Nigeria- Erosion

Overview:
The Nanka Gully is part of the region of Agulu within the Nigerian State called Ambra. The gully, which began to form in the 1850's, is now approximately 1,100 square kilometers large. Members of the Ambra State University of Technology's Department of Earth Sciences estimate the rate of gully erosion in this particular region of Ambra to now be 20-50 m year^(-1). Because of this drastic rate of erosion, the Nanka Gully is now nationally recognized as an ecological disaster zone. Nanka is located in the tropical rainforest belt of Southeastern Nigeria.

History:
In the mid ninteenth century, narrow channels within the Nanka region began to widen, rapidly. The gully system was soon after created by the erosion of the land. In 1951, the British Colonial Office began implementing extensive control programs. Although the programs are responsible for the installation of concrete dams, they were largely unsuccessful. Critics point out that because the government of Nigeria and the locals to the Nanka region have both been seperately (and arguably, exclusively) attempting to resolve the soil problem, the gully erosion persists and both parties are left with nothing. Many suggest collaboration and compromise as a first step in stopping the erosion of the Nanka Gully.



Causes:
Originally the only known cause of the gully erosion was human activity. Further and later investigation carried out by Egboka and Nwankor in 1982 show the primary reason of the erosion to be the properties of the soil. More specifically, the hydrological and geotechnological characterisitcs of the aquifer system make for a high hydrostatic pressure rate in the system. This results in less strength in the unconsolidated course sands on the walls (or what used to be, surface) of the gully area. Water in the lowest areas of the gully is also slightly acidic. This acidity is largely responsible for destruction of the concrete dams put in the gully in the mid 1800's by the British Colonial intervention programs. Another factor in the gully's erosion is that the erosion began centuries ago when proactive responses to threats of natural disasters such as erosion were not known or practiced.

Effects:
The gully erosion has led to many Nigerians losing their homes and becoming homeless. Farms and land have also been destroyed, therefore eliminating many people's livelihoods. Beyond just those living on or near the gully site, the erosion is responsible for the loss of much livestock and many crops which limits food accessible to those nearby. The obvious effects are the destruction of the land and the loss of soil fertility and general health. In one Nigerian's lifetime he estimates over 200 people died because of the gully erosion. Displacement is also a major effect of the gully erosion. In the past ten years 85% of the Nanka population has migrate because of the gully.



Solutions:
Recently, villagers in the area of used methods of afforestation, construction of drainage channels, and introduction of cover crops to attempt to slow the process of gully erosion in the region. In response to the gully erosion thus far, the Department of Geography at the University of Nigeria recommends participatory management strategies be jointly developed by the Nigerian government and the local villagers. Also recommended is the enaction of laws specifically designed for solving problems created by the erosion, as well as education for the locals to prevent the esceleration and/or repetetion of the erosion issues.

By Ellen Legard

Sources:
1. report by Department of Geography at the University of Nigeria (http://www.ehs.unu.edu/file/get/5395)
2. report by Water Resources and Environmental Pollution Unit of the Department of Earth Sciences at the Ambra State University of Techonology (http://iahs.info/redbooks/a144/iahs_144_0335.pdf)