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1.
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 km 2) 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. 相似文献
2.
Gully erosion is an important environmental issue with severe impacts. This study aimed to characterize gully erosion susceptibility and assess the capability of information value (InfVal) and frequency ratio (FR) models for its spatial prediction in Ourika watershed of the High Atlas region of Morocco. These two bivariate statistical methods have been used for gully erosion susceptibility mapping by comparing each data layer of causative factor to the existing gully distribution. Weights to the gully causative factors are assigned based on gully density. Gullies have been mapped through field surveys and Google earth high-resolution images. Lithofacies, land use, slope gradient, length-slope, aspect, stream power index, topographical wetness index and plan curvature were considered predisposing factors to gullying. The digitized gullies were randomly split into two parts. Sixty-five percent (65%) of the mapped gullies were randomly selected as training set to build gully susceptibility models, while the remaining 35% cases were used as validation set for the models’ validation. The results showed that barren and sparse vegetation lands and slope gradient above 50% were very susceptible to gully erosion. The ROC curve was used for testing the accuracy of the mentioned models. The analysis confirms that the FR model (AUC 80.61%) shows a better accuracy than InfVal model (AUC 52.07%). The performance of the gully erosion susceptibility map constructed by FR model is greater than that of the map produced by InfVal model. The findings proved that GIS-based bivariate statistical methods such as frequency ratio model could be successfully applied in gully susceptibility mapping in Morocco mountainous regions and in other similar environments. The produced susceptibility map represents a useful tool for sustainable planning, conservation and protection of land from gully processes. 相似文献
3.
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. 相似文献
4.
Digital Elevation Model (DEM) is one of the important parameters for soil erosion assessment. Notable uncertainties are observed in this study while using three high resolution open source DEMs. The Revised Universal Soil Loss Equation (RUSLE) model has been applied to analysis the assessment of soil erosion uncertainty using open source DEMs (SRTM, ASTER and CARTOSAT) and their increasing grid space (pixel size) from the actual. The study area is a part of the Narmada river basin in Madhya Pradesh state, which is located in the central part of India and the area covered 20,558 km 2. The actual resolution of DEMs is 30 m and their increasing grid spaces are taken as 90, 150, 210, 270 and 330 m for this study. Vertical accuracy of DEMs has been assessed using actual heights of the sample points that have been taken considering planimetric survey based map (toposheet). Elevations of DEMs are converted to the same vertical datum from WGS 84 to MSL (Mean Sea Level), before the accuracy assessment and modelling. Results indicate that the accuracy of the SRTM DEM with the RMSE of 13.31, 14.51, and 18.19 m in 30, 150 and 330 m resolution respectively, is better than the ASTER and the CARTOSAT DEMs. When the grid space of the DEMs increases, the accuracy of the elevation and calculated soil erosion decreases. This study presents a potential uncertainty introduced by open source high resolution DEMs in the accuracy of the soil erosion assessment models. The research provides an analysis of errors in selecting DEMs using the original and increased grid space for soil erosion modelling. 相似文献
5.
Toroud Watershed in Semnan Province, Iran is a prone area to gully erosion that causes to soil loss and land degradation. To consider the gully erosion, a comprehensive map of gully erosion susceptibility is required as useful tool for decreasing losses of soil. The purpose of this research is to generate a reliable gully erosion susceptibility map (GESM) using GIS-based models including frequency ratio (FR), weights-of-evidence (WofE), index of entropy (IOE), and their comparison to an expert knowledge-based technique, namely, Analytic Hierarchy Process (AHP). At first, 80 gully locations were identified by extensive field surveys and Google Earth images. Then, 56 (70%) gully locations were randomly selected for modeling process, and the remaining 26 (30%) gully locations were used for validation of four models. For considering geo-environmental factors, VIF and tolerance indices are used and among 18 factors, 13 factors including elevation, slope degree, slope aspect, plan curvature, distance from river, drainage density, distance from road, lithology, land use/land cover, topography wetness index (TWI), stream power index (SPI), normalized difference vegetation index (NDVI), and slope–length (LS) were selected for modeling aims. After preparing GESMs through the mentioned models, final maps divided into five classes including very low, low, moderate, high, and very high susceptibility. The receiver operating characteristic (ROC) curve and the seed cell area index (SCAI) as two validation techniques applied for assessment of the built models. The results showed that the AUC (area under the curve) in training data are 0.973 (97.3%), 0.912 (91.2%), 0.939 (93.9%), and 0.926 (92.6%) for AHP, FR, IOE, and WofE models, respectively. In contrast, the prediction rates (validating data) were 0.954 (95.4%), 0.917 (91.7), 0.925 (92.5%), and 0.921 (92.1%) for above models, respectively. Results of AUC indicated that four model have excellent accuracy in prediction of prone areas to gully erosion. In addition, the SCAI values showed that the produced maps are generally reasonable, because the high and very high susceptibility classes had very low SCAI values. The results of this research can be used in soil conservation plans in the study area. 相似文献
6.
One of the most serious limitations in studying the surface morphometry of a badland landscape is the nonavailability of a
very fine resolution data which is essential for such types of studies. Local relief of most of the badlands in India and
also from other parts of the world exhibit limited relief amplitude, often within a few meters. The paper reports a case study
carried out in a riverine badland formed along the Western Deccan Trap Region. An attempt has been made in the present paper
to extract the morphometric variables of the landscape from the DEMs derived from a high resolution field generated data,
because the accuracy of the DEM derived values are dependent on the pixel resolution of the DEM from which they are generated.
The size of the pixel resolution should be fixed differently for different landscapes depending on the landscape process in
the area. The local relief of the area is around 10 m and for such types of landscapes the topographical maps and also the
web-available DEMs are of very coarse resolutions which are not suitable for the analysis. Therefore two well defined tributary
catchments were chosen from the area under investigation and theodolite surveys were carried out, contours were generated
with 10 cm interval, DEMs were derived by using Arc GIS software. SRTM (Shuttle Radar Topography Mission) 90 m resolution
data were utilized to generate DEM for the whole basin. Hypsometric and the drainage basin parameters were extracted from
these data by using the same software. Fractal dimension of the whole basin and the sample basins were also obtained for the
same data. The morphometric data generated were used to understand the geomorphic processes operating in the area. 相似文献
7.
Gully erosion is both a significant natural hazard and an important sediment source. The design of proper prevention measures relies firstly on the prediction of the future locations of gullies. But, as recent progress has shown, methods and results in any environmental modelling greatly depend upon scale, the selection of which should be based on management needs. This research deals with predicting the spatial potential for gullying at two different scales grouped in a top-down framework, i.e. starting with a preliminary, regional scale analysis (1:100,000–1:200,000) to develop a simplified model, and performing a more detailed, intermediate level analysis at a medium scale (1:25,000–1:50,000) for the basin sector revealed as the most threatened by the process. At the same time, the study searches for relationships among: scale of analysis, area of investigation, precision and accuracy of input data, and the quality of expected results and their applicability. The study area is the Olteţ Drainage Basin (2439 km2) in southern Romania, which extends over four landform types: mountains, hills, a plateau (piedmont) and a plain. Aiming to investigate the scale effect, the same statistical method is selected for both analyses, namely Classification and Regression Trees (CART). Scale-adapted procedures and resolutions are applied for defining the dependent variable, deriving the environmental attributes and deciding the sampling strategy needed to provide information for the statistical analyses. In order to detect the degree of gullying at the regional scale, the statistical method is used over the entire basin, and gully density is selected as the target variable. For the analysis of gully susceptibility at the medium scale, within the most affected area of the Olteţ Basin identified as the piedmont sector, the single gully and the intensely gullied spot are defined as the target variables. The best validated maps obtained at the two scales are compared. The results reveal that both individual maps are characterized by statistical accuracy (a NRMSE value of 0.05–0.08 and an AUC of 0.86 for the regional scale and the medium scale models, respectively). Yet, the regional scale map is affected by high uncertainties when compared to the medium scale one. The scale dependency of results and hence the relative nature of their accuracy and reliability are highlighted in the context of both fundamental and applied research. 相似文献
8.
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. 相似文献
9.
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/km 2 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. 相似文献
10.
The geomorphic studies are extremely dependent on the quality and spatial resolution of digital elevation model(DEM)data.The unique terrain characteristics of a particular landscape are derived from DEM,which are responsible for initiation and development of ephemeral gullies.As the topographic features of an area significantly influences on the erosive power of the water flow,it is an important task the extraction of terrain features from DEM to properly research gully erosion.Alongside,topography is highly correlated with other geo-environmental factors i.e.geology,climate,soil types,vegetation density and floristic composition,runoff generation,which ultimately influences on gully occurrences.Therefore,terrain morphometric attributes derived from DEM data are used in spatial prediction of gully erosion susceptibility(GES)mapping.In this study,remote sensing-Geographic information system(GIS)tech-niques coupled with machine learning(ML)methods has been used for GES mapping in the parts of Semnan province,Iran.Current research focuses on the comparison of predicted GES result by using three types of DEM i.e.Advanced Land Observation satellite(ALOS),ALOS World 3D-30 m(AW3D30)and Advanced Space borne Thermal Emission and Reflection Radiometer(ASTER)in different resolutions.For further progress of our research work,here we have used thirteen suitable geo-environmental gully erosion conditioning factors(GECFs)based on the multi-collinearity analysis.ML methods of conditional inference forests(Cforest),Cubist model and Elastic net model have been chosen for modelling GES accordingly.Variable's importance of GECFs was measured through sensitivity analysis and result show that elevation is the most important factor for occurrences of gullies in the three aforementioned ML methods(Cforest=21.4,Cubist=19.65 and Elastic net=17.08),followed by lithology and slope.Validation of the model's result was performed through area under curve(AUC)and other statistical indices.The validation result of AUC has shown that Cforest is the most appropriate model for predicting the GES assessment in three different DEMs(AUC value of Cforest in ALOS DEM is 0.994,AW3D30 DEM is 0.989 and ASTER DEM is 0.982)used in this study,followed by elastic net and cubist model.The output result of GES maps will be used by decision-makers for sustainable development of degraded land in this study area. 相似文献
11.
This study focused on the landslide case at Su-Hua Highway 115.9k, Taiwan. A preliminary investigation was conducted on geomorphologic features change and landslide mechanisms using digital elevation models, geographical maps, and remote sensing images at different times in conjunction with geological surveys and analysis results. Using the results of geological surveys and physical model experiments, we constructed a discrete element method to simulate the process of landslide movement. The results revealed deformation in the metamorphic rock slopes upstream of 115.9k. The slopes around the erosion gully upstream presented visible slope toes cutting and tension cracks at the crest as well as unstable rock masses. According to the results of numerical simulation for typhoon Megi event, intense rains could induce slippage in the rock debris/masses in the source area, initially at a speed of 5–20 m/s. Subsequently, steeper terrain could cause the rock debris/masses to accelerate to form a high-speed (>30 m/s) debris slide quickly moving downstream to form an alluvial fan downstream by the sea. 相似文献
12.
Experiments were carried out between September 2009 and August 2010 at Bei-shi and Gao-mei in Taichung, and at Quan-xing, Chang-Hua and He-mei in Changhua. Dry-deposition flux models of metallic elements Mn, Fe, Zn, Cu and Cr bound to air particulates at five characteristic sampling sites were developed. Results concerning metallic elements Mn, Zn, Cr and Cu, revealed that Zhang’s model yielded the best results concerning the dry-deposition flux of particles of size 10 μm at Bei-shi, Chang-Hua, He-mei, Quan-xing and Gao-mei sampling sites. For the metallic element Cr, the model of Noll and Fang exhibited the best dry-deposition flux results for particles of size 10 μm at Bei-shi, He-mei and Gao-mei sampling sites. For metallic element Fe, the model of Noll and Fang yielded the best results for the dry-deposition flux of particles of size 5.6 μm at Bei-shi, Chang-Hua, He-mei and Quan-xing sampling sites. For metallic element Fe, Zhang’s model yielded the best dry-deposition flux results for particles of size 5.6 μm at the Gao-mei sampling site. For ambient air particles, Zhang’s model yielded the best average calculated/modeled ratios for particles of size 3 μm, and the model of Noll and Fang yielded the best average calculated/modeled for particles of size 10 μm. Finally, the models of both Zhang and Noll and Fang yielded more accurate predictions of the dry-deposition of metallic elements in ambient air when the particles were larger than 5.6 μm. 相似文献
13.
Watershed development and management plans are more important for harnessing surface water and groundwater resources in arid and semi-arid regions. To prepare a comprehensive watershed development plan, it becomes necessary to understand the topography, erosion status and drainage patterns of the region. This study was undertaken to determine the drainage characteristics of Pageru River basin using topographical maps on a scale of 1:50,000. The total area of the Pageru River basin is 480 km 2. It was divided into X sub-basins for analysis. The drainage patterns of the basin are dendritic and include a sixth order stream. The quantitative analysis of various aspects of a river basin drainage network characteristics reveals complex morphometric attributes. The streams of lower orders mostly dominate the basin. The development of stream segments in the basin area is more or less affected by rainfall. The elongated shape of the basin is mainly due to the guiding effect of thrusting and faulting. The erosional processes of fluvial origin have been predominately influenced by the subsurface lithology of the basin. 相似文献
14.
This study assessed temporal variation in soil erosion rates in response to energy consumption of flow (ΔE). It employed an in situ bank gully field flume experiment with upstream catchment areas with bare (BLG) or cultivated land (CLG) that drained down to bare gully headcuts. Water discharge treatments ranged from 30 to 120 L Min−1. Concentrated flow discharge clearly affected bank gully soil erosion rates. Excluding minimal discharge in the CLG upstream catchment area (30 L min−1), a declining power function trend (p ≤ 0.1) was observed with time in soil erosion rates for both BLG and CLG upstream catchment areas and downstream gully beds. Non-steady state soil erosion rates were observed after an abrupt collapse along the headcut slope after prolonged scouring treatments. However, as the experiment progressed, ΔE and energy consumption of flow per unit soil loss (ΔEu) exhibited a logarithmic growth trend (p < 0.1) at each BLG and CLG position. Although similar temporal trends in soil erosion and infiltration rates were observed, values clearly differed between BLG and CLG upstream catchment areas. Furthermore, Darcy–Weisbach friction factor (f) values in the CLG upstream catchment area were higher than the corresponding BLG area. In contrast to the BLG upstream catchment area, lower ΔEu and higher soil erosion rates were observed in the CLG upstream catchment area as a result of soil disturbances. This indicated that intensive land use changes accelerate soil erosion rates in upstream catchment areas of bank gullies and increase soil sediment transport to downstream gullies. Accordingly, reducing tillage disturbances and increasing vegetation cover in upstream catchment areas of bank gullies are essential in the dry-hot valley region of Southwest China. 相似文献
15.
Nearly 4 million hectares of land in India is affected by rill and gully erosion. It is a severe form of soil erosion rendering vast tracts of lands into wastelands giving rise to the formation of badlands. Rate of land degradation through gullying is triggered recently due to the ill-advised landuse practices all over the country. The study area represents one such badland locality along the banks of Pravara river and two of its tributaries in the Deccan trap region, Maharashtra. The area is extensively reclaimed in the last two decades for agricultural practices. The rates in the cross profile changes as well as land lowering were measured with the help of a self fabricated micro-profilometer and erosion pin method. Five first order gullies were monitored using the micro-profilometer. Results of the micro-profilometer technique reveal considerable changes in the cross-sectional areas of individual gullies in this area, which shows the dynamic soil removal mechanism operating in this region. In addition to this, two well developed gully catchments were surveyed using a theodolite and erosion pins were installed in these basins in May 2007. After one year, the exposed pinheads were measured and net gain and net loss in the volume of the sediments were calculated for both the basins. The same practice continued in May 2009. After two years of monitoring the sediment yields were calculated. Average of these two years indicates an annual sediment yield of 1.79 kg/m 2 for sample basin 1 and 0.76 kg/m 2 for sample basin 2. The calculated yield was compared with the threshold values of soil tolerance limits and it was found that the area has crossed the threshold limit of soil tolerance. 相似文献
16.
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. 相似文献
17.
A newly opened excavation in the Cassina beds of the Lower Meride Limestone (Monte San Giorgio UNESCO World Heritage List, Canton Ticino, Switzerland), has yielded a pachypleurosaurid (Reptilia: Sauropterygia) specimen which is identified as Neusticosaurus peyeri. The resulting co-occurrence of N. peyeri and N. edwardsii, the latter so far regarded as the sole species of the genus present in this horizon, challenges the hypothesis of a single anagenetic lineage in Neusticosaurus species from Monte San Giorgio. In addition, it leads to a reconsideration of the phylogenetic inferences about Neusticosaurus evolution in the Monte San Giorgio area. The stratigraphic distribution of the Neusticosaurus species in the Monte San Giorgio basin is updated on the basis of recent finds. 相似文献
18.
Flash flood forecasting of catchment systems is one of the challenges especially in the arid ungauged basins. This study is attempted to estimate the relationship between rainfall and runoff and also to provide flash flood hazard warnings for ungauged basins based on the hydrological characteristics using geographic information system (GIS). Morphometric characteristics of drainage basins provide a means for describing the hydrological behavior of a basin. The study examined the morphometric parameters of Wadi Rabigh with emphasis on its implication for hydrologic processes through the integration analysis between morphometric parameters and GIS techniques. Data for this study were obtained from ASTER data for digital elevation model (DEM) with 30-m resolution, topographic map (1:50,000), and geological maps (1,250,000) which were subject to field confirmation. About 36 morphometric parameters were measured and calculated, and interlinked to produce nine effective parameters for the evaluation of the flash flood hazard degree of the study area. Based on nine effective morphometric parameters that directly influence on the hydrologic behavior of the Wadi through time of concentration, the flash flood hazard of the Rabigh basin and its subbasins was identified and classified into three groups (High, medium, and low hazard degree). The present work proved that the physiographic features of drainage basin contribute to the possibility of a flash flood hazard evaluation for any particular drainage area. The study provides details on the flash flood prone subbasins and the mitigation measures. This study also helps to plan rainwater harvesting and watershed management in the flash flood alert zones. Based on two historical data events of rainfall and the corresponding maximum flow rate, morphometric parameters and Stormwater Management and Design Aid software (SMADA 6), it could be to generate the hydrograph of Wadi Rabigh basin. As a result of the model applied to Wadi Rabigh basin, a rainfall event of a total of 22 mm with a duration of 5 h at the station nearby the study area, which has an exceedance probability of 50 % and return period around 2 years, produces a discharge volume of 15.2?×?10 6 m 3 at the delta, outlet of the basin, as 12.5 mm of the rainfall infiltrates (recharge). 相似文献
19.
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. 相似文献
20.
Riverine sediment load, a reflection of basin erosion and sediment yield, is influenced by both climatic and human factors. Complex interaction between various factors within a basin dampens and counteracts the forces that drive sediment variations. The gross human impact index and the index estimation method have both been proposed to reflect the impacts of human activities on soil erosion and sediment yield. Sediment load and daily rainfall data from 1955 to 2010 in the upper Yangtze basin, and in the Wu, Jialing, Min and Jinsha subbasins, were collected to assess the human versus climatic impacts on sediment yield. From 1955 to 2010, the average annual runoff in the study area was 428.2 billion m 3, and the average annual suspended sediment load was approximately 0.43 billion t. There was a critical point in 1984, 1985, 1991, 1993 and 1999 when the sediment load decreased in the Wu, Jialing, upper Yangtze, Min and Jinsha river, respectively. The annual regional rainfall erosivities in the upper Yangtze basin in most years ranged between 2,500 and 3,500 MJ mm hm ?2 h ?1 year ?1 and fluctuated around 3,000 MJ mm hm ?2 h ?1 year ?1 with a small coefficient of variation of 0.11. In the Jinsha subbasin, the index indicated that increasing rainfall erosivity could not account for the reduction in riverine sediment load and that anthropogenic erosion-control measures played a key role. The index values for the Min, Jialing and Wu subbasins ranged from 76 to 97 % and for the upper Yangtze basin is 95 %, demonstrating the joint effects of precipitation and human activities in all basins, with erosion-controlling measures playing a major role in sediment load reduction. 相似文献
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