Determining Causes of Gully Erosion and Associated Rates of Change in South-east Nigeria, Using a Remote Sensing and GIS Methodology

Abstract

In this work a study of gully erosion in southeast Nigeria is presented. The study of gully development on a regional scale is currently undermined by the inherent costs associated with consistent field monitoring and the lack of historic measurements to perform time series analysis. The analysis of study area topography at 30m resolution reveals 85% of the surveyed gullies develop on concave slopes with high values of 6 plan curvatures and >50 inclines. Results also reveal high association with ferralsols soils. Statistical analysis to determine significance of variables on the proportional yearly gully change in metre squared per square metre were conducted via principle component analysis. The analysis of this work was restricted to the time periods 2006/7, 2009/10, and 2014/15. The approach did not report any existence of one singular driver of erosion across the studied years and multiple sites confirming the complexity of gullies. The PCA showed that the level of variance explained in the yearly gully change variable was most similar in PC1 (representing the component with the highest eigenvalue) to Vegetation loss, Vegetation loss and slope in the respective years.The study offers a method of monitoring gully development from early stage to maturity and exemplifies the complexity and variability of erosion drivers in the SE Nigeria region. It presents a verified approach to local and regional 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.

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

“…Hence, we have fewer gullies in urban areas than we have in rural areas (Iro, 2020a). But the case is different in rural areas where the land surfaces are unplanned; most of the surfaces are not tarred; the majority of the people still depend on the exploitation of the land for survival, hence exposing the soil surfaces; the impact of raindrops has direct contact with bare soils; runoffs were not provided with any channel; hence it follows the slope, thereby wearing off the surface of the earth and causing erosion (Igwe, 2012;Iro, 2020b). Therefore, it was discovered that in the upper Imo River basin, 61% of the gully sites were found in rural areas while 39.9% can be found in urban areas.…”

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

“…The digital elevation map of the study area is produced from the SRTM (Shuttle Radar Topography Mission) data at 30 m (1 Arc-second) resolution Rendering Digital Elevation Models (DEM) to detect changes and calculate gully dimensions of the focused gully site (to observe how slope and nature of the slope, influence gully development)". The adoption of the Digital Elevation Model for this analysis is a new method that can easily reveal the nature of the landscape (Iro 2020) [13]. Land surface topography has been reported to significantly affect the processes of runoff and erosion (Zevenbergen and Thorne, 1987).…”

“…The process of gully erosion and sediments are caused by rainfall, soil properties, and topography and can be induced by anthropogenic interference including land management practices [1]. The rainfall intensity is high in this area of Nigeria and often persists for long durations.…”