Assessing the role of soil engineering properties in gully development and enlargement in southeast Nigeria using geostatistical and novel indexical techniques

Abstract

Over many decades, land degradation, due to gully erosion and landsliding, has remained a serious threat to land-use management and economic sustainability in southeastern Nigeria. Several causative factors have been listed to be responsible for the continuous land degradation. In this study, multiple geostatistical and new indexical models were integrated to assess the role of soil engineering properties in the erosion of ten major gullies in southern Anambra State, southeast Nigeria. Gully soil samples were analyzed for properties such as particle size distribution, water content, Atterberg limits, compactness, bulk density, specific gravity, shear strength, porosity and permeability coefficients. The geotechnical analyses revealed that the gully materials are weak and have poor erosion-resistant features. The results revealed that the soils' engineering properties influence their erodibility. Interparameter relationships observed from correlation, factor, and cluster analyses showed that the engineering parameters jointly impact the erosion processes. Novel indexical methods, sand-gravel ratio (SGR) and sand-fines ratio (SFR), alongside erodibility factor confirmed that the soils are erodible. A novel entropized soil loss rate (A E ) model estimated high cumulative annual soil loss rate for the area at 0.9705. Overall, it was revealed that SW, SC, and SP soils are far more susceptible to gully erosion than CL and GP soils in the area. Artificial neural network models were developed and used to accurately (with low model errors and R 2 range of 0.956-0.997) predict the SGR, SFR and A E . The findings of this research would be helpful in advancing soil erosion investigations and in planning for effective mitigation measures, with respect to engineering properties.

Application of bivariate statistical techniques for landslide susceptibility mapping: A case study in Kaghan Valley, NW Pakistan

“…An increase in gradient certainly enhances the stresses over soil or other loose material hence, making it susceptible to failure (Dai et al, 2002). The susceptibility of landslides was believed to be increased as claimed by many researchers (Egbueri & Igwe, 2022;Egbueri et al, 2021;Lee, 2005;Pachauri & Pant, 1992). Thematic layer of slope was extracted from the DEM and measured in degrees for the current study.…”

“…It disturbs the hydrologic processes of slope and can have a negative impact on slope stability in terms of accelerating weathering and slope undercutting which results in an increase in the water level (Yalcin, 2008). An increase in water on the slope reduces friction, increases gravity and facilitates the easier movement of material downhill (Egbueri & Igwe, 2022; Egbueri et al, 2021). River map is delineated through DEM of the study area using GIS flow direction tool and buffered into four classes i.e., 0–50, 50–100, 100–150 and >150 m (Figure 4k).…”

“…An increase in water on the slope reduces friction, increases gravity and facilitates the easier movement of material downhill (Egbueri & Igwe, 2022;Egbueri et al, 2021). River map is delineated through DEM of the study area using GIS flow direction tool and buffered into four classes i.e., 0-50, 50-100, 100-150 and >150 m (Figure 4k).…”

Comparative analysis of the expansion rate and soil erodibility factor of some gullies in Nnewi and Nnobi, Southeastern Nigeria

“…Additionally, intensified rainfall augments soil erodibility 4 . Egbueri and Igwe established that Eocene Nanka Sands (Imo Basin) and Cretaceous Ajali Sandstone (Anambra Basin) are highly susceptible to erosion due to their unique soil gradation 8 . This susceptibility is further exacerbated by undulating topography, leading to the formation of large, steep gullies 4 .…”

“…The heightened slope instability during this time often leads to the failure of steep gully slope walls due to rising pore pressure levels [4][5][6] .The yearly peak of the rainy season serves as a critical point, amplifying the impact of gully erosion as it widens its catchment area [5][6][7] . Against this backdrop, the need to examine the soil loss rate and the potential consequences of urbanization on gully erosion's magnitude and intensity becomes more pressing in Nnewi and Nnobi [7][8][9] . This study reveals the underlying causes of the 2019 building collapse attributed to gully erosion in Okpunor-Egbu Umudim, Nnewi and unravels the reasons behind the differing levels of gully erosions between Nnewi, a densely populated town, and its less populated neighbour, Nnobi, both located within Anambra State.The distinction in the magnitude and intensity of gully erosions between Nnewi and Nnobi has not gone unnoticed 4,5,[10][11][12][13] .…”