Gully Sites Research Articles

Applying the Parameters of Impacted Population and Gully Social Impact Factor to Prioritize Choice of Gully Erosion Intervention Programs in Resource Limited Settings: Lessons from World Bank Funded Intervention in Anambra State, Nigeria

Background: Following a presidential request for assistance in the gully erosion menacing many States in Nigeria, the World Bank intervened through the Nigeria Erosion and Watershed Management Program (NEWMAP) in 23 States including Anambra, from 2014 - 2022. This study examined NEWMAP’s intervention in order to learn crucial lessons to improve subsequent gully remediation interventions in Anambra State. Methods: A 7-man multidisciplinary focus group was constituted to study NEWMAP’s intervention in Anambra State, determine the most striking innovation in the intervention, and explore that innovation further. Data extraction, content analysis comparative analysis, rational decision framework and the deductive model were applied to make findings and draw conclusion. Results: The study found that: (i) the most striking innovation in NEWMAP’s intervention in Anambra State is the introduction of elaborate and comprehensive package of rehabilitation of impacted population. (ii). 13 major gully erosion sites were remedied totaling 32 544.87 meters long and directly impacting a population of 163 209 persons (iii). As at June 2021, 150 000 impacted population had benefitted from micro-credit grants to engage in alternative livelihood businesses that contributed in revamping the State’s economy. (iv). The 13 gully sites remedied had a wide range of gully social impact factor, the highest three values being 101 440; 67 587.5 and 41 778; while the lowest three values are 1 204; 1 694.7 and 3 186. Conclusion: The study concludes that elaborate and comprehensive package of rehabilitation of gully impacted population is an innovation in Anambra State introduced by NEWMAP; that gully impacted population is a good measure of vulnerability; and that the parameters of impacted population and gully social impact factor are sensitive, reliable and effective parameters to prioritize choice of gully intervention programs in resource-limited settings.

GEOTECHNICAL INVESTIGATION OF GULLY EROSION SITES IN UMUALO VILLAGE, UDI LGA, ENUGU STATE SOUTHEASTERN NIGERIA

GEOTECHNICAL INVESTIGATION OF GULLY EROSION SITES IN UMUALO VILLAGE, UDI LGA, ENUGU STATE SOUTHEASTERN NIGERIA

Effects of Time and Land Use Land Cover Change (LULCC) in the Dimension of the Gully Expansion and Soil Particles Loss at Ibeziako Erosion Site in Nsukka Urban, Enugu State, Nigeria

Almost all parts of the world are threatened by one type of hazards such as soil erosion, flooding, landslide, earthquake, among others. Various types of soil erosion exist which include splash, sheet, rill and gully erosion. Gully erosion has been recognized as an important environmental threat in many parts of the world and remains the world’s biggest problem affecting the lives of man, plants and animals. Gully erosion occurs in various parts of Nigeria under geologic, climatic and soil conditions. The purpose of this study is to look at flood and soil erosion in Nsukka Urban and the erosive activities of the floods along its path ways. The study used both primary and secondary data comprising measurements, oral interviews, photographs, and satellite imageries. This study adopted a mixed method approach in data analysis and representation with ArcGIS version 10.4 software as the major analytical tool used, other calculations were either manually performed or were calculated using Microsoft Excel 2007.The results of the satellite imageries analyzed, were rendered in tables and maps. The soil particles removed from the identified gully site in the study area were calculated and projection of further annual soil loss established, pending when the erosion problem will be addressed. The management, control of flood and soil erosion required to reduce and mitigate against the adverse effect of the gullying were also proffered.

Gully Morphological Assessment and Anthropogenic Determinants in Urban and Rural Settlements of Upper Imo River Basin (UIRB) South Eastern Nigeria

Gully erosion have been proven to vary both in terms of size and number in urban and rural settlements and is caused by factors related to both human and natural phenomenon. This study assessed the gully morphological development in an urban and rural settlement with the view of finding the settlement that is more vulnerable to gully erosion development. It investigated gully development in the urban and rural settlements of UIRB; gully morphological features in settlements; and the anthropogenic factors of gully development in urban and rural settlements. A reconnaissance survey was carried out in 2016, while a detailed field survey on the sampled locations and gully sites was carried out from 2017 till early 2019. Two types of data were employed in this study. They were primary and secondary (archival) data. The secondary data set used for this study was obtained from maps (topographical and lithological) and satellite imageries obtained from USSG. Primary data used for the study were grouped into two-gully morphological data and anthropogenic data. The two data sets were obtained through field measurement, digital image analysis, and a questionnaire survey. The morphological data considered are gully length, width, depth, area slope, and elevation, while anthropogenic data involves human economic activities. The sampling technique employed was randomized systematic sampling. Three major factors considered in the course of sampling were settlement type, the number of second-order basins located within the various settlements of the upper Imo River basin, and several gullies located in the settlements of UIRB. Considering these factors 18 gully sites were randomly sampled from gullied second-order basins. Data analysis makes use of percentages, measures of variations, t-tests, and levene statistics. Results of the analysis showed that gully erosion in UIRB develops both in urban and rural settlements. 61.1% of the gullies develop in rural settlements, while 39.9% 0f the gullies develop in urban settlements. The total length, width, and area of the sampled gully sites in Upper Imo River were 6213.2 m, 1931.1, and 330,005.6 m2 (330 km2) respectively. Out of these values, the total length, width, and area found in the rural area was 3,539.2, 863.5 m, and 91,767 m2 (91.8 km2) respectively, while the total length, width, and area in the urban area was 2,674, 1,067.9 m and 238,238.4 m2 (238.2 km2) respectively. The slope where gullies are located in rural areas ranges between 84.4-89.8%, while the slope where gullies are located in urban areas of UIRB ranges between 89.4-89.7%. The elevation where gullies develop in rural areas falls between 55-142 m, while the elevation where gullies are located in urban areas ranges from 55-89.9 m. In terms of number, more gullies are fun in rural settlements than in urban settlements, but in terms of intensity and threat, they are higher in rural areas than in urban areas. Failed road construction was the major factor of gully erosion initiation and development in the urban areas, while sand mining was the major factor of gully erosion in the rural areas of the upper Imo River basin. The two major contributors to gully erosion development in the urban area were failed road construction and sand mining, while the two least contributing factors of gully erosion in the urban areas of the study area were stone mining and farming activities.

The use of Remote Sensing and GIS Methodology in the Analysis of Urualla Gully Erosion site Imo State Nigeria

The study of Urualla gully erosion is currently undermined by the inherent costs associated with consistent field monitoring and the lack of historic measurements to perform time series analysis. Remote sensing methodologies, via the Landsat archive, are used as a low-cost data source to allow analyses of gullies over the time period 2006 to 2021. In conjunction with longterm environmental variables, the Landsat data is used to establish land cover changes over the time period, via pixel-based classification, to identify its role in gully development. Aiming to link environmental characteristics and land cover changes with Urualla gully development and its rates of change, Digital Elevation Models (DEM) and remote sensing imagery are used to detect topographical and landscape characteristics and to calculate gully dimensions. Landscape analysis over the study period reveals a steady increase in Gully/Open land. The increasing area of Urualla gully consistently correlates with vegetation loss, (r= -0.97 (p<0.05)) and also, when correlated with Built-Up Area over the same period of time, the correlation shows (r= 0.97 (p<0.05). Analysis of study area topography at 30m resolution reveals that Urualla gully site developed on high slope of more than 400 . The study offers a method of monitoring Urualla gully development from early stage to maturity and exemplifies the complexity and variability of erosion drivers in the study area. It presents a verified approach in the 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.

Topo-edaphic, Vegetation Cover and Type Influence on Spatial Distribution of Gullies in Sengwa Wildlife Research Area (SWRA), North West Zimbabwe

Gully erosion is a common phenomenon in arid and semi-arid areas and is mostly influenced by soil type, topography, vegetation type and cover. The objective of the study was to determine the effect of topo-edaphic, vegetation type and cover on gully occurrence, hence map their spatial distribution in SWRA. A conventional method was used where field visit to known gully sites was done. At each site, GPS points were marked at three points, that is, at the head site, the middle and lower end of the gully. Soil samples, gully width, depth, length, vegetation type and cover were recorded for each point where GPS coordinates were collected. GPS points were overlaid on SWRA processed vegetation, soil and topographic map for analysis on the spatial distribution of gullies. Fifty-six gullies were recorded with highly affected areas on the southwestern side of the park. Associated soils types were clay and loam of the Madumabisa mudstone, colluvial and alluvial located at altitudes below 1000 meters. Gully occurrences were sighted more in mopane dominated woodlands with few recorded in areas dominated by acacia woodlands and on the edges of miombo woodlands, which occupy the high grounds of SWRA. Gully length varied from 20m in less developed gullies to 2520m for mature gullies with volumes ranging between 52m3 and 4649.4m3. Hence, topography, soil type, vegetation cover and type influence gully location and occurrence. Future research should aim to monitor changes in gully development using remote sensing as it provides a great potential for monitoring gully changes across the landscape.

EVALUATION OF SOIL PHYSICAL PROPERTY AS A DETERMINING FACTOR OF EROSION: A CASE STUDY OF BEHIND NIGERIA INSTITUTE OF LEATHER AND SCIENCE TECHNOLOGY, ZARIA

Soil Erosion is the detachment, transportation and deposition of soil sediment from one place to another. This has led to loss of lives and infrastructure in many parts of Nigeria. Soil properties play a role in it vulnerability and extent to erosion. This study aims to evaluate selected physical properties as they interact to cause erosion in the study area. The study was conducted in 2012 in a gully site in relation to its potential to erodibility of gully channel. This was done by collection of various soil samples at different depth followed by laboratory analysis to determine the plastic limit, moisture content and other engineering properties. The Results indicated that the soil samples have Atterberg limit that might be considered low, while liquid limit (LL) ranged from 25 – 30, the plasticity index (PI) ranged from 1 – 5%, which suggested that the soils are slightly plastic. Moisture content was moderate. The soil properties investigated played a major role in exacerbating the gully erosion in the area, therefore, the existing culvert should be redesigned and reconstructed taking appropriate consideration of the underlying soil properties

DETERMINATION OF THE SOCIO-ECONOMIC IMPACT OF GULLY EROSION IN KURMIN-GWARI SETTLEMENT

Sustainable development is the positive socio-economic change that does not undermine the ecological and social systems upon which communities and social systems are dependent. Land provides services to humans and other life forms as well as providing raw materials in production process. Land provides waste assimilation services as well as other ecosystem functions. The aim of this study is to assess the impact of gully erosion on the residents of Kurmin Gwari settlement, Kaduna State, Nigeria. The study intends to identify the percentage of the residents according to localities that have suffered socially and economically from gully incidents. It also intends to determine the relationship between adverse social and economic effects suffered by the affected people in the various localities of the study area. The Primary sources of data are direct observation from fieldwork and the use of questionnaire, while the secondary sources are topographic map and library materials. Descriptive statistical tools were applied to deal with the techniques of summarizing and describing data collected. Percentages, proportion and mean were applied to get expected frequencies. The result revealed that at Layin Pumpo 65% of respondents are affected by destruction of ancestral homeland by gully erosion. 100% are affected by loss of source of water supply. 72.5% find the gully site frightful. 92.5% experience trauma as a result of gully erosion in the area and 57.5% lost relatives. The study recommended that due to gully erosion and other natural environmental disasters, the need for an integrated environmental planning is paramount.

PRELIMINARY GULLY HAZARD ASSESSMENT USING 2D-ERT AND 2D-SRT GEOPHYSICAL SURVEYS: A CASE STUDY IN SOUTHEASTERN NIGERIA

Two-dimensional Electrical Resistivity Tomography (2DERT) and Seismic Refraction Tomography (2DSRT) were concurrently applied in assessment of a gully site with the view of assessing its stability and risk level. Eight profile lines oriented parallel and perpendicular to the boundary of the gully were surveyed. As a result, apparent resistivity model tomograms in the range of 1-9,000 and p-wave velocity models in the range of 300-700 were obtained from the two techniques respectively. Interpretation of the models obtained show predominance of unconsolidated clay, shale intercalates, clayey sand, sandy clay and weathered lateritic soil at shallow depths. Low amplitude undulating refracting layers, landslide slip subsurface and lose horizons were also delineated at shallow depths. The predominance of weak, clayey and unconsolidated lithology at the gully site suggests evidence of unstable gravitational equilibrium which imply environmental hazard. The plausible deductions made from the two

New Method for Automated Quantification of Vertical Spatio-Temporal Changes within Gully Cross-Sections Based on Very-High-Resolution Models

Gully erosion is one of the most prominent natural denudation processes of the Mediterranean. It causes significant soil degradation and sediment yield. Most traditional field methods for measurement of erosion-induced spatio-temporal changes are time and labor consuming, while their accuracy and precision are highly influenced by various factors. The main research question of this study was how the measurement approach of traditional field sampling methods can be automated and upgraded, while satisfying the required measurement accuracy. The VERTICAL method was developed as a fully automated raster-based method for detection and quantification of vertical spatio-temporal changes within a large number of gully cross-sections (GCs). The developed method was tested on the example of gully Santiš, located at Pag Island, Croatia. Repeat unmanned aerial vehicle (UAV) photogrammetry was used, as a cost-effective and practical method for the creation of very-high-resolution (VHR) digital surface models (DSMs) of the chosen gully site. A repeat aerophotogrammetric system (RAPS) was successfully assembled and integrated into one functional operating system. RAPS was successfully applied for derivation of interval (the two-year research period) DSMs (1.9 cm/pix) of gully Santiš with the accuracy of ±5 cm. VERTICAL generated and measured 2379 GCs, along the 110 m long thalweg of gully Santiš, within which 749 052 height points were sampled in total. VERTICAL proved to be a fast and reliable method for automated detection and calculation of spatio-temporal changes in a large number of GCs, which solved some significant shortcomings of traditional field methods. The versatility and adaptability of VERTICAL allow its application for other, similar scientific purposes, where multitemporal accurate measurement of spatio-temporal changes in GCs is required (e.g., river material dynamics, ice mass dynamics, tufa sedimentation and erosion).

A geotechnical approach to gully erosion control and management at Inyishi, Ikeduru L.G.A., Imo State, Nigeria

This research is aimed at appraising the root causes of gully erosion at Inyishi in Ikeduru Local Government Area of Imo State, Nigeria, and the possible geotechnical control and management techniques that could be applied in curbing the menace. In pursuance to these objectives, field and laboratory investigations were undertaken. The field works involved reconnaissance and chain surveys, and contouring of the gully catchments. It was observed that gullies were initiated in the research area by flow concentrations induced by environmental factors related to roads and aligned buildings constructed with inadequate drainage facilities upstream of the gully locations. Laboratory investigations carried out involved engineering analyses of soil samples collected at the gully sites and beds for the determination of the soils grain sizes, Atterberg limits, moisture content, specific gravity, permeability, shear strength and bulk density relations. A summary of the engineering properties of the soil revealed its poorly graded and sandy nature, its inadequate fine materials content, low liquid and plastic limits, which ranged between 35.80 to 42.20 % and 28.35 to 35.00 % respectively, as well as its low permeability index of 1 × 10-2cm/sec. These findings, coupled with the fact that the gully area was underlain with friable and cohesionless soil, with small time of concentration, which renders it easily disaggregated by runoff are pointers to the relative ease of water infiltration and seepage at the gully locations. The erosive power of the slope within the gully area was estimated by chain surveying of the entire catchment. The efficacy of natural local materials such as vetiver grass, wood shavings, palm kernel shells, coconut husk, bread fruit husk, dead plant mulch, etc. for the geotechnical works on gully erosion control and management was explored. General specifications on the geotechnics of managing the installed control works for their sustainable services were proffered.

A Study of the Dynamics of Soil Erosion Using Rusle2 Modelling and Geospatial Tool in Edda-Afikpo Mesas, South Eastern Nigeria

Abstract The Revised Universal Soil Loss Equation (RUSLE) was used to study the soil erosion processes in Edda-Afikpo mesas, Lower Cross River watersheds,Nigeria. The mesas occupy an area estimated at 60km2 on a surface relief of about 284m. DEM data, satellite images and basemap of the area were used. Remotely sensed data were ground-truthed through extensive field works. The results show that the process is facilitated by the Trifecta of hill slope hydrology, geology and land use practices. Steep hill Slope of values 78 % at the major hot spots, very fragile, dry and non-plastic sandy soils all aid sediment detachment. Analysis of the index properties which include Liquid Limit(LL) of 25-30,moisture content(w%) of 5.9-7.4,permeability of 1.541x10-3 – 1.636x10-3 cm/s and shear strength of 36-42 KN/m2 predispose the sediments to detachment and erosion. Based on the analysis, the amount of soil loss in the project area is about 1373.79 ton per year. Soil erosivity factor is high at the mesas(5023.83 MJ mm ha−1 h−1 yr−1 - 5069.51 MJ mm ha−1 h−1 yr−1) The sandy layer attain thickness of 50m-60m in places and with high pore pressure development, slope failure are triggered during intense storm events. In terms of vulnerability level in erosion risk, high to very high constitute 4.1% of the watershed which translate to 5.05km2 of the 59km2. The various processes occur simultaneously and are exacerbated by human factors through seasonal bush burning and development along drainage lines. The study reveals that 18.8% of the available land for development is at high to very high risk of erosion. The soil loss model has been validated and the hotspots from the map coincide with the gully sites. The results of this research can therefore be used for conservation and adaptation purposes.

Gully Erosion Problems in Selected Areas of Edo State: Factors and Control

Gully erosion is a serious ecological problem in Edo State and has negative impact on agricultural productivity, lives and properties in both urban and rural environments. This paper therefore aims at identifying factors contributing to the formation of gullies and methods of controlling them so that further environmental degradation would be averted. Three gully sites were selected from the three geo-political zones of the State. Data were collected through remote sensing, field topographical survey and soil sampling on gully walls and gully beds. Meteorological and hydrological data were also collected. Slope stability analysis was also carried out. The KerbyKirpich equation was applied to estimate the overall time of concentration and Rational formula used to determine the peak discharge. The study revealed that the selected study areas possess all the characteristics of an erosion prone area which are: rainfall of very high intensity, steep slopes resulting in large runoff and soil with low organic content and relatively low shear strength obtained from the geotechnical investigations. Results from the studies revealed that the gully width and depth varied considerably from top to bottom. The cross section shows that the gully is Ushaped for Ekehuan gully and V-shaped for Auchi and Ewu gullies, indicating a large catchment area and a large volume of discharge passing through the gully.

Anthropogenic alluvial sediments in North Carolina Piedmont gullies indicate swift geomorphic response to 18th century land-use practices

ABSTRACTGullies are common erosional features in the Piedmont of North Carolina that have often been studied as indicators of poor land-management practices. However, the timing of gully formation, and thus the specific practices that caused their formation, has been largely overlooked in the literature. Here, we use the timing of gully formation to examine the geomorphic and anthropogenic triggers for erosion in the Piedmont. To do this, we mapped 74 gullies in the landscape and found that most contained alluvium within the gully or in alluvial fans. Soil pits were dug at a subset of the gully sites (16 in alluvium, 1 in colluvium, and 1 upland comparison) and examined for soil development, organic content, and particle size. Seven charcoal fragments were sampled from the soil pits and were radiocarbon dated. Radiocarbon ages cluster in the late 1700s, which suggests that early European settlers had an immediate impact on the landscape through deforestation and agriculture. The swift response of the landscape to deforestation and agriculture indicates that the argillic Piedmont soils are pre-disposed to erosion. Our results highlight the importance of erosion prevention as reforested farmland is cleared during urban expansion.

Gully Erosion and Its Environmental Impact in Eke, Udi Local Government Area of Enugu State

This paper assessed the environmental impact of gully erosion in Eke, Udi Local Government Area of Enugu State, South East Nigeria. Data on the gully sites were collected using measuring instrument; observations were made with regards to the effects of the hazard on the study areas. Simple random sampling techniques were used to select respondents. A total of 150 questionnaires were returned out of 200 questionnaires distributed. Findings show that the gully in Enugu Eke has a mean cross-sectional dimension of 15.67 + 14.01m, that of Oma Eke 13.00 + 12.49m, while Ogui Eke has a mean cross-sectional dimension of 7.60 + 5.70m. From the mean values, differences was observed among the various study sites, however, with very high standard deviations and standard errors for Enugu Eke and Oma Eke, supported by the ANOVA results, having calculated F-value of 0.395, which is less than the critical F-value of 5.14, and the p-value of 0.69 > 0.05. The difference observed among the three study sites is not significant. Hence, the null hypothesis is accepted. The study revealed that the initiation and development of erosion gullies in the area is facilitated by natural (rainfall, topography, engineering geological properties of soil especially texture, etc) and anthropogenic factors especially road construction, excavation, drainage structure, farming, animal grazing. The study observed that gully erosion have caused a lot of pain and damage such as loss of life's, properties, communication routes, roads and has also modified the topography of the area. Recommendation made include planting of vegetative cover, construction of erosion channels, educating the populace and creating awareness on adequate practices to curtail the menace.

Colloidal nitrogen is an important and highly-mobile form of nitrogen discharging into the Great Barrier Reef lagoon

Soil-borne colloids have been linked to long-distance transport of radionuclides, metal(loid)s and nutrients. Colloid-associated nitrogen (N) will have different mechanisms of biogeochemical cycling and potential for water-borne transport over longer distances compared to dissolved N. The role that colloids play in the supply and mobility of N within catchments discharging into the Great Barrier Reef (GBR) lagoon is unexplored. Here, we examine water-dispersible clay (WDC) from soil samples collected from gullies and agricultural drains within three different land uses (sugarcane, non-agricultural land and grazing) within the Townsville area. The proportion of soil N associated with WDC was inversely correlated with total soil N, with up to 45% of the total soil N being colloid-associated in low N gully soils. Within the <0.45 µm fraction of the WDC, only 17–25% of the N was truly dissolved (<3 kDa) at the gully sites compared to 58% in the sugarcane sites. Our results demonstrate the importance of colloidal N and the inaccuracy of assuming N < 0.45 µm is dissolved in the sampled areas, as well as providing an alternate explanation for the large amounts of what has previously been defined as dissolved inorganic N in runoff from non-fertilized grazing land. In particular, they describe why non-fertilized land uses can contribute significant N < 0.45 µm, and why catchment models of nutrient export based on soil N concentrations can over-estimate loads of particulate nitrogen derived from monitoring data (N > 0.45 µm). The findings suggest that managing soil erosion may also contribute to managing N < 0.45 µm.

Mean Rate of Gully Head Advancement in Edo State, Nigeria

The issue of gully erosion is of major concern in Nigeria. The study was carried out in Edo state, Southern Nigeria. Edo State was chosen as the study area due to the fact that the magnitude of gully erosion has resulted in the loss of lives and properties, destruction of arable lands and wastage of large areas of usable land. In this study, an effort was made to identify the major gully sites in the area and determined the mean rate of gully head advancement. The result revealed that gullies in Edo North had mean rate of head advancement of 80.30 meters per a year, Edo South 52.03 meters per a year and Edo Central is 17.80 meters per year.

Evaluation of brush wood with stone check dam on gully rehabilitation

Gullies are common features throughout the Ethiopian Highlands. Induced environmental degradation comprises not only the loss of soil volume and of arable lands, but also the triggering of landslides or off-site sedimentation problems. This experiment was initiated with the aim of evaluating the effect of brush (bamboo) wood with stone check dam on soil and water conservation (gully rehabilitation) at Benishangulgumuz region of Assosa zone (Assosa district of selga-19 for two consecutive research years (2013/14-2014/15) on farm land. The gully site was selected purposively based on the prevalence of gully erosion. Biophysical and socio -economic data were collected from the gully and participant farmers to evaluate the effectiveness of the measures. The potential of the check dam to conserve the soil was evaluated by using the pin installed in front the check dam to observe the change of gully depth, cross sectional area and soil loss data were collected. A total of 22 households were sampled to assess the perception, acceptance and adoption level of the farmers using simple random sampling technique. the result indicates that the gully depth and volume of soil loss, were reduced from 0.94m to 0.58m and volume of soil loss from 468 ton/ha/yr to 204 ton/ha/yr. The interviewed farmers response also indicated that, all (100%) of them were mentioned the presence and severity of soil erosion on their farm land and which is increasing from time to time in alarming rate and where all of the farmers mentioned loss of fertile top soil and in turn yield reduction as its integral effect. 95.5% of the farmers were confident enough to rehabilitate the gully using bamboo with stone check dam by supplementing with other biological measures and all (100%) of the farmers ratified the effectiveness of the measures to rehabilitate the gully and willing to implement on their farm land thereby to disseminate the technology to non- participant farmers.

Geo-risk analysis of slopes bounding a deep gully erosion site in Uyo, Akwa-Ibom State, Southeastern Nigeria

The stability of slopes around a deep gully erosion site is the subject of this article. The site geology is the Coastal Plain Sands. To carry out stability analysis, the slopes were first characterized by deployment of cone and standard penetration tests (CPT and SPT) equipment. The slopes are highly stratified, and consist of numerous layers up to the depth of investigation which is about 37.0 m. The slope is made up of five layers of materials up to the gully valley floor. The soils of the five layers in succession from the top are clayey sand (SC), clayey/silty sand (SC–SM), gravelly clay (GC), poorly graded gravel with well graded sand mixture (GP–SW), and well graded sand (SW). Two locations on the eastern side of the of the gully site which poses serious risk to lives and properties were chosen for the analysis. The first position with the highest slope of 16.0 m gave a critical factor of safety less than 1.5 based on simplified Bishop method of analysis indicating unstable slope, while the second location results in a factor of safety greater than 1.5 suggesting a more stable slope, although there is a potential of sheet erosion on the slope at this location.

New insights into gully formation on Mars: Constraints from composition as seen by MRO/CRISM

AbstractOver 100 Martian gully sites were analyzed using orbital data collected by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and High Resolution Imaging Science Experiment on the Mars Reconnaissance Orbiter (MRO). Most gullies are spectrally indistinct from their surroundings, due to mantling by dust. Where spectral information on gully sediments was obtained, a variety of mineralogies were identified. Their relationship to the source rock suggests that gully‐forming processes transported underlying material downslope. There is no evidence for specific compositions being more likely to be associated with gullies or with the formation of hydrated minerals in situ as a result of recent liquid water activity. Seasonal CO2 and H2O frosts were observed in gullies at middle to high latitudes, consistent with seasonal frost‐driven processes playing important roles in the evolution of gullies. Our results do not clearly indicate a role for long‐lived liquid water in gully formation and evolution.