibrated 14C activity) but interestingly, there is no obvious link to high frequency forcing, such as the North Atlantic Oscillation. The high resolution component of the record highlights the relevance of varved lake sediment records for understanding erosion dynamics in undisturbed forested catchments and their link to long-term climate dynamics and future climate change. Copyright © 2010 John Wiley & Sons, Ltd. [source]

The spatial and temporal patterns of aggradation in a temperate, upland, gravel-bed river

Emma K. Raven
Abstract Intensive field monitoring of a reach of upland gravel-bed river illustrates the temporal and spatial variability of in-channel sedimentation. Over the six-year monitoring period, the mean bed level in the channel has risen by 0·17 m with a maximum bed level rise of 0·5 m noted at one location over a five month winter period. These rapid levels of aggradation have a profound impact on the number and duration of overbank flows with flood frequency increasing on average 2·6 times and overbank flow time increasing by 12·8 hours. This work raises the profile of coarse sediment transfer in the design and operation of river management, specifically engineering schemes. It emphasizes the need for the implementation of strategic monitoring programmes before engineering work occurs to identify zones where aggradation is likely to be problematic. Exploration of the sediment supply and transfer system can explain patterns of channel sedimentation. The complex spatial, seasonal and annual variability in sediment supply and transfer raise uncertainties into the system's response to potential changes in climate and land-use. Thus, there is a demand for schemes that monitor coarse sediment transfer and channel response. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Suspended sediment transport in a small Mediterranean agricultural catchment

Joan Estrany
Abstract The aim of this study is to analyze suspended sediment transport in a Mediterranean agricultural catchment under traditional soil and water conservation practices. Field measurements were conducted in Can Revull, a small ephemeral catchment (1.03 km2) on the island of Mallorca. This study uses continuous turbidity records to analyse suspended sediment transport regimes, construct and interpret multiple regression models of total suspended sediment concentration (SSC) and of SSC related to stormflow discharge, and assess the sediment loads and yields of three hydrological years (2004,2005 to 2006,2007). An annual average SSC of 17.3 mg l,1, with a maximum of 2270 mg l,1, was recorded in the middle of the winter period when rainfall intensities are high and headwater slopes are ploughed and thus bare. Strong seasonal contrasts of baseflow dynamics associated with different degrees of dilution provide a large scatter in SSC and in the derived rating curves, reflecting that other factors control the supply of suspended sediment. Multiple regression models identify rainfall intensity as the most significant variable in sediment supply. However, under baseflow conditions, physical and biological processes generate sediment in the channel that is subsequently removed during high flow. In contrast, when baseflow is not present, rainfall intensity is the only process that supplies sediment to the channel, mostly from hillslopes. Considering the study period as average in terms of total annual rainfall and intensities, suspended sediment yields were an order of magnitude lower than those obtained in other Mediterranean catchments, a factor that can be related to the historical use of soil conservation practices. Copyright © 2009 John Wiley & Sons, Ltd. [source]

The linkage between velocity patterns and sediment entrainment in a forced-pool and riffle unit

D. M. Thompson
Abstract A field-based project was initiated in order to characterize velocities and sediment entrainment in a forced-pool and riffle sequence. Three-dimensional velocities and turbulence intensities were measured with an acoustic Doppler velocimeter at 222 different points at three similar flows that averaged approximately 4·35 m3 s,1 within a large pool,riffle unit on North Saint Vrain Creek, Colorado. Sediment-sorting patterns were observed with the introduction of 500 tracer particles painted according to initial seeding location. Tracer particles moved sporadically during a 113 day period in response to the annual snowmelt peak flow, which reached a maximum level of 14·8 m3 s,1. Velocity data indicate high instantaneous velocities and turbulence levels in the centre of pools. Patterns of sediment deposition support the notion that stream competence is higher in the pool than the downstream riffle. Flow convergence around a large channel constriction appears to play a major role in multiple processes that include helical flow development and sediment routing, and backwater development with low velocities and turbulence levels above the constriction that may locally limit sediment supply. Jet flow, flow separation, vortex scour and turbulence generation enhance scour in the centre of pools. Ultimately, multiple processes appear to play some role in maintenance of this forced pool and the associated riffle. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Historic and contemporary sediment transfer in an upland Pennine catchment, UK

V. J. Holliday
Abstract A sediment budget for an upland catchment,reservoir system at Burnhope Reservoir, North Pennines, UK has been developed. This provides a framework for quantifying historic and contemporary sediment yields and drainage basin response to disturbance from climate change and human activities in the recent past. Bathymetric survey, core sampling, 137Cs dating and aerial photographs have been used to assess sediment accumulation in the reservoir. The average reservoir sedimentation rate is 1·24 cm yr,1 (annual sediment yield 33·3 t km,2 yr,1 ± 10%, trap efficiency 92%). Mean annual reservoir sedimentation over the 67 year period has been estimated at 592 t ± 10%. Inputs of suspended sediment from direct catchwater streams account for 54% of sediment supply to the budget (best estimate yield of 318 t yr,1 ± 129%), while those from actively eroding reservoir shorelines contribute 328 t yr,1 ± 92%. Sediment yield estimates from stream monitoring and reservoir sedimentation are an order of magnitude lower than those reported from South Pennine reservoirs of comparable drainage basin area. Analysis of historical rainfall series for the catchment shows fluctuations in winter and summer rainfall patterns over the past 62 years. From 1976 to 1998 there has been a diverging trend between winter and summer rainfall, with a large increase in winter and a gradual decrease in summer totals. Periods of maximum variation occur during the summer drought events of the late 1970s, early 1980s and mid-1990s. Analysis of the particle size of core sediments highlights abrupt increases in sand-sized particles in the top 20 cm of the core. Based on the 137Cs chronology, these layers were deposited from the late 1970s onwards and relate to these diverging rainfall records and rapidly fluctuating reservoir levels. This provides evidence of potential sediment reworking within the reservoir by rapid water-level rise after drought. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Effects of forest harvesting on the occurrence of landslides and debris flows in steep terrain of central Japan

Fumitoshi Imaizumi
Abstract Landslides and debris flows associated with forest harvesting can cause much destruction and the influence of the timing of harvesting on these mass wasting processes therefore needs to be assessed in order to protect aquatic ecosystems and develop improved strategies for disaster prevention. We examined the effects of forest harvesting on the frequency of landslides and debris flows in the Sanko catchment (central Japan) using nine aerial photo periods covering 1964 to 2003. These photographs showed a mosaic of different forest ages attributable to the rotational management in this area since 1912. Geology and slope gradient are rather uniformly distributed in the Sanko catchment, facilitating assessment of forest harvesting effects on mass wasting without complication of other factors. Trends of new landslides and debris flows correspond to changes in slope stability explained by root strength decay and recovery; the direct impact of clearcutting on landslide occurrence was greatest in forest stands that were clearcut 1 to 10 yr earlier with progressively lesser impacts continuing up to 25 yr after harvesting. Sediment supply rate from landslides in forests clearcut 1 to 10 yr earlier was about 10-fold higher than in control sites. Total landslide volume in forest stands clearcut 0 to 25 yr earlier was 5·8 × 103 m3 km,2 compared with 1·3 × 103 m3 km,2 in clearcuts >25 yr, indicating a fourfold increase compared with control sites during the period when harvesting affected slope stability. Because landslide scars continue to produce sediment after initial failure, sediment supply from landslides continues for 45 yr in the Sanko catchment. To estimate the effect of forest harvesting and subsequent regeneration on the occurrence of mass wasting in other regions, changes in root strength caused by decay and recovery of roots should be investigated for various species and environmental conditions. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Sedimentological, modal analysis and geochemical studies of desert and coastal dunes, Altar Desert, NW Mexico

J. J. Kasper-Zubillaga
Abstract Sedimentological, compositional and geochemical determinations were carried out on 54 desert and coastal dune sand samples to study the provenance of desert and coastal dunes of the Altar Desert, Sonora, Mexico. Grain size distributions of the desert dune sands are influenced by the Colorado River Delta sediment supply and wind selectiveness. The desert dune sands are derived mainly from the quartz-rich Colorado River Delta sediments and sedimentary lithics. The dune height does not exert a control over the grain size distributions of the desert dune sands. The quartz enrichment of the desert dune sands may be due to wind sorting, which concentrates more quartz grains, and to the aeolian activity, which has depleted the feldspar grains through subaerial collisions. The desert dune sands suffer from little chemical weathering and they are chemically homogeneous, with chemical alteration indices similar to those found in other deserts of the world. The desert sands have been more influenced by sedimentary and granitic sources. This is supported by the fact that Ba and Sr concentration values of the desert sands are within the range of the Ba and Sr concentration values of the Colorado River quartz-rich sediments. The Sr values are also linked to the presence of Ca-bearing minerals. The Zr values are linked to the sedimentary sources and heavy mineral content in the desert dunes. The Golfo de Santa Clara and Puerto Peñasco coastal dune sands are influenced by long shore drift, tidal and aeolian processes. Coarse grains are found on the flanks whereas fine grains are on the crest of the dunes. High tidal regimens, long shore drift and supply from Colorado Delta River sediments produce quartz-rich sands on the beach that are subsequently transported into the coastal dunes. Outcrops of Quaternary sedimentary rocks and granitic sources increase the sedimentary and plutonic lithic content of the coastal dune sands. The chemical index of alteration (CIA) values for the desert and coastal dune sands indicate that both dune types are chemically homogeneous. The trace element values for the coastal dune sands are similar to those found for the desert dune sands. However, an increase in Sr content in the coastal dune sands may be due to more CaCO3 of biogenic origin as compared to the desert dune sands. Correlations between the studied parameters show that the dune sands are controlled by sedimentary sources (e.g. Colorado River Delta sediments), since heavy minerals are present in low percentages in the dune sands, probably due to little heavy mineral content from the source sediment; grain sizes in the dune sands are coarser than those in which heavy minerals are found and/or the wind speed might not exert a potential entrainment effect on the heavy mineral fractions to be transported into the dune. A cluster analysis shows that the El Pinacate group is significantly different from the rest of the dune sands in terms of the grain-size parameters due to longer transport of the sands and the long distance from the source sediment, whereas the Puerto Peñasco coastal dune sands are different from the rest of the groups in terms of their geochemistry, probably caused by their high CaCO3 content and slight decrease in the CIA value. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Sediment budget for an eroding peat-moorland catchment in northern England

Martin Evans
Abstract This paper describes a detailed contemporary sediment budget from a small peat-covered, upland catchment in Upper Teesdale, northern England. The sediment budget was constructed by measuring: (1) sediment transfers on slopes, (2) sediment flux on the floodplain and through the main stream channel and (3) sediment yield at the catchment outlet. Measurements were taken over a four-year monitoring period between July 1997 and October 2001 when interannual variations in runoff were relatively small. Three sites were selected to represent the major erosion subsystems within the catchment: an area of bare peat flats, a pair of peat gullies, and a 300 m channel reach. Collectively the sites allow detailed characterization of the main patterns of sediment flux within the catchment and can be scaled up to provide an estimate of the sediment budget for the catchment as a whole. This constitutes the first attempt to provide a complete description of the functioning of the sediment system in eroding blanket peatlands. Results demonstrate that fluvial suspended sediment flux is controlled to a large degree by channel processes. Gully erosion rates are high but coupling between the slopes and channels is poor and therefore the role of hillslope sediment supply to catchment output is reduced. Consequently contemporary sediment export from the catchment is controlled primarily by in-channel processes. Error analysis of the sediment budgets is used to discuss the limitations of this approach for assessing upland sediment dynamics. A 60 per cent reduction in fluvial suspended sediment yield from Rough Sike over the last 40 years correlates with photographic evidence of significant re-vegetation of gullies over a similar period. This strongly suggests that the reduced sediment yields are a function of increased sediment storage at the slope,channel interface, associated with re-vegetation. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Modelling land use changes and their impact on soil erosion and sediment supply to rivers

Anton J. J. Van Rompaey
Abstract The potential for surface runoff and soil erosion is strongly affected by land use and cultivation. Therefore the modelling of land use changes is important with respect to the prediction of soil degradation and its on-site and off-site consequences. Land use changes during the past 250 years in the Dijle catchment (central Belgium) were analysed by comparing four historical topographic maps (1774, 1840, 1930 and 1990). A combination of land use transformation maps and biophysical land properties shows that certain decision rules are used for the conversion of forest into arable land or vice versa. During periods of increasing pressure on the land, forests were cleared mainly on areas with low slope gradients and favourable soil conditions, while in times of decreasing pressure land units with steep and unfavourable soil conditions were taken out of production. Possible future land use patterns were generated using stochastic simulations based on land use transformation probabilities. The outcome of these simulations was used to assess the soil erosion risk under different scenarios. The results indicate that even a relatively limited land use change, from forest to arable land or vice versa, has a significant effect on regional soil erosion rates and sediment supply to rivers. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Structural patterns in coarse gravelriver beds: typology, survey and assessment of the roles of grain size and river regime

Lea Wittenberg
The concept of river-bed stability as indexed by the occurrence of stable bed forms was examined in humid-temperate perennial streams and in Mediterranean ephemeral streams. The study examined the structural patterns of bed forms and their spatial distribution between temperate-humid and Mediterranean streams. Study sites in Northumberland, UK, and Mt. Carmel, Israel, were selected for their morphometric similarity, despite the contrast in climate, vegetation and hydrological regime. Fieldwork was based on a large number of Wolman grain size distributions and structure measurements along cross-sections at seven sites; Differences in mean grain size of bed structures were estimated using the general linear model (GLM) procedure and Duncan's multiple range test. Based on field evidence, river-bed configurations were divided into structural categories, according to the depositional setting of each measured particle on the river bed. Statistical analysis confirmed former qualitative descriptions of small-scale bed forms. The study identified spatial segregation in bed form distribution. In general, 30,40%of the bed material in the surveyed perennial streams was clustered, in contrast to approximately 10%in the ephemeral counterparts. The sorting index revealed higher values for the perennial streams, namely 2.39,3.59 compared with 1.73,2.07 for the ephemeral counterparts. It is suggested that the degree of sediment sorting and the proportion of clusters are strongly related. Sediment sorting, sediment supply and the hydrological regime explain the mechanism of cluster formation. It is assumed that climate shifts or human interference within river basins might affect the regional characteristic flood hydrograph, and consequently alter the sedimentary character of the river bed. In the case where river bed stability is reduced owing to changes in cluster bed form distribution, rivers that normally do not yield a significant amount of sediment might be subject to notable sedimentation problems. [source]

Debris-covered Glaciers and Rock Glaciers in the Nanga Parbat Himalaya, Pakistan

John F. Shroder
The origin and mobilization of the extensive debris cover associated with the glaciers of the Nanga Parbat Himalaya is complex. In this paper we propose a mechanism by which glaciers can form rock glaciers through inefficiency of sediment transfer from glacier ice to meltwater. Inefficient transfer is caused by various processes that promote plentiful sediment supply and decrease sediment transfer potential. Most debris-covered glaciers on Nanga Parbat with higher velocities of movement and/ or efficient debris transfer mechanisms do not form rock glaciers, perhaps because debris is mobilized quickly and removed from such glacier systems. Those whose ice movement activity is lower and those where inefficient sediment transfer mechanisms allow plentiful debris to accumulate, can form classic rock glaciers. We document here with maps, satellite images, and field observations the probable evolution of part of a slow and inefficient ice glacier into a rock glacier at the margins of Sachen Glacier in c. 50 years, as well as several other examples that formed in a longer period of time. Sachen Glacier receives all of its nourishment from ice and snow avalanches from surrounding areas of high relief, but has low ice velocities and no efficient system of debris removal. Consequently it has a pronounced digitate terminus with four lobes that have moved outward from the lateral moraines as rock glaciers with prounced transverse ridges and furrows and steep fronts at the angle of repose. Raikot Glacier has a velocity five times higher than Sachen Glacier and a thick cover of rock debris at its terminus that is efficienctly removed. During the advance stage of the glacier since 1994, ice cliffs were exposed at the terminus, and an outbreak flood swept away much debris from its margins and terminus. Like the Sachen Glacier that it resembles, Shaigiri Glacier receives all its nourishment from ice and snow avalanches and has an extensive debris cover with steep margins close to the angle of repose. It has a high velocity similar to Raikot Glacier and catastrophic breakout floods have removed debris from its terminus twice in the recent past. In addition, the Shaigiri terminus blocked the Rupal River during the Little Ice Age and is presently being undercut and steepened by the river. With higher velocities and more efficient sediment transfer systems, neither the Raikot nor the Shaigiri form classic rock-glacier morphologies. [source]

Hyporheic Exchange in Mountain Rivers II: Effects of Channel Morphology on Mechanics, Scales, and Rates of Exchange

John M. Buffington
We propose that the mechanisms driving hyporheic exchange vary systematically with different channel morphologies and associated fluvial processes that occur in mountain basins, providing a framework for examining physical controls on hyporheic environments and their spatial variation across the landscape. Furthermore, the spatial distribution of hyporheic environments within mountain catchments represents a nested hierarchy of process controls. Large-scale process drivers (geology, climate, fire, and land use) impose a suite of watershed conditions (topography, streamflow, sediment supply, and vegetation) on the fluvial system. Different combinations of imposed watershed conditions result in different reach-scale channel morphologies (e.g. step-pool, pool-riffle, and braided) that, in turn, structure hyporheic processes (e.g. pressure divergence, spatial variation of hydraulic conductivity) and resultant hyporheic environments (scales and rates of hyporheic exchange). Consequently, a holistic view of natural and anthropogenic drivers over a range of spatial and temporal scales is needed for understanding hyporheic ecosystems. [source]

Sedimentation and tectonics: the marine Silurian,basal Lower Old Red Sandstone transition in southwest Wales

Robert D. Hillier
Abstract Both regional and localized tectonic events controlled deposition within the Wenlock and early Ludlow of SW Wales. Estuarine deposits within north,south-tending incised valleys dominate the youngest (Homerian) Gray Sandstone Group, valley incision being probably related to changing base-levels associated with Avalonia/Laurentian collision. Available accommodation space was outpaced by sediment supply, with the Red Cliff Formation (Late Ludfordian) defining a conformable transition from marine to Old Red Sandstone (ORS) deposition within the Marloes Peninsula. Sedimentation was dominated by fine-grained pedified siliciclastics, with subordinate fine-grained ephemeral sheet-flood sandstones. Local palaeocurrents indicate sediment transport from the south and west, though long-distance transport from a distant Laurentian provenance is assumed. A probable tectonically generated sequence boundary marks the base of petrographically distinctive, multi-storey pebbly sandstones of the Albion Sands Formation, deposited within the hangingwall valley of the active east,west-trending Wenall Fault. Sediment accommodation space was controlled by proximity to the tip-point of this important growth fault within the Lower ORS. Debris-flow-dominated fans, shed from both the hangingwall and footwall of the Wenall Fault, deposited the Lindsway Bay Formation, an exotic-clast conglomerate unit sourced predominantly from the south and west. It is uncertain as to whether movement along the Wenall Fault was caused by collision-related transtension, or rifting associated with the southern margin of Avalonia. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Depositional environment and sequence architecture of the Silurian Coralliferous Group, Southern Pembrokeshire, UK

Robert D. Hillier
Abstract The Lower Silurian siliciclastic Coralliferous Group is shown to have been deposited in an intra-shelf position 10,15,km south of the palaeogeographic shelf-break of the Welsh Basin. After a phase of thermal subsidence related to the development of the predominantly Llandovery Skomer Volcanic Group, the shelf basin was transgressed. This transgression was punctuated by an episode of tectonic uplift in southern Pembrokeshire, resulting in subaerial exposure of the shelf and a significant basinward shift in sedimentary environments. Erosion and sediment bypass ensued, with coarse-grained low-sinuosity fluvial channels transporting sediment to the northerly Welsh Basin, where significant submarine fans developed. During the early Telychian, renewed transgression took place, with lowstand gravels being ravined and reworked into parasequences of the transgressive systems tract. These thin, coarse-grained parasequences record deposition within high-energy wave-dominated shoreface/inner shelf environments. Further coastal onlap resulted in the closing down of significant coarse-grained sediment supply, with the remaining Coralliferous Group being dominated by wave-influenced silts, mud-shales and thin sandstones comprising the highstand systems tract. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Stratigraphic Control of Flow and Transport Characteristics

GROUND WATER, Issue 6 2006
Dwaine Edington
Ground water flow and travel time are dependent on stratigraphic architecture, which is governed by competing processes that control the spatial and temporal distribution of accommodation and sediment supply. Accommodation is the amount of space in which sediment may accumulate as defined by the difference between the energy gradient and the topographic surface. The temporal and spatial distribution of accommodation is affected by processes that change the distribution of energy (e.g., sea level or subsidence). Fluvial stratigraphic units, generated by FLUVSIM (a stratigraphic simulator based on accommodation and sediment supply), with varying magnitudes and causes of accommodation, were incorporated into a hydraulic regime using MODFLOW (a ground water flow simulator), and particles were tracked using MODPATH (a particle-tracking algorithm). These experiments illustrate that the dominant type of accommodation process influences the degree of continuity of stratigraphic units and thus affects ground water flow and transport. When the hydraulic gradient is parallel to the axis of the fluvial system in the depositional environment, shorter travel times occur in low,total accommodation environments and longer travel times in high,total accommodation environments. Given the same total accommodation, travel times are longer when sea-level change is the dominant process than those in systems dominated by subsidence. [source]

Hydrometeorological controls and erosive response of an extreme alpine debris flow

Lorenzo Marchi
Abstract On 29 August, 2003, an intense convective storm system affected the Fella River basin, in the eastern Italian Alps, producing rainfall peaks of approximately 390 mm in 12 h. The storm triggered an unusually large debris flow in the ungauged Rio Cucco basin (0·65 km2), with a volume of approximately 78 000 m3. The analysis of the time evolution of the rainstorm over the basin has been based on rainfall estimates from radar observations and data recorded by a raingauge network. Detailed geomorphological field surveys, carried out both before and after the flood of August 2003, and the application of a distributed hydrological model have enabled assessment of flood response, estimation of erosion volumes and sediment supply to the channel network. The accounts of two eyewitnesses have provided useful elements for reconstructing the time evolution and the flow processes involved in the event. Liquid peak discharge estimates cluster around 20 m3 s,1 km,2, placing this event on the flood envelope curve for the eastern Italian Alps. The hydrological analysis has shown that the major controls of the flood response were the exceptional cumulated rainfall amount, required to exceed the large initial losses, and the large rainfall intensities at hourly temporal scales, required to generate high flood response at the considered basin scale. Observations on the deposits accumulated on the alluvial fan indicate that, although the dominant flow process was a debris flow, sheetflood also contributed to fan aggradation and fluvial reworking had an important role in winnowing debris-flow lobes and redistributing sediment on the fan surface. This points out to the large discharge values during the recession phase of the flood, implying an important role for subsurface flow on runoff generation of this extreme flash flood event. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Suspended sediment dynamics in a steep, glacier-fed mountain stream, Place Creek, Canada

G. Richards
Abstract This study examined suspended sediment concentration (SSC) during the ablation seasons of 2000 and 2001 in Place Creek, Canada, a steep, glacier-fed mountain stream. Comparison of stream flow in Place Creek with that in an adjacent, almost unglacierized catchment provided a rational basis for separating the ablation seasons into nival, nival,glacial, glacial and autumn recession subseasons. Distinct groupings of points in plots of electrical conductivity against discharge supported the validity of the subseasonal divisions in terms of varying hydrological conditions. Relationships between SSC and discharge (Q) varied between the two study seasons, and between subseasons. Hysteresis in the SSC,Q relationship was evident at both event and weekly time-scales. Some suspended sediment released from pro-glacial Place Lake (the source of Place Creek) appeared to be lost to channel storage at low flows, especially early in the ablation season, with re-entrainment at higher flows. Multiple regression models were derived for the subseasons using predictor variables including Q, Q2, the change in Q over the previous 3 h, cumulative discharge over the ablation season, total precipitation over the previous 24 h and SSC measured at 1500 hours as an index value for each day. The models produced adjusted R2 values ranging from 0·71 to 0·91, and provided tentative insights into the differences in SSC dynamics amongst subseasons. Introduction of the index value of SSC significantly improved the model fit during the nival,glacial and glacial subseasons for both years, as it adjusts the model to the current condition of sediment supply. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Detailed measurements of thickness and grain size of a widespread onshore tsunami deposit in Phang-nga Province, southwestern Thailand

ISLAND ARC, Issue 3 2010
Shigehiro Fujino
Abstract Measurements of thickness and grain size along flow-parallel transects across onshore deposits of the 2004 Indian Ocean tsunami revealed macroscopic horizontal variations and provided new insights into tsunami sedimentation. The tsunami caused severe erosion of beaches, river mouths, and the shallow seafloor along the coast of southwestern Thailand and supplied sufficient sediment to deposit a kilometer-wide blanket of sand on the land surface. The tsunami deposits generally fine landward with some fluctuations caused by local entrainment and settlement of sediments. Sediments of medium and fine sand are restricted to a few hundreds of meters inland from their source, whereas finer grained sediments were suspended longer and deposited 1 km or more inland. Although the thickness of the tsunami deposits is strongly influenced by local topography, they generally thin landward. In areas of low-relief topography, the rate of landward thinning is exponential and reflects the dominance of sediment supply to nearshore areas over that to areas farther inland. [source]

Holocene coastal environmental changes on the periphery of an area of glacio-isostatic uplift: an example from Scapa Bay, Orkney, UK,

A. C. de la Vega-Leinert
Abstract The first detailed investigation of a deep, coastal, sedimentary basin in Orkney reveals a complex Holocene history of back-barrier morphodynamics. At Scapa Bay, the sea flooded a freshwater marsh after ca. 9400,yr BP at ca. ,5.4,m OD. Before ca. 7800 BP, abundant sediment from nearby cliffs was mobilised inland into a series of gravel barriers across the valley mouth. By ca. 7500 BP, direct marine influence was restricted in the back-barrier area, although saltmarsh persisted until ca. 5900 BP. By then, at least four gravel ridges had enclosed the backing lagoon, where freshwater inputs became dominant. As terrestrial sediments filled the basin, another freshwater marsh developed. The multiple barrier complex demonstrates progradation resulting from continuous sediment supply in a sheltered embayment. The progressively rising height of the barrier crests seawards probably resulted from a combination of factors such as barrier morphodynamics, increased storminess and long-term rising relative sea levels. The dominant vegetation surrounding Scapa Bay changed from open grassland to scrub ca. 9400 BP, then to deciduous woodland ca. 7800 BP, and to dwarf-shrub heath ca. 2600 BP, the latter probably a response to a combination of climate change and human activity. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Critical Evaluation of How the Rosgen Classification and Associated "Natural Channel Design" Methods Fail to Integrate and Quantify Fluvial Processes and Channel Response,

A. Simon
Abstract:, Over the past 10 years the Rosgen classification system and its associated methods of "natural channel design" have become synonymous to some with the term "stream restoration" and the science of fluvial geomorphology. Since the mid 1990s, this classification approach has become widely adopted by governmental agencies, particularly those funding restoration projects. The purposes of this article are to present a critical review, highlight inconsistencies and identify technical problems of Rosgen's "natural channel design" approach to stream restoration. This paper's primary thesis is that alluvial streams are open systems that adjust to altered inputs of energy and materials, and that a form-based system largely ignores this critical component. Problems with the use of the classification are encountered with identifying bankfull dimensions, particularly in incising channels and with the mixing of bed and bank sediment into a single population. Its use for engineering design and restoration may be flawed by ignoring some processes governed by force and resistance, and the imbalance between sediment supply and transporting power in unstable systems. An example of how C5 channels composed of different bank sediments adjust differently and to different equilibrium morphologies in response to an identical disturbance is shown. This contradicts the fundamental underpinning of "natural channel design" and the "reference-reach approach." The Rosgen classification is probably best applied as a communication tool to describe channel form but, in combination with "natural channel design" techniques, are not diagnostic of how to mitigate channel instability or predict equilibrium morphologies. For this, physically based, mechanistic approaches that rely on quantifying the driving and resisting forces that control active processes and ultimate channel morphology are better suited as the physics of erosion, transport, and deposition are the same regardless of the hydro-physiographic province or stream type because of the uniformity of physical laws. [source]

A method for improving predictions of bed-load discharges to reservoirs

Vicente L. Lopes
Abstract Effective management options for mitigating the loss of reservoir water storage capacity to sedimentation depend on improved predictions of bed-load discharges into the reservoirs. Most predictions of bed-load discharges, however, are based on the assumption that the rates of bed-load sediment availability equal the transport capacity of the flow, ignoring the spatio-temporal variability of the sediment supply. This paper develops a semiquantitative method to characterize bed-load sediment transport in alluvial channels, assuming a channel reach is non-supply limited when the bed-load discharge of a given sediment particle-size class is functionally related to the energy that is available to transport that fraction of the total bed-load. The method was applied to 22 alluvial stream channels in the USA to determine whether a channel reach had a supply-limited or non-supply-limited bed-load transport regime. The non-supply-limited transport regime was further subdivided into two groups on the basis of statistical tests. The results indicated the pattern of bed-load sediment transport in alluvial channels depends on the complete spectrum of sediment particle sizes available for transport rather than individual particle-size fractions represented by one characteristic particle size. The application of the method developed in this paper should assist reservoir managers in selecting bed-load sediment transport equations to improve predictions of bed-load discharge in alluvial streams, thereby significantly increasing the efficiency of management options for maintaining the storage capacity of waterbodies. [source]

Evolution of the Irrawaddy delta region since 1850

We present a time series of coastline change for the Irrawaddy delta region of Myanmar using the earliest available navigation chart from 1850, and a set of topographic maps and satellite imagery dating from 1913 to 2006. Despite the large sediment load delivered annually to the gulf by the Irrawaddy and Salween Rivers, the coastline has been largely stable for 156 years, advancing at an average rate of no more than 0.34 km per century since 1925. The long-term average rate of increase in land area across the study area between 1925 and 2006 is 4.2 km2/year, but this masks a period of more rapid accumulation between 1925 and 1989 (8.7 km2/year), followed by a period of net erosion at a rate of 13 km2/year until 2006. Less than 9% of the sediment load delivered to the study region by the Irrawaddy, Salween and Sittoung Rivers has contributed to the observed progradation, with the remainder being exported into the Gulf of Martaban to depths below low tide level, or filling any accommodation space created due to subsidence or sea level rise. In contrast to many deltas worldwide, we suggest that the coastline encompassing the Irrawaddy delta and the Salween River is more or less in equilibrium, and that sediment deposition currently balances subsidence and sea level rise. Myanmar has fewer large dams relative to its Asian neighbours, and the Salween is currently undammed. This is forecast to change in the next 5,10 years with extensive damming projects on the mainstem of the Salween under consideration or construction, and the sediment retention will cause losses in sediment supply to the Gulf of Martaban, and retreat of the delta. This could impact the densely populated delta region and Yangon, and further exacerbate the impacts of extreme events such as Cyclone Nargis in 2008. [source]

Trajectory analysis: concepts and applications

BASIN RESEARCH, Issue 5 2009
W. Helland-Hansen
ABSTRACT Shoreline and shelf-edge trajectories describe the migration through time of sedimentary systems, using geomorphological breaks-in-slope that are associated with key changes in depositional processes and products. Analysis of these trajectories provides a simple descriptive tool that complements and extends conventional sequence stratigraphic methods and models. Trajectory analysis offers four advantages over a sequence stratigraphic interpretation based on systems tracts: (1) each genetically related advance or retreat of a shoreline or shelf edge is viewed in the context of a continuously evolving depositional system, rather than as several discrete systems tracts; (2) subtle changes in depositional response (e.g. within systems tracts) can be identified and honoured; (3) trajectory analysis does not anticipate the succession of depositional events implied by systems-tract models; and (4) the descriptive emphasis of trajectory analysis does not involve any a priori assumptions about the type or nature of the mechanisms that drive sequence development. These four points allow the level of detail in a trajectory-based interpretation to be directly tailored to the available data, such that the interpretation may be qualitative or quantitative in two or three dimensions. Four classes of shoreline trajectory are recognized: ascending regressive, descending regressive, transgressive and stationary (i.e. nonmigratory). Ascending regressive and high-angle (accretionary) transgressive trajectories are associated with expanded facies belt thicknesses, the absence of laterally extensive erosional surfaces, and relatively high preservation of the shoreline depositional system. In contrast, descending regressive and low-angle (nonaccretionary) transgressive trajectories are associated with foreshortened and/or missing facies belts, the presence of laterally extensive erosional surfaces, and relatively low preservation of the shoreline depositional system. Stationary trajectories record shorelines positioned at a steeply sloping shelf edge, with accompanying bypass of sediment to the basin floor. Shelf-edge trajectories represent larger spatial and temporal scales than shoreline trajectories, and they can be subdivided into ascending, descending and stationary (i.e. nonmigratory) classes. Ascending trajectories are associated with a relatively large number and thickness of shoreline tongues (parasequences), the absence of laterally extensive erosional surfaces on the shelf, and relatively low sediment supply to the basin floor. Descending trajectories are associated with a few, thin shoreline tongues, the presence of laterally extensive erosional surfaces on the shelf, and high sediment supply to basin-floor fan systems. Stationary trajectories record near-total bypass of sediment across the shelf and mass transfer to the basin floor. [source]

Influence of point-source sediment-supply on modern shelf-slope morphology: implications for interpretation of ancient shelf margins

BASIN RESEARCH, Issue 5 2009
Cornel Olariu
ABSTRACT Present sea-floor bathymetry indicates that the continental-shelf and shelf-break morphology have some unique and predictable characteristics in areas with and without high sediment supply. Using a global bathymetry dataset in open shelf areas in front of rivers that discharge over 25 × 106 tons of sediment per year, five distinct accretionary types of shelf-break are distinguished based on along-shelf gradient variability and inferred shelf-break trajectory. Morphological characteristics of river-mouth shelves (compared with adjacent areas lateral to the immediate fairway of the river) are: (1) an overall lower gradient and greater width, and (2) a relatively high slope gradient/shelf gradient ratio. The exceptions are shelves with active shelf-edge deltas; these are narrower, steeper and have an attenuated shelf break in front of rivers. These observations are at seismic scale and have direct implications for the recognition and positioning of principal cross-shelf, supply fairways on ancient shelves or shelf margins, and therefore the potential by-pass routes for deepwater sands. Higher slope/shelf gradient ratios in areas of actively accreting margins, where the shelf-break is more prominent and easier to recognize on seismic data compared with adjacent areas, predict areas with high sediment supply. Along-strike morphological changes on supply-dominated shelves suggest that identification of the sediment-feed route and depocenter relative to the shelf break during a relative sea level cycle are critical for understanding/predicting the 3-D architecture of the shelf-slope-basin floor clinoform. [source]

Relationships between morphological and sedimentological parameters in source-to-sink systems: a basis for predicting semi-quantitative characteristics in subsurface systems

BASIN RESEARCH, Issue 4 2009
Tor O. Sømme
ABSTRACT The study of source-to-sink systems relates long-term variations in sediment flux to morphogenic evolution of erosional,depositional systems. These variations are caused by an intricate combination of autogenic and allogenic forcing mechanisms that operate on multiple time scales , from individual transport events to large-scale filling of basins. In order to achieve a better understanding of how these mechanisms influence morphological characteristics on different scales, 29 submodern source-to-sink systems have been investigated. The study is based on measurements of morphological parameters from catchments, shelves and slopes derived from a ,1 km global digital elevation model dataset, in combination with data on basin floor fans, sediment supply, water discharge and deposition rates derived from published literature. By comparing various morphological and sedimentological parameters within and between individual systems, a number of relationships governing system evolution and behaviour are identified. The results suggest that the amount of low-gradient floodplain area and river channel gradient are good indicators for catchment storage potential. Catchment area and river channel length is also related to shelf area and shelf width, respectively. Similarly to the floodplain area, these parameters are important for long-term storage of sediment on the shelf platform. Additionally, the basin floor fan area is correlative to the long-term deposition rate and the slope length. The slope length thus proves to be a useful parameter linking proximal and distal segments in source-to-sink systems. The relationships observed in this study provide insight into segment scale development of source-to-sink systems, and an understanding of these relationships in modern systems may result in improved knowledge on internal and external development of source-to-sink systems over geological time scales. They also allow for the development of a set of semi-quantitative guidelines that can be used to predict similar relationships in other systems where data from individual system segments are missing or lacking. [source]

Widespread syn-sedimentary deformation on a muddy deep-water basin-floor: the Vischkuil Formation (Permian), Karoo Basin, South Africa

BASIN RESEARCH, Issue 4 2009
W. C. Van Der Merwe
ABSTRACT The ,380-m-thick mudstone,siltstone-dominated Vischkuil Formation represents the initiation phase of a 1.3-km-thick prograding basin floor to slope to shelf succession that marks a significant increase in the rate of siliciclastic sediment supply to the early Karoo Basin in the Permian. In the upper Vischkuil Formation three well exposed, widespread (,3000 km2) 10,70-m-thick intervals of deformed strata are encased within undeformed sediments. Such chaotic mass movement deposits that are mappable over areas comparable with seismic-scale mass transport deposits are commonly associated with submarine slope settings. However, the surrounding lithofacies and the correlation of distinctive marker beds indicate that these deformation intervals developed in a distal low gradient basin floor setting. The deformed intervals comprise a lower division of tight down-flow verging folds dissected by thrust planes that sole out onto a highly sheared décollement surface that are interpreted as slides. The lower divisions are overlain by an upper division of chaotic lithofacies with large contorted clasts of sandstone supported by a fine-grained matrix interpreted as a debrite. The juxtaposition of these lithofacies, the distribution of thickness of the divisions, and their close kinematic relationships indicate that the emplacement of the debris-flows triggered and drove the underlying slide, in a low-gradient distal setting. Individual beds in the deformed intervals can be mapped laterally into undeformed strata indicating limited movement of the slide. Therefore, widespread zones of syn-sedimentary deformation in deep-water settings do not necessarily indicate a slope setting and should not be used as single criterion to determine depositional setting. When associated with major debrites they may be developed on a flat basin floor. [source]

A Bayesian approach to inverse modelling of stratigraphy, part 1: method

BASIN RESEARCH, Issue 1 2009
Karl Charvin
ABSTRACT The inference of ancient environmental conditions from their preserved response in the sedimentary record still remains an outstanding issue in stratigraphy. Since the 1970s, conceptual stratigraphic models (e.g. sequence stratigraphy) based on the underlying assumption that accommodation space is the critical control on stratigraphic architecture have been widely used. Although these methods considered more recently other possible parameters such as sediment supply and transport efficiency, they still lack in taking into account the full range of possible parameters, processes, and their complex interactions that control stratigraphic architecture. In this contribution, we present a new quantitative method for the inference of key environmental parameters (specifically sediment supply and relative sea level) that control stratigraphy. The approach combines a fully non-linear inversion scheme with a ,process,response' forward model of stratigraphy. We formulate the inverse problem using a Bayesian framework in order to sample the full range of possible solutions and explicitly build in prior geological knowledge. Our methodology combines Reversible Jump Markov chain Monte Carlo and Simulated Tempering algorithms which are able to deal with variable-dimensional inverse problems and multi-modal posterior probability distributions, respectively. The inverse scheme has been linked to a forward stratigraphic model, BARSIM (developed by Joep Storms, University of Delft), which simulates shallow-marine wave/storm-dominated systems over geological timescales. This link requires the construction of a likelihood function to quantify the agreement between simulated and observed data of different types (e.g. sediment age and thickness, grain size distributions). The technique has been tested and validated with synthetic data, in which all the parameters are specified to produce a ,perfect' simulation, although we add noise to these synthetic data for subsequent testing of the inverse modelling approach. These tests addressed convergence and computational-overhead issues, and highlight the robustness of the inverse scheme, which is able to assess the full range of uncertainties on the inferred environmental parameters and facies distributions. [source]

Distinguishing tectonic from climatic controls on range-front sedimentation

BASIN RESEARCH, Issue 4 2007
M. C. Quigley
ABSTRACT Geologic and chronometric studies of alluvial fan sequences in south-central Australia provide insights into the roles of tectonics and climate in continental landscape evolution. The most voluminous alluvial fans in the Flinders Ranges region have developed adjacent to catchments uplifted by Plio-Quaternary reverse faults, implying that young tectonic activity has exerted a first-order control on long-term sediment accumulation rates along the range front. However, optically stimulated luminescence (OSL) dating of alluvial fan sequences indicates that late Quaternary facies changes and intervals of sediment aggradation and dissection are not directly correlated with individual faulting events. Fan sequences record a transition from debris flow deposition and soil formation to clast-supported conglomeritic sedimentation by ,30 ka. This transition is interpreted to reflect a landscape response to increasing climatic aridity, coupled with large flood events that episodically stripped previously weathered regolith from the landscape. Late Pleistocene to Holocene cycles of fan incision and aggradation post-date the youngest-dated surface ruptures and are interpreted to reflect changes in the frequency and magnitude of large floods. These datasets indicate that tectonic activity controlled long-term sediment supply but climate governed the spatial and temporal patterns of range-front sedimentation. Mild intraplate tectonism appears to have influenced Plio-Quaternary sedimentation patterns across much of the southern Australian continent, including the geometry and extent of alluvial fans and sea-level incursions. [source]

Linkage of Sevier thrusting episodes and Late Cretaceous foreland basin megasequences across southern Wyoming (USA)

BASIN RESEARCH, Issue 4 2005
Shao-Feng Liu
ABSTRACT Deposition and subsidence analysis, coupled with previous structural studies of the Sevier thrust belt, provide a means of reconstructing the detailed kinematic history of depositional response to episodic thrusting in the Cordilleran foreland basin of southern Wyoming, western interior USA. The Upper Cretaceous basin fill is divided into five megasequences bounded by unconformities. The Sevier thrust belt in northern Utah and southwestern Wyoming deformed in an eastward progression of episodic thrusting. Three major episodes of displacement on the Willard-Meade, Crawford and ,early' Absaroka thrusts occurred from Aptian to early Campanian, and the thrust wedge gradually became supercritically tapered. The Frontier Formation conglomerate, Echo Canyon and Weber Canyon Conglomerates and Little Muddy Creek Conglomerate were deposited in response to these major thrusting events. Corresponding to these proximal conglomerates within the thrust belt, Megasequences 1, 2 and 3 were developed in the distal foreland of southern Wyoming. Two-dimensional (2-D) subsidence analyses show that the basin was divided into foredeep, forebulge and backbulge depozones. Foredeep subsidence in Megasequences 1, 2 and 3, resulting from Willard-Meade, Crawford and ,early' Absaroka thrust loading, were confined to a narrow zone in the western part of the basin. Subsidence in the broad region east of the forebulge was dominantly controlled by sediment loading and inferred dynamic subsidence. Individual subsidence curves are characterized by three stages from rapid to slow. Controlled by relationships between accommodation and sediment supply, the basin was filled with retrogradational shales during periods of rapid subsidence, followed by progradational coarse clastic wedges during periods of slow subsidence. During middle Campanian time (ca. 78.5,73.4 Ma), the thrust wedge was stalled because of wedge-top erosion and became subcritical, and the foredeep zone eroded and rebounded because of isostasy. The eroded sediments were transported far from the thrust belt, and constitute Megasequence 4 that was mostly composed of fluvial and coastal plain depositional systems. Subsidence rates were very slow, because of post-thrusting rebound, and the resulting 2-D subsidence was lenticular in an east,west direction. During late Campanian to early Maastrichtian time, widespread deposits of coarse sediment (the Hams Fork Conglomerate) aggraded the top of the thrust wedge after it stalled, prior to initiation of ,late' Absaroka thrusting. Meanwhile Megasequence 5 was deposited in the Wyoming foreland under the influence of both the intraforeland Wind River basement uplift and the Sevier thrust belt. [source]

Impact of storms on mixed carbonate and siliciclastic shelves: insights from combined diffusive and fluid-flow transport stratigraphic forward model

BASIN RESEARCH, Issue 4 2004
A. Quiquerez
A quantitative stratigraphic model of mixed carbonate/siliciclastic continental shelves is presented to investigate the relationships between depositional processes and stratigraphic responses at long-term, large spatial scales. A diffusion model is combined with a fluid-flow approach to simulate both long-term factors, i.e. the processes controlling large-scale architecture, and short-term processes, i.e. sediment redistribution by storms. Any net sediment accumulation is the result of the succession of a storm and a fair-weather period. Sediments are mobilized by waves and advected by low-frequency currents during storm events. Sediments are then reworked and redistributed downslope by diffusive processes during fair-weather period. The results are successful in capturing several major characteristics of both modern and ancient depositional systems (geometry, differential preservation, net accumulation rates). The study highlights the importance of waves and unidirectional currents. Depositional geometry and shelf morphology depend on the balance between available sediment supply (generated in situ or detrital) and the transport energy, which is related to the style of sediment transport (diffusive or advective), and to the magnitude and frequency of storms. [source]