Soil Erosion Susceptibility Mapping of Imo River Basin Using Modified Geomorphometric Prioritisation Method

Abstract

Gullies and other forms of erosion have been the greatest environmental problem and catastrophe in most high- and low-income countries. The challenge posed by soil erosion has compromised agricultural productivity, environmental biodiversity and food safety for the world's population. It is important to identify vulnerable areas to soil erosion in each region to initiate remedial measures. This study demonstrates the use of watershed morphometry coupled with weighted sum analysis (WSA) to estimate the soil erosion susceptibility of the Imo River Basin sub-watersheds (SWs) in South-Eastern Nigeria using satellite remote-sensing data and geographic information system (GIS) analysis. To this end, Shuttle Radar Topography Mission (SRTM), a Digital Elevation Model (DEM) with 30 m spatial resolution was used to extract and analyse 18 morphometric parameters including basic, linear, shape and relief. The method of receiver operating characteristics (ROC) curves was used to validate the model's prediction accuracy. This morphometry-based analysis resulted in the SWs being classified into zones of low, medium, high and very high erosion susceptibility. With regard to erosion susceptibility, 41.51% of the basin (2494.68 km2) is in the very high priority zone; while 10.50%, 44.33% and 3.66% of the basin are in the high, medium and low priority zones respectively. Validation of the final erosion susceptibility map showed a prediction accuracy of 81%. The use of satellite imagery and morphometric analysis in this study was cost- and time-effective for identifying areas susceptible to soil erosion.

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

“…These were carefully put in well-labelled sampling bags to avoid mixing up the location details. A total of fifteen (15) representative samples-ten (10) samples from Nnewi and five (5) from Nnobi were analyzed in the Civil Engineering Laboratory of the University of Nigeria Nsukka. The laboratory analysis to obtain the geotechnical and other properties of the samples such as specific gravity (ASTM D854-14), permeability (ASTM D5084-16), shear strength parameters (ASTM D3080-11)-cohesion (C) and angle of internal friction (Ø), particle size distribution, Optimum Moisture Content (OMC) using ASTM D698-12, Maximum Dry Density (MDD) using ASTM D698-12, Natural Moisture Content (NMC) using ASTM D2216-19, Atterberg limits using ASTM D4318-17-Liquid Limit (LL), Plastic Limit (PL) and Plasticity Index (PI) were determined.…”

“…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] . This observation prompted a more comprehensive investigation to discern the factors responsible for these disparities, considering their comparable geomorphological and climatic attributes.…”

“…The distinction in the magnitude and intensity of gully erosions between Nnewi and Nnobi has not gone unnoticed 4,5,[10][11][12][13] . This observation prompted a more comprehensive investigation to discern the factors responsible for these disparities, considering their comparable geomorphological and climatic attributes.…”