Erosive Power Research Articles

Susceptibilidade a erosão na bacia hidrográfica do córrego Guariroba, Campo Grande, Mato Grosso do Sul

A captação de água para o abastecimento humano na cidade de Campo Grande é feita em mananciais superficiais e aquíferos, dos quais o reservatório Guariroba é a principal fonte superficial. O objetivo deste estudo foi avaliar a susceptibilidade a erosão e o uso e cobertura da terra na bacia hidrográfica do Córrego do Guariroba, a fim de subsidiar a gestão ambiental. Atributos topográficos extraídos de um modelo digital de elevação obtido por fotogrametria foram utilizados para avaliar a susceptibilidade a erosão. O índice de vegetação por diferença normalizada (NDVI), obtida de imagens Sentinel 2B, foi usado para a análise do uso e cobertura da terra. Os atributos topográficos mostraram os locais mais susceptíveis ao desenvolvimento dos processos erosivos, que, encontram-se ao longo dos cursos d'água, nas cabeceiras de drenagem e em vertentes côncavas convergentes. Nesses locais os fluxos superficiais têm maior energia, consequentemente, o poder erosivo é maior, aumentando a susceptibilidade a perda de sedimento e poluentes adsorvidos. A vegetação natural remanescente encontra-se ao longo dos cursos d’água e em pequenos fragmentos. Plantios de eucalipto avançam em áreas de pastagens formando mosaicos na paisagem. Os mapas gerados podem ser utilizados pelos gestores na identificação das áreas prioritárias para recuperação ambiental.

Temporal and spatial variation of soil erosion in wooded rangelands of southwest Spain

AbstractChanges in land use are common in Mediterranean areas and are reported as having produced changes in the intensity of soil erosion. Dehesas are rangelands with a disperse tree cover, widespread in the south‐western part of the Iberian Peninsula and similar ecosystems are also common in other areas with a Mediterranean climate. The aim of the present study is to analyse temporal and spatial variations of soil erosion rates estimated along three hillsides, located in two farms (Buitrera and Parapuños) in southwest Spain. To understand the temporal variation, soil erosion rates were studied in light of land use‐management changes that took place during the last few centuries. Results indicate very low erosion rates prior to the 18th century in both farms. In Buitrera, a first increase of soil loss rates was identified during the period 1831‐1897, amounting to 7.4 t ha‐1 y‐1. A further increase took place during the 20th century, reaching a mean erosion rate of 29.1 t ha‐1 y‐1. In Parapuños, data points to a significant increase from 1881 onwards, with an estimated mean erosion rate of 18.5 t ha‐1 y‐1. Those increases were presumably connected with an intensification of land use, such as cultivation and excessive livestock populations. Regarding spatial variation, the bare surface and the erosive power of run‐off along the hillsides accounts for 76% of the soil erosion rates dispersion. At a local scale, the variability of erosion rates could not be explained, because of (i) uncertainty related to the micromorphology of the past soil surface and (ii) the role of tillage erosion in the past. However, the results obtained offer valuable data on the temporal and spatial variation of erosion rates in dehesas at the hillslope scale and a similar approach could be used for other rangelands with a disperse tree cover. © 2019 John Wiley & Sons, Ltd.

Stratigraphic architecture and hierarchy of fluvial overbank splay deposits

Splay deposits represent an important sand-prone component of the otherwise fine-grained stratigraphic record of fluvial overbank systems. This work presents a hierarchical approach to the classification and palaeoenvironmental interpretation of ancient preserved splay deposits supported by the analysis of the stratigraphic architecture of 11 exhumed examples from the Jurassic Morrison Formation and the Cretaceous Mesaverde Group (western USA) and analysis of the morphology of splays from nine modern fluvial systems. A hierarchical arrangement of splay deposits is proposed, categorized into lithofacies, beds, elements and complexes. Recognition criteria for each tier of the hierarchy include identification of bounding surfaces, thinning and fining trends of splay elements and complexes, and palaeocurrent variability. Progradational and compensational stacking trends control the stratal architecture of splay deposits, and these are influenced by the following factors: (1) the rate of local accommodation generation, which influences the erosive power of floodwaters and whether splay elements are laterally offset owing to compensational stacking; (2) the nature of the topographic confinement of the floodplain; (3) the preservation potential linked to migration direction of channel. Splay bodies can contribute volume to fluvial reservoirs and may form significant connectors that link otherwise isolated primary channel bodies, thereby enhancing reservoir connectivity. Supplementary material: Thickness and facies types with global positioning system (GPS) coordinates, length and width v. thickness, and modern data and coordinates are available at https://doi.org/10.6084/m9.figshare.c.4461026

Competing Effects of Mountain Uplift and Landslide Erosion Over Earthquake Cycles

AbstractLarge earthquakes can construct mountainous topography by inducing rock uplift but also erode mountains by causing landslides. Observations following the 2008 Wenchuan earthquake show that landslide volumes in some cases match seismically induced uplift, raising questions about how the actions of individual earthquakes accumulate to build topography. Here we model the two‐dimensional surface displacement field generated over a full earthquake cycle accounting for coseismic deformation, postseismic relaxation, landslide erosion, and erosion‐induced isostatic compensation. We explore the related volume balance across different seismotectonic and topographic conditions and revisit the Wenchuan case in this context. The ratio (Ω) between landslide erosion and uplift is most sensitive to parameters determining landslide volumes (particularly earthquake magnitudeMw, seismic energy source depth, and failure susceptibility, as well as the seismological factor responsible for triggering landslides), and is moderately sensitive to the effective elastic thickness of lithosphere,Te. For a specified magnitude, more erosive events (higher Ω) tend to occur at shallower depth, in thicker‐Telithosphere, and in steeper, more landslide‐prone landscapes. For given landscape and seismotectonic conditions, the volumes of both landslides and uplift to first order positively scale withMwand seismic momentMo. However, higherMwearthquakes generate lower landslide and uplift volumes per unitMo, suggesting lower efficiency in the use of seismic energy to drive topographic change. With our model, we calculate the long‐term average seismic volume balance for the eastern Tibetan region and find that the net topographic effect of earthquakes in this region tends to be constructive rather than erosive. Overall, destructive events are rare when considering processes over the full earthquake cycle, although they are more likely if only considering the coseismic volume budget (as was the case for the 2008 Wenchuan earthquake where landsliding substantially offset coseismic uplift). Irrespective of the net budget, our results suggest that the erosive power of earthquakes plays an important role in mountain belt evolution, including by influencing structures and spatial patterns of deformation, for example affecting the wavelength of topography.

Evaluation of Cavitation Erosion Intensity in a Microscale Nozzle Using Eulerian–Lagrangian Bubble Dynamic Simulation

In the present study, cavitation erosion is investigated by implementing an Eulerian–Lagrangian approach. Three-dimensional two-phase flow is simulated in a microscale nozzle using Reynolds-averaged Navier–Stokes (RANS) solver along with realizable k−ε turbulence model and Schnerr–Sauer cavitation model. The numerical results are in agreement with experimental observations. A modified form of Rayleigh–Plesset–Keller–Herring equation along with bubble motion equation is utilized to simulate bubble dynamics. Average values of mixture properties over bubble surface are used instead of bubble-center values in order to account for nonuniformities around the bubble. A one-way coupling method is used between Lagrangian analysis and RANS solution. The impact pressure resulted from bubble collapse is calculated for evaluation of erosion in diesel and soy methyl ester (SME) biodiesel in different situations. The results show that the initial size of the bubbles is an important factor for determining the intensity of erosion. So, the bubbles erosive power increases when their initial radius increases. It is also found that the intensity of erosion in diesel is much higher than that of biodiesel and this is because of the differences in fuels properties, especially in viscosity and vapor pressure. The effect of bubbles initial position on erosion intensity is also investigated in this study, and it is found that bubbles with the highest distance from sheet cavity termination have the highest contribution in erosion rate.

Collapse and failure of ancient agricultural stone terraces: On-site geomorphic processes, pedogenic mechanisms, and soil quality

Water is the major limiting factor for primary productivity in drylands. In ancient times, stone terraces aimed at runoff harvesting and soil erosion control were established, allowing agricultural crop production. Land abandonment and cease of maintenance have led to the collapse and failure of terraces in the hinterlands of the Roman/Byzantine city of Avdat in the arid Negev Desert, Israel. The objective of this study was to assess the geomorphic processes and pedogenic mechanisms related to terrace collapse, and their on-site impact on soil quality. We studied key properties of the top 10 cm of soil in intact-terrace plots and partially-collapsed terrace plots, as well as in ‘natural’ lands. Unexpectedly, the soil texture was finer in the partially collapsed-terrace plots (clay loam) than that in the intact-terrace plots (loam). This was attributed to transportation of mineral material by rolling, which sorts out the large primary particles. This process, which characterizes rill erosion of high erosive power, is probably the predominant surface process in this study. The soil penetration resistance was significantly greater in the partially-collapsed terrace plots, and was attributed to the continuous removal of recently deposited loose sediments and exposure of the underlying, compacted older sediments. Soil stoniness, which was 16-fold greater in the partially-collapsed terrace plots, was also attributed to soil erosion. Unexpectedly, the total organic carbon was similar in both terrace states. Yet, labile organic carbon was 41% lower in soil of the partially-collapsed terrace plots, suggesting greater susceptibility of this fraction to erosional processes. The low electrical conductivity in the soil of the intact-terrace plots, was attributed to the better leaching of salts. The soil's calculated available water capacity was 42% greater in the intact-terrace plots. The study suggests that these processes and mechanisms strengthen each other through a chain of feedbacks, resulting in accelerated degradation of the collapsed-terrace lands.

Drainage Characteristics of Tectonically Active Area: An Example from Mawar Basin, Jammu and Kashmir, India

Abstract Geomorphic and neo tectonic studies have been carried out for the first time in Mawar basin of the Kashmir valley. On the basis of field investigations and geomorphic data derived from toposheets and satellite imageries, with the help of Arc GIS (10.3) and Global Mapper (18) the relationship between morphology and tectonics has been investigated in Mawar basin, which lies to the northwest of Kashmir valley. The morphotectonic aspects like mountain front sinuosity (Smf), hypsometric integral (Hi), have been studied to relate the tectonic forces with erosive power and identify the areas where field investigations are required. The field interpretation indicates that the landforms of the area are structurally controlled and mainly consist of tectonic linear, parallel striking ridges and valleys. The course of Mawar is mostly controlled by the Mawar fault striking east–west and local structures present in the area. General morphometric parameters like assymetry factor (Af), transverse topography symmetry (T), stream length gradient (SL) and valley floor width to height ratio (Vf) have been computed to draw the conclusion of tectonic activity on the drainage. The Af and T suggest that the basin has shifted to the right side and the Mawar river has shifted to the left side when facing downstream. The SL values indicate that the river has fluctuations in gradient/knickpoints at 6.8, 10 and 18 km from the source. However the Vf values infer the basin has deeply incised V-shaped valleys. All the quantified geomorphic indices and their interrelationship with the geomorphology are useful in comparing different drainage basins in terms of tectonic character and are helpful in delineating the areas where more detailed works will be fruitful. The results of computed geomorphic indices, geomorphology and the structures present in the Karewas (Plio Pleistocene) deposits inferred that the basin has shown activity in Pleistocene period, suggesting the basin is tectonically active.

Numerical simulation of the cavitation micro–jet velocity and erosion on a plane–convex hydrofoil with semicylindrical obstacle

The present study deals with the numerical study of the cavitation micro–jet velocity and erosion on a plane–convex hydrofoil with semicylindrical obstacle, which induces a big cluster of cavities with a strong erosive power. The proposed model predicts micro-jet velocities based on energy conservation by assuming potential and kinetic energies at the start and the end of the cavity collapses. Homogeneous mixture flow, implicit LES and Zwart-Gerber-Belamri cavitation model have been used for the numerical simulation of the unsteady cavitating flow using OpenFOAM, whilst for the micro-jet estimation, Python language coupled with OpenFOAM’s calculator have been used. Results clearly show that the implemented model captures adequately the phenomenon and enables to identify attacked areas. Outcomes agree reasonably with the experimental results obtained by Escaler at the High Speed Cavitation Tunnel of the École Polytechnique Fédérale de Lausanne (EPFL). Furthermore, the proposed model has been compared with Li’s and Peters’ ones for a better understating of the improvements.

Spatial Variabilities of Runoff Erosion and Different Underlying Surfaces in the Xihe River Basin

Runoff erosion capacity has significant effects on the spatial distribution of soil erosion and soil losses. But few studies have been conducted to evaluate these effects in the Loess Plateau. In this study, an adjusted SWAT model was used to simulate the hydrological process of the Xihe River basin from 1993 to 2012. The spatial variabilities between runoff erosion capacity and underlying surface factors were analyzed by combining spatial gradient analysis and GWR (Geographically Weighted Regression) analysis. The results show that the spatial distribution of runoff erosion capacity in the studying area has the following characteristics: strong in the north, weak in the south, strong in the west, and weak in the east. Topographic factors are the dominant factors of runoff erosion in the upper reaches of the basin. Runoff erosion capacity becomes stronger with the increase of altitude and gradient. In the middle reaches area, the land with low vegetation coverage, as well as arable land, show strong runoff erosion ability. In the downstream areas, the runoff erosion capacity is weak because of better underlying surface conditions. Compared with topographic and vegetation factors, soil factors have less impact on runoff erosion. The red clay and mountain soil in this region have stronger runoff erosion capacities compared with other types of soils, with average runoff modulus of 1.79 × 10−3 m3/s·km2 and 1.68 × 10−3 m3/s·km2, respectively, and runoff erosion power of 0.48 × 10−4 m4/s·km2 and 0.34 × 10−4 m4/s·km2, respectively. The runoff erosion capacity of the alluvial soil is weak, with an average runoff modulus of 0.96 × 10−3 m3/s·km2 and average erosion power of 0.198 × 10−4 m4/s·km2. This study illustrates the spatial distribution characteristics and influencing factors of hydraulic erosion in the Xihe River Basin from the perspective of energy. It contributes to the purposeful utilization of water and soil resources in the Xihe River Basin and provides a theoretical support for controlling the soil erosion in the Hilly-gully region of the Loess Plateau.

Critical runoff depth estimation for incipient motion of non-cohesive sediment on loose soil slope under heavy rainfall

Incipient motion of non-cohesive sediment, as a branch of water erosion, has been studied for decades, and criteria proposed in predicting incipient motion mainly focus on dimensionless shear stress and shear velocity. The two parameters could provide runoff erosive power, however, are invisible and not easy-measured in experiment. In this paper, critical runoff depth was recognized as another parameter, which is visible, measurable, and closely connected with shear velocity. To get it, a mathematical model coupling surface flow and subsurface flow was established, and they are governed by Navier‒Stokes equation and Brinkman‒extended Darcy equation, respectively. Velocity derived from the model could be indirectly applied in particle force analysis and finally a new criterion about critical runoff depth was obtained. Accuracy of the criterion was verified by comparison of experimental and theoretical values, e.g. theoretical critical runoff depth ranges from 2.71 ∼ 1.14 mm with a slope angle range of 20 ∼ 28° and mean particle diameter of 2.5 mm while the corresponding experiment values ranges from 3 ∼ 1 mm and the absolute errors are less than 0.3 mm. Compared with Yang’s formula, this criterion could also be applied in predicting incipient motion of non-cohesive sediment for its significant advantages of high accuracy and concise formulation.

Sedimentology and the facies architecture of the Ghaggar‐Hakra Formation, Barmer Basin, India: Implications for early Cretaceous deposition on the north‐western Indian Plate margin

AbstractFluvial strata of the Lower Cretaceous Ghaggar‐Hakra Formation are exposed in fault blocks on the central‐eastern margin of the Barmer Basin, Rajasthan. The sedimentology of these outcrops are described from 114 logs (thicknesses up to 100 m) and 53 two‐dimensional correlation panels. The formation comprises three distinct channel belt sandstone packages defined as the Darjaniyon‐ki Dhani, Sarnoo and Nosar sandstones separated by thick siltstone‐dominated floodplain successions. The sediments were deposited in a sub‐tropical, low sinuosity fluvial system that matures into a highly sinuous fluvial system. The Nosar Sandstone, the youngest of the three packages, exhibits a significant increase in energy and erosive power compared to those underlying it. This distinct change in fluvial style is interpreted as being rejuvenation due to an actively developing rift network forming accommodation space, rather than climatic controls acting on part of the depositional system. Consequently, the Ghaggar‐Hakra Formation at outcrop represents Lower Cretaceous syn‐rift deposition within the Barmer Basin with active localized fault movement from Nosar Sandstone times onward. These findings provide sedimentological evidence in support of pre‐Palaeogene northwest–southeast extension in the Barmer Basin. Moreover, they imply Cretaceous extension took place widely along the northern extremity of the West Indian Rift System consistent with plate tectonic models of the break‐up of Gondwana and evolution of the Indian Ocean. Outcrops of Lower Cretaceous strata are patchy across India and Pakistan. This study provides valuable material which, when combined with the available published data, facilitates a re‐evaluation of Lower Cretaceous palaeogeography for the north‐west Indian Plate. The reconstruction demonstrates a complex fluvial system, where the sediments are preserved sporadically as early syn‐rift strata. The findings imply a high preservation potential for early Cretaceous fluvial successions within rifted fault blocks near Saraswati and Aishwarya of the Barmer Basin beneath the Palaeogene fill that likely have significant potential for further hydrocarbon exploration.

Identifying the driving factors of sediment delivery ratio on individual flood events in a long-term monitoring headwater basin

The Sediment Delivery Ratio (SDR) has multi-fold environmental implications both in evaluating the soil and water losses and the effectiveness of conservation measures in watersheds. Various factors, including hydrological regime and watershed properties, may influence the SDR at interannual timescales. However, the effect of certain important dynamic factors, such as rainfall peak distribution, runoff erosion power and sediment bulk density, on the sediment delivery ratio of single flood events (SDRe) has received little attention. The Qiaogou headwater basin is in the hilly-gully region of the Chinese Loess Plateau, and it encompasses a 0.45 km2 catchment. Three large-scale field runoff plots at different geomorphological positions were chosen to obtain the observation data, and the 20-year period between 1986 and 2005 is presented. The results showed that the SDRe of the Qiaogou headwaters varied from 0.49 to 2.77. Among the numerous influential factors, rainfall and runoff were the driving factors causing slope erosion and sediment transport. The rainfall erosivity had a significant positive relationship with the sediment transport modulus (R2=0.85, P<0.01) but had no significant relationship with SDRe. The rainfall peak coefficient was significantly positively correlated with the SDRe (R2=0.64, P<0.05), indicating the influence of rainfall energy distribution on the SDRe. The runoff erosion power index was not only significantly related to the sediment transport modulus (R2=0.84, P<0.01) but also significantly related to the SDRe (R2=0.57, P<0.01). In addition, the relative bulk density was significantly related to the SDRe, indicating that hyper-concentrated flow characteristics contributed to more transported sediment in the catchment. Thus, the rainfall peak coefficient, runoff erosion power and sediment relative bulk density could be used as dynamic indexes to predict the SDRe in the hilly areas of the Chinese Loess Plateau.

Dual wave farms and coastline dynamics: The role of inter-device spacing

In dual wave farms, i.e., arrays of wave energy converters (WECs) with a dual function – generation of renewable power and mitigation of coastal erosion – the spacing between the WECs is a fundamental design parameter. The present research has the objective of establishing how this parameter affects the shoreline evolution behind the array and, on this basis, to propose and apply a method to determine the optimum spacing for coastal protection. The method is demonstrated on a beach subjected to severe erosion. Five case studies are considered: four with different inter-WEC spacings, and one without the wave farm (baseline). A spectral wave propagation model is applied to analyse the variations in significant wave height behind the WEC array. Longshore sediment transport rates are calculated, and a shoreline model is applied. We find that in all the case studies the dry beach area is greater than in the baseline (no farm) case study, which proves the capacity of the dual WEC array to mitigate the erosive trends of the system. Importantly, we obtain that the inter-WEC spacing plays a fundamental role in the evolution of the shoreline and, consequently, in the effectiveness of the WEC array for coastal protection. The case studies with intermediate spacings yield the best performance in terms of dry beach area. More generally, the benefits of dual wave farms in terms of protection of coastal properties and infrastructure, and the ensuing savings in conventional coastal defence measures (coastal structures, beach nourishment, etc.) contribute to the development of wave energy by enhancing its economic viability. The methodology presented in this paper can be used to optimize the design of dual wave farms elsewhere.

Rainfall extremes modeling under shortage of data and uncertainty in the Pampean region (Argentina)

The assessment of the surface runoff capacity of storms is essential for the design of drainage infrastructure, for the management of rainfall excesses and the control of soil erosion. The knowledge of precipitation intensity values at scales larger than the daily is a key in this process. However, the available information in the region is reduced, due to the lack of instruments and historical data. An alternative to solve this problem consists of the search of mathematical relations for the scale change from daily values, more common and available, to sub-hourly values, necessary for the estimation of runoff volumes in small basins as well as erosive power of rainfall. The first results obtained in the experimentation and search of mathematical relations for the change of temporal scale for values of intensity of precipitation, valid for a wide territory with clear climatic and ecological variability are presented in this paper. The main objective of this work was to investigate the property of scale invariance in rainfall intensity and its application to the construction of IDF curves by simple scaling. The regionalization of the values obtained in the areas of study was established as a complementary objective. The hypothesis of the scale invariance and the possibility of applying simple scaling to precipitation intensity values have been verified using both pluviographic and pluviometric data recorded over the Argentina's Pampean region in climatically and ecologically different localities. The present work provides the criteria and reference values for the construction and updating of the IDF curves in the region, where they are highly necessary, leading to advances in hydrology in areas with little or no rainfall information. The results provide new evidence on scaling relations in hydrological variables, which are useful for application in cases where reference information is scarce. This contributes to the knowledge of local precipitation characteristics and provides reference values to be used in practical applications.

Reframing community boundaries: the erosive power of new media spaces in authoritarian societies

ABSTRACTThis study examines the role of digital media within the Ultra-Orthodox Jewish community in Israel, a conservative closed community, whose leadership is unable or unwilling to control the effects of digital media on the rank-and-file. Over the past decade, digital media have played an important role for challenging authoritarian rule around the globe. Especially in ideological communities sustained by strict taboos, digital media hold the potential to subvert hegemonic discourses. In this study, we make use of an incident that forced Israel’s Ultra-Orthodox community to address its long-standing taboo and hateful attitudes toward LGBT and Queer issues. In July 2015, an Ultra-Orthodox community member attacked participants of the Jerusalem Gay Pride Parade, murdering one and wounding six. While traditional community media attempted to ignore the event, two major Ultra-Orthodox news websites fell outside the control exercised by the community leadership, and enabled subversive discussions within the Ultra-Orthodox community. Through a process of negotiating the meaning of the attack, these discussions resulted in a reframing of the boundaries of the community, breaking a path for further contestation and debate. Using grounded theory analysis, this article contributes to a better understanding of the role of digital media in enabling contestation and challenging established power structures within authoritarian closed communities.

Rill erosion processes on a steep colluvial deposit slope under heavy rainfall in flume experiments with artificial rain

Understanding rill erosion processes is important in the prediction of soil erosion and the prevention of soil loss. However, limited information is available concerning the impacts of rainfall on rill erosion on steep slopes. Colluvial deposits with steep slopes make up the packed material underlying the collapsing walls in benggang, which collapse due to hydraulic pressure and gravity. They contain loose materials and large amounts of coarse particles. The objectives of this study were to investigate the impacts of rainfall intensity and slope gradient on the rill erosion process, rill development and rill flow dynamic mechanisms on the steep slopes of colluvial deposits. The colluvial soils were subjected to simulated rainfall in a 5-m2 (5-m by 1-m) flume at heavy rainfall intensities (100, 120, and 140 mm h−1) and on five steep slopes (20, 25, 30, 35, and 40°). Rill erosion contributed significantly to colluvial slope erosion; on average, rills accounted for 61% of the soil loss, and the effects of slope gradient were greater than those of the rainfall intensity. After rill development, rill density, rill length, width, and depth all significantly increased. Correspondingly, the soil loss rate sharply raised and irregularly fluctuated. Moreover, the collapse of rill heads or sidewalls tended to increase the relative contribution to rill erosion and rill development. The rill flow was characterized by transitional and subcritical flow regimes. The rill flow velocity was the most sensitive hydraulic parameter, and the unit stream power provided the optimal hydrodynamic parameter to characterize the dynamic mechanisms of rill erosion on colluvial deposits. The collapse of rill heads or sidewalls could result in negative values for critical shear stress, critical stream power, and critical unit stream power of rill erosion, which were −19 Pa, −5.3 N m−1 s−1, and −0.09 m s−1, respectively. These results provide a better understanding of the mechanism of rill erosion on steep slopes.

Seismic signature of turbulence during the 2017 Oroville Dam spillway erosion crisis

Abstract. Knowing the location of large-scale turbulent eddies during catastrophic flooding events improves predictions of erosive scour. The erosion damage to the Oroville Dam flood control spillway in early 2017 is an example of the erosive power of turbulent flow. During this event, a defect in the simple concrete channel quickly eroded into a 47 m deep chasm. Erosion by turbulent flow is difficult to evaluate in real time, but near-channel seismic monitoring provides a tool to evaluate flow dynamics from a safe distance. Previous studies have had limited ability to identify source location or the type of surface wave (i.e., Love or Rayleigh wave) excited by different river processes. Here we use a single three-component seismometer method (frequency-dependent polarization analysis) to characterize the dominant seismic source location and seismic surface waves produced by the Oroville Dam flood control spillway, using the abrupt change in spillway geometry as a natural experiment. We find that the scaling exponent between seismic power and release discharge is greater following damage to the spillway, suggesting additional sources of turbulent energy dissipation excite more seismic energy. The mean azimuth in the 5–10 Hz frequency band was used to resolve the location of spillway damage. Observed polarization attributes deviate from those expected for a Rayleigh wave, though numerical modeling indicates these deviations may be explained by propagation up the uneven hillside topography. Our results suggest frequency-dependent polarization analysis is a promising approach for locating areas of increased flow turbulence. This method could be applied to other erosion problems near engineered structures as well as to understanding energy dissipation, erosion, and channel morphology development in natural rivers, particularly at high discharges.

Spatial and temporal variations of rainfall-runoff erosivity (R) factor in Kakheti, Georgia

Abstract Soil erosion is a very complicated process. Rainfall erosivity is one of the main factors affecting on soil erosion. The erosive power of precipitation is accounted for by the rainfall erosivity factor (R-factor). Rainfall erosivity (R-factor) itself is a very important factor in soil erosion modeling. R-factor is a product of rainfall kinetic energy and rainfall intensity. Rainfall intensity change is one of the main indicators of climate change. It has a great influence on agriculture as one of the main factors causing soil erosion. Information of rainfall erosivity is rarely available with good spatial and temporal coverage. Accurate estimation of rainfall erosivity requires continuous rainfall data. Because many parts of the world still do not have detailed rainfall intensity data available, many studies have been performed to estimate R-factor based on available rainfall data. There are several alternative methods cited in science literature. This study aims to evaluate the temporal as well as the spatial distribution of rainfall erosivity and to calculate average annual rainfall erosivity for three study periods (1936–1962; 1963–1989; 1990–2016) in Kakheti, east Georgia. As far as Kakheti is the agrarian region, frequency and intensity of the rain are very important factors in agriculture point of view. Our study provides the assessment of rainfall erosivity potential with use of modern research methods for five weather stations (Telavi, Gurjaani, Sagarejo, Dedoplistskaro and Lagodekhi) in Kakheti. Rainfall erosivity potential was determined for every weather stations in Kakheti region from literature and records from meteorological stations. Then the same factor was determined by the selected methods (for each method separately), and the outcomes was compared, which allows us to determine the validity of a particular method for the study area. From the three methods used in the study process, method by Loureiro & Cautinho was finally used for the assessment rainfall erosivity during three study periods.

Excavation of subglacial bedrock channels by seasonal meltwater flow

AbstractSubglacial water flow drives the excavation of a variety of bedrock channels including tunnel valleys and inner gorges. Subglacial floods of various magnitudes – events occurring once per year or less frequently with discharges larger than a few hundred cubic metres per second – are often invoked to explain the erosive power of subglacial water flow. In this study we examine whether subglacial floods are necessary to carve bedrock channels, or if more frequent melt season events (e.g. daily production of meltwater) can explain the formation of substantial bedrock channels over a glacial cycle. We use a one‐dimensional numerical model of bedrock erosion by subglacial meltwater, where water flows through interacting distributed and channelized drainage systems. The shear stresses produced drive bedrock erosion by bed‐ and suspended‐load abrasion. We show that seasonal meltwater discharge can incise an incipient bedrock channel a few tens of centimetres deep and several metres wide, assuming abrasion is the only mechanism of erosion, a particle size of D=256 mm and a prescribed sediment supply per unit width. Using the same sediment characteristics, flood flows yield wider but significantly shallower bedrock channels than seasonal meltwater flows. Furthermore, the smaller the shear stresses produced by a flood, the deeper the bedrock channel. Shear stresses produced by seasonal meltwater are sufficient to readily transport boulders as bedload. Larger flows produce greater shear stresses and the sediment is carried in suspension, which produces fewer contacts with the bed and less erosion. We demonstrate that seasonal meltwater discharge can excavate bedrock volumes commensurate with channels several tens of metres to a few hundred metres wide and several tens of metres deep over several thousand years. Such simulated channels are commensurate with published observations of tunnel valleys and inner gorges. Copyright © 2018 John Wiley &amp; Sons, Ltd.

The influence of basal-ice debris on patterns and rates of glacial erosion

Glaciers have played a key role for shaping much of Earth's high topography during the cold periods of the Late Cenozoic. However, despite of their distinct influence on landscapes, the mechanisms of glacial erosion, and the properties that determine their rate of operation, are still poorly understood. Theoretical models of subglacial erosion generally highlight the influence of basal sliding in setting the pace of erosion, but they also point to a strong influence of other subglacial properties, such as effective bed pressure and basal-ice debris concentration. The latter properties are, however, not easily measured in existing glaciers, and hence their influence cannot readily be confirmed by observations.In order to better connect theoretical models for erosion to measurable properties in glaciers, we used computational landscape evolution experiments to study the expected influence of basal-ice debris concentration for subglacial abrasion at the scale of glaciers. The computational experiments couple the two erosion processes of quarrying and abrasion, and furthermore integrate the flow of ice and transport of debris within the ice, thus allowing for the study of dynamic feedbacks between subglacial erosion and systematic glacier-scale variations in basal-ice debris concentration. The experiments explored several physics-based models for glacial erosion, in combination with different models for basal sliding to elucidate the relationship between sliding speed, erosion rate and basal-ice debris concentration. The results demonstrate how differences in debris concentration can explain large variations in measured rates. The experiments also provide a simple explanation for the observed dependence of glacier-averaged rate of erosion on glacier size: that large glacier uplands feed more debris into their lower-elevation parts, thereby strengthening their erosive power.