Thesis Abstract

Abstract
Gully erosion is a severe form of land degradation that poses a significant threat to soil resources and land productivity in many regions worldwide, including Eastern Nigeria. This study aimed to characterize and map gully erosion features in two distinct geological formations (the Asu River Group and the Nanka Sands) in Eastern Nigeria using a combination of field surveys, Geographic Information System (GIS) techniques, and remote sensing data. Field surveys were conducted to assess the morphological characteristics of gullies in the study area, including their length, width, depth, and cross-sectional shape. The gully erosion features were found to vary in size and morphology between the two geological formations, with gullies in the Asu River Group generally being larger and deeper compared to those in the Nanka Sands. GIS techniques were employed to analyze the spatial distribution and density of gullies within the study area. Digital Elevation Models (DEMs) were used to derive slope and aspect maps, which helped identify areas with high susceptibility to gully erosion. The results showed that gully erosion features were more prevalent in areas with steep slopes and specific orientations, highlighting the role of topography in the development of gullies in Eastern Nigeria. Remote sensing data, including Landsat imagery, were utilized to map the extent of gully erosion features in the study area. Supervised classification techniques were applied to differentiate gully erosion features from other land cover types, allowing for the generation of accurate gully maps. The maps revealed the spatial distribution of gullies within the two geological formations and provided valuable information for land use planning and erosion control efforts. Overall, this study provides a comprehensive characterization and mapping of gully erosion features in two geological formations of Eastern Nigeria. The findings highlight the importance of considering geological factors, topography, and land cover characteristics in understanding the dynamics of gully erosion in the region. The maps generated in this study can serve as essential tools for policymakers and land managers to implement effective erosion control measures and sustainable land management practices in Eastern Nigeria.

Thesis Overview

With the aid of Global Positioning System (GPS) and Satellite Aerial Photo, a comparative
characterization and mapping of soil gully erosion features on two geological formations
were carried out in Nsukka area of eastern Nigeria. The two geological formations were
Ajali and Mamu formations. The study involved the use of base map created using a
Geographic Information System (GIS) (GPS Track Marker) and Satellite Photo downloaded
from the internet using the same GIS (GPS Track Marker). This aided the field work for
erosion site study and data collection. A total of seventy (70) erosion sites with an average
length of about 1606.5 meters, average width of about 64.2 meters and average depth of 8.6
meters were visited in Ajali formation. On the other hand, only nine with an average length
of about 484.2 meters, average width of about 6.5 meters and an average depth of about 3.7
meters were visited in Mamu. In Ajali formation, forty three new erosion sites were
identified to add to the twenty seven old sites while in Manu formation only five new sites
were identified to add to the four old sites. Three profile pits were dug in each formation to
represent the soils. They are sites of Ada (Mpt1), Agu-Orba (Mpt2) and Agu-Ekwegbe
(Mpt3) on Mamu Formation while Iheaka (Apt1), Ede-Oballa (Apt2) and Aku (Apt3) were
sites on Ajali Formation.

The soils from the pits were sampled and analyzed for some physical and chemical properties. The properties were, colour, texture, soil reaction, organic matter, exchangeable bases, total nitrogen and available phosphorus, exchangeable acidity, cation exchange capacity, and aggregate stability. There was a significant difference in the value of gully length and width while the depth was statistically the same. There was a positive significant correlation between length and width (r = 0.409), depth and width (r = 0.862), but non significant correlation between length and depth (r = 0.188) in Mamu Formation, while a positive and significant correlation was found between length and depth (r = 0.635), length and width (r = 0.578), depth and width (r = 0.689) in Ajali formation. The results of the soil percentage state of aggregation (PSA) and percentage aggregate stability (PAS) was low at both soils. There was no significant difference between their mean weight diameters (MWD). Their low MWD values (1.1mm) in the soil of Mamu formation and 1.2mm in the soil of Ajali formation were indication that the soil were highly susceptible to erosion. Both soils of the studied area have low silt content (8% in the soil of Ajali and 5% in the soil of Mamu), but moderate to high fine sand values (18% in Ajali and 49% in Mamu). These could be one of the factors promoting the soil erodibility. At micro