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

Abstract

The study of gully development on a regional scale is currently threatened by the intrinsic costs associated with steady field tracking and monitoring and the lack of historic measurements to perform time series analysis. The research objective is to develop a low-cost GIS and Remote Sensing methodology for monitoring and quantifying gully erosion and development over time, identifying the impact and incorporating analysis of environmental factors and land use change. The analysis of study area topography at 30 m 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.