Assessment of Stability of Soils of Imo River Watershed, Southeastern Nigeria

Abstract The coefficients of linear expansion and Atterberg limits are key geotechnical properties that greatly impact the shrink-swell behavior, productivity, and stability of soils. This study concentrated on assessing soil stability within the Imo River watershed in Southeastern Nigeria, using a stratified sampling technique based on the topographical map of the region. The watershed was divided into three sections: the upper course (Isuochi), middle course (Amuzu), and lower course (Obigbo). For this investigation, nine profile pits were dug in each section of the river, with three pits collected from upslope, midslope, and footslope areas. The experimental setup utilized a factorial design within a randomized complete block design (RCBD), replicated three times, incorporating three land units (upper course - Isuochi, middle course - Amuzu, lower course - Obigbo) as factor A, three slope positions (upslope, midslope, footslope) as factor B, and six distinct depths (0-20 cm, 20-40 cm, 40-70 cm, 70-110 cm, 110-150 cm, 150-198 cm) as factor C. The excavation and profiling of the soils adhered to the guidelines established by FAO in 2006. A handheld GPS device was utilized to geo-reference the soil samples. In total, 27 profile pits were analyzed in this research. Routine analyses were performed on the collected samples. Simple correlation and multiple regression analyses were applied to the data using the Proc Mixed Model of SAS software (P<0.05). Results indicated that the soils in Isuochi showed a significantly greater variation in clay content and moisture (Mc), while the soils in Amuzu exhibited a lower significant variation in both Mc and clay (P<0.05). Among the various slope positions, the footslope had the highest levels of clay and moisture content (P<0.0001). In relation to depth, both clay and moisture content were significantly higher in the subsurface horizons compared to the surface horizons (P<0.0001). Bulk density (Bd) measurements were significantly elevated in soils from Obigbo and reduced in soils from Amuzu (P<0.0001). Additionally, Bd was notably increased in the subsurface horizons and decreased in the surface horizons (P<0.0001). Saturated hydraulic conductivity (Ksat) measurements were significantly higher in the soils of Amuzu compared to those of Obigbo (P<0.0001). The variables of clay, moisture content, bulk density, and Ksat were influenced by the interactions between location and slope, as well as location and depth at P<0.05. Liquid limit (LL) and plastic limit (PL) values were significantly more pronounced in the soils of Isuochi and less so in the soils of Amuzu (P<0.0001). The Coefficient of Linear Extensibility (COLE) indicated marked shrinkage greater than 0.06 at 20-30% volume change for the soils of Isuochi, whereas slight shrinkage was recorded in the soils of Amuzu (0.00-0.03). COLE exhibited a significant correlation (P<0.05) with LL (r=0.83), PL (r=0.78), and clay (r=0.88). A regression model illustrated a robust connection between COLE (the dependent variable) and independent factors (moisture content, organic matter, sand, silt, clay, plasticity index), characterized by a high R2 value of 0.86 and a low root mean square error (RMSE) of 0.01. It is recommended that suitable agricultural waste be used to amend compacted soils to enhance their productivity