Erosion Rate Data Research Articles

Stochastic in Space and Time: 2. Effects of Simulating Orographic Gradients in Daily Runoff Variability on Bedrock River Incision

AbstractThe extent to which climate and tectonics can be coupled rests on the degree to which topography and erosion rates scales linearly. The stream power incision model (SPIM) is commonly used to interpret such relationships, but is limited in probing mechanisms. A promising modification to stream power models are stochastic‐threshold incision models (STIM) which incorporate both variability in discharge and a threshold to erosion. In this family of models, the form of the topography erosion rate relationship is largely controlled by runoff variability. Applications of STIM typically assume temporally variable, but spatially uniform and synchronous runoff generating events, an assumption that is likely broken in regions with complicated orography. To address this limitation, we develop a new 1D STIM model, which we refer to as spatial‐STIM. This modified version of STIM allows for stochasticity in both time and space and is driven by empirical relationships between topography and runoff statistics. Coupling between mean runoff and runoff variability via topography in spatial‐STIM generates highly nonlinear relationships between steady‐state topography and erosion rates. We find that whether the daily statistics of runoff are spatially linked or unlinked, which sets whether there is spatial synchronicity in the recurrence interval of runoff generating events, is a fundamental control on landscape evolution. Many empirical topography—erosion rate data sets are based on data that span across the endmember scenarios of linked versus unlinked behavior. It is thus questionable whether singular SPIM relationships fit to those data can be meaningfully related to their associated hydroclimatic conditions.

One Million Years of Climate-Driven Rock Uplift Rate Variation on the Wasatch Fault Revealed by Fluvial Topography

Displacement along the Wasatch Fault, Utah, has created the Wasatch Range. Owing to its topographic prominence, location on the eastern boundary of the Basin and Range, presently active fault slip, and proximity to Utah’s largest cities, the range and fault have garnered much attention. On the 102–103 year timescale, the behavior, displacement and seismic history of the Wasatch Fault has been well categorized in order to assess seismic hazard. On the 107 year timescale, the rock uplift rate history of the Wasatch range has also been resolved using thermochronometric data, owing to its importance in inferring the history of extension in the western US. However, little data exists that bridges the gap between these two timescales. Here, we infer an approximately 1 Ma rock uplift rate history from analysis of three river networks located in the center of the range. Our recovered rock uplift rate histories evidence periodic changes to rock uplift on the Wasatch Fault, that coincide with climate driven filling and unfilling of lakes in the Bonnneville Basin. To ensure our rock uplift rate histories are robust, we use field data and previously published cosmogenic 10Be erosion rate data to tightly constrain the erodibility parameter, and investigate an appropriate value for the slope exponent of the stream power model, n. We use our river network inversion to reconcile estimates of erodibility from a number of methodologies and show that the contrast between bedrock and bedload strength is an important factor that determines erodibility.

Quantifying drainage divide migration in active orogens: Insights from the eastern margin of the Tibetan Plateau

Landscape of active orogens results from a competition balance between tectonic rock uplift and erosion. Drainage divide migration is a useful approach for quantifying the landscape evolution and the underpinning drivers, because the fluvial networks adjust their geometry in response to spatiotemporal changes in rock uplift, climate and lithology. Many quantitative geomorphological metrics, such as χ-anomaly, Gilbert metrics, have been proposed to analyze the drainage divide migration. However, their interpretations often yield inconsistent results, especially in tectonically active orogens with spatial changes in rock uplift. The highly elevated and tectonically active eastern margin of the Tibetan Plateau has been studied by multiple methods of different time-scales, producing abundant structural and erosion rates determinations needed for evaluating the landscape stability and evolution. Here, we evaluated the effectiveness of χ- and Gilbert metrics in quantifying the stability of the Longmenshan-Minshan divide parallel with the plateau margin, by comparing with erosion rate data of different time scales, rock uplift predicted by upper crustal structures, bedrock lithology, precipitation. Our analyses reveal that the divide has reached dynamic steady state, as shown by the consistent cross-divide Gilbert metrics and consistent spatial changes of short, medium and long-term erosion rates, indicating the overall balance between the erosion and rock uplift. The spatial changes in rock uplift underpinned by reverse faulting along a listric upper crustal fault also explains the development of cross-divide χ-anomaly that cannot be used as an index for divide migration in regions with spatially nonuniform rock uplift. The formation of the long-term stable drainage divide in the EMTP serves as a natural laboratory for studying the divide formation and evolution in response to a phase of non-uniform rock uplift. We infer that in regions of this kind, drainage divide forms and evolves from uplift-driven to erosion-driven migration, via an intervening stable state.

Erosion rate maps highlight spatio-temporal patterns of uplift and quantify sediment export of the Northern Andes

Erosion rates are widely used to assess tectonic uplift and sediment export from mountain ranges. However, the scarcity of erosion rate measurements often hinders detailed tectonic interpretations. Here, we present 25 new cosmogenic nuclide-derived erosion rates from the Northern Andes of Colombia to study spatio-temporal patterns of uplift along the Central and Eastern Cordillera. Specifically, we combine new and published erosion rate data with precipitation-corrected normalized channel steepness measurements to construct high-resolution erosion rate maps. We find that erosion rates in the southern Central Cordillera are relatively uniform and average ∼0.3 mm/a. In the northern Central Cordillera rapidly eroding canyons dissect slowly eroding, low-relief surfaces uplifting since 8.3−2.6+3.7 Ma, based on a block uplift model. We interpret that persistent steep slab subduction has led to an erosional steady-state in the southern Central Cordillera, whereas in the northern Central Cordillera, Late Miocene slab flattening caused an acceleration in uplift, to which the landscape has not yet equilibrated. The Eastern Cordillera also displays pronounced erosional disequilibrium, with a slowly eroding central plateau rimmed by faster eroding western and eastern flanks. Our maps suggest Late Miocene topographic growth of the Eastern Cordillera, with deformation focused along the eastern flank, which is also supported by balanced cross-sections and thermochronologic data. Spatial gradients in predicted erosion rates along the eastern flank of the Eastern Cordillera suggest transient basin-ward migration of thrusts. Finally, sediment fluxes based on our erosion maps, suggest that the Eastern Cordillera exports nearly four times more sediment than the Central Cordillera. Our analysis shows that accounting for spatial variations in erosion parameters and climate reveals important variations in tectonic forcing that would otherwise be obscured in traditional river profile analyses. Moreover, given relationships between tectonic and topographic evolution, we hypothesize that spatio-temporal variations in slab dip are the primary driver of the dynamic landscape evolution of the Northern Andes, with potentially superposed effects from inherited Mesozoic rift structures.

Time-scaled study on the erosion in circulating fluidized bed based on CPFD method

In this paper, the erosion characteristics in a circulating fluidized bed (CFB) were investigated on time scale with Euler-Lagrange model based computational particle fluid dynamics (CPFD). By analyzing average erosion rate data, two different erosion characteristics were found. In addition to the common linear erosion caused by downflow particles, another type of erosion is characterized by step growth and is caused by upwelling particles. Linear erosion at the height of 0.1 m is close to that at 0.2 m from the air distributor, but the value of stepped erosion at 0.1 m is much greater than that at 0.2 m. The simulation results show that stepped erosion is the main cause of erosion in the simulated object, accounting for about 70% of the total erosion. The present numerical study implies that the special gas-solid flow of CFB will bring different characteristics of erosion, and the anti-wear method should be targeted at the causes of erosion.

Erosion Rate in Post-Coal Mining Reclamation Area in Kutai Kartanegara District, Indonesia

Erosion is the transport of parts of the soil from one place to another by natural agent, namely water, and wind. Mining in Indonesia generally uses open-pit mining methods. Generally, open pit mining has a very high erosion rate due to damage to soil aggregation and high interaction with rainwater. This study aims to determine the erosion rate and hazard class in the post-coal mining reclamation area. The research location was in the Jembayan Muarabara Group, Kutai Kartanegara Regency, East Kalimantan Province, from February 2021 to May 2021. The erosion rate measurement in this study used the stick method by measuring the erosion rate based on the change in soil surface loss in centimetres (cm) units. Erosion rate data collection is carried out periodically every month. The results showed that the highest erosion was in the Disposal area, namely 558.55 - 1341.94 tons/ha/year, including class V (very high), in the Stock Soil area with an erosion rate of 471.79 - 693.51 tons/ha/year including class IV (high) to class V (very high) and the lowest erosion rate in the reclamation area in 2019, namely 189.51 - 673.88 tons/ha/year including class IV (high) to class V (very high). Factors that affect the magnitude of the erosion rate are land cover vegetation, soil slope, and the soil's physical properties.

A method to determine the uncertainties of solid particle erosion measurements utilizing machine learning techniques

The ability to predict solid particle erosion is a vital task for the integrity management of pipelines carrying solid particles in many industries. Usually, the accuracy of predicted values is assessed by comparing them with the measured erosion of some cases where data is available. Thus, defining the uncertainties of the experimental data of erosion is crucial to evaluate the reliability of the predictions of solid particle erosion and consequently, the decisions made based on these predictions. The databases gathered by many investigators that include erosion data of various test cases have been considered for this uncertainty investigation. These cases include erosion rate data collected using the ultrasonic thickness measurement technique for gas-sand flows in 0.0508, 0.0762, and 0.1016-m elbow geometries with various particle sizes (75,150,300,550 μm) and air velocities vary in the range between 11 up to 202 m per seconds. This study aims to develop a framework for defining the uncertainties of erosion experiments. For this purpose, first, the uncertainties of repeated experiments were estimated and then analytical analysis was used to generalize these results to cases where repeated results were unavailable. Based on this idea, a correlation between erosion and the most effective parameters was developed. Then, machine learning algorithms were used to determine a correlation between the erosion rate and chosen parameters including material hardness, pipe size, particle size, and flow velocity. The framework of the current model/method is based on the combined results of analytical analysis and machine learning procedure, and the estimated uncertainties are presented by lower and upper bounds curves of erosion data.

How does climate affect the topography in tectonically active orogens

AbstractA central theme in geomorphology is the quantitative determination of the relationship between topography and its controlling factors, such as tectonics, lithology, and climate. However, rather than relief and slope, channel steepness (ksn) is a more effective metric for topography, and together with the abundance of beryllium‐10 (10Be) erosion rate data, it provides a more convenient means of quantitatively revealing the relationship between topography and its driving factors. A power‐law relationship between ksn and 10Be erosion rates has been widely demonstrated, which indicates the dominant control of tectonics on topography, while the dominant control of climate has not been clearly revealed. In this study we selected nine tectonically active regions, comprising 241 catchments, covering a wide range of mean annual precipitation values, and by extracting ksn values and hypsometric curves, we obtained the relationship between ksn and erosion rates. The results show that the power‐law relationship differs between regions, largely due to differences in the erosion coefficient, K. After separating the influences of lithology and climate, we found that although soft sedimentary rocks will increase the erosion coefficient, precipitation plays the main role in controlling the erosion coefficient, resulting in a linear relationship between precipitation and K. This relationship clearly demonstrates the occurrence of higher relief under a drier climate, even with similar rates of tectonic uplift.

Pre-agricultural soil erosion rates in the midwestern United States

Abstract Erosion degrades soils and undermines agricultural productivity. For agriculture to be sustainable, soil erosion rates must be low enough to maintain fertile soil. Hence, quantifying both pre-agricultural and agricultural erosion rates is vital for determining whether farming practices are sustainable. However, there have been few measurements of pre-agricultural erosion rates in major farming areas where soils form from Pleistocene deposits. We quantified pre-agricultural erosion rates in the midwestern United States, one of the world's most productive agricultural regions. We sampled soil profiles from 14 native prairies and used in situ–produced 10Be and geochemical mass balance to calculate physical erosion rates. The median pre-agricultural erosion rate of 0.04 mm yr–1 is orders of magnitude lower than agricultural values previously measured in adjacent fields, as is a site-averaged diffusion coefficient (0.005 m2 yr–1) calculated from erosion rate and topographic curvature data. The long-term erosion rates are also one to four orders of magnitude lower than the assumed 1 mm yr–1 soil loss tolerance value assigned to these locations by the U.S. Department of Agriculture. Hence, quantifying long-term erosion rates using cosmogenic nuclides provides a means for more robustly defining rates of tolerable erosion and for developing management guidelines that promote soil sustainability.

Across-strike asymmetry of the Andes orogen linked to the age and geometry of the Nazca plate

Abstract The crest of the Andes—the trace of the highest mountain topography—weaves back and forth, in places near the coastline, in others farther inland. Its position reflects the asymmetric distribution of orogen mass and coincides with asymmetry of orographic precipitation. This coincidence is thought to reflect a primary influence of orographic precipitation on accumulated orogenic mass whereby the more erosive (wetter) side promotes crest migration toward the less erosive (drier) side. However, whether this remains the case after excluding tectonic controls on the size and asymmetry of the wedge is an open question. We assessed relationships between precipitation, erosion rates, and the macromorphology of the Andes. We find that precipitation rates cannot sufficiently explain orogen asymmetry after statistically controlling for the age or dip of the Nazca slab. Slab age and dip are known to primarily affect mountain building in the Andes by impacting stress and strain propagation into the retro-arc region, thus better explaining the position of the mountain chain within the orogenic wedge. Accordingly, using basin-wide erosion rate, topographic, and precipitation data, we find that precipitation possibly influences erosional efficiency in semi-arid Andean landscapes but falls short in explaining the variability of erosion rates in regions of high orographic precipitation. We conclude that the orographic effect cannot change the Andean macromorphology that is set by bottom-up tectonic processes.

Demonstration of One Hundred Kilogram Xenon Throughput by a Low-Power Hall Thruster

The Hall thruster component of the Ascendant Sub-Kilowatt Transcelestial Electric Propulsion System (known ASTRAEUS) successfully demonstrated a propellant throughput of over 100 kg of xenon and demonstrated a total of of impulse in a long-duration wear test. The thruster was operated for a total of 7205 h, with the test broken into five segments each with a different discharge power between 200 and 1350 W: 3291 h at 300 V/1000 W, 1739 h at 500 V/1000 W, 416 h at 400 V/600 W, 388 h at 200 V/200 W, and 1371 h at 300 V/1350 W. Telemetry and temperature measurements periodically recorded throughout the test revealed constant performance across each test segment and over the full test duration. Each segment was sufficiently long to obtain erosion rate data on the thruster by an optical profilometer. Subnominal magnetic field strengths were inadvertently applied to the thruster during the first 5 khr of the test due to an electrical ground-support equipment issue, which caused a downstream shift of the discharge plasma and higher erosion of the thruster’s pole covers than originally expected. This issue was corrected for the latter three test segments; however, the thruster performance and operational behavior at all reference operating conditions remained unaffected. The long-duration wear test was voluntarily terminated after the thruster processed 100.3 kg of xenon (Xe). This marks the world’s first long-duration wear test of a low-power magnetically shielded Hall thruster with a center-mounted hollow cathode wherein over 100 kg Xe throughput was demonstrated.

Prediction of Erosion and Sedimentation in Micro Catchment Area of Air Lanang Using Soil and Water Assessment Tool (SWAT) Model

This research aims to obtain erosion and sedimentation rate data in the micro catchment area of Air Lanang using soil and water assessment tool (SWAT) modelling within existing and scenario land uses. Geographically, the study area is located between latitude 3°26`23.48” - 3°31`46.09” S and longitude 102°24`11.74” - 102°28`26.35” E with a total area of 2987.06 ha. Soil analysis was conducted in the Soil Science Laboratory, Faculty of Agriculture, University of Bengkulu. The research data was analysed using SWAT model. Recorded data in this study were including soil analysis data, soil type map from land unit and soil map book Bengkulu sheet (0912) Sumatra, data of status area from KLHK, Digital Elevation Model National data from BIG, a set of climate data from BMKG, data of administrative border from RBI map Bengkulu Province and data of land use from the interpretation of satellite image and ground checking, as well as the scenario land use which was prepared following the community forest program from the government in the protected forest by converting the coffee plantation located within the protected forest area to woody plants with economic, social and conservative values. The results showed total erosion in the micro catchment area of Air Lanang with the existing land use in 2020 was 820731.87 ton year-1, while in the scenario land use was 288212.45 ton/year which were classified to very light, light, moderate, heavy and very heavy in class erosion. Based on the existing land use data, there was a decrease of erosion in the moderate to very heavy class of erosion for 7.27 % resulting in the very light and light class of erosion become 15.55 % after the simulation of the scenario land use model. The use of scenario land use model is effective to decrease erosion and sedimentation rate. The total sedimentation in the micro catchment area of Air Lanang in existing land use in 2020 was 354949.98 ton year-1 with the highest sedimentation in sub-basin 2 while the lowest sedimentation was found in sub-basin 12. On the other hand, the total sedimentation in the scenario land use model was 137365.04 ton year-1. The reduction of total sedimentation in existing land use in 2020 to the scenario land use model was 36.76 %.

Combining a saltation impact sensor and a wind tunnel to explore wind erosion processes—A case study in the Zhundong mining area, Xinjiang, China

The properties of surface soil determine its erodibility, the wind force determines the soil erosion intensity, and both factors determine the amount of soil erosion. In the Zhundong mining area in Xinjiang, China, continuous mining and construction activities in the past 10 years have resulted in the destruction of surface crust formed by precipitation, the gradual refinement of soil, and an increase in erodibility. To accurately describe the impact of human construction on local wind erosion, we installed a saltation impact sensor in a wind tunnel to explore the soil responses to wind erosion and changes in the wind erosion rate caused by anthropogenic interference. We artificially manipulated the soil moisture, crust coverage, and particle size, and subjected the soils to different wind speeds. The results show that, first, in soil crust and moisture experiments, a sensor can effectively monitor the process and amount of wind erosion, but the monitoring efficiency of the sensor is greatly reduced after an overall change in soil particle size. Second, the wind erosion processes in the three test groups are roughly the same: the wind starts to drive the soil particles to move for the first 0 to 30 s. Then, the number of released soil particles increases rapidly with increasing wind speed from 30 to 240 s, gradually decreases after the wind speed stabilizes from 240 to 480 s, and then remains consistent after 480 s. Third, a uniform distribution of the crust rather than a concentrated distribution of the crust can reduce soil erosion by 20%. The presence of a crust can effectively prevent erosion in the early stage of wind erosion, and the more complete the surface crust on the soil, the better it can resist continuous wind erosion. Fourth, moisture in the soil effectively impedes erosion by increasing the wind speed required to move particles in the early stage; however, continuous erosion decreases the soil moisture, and the proportion of eroded soil gradually increases in the later stage. Fifth, the erosion rate data show that particle size change can result in a maximum wind erosion rate of 2,599 g m^–2 min^–1 and is the most influential factor for wind erosion.

Soil Erosion Susceptibility Mapping in Kozetopraghi Catchment, Iran: A Mixed Approach Using Rainfall Simulator and Data Mining Techniques

Soil erosion determines landforms, soil formation and distribution, soil fertility, and land degradation processes. In arid and semiarid ecosystems, soil erosion is a key process to understand, foresee, and prevent desertification. Addressing soil erosion throughout watersheds scales requires basic information to develop soil erosion control strategies and to reduce land degradation. To assess and remediate the non-sustainable soil erosion rates, restoration programs benefit from the knowledge of the spatial distribution of the soil losses to develop maps of soil erosion. This study presents Support Vector Machine (SVM), Random Forest (RF), and adaptive boosting (AdaBoost) data mining models to map soil erosion susceptibility in Kozetopraghi watershed, Iran. A soil erosion inventory map was prepared from field rainfall simulation experiments on 174 randomly selected points along the Kozetopraghi watershed. In previous studies, this map has been prepared using indirect methods such as the Universal Soil Loss Equation to assess soil erosion. Direct field measurements for mapping soil erosion susceptibility have so far not been carried out in our study site in the past. The soil erosion rate data generated by simulated rainfall in 1 m2 plots at rainfall rate of 40 mmh−1 was used to develop the soil erosion map. Of the available data, 70% and 30% were randomly classified to calibrate and validate the models, respectively. As a result, the RF model with the highest area under the curve (AUC) value in a receiver operating characteristics (ROC) curve (0.91), and the lowest mean square error (MSE) value (0.09), has the most concordance and spatial differentiation. Sensitivity analysis by Jackknife and IncNodePurity methods indicates that the slope angle is the most important factor within the soil erosion susceptibility map. The RF susceptibility map showed that the areas located in the center and near the watershed outlet have the most susceptibility to soil erosion. This information can be used to support the development of sustainable restoration plans with more accuracy. Our methodology has been evaluated and can be also applied in other regions.

Erosion behaviour of boiler component materials at room temperature and 400 °C temperature

Degradation of boiler tube components in Indian thermal power plants is mainly done through solid particle erosion due to exposure in erosive ash environment. Some important parameter such as hardness, erodent velocity, temperature, impact angle, shape and size are majorly affected the erosion wear. In this study, the erosion wear behaviour of SAE 208 grade steel, SAE213-T12 boiler steel, SAE213-T91 boiler steel and IS 2062 structural steel were investigated using an air jet erosion test rig. The erosion tests were carried out at the impact angles of 30° and 90°, impact velocity of 42.3 m/s at room temperature and 400 °C. The position of sample holder was adjusted in such a way that erosion wear scar occur at the central region of the samples. For each experiment, the erosion test was continued until the steady state erosion rate was achieved as per ASTM standard. The variation in erosion rate data has been plotted against cumulative mass of erodent for boiler and structural steel samples. The steady state erosion rates for different steel samples are calculated and compared. The surfaces of tested samples are analyzed using scanning electron microscopy to understand the erosion mechanism. The results showed that the ductile behaviour of erosion mechanism is dominated at both room temperature and 400 °C temperature. Mechanism involved at 90° impact angle is plastic deformation with formation of craters and at 30° impact angle is cutting and ploughing.

Global evaluation of erosion rates in relation to tectonics

Understanding the mechanisms and controlling factors of erosion rates is essential in order to sufficiently comprehend bigger processes such as landscape evolution. For decades, scientists have been researching erosion rates where one of the main objectives was to find the controlling factors. A variety of parameters have been suggested ranging from climate-related, basin morphometry and the tectonic setting of an area. This study focuses on the latter. We use previously published erosion rate data obtained mainly using 10Be and sediment yield and sediment yield data published by the United States Geological Survey. We correlate these data to tectonic-related factors, i.e., distance to tectonic plate boundary, peak ground acceleration (PGA), and fault distribution. We also examine the relationship between erosion rate and mean basin slope and find significant correlations of erosion rates with distance to tectonic plate boundary, PGA, and slope. The data are binned into high, medium, and low values of each of these parameters and grouped in all combinations. We find that groups with a combination of high PGA (> 0.2.86 g) and long distance (> 1118.69 km) or low PGA (< 0.68 g) and short distance (< 94.34 km) are almost inexistent suggesting a strong coupling between PGA and distance to tectonic plate boundary. Groups with low erosion rates include long distance and/or low PGA, and groups with high erosion rates include neither of these. These observations indicate that tectonics plays a major role in determining erosion rates, which is partly ascribable to steeper slopes produced by active crustal movements. However, our results show relatively unclear correlation of slope with erosion rates, pointing to problems with using mean basin-wide slope as a slope indicator because it does not represent the complex slope distribution within a basin.

Mass-Transfer Model for Steel, Slag, and Inclusions during Ladle-Furnace Refining

AbstractPrecise control of inclusion and molten steel compositions during ladle-furnace refining is important to obtain high-quality steel. Mass-transfer behavior affects these compositions. A model was developed to investigate the mass transfer occurring between molten steel, slag, inclusions, and the refractory during ladle-furnace refining, using two-film theory to describe the reactions. A coupled-reaction model based on the CaO–Al2O3–MgO–SiO2–FeO–P2O5 slag and Mn–Si–Al–Ca–Mg–P–S–O steel systems was applied to describe the reactions between molten steel and slag; the reactions between the refractory lining and slag or steel were described using average industrial erosion rate data. The model was used to calculate changes in the compositions of molten steel and slag, oxygen activity at the slag–molten steel interface, and composition of the inclusions. The calculated results agreed with operational results for a 100 t ladle furnace at the Tangsteel plant in China.

Comparing Sediment Trap Data with Erosion Models for Evaluation of Forest Haul Road Stream Crossing Approaches

Abstract. Soil erosion and sediment delivery models have been developed to estimate the inherent complexities of soil erosion, but most models are not specifically modified for forest operation applications. Three erosion models, the Universal Soil Loss Equation for forestry (USLE-Forest), Revised Universal Soil Loss Equation Version 2 (RUSLE2), and Water Erosion Prediction Project (WEPP), were compared to one year of trapped sediment data for 37 forest haul road stream crossings. We assessed model performance from five variations of the three erosion models: USLE-Roadway, USLE-Soil Survey, RUSLE2, WEPP-Default, and WEPP-Modified. Each road approach was categorized into one of four levels of erosion (very low, low, moderate, and high) based on trapped erosion rate data and erosion rates reported in recent peer-reviewed literature. Model performance metrics included: (1) summary statistics and nonparametric analysis, (2) linear relationships, (3) percent agreement within erosion categories and tolerable error ranges, and (4) contingency table metrics. Sediment trap data varied from negligible ( -1 year -1 . The soil erosion models evaluated could estimate erosion within 5 Mg ha -1 year -1 for most approaches having erosion rates less than 11.2 Mg ha -1 year -1 , while models estimates varied widely for approaches that eroded at rates above 11.2 Mg ha -1 year -1 . Kruskal-Wallis nonparametric analyses revealed that only WEPP-Modified estimates were not significantly different from trapped sediment data (p ≥ 0.107). While WEPP-Modified ranked best for most model performance metrics, the time, effort, modeling expertise, and uncertainty associated with model results may discourage the use of WEPP as a forest management tool. WEPP is better suited for researchers and government agencies that have the capability to measure extensive parameter data. Additional sensitivity analysis is needed to expand default parameters for forest roads within the WEPP and USLE models.

A nondimensional framework for exploring the relief structure of landscapes

Abstract. Considering the relationship between erosion rate and the relief structure of a landscape within a nondimensional framework facilitates the comparison of landscapes undergoing forcing at a range of scales, and allows broad-scale patterns of landscape evolution to be observed. We present software which automates the extraction and processing of relevant topographic parameters to rapidly generate nondimensional erosion rate and relief data for any landscape where high-resolution topographic data are available. Individual hillslopes are identified using a connected-components technique which allows spatial averaging to be performed over geomorphologically meaningful spatial units, without the need for manual identification of hillslopes. The software is evaluated on four landscapes across the continental United States, three of which have been studied previously using this technique. We show that it is possible to identify whether landscapes are in topographic steady state. In locations such as Cascade Ridge, CA, a clear signal of an erosional gradient can be observed. In the southern Appalachians, nondimensional erosion rate and relief data are interpreted as evidence for a landscape decaying following uplift during the Miocene. An analysis of the sensitivity of this method to free parameters used in the data smoothing routines is presented which allows users to make an informed choice of parameters when interrogating new topographic data using this method. A method to constrain the critical gradient of the nonlinear sediment flux law is also presented which provides an independent constraint on this parameter for three of the four study landscapes.

Variability of rock erodibility in bedrock‐floored stream channels based on abrasion mill experiments

AbstractWe quantify variations in rock erodibility, Kr, within channel cross sections using laboratory abrasion mill experiments on bedrock surfaces extracted from streams with sandstone bedrock in Utah and basaltic bedrock in the Hawaiian Islands. Samples were taken from the thalweg and channel margins, the latter at a height that is inundated annually. For each sample, a sequence of abrasion mill experiments was completed to quantify variations in erosion rate with erosion depth. Erosion rate data from these experiments shows two things. First, the erosion rate from channel margin samples is greater than for thalweg samples, with the greatest difference observed for the rock surface that was exposed in the stream channel. Second, erosion rate decreases with depth beneath the original rock surface, by an order of magnitude in most cases. The erosion rate becomes steady at depths of 1–3 mm for channel margin samples and 0.1–0.4 mm for thalweg samples. Because only rock properties and microtopography vary throughout the sequence of mill experiments, these results suggest that Kr of the bedrock surface exposed in stream channels is higher at the margins than near the channel center and that Kr decreases over depths of ~1 mm. The simplest explanation for these patterns is that Kr is enhanced, at the bedrock surface and along the channel margins, due to the effects of weathering on rock strength and surface roughness. We hypothesize that a balance exists between weathering‐enhanced erodibility and episodic incision to allow channel margins to lower at rates similar to the thalweg.