Gully Development Research Articles

Sediment source and volume of soil erosion in a gully system using UAV photogrammetry

Gully erosion is a severe way of land degradation. Gullies threaten the sustainability of agro-ecosystems, causing quantitative and qualitative reduction of groundwater, farmland productivity, and waterways sedimentation. Since the gully development on the surface begins with water flow and sheet erosion, accurate monitoring of the erosive processes in a gully system and its quantification is key for the development of effective strategies to control soil erosion in gullies. Here, we demonstrate the first use of unmanned aerial vehicle (UAV) [...]

Spatial differentiation of gully clusters based on the regional scale: an example from northeastern China.

Gully erosion represents a serious environmental threat around the world, but their spatial distribution law are unclear at the regional scale. To quantitatively characterize the spatial distribution model of gullies and determine the regularity of regional differentiation, this paper used spatial analyst and statistics method to study the spatial distribution of gullies in 34 sample areas of northeastern China based on interpretations of high-resolution remote sensing images. The results showed that the kernel density could quantitatively describe the continuous spatial clustering of gullies. Gullies in northeastern China had the characteristics of a spatially unbalanced distribution at the scale of the sample area. The average kernel density of the 34 sample areas (Moran’s I was 0.43, P¡0.01P < 0.01) also indicated clustering distribution at the regional scale. The horizontal clustering characteristics of gullies exhibited an azonal distribution of being low values in the middle plain and high values on the three mountainous areas. The average kernel density in the southeastern part of the study area was highest (maximum value of 2.38). In the vertical direction, gullies were relatively undeveloped in low- and high-altitude areas, while middle-altitude areas were beneficial to the development of gullies. The effect of height differences on gully development was more significant than altitude. As the height difference increased, gullies tended to be more clustered, which can be expressed by a power function. The results of this study will not only help to understand the regional differentiation characteristics of gullies but will also provide a scientific reference for the study of spatial distribution of gullies in future.

Novel Ensemble of Multivariate Adaptive Regression Spline with Spatial Logistic Regression and Boosted Regression Tree for Gully Erosion Susceptibility

The extreme form of land degradation through different forms of erosion is one of the major problems in sub-tropical monsoon dominated region. The formation and development of gullies is the dominant form or active process of erosion in this region. So, identification of erosion prone regions is necessary for escaping this type of situation and maintaining the correspondence between different spheres of the environment. The major goal of this study is to evaluate the gully erosion susceptibility in the rugged topography of the Hinglo River Basin of eastern India, which ultimately contributes to sustainable land management practices. Due to the nature of data instability, the weakness of the classifier andthe ability to handle data, the accuracy of a single method is not very high. Thus, in this study, a novel resampling algorithm was considered to increase the robustness of the classifier and its accuracy. Gully erosion susceptibility maps have been prepared using boosted regression trees (BRT), multivariate adaptive regression spline (MARS) and spatial logistic regression (SLR) with proposed resampling techniques. The re-sampling algorithm was able to increase the efficiency of all predicted models by improving the nature of the classifier. Each variable in the gully inventory map was randomly allocated with 5-fold cross validation, 10-fold cross validation, bootstrap and optimism bootstrap, while each consisted of 30% of the database. The ensemble model was tested using 70% and validated with the other 30% using the K-fold cross validation (CV) method to evaluate the influence of the random selection of training and validation database. Here, all resampling methods are associated with higher accuracy, but SLR bootstrap optimism is more optimal than any other methods according to its robust nature. The AUC values of BRT optimism bootstrap, MARS optimism bootstrap and SLR optimism bootstrap are 87.40%, 90.40% and 90.60%, respectively. According to the SLR optimism bootstrap, the 107,771 km2 (27.51%) area of this region is associated with a very high to high susceptible to gully erosion. This potential developmental area of the gully was found primarily in the Hinglo River Basin, where lateral exposure was mainly observed with scarce vegetation. The outcome of this work can help policy-makers to implement remedial measures to minimize the damage caused by erosion of the gully.

UAV and LiDAR Data in the Service of Bank Gully Erosion Measurement in Rambla de Algeciras Lakeshore

The Rambla de Algeciras lake in Murcia is a reservoir for drinking water and contributes to the reduction of flooding. With a semi-arid climate and a very friable nature of the geological formations at the lakeshore level, the emergence and development of bank gullies is favored and poses a problem of silting of the dam. A study was conducted on these lakeshores to estimate the sediment input from the bank gullies. In 2018, three gullies of different types were the subject of three UAV photography missions to model in high resolution their low topographic change, using the SfM-MVS photogrammetry method. The combination of two configurations of nadir and oblique photography allowed us to obtain a complete high-resolution modeling of complex bank gullies with overhangs, as it was the case in site 3. To study annual lakeshore variability and sediment dynamics we used LiDAR data from the PNOA project taken in 2009 and 2016. For a better error analysis of UAV photogrammetry data we compared spatially variable and uniform uncertainty models, while taking into account the different sources of error. For LiDAR data, on the other hand, we used a spatially uniform error model. Depending on the geomorphology of the gullies and the configuration of the data capture, we chose the most appropriate method to detect geomorphological changes on the surfaces of the bank gullies. At site 3 the gully topography is complex, so we performed a 3D distance calculation between point clouds using the M3C2 algorithm to estimate the sediment budget. On sites 1 and 2 we used the DoD technique to estimate the sediment budget as it was the case for the LiDAR data. The results of the LiDAR and UAV data reveal significant lakeshore erosion activity by bank gullies since the annual inflow from the banks is estimated at 39 T/ha/year.

Indoor model test of red clay slope under evaporation-rainfall

Evaporation-rainfall is one of the main causes of red clay slope failure. In order to explore the evolution law and mechanism of red clay slope failure under evaporation-rainfall, this paper takes Guizhou red clay as the research object, establishes slope model in laboratory, and analyzes the failure characteristics, failure mode and failure mechanism of red clay slope under evaporation-rainfall. The test results show that the failure mode of red clay slope under evaporation-rainfall is: splash erosion and surface erosion stage → crack development stage → gully formation stage → gully development stage → local collapse stage → slope foot collapse stage. During the test, there is no obvious sliding surface on the slope. In the process of rainfall, the free water inside the slope converges to the foot of the slope under the action of gravity, which results in the maximum moisture content at the foot of the slope, and the strength of the soil decreases sharply. The local collapse occurs at the foot of the slope first. When several collapses are connected and the structure of the slope foot cannot support the weight of the upper shallow soil, the collapse occurs to the middle and upper part of the slope exhibition.

Monitoring long-term gully erosion and topographic thresholds in the marginal zone of the Chinese Loess Plateau

Gully erosion has been widely regarded as an extreme process of land degradation around the world. Gully development rate and topographic thresholds obtained by measuring the morphological parameters of multiple gullies and their influencing factors are important indicators used to characterize gully activity and potential locations of gully initiation. However, existing gully measurement and observation methods are time-consuming and labor-intensive, and usually only a single or several gullies can be measured at a time. The objectives of this study are to develop a multi-scale gully erosion monitoring method by combining unmanned aerial vehicle (UAV) technology with historical aerial photogrammetry and a field survey, achieve the measurement of gully morphological parameters (length, width, depth, area, width-depth ratio, cross-sectional area and volume) and environmental factors (land use, slope gradient and drainage basin area) for numerous gullies in larger regions, and finally, solve the issue of the accurate calculation of regional topographic thresholds and gully development rates. We applied a multi-scale gully erosion monitoring method in the marginal zone of the Chinese Loess Plateau to investigate the gully changes from 1959 to 2018 and further identified long-term gully development patterns and their main control factors. We identified 46 permanent gullies via a field survey. Long-term developments in 30 permanent gullies were obtained using historical aerial photographs and UAV images. The topographic threshold relationship between the upslope drainage basin area (A) and local slope gradient (S) was determined using the remaining 16 incipient gullies derived from UAV images. The results indicated that the gully dimensions experienced significant expansion; the linear gully-head retreat was considerably stronger than the gully widening and deepening. The contribution of the eroded volume from the gully-head retreat to the total eroded volume was 6.1 times that of the gully sidewall retreat, indicating that gully-head retreat was the primary mechanism for gully development during the study period. The area of the gully-head drainage basin played a more significant role than the slope gradient and land use to explain the gully-head retreat. The S-A topographic threshold relationship was S = 0.0478A−0.4915, implying that overland flow erosion was the dominant gully erosion process in the study area. Our results provide the gully development rate and topographic threshold relationship in the marginal zone of the Loess Plateau and clarify the potential location of gully development, while proposing that effective reduction of the drainage basin area can aid in curbing gully erosion. This study suggests a multi-scale gully erosion monitoring method for rapidly and precisely obtaining long-term gully development characteristics in various regions.

Spatial variation of gully development in the loess plateau of China based on the morphological perspective

Gullies characterized by frequent material exchange have profoundly affected the loess landforms evolution in the Loess Plateau of China. Accompanying gully development, various types of gullies have shaped the distinctive loess landforms. Thus, the spatial variations of gully morphology map the regional differences of gully development and loess landforms. Based on 6 key test areas with 5 m resolution DEM and 156 evenly distributed test areas with 25 m resolution DEM, a comprehensive gully-shape index system of topographic feature points, lines, and surfaces was constructed to describe spatial differences of the gully development. After comparing gully-shape indexes in the key test areas, an obvious correlation existed between these indexes and loess landform types. The gully development degree was low in Shenmu and Chunhua, high in Suide, Yanchuan, and Ganquan, while Yijun lay in-between. Using the method of Universal Kriging interpolation, a series of spatial interpolation maps of the gully-shape indexes were obtained, which revealed gully development degree in the whole Loess Plateau. Overall, The active areas of gully development were basically distributed along loess hilly ridges, loess hills, loess ridges, and in a few medium mountain areas, while the inactive areas were basically distributed in the thin loess coverage areas, including plains, river terraces, aeolian dunes, and a few loess platforms. Finally, the gully development regionalization was realized, which contained 6 subzones. These results provided significant references for loess landform research and soil erosion management in the Loess Plateau.

Evaluation of gully development over several years using GIS and fractal analysis: a case study of the Palmital watershed, Minas Gerais (Brazil)

Soil erosion affects agricultural production by reducing the area of rural properties and altering the dynamics of watersheds. Gullies are a complex and irregular type of erosion form that can reach large dimensions, and studying gullies to stabilize erosion processes is a challenge. This study aims to understand their environmental relationships as a basis for future research and to recover land degraded by soil erosion. We combined mapping techniques using geographic information system (GIS) with temporal evolution of land use and fractal dimensions of gullies using FracLac to determine the stability of gullies in a watershed in south Minas Gerais (Brazil). We used R software to apply linear regressions and tested the statistics to verify the compatibility of the model. Environmental characteristics of the watershed contribute to the formation of gullies, but human activities influence the deflagration of these features. The temporal evolution of the land use demonstrated that nearly 50% of the watershed was used as pastures throughout the years, which contributed to soil degradation. The evolution of the fractal dimension showed fluctuations over the years, indicating that the gullies are not stable. The regressions suggest that the vegetation, geology, land use, channel order, and curvature may influence the fractal dimensions of gullies. We concluded that human activity influences the evolution of gullies; the use of techniques such as vegetation measures can contribute to the stabilization of gullies. We also concluded that fractal analysis is an interesting tool for performing environmental evaluations of irregular and complex features, such as gullies.

Gully formation in headwater catchments under sugarcane agriculture in Brazil

Gully development following agricultural land use change is well documented in many tropical developing countries. However, the impact of specific agricultural intensification practices on gully formation, such as the construction of unpaved roads and contour terracing, remains poorly understood. We studied gully formation in catchments with sugarcane agriculture to inform sustainable agricultural management in Brazil. Through field surveys in ten first-to second-order catchments, we mapped erosional features and described gullying along an incision gradient from rill, to ephemeral and permanent gullies. We documented formation of >130 erosional features that concentrated mainly (96%) on dirt roads along the outer margins of streamside vegetation and bordering transitions from hillslope to hollow. We further established a slope-contributing area threshold for gullying, highlighting high susceptibility to gully formation on dirt roads and contour terraces. Key implications of our findings include targeted enhancements of riparian buffers that extend beyond concave topographies as well as the use of topographic thresholds as a benchmark for gully formation along dirt roads in Brazilian sugarcane fields.

Determining Causes of Gully Erosion and Associated Rates of Change in South-East Nigeria, using a Remote Sensing and GIS Methodology

The study of gully development on a regional scale is currently threatened by the intrinsic costs associated with steady field tracking and monitoring and the lack of historic measurements to perform time series analysis. The research objective is to develop a low-cost GIS and Remote Sensing methodology for monitoring and quantifying gully erosion and development over time, identifying the impact and incorporating analysis of environmental factors and land use change. The analysis of study area topography at 30 m resolution reveals 85% of the surveyed gullies develop on concave slopes with high values of 6 plan curvatures and >50 inclines. Results also reveal high association with ferralsols soils. Statistical analysis to determine significance of variables on the proportional yearly gully change in metre squared per square metre were conducted via principle component analysis. The analysis of this work was restricted to the time periods 2006/7, 2009/10 and 2014/15. The approach did not report any existence of one singular driver of erosion across the studied years and multiple sites confirming the complexity of gullies. The PCA showed that the level of variance explained in the yearly gully change variable was most similar in PC1 (representing the component with the highest eigenvalue) to Vegetation loss, Vegetation loss and slope in the respective years. The study offers a method of monitoring gully development from early stage to maturity and exemplifies the complexity and variability of erosion drivers in the SE Nigeria region. It presents a verified approach to local and regional monitoring of gullies, enacted through use of low budget/computing cost remote sensing and classification technologies and serves to embolden civilian and governmental efforts to manage the societal and environmental menace of gully erosion.

Assessment of gully development using geomorphic change detection between pre- and post-urbanization scenarios

Urbanization processes have caused changes in the runoff behavior, especially by impervious surfaces produced by paving and buildings. Impermeable surfaces prevent the infiltration of rainwater, increasing the volume and speed of runoff. Besides, inadequate urban planning coupled with heavy rains promotes the evolution of erosion processes, especially in peri-urban areas. This research aims to identify spatial patterns of geomorphic change in the gully areas due to urbanization in the city of Jacarei (SP). The methodology has the following steps: (1) elaboration of the Digital Elevation Model (DEM) from stereophotogrammetric techniques; (2) elaboration of the pre- and post-urbanization DEM; (3) extraction of contributing area using the D-Infinity method and of the topographic indices (topographic wetness, stream power, and compound topographic); and (4) calculate the difference between the pre- and post-urbanization topographic attributes. The preparation of the pre- and post-urbanization DEM used the MATCH-T DSM and DTMaster modules, both belonging to the INPHO system. Photogrammetric techniques allow the generation of digital models suitable for hydrological studies. The urbanization exposed an evident influence on the triggering of erosion, evidencing an increase of all topographic indices in areas that develop gullies.

Multitemporal Analysis of Gully Erosion in Olive Groves by Means of Digital Elevation Models Obtained with Aerial Photogrammetric and LiDAR Data

Gully erosion is one of the main processes of soil degradation, representing 50%–90% of total erosion at basin scales. Thus, its precise characterization has received growing attention in recent years. Geomatics techniques, mainly photogrammetry and LiDAR, can support the quantitative analysis of gully development. This paper deals with the application of these techniques using aerial photographs and airborne LiDAR data available from public database servers to identify and quantify gully erosion through a long period (1980–2016) in an area of 7.5 km2 in olive groves. Several historical flights (1980, 1996, 2001, 2005, 2009, 2011, 2013 and 2016) were aligned in a common coordinate reference system with the LiDAR point cloud, and then, digital surface models (DSMs) and orthophotographs were obtained. Next, the analysis of the DSM of differences (DoDs) allowed the identification of gullies, the calculation of the affected areas as well as the estimation of height differences and volumes between models. These analyses result in an average depletion of 0.50 m and volume loss of 85000 m3 in the gully area, with some periods (2009–2011 and 2011–2013) showing rates of 10,000–20,000 m3/year (20–40 t/ha*year). The manual edition of DSMs in order to obtain digital elevation models (DTMs) in a detailed sector has facilitated an analysis of the influence of this operation on the erosion calculations, finding that it is not significant except in gully areas with a very steep shape.

Effect of joint structure and slope direction on the development of collapsing gully in tuffaceous sandstone area in South China

This study focuses on the collapsing gullies in tuffaceous sandstone area and investigates the slope direction and morphological characteristics of the main and branch gullies. Furthermore, we assess the structural characteristics of the rock joints within this area, including their strike, dip direction and dip angle. The results show that there are 405 collapsing gullies in the study area. The slope directions associated with collapsing gullies and the directions of the main gullies largely fall within the ranges of NE20°-NE90°, SE90°-SE160°, SW240°-SW270°, and NW270°-NW290°. The collapsing gullies include 1103 branch gullies in total, most of which have directions that fall within the ranges of NE20°-NE40°, NE50°-NE70°, NW280°-NW300°, and NW330°-NW350°. The joints in the bedrock are directional and regional, and they can be divided into two main groups. The number of southward dip directions is greater than the number of northward dip directions, and most of the measured dip angles are greater than 60°. The mean dip angle is greatest for joints with measured strike values of NW280°-NW290°, with a value of 85.2°. The development of collapse gullies is affected by both the slope direction and joints. The slope direction determines the direction of the main gullies, with a correlation coefficient of 0.809 (P<0.01). The branch gullies are mainly affected by joints, with a correlation coefficient of 0.876 (P<0.01). The joint structure also influences the degree of development of the collapsing gullies, and the average depth of the gullies that parallel the dominant joint orientation is significantly larger than that of gullies with other directions. Moreover, the average depth of the gullies associated with the dip angle of 85.2° measured relative to the joint strike is 6.89 m, which is significantly greater than that associated with lower dip angles. The dip angles of joints have an important effect on the infiltration of water, and high dip angles accelerate the erosion associated with collapsing gullies.

Using high-resolution aerial images to study gully development at the regional scale in southern China

There are 239,100 gullies in southern China, which cause the degradation of ecological system. However, studies on gully development at the regional scale is relatively lack. The purpose of this study is to analyze the regional gully dynamics and explore how land use and topographic factors affect gully development. Input data consists of land use maps derived from high-resolution images from 2004 to 2014, and topography maps from a digital elevation model with a pixel size of 8 m × 8 m in two 25-km2 study sites of Anxi (AX) and Xingning county (XN). The following results were obtained: (1) AX gullies decreased from 2006 to 2014 while XN first increased from 2004 to 2009, and then decreased from 2009 to 2014. Both AX and XN gully area in percentage of the total area ranged from 1% to 3%, which was higher than the average 0.25% of the whole southern China by the artificial survey in 2005. (2) Most of AX and XN gullies occurred along the ridgeline and had the close relationships with the upstream contributing area and slope gradient. (3) New gullies developed on the exposed land and forestland. The lost gullies were converted into forestland and grassland. In fact, most of these gullies were only covered by vegetation, not real disappearance. These results proved that gully decreased, but construction of roads and buildings intensified gully development. Consequently, these findings reveal that vegetation protection and ecological restoration should be adopted in southern China.

Land-Cover Removal and Gully Development in Southeast Nigeria: A 30-Year Analysis with Pixel and OBIA Approaches in Juxtaposition

In this study a study of gully erosion in southeast Nigeria is presented. The study of gully development on a regional scale is currently undermined by the inherent costs associated with consistent field monitoring and the lack of historic measurements to perform time series analysis. As a result, there are very few studies which implement long term analyses of gullies in the region as a collective. Consequently, the building of knowledge of the role of environmental changes on the development of gullies is inhibited. Remote sensing methodologies, via the Landsat archive, are used as low economic data source that assisted in the analyses of gullies over the time period 1986 to 2015. The Landsat data is used to establish land cover changes over the time period, via pixel and object-based classification, to identify its role in gully development. The use of classification for this purpose identifies this study as a first of its kind in Nigeria. Aiming to link environmental characteristics and land cover changes with gully development and erosion rates at multiple current locations. In terms of the correlation between vegetation area and gully/openland development, Pixel based classification produced a correlation of r = -0.9 (p<0.05). A similar strength of correlation was exhibited for OBIA with r = -0.9 (p<0.05) with both results indicating a very strong and significant negative correlation between the amount of vegetated area and Gully/open-land development over the study period 1986-2015.

The impact of hydrogeomorphological characteristics on gullying processes in erosion-prone geological units in parts of southeast Nigeria

ABSTRACT Hydrogeomorphic factors were suspected to contribute to the persistent gully erosion taking place in Nanka, Ogwashi and Benin formations underlying the southern Anambra State, Nigeria. Therefore, this study investigated the impact of hydrology and geomorphology on gully development and expansion in this area using integrated field survey, hydrological, geotechnical and geomorphological approaches. Field survey and hydrological results revealed that the study area is characterized by numerous surface water bodies and shallow groundwater systems. Both the surface waters and groundwater have a westward flow direction, from areas of high elevations on the Nanka Formation to areas of low elevations on the Ogwashi and Benin formations. Geotechnical results revealed that the soils are permeable, weak, easily dispersible and collapsible. Geomorphological analysis showed that the area is characterized by uneven badland topography, high gully slope gradients, concave slopes, poor land-use practices, and low vegetation cover. Generally, the results of this study indicated that hydrogeomorphology and soil engineering properties substantially influence the gullying processes in the area. However, areas underlain by the Nanka Formation have higher gullying intensity than in areas underlain by the Ogwashi and Benin formations due to variations in their hydrogeomorphological characteristics.

Head-cut gully erosion susceptibility modelling based on ensemble Random Forest with oblique decision trees in Fareghan watershed, Iran

Gully erosion is the most active hydro-geomorphological phenomenon in the continental areas due to the high erosion rates triggered by the gully system. Monitoring and modelling gully development and gully distribution will contribute to understand landforms evolution and risk assessment. The purpose of the current research is to model head-cut gully erosion susceptibility (HCGES) using support vector machine (SVM), random forest (RF) and novel ensemble model of random forest with four Oblique methods (Logistic Regression, Ridge Regression, Partial least squares (PLS) and Support vector machine (SVM)) (hereafter called ensemble ORF) data mining models in Fareghan watershed, Hormozghan province, Iran. For this purpose, 14 variables influencing the gully development, were prepared and 145 head-cut gully erosion locations were identified in the study area. The efficiency of SVM, RF, ensemble ORF were evaluated based on receiver operating characteristic (ROC), the results have shown that all these three models are highly accurate and robust in predicting the head-cut gully erosion susceptibility zones. The results of the models were evaluated based on the area under the receiver operatic characteristic curve (AUC) in the validation stage presented that the efficiency of these models are 0.91, 0.94, and 0.96, respectively. Altitude and distance from the road in all three models were more important than other variables. The findings of this research will contribute to develop gully control strategies and to prevent the gully initiation where gully erosion is more susceptible.

Morphological signature of gully development by rapid slide retrogression in a layered coarse-grained delta foreslope

Abstract Coarse-grained deltas are often characterized by steep foreslopes (often more than 10°) that are traversed by delta-front channels. The channels thus erode into relatively steeply inclined bedding. In this context, the slopes flanking the channels can be steeper than the friction angle since they include a component of dip related to the delta-front slope as well as the channel-related erosion slope. In this study, part of the Busu River delta (Papua New Guinea) was imaged using a high-resolution multibeam bathymetry survey over an area where the angle of the slopes flanking the channels locally reaches 50°. A detailed analysis of the delta slope morphology has revealed an additional source of instability due to erosion within the main channels. In some places, erosion cuts into the channel flank forming a local knickpoint inclined in a direction approaching that of the bed dip. The cut can then initiate breaching or static liquefaction failure from that point up to the crest of the interfluve resulting in a V-shaped gully.

Gully Head-Cut Distribution Modeling Using Machine Learning Methods—A Case Study of N.W. Iran

To more effectively prevent and manage the scourge of gully erosion in arid and semi-arid regions, we present a novel-ensemble intelligence approach—bagging-based alternating decision-tree classifier (bagging-ADTree)—and use it to model a landscape’s susceptibility to gully erosion based on 18 gully-erosion conditioning factors. The model’s goodness-of-fit and prediction performance are compared to three other machine learning algorithms (single alternating decision tree, rotational-forest-based alternating decision tree (RF-ADTree), and benchmark logistic regression). To achieve this, a gully-erosion inventory was created for the study area, the Chah Mousi watershed, Iran by combining archival records containing reports of gully erosion, remotely sensed data from Google Earth, and geolocated sites of gully head-cuts gathered in a field survey. A total of 119 gully head-cuts were identified and mapped. To train the models’ analysis and prediction capabilities, 83 head-cuts (70% of the total) and the corresponding measures of the conditioning factors were input into each model. The results from the models were validated using the data pertaining to the remaining 36 gully locations (30%). Next, the frequency ratio is used to identify which conditioning-factor classes have the strongest correlation with gully erosion. Using random-forest modeling, the relative importance of each of the conditioning factors was determined. Based on the random-forest results, the top eight factors in this study area are distance-to-road, drainage density, distance-to-stream, LU/LC, annual precipitation, topographic wetness index, NDVI, and elevation. Finally, based on goodness-of-fit and AUROC of the success rate curve (SRC) and prediction rate curve (PRC), the results indicate that the bagging-ADTree ensemble model had the best performance, with SRC (0.964) and PRC (0.978). RF-ADTree (SRC = 0.952 and PRC = 0.971), ADTree (SRC = 0.926 and PRC = 0.965), and LR (SRC = 0.867 and PRC = 0.870) were the subsequent best performers. The results also indicate that bagging and RF, as meta-classifiers, improved the performance of the ADTree model as a base classifier. The bagging-ADTree model’s results indicate that 24.28% of the study area is classified as having high and very high susceptibility to gully erosion. The new ensemble model accurately identified the areas that are susceptible to gully erosion based on the past patterns of formation, but it also provides highly accurate predictions of future gully development. The novel ensemble method introduced in this research is recommended for use to evaluate the patterns of gullying in arid and semi-arid environments and can effectively identify the most salient conditioning factors that promote the development and expansion of gullies in erosion-susceptible environments.

Investigation of physical factors influencing permanent gully development in southern Gombe state, Northeast Nigeria

The incidence of gully erosion in Gombe state is a vexed issue. It is a common occurrence and effects have reached alarming proportions and have directly affected the socioeconomic life of the people. Despite the growing concern, the evaluations of permanent gullies in the State are scarce. Assessments of contributing factors in the area have focused on human component while the physical factors are underestimated. The aim of this paper was to investigate physical factors influencing permanent gully development in southern Gombe state, Northeastern Nigeria. The study based on geomorphological study of four catchments prone to gully erosion. Gully geometric growth was observed during onset, wet, and cessation periods of rainfall. Field observation revealed that a combination of gully bank erosion processes and gully bed basal sapping are found to enhance gully development. The association between gully recession and observed physical factors (rainfall volume, slope, and runoff-contributing area) was determined using univariate analysis. The results showed significant relationship between slope of gully head and linear retreat during onset (r = 0.55) and cessation (r = 0.40) periods. Similarly, rainfall volume and gully head retreat showed a strong relationship in the onset (r = 0.0.59) and moderate during cessation period (r = 0.34). Strong and positive relationship was observed between total gully head retreat and the runoff-contributing area (r = 0.62), while maximum gully activity took place in the onset (65%) period. These results indicate that permanent gully development in the study area have a strong relationship with physical factors.