Erodible Surface Research Articles

Assessing Landscape Dust Emission Potential Using Combined Ground‐Based Measurements and Remote Sensing Data

AbstractModeled estimates of eolian dust emission can vary by an order of magnitude due to the spatiotemporal heterogeneity of emissions. To better constrain location and magnitude of emissions, a surface erodibility factor is typically employed in models. Several landscape‐scale schemes representing surface dust emission potential for use in models have recently been proposed, but validation of such schemes has only been attempted indirectly with medium‐resolution remote sensing of mineral aerosol loadings and high‐resolution land surface mapping. In this study, we used dust emission source points identified in Namibia with Landsat imagery together with field‐based dust emission measurements using a Portable In‐situ Wind Erosion Laboratory wind tunnel to assess the performance of schemes aiming to represent erodibility in global dust cycle modeling. From analyses of the surface and samples taken at the time of wind tunnel testing, a Boosted Regression Tree analysis identified the significant factors controlling erodibility based on Portable In‐situ Wind Erosion Laboratory dust flux measurements and various surface characteristics, such as soil moisture, particle size, crusting degree, and mineralogy. Despite recent attention to improving the characterization of surface dust emission potential, our assessment indicates a high level of variability in the measured fluxes within similar geomorphologic classes. This variability poses challenges to dust modeling attempts based on geomorphology and/or spectral‐defined classes. Our approach using high‐resolution identification of dust sources to guide ground‐based testing of emissivity offers a valuable means to help constrain and validate dust emission schemes. Detailed determination of the relative strength of factors controlling emission can provide further improvement to regional and global dust cycle modeling.

Coupled sedimentological and geotechnical data analysis of surficial sediment layer characteristics in a tidal estuary

In situ geotechnical testing of surficial sediment layers in areas of active sediment dynamics can provide essential information about physical and geotechnical variations of sediment properties, which have the potential to contribute to engineering activities in subaqueous environments. Portable free fall penetrometers have been used for the rapid geotechnical investigation of subaqueous sediment layers. However, data analysis methods and interpretation are still hampered by a lack of understanding of surficial sediment layer mechanics. Field measurements were conducted at four different locations along the York River Estuary in Virginia, USA. A portable free fall penetrometer was deployed 45 times, and complementary sediment samples were collected. The collected samples were tested and analyzed to obtain vertical profiles of bulk densities and grain size distribution through the upper seabed, X-ray images of sediment texture, and the erodibility of the sediment surfaces. The data were investigated regarding the impact of sedimentological characteristics on the in situ geotechnical behavior of surface sediments. With regard to processes and forces governing the resistance against the penetrating object at the surface of the seabed, the role of soil drag and soil buoyancy was explored. The results indicated that soil buoyancy has a limited influence on the sediment resistance, but soil drag seemed to have a significant impact, especially in the case of loose sand or soft mud top layers. The erodibility of surficial sediments appeared inversely proportional to the geotechnical sediment strength, providing empirical insight into a possible correlation of sediment strength and erodibility. In conclusion, a coupled analysis of geotechnical and sedimentological properties of surficial layers allowed insights into a potential transition from fluid-like to soil behavior of the uppermost seabed surface layers, and potential relations between sedimentological characteristics and in situ geotechnical properties.

Raman Microspectroscopy Study of the Hydrolytic Degradation of Polyanhydride Network Polymers.

Raman microspectroscopy was employed in this work to study the degradation of a polyanhydride network polymer synthesized from 4-pentenoic anhydride and pentaerythritol tetrakis(3-mercaptopropionate) monomers in order to illustrate the utility of this method and improve the understanding of the polyanhydride degradation and erosion. Disk-shaped polymer samples were immersed in buffer solutions for different periods of time, and hydrolytic degradation was monitored spatially and temporally via kinetic Raman studies at various depths of penetration into the samples. Erosion, meanwhile, was monitored via mass loss measurements. Dispersive Raman microspectroscopy is shown to be a particularly valuable tool for the study of the hydrolytic degradation of these materials. It confirms that these thiol-ene polyanhydrides are indeed surface eroding, while also revealing that degradation starts to occur at the core of samples on a short time scale (less than 5 h). At any given degradation time, there is a concentration gradient of the unreacted anhydride, with the unreacted anhydride concentration increasing from the outer edge to the center of the polymer samples. Further, the anhydride functionality is found to decrease approximately linearly with degradation time at all depths in the samples, though the degradation rate does appear to increase slightly as degradation occurs.

A simple model to estimate emission of wind-blown particles from a granular bed in comparison to wind tunnel experiments

Dust emissions due to aeolian erosion of exposed granular materials are strongly influenced by grain size distribution. Non-erodible particles that are too heavy to be lifted into the air play a protective role in the aeolian erosion process attenuating emission, which is known as the pavement phenomenon. To date, there is no approach that reliably predicts the reduction in emissions caused by their presence on an aggregate surface. In this work, an analytical model was developed to quantify emissions from particle beds with a wide size distribution. As non-erodible particles accumulate, changes in surface characteristics create increasing shelter for the erodible portion of the bed until the shear on the erodible surface reaches a minimum and emissions cease. The proposed emission model describes the relationship between this minimum value of wind shear and the eroded depth of the bed after the pavement, which in turn gives the emitted mass. In addition, wind tunnel experiments were carried out in order to broaden knowledge of the pavement phenomenon and validate the modelling. A bimodal particle size distribution of sand with erodible and non-erodible particles was used for the tested velocities. Three experimental measurements were carried out: (i) continuous weighing of the emitted mass, (ii) eroded depth of the bed at regular time intervals and (iii) final cover rates of the non-erodible particles using digital analysis of sand bed pictures after experiments. Good agreement between the modelling and experimental results was found. The emission model proposed herein is a simple algebraic expression that demands low computational effort. This approach may serve as a base for an emission model for application in granular materials stockpiles.

Design and synthesis of multivalent α-1,2-trimannose-linked bioerodible microparticles for applications in immune response studies of Leishmania major infection.

Leishmaniasis, a neglected tropical disease, currently infects approximately 12 million people worldwide with 1 to 2 million new cases each year in predominately underdeveloped countries. The treatment of the disease is severely underdeveloped due to the ability of the Leishmania pathogen to evade and abate immune responses. In an effort to develop anti-leishmaniasis vaccines and adjuvants, novel carbohydrate-based probes were made to study the mechanisms of immune modulation. In this study, a new bioerodible polyanhydride microparticle was designed and conjugated with a glycodendrimer molecular probe. This molecular probe incorporates a pathogen-like multivalent display of α-1,2-trimannose, for which a more efficient synthesis was designed, with a tethered fluorophore. Further attachment of the glycodendrimer to a biocompatible, surface eroding microparticle allows for targeted uptake and internalization of the pathogen-associated oligosaccharide by phagocytic immune cells. The α-1,2-trimannose-linked bioerodible microparticles were found to be safe after administration into the footpad of mice and demonstrated a similar response to α-1,2-trimannose-coated latex beads during L. major footpad infection. Furthermore, the bioerodible microparticles allowed for investigation of the role of pathogen-associated oligosaccharides for recognition by pathogen-recognition receptors during L. major-induced leishmaniasis.

RELEASE KINETICS – CONCEPTS AND APPLICATIONS

he release of drug from the formulations plays significant role especially when it comes to modified release as well as in immediate release dosage forms. Several factors like physicochemical properties of drugs, excipients, dosage form design, manufacturing process variables and design impact drug release from dosage form.It is essential to study the release pattern of drug from dosage form as it governs the efficacy of the dosage form. Several models facilitate the understanding of release pattern thus enabling to design an effective formulation. A few of the various models used by researchers to study the release profile are explained in this review which includes: Higuchi model -describes the drug release from a matrix system. Hixson-Crowell cube root law -describes the release from systems where there is a change in surface area and diameter of particles. Korsmeyer and Peppas developed an empirical equation to analyze both Fickian and non-Fickian release of drug from swelling and nonswelling polymeric delivery systems. Baker and Lonsdale developed the model from Higuchi model explaining the drug release from spherical matrices. The Weibull equation which describes drug dissolution and release from dosage forms, it expresses the accumulated fractio n of drug‘m’ in solution at time‘t’. Hopfenberg model correlates the drug release from surface eroding polymers. The exponential model known as Gompertz model which describe in-vitro dissolution profile. The Gallagher and Corrigan model which describes the fraction of drug released from the biodegradable polymeric system. The Cooney model which describes about spheres and cylinders undergoing surface erosion.

Erosion-deposition regime formation in granular column collapse over an erodible surface

In this paper, the collapse of a granular column over an erodible bed is investigated experimentally and numerically. Four series of experiments are performed using different materials in order to understand the occurrence of the erosion and its evolution. Three different erosion-deposition regimes are observed in experiments, which primarily depend on the difference in material properties between the column and erodible bed but vary little with the initial aspect ratio of the column. Once the erosion process occurs, the collapsing flow has both longer initial acceleration and final deceleration phases but a shorter intermediate period of constant-velocity flow, a phenomenon that is more prominent when the flow front of collapsing material eventually penetrates into bed material. However, the overall flowing duration satisfies a proportional relationship with the free-fall time of granular column ${\ensuremath{\tau}}_{c}$ for both erosion regimes, almost identical to that observed on a rigid substrate. Furthermore, the mechanism of the erosion is discussed based on the evolution of velocity field and the migration of the interface between static and flowing materials. The proposed equation of motion for the flow front shows that the particle density ratio of the column and the erodible bed plays a crucial role in the formation of different erosion-deposition regimes. In addition to reproducing various deposit morphologies observed in our experiments, our numerical simulation results also confirm the existence of critical particle density ratios that correspond to regime transitions and are almost independent of the initial aspect ratio of the column.

The surface eroding thermocouple for fast heat flux measurement in DIII-D.

A novel type of surface eroding thermocouple (SETC) has been tested and demonstrated in the small angle slot (SAS) divertor of DIII-D for fast local heat flux measurements. The thermojunction of the SETC is formed between two thin (10 μm) ribbons, which are filed over to create microfiber junctions. These thermocouples are able to be exposed directly to the plasma at surface temperatures exceeding 2000 °C and are capable of sub-10 ms time resolution. Before installation in SAS, the SETCs were exposed in the lower DIII-D divertor during L-mode and H-mode discharges, from which results are presented. In preliminary tests, SETCs proved to be a qualified diagnostic to accurately measure both the intra-edge localized mode (ELM) and inter-ELM heat flux during H-mode shots with high frequency ELMs (hundreds of Hz) and to resolve heat flux profiles during strike point sweeps. The heat fluxes measured by using SETCs are consistent with the heat fluxes measured by using IR cameras and Langmuir probes. These new diagnostic capabilities will complement the existing IR camera measurements and will be of particularly significant value to measure surface heat flux in the SAS divertor or other regions where the IR camera lacks line of sight.

Simulating the meteorology and PM10 concentrations in Arizona dust storms using the Weather Research and Forecasting model with Chemistry (Wrf-Chem)

ABSTRACTNine dust storms in south-central Arizona were simulated with the Weather Research and Forecasting with Chemistry model (WRF-Chem) at 2 km resolution. The windblown dust emission algorithm was the Air Force Weather Agency model. In comparison with ground-based PM10 observations, the model unevenly reproduces the dust-storm events. The model adequately estimates the location and timing of the events, but it is unable to precisely replicate the magnitude and timing of the elevated hourly concentrations of particles 10 µm and smaller ([PM10]).Furthermore, the model underestimated [PM10] in highly agricultural Pinal County because it underestimated surface wind speeds and because the model’s erodible fractions of the land surface data were too coarse to effectively resolve the active and abandoned agricultural lands. In contrast, the model overestimated [PM10] in western Arizona along the Colorado River because it generated daytime sea breezes (from the nearby Gulf of California) for which the surface-layer speeds were too strong. In Phoenix, AZ, the model’s performance depended on the event, with both under- and overestimations partly due to incorrect representation of urban features. Sensitivity tests indicate that [PM10] highly relies on meteorological forcing. Increasing the fraction of erodible surfaces in the Pinal County agricultural areas improved the simulation of [PM10] in that region. Both 24-hr and 1-hr measured [PM10] were, for the most part, and especially in Pinal County, extremely elevated, with the former exceeding the health standard by as much as 10-fold and the latter exceeding health-based guidelines by as much as 70-fold. Monsoonal thunderstorms not only produce elevated [PM10], but also cause urban flash floods and disrupt water resource deliveries. Given the severity and frequency of these dust storms, and conceding that the modeling system applied in this work did not produce the desired agreement between simulations and observations, additional research in both the windblown dust emissions model and the weather research/physicochemical model is called for.Implications: While many dust storms can be considered to be natural, in semi-arid climates such storms often have an anthropogenic component in their sources of dust. Applying the natural, exceptional events policy to these storms with strong signatures of anthropogenic sources would appear not only to be misguided but also to stifle genuine regulatory efforts at remediation. Those dust storms that have resulted, in part, from passage over abandoned farm land should no longer be considered “natural”; policymakers and lawmakers need to compel the owners of such land to reduce its potential for windblown dust.

Depth-averaged modelling of granular dike overtopping

Failure of river dikes due to overtopping is a dangerous phenomenon to be avoided, and a complex unsteady sediment transport problem that is under intense scientific consideration. Mathematical modelling of these flows is conducted using one-dimensional families of models based on different conceptual approximations, including (i) a clear-water layer and bed-load layer approach; (ii) a mixture flow approach dividing the sediment transport into bed and suspended load transport modes; and (iii) a two-phase approach formulating the mass and momentum conservation equations for the water and sediment phases separately. These families of conceptual models involve a vertical momentum balance reducing to hydrostatic pressure distribution. As discussed in previous works, numerical results might be improved by relaxing this closure hypothesis. Herein, a vertically-averaged RANS model is presented for a water–sediment mixture, conceptually divided into suspended/bed-load layers, overtopping the erodible dike surface under non-equilibrium sediment transport and non-hydrostatic fluid pressure conditions. The model is critically compared with experimental data and Saint-Venant type simulations, resulting in improved predictions of the dike crest reach. However, the erosion at the dike toe is overpredicted, stating a limitation of depth-averaged modelling.

Predictive model for local scour downstream of hydrokinetic turbines in erodible channels

Inspired by recent theoretical advances in bridge scour research, a modeling framework is derived to predict the scour induced by Hydrokinetic turbines on erodible river bed surfaces. Using a mixed scaling formulation of the Reynolds stresses, the turbine performance is linked to the scour evolution.

Elastic wave generated by granular impact on rough and erodible surfaces

The elastic waves generated by impactors hitting rough and erodible surfaces are studied. For this purpose, beads of variable materials, diameters, and velocities are dropped on (i) a smooth PMMA plate, (ii) stuck glass beads on the PMMA plate to create roughness, and (iii) the rough plate covered with layers of free particles to investigate erodible beds. The Hertz model validity to describe impacts on a smooth surface is confirmed. For rough and erodible surfaces, an empirical scaling law that relates the elastic energy to the radius Rb and normal velocity Vz of the impactor is deduced from experimental data. In addition, the radiated elastic energy is found to decrease exponentially with respect to the bed thickness. Lastly, we show that the variability of the elastic energy among shocks increases from some percents to 70% between smooth and erodible surfaces. This work is a first step to better quantify seismic emissions of rock impacts in natural environment, in particular on unconsolidated soils.

Amplification factors to estimate wind erosion of piles of soil with different heights: Numerical simulation and structure-from-motion photogrammetry verification

In this study, we propose amplification factors of single conical piles with different heights and sizes to describe wind erosion acceleration effects of piles compared to flat erodible surfaces. It is not difficult using traditional wind erosion models to estimate wind erosion of flat agricultural land or pastoral surfaces. However, in the current form these models cannot be used for elevated surfaces such as dunes or piles, which may lead to more serious dust emission and air pollution. A computational fluid dynamics simulation was used to refine a wind erosion estimation method of pile from the US Environmental Protection Agency (USEPA) by dividing the pile surface into multiple subareas with constant wind speed for each subarea and then obtaining ratios of pile erosion to the corresponding flat surface by calculating the total erosion rate of the pile and that of a flat surface with the same floor area. The ratios as amplification factors, <i>E_amp</i>, for six pile sizes (from 1 to 12 m) and five wind speed scenarios covering most erosive daily wind speeds from 824 stations throughout China were analyzed and fitted to equations to enable consideration of other heights and wind speed conditions. The changing patterns of the factors were verified using experimental surveys of two plots via the structure-from-motion photogrammetry method, which generated high-resolution digital elevation maps and detected detailed erosion changes. The erosion from a stockpile surface was found to be 2.52 to 7.16 times that from a flat surface with the same floor area, and the influence of pile height on amplification factor could be expressed by a logarithmic equation. These factors can be easily applied to estimate pile erosion by multiplying them by wind erosion results for flat surfaces obtained from other indexes or models. The procedure described in this paper can be extended to consider amplification or reduction effects of dunes, hills, piles, pits, and gullies with different shapes or configurations in relation to wind erosion. Furthermore, the reliability of wind erosion estimation over complex surfaces can be improved to implement specific soil conservation practices.

Unlocking the Potential of Poly(Ortho Ester)s: A General Catalytic Approach to the Synthesis of Surface-Erodible Materials.

Poly(ortho ester)s (POEs) are well‐known for their surface‐eroding properties and hence present unique opportunities for controlled‐release and tissue‐engineering applications. Their development and wide‐spread investigation has, however, been severely limited by challenging synthetic requirements that incorporate unstable intermediates and are therefore highly irreproducible. Herein, the first catalytic method for the synthesis of POEs using air‐ and moisture‐stable vinyl acetal precursors is presented. The synthesis of a range of POE structures is demonstrated, including those that are extremely difficult to achieve by other synthetic methods. Furthermore, application of this chemistry permits efficient installation of functional groups through ortho ester linkages on an aliphatic polycarbonate.

Vegetation in Drylands: Effects on Wind Flow and Aeolian Sediment Transport

Drylands are characterised by patchy vegetation, erodible surfaces and erosive aeolian processes. Empirical and modelling studies have shown that vegetation elements provide drag on the overlying airflow, thus affecting wind velocity profiles and altering erosive dynamics on desert surfaces. However, these dynamics are significantly complicated by a variety of factors, including turbulence, and vegetation porosity and pliability effects. This has resulted in some uncertainty about the effect of vegetation on sediment transport in drylands. Here, we review recent progress in our understanding of the effects of dryland vegetation on wind flow and aeolian sediment transport processes. In particular, wind transport models have played a key role in simplifying aeolian processes in partly vegetated landscapes, but a number of key uncertainties and challenges remain. We identify potential future avenues for research that would help to elucidate the roles of vegetation distribution, geometry and scale in shaping the entrainment, transport and redistribution of wind-blown material at multiple scales. Gaps in our collective knowledge must be addressed through a combination of rigorous field, wind tunnel and modelling experiments.

Predictive performance of rainfall thresholds for shallow landslides in Switzerland from gridded daily data

AbstractA high‐resolution gridded daily precipitation data set was combined with a landslide inventory containing over 2000 events in the period 1972–2012 to analyze rainfall thresholds which lead to landsliding in Switzerland. We colocated triggering rainfall to landslides, developed distributions of triggering and nontriggering rainfall event properties, and determined rainfall thresholds and intensity‐duration ID curves and validated their performance. The best predictive performance was obtained by the intensity‐duration ID threshold curve, followed by peak daily intensity Imax and mean event intensity Imean. Event duration by itself had very low predictive power. A single country‐wide threshold of Imax = 28 mm/d was extended into space by regionalization based on surface erodibility and local climate (mean daily precipitation). It was found that wetter local climate and lower erodibility led to significantly higher rainfall thresholds required to trigger landslides. However, we showed that the improvement in model performance due to regionalization was marginal and much lower than what can be achieved by having a high‐quality landslide database. Reference cases in which the landslide locations and timing were randomized and the landslide sample size was reduced showed the sensitivity of the Imax rainfall threshold model. Jack‐knife and cross‐validation experiments demonstrated that the model was robust. The results reported here highlight the potential of using rainfall ID threshold curves and rainfall threshold values for predicting the occurrence of landslides on a country or regional scale with possible applications in landslide warning systems, even with daily data.

A coupled vegetation/sediment transport model for dryland environments

AbstractDryland regions are characterized by patchy vegetation, erodible surfaces, and erosive aeolian processes. Understanding how these constituent factors interact and shape landscape evolution is critical for managing potential environmental and anthropogenic impacts in drylands. However, modeling wind erosion on partially vegetated surfaces is a complex problem that has remained challenging for researchers. We present the new, coupled cellular automaton Vegetation and Sediment TrAnsport (ViSTA) model, which is designed to address fundamental questions about the development of arid and semiarid landscapes in a spatially explicit way. The technical aspects of the ViSTA model are described, including a new method for directly imposing oblique wind and transport directions onto a cell‐based domain. Verification tests for the model are reported, including stable state solutions, the impact of drought and fire stress, wake flow dynamics, temporal scaling issues, and the impact of feedbacks between sediment movement and vegetation growth on landscape morphology. The model is then used to simulate an equilibrium nebkha dune field, and the resultant bed forms are shown to have very similar size and spacing characteristics to nebkhas observed in the Skeleton Coast, Namibia. The ViSTA model is a versatile geomorphological tool that could be used to predict threshold‐related transitions in a range of dryland ecogeomorphic systems.

Characterizing turbulent wind flow around dryland vegetation

AbstractWind flow has been studied in situations where it encounters porous and solid windbreaks, but there has been a lack of research exploring turbulent wind dynamics around and in the lee of real vegetation elements. In dryland contexts, sparse vegetation plays an important role in modulating both the erosivity of the wind and the erodibility of surfaces. Therefore, understanding the interactions between wind and vegetation is key for improving wind erosion modelling in desert landscapes. In this study, turbulent wind flow around three typical dryland vegetation elements (a grass clump, a shrub, and a tree) was examined in Namibia using high‐frequency (10 Hz) sonic anemometry. Spatial variations in mean wind velocity, as well as Reynolds stresses and coherent turbulent structures in the flow, were compared and related to the porosities and configurations of the study elements. A shelter parameter, originally proposed by Gandemer (, Journal of Wind Engineering and Industrial Aerodynamic 4: 371–389), was derived to describe the combined impact of the different elements on the energy and variability of horizontal wind flow. Wind velocity was reduced by 70% in the immediate lee of the grass and 40% in the lee of the shrub, but velocity recovered exponentially to equilibrium over the same relative distance in both cases (~9 element heights downwind). Quadrant analysis of the high‐frequency wind flow data revealed that the grass clump induced a small recirculation zone in its lee, whereas the shrub did not. Also, higher Reynolds shear stress and higher ‘flow positivity magnitude’ [ratio of Q1 (outward interaction) and Q4 (sweep) quadrants to Q2 (ejection) and Q3 (inward interaction) quadrants] was generally observed in the wake of the grass. These differences arose because the porosity of the grass clump (53%) was lower than the porosity of the shrub (69%), and thus bleed flow through the shrub was more significant. The bluff‐body behaviour of the grass resulted in a more intense and more extensive sheltering effect than the shrub, which implies that overall sediment transport potential is lower in the wake of the grass. The tree displayed a different wake structure to the grass and shrub, owing to the elevation of its crown. A ‘bottom gap’ effect was observed, whereby wind velocities increased possibly due to streamline compression in the gap between the ground and the underside of the tree crown. Differences in flow momentum between the bottom gap and the low‐pressure leeward region of the crown are a probable explanation for the formation of a large recirculation vortex. The bottom gap effect led to decreased sheltering up to three tree heights downwind, but the surface became increasingly protected by the frontal impact of the crown over a further eight tree heights downwind (~30 m). The extraction of momentum from the air by the tree therefore resulted in a far more extensive sheltering effect compared to the grass and shrub. This study represents an important investigation of the impact of different vegetation types on turbulent wind flow, and results can be integrated as parameterizations into spatial sediment transport models that explore landscape‐scale change on semi‐vegetated desert surfaces. Copyright © 2016 The Authors. Earth Surface Processes and Landforms Published by John Wiley &amp; Sons Ltd.

New insights into the wind‐dust relationship in sandblasting and direct aerodynamic entrainment from wind tunnel experiments

AbstractNumerous parameterizations have been developed for predicting wind erosion, yet the physical mechanism of dust emission is not fully understood. Sandblasting is thought to be the primary mechanism, but recent studies suggest that dust emission by direct aerodynamic entrainment can be significant under certain conditions. In this work, using wind tunnel experiments, we investigated some of the lesser understood aspects of dust emission in sandblasting and aerodynamic entrainment for three soil types, namely, clay, silty clay loam, and clay loam. First, we explored the role of erodible surface roughness on dust emitted by aerodynamic entrainment. Second, we compared the emitted dust concentration in sandblasting and aerodynamic entrainment under a range of wind friction velocities. Finally, we explored the sensitivity of emitted dust particle size distribution (PSD) to soil type and wind friction velocity in these two processes. The dust concentration in aerodynamic entrainment showed strong positive correlation, no significant correlation, and weak negative correlation, for the clay, silty clay loam, and clay loam, respectively, with the erodible soil surface roughness. The dust in aerodynamic entrainment was significant constituting up to 28.3, 41.4, and 146.4% compared to sandblasting for the clay, silty clay loam, and clay loam, respectively. PSD of emitted dust was sensitive to soil type in both sandblasting and aerodynamic entrainment. PSD was sensitive to the friction velocity in aerodynamic entrainment but not in sandblasting. Our results highlight the need to consider the details of sandblasting and direct aerodynamic entrainment processes in parameterizing dust emission in global/regional climate models.

A model for assessing water quality risk in catchments prone to wildfire

Summary Post-fire debris flows can have erosion rates up to three orders of magnitude higher than background rates. They are major sources of fine suspended sediment, which is critical to the safety of water supply from forested catchments. Fire can cover parts or all of these large catchments and burn severity is often heterogeneous. The probability of spatial and temporal overlap of fire disturbance and rainfall events, and the susceptibility of hillslopes to severe erosion determine the risk to water quality. Here we present a model to calculate recurrence intervals of high magnitude sediment delivery from runoff-generated debris flows to a reservoir in a large catchment (>100 km 2 ) accounting for heterogeneous burn conditions. Debris flow initiation was modelled with indicators of surface runoff and soil surface erodibility. Debris flow volume was calculated with an empirical model, and fine sediment delivery was calculated using simple, expert-based assumptions. In a Monte-Carlo simulation, wildfire was modelled with a fire spread model using historic data on weather and ignition probabilities for a forested catchment in central Victoria, Australia. Multiple high intensity storms covering the study catchment were simulated using Intensity–Frequency–Duration relationships, and the runoff indicator calculated with a runoff model for hillslopes. A sensitivity analysis showed that fine sediment is most sensitive to variables related to the texture of the source material, debris flow volume estimation, and the proportion of fine sediment transported to the reservoir. As a measure of indirect validation, denudation rates of 4.6–28.5 mm ka −1 were estimated and compared well to other studies in the region. From the results it was extrapolated that in the absence of fire management intervention the critical sediment concentrations in the studied reservoir could be exceeded in intervals of 18–124 years.