|University of Port
Victor Sunday and Onyemachi Praise K. C.
University of Port Harcourt
Choba, Rivers State, Nigeria
It is not an over statement that the modern man attaches much importance to his immediate environment. This is obvious in the way he is concerned with environmental distortions, hazards, disasters etc, some of which he could handle by himself; and needs the services of experts to combat other seemingly difficult environmental imbalances. Such environmental distortions like climate change, earthquakes, flooding and mudslides, erosions, landslides etc jeopardize man’s effort to avert these problems. It is sad to know that erosion in the south east geopolitical zone of Nigeria is a rampant issue and a menace. Erosion sites are not rare in all the states that constitute the zone, especially in Umuahia, the capital city of Abia State. Environmental monitoring, mapping and protection of erosion sites in the zone have created much awareness that this challenge could be controlled, and others saved. This study aims at monitoring, mapping, and protecting these erosion menaces in Umuahia, and other sites in the south east states of Nigeria, could be controlled through monitoring, mapping and protection; using remote sensing, digital satellite mapping and geographic information system (GIS) to control natural disasters like gully erosion in south eastern Nigeria, especially Umuahia.
Globally, environmental issues have become major concerns to governments and citizens of various nations, including Nigeria. The environment, which is at the heart of economic, social, cultural and human activities, has been disrupted by man’s neglect and abuse of the environment. Pollution, deforestation, erosion, landslides, global warming etc are the aftermaths of this abuse in the ecosystem. The issue of protection, mapping and monitoring becomes paramount in the face of the increasing population resident in the south east geopolitical zone of the country. They are severely impoverished, particularly the rural dwellers due to environmental degradation and to increasing population impact on the environmental resources. Umuahia is a case study.
The environmental resources, most especially the land and soil resources are greatly threatened by soil and gully erosion. The topographical setting of the area, which is located within the tropics, and has high population density, is among the major factors that may trigger the genetic history of the area. Waugh, (1995) stated that “natural (environmental) balance is being disturbed by mismanagement with increasing frequency and serious consequences”. Recent estimates suggest that about seven per cent (7%) of the world’s topsoil is lost yearly to erosion in all ramifications. In fact, the World Resources Institute claims that Burkina Faso loses 25 tonnes of soil per hectare per year (Kalu 2001. 3). Other reports on this issue reveal that Ethiopia loses 42 tonnes, Nepal 70, Decan Plateau (India) 100, and Loess Plateau of north China 251 tonnes (Waugh 1995). Also, the soil survey of England and Wales claims that 44 per cent of arable soils in the United Kingdom, an area once considered not to be under threat, are now at risk.
In Nigeria, Agulu-Nanka in Anambra State is an area badly affected by water erosion — up to 250 tonnes per hectare have been lost in severe storms. Other comparable erosion sites are Ebem – Ohafia: about 150 tonnes/hectare (under control), and Isukwuato gully erosion comprising six major erosion sites. These sites are Ugwuntu, Ogudasaa, Amokwe. Amaiyi – Ohuu 1 and 2, Ahaba, Umunnekwu Agbo, and Abia State University Uturu Campus (Kalu 2001.3).
|Fig. 1 Amuzukwu-Mbom Erosion
Site (Over 10m deep)
|Fig. 2 Ajata-Iyienyi Erosion Site
(covered by vegetation naturally
checking the menace, over 25m deep)
Umuahia region comprises Umuahia North and South Local Government Areas that make the capital city of Abia State. Seven (7) major gully erosion sites have been identified: Amuzukwu – Mbom, Isieke, Isiadu – Amaeke, Amuzuoro Okwuta, Ajata – Iyieny (Figs.1 – 6), and Umunwanwa; with Amuzukwu – Mbom gully cutting off the road linking Amuzukwu and Mbom communities, respectively; destroying arable land for agricultural purposes. The above mentioned erosion sites are found in the southeastern part of the country, hence the call for environmental monitoring, mapping and protection of erosion sites before they get out of control. It is in this regard that the Federal Government of Nigeria in its renewed interest to find a lasting solution to the ecological disequilibrium in the country necessitated the study objectives of the subject – Environmental Monitoring, Mapping and Protection of Erosion Sites (Erosion Disaster) in Parts of Southeastern Nigeria– Umuahia as a case study.
In this paper, the issues in protecting, mapping and monitoring are addressed to solve the problem of gully erosion in southeastern Nigeria, particularly in Umuahia. These issues will be examined as an approach to environmental protection, mapping and monitoring of gully erosion in the region.
|Fig. 3 Isieke Erosion Site (Over
|Fig. 4 Amuzuoro Erosion Site
threatening the road to the
community (over 20m deep)
Impact of Erosion Sites in Umuahia
Soil – gully erosion involves the processes of detachment of soil particles from the parent soil mass, transportation of the detached materials down slope and deposition of the particles (Ellison 1946). As soil – gully erosion is a perfectly natural phenomenon, erosion processes require energy input. In Umuahia, the primary agent generating the energy is rain water; operations such as splash and overland flow. The raindrop striking on the soil surface expends its kinetic energy in detaching soil particles. The erosion sites identified in Umuahia are mainly rural, located in areas whose primary occupation is farming. Unfortunately, these sites involve lands used by these rural dwellers for agricultural purposes (farming), which has been harmed by the devastating effects of gully erosion.
A systematic study of these erosion sites reveals that some roads in these places are being threatened by the disaster. For instance, Amuzukwu – Mbom road, which was motorable before, has completely been cut off so that the two communities cannot interact with each other (Fig. 1). Also Ajata – Iyienyi gully is threatening the Bende road that links Umuahia to Bende Local Government Area (Fig. 2). It is in the light of these that environmental monitoring, mapping and protection of erosion sites are imperative. In this region, the primary occupation of the areas within these sites has been reduced as a result of this devastating effect– the erosion that has claimed acres of land meant for agriculture (farming).
|Fig. 5 Okwuta Erosion Site (over
|Fig. 6 Amaeke-Isiadu Erosion Site
(over 20m deep)
Environmental Monitoring Of Erosion Sites in South East Nigeria (Umuahia)
The federal government through its agency known as the National Space Research and Development Agency, in a workshop on”Comprehensive Mapping and Monitoring of the Impact of Gully Erosion Problems in Southeastern Nigeria”, reiterated its commitment to tackle gully erosion problems in the region with Umuahia not left out. The move includes establishing a strong monitoring team. The use of satellite observation with spatial resolution using (Nigerian Sat 1) and other indices like geographic information system (GIS) techniques provide periodic inspection across the region by the monitoring team and complementary satellite observation and monitoring. With all these measures put in place, environmental monitoring, mapping and protection of erosion (erosion disaster) in part of southeastern Nigeria will bring a deep relief to the occupants of the affected areas, and salvage the situation to prevent further damages and losses of agricultural lands.
Several erosion sites were identified in the region. The population of residents and their activities in the areas already prone to this natural disaster facilitated massive gully erosion actions. The consequences have far reaching impacts on the socio-economic, cultural and political well-being of the population in the region. A lot of damage was observed and expectations are high for the federal government’s preparedness to control the massive gully erosion sites on a large scale through various modalities like remote sensing (satellite observation and geographic information system (GIS) as well as regular field inspection on these sites.
Ellison, W. D. (1946). “Soil Detachment and Transportation”, cited in Land Use and Conservation in Nigeria, University of Nigeria Press, Nsukka. Pp. 81.
Obienusi, E. A. and Ahiadu, H. O (2008). “Conservation, Management and Monitoring of Gully Erosion in South Eastern Nigeria”. A paper submitted for presentation at a workshop on “Comprehensive Mapping of the Impact of Gully Erosion In South Eastern Nigeria Using Satellite Remote Sensing and GIS Technique 2008”. Department of Geography and Meteorology, Nnamdi Azikiwe University, Akwa, Anambra State.
Kalu A. O (2001). “Soil Erosion and Landslide: 21st Century Environmental Issues and Challenges to rural Development in Nigeria”. Department of Urban and Regional Planning, Abia State University, Uturu, Abia State. MURP, seminar paper unpublished.
Waugh (1995) quoted by Kalu A. O in “Soil Erosion and Landslide: 21st Century Environmental Issues and Challenges to Rural Development in Nigeria.”