Quantification Of Sediment Transport Research Articles

Turbulence Intermittency Effects on the Initiation Threshold of Sediment Motion in Natural Waters

AbstractThe initiation threshold of sediment motion, a key component in quantifying sediment transport, has potential link to intermittent turbulence bursts. Here, we elaborated in situ experiments on coastal sea bottom covered with cohesive sediments, to obtain intermittency parameters. The variable “waiting time” between turbulence bursts was utilized to capture the occurrence of sediment initiation events in natural waters. A relationship between waiting time and shear stress reveals the different intermittency features of sediment flux time series before and after reaching the threshold, which can be used to determine the initiation threshold of sediment motion. Multi‐site results demonstrate the limitations of traditional empirical formulae for fine‐grained sediments, where cohesiveness becomes more pronounced as grain size decreases and the deviation can reach 600%. The empirical formula was modified using grain size, and the modified calculations were in good agreement with observed values, which will greatly assist in sediment transport and geomorphology model predictions.

Testing magnetic tracers as indicators of sediment transport in a wave flume experiment

AbstractThe in situ measurement of sediment transport in wave‐dominated environments presents significant challenges and currently often relies upon the use of fluorescent sediment tracers. However, this method is constrained by challenges in conducting unbiased and representative sampling, as well as facing overall logistical complexities and labour‐intensive procedures. Whilst other tracer techniques are available, such as using magnetic tracers, their performance in tracking sediment transport has not been quantified. The objective of this study is to assess the effectiveness of magnetic tracers in evaluating net transport rates and tracer dispersal patterns. Conducted in a controlled large wave flume, the experiments simultaneously employed fluorescent and magnetic tracers, allowing a comprehensive comparison of the tracers' dispersion patterns and the net transport rates. Results show that the dispersal of magnetic and fluorescent tracers displays a high degree of spatial coherence in both horizontal and vertical dimensions. Similarly, net transport rates are comparable (<16% difference), both showing net transport in the direction of the wave propagation (towards onshore) driven by non‐linear and streaming effects. Magnetic tracer recovery rate (49%) was lower than for fluorescent tracers (73%) and is attributed to the loss of magnetic ink from particles; an aspect of the magnetic technique that requires improvement. This study therefore indicates that the use of magnetic tracers to quantify sediment transport is an effective method with the advantages of being significantly less labour‐intensive than using the commonly applied fluorescent sediment tracer method.

Seismic Signature of Rain and Wind Inferred From Seismic Data

AbstractSeismic stations are increasingly used to monitor river activity and to quantify sediment transport during flood events. In tropical regions, cyclone‐induced floods are often associated with heavy rain and strong wind episodes, generating complex seismic records involving the simultaneous signature of water, sediment, rainfall and wind. Hence, seismic characterization of rain and wind is then required to better decipher each process and improve our understanding of the river seismic signature. In this study, we investigate experimentally the seismic response of rain and wind using data recorded by geophones deployed in various soil types and at different burial depth (BD), co‐located with various meteorological instruments. Our results show that the power spectral density (PSD) of the seismic noise intensifies at a frequency between 60 and 500 Hz for rain and 5 and 500 Hz for wind, in the presence of rain precipitation as low as 0.025 mm/min and/or wind speed ≥3 m/s. PSD analysis indicates that the seismic signal associated with rain decreases with the BD with a value of ∼2–5 dB in a depth difference of 10 cm. We also observe that each soil type has its own seismic signature. The 4‐min root mean square correlation between the seismic signal amplitude and the rain precipitation suggests that they best correlate with Pearson coefficient >0.90 at BD of 30 cm. The transfer function between the precipitation rate (or kinetic energy) and the seismic signal amplitude shows that the signal recorded by the geophone can be used as a robust proxy for these parameters.

Transport and deposition processes of the sediment depocenter off the Shandong Peninsula: An observational study

The long-distance transport of Yellow River sediments has formed an omega-shaped (‘Ω’) distal muddy deposit in the Yellow Sea. Numerous studies have investigated the sediment dynamics and sedimentary evolution of the deposit, but several key questions remain unanswered due to insufficient observations. To reveal the mechanisms of sediment dynamics and quantify sediment transport and deposition processes, this study collected field datasets in the depocenter of the muddy deposit off the Shandong Peninsula. Bottom mounted tripods were deployed from August 18 to 27, 2017, and from February 23 to March 2, 2018, during which two strong wind events with speeds of over 10.8 m/s occurred. The results showed that near-bed suspended sediment concentration responded directly to varying hydrodynamic conditions, and significant differences in suspended sediment concentration between two wind events could be ascribed to a number of factors (e.g., tidal current, wave periods, wind stress, turbulence). The harmonic analysis demonstrated that suspended sediment variations during the spring tide were directed mainly by resuspension, while resuspension and advection contributed equally at neap tide. The variations in background suspended sediment concentration can be ascribed to the residual current. Furthermore, the sediment transport pattern is similar to the pattern of water circulation. Generally, the along-shore suspended sediment flux is about one order of magnitude higher than the cross-shore flux. In summer, the suspended sediment was transported mainly downcoast. In winter, sediment was transported downcoast during wavy periods and upcoast during calm periods. Advection dominated sediment flux in most cases, except during wavy periods when local resuspension increased significantly, and the contribution of resuspension term to along-shore flux was up to 87%. Meanwhile, cross-shore flux also increased significantly under strong winds, which was simultaneously modulated by downcoast and offshore winds. After statistical analysis, we found that offshore winds controlled the cross-shore sediment transport in winter. Using parameterized calculation and statistical analysis, the average accumulation rate of the study site was estimated to be 0.6 cm/yr. During calm periods, lower background sediment concentration in summer led to lower deposition rates than in winter. In addition, the frequent strong wind events in winter cause extremely high erosion rates. This study provides new perspectives on quantitative variations in suspended sediment transport and regional erosion/deposition from synoptic to seasonal variations in the distal mud deposit.

Machine learning methodology for determination of sediment particle velocities over sandy and rippled bed

The physics and quantification of sediment transport are still a challenge for scientists and engineers. Measurements of wave-induced sediment velocities may be conducted only in selected laboratories and require weeks of pre-tests and a very experienced team. In this study, student psychology-based optimization (SPBO) algorithm was applied to develop new integrated machine learning methods for the determination of wave-induced non-cohesive sediment particle velocities over a rippled bed by incorporating the outcome of particle image velocimetry. Easily measurable data comprising sediment characteristics, bedform details, and hydrodynamic conditions were used to train the machine learning models. The developed techniques determine well the sediment particle horizontal velocity over a horizontal profile. The analysis shows that the derived models nearly perfectly predict observed data. The proposed methodology provides insight into the physics of sediment processes and may also be applied to interpret measurement data and verify sediment transport models.

Monitoring and modeling sediment transport in space in small loess catchments using UAV-SfM photogrammetry

Sediment transport rates are widely used in studies of soil erosion, hydrological simulation, and regional ecological assessment. Although traditional field hydrological stations can provide a global sediment transport rate for observation areas, quantifying sediment transport rates in space is still challenging. This study presents a work frame for monitoring and modeling sediment transport in space using recently ongoing UAV-SfM photogrammetry. First, the DEMs of difference (DoDs) were obtained by repeated UAV surveys. Then, we used the root mean square error (RMSE) and precision map (spatially distributed errors) to detect topographic changes at different confidence levels and analyzed the relations between detected changes and the thresholding of confidence level. Finally, we compared different routing solutions for inferring the sediment transport rates in space based on the observed topographic changes. Results show that the thresholding of confidence level will lose observations and may underestimate global sediment transport rates. The sensitivity of observation loss to the confidence level by using the precision map is lower than that by using RMSE, suggesting that the use of the precision map is more suitable for topographic change detection. In terms of the spatially distributed sediment transport rates, the multiple flow routing based on slope exponent (MFD-se) shows superior performance than the multiple flow routing based on maximum downslope gradient (MFD-md) and eight-node (D-8) routing. The negative sediment transport in the study areas ranges from 2.53% to 7.85% by using MFD-se routing. Moreover, the use of thresholding of confidence level is beneficial to reduce negative transport. The proposed work frame can conveniently provide a detailed spatial distribution of sediment transport rates, which would provide a new perspective for studies of earth surface processes.

Titan’s Prevailing Circulation Might Drive Highly Intermittent, Yet Significant Sediment Transport

AbstractTitan, the largest moon of Saturn, is characterized by gigantic linear dunes and an active dust cycle. Much like on Earth, these aeolian processes are caused by the wind‐driven saltation of surface grains. It is still unclear, however, how saltation on Titan can occur despite the typically weak surface winds and the potentially cohesive surface grains. Here, we explore the hypothesis that saltation on Titan may be sustained at lower wind speeds than previously thought, primarily through granular splash rather than aerodynamic lifting of surface grains. We propose a saltation mass flux parameterization for Titan and use it to quantify sediment transport with a general circulation model. The results suggest that Titan's prevailing circulation can generate highly intermittent yet significant saltation, with mass fluxes of the order of 104 kg m−1 year−1, and that Titan dunes may be formed primarily by fine grains, approximately 0.1 mm in size.

Equilibrium sediment transport by dilute turbidity currents: Comparison of competence‐based and capacity‐based models

AbstractEquilibrium sediment transport is the condition of zero net entrainment and deposition by sediment‐transporting flow (i.e. grade or regime). Here criteria for equilibrium sediment transport, or those used as proxies for equilibrium (for example, onset of erosion, onset of particle setting or suppression of turbulence) for dilute, suspended‐load‐dominated, turbidity currents, are tested against laboratory and natural data. The examined criteria are restricted to those describing flow over a bed of loose particulate material involving non‐cohesive sediment. Models include both monodisperse and polydisperse formulations that represent sediment non‐uniformity by using a single characteristic grain size or discretization of the grain‐size distribution, respectively. Analysis shows that a polydisperse‐type flux‐balance model, that equates erosional and depositional fluxes and where erosion is related to the power used to lift sediment mass from the bed (the ‘Flow‐Power Flux‐Balance’ model) provides predictions most consistent with observational data. Other equilibrium models tested, monodisperse or polydisperse, fail to predict realistic bed slopes and/or flow durations for concentrations, velocities and depths within limits for natural flows. Results of the Flow‐Power Flux‐Balance model are used to quantify sediment transport fields, equilibrium Shields numbers and slopes for turbidity currents of variable flow and particle properties.

Sediment Connectivity: A Framework for Analyzing Coastal Sediment Transport Pathways

AbstractConnectivity provides a framework for analyzing coastal sediment transport pathways, building on conceptual advances in graph theory from other scientific disciplines. Connectivity schematizes sediment pathways as a directed graph (i.e., a set of nodes and links). This study presents a novel application of graph theory and connectivity metrics like modularity and centrality to coastal sediment dynamics, exemplified here using Ameland Inlet in the Netherlands. We divide the study site into geomorphic cells (i.e., nodes) and then quantify sediment transport between these cells (i.e., links) using a numerical model. The system of cells and fluxes between them is then schematized in a network described by an adjacency matrix. Network metrics like link density, asymmetry, and modularity quantify system‐wide connectivity. The degree, strength, and centrality of individual nodes identify key locations and pathways throughout the system. For instance, these metrics indicate that under strictly tidal forcing, sand originating near shore predominantly bypasses Ameland Inlet via the inlet channels, whereas sand on the deeper foreshore mainly bypasses the inlet via the outer delta shoals. Connectivity analysis can also inform practical management decisions about where to place sand nourishments, the fate of nourishment sand, or how to monitor locations vulnerable to perturbations. There are still open challenges associated with quantifying connectivity at varying space and time scales and the development of connectivity metrics specific to coastal systems. Nonetheless, connectivity provides a promising technique for predicting the response of our coasts to climate change and the human adaptations it provokes.

Estimating River Sediment Discharge in the Upper Mississippi River Using Landsat Imagery

With the decline of operational river gauges monitoring sediments, a viable means of quantifying sediment transport is needed. In this study, we address this issue by applying relationships between hydraulic geometry of river channels, water discharge, water-leaving surface reflectance (SR), and suspended sediment concentration (SSC) to quantify sediment discharge with the aid of space-based observations. We examined 5490 Landsat scenes to estimate water discharge, SSC, and sediment discharge for the period from 1984 to 2017 at nine gauging sites along the Upper Mississippi River. We used recent advances in remote sensing of fluvial systems, such as automated river width extraction, Bayesian discharge inference with at-many-stations hydraulic geometry (AMHG), and SSC-SR regression models. With 621 Landsat scenes available from all the gauging sites, the results showed that the water discharge and SSC retrieval from Landsat imagery can yield reasonable sediment discharge estimates along the Upper Mississippi River. An overall relative bias of −25.4, mean absolute error (MAE) of 6.24 × 104 tonne/day, relative root mean square error (RRMSE) of 1.21, and Nash–Sutcliffe Efficiency (NSE) of 0.49 were obtained for the sediment discharge estimation. Based on these statistical metrics, we identified three of the nine gauging sites (St. Louis, MO; Chester, IL; and Thebes, IL), which were in the downstream portion of the river, to be the best locations for estimating water and sediment discharge using Landsat imagery.

Quantifying flow resistance in mountain streams using computational fluid dynamics modeling over structure‐from‐motion photogrammetry‐derived microtopography

AbstractFlow resistance in mountain streams is important for assessing flooding hazard and quantifying sediment transport and bedrock incision in upland landscapes. In such settings, flow resistance is sensitive to grain‐scale roughness, which has traditionally been characterized by particle size distributions derived from laborious point counts of streambed sediment. Developing a general framework for rapid quantification of resistance in mountain streams is still a challenge. Here we present a semi‐automated workflow that combines millimeter‐ to centimeter‐scale structure‐from‐motion (SfM) photogrammetry surveys of bed topography and computational fluid dynamics (CFD) simulations to better evaluate surface roughness and rapidly quantify flow resistance in mountain streams. The workflow was applied to three field sites of gravel, cobble, and boulder‐bedded channels with a wide range of grain size, sorting, and shape. Large‐eddy simulations with body‐fitted meshes generated from SfM photogrammetry‐derived surfaces were performed to quantify flow resistance. The analysis of bed microtopography using a second‐order structure function identified three scaling regimes that corresponded to important roughness length scales and surface complexity contributing to flow resistance. The standard deviation σz of detrended streambed elevation normalized by water depth, as a proxy for the vertical roughness length scale, emerges as the primary control on flow resistance and is furthermore tied to the characteristic length scale of rough surface‐generated vortices. Horizontal length scales and surface complexity are secondary controls on flow resistance. A new resistance predictor linking water depth and vertical roughness scale, i.e. H/σz, is proposed based on the comparison between σz and the characteristic length scale of vortex shedding. In addition, representing streambeds using digital elevation models (DEM) is appropriate for well‐sorted streambeds, but not for poorly sorted ones under shallow and medium flow depth conditions due to the missing local overhanging features captured by fully 3D meshes which modulate local pressure gradient and thus bulk flow separation and pressure distribution. An appraisal of the mesh resolution effect on flow resistance shows that the SfM photogrammetry data resolution and the optimal CFD mesh size should be about 1/7 to 1/14 of the standard deviation of bed elevation. © 2019 John Wiley & Sons, Ltd.

Cosmogenic 3He in alluvial metal and alloy grains: Assessing the potential for quantifying sediment transport times

We have measured the He isotope composition in detrital native gold, copper, silver, Pt3Fe and OsIr alloy grains from placer deposits in order to assess the extent to which cosmogenic He can be quantified and used to determine the exposure history of grains in sedimentary systems. 3He/4He ratios (0.1–273 Ra) exceed values typical of radiogenic He. 4He is dominantly the result of the decay of U and Th, or 190Pt in the case of Pt-rich alloys. 3He concentrations in grains from alluvial deposits range from 0.05 to 2 × 108 at g−1 and appears to be dominantly cosmogenic in origin. The absence of significant nucleogenic or mantle-derived 3He in metals is tentatively confirmed by the analysis of grains from underground mine workings. The implantation of cosmogenic He is not the main source of 3He in alluvial metals but can be relatively important for small grains. New GEANT4-based calculations predict the production rate of 3He (including in precursor 3H) from Au and Pt to be approximately 25 at g−1 yr. Using this we determine that cosmogenic 3He concentrations in the detrital grains record minimum exposure times of between 0.5 and 7 million years that generally increase with distance from the putative source. Paired fragments from three large grains show that there is considerable heterogeneity in cosmogenic He concentrations that may reflect the complex origin of detrital metal grains. This work suggests that cosmogenic He in detrital metals and minerals may find use for providing the chronology of sedimentary processes.

Field Observations of Turbulence, Sand Suspension, and Cross‐Shore Transport Under Spilling and Plunging Breakers

AbstractMeasurements of wave orbital velocity, near‐bed turbulence levels, and sediment suspension were obtained under plunging and spilling breakers in the outer surf zone on the beach at Vejers, Denmark. For the same range of relative wave heights and indicators of wave nonlinearity, we observed significantly larger suspended sediment concentrations and onshore‐directed rates of suspended sediment transport under (long period) plunging breakers, compared to (short period) spilling breakers. This is consistent with the long‐held understanding that, for a given beach slope, onshore transport and beach accretion are associated with longer‐period waves and offshore transport and erosion are associated with shorter‐period waves. An intra‐wave analysis of hydrodynamics and sediment suspension revealed that the main reason for the larger suspended sediment transport rates under plunging waves was (i) larger time‐averaged suspended sediment loads under plunging waves, and (ii) a larger difference in cumulated sediment load under the wave crest phase compared to the wave trough phase for plunging breakers. This latter difference was due to an earlier arrival at the seabed of higher levels of turbulent kinetic energy under plunging waves compared to spilling waves. Hence, both magnitude and timing within the wave cycle of turbulent kinetic energy production are important in a quantification of sediment transport under breaking waves. For ensemble‐averaged intense suspension events, contributing roughly 50% of the total sediment suspension during individual records, we found that instantaneous near‐bed sediment load was linearly related to instantaneous levels of Froude‐scaled turbulent kinetic energy.

Quantifying Sediment Transport Dynamics on Alluvial Fans From Spatial and Temporal Changes in Grain Size, Death Valley, California

How information about sediment transport processes is transmitted to the sedimentary record remains a complex problem for the interpretation of fluvial stratigraphy. Alluvial fan deposits represent the condensed archive of sediment transport, which is at least partly controlled by tectonics and climate. For three coupled catchment‐fan systems in northern Death Valley, California, we measure grain size across 12 well‐preserved Holocene and late‐Pleistocene surfaces, mapped in detail from field observations and remote sensing. Our results show that fan surfaces correlated to the late Pleistocene are, on average, 30–50% coarser than active or Holocene fan surfaces. We adopt a self‐similar form of grain size distribution based on the observed stability of the ratio between mean grain size and standard deviation downstream. Using statistical analysis, we show that fan surface grain size distributions are self‐similar. We derive a relative mobility function using our self‐similar grain size distributions, which describes the relative probability of a given grain size being transported. We show that the largest mobile grain sizes are between 20 and 35 mm, a value that varies over time and is clearly lower in the Holocene than in the Pleistocene; a change we suggest is due to a drier climate in the Holocene. These results support recent findings that alluvial fan sedimentology can record past environmental change and that these landscapes are potentially sensitive to climatic change over a glacial‐interglacial cycle. We demonstrate that the self‐similarity methodology offers a means to explore changes in relative mobility of grain sizes from preserved fluvial deposits.

Quantification and study of monthly variation of suspended sediment loads in Tafna basin – Algeria

Abstract The magnitude of the phenomenon is disproportionate in semi-arid or in temperate climates. Thus Algeria is one of the most affected countries by this phenomenon and its consequences. To enable a rapid response to the request of engineers and managers to quantify sediment transport at the outlet of a watershed, a simple, easy tool to implement was developed. The principle adopted is based on hydrometric data sets from gauging stations with seasonal and annual time steps to define a suitable method for estimating sediment production. The sediment study was conducted by analysing the daily flows. Pierre du Chat station at the outlet of the Tafna basin served as an application. The obtained results are entirely satisfactory because the correlation coefficients of model Qss = f(Q) range between 72 and 95%. This method, once refined can be generalized to all watersheds in northern Algeria.

The morphosedimentary behaviour of a headland–beach system: Quantifying sediment transport using fluorescent tracers

Embayed beaches occurring along rocky coasts with headlands controlling hydrosedimentary processes are considered to be constrained sedimentary systems with little longshore sediment transfer between them. Such beaches are likely to narrow under rising sea level and a deficit of fluvial sediment, and because beaches act to dissipate wave energy, cliff erosion is expected to increase. Knowledge of hydrosedimentary processes in fetch-limited environments such as embayed beaches is therefore a fundamental management tool in erosion-prone coastal areas such as the Algarve region (southern Portugal). The main objective of this work is to quantify longshore sediment transport (LST) using a sedimentary tracer and compare the results with the ones derived via empirical formulae from several authors. To achieve this, we establish the spatial and temporal patterns of stained sediment, and relate these to marine climate data over six tidal cycles for three adjacent embayed beaches. The values of displaced sand estimated using tracer and scaled to mixed layer depth were compared with the results of five well-known LST formulae to assess the applicability of each model to mesotidal environments. Of the LST formulae used, the CERC (2013) shows to be the most accurate in our study area.This study demonstrates the efficacy of using tracers for tracking and quantifying the sediment transport and as a basis for assessing the viability of different LST formulae for representing transport in these types of environments. The work also shows the importance of the morphological control of hydrosedimentary processes, including the disruption of longshore drift and the sediment transfer promoted by shore platforms.

On extracting sediment transport information from measurements of luminescence in river sediment

AbstractAccurately quantifying sediment transport rates in rivers remains an important goal for geomorphologists, hydraulic engineers, and environmental scientists. However, current techniques for measuring long‐time scale (102–106 years) transport rates are laborious, and formulae to predict transport are notoriously inaccurate. Here we attempt to estimate sediment transport rates by using luminescence, a property of common sedimentary minerals that is used by the geoscience community for geochronology. This method is advantageous because of the ease of measurement on ubiquitous quartz and feldspar sand. We develop a model from first principles by using conservation of energy and sediment mass to explain the downstream pattern of luminescence in river channel sediment. We show that the model can accurately reproduce the luminescence observed in previously published field measurements from two rivers with very different sediment transport styles. The model demonstrates that the downstream pattern of river sand luminescence should show exponential‐like decay in the headwaters which asymptotes to a constant value with further downstream distance. The parameters from the model can then be used to estimate the time‐averaged virtual velocity, characteristic transport lengthscale, storage time scale, and floodplain exchange rate of fine sand‐sized sediment in a fluvial system. The sediment transport values predicted from the luminescence method show a broader range than those reported in the literature, but the results are nonetheless encouraging and suggest that luminescence demonstrates potential as a sediment transport indicator. However, caution is warranted when applying the model as the complex nature of sediment transport can sometimes invalidate underlying simplifications.

Sediment transport in steep forested catchments – An assessment of scale and disturbance

Stream sediment loads (both bedload and suspended sediment) are problematic to measure due to the time and equipment needed. There is a dearth of such data sets globally let alone for Australia. However, such data are needed to quantify sediment transport type and rates, landscape evolution, effect of human disturbance as well as patterns and temporal response. Here we present the findings from 8 steepslope forested catchments dominated by headwater streams (size range 15–100ha) in south-eastern Australia where both bedload and suspended load have been measured over multiple years. The results demonstrate that suspended load is the dominant component and there is no consistent suspended to bedload ratio for the catchments. The suspended sediment to bedload ratio appears to be catchment specific. There was no relationship between total load (or bedload/suspended load) and average catchment slope, stream length, shape or any geomorphic descriptor. However catchment total load was found to be significantly related to catchment area. Of the 8 catchments examined here, 6 had been harvested for timber in previous decades (with large areas of forest removed) while 2 catchments had minimal disturbance (Control catchments). There was no difference in sediment loads from the harvested and Control catchments. The results demonstrate that although land disturbance had previously occurred the management practices employed in each catchment were effective in the long term. This provides confidence that the forest harvesting and subsequent management do not produce detrimental effects in the medium to long term. An assessment of erosion rates and likely soil production rates suggests that the catchments are eroding soil at the rate it is being produced.

Sediment output from a post-mining catchment – Centennial impacts using stochastically generated rainfall

Computer based landscape evolution models can provide insight into both erosion rates and processes (i.e. sheetwash, rill, gully erosion). One important data requirement of these models is long term, high quality, high-temporal resolution rainfall data (given that the physical nature of the erosion process is strongly related to rainfall). However, in many cases such data is limited - data is often short, incomplete or not of a sufficient temporal resolution. Therefore, the aim of this study was to test the sensitivity of modelled erosion rates to small changes in rainfall input. To achieve this we firstly assess the existing rainfall data from an established weather station and secondly, stochastically generate rainfall time series based on the longest and most reliable rainfall data. We then test the sensitivity of different rainfall sequences on sediment output using a well-tested landscape evolution and sediment transport model (CAESAR-Lisflood) over a simulated period of 100y on a proposed rehabilitated mine landform. It was found that each rainfall scenario produces a unique pattern of erosion (i.e. the location and extent of the gullies is variable). Further, each rainfall scenario produces a unique pattern of sediment output that suggests non-linear processes. Importantly, this is the first time stochastically generated rainfall has been employed in landform evolution modeling and provides a statistical approach to quantify sediment transport and landform evolution. The method demonstrates a risk based approach and allows rainfall, runoff and sediment transport studies to be conducted in data poor environments. The findings clearly demonstrate that rainfall variability can greatly affect sediment transport and form of erosion as well as landscape evolution. This information is of particular importance for the design and testing of rehabilitated landscape systems such as post-mining landscapes.

Quantification of sediment transport by rockfall and rockslide processes on a proglacial rock slope (Kaunertal, Austria)

Rockfalls and rockslides are significant geomorphic processes on high alpine proglacial rock slopes. In this study, we quantitatively evaluate sediment transport on a recently deglaciated rock slope that is directly connected to the shrinking Gepatschferner glacier, by multi-temporal terrestrial and airborne LiDAR observations. According to the LiDAR measurements, sediment transport by gravitational mass movements on this single proglacial rock slope (0.2km2) yielded 159GJ/a geomorphic work. The most significant part (141GJ/a) was released by rockfall while 18GJ/a were performed by the sliding activity of a 1,250,000m3 large unstable rock mass. The results indicate that slope development and talus formation in proglacial environments may be a rapid process despite of being caused by continuous rockfall activity over several millennia.