**1. Introduction**

Soil erosion is perhaps one of the leading threats to land use in many regions of the world regardless of the piling volume of research on soil erosion agenda [1]. Precisely, about 7348 articles were published on soil erosion between 2016 and 2018 alone, compared to the whole of the twentieth Century publications with just about 5698 articles [2]. Despite this long history and huge volume of research, soil erosion studies in most parts of sub-Saharan Africa, particularly Nigeria, are still grossly insufficient. Soil erosion event implies the net long-term balance of all activities that displaces soil from its initial location to another destination by any entrainment agent(s) [3]. Water and wind agents are largely responsible for soil erosion phenomena witnessed across the globe. However, [4] reported other agents of soil erosion

to include mass wasting by soil slumping, explosion cratering, trench digging, land leveling, soil quarrying, and crop harvesting activities. Of all these agents, water erosion affects larger land area and has received more research attention than wind, plus all other erosion agents [5]. Gully erosion is likely to be the largest source of soil sediment yield among the other water-induced erosion types. It is formed where sufficient concentrated water flow occurs to incise soils progressively downwards until it contacts an underlying hard material(s). Classical gullies are incised channels that cannot be filled in by normal tillage operations, compared to the ephemeral (transient) gully (EG) erosion features [6, 7].

In recent years, few studies on the development, field processes and distributions of ephemeral or classical gully erosion features over the Mubi regional landscape were reported as either measured or predicted with empirical or physically-based models by a few erosion research scholars. These research efforts are largely tied to the pressing need to generate a local databank for consultations, as erosion datasets from other foreign places might not truly represent the local field conditions of the Mubi region. Essentially, [8] reported that local adaptation of scarce process-based models and erosion results from one region may not apply to another, due to differences in study methods, making data accuracy, reliability, and credibility debatable. This chapter, therefore, intends to, (i) review the few reports on soil erosion studies around the Mubi area, and (ii) harmonize the research views and highlight the salient ideas where agreement is less firmly established towards holistic management implementation options by potentially interested land users in the region, and perhaps, also to serve as reference material to the neighboring regions.

Mubi area which is situated in the Northeastern part of Nigeria on the western hillside of the Mandara Mountains gives its high and undulating topography that spurs runoff, surface incisions, and gullying with a consequently high soil loss rates along the region [9–12]. Previous studies on soil erosion features in the Mubi region were reported largely on both the classical and ephemeral gully (EG) erosion, and only a few or no works were carried out on splash, sheet, and rill erosion features. Thus, there is still a dearth of information concerning the splash, sheet, rill, and stream bank sloughing erosion activities in the region. The EG erosion is a recently recognized erosion class in the context of global erosion that still lacks both sufficient models and datasets to test and/or predict its processes [13, 14], while the classical gully is the advanced form of EG erosion feature with deeper (>0.3 m depth) and wider (>2.0 cm width) channels [6, 7, 13]. The menace of soil erosion has generated huge management concerns in recent times. Both government and private donors have devoted some attention to addressing the effects felt by residents along the riverine and/or floodplain sections of the Mubi region. More efforts are still expected to study and report erosion activities and consequent implications to both farmers and residents in the Mubi region. It is hoped that published reports on soil erosion studies are consulted and conned in this text and their views understood and refocused for better understanding and field use in the region.
