Effects of gully erosion and gully filling on soil depth and crop production in the black soil region, northeast China

Gully erosion is a very serious problem in the black soil region of northeast China. Gully filling is often adopted for controlling gully erosion by local farmers and thus causes more serious soil erosion. In this study an ephemeral gully (EG, 74 m) and a classical gully (CG, 52 m) connected at the gully’s headcut were selected as the study site. Two comparisons were made to explore the effects of gully erosion and the subsequent gully filling on soil depth and soybean yield: (1) soil depth between 81 sample points in the study site and 11 reference points along the same slope with the gully; (2) soybean yield between 81 sample points in the study site and 30 baseline locations near the study site. The results indicated that gully erosion caused the reduction of soil depth and soybean yield. Although filling gullies with soil from adjacent areas seemed to be an expedient way to remediate the gullies, it resulted in substantial soybean yield reduction. Gully erosion reduced the soil depth and soybean yield in 74.4 and 83.9 % of the study site, respectively. The soybean yield reduction ratio was 34.5 % for the whole study site and 2.6 % for the black soil region. Soil depth was the most important soil property indicator to reduce yield. Every 1 cm decrease in soil depth in the areas adjacent to gullies due to infilling activities resulted in a 2 % decrease in yield. More significant was the deposition of sediment from gully erosion, which completely eliminated soybean yield. Currently, effective soil and water conservation measures are not known and adopted by local farmers extensively. In the future, once some measures for preventing soil erosion, in particular gully erosion, were proved effective, these technologies should be disseminated among local farmers.     

An integrated assessment of soil erosion dynamics with special emphasis on gully erosion in the Mazayjan basin,southwestern Iran

Soil erosion by water is a significant problem in arid and semi-arid areas of large parts of Iran. Water erosion is one of the most effective phenomena that leads to decreasing soil productivity and pollution of water resources; especially, in the Mazayjan watershed in the southwest of Fars Province gully erosion contributes to the sediment dynamics in a significant way. Consequently, the intention of this research is to identify the different types of soil erosion processes acting in the area and to assess the process dynamics in an integrative way. Therefore, we applied GIS and satellite image analysis techniques to derive input information for the numeric models. For sheet and rill erosion the Unit Stream Power-based Erosion Deposition Model (USPED) was utilized. The spatial distribution of gully erosion was assessed using a statistical approach, which used three variables (stream power index, slope, and flow accumulation) to predict the spatial distribution of gullies in the study area. The eroded gully volumes were estimated for a 7-year period by fieldwork and Google Earth high-resolution images. Finally the gully retreat rates were integrated into the USPED model. The results show that the integration of the SPI approach to quantify gully erosion with the USPED model is a suitable method to qualitatively and quantitatively assess water erosion processes. The application of GIS and stochastic model approaches to spatialize the USPED model input yields valuable results for the prediction of soil erosion in the Mazayjan catchment. The results of this research help to develop an appropriate management of soil and water resources in the southwestern parts of Iran.     

Gully development in eastern Romania: a case study from Falciu Hills

The gullied systems from the Falciu Hills within the Chioara catchment (2997 ha) consist of both main types of gullies, discontinuous and large continuous ones along valley bottoms, and lots of ephemeral gullies. Several methods have been used to measure and estimate gully characteristics. Then, the gully development stages, the effect of the natural conditions, and especially the impact of land management on gullying in the Falciu Hills over the last two centuries have been defined. In addition, the role of gully erosion in triggering landslides has also been studied. Two main periods have been distinguished (until 1960 and 1961–2012) for assessing major characteristics of land degradation. The results show that total gully area in the Chioara catchment is 66.4 ha excepting for the ephemeral gullies, and areas occupied by gullies from the five study sub-catchments (2334 ha) account for two-thirds. Total length of the main gully network in the entire catchment is 33.2 km from which the five sub-catchments account for 71 %. The mean gully density of 1.11 km km⁻² supports the evidence that here gullying is the major environmental threat. Half of the gully areal growth and three-quarters of the new landslide area occurred over the 1961–2012 period. Delayed deforestation peaking during 1830–1930 and land conversion to arable use resulted in severe soil erosion, high aggradation along the non-gullied valley bottoms, and severe gullying. The average gully head retreat rate over the last two centuries from four trunk continuous gullies is 14 m year⁻¹, and the sediment yield from gullying only accounted for 54–69 % of the sediment mass produced by water erosion. The evolution of gullies is linked to major land-use changes in the study area. Despite a decreasing tendency of gullying and catchment area over the last half century, gullying still remains problematically high in East Romania.

     

Relating soil erosion and sediment yield to geomorphic features and erosion processes at the catchment scale in the Spanish Pre-Pyrenees

Erosion and sediment redistribution are important processes in landscape changes in the short and long term. In this study, the RMMF model of soil erosion and the SEDD model of sediment delivery were used to estimate annual soil loss and sediment yield in an ungauged catchment of the Spanish Pre-Pyrenees and results were interpreted in the context of the geomorphic features. The Estaña Catchment is divided into 15 endorheic sub-catchments and there are 17 dolines. Gullies and slopes were the main erosive geomorphic elements, whereas the colluvial, alluvial, valley floor, and doline deposits were depositional elements. Spatially distributed maps of gross soil erosion, sediment delivery ratio (SDR), and sediment yield (SY) were generated in a GIS. Severe erosion rates (>100 Mg ha^?1 year^?1) were found in gullies, whereas mean and maximum erosion rates were very high on slopes developed on Keüper Facies and high in soils on Muschelkalk Facies. Where crops are grown, the depositional-type geoforms were predicted by the models to have an erosive dynamic. Those results were consistent with the rates of erosion quantified by ¹³⁷Cs which reflects the significant role of human activities in triggering soil erosion. Catchment area was positively correlated with erosion rate, but negatively correlated with SDR and SY. The latter were negatively correlated with the proportion of the surface catchment covered with forests and scrublands. The topography of the area influenced the high SDR and SY in the dolines and valley floors near the sinks. Intra-basin stored sediment was 59.2% of the total annual eroded soil in the catchment. The combination of the RMMF and SEDD models was an appropriate means of assessing the effects of land uses on soil erosion and obtaining a better understanding of the processes that underlie the geomorphic changes occurring in mountainous environments of the Mediterranean region.     

Assessment of soil erosion risk using SWAT model

Soil erosion is one of the most serious land degradation problems and the primary environmental issue in Mediterranean regions. Estimation of soil erosion loss in these regions is often difficult due to the complex interplay of many factors such as climate, land uses, topography, and human activities. The purpose of this study is to apply the Soil and Water Assessment Tool (SWAT) model to predict surface runoff generation patterns and soil erosion hazard and to prioritize most degraded sub-catchment in order to adopt the appropriate management intervention. The study area is the Sarrath river catchment (1,491 km²), north of Tunisia. Based on the estimated soil loss rates, the catchment was divided into four priority categories for conservation intervention. Results showed that a larger part of the watershed (90 %) fell under low and moderate soil erosion risk and only 10 % of the watershed was vulnerable to soil erosion with an estimated sediment loss exceeding 10 t?ha^?1?year^?1. Results indicated that spatial differences in erosion rates within the Sarrath catchment are mainly caused by differences in land cover type and gradient slope. Application of the SWAT model demonstrated that the model provides a useful tool to predict surface runoff and soil erosion hazard and can successfully be used for prioritization of vulnerable areas over semi-arid catchments.     

Comparison of volumetric and remote sensing methods (TLS) for assessing the development of a permanent forested loess gully

The gully systems develop a compact network dissecting the loess cover of the NW part of the Lublin Upland. They are overgrown by dense and multi-storey forest assemblages. It is very difficult to apply teledetection techniques, GPS positioning, and geodesic tools, such as a laser rangefinder or total station, for monitoring of gully development. The detailed research, involving the comparison of traditional and modern methods, was conducted in a gully with a secondary erosional dissection, developing in the gully bottom with varied intensity for the last 15 years. In the period of comparative research (2012/2013), the rate of development of the erosional dissection was measured by means of traditional methods as well as a Leica HDS 7000 laser scanner. 3D laser scanning permitted precise terrain modelling and the assessment of qualitative and quantitative spatial changes. This paper compares the results of three measurement campaigns. The analysis showed intensive development of the dissection, manifested in an increase in its volume (37 %), retreat of the erosion scarp (32 m), deep erosion (19 %), and lateral erosion (27 %). Registered moderate snowmelt in 2013 caused the volume dissection to increase by 57 m³, mainly as a result of the gully bottom scouring. During heavy rainfalls in June, the landforms were widened by a further 217 m³ and observed deepening and widening of erosive potholes. The prevalence of deep erosion resulted in the transformation back into a V-shaped cross section. A total of 37.3 Mg km⁻² of material was discharged from the gully catchment during snowmelt runoffs in 2013. A precipitation event in June 2013 caused the discharge of 856.9 Mg km⁻² of material from the catchment. The obtained results confirm that snowmelt erosion determines the spatial development of perennial gullies, but the volume of material discharged from the catchment depends on the occurrence of extreme precipitation during the warm season.

     

Analysis of fundamental physical factors influencing channel bank erosion: results for contrasting catchments in England and Wales

Channel bank erosion processes are controlled by numerous factors and as such are both temporally and spatially variable. The significance of channel bank erosion to the sediment budget is difficult to quantify without extensive fieldwork/data analysis. In this study, the importance of key physical factors controlling channel bank erosion, including channel slope, upstream catchment area, channel confinement, and sinuosity, was explored using regression analysis. The resulting analysis can be used in practical studies to provide a first approximation of bank erosion rates (in catchments similar to those investigated). A data set of channel bank erosion rates covering eight contrasting river catchments across England and Wales, over a time period of up to 150 years, was created using a modified GIS methodology. The best predictors were found to be upstream area, channel confinement, and sinuosity with respect to dimensionless width-averaged retreat rates (m m^?1 yr^?1). Notwithstanding these relationships, the results highlight the variability of the magnitude of sediment production by channel bank erosion both within and between catchments.     

The morphological characteristics of gully systems and watersheds in Dry-Hot Valley,SW China

Gully systems and watersheds are geomorphic units with clear boundaries that are relatively independent of basin landscapes and play an important role in natural geography. In order to explore the morphological characteristics of gully systems and watersheds in the Dry-Hot Valley [South West (SW) China], gullies are interpreted from online Google images with high resolution and watersheds are extracted from digital elevation model at a scale of 1:50,000. The results show that: (1) There are 17,382 gullies (with a total area of 1141.66 km²) and 42 watersheds in the study area. (2) The average gully density of the study area (D) is 4.29 km/km², gully frequency (F) is 14.39 gullies/km², the branching ratio (B) is 5.13, the length ratio (L) is 3.12, and the coefficient of the main and tributary gullies (M) is 0.06. The degree of gully erosion is strong to extremely strong, the main development intensity of gully erosion ranges from intense to moderate, and the type of gully system is tributary. (3) The watershed areas (A) are between 0.39 and 96.43 km², the relief ratio (R) is from 0.10 to 0.19, the circularity ratio (C) is from 0.30 to 0.83, the texture ratio (T) is from 0.82 to 39.35, and the dominant geomorphological texture type is fine. (4) There is a quantitative relationship between F and D:F?=?0.624D² (R?=0.84) and T is closely related to D, F, M (R²?>?0.7). A, R and C are related to M (R²?>?0.5). The development of gully systems is the result of coupling effects between multiple factors. In this area, the degree of erosion and the condition of the main and tributary gullies can be controlled by the degree of topographic breakage in the watershed, which provides some theoretical basis for the evaluation of gully erosion by the latter. In addition, the scale, relief, and shape have a significant impact on the locations of the main and tributary gullies. For tributary gullies, attention should be paid to the interception and control of runoff and sediment in the small confluence branches in order to prevent gully expansion and head advance. These features can inform the development of targeted measures for the control of soil erosion.     

Geomorphology and GIS analysis for mapping gully erosion susceptibility in the Turbolo stream catchment (Northern Calabria, Italy)

This work summarizes the results of a geomorphological and bivariate statistical approach to gully erosion susceptibility mapping in the Turbolo stream catchment (northern Calabria, Italy). An inventory map of gully erosion landforms of the area has been obtained by detailed field survey and air photograph interpretation. Lithology, land use, slope, aspect, plan curvature, stream power index, topographical wetness index and length-slope factor were assumed as gully erosion predisposing factors. In order to estimate and validate gully erosion susceptibility, the mapped gully areas were divided in two groups using a random partitions strategy. One group (training set) was used to prepare the susceptibility map, using a bivariate statistical analysis (Information Value method) in GIS environment, while the second group (validation set) to validate the susceptibility map, using the success and prediction rate curves. The validation results showed satisfactory agreement between the susceptibility map and the existing data on gully areas locations; therefore, over 88% of the gullies of the validation set are correctly classified falling in high and very high susceptibility areas. The susceptibility map, produced using a methodology that is easy to apply and to update, represents a useful tool for sustainable planning, conservation and protection of land from gully processes. Therefore, this methodology can be used to assess gully erosion susceptibility in other areas of Calabria, as well as in other regions, especially in the Mediterranean area, that have similar morphoclimatic features and sensitivity to concentrated erosion.     

Identifying sediment sources from the inter-gully area and gully area in a small watershed in the Loess Hilly Region of China

Understanding the sediment source is very significant for erosion control in small watersheds. On the Loess Plateau of China, over 110 thousands of check dams were constructed in the past 60 years, which played an important role in controlling soil loss and also kept much information of erosion and sediment yield in the past. The objective of this investigation is to identify the sediment source by the ¹³⁷Cs tracing method in a small watershed in the Loess Hilly Region of China. Fifty-five sampling sites were selected from the watershed (44 from the inter-gully area, 7 from the gully sides and 4 from the reference sites), and a total of 114 soil samples were collected from three sediment profile cores at the Sidizui watershed check dam constructed in 1959. Based on the erosion rate from the inter-gully area by the ¹³⁷Cs models, and the total erosion amount deposited in the check dam since 1963, the relative contributions of sediment from the inter-gully area and gully area were estimated during 1963–2013. By comparing the difference of ¹³⁷Cs activities of surface soils from the check dam (deposited in the 2011–2013 flood events), the inter-gully and gully areas, the relative contributions of sediment derived from the two source areas to the flood sediment during recent years (2011–2013) were estimated by a simple mixing model. Results showed that the erosion rate from the inter-gully area was about 3054 t/km² a during 1963–2013, and the relative contributions of sediment from the inter-gully area and gully area were estimated to be 27 and 73%, respectively. The sediment from the inter-gully area was about 20% of the total sediment yield amount to the 2011–2013 floods, and from the gully area it was about 80%. The relative contribution of sediment from the inter-gully or gully area was not a fixed value in the watershed. Both of the inter-gully erosion and gully erosion should be simultaneously controlled, and more erosion control measures on the gully area should be taken in the subsequent watershed management in order to reduce the erosion amount in this region.     

Spatial estimation of soil erosion risk using RUSLE/GIS techniques and practices conservation suggested for reducing soil erosion in Wadi Mina watershed (northwest,Algeria)

The Wadi Mina Watershed, western area of Algeria is characterized by rare and irregular rains and a fragile and weak vegetable cover. The sediments resulting from erosion are transported and contributed to silting dam Sidi Mhamed Benaouda. The combination of the thematical maps of the various erosive factors according to the Revised Universal Soil Loss Equation (RUSLE) in SIG by ArcGIS 10.2 software provided a reliable forecast of the annual rates of soil loss by delimiting the areas prone to erosive risk in the catchment above mentioned. The estimated potential average annual soil loss is 11.2 t/ha/yr., and the potential erosion rates from recognized erosion classes ranged from 0.0 to plus 100 t/ha/yr. About 50% of the catchment area was predicted to have very low to low erosion risk, with soil loss between 0 and 7.4 t/ha/yr. Erosion risk is moderate over 13.9% of the catchment, where calculated soil loss is between 7.4 and 12 t/ha/yr. Erosion risk is high to dangerous over 36.1% of the catchment, where calculated soil loss is more than 12 t/ha/yr. According to this study, it appeared clearly that we must intervene quickly by using reliable and effective conservation techniques.     

A simple DEM assessment procedure for gully system analysis in the Lake Manyara area,northern Tanzania

Gully erosion is a major threat concerning landscape degradation in large areas along the northern Tanzanian Rift valley. It is the dominant erosion process producing large parts of the sediments that are effectively conducted into the river network. The study area is located in the Lake Manyara—Makuyuni River catchment, Arusha, northern Tanzania. During fieldwork, we measured topographic data of eight gully systems close to Makuyuni Town. The main focus of this study is to assess gully erosion dynamics using improved DEMs with original resolutions of 30 and 20 m, respectively. We assessed terrain characteristics to extract information on environmental drivers. To improve the DEM, we integrated information deduced from satellite images as well as from acquired GPS field data. Topographic indices such as Stream Power Index or Transport Capacity Index were derived from the re-interpolated DEM. To evaluate gully evolution, we assessed also the longitudinal slope profiles. Finally, the gully evolution phases of each gully were classified according to the concept proposed by Kosov et al. (Eksperimental’naya geomorfologiya, vol 3. Moscow University, Moskva, pp 113–140, 1978). The re-interpolated DEMs revealed a positive response especially for the more developed gullies. We show that the extraction of information on this spatial process scale based on “low-resolution” data is feasible with little additional fieldwork and image interpretation. In fact, areas identified as having a greater risk of gully erosion have been confirmed by observations and surveys carried out in the field.     

A GIS-based approach for gully erosion susceptibility modelling: a test in Sicily, Italy

The aim of this study is to analyze the susceptibility conditions to gully erosion phenomena in the Magazzolo River basin and to test a method that allows for driving the factors selection. The study area is one of the largest (225 km²) watershed of southern Sicily and it is mostly characterized by gentle slopes carved into clayey and evaporitic sediments, except for the northern sector where carbonatic rocks give rise to steep slopes. In order to obtain a quantitative evaluation of gully erosion susceptibility, statistical relationships between the spatial distributions of gullies affecting the area and a set of twelve environmental variables were analyzed. Stereoscopic analysis of aerial photographs dated 2000, and field surveys carried out in 2006, allowed us to map about a thousand landforms produced by linear water erosion processes, classifiable as ephemeral and permanent gullies. The linear density of the gullies, computed on each of the factors classes, was assumed as the function expressing the susceptibility level of the latter. A 40-m digital elevation model (DEM) prepared from 1:10,000-scale topographic maps was used to compute the values of nine topographic attributes (primary: slope, aspect, plan curvature, profile curvature, general curvature, tangential curvature; secondary: stream power index; topographic wetness index; LS-USLE factor); from available thematic maps and field checks three other physical attributes (lithology, soil texture, land use) were derived. For each of these variables, a 40-m grid layer was generated, reclassifying the topographic variables according to their standard deviation values. In order to evaluate the controlling role of the selected predictive variables, one-variable susceptibility models, based on the spatial relationships between each single factor and gullies, were produced and submitted to a validation procedure. The latter was carried out by evaluating the predictive performance of models trained on one half of the landform archive and tested on the other. Large differences of accuracy were verified by computing geometric indexes of the validation curves (prediction and success rate curves; ROC curves) drawn for each one-variable model; in particular, soil texture, general curvature and aspect demonstrated a weak or a null influence on the spatial distribution of gullies within the studied area, while, on the contrary, tangential curvature, stream power index and plan curvature showed high predictive skills. Hence, predictive models were produced on a multi-variable basis, by variously combining the one-variable models. The validation of the multi-variables models, which generally indicated quite satisfactory results, were used as a sensitivity analysis tool to evaluate differences in the prediction results produced by changing the set of combined physical attributes. The sensitivity analysis pointed out that by increasing the number of combined environmental variables, an improvement of the susceptibility assessment is produced; this is true with the exception of adding to the multi-variables models a variable, as slope aspect, not correlated to the target variable. The addition of this attribute produces effects on the validation curves that are not distinguishable from noise and, as a consequence, the slope aspect was excluded from the final multi-variables model used to draw the gully erosion susceptibility map of the Magazzolo River basin. In conclusion, the research showed that the validation of one-variable models can be used as a tool for selecting factors to be combined to prepare the best performing multi-variables gully erosion susceptibility model.     

Estimation of soil erosion using RUSLE in Caijiamiao watershed,China

Soil erosion is a serious environmental and production problem in China. In particular, natural conditions and human impact have made the Chinese Loess Plateau particularly prone to intense soil erosion area. To decrease the risk on environmental impacts, there is an increasing demand for sound, and readily applicable techniques for soil conservation planning in this area. This work aims at the assessment of soil erosion and its spatial distribution in hilly Loess Plateau watershed (northwestern China) with a surface area of approximately 416.31 km². This study was conducted at the Caijiamiao watershed to determine the erosion hazard in the area and target locations for appropriate initiation of conservation measures using the revised universal soil loss equation (RUSLE). The erosion factors of RUSLE were collected and processed through a geographic information system (GIS)-based approach. The soil erosion parameters were evaluated in different ways: The R-factor map was developed from the rainfall data, the K-factor map was obtained from the soil map, the C-factor map was generated based on Landsat-5 Thematic Mapper image and spectral mixture analysis, and a digital elevation model with a spatial resolution of 25 m was derived from topographic map at the scale of 1:50,000 to develop the LS-factor map. Support practice P factor was from terraces that exist on slopes where crops are grown. By integrating the six-factor maps in GIS through pixel-based computing, the spatial distribution of soil loss in the study area was obtained by the RUSLE model. The results showed that spatial average soil erosion at the watershed was 78.78 ton ha^?1 year^?1 in 2002 and 70.58 ton ha^?1 year^?1 in 2010, while the estimated sediment yield was found to be 327.96 × 10⁴ and 293.85 × 10⁴ ton, respectively. Soil erosion is serious, respectively, from 15 to 35 of slope degree, elevation area from 1,126 to 1,395 m, in the particular area of soil and water loss prevention. As far as land use is concerned, soil losses are highest in barren land and those in waste grassland areas are second. The results of the study provide useful information for decision maker and planners to take appropriate land management measures in the area. It thus indicates the RUSLE–GIS model is a useful tool for evaluating and mapping soil erosion quantitatively and spatially at a river watershed scale on a cell basis in Chinese Loess Plateau and for planning of conservation practices.     

Geospatial assessment of soil erosion intensity and sediment yield: a case study of Potohar Region,Pakistan

Estimation of spatial extent of soil erosion, one of the most serious forms of land degradation, is critical because soil erosion has serious implications on soil fertility, water ecosystem, crop productivity and landscape beauty. The primary objective of the current study was to assess and map the soil erosion intensity and sedimentation yield of Potohar region of Pakistan. Potohar is the rainfed region with truncated and complex topography lying at the top of the Indus Basin, the world’s largest irrigation networks of canals and barrages. Spatially explicit Revised Universal Soil Loss Equation (RUSLE) Model integrated with Remote Sensing-GIS techniques was used for detecting/mapping of erosion prone areas and quantification of soil losses. The results show that the Potohar region is highly susceptible to soil erosion with an average annual soil loss of 19 tons ha^?1 year^?1 of which the maximum erosion (70–208 tons ha^?1 year^?1) was near the river channels and hilly areas. The sediment yield due to the erosion is as high as 148 tons ha^?1 year^?1 with an average of 4.3 tons ha^?1 year^?1. It was found that 2.06% of the total area falls under severe soil erosion, 13.34% under high erosion, 15.35% under moderate soil erosion while 69.25% of the area lies in the low (tolerable) soil erosion. Chakwal and Jhelum districts of the region are seriously affected by erosion owing to their topography and soil properties. The information generated in this study is a step forward towards proper planning and implementation of strategies to control the erosion and for protection of natural resources. It is, hence, necessary that suitable water harvesting structures be made to control water to prevent soil erosion and provision of water in the lean season in this region. Tree plantation and other erosion control practices such as strip cropping can also minimize soil erosion in this region.     

Statistical analyses and controls of root-zone soil moisture in a large gully of the Loess Plateau

Soil moisture variability and controls are little known in large gullies of the Loess Plateau which represent complex topography with steep slopes. This study analyzed spatial–temporal variability of soil moisture at the 0–20, 20–40, 40–60, and 60–80 cm depths in a large gully of the Loess Plateau based on root-zone soil moisture measurements for 3 years (2009–2011). The result showed that mean soil moisture, standard deviation (SD), and coefficient of variation, were highly dependent on depth; the highest mean value was observed at the 20–40 cm depth, while the lowest one was at the 0–20 cm depth. The SD increased with mean soil moisture for various depths as soil moisture was relatively wet; however, a transition that SD decreased with mean soil moisture occurred when soil moisture was relatively dry. Positive correlations exist between moisture contents over different depths, and that the relationships of the neighboring layers are relatively high with R ² from 0.70 to 0.76. Correlation analysis, principle component analysis, and stepwise multiple regression analysis showed that soil particle size distribution and topography (slope and elevation) were the main environmental factors controlling soil moisture variability in the large gully.     

Assessing space–time variations of denudation processes and related soil loss from 1955 to 2016 in southern Italy (Calabria region)

Studies on denudation processes and soil loss rates can provide insight into the landscape evolution, climate change, and human activities, as well as on land degradation risk. The aims of this study were to analyze the space–time distribution of denudation processes and evaluate the soil loss changes occurred during the period 1955–2016 by using an approach integrating geomorphological, geospatial and modeling analysis. The study area is a representative stream catchment of the Crati Valley (Calabria, southern Italy), which is affected by severe erosion processes. The combined use of aerial photographs interpretation, field survey, geostatistics, and GIS processing has allowed to characterize the types of denudation processes and land use change in space and time. Revised universal soil loss equation implemented in GIS environment was used to estimate the space–time pattern of soil loss and the soil erosion rates for each investigated year. The results showed that from 1955 to 2016, the study area was highly affected by denudation processes, mainly related to landslides and water erosion (slope wash erosion and gully erosion). Comparison of denudation processes maps showed that the total area affected by erosion processes has increased by about 31% and the distribution of geomorphic processes and their space–time evolution resulted from the complex interrelation between geoenvironmental features and human activities. The main land use changes concerned a decrease in areas covered by woodland, scrubland and pasture and an increase in croplands and barren lands that favored erosion processes. The most susceptible areas to soil loss in both years were mapped, and the mean soil loss rates for the study area were 6.33 Mg ha^?1 y^?1 in 1955 and 10.38 Mg ha^?1 y^?1 in 2016. Furthermore, the soil loss in 2016 has increased by about 64% compared to 1955. Finally, the results showed that integrating multi-temporal analysis of denudation processes, land use changes and soil loss rates might provide significant information on landscape evolution which supports decision makers in defining soil management and conservation practices.     

Assessment of the potential of semi-arid plants to reduce soil erosion in the Konartakhteh watershed,Iran

Soil erosion is a major environmental problem in arid and semi-arid areas. Although bioengineering is important in preventing soil erosion, plant architecture and mechanical properties in these areas are rarely studied. In this study, in order to evaluate the potential of native plants to reduce soil erosion in semi-arid regions, their above-ground (e.g., stem density, radius of the stem, etc.) and below-ground (e.g., root area ratio, root tensile strength, etc.) characteristics were measured in the field and laboratory. Five indicators, namely, stem density (SD), sediment obstruction potential (SOP), plant stiffness (MEI), relative soil detachment (RSD), and root cohesion (Cr), were taken into account. Each indicator was scored according to a five-point scale (0?=?low, 4?=?high), and then, the score of each indicator was represented on an ameba diagram. Finally, for understanding traits of plants and evaluating their potential to control rill and gully erosion, the area occupied by the ameba diagram was studied. The results indicated that the shrub Ziziphus spina-christi (MEI?=?108.35 N, RSD?=?0.398, Cr?=?8.34 kPa, SOP?=?0.097, and SD?=?0.00270) is a very suitable native plant species for controlling both the gully and rill erosion. In addition, Scariola orientalis is effective for sediment obstruction, but its low scores on the MEI and RSD indicators imply that it is not able to control gully development. Furthermore, Noaea mucronata, Platychaete glaucescens, Astragalus gummifer, Alhagi persarum, Lycium shawii, and Prosopis farcta have a distinct potential to reduce the rate of gully erosion. These results have wide applicability for adopting soil conservation measures to other semi-arid environments.     

Susceptibility mapping of gully erosion using GIS-based statistical bivariate models: a case study from Ali Al-Gharbi District,Maysan Governorate,southern Iraq

This work aims to evaluate the predictive capability of three bivariate statistical models, namely information value, frequency ratio, and evidential belief functions, in gully erosion susceptibility mapping in northeastern Maysan Governorate (Ali Al-Gharbi District) in southern Iraq. The gully inventory map, consisting of 21 gullies of different sizes, was prepared based on the interpretation of remotely sensed data supported by field survey. The gully inventory data (polygon format) were randomly partitioned into two sets: 14 gullies for build and training the bivariate model, and the remaining 7 gullies for validating purposes. Twelve gully influential factors were selected based on data availability and the literature review. The selected factors were related to lithology, geomorphology, soil, land cover, and topography (primary and secondary) settings. Analysis of factor importance using information gain ratio proved that out of 12 gully influential factors, eight were of more importance in developing gullies (the average merit was greater than zero). The most important factors and the training gully inventory map were used to generate three gully erosion susceptibility maps based on the three bivariate models used. For validation, the area under the operating characteristics curves for both success and prediction rates was used. The results indicated that the highest prediction rate of 82.9% was achieved using the information value technique. All the bivariate models had prediction rates greater than 80%, and thus they were regarded as very good estimators. The final conclusion was that the bivariate models offer advanced techniques for mapping gully erosion susceptibility.     

Investigation of RS and GIS techniques on MPSIAC model to estimate soil erosion

Soil erosion due to surface water is a standout among the serious threat land degradation problem and an hazard environmental destruction. The first stage for every kind of soil conservation planning is recognition of soil erosion status. In this research, the usability of two new techniques remote sensing and geographical information system was assessed to estimate the average annual specific sediments production and the intensity erosion map at two sub-basins of DEZ watershed, southwest of Lorestan Province, Iran, namely Absorkh and Keshvar sub-basins with 19,920 ha, using Modified Pacific Southwest Inter-Agency Committee (MPSIAC) soil erosion model. At the stage of imagery data processing of IRS-P6 satellite, the result showed that an overall accuracy and kappa coefficient were 90.3% and 0.901, respectively, which were considered acceptable or good for imagery data. According to our investigation, the study area can be categorized into three level of severity of erosion: moderate, high, and very high erosion zones. The amount of specific sediments and soil erosion predicted by MPSIAC model was 1374.656 and 2396.574 m³ km^?2 year^?1, respectively. The areas situated at the center and south parts of the watershed were subjected to significant erosion because of the geology formation and ground cover, while the area at the north parts was relatively less eroded due to intensive land cover. Based on effective of nine factors, the driving factors from high to low impact included: Topography > Land use > Upland erosion > Channel erosion > Climate > Ground cover > Soil > Runoff > Surface geology. The measured sediment yield of the watershed in the hydrometric station (Keshvar station) was approximately 2223.178 m³ km^?2 year^?1 and comparison of the amount of total sediment yield predicted by model with the measured sediment yield indicated that the MPSIAC model 38% underestimated the observed value of the watershed.