Understanding Of Erosion Processes Research Articles

Quaternary landscape evolution in the San Jacinto fault zone, Peninsular Ranges of Southern California: Transient response to strike-slip fault initiation

Well-constrained case studies of transient landscape response to external forcing are needed to improve our understanding of erosion processes in tectonically active mountain belts. The Peninsular Ranges portion of the San Jacinto fault zone (SJFZ) is an excellent location for such a study because it displays pronounced geomorphic disequilibrium resulting from initiation of a major strike-slip fault in the past 1.0 to 2.5 million years. We recognize two geomorphic domains in this region: (1) a relict low-relief upland domain consisting of broad flat valleys and low-gradient streams and (2) very steep, rough topography with deeply incised canyons and retreating erosional knickpoints. Pleistocene sediments exposed along and near the SJFZ include fluvial conglomerate, sandstone, and mudstone, with weak paleosols and west- to NW-directed paleocurrents. These sediments accumulated in a low-gradient stream system (represented by domain 1) during an early phase of slip in the SJFZ, prior to the modern phase of erosion and degradation (domain 2). Late Pliocene or early Pleistocene initiation of the SJFZ triggered a wave of headward erosion and stream capture that is still migrating NW along the fault zone. Using the total distance that capture points have migrated along the fault zone and a range of possible ages for fault initiation, the rate of knickpoint retreat is estimated at ∼ 12 to 44 km/my. To explore the signal of transient geomorphic response to fault initiation, we analyzed 23 tributaries along an ∼ 20-km portion of the main fault valley within domain 2. The analysis reveals three zones with distinctive morphologies: (1) strongly convex longitudinal profiles in the NW, (2) a large (ca. 5–6 km 2) landslide in the central zone, and (3) concave tributaries in the SE with profile complexity decreasing and catchment area increasing from NW to SE. The distribution of these zones suggests close spatial and temporal association of active fault slip, bedrock incision, deep-seated landslides, and erosional modification. The fundamental driving force behind these processes is profound geomorphic disequilibrium resulting from initiation of the SJFZ. We suggest that landslides may have played a significant role in shaping the morphology of this fault zone, and that the influence of landslides may be underestimated in areas where characteristic landforms and deposits are obscured by later erosion and faulting.

Morphopedological study of the Arroio Guassupi water basin, São Pedro do Sul - Rio Grande do Sul (RS): basis for understanding erosion processes

INTRODUCTION Soil erosion represents one of the most serious environmental problems, jeopardising food production in terms of quality and quantity. It is, therefore, strictly linked to scarcity and starvation. Bertoni & Lobardi Neto (1990) point out that eroded lands have had their productive capacity reduced, making the struggle against erosion fundamental in some parts of the world. In Brazil, around 600 million tons of agricultural soil are lost per year (BAHIA et al 1992). According to Infanti Jr & Fornasari Filho (1998), the phenomena related to erosion formation are caused by two main types of factors or agents: the anthropogenic type, such as deforestation, mining activities and ways of using and occupying the soil (agriculture, construction works, urbanisation, etc.), which precipitates the erosion process immediately or after some time; and the natural type, which will determine the intensity of the processes. In this group, we can highlight the rain, vegetation cover, relief, soils and bedrock. When the erosion process takes place under natural or non-disturbed conditions, a permanent balance is established, and no greater damage occurs. However, when this balance is broken, erosion creates serious problems, not only in agriculture, by generating a gradual loss of productivity, but also in the management of water resources, contaminating them with sediment. According to Fendrich (1997), this situation is deepened by the unsuitable management of land, which is due to the disrespectful and devastating action of men, as well as the lack of agricultural education programmes which could provide the grower with the knowledge to make better use of land and water. In the face of this context, the goal of this research is to identify and to analyse, through the morphopedological approach, the relationship between soil, relief and bedrock in

Validation of agricultural non-point source (AGNPS) pollution model in Kori watershed, South Wollo, Ethiopia

Soil erosion is a major problem on the Ethiopian highlands. The poor soil management and land use practices are the causes of high soil erosion rate. Despite the extensive soil and water conservation programs launched by the Government of Ethiopia throughout the country, the achievements are far from satisfactory. One of the reasons was the inappropriate method used for assessment of soil erosion processes.This study was conducted to test and validate the agricultural non-point source (AGNPS) model in Kori gauged-watershed, South Wollo zone. Primary and secondary data collection methods were used to derive the spatial and attribute data. The primary data collection involved field survey. The soil conservation research project (SCRP) has collected hydrology and soil erosion data in the catchment since 1981. Some of the input parameters were also determined from digitized slope map using GIS.Ten rainfall events from 1989 and 1993 were used to calibrate the model. Sensitivity analysis conducted on the AGNPS model showed that curve number (CN) and universal soil loss equation (USLE) C factor were the most sensitive parameters and were subjected to calibration.The model calibration resulted in model efficiencies of 0.73, 0.53 and 0.90 for surface runoff, peak runoff rate, and sediment yield, respectively. The correlation coefficients were 0.87, 0.81 and 0.99, respectively, all significant at p≤0.01. Eight rainfall events from 1992 were used to validate the model. Validation results produced model efficiencies of 0.86, 0.65 and 0.88 for surface runoff, peak runoff rate and sediment yield, respectively. Surface runoff and peak flow simulations were improved in the validation stage. The corresponding correlation coefficients were 0.94, 0.90 and 0.98, all significant at p≤0.01, which showed the high linear correlation between measured and predicted values. It can be concluded that the AGNPS model is a useful prediction tool for understanding erosion processes on the Ethiopian highlands and for locating and targeting specific areas within the watershed that have high potential for soil loss, thus helping the conservation planner to design conservation plans.

Managing water quality in wetlands with forestry BMP's

Forested wetlands are uniquely critical areas in forest operations that present special challenges to protect water quality. These locations are a direct interface between the impacts of forest operations and water. BMP's are designed to minimize nonpoint source pollution, but much of the science behind current guidelines is based on an understanding of erosion processes in upland situations. In wetlands and around temporary stream crossings, redirection of flow, sedimentation processes, and alterations of flow velocity become important. Existing forested wetland BMP's appear to adequately address water quality protection. If existing BMP's became prescriptive regulations, however, there is potential for mis-application and unintended ecological impacts.

Using Rare‐Earth Oxide Tracers for Studying Soil Erosion Dynamics

Spatially averaged soil erosion data provide little information on soil erosion dynamics. Dynamically varied, spatially distributed erosion data are needed to better understand erosion processes and thoroughly evaluate process‐based erosion prediction models. The objectives of this study are to examine the feasibility of direct mixing rare‐earth element (REE) oxides with soil materials to trace soil erosion at a plot scale and to explore further the potential of using this technique to study soil erosion dynamics. Five REE oxide powders were mixed with a Camden silt soil (fine, silty, mixed, mesic Typic Hapludalt) at five slope positions. Six rainstorms were applied to a 4 by 4 m soil bed at a 10% slope. Runoff was collected during the rains and surface soil was sampled after each rain. All samples were extracted for REE with a quick acid‐leaching method and extracts were analyzed by inductively coupled plasma mass spectrometry (ICPMS). Mean error of REE‐derived sediment discharge relative to measured total across six rainstorms was 14.5%. Our results demonstrate that the REE‐tracing technique is feasible and sound, being capable of producing both spatially and temporally distributed erosion data. Results indicate that the most severe erosion occurred in the upper middle section of a uniform slope, and total sediment delivery from each segment was positively related to amounts of sediment deposition on the entire slope from that segment. This technique has the potential to bring new perspectives to soil erosion research.

A new index for rainfall erosivity on a physical basis

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Erosion and Sedimentation Processes on Irrigated Fields

Soil erosion is sometimes excessive during furrow irrigation and under center pivot sprinkler systems. An understanding of erosion processes is required to predict and develop management practices to reduce irrigation induced erosion. Little erosion process research has been carried out under irrigation, but much of the extensive channel sediment transport and rainfall-induced erosion process research can be adapted to irrigated conditions. Soil erosion occurs when fluid in motion detaches and transports soil particles. Sedimentation occurs when the fluid transport capacity decreases to less than the sediment load. Hydraulic forces of moving water and soil factors such as aggregate stability and particle size determine erosion and sedimentation. Under furrow irrigation, the shear of the overland flow against the soil provides the detachment force and is a primary factor determining channel transport capacity. With sprinkler irrigation, water drop energy detaches particles, some of which may be transported downslope by shallow interrill flow if the water application rate exceeds the soil infiltration rate.

Interrill Erodibility of Some Ohio Soils Based on Field Rainfall Simulation

AbstractPrediction of soil erodibility and an understanding of erosion processes are vital to sustained productive use of agricultural land. Interrill erodibilities (Ki) of five Ohio soils were assessed and compared with predicted Ki using the Water Erosion Prediction Project equation (WEPP‐K). A portable rainfall simulator was used to apply ∼ 70 mm h‐1 intensity rain for 1 h on 0.75‐m2 field plots representing crop row sideslopes. The soils studied included Miamian (fine, mixed, mesic Typic Hapludalf) and Riddles (fine‐loamy, mixed, mesic Typic Hapludalf) silt loams, Crosby silt loam (fine, mixed, mesic Aeric Ochraqualf), Kokomo silty‐clay loam (fine, mixed, mesic Typic Argiaquoll) and Mechanicsburg loam (fine‐loamy, mixed, mesic Ultic Hapludalf). The value of Ki determined for each soil was related to selected physical and chemical properties. Values of Ki varied significantly between soils and ranged from 1.23 ± 0.09 to 1.97 ± 0.60 × 10‐6 kg s m‐4. Interrill erodibility was negatively correlated with water‐stable aggregates (WSA) >0.25 mm (r2 = 0.50), WSA > 0.5 mm (r = 0.49), and organic C (r2 = 0.61), and positively correlated with Middleton's dispersion ratio (r2 = 0.84) and the ratio of water‐dispersible clay to total clay (r2 = 0.70). The WEPP‐Ki differed from measured values by ∼ 10 to 40%, ranging from 1.1 to 2.0 kg s m‐4. There was no correlation between WEPP‐Ki and measured Ki.

Sputtering of condensed gases by nuclear stopping: Chemical aspects

Sputtering of room-temperature solids has been studied now for nearly a century and a 1 half, and an enormous body of data on the various aspects of sputtering of these materials has been collected. Sputtering of the much more fragile and elusive condensed gases, however, has been studied systematically only for the last dozen years. The motivation for studying condensed gases comes primarily from the need to quantify erosion rates and chemical transformations of icy astronomical objects such as comets and certain Saturnian and 2-11 Jovian satellites, the need to understand erosion processes of pellets of solid hydrogen and deuterium injected into plasma devices, 12'13 and the need to understand the effects of high-energy particles impacting on cryopumping surfaces 14'15 ~ such as those found in fusion reactors. Additional motivation has been provided, particularly in our laboratory, by the discovery that the sputtering of these surfaces induces interesting chemical transformations in the residual solid 1619 and forms an excellent intense source of a broad range of cluster ions 16'19-32 which are difficult to generate by other means. Finally, an understanding of the detailed nature of the processes that lead to the ejection of ions from chemically simple frozen gases may provide insight into the mechanisms underlying the currently very popular tools of analytical chemistry, secondary ion mass spectrometry (SIMS) and fast-atom-bombardment mass spectrometry (FABMS). Considerable progress has been made in the relatively short time that condensed gases have been studied, and the physical and chemical processes specific to this type of target are beginning to be understood. Enough is now known that a number of general observations are commonly accepted. The sputtering yield is independent of temperature below a threshold; measured yields are as much as an order of magnitude greater than those predicted by standard linear cascade theory and increase rapidly with increasing stopping power; the kinetic energy distribution of the sputtered material retains the E 2 tail characteristic of a linear cascade but peaks at a very low energy; the large cluster ions which are observed preferentially retain polar or polarizable solvating units; only selective chemical transformations occur when reactive frozen gases or mixtures of gases are sputtered; and sputtering yields of condensed inert gases have been observed to decrease with increasing ion dose from a high initial value. Most of these observations have been summarized in a number of recent reviews which emphasize various areas of interest. Schou has discussed primarily the electronic sputter33 ing of condensed gases. Sigmund has presented the current state of theoretical work on

Migration Patterns of an Asymmetric Meandering River: The Rouge River, Quebec

The migration patterns responsible for the asymmetry of highly sinuous Rouge River meanders are described and related to the hydraulic and sediment transport patterns controlling bank erosion in these bends. Two elements of the overall migration patterns play important roles in maintaining asymmetry, and raise fresh questions concerning our understanding of erosion processes: significant outer bank erosion starts remarkably early at bend entrances, well before crossover of the high velocity filament. In addition, such erosion extends far along the cross‐valley reaches, despite the very gentle channel curvatures between meander apices. Data on high‐flow suspended sediment transport and helix structure suggest how, beyond the control exerted by near‐bank shear stresses, the spatial patterns of near‐bed primary and secondary flows can also exert an influence on the distribution of bank erosion, by controlling the evacuation of the influxes of eroded bank materials.

Soil erosion— Sediment yield research in progress

The pace of research to understand erosion processes and to determine soil erosion rates and sediment yields has quickened in recent years. Many soil and water conservation planners have recognized the need to more fully understand the complex forces affecting detachment and movement of soil from erosion source to point of deposition.We learned long ago that deposited sediment limits the useful life of conservation structures and that we must optimize conservation designs because of a dwindling supply of good sites. More recently, with the advent of increased environmental concern, the necessity for the broadest consideration of all proposed developments and for predicting the environmental impact of optional soil and water conservation plans has been emphasized. The new awareness of the tremendous volume of urban and right‐of‐way construction erosion and its impact on society has intensified our concern. Furthermore, since sediment is a carrier of agricultural chemicals, the priority for a fuller understanding of soil erosion rates and watershed sediment yields has increased.