CHAPTER ONE
1.0      INTRODUCTION
1.1   BACKGROUND OF STUDY
Erosion is one of the surface processes that sculpture the earth’s landscape and constitutes one of the global environmental problems. Soil erosion is perhaps the most serious mechanism of land degradation in the tropics (ElSwaify, et al., 2002). However, gully is visually the most impressive of all types of erosion (El-Swaify, 2000). Gully erosion is a well-defined water worn channel (Monkhouse and Small, 2008).
It is a recently extended drainage channel that transmits ephemeral flow, steep side, steeply sloping or vertical head scarf with a width greater than 0.3 m and a depth greater than 0.6 m (Brice, 2006). It is a V or U-shaped trench in unconsolidated materials with a minor channel in the bottom, but not necessarily linked to a major stream (Graf, 2003).
Similarly, Bettis III (2005) defined gully as a relatively deep, vertical-walled channel recently formed within a valley where no well-defined channel previously existed. Gully erosion is an advanced stage of rill erosion where surface channels have been eroded to the point where they cannot be smoothened over by normal tillage operations (Hilborn, 2005).
Gullies can be active (actively eroding) or inactive (stabilized). The former, according to Poesen et al. (2003), can occur where the erosion is actively moving up in the landscape by head-cut migration. The causes of gully erosion are poorly understood but the processes and factors involved in its growth and degradation are well-known (Bettis III, 2005). The research has shown that gully processes had happened in the past even without human influence or interference. Thus, the phenomenon of gully erosion is either naturally induced or artificially-induced, or both. Like in other parts of the world, gully erosion is one of the major environmental challenges facing Nigeria.
The available literatures on the subject show that this menace is more predominant in the eastern half of the country compared to the western half. South-eastern part of Nigeria is more affected than its north-eastern counterpart. Soil erosion in the former has been identified as the most threatened environmental hazards in the country (Albert, et al. 2006). Anambra State is the most affected of all the states in Nigeria where Agulu, Nanka and Oko communities of the state are the worst hit. Available literatures have clearly reiterated the fact that the underlying geology exerts a major of control on gully development and, more often than not, the process is rock type dependent as some rocks are more susceptible to erosion than the others. There is therefore a need to briefly review the geology of Nigeria with a view to recognizing why the phenomenal gully erosion is more prevalent in one part of the country than in the other.
1.2   STATEMENT OF THE PROBLEM
          Erosion generally degrades land and affects not just plants and animal but is capable of taking away human’s life, though it a natural disaster but ways of preventing it can be thought about. Gully erosion seems to be a factor of discourse every rainy season because maybe the government have decided to pay deaf ears to this menace, sometimes because they must have tried to work on it but the solution was not long lasting and they thought intervening again will just be a total waste of money thereby feeling discouraged. Finally, several studies has been carried out on the effect of erosion on agricultural produce but not even a single research has been carried out on the effects of gully erosion on the environment a case study of Oko, Anambra state.