Transport Sediment Research Articles

Chemical Constituents of Fugitive Dust

Wind erosion selectively winnows the fine, most chemically concentrated portions of surface soils and results in the inter-regional transport of fugitive dust containing plant nutrients, trace elements and other soil-borne contaminants. We sampled and analyzed surface soils, sediments in transport over eroding fields, and attic dust from a small area of the Southern High Plains of Texas to characterize the physical nature and chemical constituents of these materials and to investigate techniques that would allow relatively rapid, low cost techniques for estimating the chemical constituents of fugitive dust from an eroding field. From chemical analyses of actively eroding sediments, it would appear that Ca is the only chemical species that is enriched more than others during the process of fugitive dust production. We found surface soil sieved to produce a sub-sample with particle diameters in the range of 53-74 microm to be a reasonably good surrogate for fugitive dust very near the source field, that sieved sub-samples with particle diameters <10 microm have a crustal enrichment factor of approximately 6, and that this factor, multiplied by the chemical contents of source soils, may be a reasonable estimator of fugitive PM(10) chemistry from the soils of interest. We also found that dust from tractor air cleaners provided a good surrogate for dust entrained by tillage and harvesting operations if the chemical species resulting from engine wear and exhaust were removed from the data set or scaled back to the average of enrichment factors noted for chemical species with no known anthropogenic sources. Chemical analyses of dust samples collected from attics approximately 4 km from the nearest source fields indicated that anthropogenic sources of several environmentally important nutrient and trace element species are much larger contributors, by up to nearly two orders of magnitude, to atmospheric loading and subsequent deposition than fugitive dust from eroding soils.

Eolian depositional episodes controlled by Late Quaternary relative sea level changes on the Imbituba–Laguna coast (southern Brazil)

The Late Quaternary coastal eolian deposits of the Imbituba–Laguna region (Santa Catarina State, southern Brazil) comprise two “eolian depositional sequences”, separated by an unconformity. The older eolian sequence, A, is correlated to the relative sea level rise of the Last Interglacial period. The eolian sequence B was initiated during the relative sea level rise in the post -glacial period and extends up to active dunefields. The correspondence between the two eolian depositional episodes represented by these sequences and the relative sea level highstand phases is confirmed by thermoluminescence and optically stimulated luminescence dating. This correspondence is explained by a conceptual model that links the availability of coastal sediments for eolian transport with relative sea level changes. The link between relative sea level changes and coastal eolian sedimentation can be used to integrate coastal eolian systems to the sequence stratigraphy model.

Physical criteria for distinguishing sandy tsunami and storm deposits using modern examples

Modern subaerial sand beds deposited by major tsunamis and hurricanes were compared at trench, transect, and sub-regional spatial scales to evaluate which attributes are most useful for distinguishing the two types of deposits. Physical criteria that may be diagnostic include: sediment composition, textures and grading, types and organization of stratification, thickness, geometry, and landscape conformity. Published reports of Pacific Ocean tsunami impacts and our field observations suggest that sandy tsunami deposits are generally < 25 cm thick, extend hundreds of meters inland from the beach, and fill microtopography but generally conform to the antecedent landscape. They commonly are a single homogeneous bed that is normally graded overall, or that consists of only a few thin layers. Mud intraclasts and mud laminae within the deposit are strong evidence of tsunami deposition. Twig orientation or other indicators of return flow during bed aggradation are also diagnostic of tsunami deposits. Sandy storm deposits tend to be > 30 cm thick, generally extend < 300 m from the beach, and will not advance beyond the antecedent macrotopography they are able to fill. They typically are composed of numerous subhorizontal planar laminae organized into multiple laminasets that are normally or inversely graded, they do not contain internal mud laminae and rarely contain mud intraclasts. Application of these distinguishing characteristics depends on their preservation potential and any deposit modifications that accompany burial. The distinctions between tsunami and storm deposits are related to differences in the hydrodynamics and sediment-sorting processes during transport. Tsunami deposition results from a few high-velocity, long-period waves that entrain sediment from the shoreface, beach, and landward erosion zone. Tsunamis can have flow depths greater than 10 m, transport sediment primarily in suspension, and distribute the load over a broad region where sediment falls out of suspension when flow decelerates. In contrast, storm inundation generally is gradual and prolonged, consisting of many waves that erode beaches and dunes with no significant overland return flow until after the main flooding. Storm flow depths are commonly < 3 m, sediment is transported primarily as bed load by traction, and the load is deposited within a zone relatively close to the beach.

Shelf to slope sedimentation processes and the impact of Plio–Pleistocene glaciations in the northeast Atlantic, west of Ireland

The eastern margin of the Rockall Trough, between 54°30′ and 56°30′N, straddles the southern limit of the glaciated North Atlantic margin. A complex system of canyons, channels and slope failure features on the steep margins of the trough is resolved on the TRIM (TOBI Rockall Irish Margins Project) deep-towed sidescan survey. The canyons consist of a complex headwall gullied region, produced by multiple slope failure events, and interconnect to form a cauliform pattern in plan view. Individual gullies are U-shaped in cross-section in the upper parts of the margin and are connected downslope to single, deeply-incised, V-shaped channels. These channels feed extensive aprons of sediment on the lower slope supplied by failure of the headwall regions and sediment transport along the shelf into the canyon headwalls. The change in the canyon morphology systems reflects a more abundant supply of glaciomarine sedimentary debris from Pleistocene ice sheets, whose southerly limit lay along this part of the eastern Rockall margin. A good correlation between acoustic sidescan backscatter and more deeply penetrating 3.5 kHz profiler data suggests that sediment transport pathways were stable through time. Slope failure escarpments occur in association with the canyon systems along the upper part of the slope. Canyons are absent in the north of the area where the slope gradient is lowest. This is interpreted as the result of progradation of sheet-like flows of glaciomarine debris across the southern part of the Donegal Fan. A poor correlation between acoustic backscatter and sub-bottom profile data indicates that sediment transport pathways varied through time in the region. Evidence for strong northeast-flowing bottom currents is present along the upper slope and shelf. These currents transport and sort sediments along the entire eastern margin of the Rockall Trough from the south of the Porcupine Bank to the Hebrides Terrace Seamount.

Comparison of Bulk and Bin Warm-Rain Microphysics Models Using a Kinematic Framework

This paper discusses the development and testing of a bulk warm-rain microphysics model that is capable of addressing the impact of atmospheric aerosols on ice-free clouds. Similarly to previous two-moment bulk schemes, this model predicts the mixing ratios and number concentrations of cloud droplets and drizzle/raindrops. The key elements of the model are the relatively sophisticated cloud droplet activation scheme and a comprehensive treatment of the collision–coalescence mechanism. For the latter, three previously published schemes are selected and tested, with a detailed (bin) microphysics model providing the benchmark. The unique aspect of these tests is that they are performed using a two-dimensional prescribed-flow (kinematic) framework, where both advective transport and gravitational sedimentation are included. Two quasi-idealized test cases are used, the first mimicking a single large eddy in a stratocumulus-topped boundary layer and the second representing a single shallow convective cloud. These types of clouds are thought to be the key in the indirect aerosol effect on climate. Two different aerosol loadings are considered for each case, corresponding to either pristine or polluted environments. In general, all three collision–coalescence schemes seem to capture key features of the bin model simulations (e.g., cloud depth, droplet number concentration, cloud water path, effective radius, precipitation rate, etc.) for the polluted and pristine environments, but there are detailed differences. Two of the collision–coalescence schemes require specification of the width of the cloud droplet spectrum, and model results show significant sensitivity to the specification of the width parameter. Sensitivity tests indicate that a one-moment version of the bulk model for drizzle/rain, which predicts rain/drizzle mixing ratio but not number concentration, produces significant errors relative to the bin model.

内湾における粒径を考慮した底質堆積モデルの開発

This study presents the modeling for the formation and characteristics of sediment layer in Tokyo bay over the time scale of several years. The model includes hydrodynamics, wave, bed shear stress and multi-class sediment models in order to simulate the sediment processes both in water body and bed layer. The sediment model accounts for sediment transport, settling, deposition, resuspension and burial sedimentation processes and is able to reproduce the accumulation of bed sediments. By the concept of multi-class particles, the important information of bed layer characteristics, for instance, the spatial distribution of particle sizes and the water content ratio are provided. Moreover, the numerical experiment was carried out to describe the mechanism of sediment accumulation investigated in the field.

低エネルギー管路土砂輸送システムの基礎的研究

Conventional pipeline sand transportation systems generally consume excessive amount of energy to ensure the system to transport sediments without causing problems such as blockage of the system. These systems are thus economically inefficient although the safety operation factor of the system may be relatively high. On the other hand, some systems aim to utilize clean energy such as water head to transport sediments. While these systems, consuming relatively low energy, may have only small sediment transport rates, the system may be operated for longer duration of time without having significant impacts on the surrounding environment. The ultimate goal of this research is thus to develop such low-energy sand-bypassing systems. This paper especially aims to investigate the sediment transport characteristics in the pipe flow especially when the flow velocity is relatively low.

Buffers, barriers and blankets: The (dis)connectivity of catchment-scale sediment cascades

Catchment configuration and the nature of connectivity within and between landscape compartments affect the operation of sediment cascades and geomorphic responses to disturbance events of differing magnitude and frequency. This paper introduces the concept of landform impediments, termed buffers, barriers and blankets, that impede sediment conveyance by limiting the connectivity between landscape compartments. Buffers restrict sediment delivery to channels, barriers inhibit sediment movement along channels, and blankets drape channel or floodplain surfaces affecting the accessibility of sediment to entrainment. These features operate as a series of switches which turn on/off processes of sediment delivery, determining the effective catchment area at any given time. Using previously documented examples, the role of these features in affecting the operation of sediment cascades in a low relief, passive landscape setting such as the Australian landmass is contrasted to examples from high relief, uplifting settings in New Zealand. The Australian examples are further explored by examining how changes to landscape connectivity brought about by human disturbance since European settlement have impacted upon landscape sensitivity and prospects for river recovery. This approach to analysis of impediments to sediment conveyance is generic and can be applied in any environmental setting.

Swash–groundwater interaction on a steep gravel beach

Groundwater responses to swash motions were observed on a natural gravel beach at Slapton Sands, UK. Detailed hydrodynamic measurements of swash depth, flow velocity and groundwater elevation were made using a cross-shore array of pressure transducers and current metres. The groundwater-level remained closely linked to the tidal elevation throughout the flood and ebb stages of the tide and prevented the formation of an elevated seepage face. The swash and groundwater spectra were dominated by a broad band of incident-frequency energy, but both displayed an increasing contribution of low-frequency energy moving landwards. A behavioural divergence was identified across the swash zone as groundwater motions were observed when no swash is overhead on the beach face. Fourier analysis and cross-correlations assisted to identify the role of two distinct pathways in the transferral of fluid from the swash to the groundwater. One that causes instantaneous swash-frequency groundwater-level rises via an energy flux through the saturated lower beachface. A second pathway, lagged by up to 4 s, was caused by vertical infiltration from large swashes across the unsaturated upper beachface. Infiltration across the upper-swash zone causes the backwash discharge to be weakened by 50% compared to the uprush discharge, severely limiting the ability of the backwash to transport sediment. The lack of tidal-scale groundwater-level asymmetry ensures that the upper beachface remains unsaturated throughout the whole tidal cycle and allows continued infiltration. It is concluded that this persistent infiltration has important consequences for the morphological changes commonly observed on gravel beaches by allowing accretion in the upper-swash at all stages of the tide.

Large internal waves in Massachusetts Bay transport sediments offshore

A field experiment was carried out in Massachusetts Bay in August 1998 to assess the role of large-amplitude internal waves (LIWs) in resuspending bottom sediments. The field experiment consisted of a four-element moored array extending from just west of Stellwagen Bank (90-m water depth) across Stellwagen Basin (85- and 50-m water depth) to the coast (24-m water depth). The LIWs were observed in packets of 5–10 waves, had periods of 5–10 min and wavelengths of 200–400 m, and caused downward excursions of the thermocline of as much as 30 m. At the 85-m site, the current measured 1 m above bottom (mab) typically increased from near 0 to 0.2 m/s offshore in a few minutes upon arrival of the LIWs. At the 50-m site, the near-bottom offshore flow measured 6 mab increased from about 0.1 to 0.4–0.6 m/s upon arrival of the LIWs and remained offshore in the bottom layer for 1–2 h. The near-bottom currents associated with the LIWs, in concert with the tidal currents, were directed offshore and sufficient to resuspend the bottom sediments at both the 50- and 85-m sites. When LIWs are present, they may resuspend sediments for as long as 5 hours each tidal cycle as they travel westward across Stellwagen Basin. At 85-m water depth, resuspension associated with LIWs is estimated to occur for about 0.4 days each summer, about the same amount of time as caused by surface waves.

Catchment-scale (dis)connectivity in sediment flux in the upper Hunter catchment, New South Wales, Australia

(Dis)connectivity within and between landscape compartments affects the extent and rate of transfer of energy and matter through catchments. Various landforms may impede sediment conveyance in a river system, whether laterally to the channel (termed buffers) or longitudinally along the channel itself (termed barriers). A generic approach to analysis of landscape (dis)connectivity using slope threshold analysis in GIS, tied to air photograph interpretation and field mapping of buffers and barriers, is tested in the upper Hunter catchment, Australia. Under simulated conditions, effective catchment area, which is a measure of the proportion of a catchment that has the potential to contribute sediment to the channel network, varies from 73% to just 3% of the total catchment area for differing subcatchments in the upper Hunter. This variability can be explained by the spatial distribution and assemblage of buffers and barriers in each subcatchment. Multiple forms of disconnectivity are evident in some subcatchments, such that when one buffer or barrier is breached, other features still impede sediment transfer within the system. The importance of the position of buffers and barriers within any given subcatchment is emphasised. Spatial variability in valley width exerts a critical control on catchment connectivity, with more efficient sediment conveyance in narrow valleys relative to wider valleys characterised by piedmonts, terraces, fans and extensive floodplains in which conveyance is impeded. This variability reflects the landscape history and geological setting of each subcatchment. The framework developed in this paper can be used to assess the impact of natural or human-induced buffers and barriers on catchment-scale sediment flux in any landscape setting, providing a physical template atop which other biogeochemical fluxes could be examined.

Sediment trend analysis of the hylebos waterway: Implications for liability allocations

Sediment trend analysis of the hylebos waterway: Implications for liability allocations

Coastal aeolian dune development, Sólheimasandur, southern Iceland

A coastal aeolian dune field on the distal parts of Sólheimasandur, southern Iceland is currently undergoing active construction. Ongoing sand deflation in the foreshore is demonstrated by the preservation of sand ridges in the downwind lee of obstacles, while a backshore sandsheet is characterised by actively accumulating long-wavelength wind ripples. The main region of aeolian accumulation is in the immediate backshore where sand has accumulated to a thickness of up to 8 m and is largely stabilized by vegetation. Surrounding interdune areas have undergone repeated flooding by fluvial incursions from the adjacent Jökulsá River, and are characterised by mud drapes which lap against the lower flanks of neighbouring dunes. Widespread sand adhesion structures testify to the often damp nature of the substrate. Over 1200 vegetated and stabilized dunes (nebkhas) occupy a 5 km 2 area of wind-deflated gravel sandur plain downwind from the main site of aeolian accumulation. The nebkhas show strong relationships between plan form shape and height, indicating that they have attained equilibrium morphology for the prevailing climatic conditions. Within the nebkha field, dunes demonstrate a predictable downwind decrease in height, spatial concentration and degree of sand stabilization. A time series of aerial photographs documents the temporal evolution of the dune field and demonstrates that aeolian accumulation commenced about 1940 and has been ongoing to the present day. Prior to 1940, repeated outburst floods associated with catastrophic lake drainage events from the Sólheimajökull glacier 8 km inland were of sufficient magnitude to repeatedly destroy any incipient aeolian bedforms that developed. Although strong onshore winds and high rates of sediment supply promote aeolian sediment transport, dune field development is rare in humid boreal and sub-arctic climates as encountered in southern Iceland because the availability of sediment for aeolian transport is usually severely limited by damp substrate conditions. Thus, the airflow tends to be undersaturated with respect to its potential sand transporting capacity and dune construction can only occur because of the stabilizing influence of vegetation.

Facies Architecture of Flexural Margin Lowstand Delta Deposits in Lake Edward, East African Rift: Constraints from Seismic Reflection Imaging

Abstract Lake Edward is single half-graben rift basin unique in the East African Rift System as a result of its connection to Lake George via the Kazinga Channel, a paleo–river valley which is incised into the flexural margin of the lake. Using recently acquired normal-incidence seismic reflection data and thirty-three lake-bottom sediment samples, we examine the consequences of this hydrologic connection for understanding depositional processes and facies development along the flexural margin of Lake Edward. Three depositional sequences were defined in the study area based on top and bottom discordances of seismic reflections. Climatically induced changes in lake level appear to have forced sequence development. Sequence I deposits indicate that highstand conditions prevailed earlier in the Pleistocene. Evidence for high-frequency lake-level change comes from lowstand delta clinoforms in two separate stratigraphic intervals on the flexural margin. An older lowstand event occurred during Sequence II time and reduced lake level by at least ~ 37 m. A younger lowstand event occurred during the deposition of Sequence III and reduced lake level by ~ 18 m. Clastic sedimentation on the flexural margin of Lake Edward is strongly modified by inflow from the Kazinga Channel and Lake George during periods of lowered lake level. We suggest that the presence of an incised valley at the margin of the rift controls the stratigraphic development of clinoforms diagnostic of lowstand deltaic sedimentation. The morphology and orientation of these clinoforms suggest that discharge from Lake George during arid periods utilized the Kazinga Channel to transport sediment toward the exposed flexural margin of Lake Edward. Dipping reflections in sigmoid-oblique clinoforms suggest that these flows were capable of transporting sediment loads that included coarse grain sizes. Deposition by this process occurred several times during the late-Quaternary history of Lake Edward, and represents an important modern analogue for linked incised valley-lacustrine delta sequences in the stratigraphic record.

Long waves in erodible channels and morphodynamic influence

Like most media, open channel flows propagate information through waves. When the channel boundary is fixed, the vectors of information consist typically of surface gravity waves. In the less straightforward case of channels with cohesionless bed and possibly erodible banks, other types of waves arise from the erodible nature of the boundaries and the ability of the stream to transport sediments. In this paper we restrict our attention to the important case of long waves, which can be described by employing the shallow water approximation for the flow field and a quasi‐equilibrium assumption for sediment transport on weakly sloping beds. We focus on a major issue: In which direction is information propagated? This is a problem raised and partially solved by de Vries in the context of one‐dimensional morphological modeling as early as 1965. We review some of the available knowledge on this subject, viewed in a more general context where vectors of information can be a variety of waves: purely longitudinal one‐dimensional sediment waves, two‐dimensional waves driven by large‐scale bed forms (bars), and plan form waves carrying information related to the planform shape of the channel. Both linear and nonlinear, migrating and stationary waves are considered. It turns out that the role played by the Froude number in determining the direction of one‐dimensional perturbations of bed topography is somewhat taken by the aspect ratio of the channel when large‐scale two‐dimensional bed forms as well as planform waves are considered.

A morpho-statistical classification of mountain stream reach types in southeastern Australia

The concepts of sediment transport capacity ( Q c) and sediment supply ( Q s) have shown promise in broadly differentiating mountain streams. The important role of lithology in determining reach characteristics is also noted but as yet not fully included in existing process domain frameworks. This study uses topographic and grain size surveys undertaken over 42 channel reaches with slopes between 0.01 and 0.20 m/m to describe mountain stream morphology in southeastern Australia. Reaches with two different lithologies are surveyed to specifically address the role of lithology in resultant channel morphology. Spatial autocorrelation analysis based on Moran's I is used to detect the frequency and occurrence of in-stream features, such as bars and pools. These data are combined with the grain size data to describe eight dominant reach morphologies. Most channel morphologies display broad characteristics similar to previous accounts of mountain streams, although a number of intermediate morphologies affecting subtle variations in form and process where evident. There was no significant longitudinal arrangement of the observed morphologies, particularly with respect to catchment area and slope. This is related to the strongly segmented longitudinal profiles characteristic of these streams where increasing catchment area does not result in a commensurate decrease in slope. Five of the eight channel morphologies identified are lithology dependent with respect to grain size and shape. Regime diagrams applied to quantify the physical controls on the different reach morphologies identified different Q c– Q s domains for most morphologies. However, some lithology-dependent morphologies could not be differentiated supporting the need to incorporate the effects of dominant grain shape (or sphericity) in assigning dimensionless critical shear stress values in determining Q s. Overall, the differences in mountain stream reach morphologies described in this study reflect the characteristic segmentation of the longitudinal profiles of these streams and contrasts in the supply and breakdown of parent material.

Macrofaunal modification of porewater advection: role of species function, species interaction, and kinetics

Sedimentary habitats are complex associations of biotic, chemical, and physical pro- cesses comprising 'ecosystem function'. The relative importance of these processes to biogeochemi- cal cycling in highly reactive, permeable sediments remains poorly understood. We report results from several field experiments in a muddy-sand intertidal flat dominated by 2 functionally different types of bioturbating macrofauna in False Bay, Washington, USA: (1) the arenicolid polychaete Abarenicola pacifica and (2) 2 species of thalassinid shrimp (Upogebia pugettensis and Neotrypaea californiensis). Experimental plots composed primarily of one of the study taxa or mixed communities of both were evaluated for their effects on porewater advection, solute concentrations, and sediment characteristics. Fluorescein-impregnated acrylamide gels were used to infer rates of transport, and acrylamide gel peepers were used to record porewater concentrations of diagenetically important constituents among experimental plots. Laboratory studies evaluated rates of diffusive transport in non-bioturbated sediments for comparative analysis. We found that (1) functionally different macro- fauna affect rates of porewater advection in permeable sediments, (2) organism effects are not attrib- utable to changes in average measures of sediment granulometry, (3) species interactions may further complicate the advective environment and the resulting diagenetic processes, and (4) species effects vary according to reaction rate kinetics. We hypothesize that species-related effects on trans- port are due to inhibition of arenicolid feeding by thalassinid tubes that serve to block sediment fluidization and advective flow. Thus, specific behaviors and interactions among organisms appear to affect transport rates and sediment function in advectively permeable habitats. The results indicate the importance of integrating behavior, kinetics, and transport into future studies of sedimentary biodiversity and ecosystem function.

Recent Summer Climate Recorded in Complex Varved Sediments, Nicolay Lake, Cornwall Island, Nunavut, Canada

The recent (1950–1996) varve record from the proximal sediments in Nicolay Lake, Cornwall Island, Nunavut, Canada (77°46′ N, 94°40′ W) contains distinct subannual rhythmites. Deposition of these subannual rhythmites is due primarily to nival snow melt, with additional sedimentary units resulting from major summer precipitation and subaqueous mass wasting events. In order to evaluate the potential hydroclimatic signal contained in the varves from the unglacierized catchment, the nival deposition record was estimated by delineating the initial subannual rhythmite within each varve. When the record is split into temporal segments based on two phases that exhibit different sediment deposition patterns in the lake, the nival rhythmites are significantly correlated to annual cumulative melting degree days (MDD) from the nearest weather station Isachsen (78°47′ N, 103°32′ W) (1950–1962 AD and 1963–1977 AD with r = 0.55 and r = 0.82, respectively). A similar analysis with data from Resolute (74°43′ N, 94°59′ W) yields slightly weaker correlations (1950–1962 AD, r = 0.60; 1963–1994, r = 0.59). The strong positive correlation with both the Isachsen and Resolute thermal records suggests that the paleoclimatic signal in the sediments reflects regional climate conditions. Notably, the signal is strongest when the entire melt season is considered; weaker correlations with instrumental weather records are associated with comparisons limited to the peak melt or early season melt periods. We attribute this to the ongoing supply of snowmelt through the season in this polar region and the availability of sediment for transport throughout the melt season. These results indicate that a high resolution hydroclimatic signal is present in the sediments from Nicolay Lake and can be used for paleoclimate reconstruction provided sedimentary depositional controls are taken into account.

Changing pattern of accretion/erosion of the modern Yellow River (Huanghe) subaerial delta, China: Based on remote sensing images

The Yellow River shifted from the Diaokou course to the Qingshuigou course in 1976, and shifted again at the north bank of the Qingshuigou course in 1996. As a result, the entire modern Yellow River Delta has experienced complicated patterns of erosion and accretion. Multitemporal remote sensing data of Landsat MSS and TM from 1976 to 2000, totaling twenty scenes, were used to examine the changing pattern of accretion and erosion of the modern Yellow River subaerial delta with GIS tools. During the period 1976 to 2000, the maximum erosion occurred at the head of the last two abandoned promontories, Diaokou and Shenxiangou promontories, where the coastline retreated landward over − 7 and − 4.5 km, respectively, with mean net erosion rates of − 0.29 and − 0.19 km/a, respectively. In contrast, the maximum accretion occurred at the head of the Qingshuigou Promontory where the coastline advanced seaward over 20 km with a mean net accretion rate of 0.83 km/a. The coastline at the head of the Q 8 Promontory also advanced seaward 7 km with a mean net accretion rate of 0.29 km/a during the period 1996 to 2000. Total area of the Diaokou and Shenxiangou promontories was reduced by − 141.3 km 2 with a mean net erosion rate of − 6.03 km 2/a. Total area of the Qingshuigou and Q 8 promontories increased by 384.16 and 11.88 km 2, respectively, with mean net accretion rates of 16.4 and 3.03 km 2/a, respectively. Relative to the Diaokou, Shenxiangou and Qingshuigou promontories, the west area of the Diaokou Promontory and south area of the Qingshuigou Promontory were relatively stable, although minor erosion occurred. The general pattern of accretion and erosion of the modern Yellow River subaerial delta was divided into three stages: rapid accretion stage (1976–1984), accretion–erosion adjustment stage (1985–1995), and slow erosion stage (1996–present). The factors affecting the pattern of erosion and accretion over the Yellow River Delta, such as structural geology, the Yellow River sediment discharge, coastal processes, meteorological conditions, human activity, sea level rise and land subsidence were summarized. The cumulative area of increase over the entire subaerial delta is closely correlated with the cumulative Yellow River sediment discharge. Wave-induced longshore current is the major driving force to transport sediment from eroded areas along the last two abandoned promontories, Diaokou and Shenxiangou promontories, mostly westerly and partially easterly. Together with these coastal processes is the geographical shift of the Yellow River course associated with its discharge regime after 1976, leading to the accretion along the present Qingshuigou Promontory and then the Q 8 Promontory.

Impact of iron ore mining on suspended sediment response in a tropical catchment in Kudremukh, Western Ghats, India

Available secondary suspended sediment data from the 1980s was analyzed together with new data collected during 2001–2003 at instrumented sites upstream and downstream of open-cast mining activities (∼4.2 km 2) in an enclosure within the Kudremukh National Park in south India. More than 50% of the suspended sediment load in both the Bhadra River and Bhadra Reservoir comes from mining-affected lands that occupy <1% of the total catchment area (1968 km 2). For baseflow conditions during the post-monsoon period of 2001, 0.02 Mg km −2 day −1 of suspended sediment was discharged at the upstream site compared with 0.74 Mg km −2 day −1 downstream of the mine. During the 2002 and 2003 monsoons, these rates increased to about 1.99 and 7.89 Mg km −2 day −1 for upstream and downstream sites, respectively. The specific sediment yield above the mine is 239 Mg km −2 year −1 versus 947 Mg km −2 year −1 downstream. Sediment concentration downstream was significantly higher than upstream for all conditions. The current annual suspended sediment load below the mine ranges from 100,000 to over 150,000 Mg, depending on the size and frequency of large rain events. During the 2002 and 2003 monsoon seasons, 20–30% of the total suspended sediment load during the sampling period of 67 and 123 days, respectively, was transported in one single day and over one-third of the total recorded suspended load is discharged in less than 4 days in each monsoon. Daily rainfall and maximum hourly rainfall intensity were reasonable predictors of daily sediment loads downstream of the mine ( R 2 = 0.71 and 0.575, respectively; p < 0.001). However, the upstream response was not predicted well by these variables, suggesting an absence of rapid overland pathways and/or reduced availability of easily transportable sediment on the less-disturbed lands above the mining area. Large episodic sediment events downstream of the mine were associated with daily rainfall >150 mm and hourly intensities exceeding 20 mm. One hundred and nine such episodic events occurred between 1990 and 2001 alone. A conservative estimate of the total suspended sediment load in the Bhadra River after mining commenced in the 1980s is 1.37 × 10 6 Mg, although the actual value could be considerably higher, up to 10 7 Mg. Comparison of historic data and another study in 1994, with recent measurements confirm that mining and associated activities in Kudremukh National Park are the greatest sources of sediment entering the Bhadra River; and the Bhadra river carries considerably more sediment now than before mining started damaging riverine ecosystems and disrupting downstream water resources.