Off-site Effects Of Soil Erosion Research Articles

Event-based soil erosion and sediment yield modelling for calculating long-term reservoir sedimentation in the Alps

ABSTRACT Among the most characteristic offsite effects of soil erosion, reservoir sedimentation is one of the longlasting problems pertaining to storage capacity and dam operations. In this work, sedimentation rates of the Fortezza reservoir in South Tyrol (Italian Alps) are analysed for nine erosive events over 14 months. Sediment rates are calculated through a modified Universal Soil Loss Equation (USLE) combined with a Sediment Delivery Ratio (SDR) module at 2.5 m resolution. The topographic factor is adjusted to the Alpine terrain, and an additional factor is included to consider the nonerodible parts of the basin. The results are validated against a 14-month sediment yield obtained by high-resolution (0.2 m) reservoir bathymetric analyses. The calculated sediment yield has an absolute deviation of 4.8% from the measured one. The results indicate that these methods can be successfully applied for the estimation of reservoir sedimentation rates in the Alps.

Distribution and formation of soil balls under heavy rainstorm conditions in the northern Loess Plateau

The occurrence of a peculiar phenomenon called “soil balls” was observed in Dingbian County, northern Loess Plateau, due to an extremely heavy rainstorm on July 10, 2022. Determining the distribution characteristics and formation of these soil balls is crucial for enriching the knowledge and the precise prevention and control of soil erosion on the Loess Plateau. This research is particularly significant in studying the off-site effects of soil erosion caused by rainstorm and flooding disasters. This study conducted a comprehensive analysis through field investigation and drone aerial photography in the three dam-controlled watersheds selected. The results showed that the soil balls originated from the soil clods generated by landslides and collapses that occurred within the watersheds during heavy rainstorms. Under the action of hyperconcentrated flows, the soil clods were transported downstream. The size of the soil balls is mainly in the range of 20–60 cm in diameter, accounting for 81% of the total soil balls in the dam lands, with significant differences in the morphology at different locations within a dam land region. The average area density and volume density of soil balls in the dam lands of the watersheds are 0.13–0.25 m2 m−2 and 0.05–0.11 m3 m−2, respectively. In each watershed, the area density and volume density of the soil balls exhibit the following order: one-third of the dam land nearest from the dam wall > the middle one-third of the dam land > one-third of the dam land furthest the dam wall. The total erosion intensity of landslides and collapses in the three watersheds was 18,730, 5,213, and 9,879 m3 km−2, respectively. The sediment transport ratio of landslides and collapses expressed by the soil balls in the dam land is at least 4–10%. The study also indicated that the volume of landslides and collapses, the shape coefficient of the watershed, the density of the confluence paths, and the peak discharge had a significant impact on the volume density distribution of the soil balls in the dam lands. We recommend implementing certain measures in similar watersheds, including converting steep slopes into terraced fields or grasslands, constructing water storage and drainage facilities, building energy dissipation measures in channels, and reinforcing check dams, to reduce the risk of soil ball events occurring under heavy rainstorm conditions, and protect the ecological environment on the Loess Plateau.

Soil Erosion and Sedimentation Rate in the Blue Nile River Basin of Ethiopia

Substantial runoff is a feature of the Ethiopian Nile River Basin because its soils are erodible and poorly organized, resulting in high soil loss and sedimentation rates. The rate of soil erosion and sedimentation in the basin was reported to be quite variable, which could be owing to the methodology utilized and data quality used. By reviewing recent studies, this review primarily aimed to give information on the range of soil erosion and sedimentation rates. Recent studies at small watersheds and basin levels were reviewed. Soil loss and sedimentation rates in Ethiopia's Blue Nile River Basin ranged from 16 to 67.37ton ha^-1 year^-1 and 4.2 to 18ton ha^-1 year^-1, respectively. Similarly, at watersheds level soil loss and sedimentation rates were reported to range from 8.25 to 100ton ha^-1 year^-1 and 1.1 to 43.34ton ha^-1 year^-1 respectively. Hence it is concluded that high soil erosion and sedimentation rates are serious problems in the basin. So, appropriate soil and water conservation measures are recommended throughout the basin to reduce both on-site and off-site effects of soil erosion. It is also highly advised to utilize uniform techniques and a common data source for soil erosion and sedimentation rates estimation at different levels.

Long-term effectiveness of indigenous and introduced soil and water conservation measures in soil loss and slope gradient reductions in the semi-arid Ethiopian lowlands

Across the world, on-site and off-site effects of soil erosion accelerated by anthropogenic land-use/cover changes have been partly offset by the implementation of soil and water conservation (SWC) measures. However, studies evaluating the effectiveness of SWC over longer periods are currently rare. The dimensions of the terraced fields and SWC were measured at 242 sample fields that had slope gradients between 2.0 and 6.5% in three villages in the semi-arid Ethiopian Rift Valley (Ethiopian lowlands). In the study area, both indigenous contour weed hedgerows (denber) and introduced bund techniques, such as soil and stone bunds, are observed as major SWC measures. The establishment of the oldest SWC dated back to 65 years ago. Long-term effectiveness of the SWC was assessed in terms of the reduction in soil loss rates and slope gradient change of the terraced fields. Long-term quantitative assessment of SWC across the world has been conducted only in highlands; however, no case studies were conducted in lowlands. It is partly because the model that assessed the long-term effectiveness of SWC measures for the highlands appears to be inapplicable to lowlands. In the lowland model used in this study, the mid-point of the field was connected with that of the upper and lower fields by straight lines, which were assumed to represent the original slopes before the SWC establishment. The difference in slope gradient between the present slope and the original slope of the field without SWC was used for the estimates of slope reduction. The measured mass of the soil loss zone of the field was used to determine the long-term mean intra-field soil loss rate, while that of the sediment deposition zone was used to determine the long-term mean intra-field sediment accumulation rate behind the lower SWC. The mean net soil loss from the terraced fields was 19.6 Mg ha−1 yr−1, which was higher than that in the semi-arid northwestern highlands (Tigray); however, that from the stone bund fields was 13.7 Mg ha−1 yr−1, which was lower than that in Tigray. The soil and stone bunds retained 52–72% of the intra-field soil loss, compared to 34% retained by the denber. Slope gradients were reduced annually by 0.03% grade for the denber fields and 0.17–0.28% grades for the soil and stone bunds fields. Uncertainty analysis proved these estimates had relative uncertainty of <10% in general. All the SWC measures investigated in this study were effective in reducing soil loss from cropland and in reducing slope gradients of cropland in Ethiopian lowlands. Farmers’ efforts to place eliminated weeds on the lower hedgerows and bunds and a subsequent regeneration mechanism of weed hedgerows sustain the long-term effectiveness of not only denbers but also other bunds even without any extra maintenance efforts by farmers in the Rift Valley.

On-site and Off-site Effects of Soil Erosion: Causal Analysis and Remedial Measures in Agricultural Land - a Review

Soil erosion is one of the main factors causing land degradation. Furthermore, loss of soil nutrients ultimately causes worldwide reduction of agricultural productivity and water quality deterioration. Therefore, soil erosion control measures are required as an aspect of catchment management. The general purpose of this paper review is to make an overview of soil erosion throughout the world in order to highlight required studies on which to be based when proposing appropriate erosion control measures for agricultural fields. Different scientific documents including journal articles, internet materials, conference papers and books were used as research materials to achieve the objectives of the present work. This methodology enabled the researcher to make a synthesis of various researchers’ views on this topic. Principally, this review focused on the effects and remedial measures of soil erosion. The research findings highlighted that soil erosion affects greatly the agricultural land, human properties and aquatic ecosystem. Both on-site and off-site effects are analyzed. Sediment transport in rivers resulted from soil erosion impacts on bridges, hydropower plants, water treatment plants and water bodies such as lakes and water reservoirs. The present review article strongly recommends the followings: (1) Performance improvement of the existing erosion control measures; (2) Promotion of new soil erosion adaptive measures; (3) Farmers trainings on Best Management Practices of soil erosion control and (4) Sensitization of governmental institutions and Non-governmental organizations (NGOs) to be extensively involved in soil erosion management.&#x0D; Keywords: Erosion causes, erosion effects, erosion control measures

Sediment Yield Source Identification in Gilgel Gibe-I Catchment Using GIS-based RUSLE and SEDD Models for Soil Conservation Planning, South West Ethiopia

Onsite and off-site effects of soil erosion are the biggest global environmental problems. Some of the offsite problems are silting of dams and reservoir, disruption of lake ecosystems, and increased downstream flooding. Gilgel Gibe-1 catchment has been also subjected to sedimentation and other offsite problems. This study was aimed to identify the source of sediment yield in Gilgel Gibe-1 catchment using GIS-based RUSLE and SEDD models for soil conservation planning. Primary and secondary data from different sources were used to estimate soil loss from the catchment using GIS-based RUSLE model. Rainfall-runoff erosivity, soil erodibility, topographic effect, surface coverage, and land management practice of the catchment were used as an input to RUSLE model. Sediment Delivery Ratio was estimated using the SEDD model. The result of this study shows the mean annual soil loss of the catchment is 62.98 t ha -1 year -1 which are about 26.56x106 t year -1 and the mean sediment delivery ratio is 0.1367. The mean annual sediment yield of the catchment is 8.61t ha -1 year -1 and the overall catchment area contributes about 3.63x106t year -1 sediment to the reservoir at the dam site. On the bases of mean annual sediment yield, a source of sediment yield areas are identified and prioritized. Accordingly, SW4, SW5, SW3, SW6, SW7, SW8, SW9, SW2, and SW1 got priority level in the order of 1 to 9. Sediment yield &gt;10 t ha -1 year -1 covers 15.75% of the catchment area and 0-5 t ha -1 year -1 covers 78.22%, of the catchment. The result of this study indicates the catchment and reservoir are under the problem of soil loss and siltation, respectively. Therefore, it is recommended that immediate action, soil, and water conservation measures, should be taken in the catchment according to the priority of sub-watersheds and further detail study is suggested with the support of experimental test plots. Keywords: GIS, RUSLE, SEDD, Sediment Yield, Soil Loss, Sub-watershed. DOI : 10.7176/JEES/9-2-04

Comparison of two concepts for assessment of sediment transport in small agricultural catchments

Abstract The erosion, transport and deposition of sediments in small valley reservoirs represent a significant impact on their operations, mainly with regard to reducing the volume of their accumulation. The aim of this study is a comparison and uncertainty analysis of two modelling concepts for assessment of soil loss and sediment transport in a small agricultural catchment, with an emphasis on estimating the off-site effects of soil erosion resulted in sedimentation of a small water reservoir. The small water reservoir (polder) of Svacenicky Creek which was built in 2012, is a part of the flood protection measures in Turá Lúka and is located in the western part of Slovakia, close to the town of Myjava. The town of Myjava in recent years has been threatened by frequent floods, which have caused heavy material losses and significantly limited the quality of life of the local residents. To estimate the amount of soil loss and sediments transported from the basin, we applied two modelling concepts based on the USLE/SDR and WaTEM/SEDEM erosion models and validated the results with the actual bathymetry of the polder. The measurements were provided by a modern Autonomous Underwater Vehicle (AUV) hydrographic instrument. From the sediment data measured and the original geodetic survey of the terrain conducted at the time of the construction of the polder, we calculated changes in the storage volume of the polder during its four years of operation. The results show that in the given area, there has been a gradual clogging of the bottom of the polder caused by water erosion. We estimate that within the four years of the acceptance run, 10,494 m3 of bottom sediments on the Svacenicky Creek polder have accumulated. It therefore follows that repeated surveying of the sedimentation is very important for the management of the water reservoir.

Identification and prioritization of critical erosion areas based on onsite and offsite effects

Accelerated soil erosion is considered as one of serious agro-environmental threats to sustainable development all over the word. Tolerable erosion concept is a tool for awareness and assessment of soil erosion status and its economic, social, and environmental hazards. This study was conducted to design a framework for evaluating and identifying spatial patterns of erosion hazard in Haji-Ghushan watershed, based on tolerable erosion concept, by using the SWAT model. The framework was consisted of two parts: the erosion tolerance index (ETI), and the sediment-phosphorous index (SPI) for evaluating onsite and offsite effects of soil erosion, respectively. Four hazard levels were defined for each index. The results of sediment simulation indicated that the maximum rate of erosion belonged to agricultural lands located on steep slopes in the central part of the watershed, and the minimum rate was from forest lands, despite their steep slopes. The map of spatial distribution of erosion hazard showed that, in terms of both onsite and offsite effects, a major part of the watershed (around 65%) had experienced an erosion rate lower than the erosion tolerance threshold; hence, these areas were not faced with erosion hazard. The spatial distribution of the areas exposed to the onsite erosion hazard, however, was differed from those confronted by the offsite erosion hazard. Identified high hazard areas based on the erosion offsite impacts were mainly located in sub-basins close to the watershed outlet where the sediment and phosphorous yield was high due to the high sediment-phosphorous delivery ratio. High hazard areas with high risk of soil degradation and productivity reduction are distributed throughout the watershed, depending on the magnitude of the erosion rate. These findings revealed that, in addition to erosion rate, sediment delivery ratio is also an important parameter in evaluating soil erosion hazard. For achieving the sustainable agro-environment, it is necessary to consider both the onsite and offsite effects of soil erosion to identify the high hazard areas. Also the results showed that the designed framework was capable of identifying the high hazard and hot spot areas well. The findings of this study are useful for officials and policy makers of soil conservation and environmental protection agencies in the region.

Extensive management of field margins enhances their potential for off-site soil erosion mitigation

Soil erosion is a widespread problem in agricultural landscapes, particularly in regions with strong rainfall events. Vegetated field margins can mitigate negative impacts of soil erosion off-site by trapping eroded material. Here we analyse how local management affects the trapping capacity of field margins in a monsoon region of South Korea, contrasting intensively and extensively managed field margins on both steep and shallow slopes. Prior to the beginning of monsoon season, we equipped a total of 12 sites representing three replicates for each of four different types of field margins (“intensive managed flat”, “intensive managed steep”, “extensive managed flat” and “extensive managed steep”) with Astroturf mats. The mats (n = 15/site) were placed before, within and after the field margin. Sediment was collected after each rain event until the end of the monsoon season.The effect of management and slope on sediment trapping was analysed using linear mixed effects models, using as response variable either the sediment collected within the field margin or the difference in sediment collected after and before the field margin.There was no difference in the amount of sediment reaching the different field margin types. In contrast, extensively managed field margins showed a large reduction in collected sediment before and after the field margins. This effect was pronounced in steep field margins, and increased with the size of rainfall events. We conclude that a field margin management promoting a dense vegetation cover is a key to mitigating negative off-site effects of soil erosion in monsoon regions, particularly in field margins with steep slopes.

Spatial scale impact on daily surface water and sediment fluxes in Thukela river, South Africa

The on- and off-site effects of soil erosion in many environments are well known, but there is still limited understanding of the soil loss fluxes in downstream direction due, among other factors, to scarce and poor quality. A four year study to (i) evaluate water and sediment fluxes at different spatio-temporal scales and (ii) interpret the results in terms of processes involved and the controlling factors, was conducted in Thukela basin, South Africa. Five hierarchically nested catchments; namely microcatchment (0.23 km2), subcatchment (1.20 km2), catchment (9.75 km2), sub-basin (253 km2) and basin (29,038 km2), were used in addition to fifteen (1 m2) microplots and ten (10 m2) plots on five locations within the microcatchment. The results showed 19% decrease of unit-area runoff (q) from 3.1 L m−2 day−1 at microplot to 2.5 L m−2 day−1 at plot scale followed by steeper (56%) decrease at microcatchment scale. The q decreased in downstream direction to very low level (q ≤ 0.26 L m−2 day−1). The changes in q were accompanied by initial 1% increase of soil loss (SL) from 18.8 g m−2 day−1 at microplot to 19.1 g m−2 day−1 at plot scale. The SL also decreased sharply (by 39 fold) to 0.50 g m−2 day−1 at microcatchment scale, followed by further decrease in downstream direction. The decrease of q with spatial scale was attributed to infiltration losses, while initial increase of SL signified greater competence of sheet than splash erosion. The decrease of SL beyond the plot scale was attributed to redistribution of the soil on the hillslope and deposition on the stream channel upstream of the microcatchment outlet. Therefore, erosion control strategies focussing on the recovery of vegetation on the slope and stabilisation of gullies are recommended.

A high-resolution map of direct and indirect connectivity of erosion risk areas to surface waters in Switzerland—A risk assessment tool for planning and policy-making

Off-site effects of soil erosion are becoming increasingly important, particularly the pollution of surface waters. In order to develop environmentally efficient and cost effective mitigation options it is essential to identify areas that bear both a high erosion risk and high connectivity to surface waters. This paper introduces a simple risk assessment tool that allows the delineation of potential critical source areas (CSA) of sediment input into surface waters concerning the agricultural areas of Switzerland. The basis are the erosion risk map with a 2m resolution (ERM2) and the drainage network, which is extended by drained roads, farm tracks, and slope depressions. The probability of hydrological and sedimentological connectivity is assessed by combining soil erosion risk and extended drainage network with flow distance calculation. A GIS-environment with multiple-flow accumulation algorithms is used for routing runoff generation and flow pathways. The result is a high resolution connectivity map of the agricultural area of Switzerland (888,050ha). Fifty-five percent of the computed agricultural area is potentially connected with surface waters, 45% is not connected. Surprisingly, the larger part of 34% (62% of the connected area) is indirectly connected with surface waters through drained roads, and only 21% are directly connected. The reason is the topographic complexity and patchiness of the landscape due to a dense road and drainage network. A total of 24% of the connected area and 13% of the computed agricultural area, respectively, are rated with a high connectivity probability. On these CSA an adapted land use is recommended, supported by vegetated buffer strips preventing sediment load. Even areas that are far away from open water bodies can be indirectly connected and need to be included in planning of mitigation measures. Thus, the connectivity map presented is an important decision-making tool for policy-makers and extension services. The map is published on the web and thus available for application.

Economic and institutional incentives for managing the Ethiopian highlands of the Upper Blue Nile Basin: A latent class analysis

This article identifies incentives that motivate land users to participate in the management of private and communal lands in the Ethiopian highlands of the Upper Blue Nile Basin, where on-farm and off-farm impacts of soil erosion are threatening the livelihoods of millions of farmers and damaging water infrastructure across the Blue Nile River System. A choice experiment was set up requiring farmers to contribute with labour and to implement specific watershed management (WM) activities in exchange for subsidised credit facilities, better opportunities for livestock production in the form of grazing land reform, and an additional extension service. Thus, we address farmers’ combined choice of management of private and communal lands. We use a latent class model with attribute non-attendance for one class to accommodate the preferences of farmers who always select the status quo option without making a trade-off for experimentally designed policy attributes. Moreover, we estimate individual specific and socio-spatial group specific preferences across 90 units. Farmers’ preference within the same socio-spatial unit is fairly homogeneous. Apart from the non-attendance class, the study reveals two classes. One class, which is probably dominated by literate farmers and farmers who have easy credit access, is willing to contribute more labour and requires fewer subsidies than the other class. Furthermore, the two groups have opposite viewpoints on management (semi-privatisation of common land). Our results also revealed that the seasonal concentration of the WM workload is less preferred by all farmers than an evenly distributed workload. Thus, policy design to address both the on-site and off-site effects of soil erosion in the Ethiopian highlands of the Upper Blue Nile Basin should consider the workload distribution of various aspects of WM, as well as the heterogeneity of preference for incentives across different groups of farmers.

Soil erosion tolerance and water runoff control: minimum environmental standards

Council Regulations (EC) No 1257/1999 and the EU Soil Thematic Strategy give great importance to soil and land conservation to develop knowledge driven governance for rural development. In the hilly areas of Italy cultivated intensively, and especially in the ones devoted to viticulture, agricultural practices determine high loss of soil with consequent degradation of the soil resource. In addition to it, offsite effects of soil erosion can be unsustainable, due to sediment transfer to the channel network and infrastructures. In order to achieve a sustainable rural development there is a need for tools and instruments to allow European regional administrations, to develop, implement, manage and monitor rural development plans. To counteract the environmental threats intensified by agricultural activity, the environmental functions “soil erosion control” and “water runoff control” were investigated in the Chianti area by using GIS. To determine the EMR (Environmental Minimum Requirements) values for soil erosion the “regeneration” capability of soils was considered, and the value of estimated soil loss was compared with the value of soil reformation. A scenario analysis was also performed to evaluate the effectiveness of the agroenvironmental measure “grass cover” in reducing erosion. The concept of tolerable erosion based on soil productivity and soil reformation rate only is reductive and off-site effects of soil erosion should be also taken into account. For this reason, it was proposed to extend the concept of hydrogeological risk to soil erosion by implementing the notion of soil erosion tolerance (T) with the new concept of environmental risk of soil erosion (ERSE). The new ERSE index takes into account all the in- and off-farm externalities of soil erosion. For this reason, it can be considered an aggregated environmental indicator that enables policy makers to evaluate the impacts of soil erosion by following an holistic approach.

Predicting soil erosion and sediment yield at the basin scale: Scale issues and semi-quantitative models

Basin sediment yield is the product of all sediment producing processes and sediment transport within a basin. Consequently, the prediction of basin sediment yield should take into consideration all different erosion and sediment transport processes. However, traditional physics-based, conceptual, and empirical or regression models have not been able to describe all these processes due to insufficient systems knowledge and unfeasible data requirements. Therefore, the applicability of these models at the basin scale is troublesome. This paper first illustrates the relation between basin area, dominant erosion processes, and sediment yield by a combination of measured sediment yield at different spatial scales in Mediterranean environments. This clearly reveals that soil erosion rates measured at one scale are not representative for sediment yield at another scale level. Second, the most important semi-quantitative models developed for erosion and sediment yield assessments at the basin scale are reviewed. Most of these models use environmental factors to characterise a drainage basin in terms of sensitivity to erosion and sediment transport. Six of the nine models discussed (PSIAC, FSM, VSD, Gavrilovic, CSSM, WSM) include sheet-, rill-, gully, bank erosion, landslides, and connectivity, at least partly, in the assessment of basin sediment yield. The low data requirements and the fact that practically all significant erosion processes are considered makes them especially suited for estimating off-site effects of soil erosion. The other three models (EHU, CORINE, FKSM) focus mainly on sheet and rill erosion and provide quantitative descriptions of the sensitivity to erosion at basin or even regional scales. These models thus focus mainly on on-site problems of soil erosion. Most of the semi-quantitative models might benefit from a more quantitative description of factors used to characterise the basin. Though an equilibrium should be found between the extra effort and increase in model performance, the increased availability of spatially distributed topographic data as well as high-resolution satellite imagery will probably make this feasible in the near future.

Measuring Sustainable Cotton Production Using Total Factor Productivity

Continuous cotton (Gossypium hirsutum L.) production was examined using data from Alabama's long-term Old Rotation experiment (c. 1896). Index values were used to examine trends in productivity and sustainability for 95 yr. Treatments studied were those receiving (i) no N fertilizers and no winter legumes for 95 yr, (ii) only winter legumes as a source of N, and (iii) chemical fertilizer N. Three sets of index numbers were calculated from all inputs and outputs involved in the production systems: (i) total factor productivity (TFP), which accounts for an direct production inputs, but which does not consider production externalities; (ii) productivity relative to a base plot; and (iii) total social factor productivity (TSFP), which accounts for all direct production inputs as well as externalities of soil erosion and pesticide use. Viewed from the 95-yr perspective of the Old Rotation experiment, all three treatments fulfill at least one criterion required for a system to be considered sustainable. Output per unit of input is higher in 1991 than in 1896, even when externalities are valued. None of the systems showed a linear trend in output or TFP over the life of the experiment; productivity cycles are present in all three systems, despite a positive overall trend. An average annual rate of TSFP growth of 1.8%/yr was attained- Accounting for erosion and pesticide externalities reduced the annual productivity growth rate by 0.2%/yc The system that has neither an organic nor a chemical source of added N was less productive and less sustainable than the two other systems with a 0.3%/yr TSFP growth rate. The plots using organic and chemical sources of N had similar productivity impacts. Valuing soil erosion and pesticide externalities had only a modest effect on measured productivity. The most dramatic single event to affect the productivity of cotton farming was the introduction of the mechanical cotton picker. The impact of this technology was powerful enough to offset the effect of many other changes in the system.