Land susceptibility to soil erosion in Orashi Catchment, Nnewi South, Anambra State, Nigeria

Abstract

Abstract. Soil erosion is one of the most critical environmental hazards that causes land degradation and water quality challenges. Specifically, this phenomenon has been linked, among other problems, to river sedimentation, groundwater pollution and flooding. This paper assesses the susceptibility of Orashi River Basin (ORB) to soil erosion for the purpose of erosion control measures. Located in the South Eastern part of Nigeria, the ORB which covers approximately 413.61 km 2 is currently experiencing one of the fastest population growth rate in the region. Analysis of the soil erosion susceptibility of the basin was based on four factors including; rainfall, Land use/Land cover change (LULC), slope and soil erodibility factor (k). The rainfall was assumed to be a constant and independent variable, slope and soil types were categorised into ten (10) classes each while the landuse was categorised into five classes. Weight was assigned to the classes based on the degree of susceptibility to erosion. An overlay of the four variables in a GIS environment was used to produce the basin susceptibility to soil erosion. This was based on the weight index of each factors. The LULC analysis revealed that built-up land use increased from 26.49 km 2 (6.4 %) in year 1980 to 79.24 km 2 (19.16 %) in 2015 at an average growth rate of 1.51 km 2 per annum while the light forest decreased from 336.41 km 2 (81.33 %) in 1980 to 280.82 km 2 (67.89 %) in 2015 at an average rate 1.59 km 2 per annum. The light forest was adjudged to have the highest land cover soil erosion susceptibility. The steepest slope ranges between 70 and 82 • (14.34 % of the total land area) and was adjudged to have the highest soil susceptibility to erosion. The total area covered of the loamy soil is 112.37 km 2 (27.07 %) with erodibility of 0.7. In all, the overlay of all the variables revealed that 106.66 km 2 (25.70 %) and 164.80 km 2 (39.7 %) of the basin has a high and very high susceptibility to soil erosion. The over 50 % high susceptibility of catchment has serious negative implications on the surface water in terms of water quality and downstream siltation with great consequences on biodiversity and ecosystem services including domestic and industrial usage.

Soil Vulnerability Assessment of Afikpo South Local Government Area, Ebonyi State, Nigeria

“…Soil erodibility factor (K factor) is the soil loss rate per erosion index unit for a specified soil as measured on a standard plot, which is defined as a 72.6ft (22.1m) length of uniform 9% slope in continuous clean-tilled fallow [11]. Soil erodibility factor measures the susceptibility of soil particles or surface materials to transportation and detachment by the amount of rainfall and runoff input [8]. K factor takes into account the integrated effect of rainfall, runoff and infiltration on soil loss [9].…”

“…Cover Management Factor (C) is the ratio of soil loss from a particular site with a specified cover and management to soil loss from a standard unit plot [9]. This simply means the ratio of soil loss of a specific crop to the soil loss under the condition of continuous bare fallow [8]. This value includes the effects of cover, crop sequence, productivity level, length of the growing season, tillage practices, residue management, and the expected time distribution of erosive rainstorms.…”

“…Support practice factor is the soil loss ratio with a specific support practice to the corresponding soil loss with up and downslope tillage [8].…”

“…The situation has become critical with an increase in population, urbanization, deforestation and intensified rainfall. There is a need for policies that encourage soil retention strategies, land-improving investments and better land management [6].Causes of gully erosion have been traced to poor land management coupled with a lack of innovation and awareness measure [7,8]. The study was aimed to estimate the rate of annual soil loss in terms of Revised Universal Soil Loss Equation (RUSLE) in Afikpo South Local Government region using remote sensing and Geographic Information System (GIS) techniques.…”

The Underlying Factors of Soil Susceptibility to Erosion in Central Parts of Southeastern Nigeria

“…Soil erosion is one of the very most important environmental challenges that are responsible for land degradation, poor water quality, stream water pollution and flooding (Odunuga, et. al., 2018).…”