Scholarly Journal of Scientific Research and Essay (SJSRE) Vol. 2(6), pp. 85-95, June 2013 Available online at http://www.scholarly-journals.com/SJSRE

ISSN 2315-6163 © 2013 Scholarly-Journals

Full Length Research Paper

Geospatial application in mapping gully erosion sites in Jos, Plateau State, Nigeria

Ogwuche Jonathan1* and Bulus Joshua2

1Department of Geography, Benue State University, Makurdi, Benue State, Nigeria.

2Plateau State Ministry of Lands and Survey, Jos, Plateau State, Nigeria.

Accepted 3 June, 2013

Gully erosion is a geo-environmental issue in the Jos Plateau, which requires a spatial mapping of the area if sustainable remediation is to be achieved. Using geospatial information technology that involved the use of GPS, high resolution satellite imagery (Quick Bird) and Aster data, the data were processed (georeferenced, sub-mapped, buffered and digitized). The study produced a topographic map, Digital Elevation Model (DEM), and buffered to show the vulnerability of the area to gully erosion. The study also identified 38 gully erosion sites, and revealed that eroded lands and mining ponds occupy 4.06 and 2.92% of the land area in the area. It is suggested, among others, that the abandoned mine ponds be used as dams for dry season farming, and a comprehensive environmental planning for Jos town. Key words: Geospatial information system, digital elevation model (DEM), gully erosion.

INTRODUCTION The environment and its resources are the keys to sustainable development. However, all developmental activities tailored to achieve socio-economic and infrastructural development in Nigeria leave behind negative impacts on the physical, biological and hydrological environments (Sumaila, 1989).

Erosion is one of the physical manifestations of environmental degradation, which can be facilitated by causative factors of wind and water. However, the most prominent of these factors is soil erosion by water, and its rate and magnitude are controlled by the factors of rainfall intensity and run-off, soil credibility, slope gradient and length, and vegetation cover (Wall et al., 1987).

Accelerated erosion can be divided into sheet, rill and gully erosion (Shrestha, 2007). However, this paper is concerned with gully erosion. Gullies are relatively permanent steep-sided water courses which experience ephemeral flows during rainstorm (Morgan, 2005). The size of the gullies varies from shallow 0 to1 m deep gullies to over 20 m deep ravines (Bergsma, 1996).

The process of gully erosion is known to be accelerated *Corresponding author. E-mail: ogwuche.jonathan@yahoo.com.

by human activities, and the type of materials it affects is often highly fertile for agricultural purposes (Khewhie et al., 2002). This means that gully erosion represents a highly significant problem in arable areas, affecting soil production capacity, damages unpaved roads, and leads to barriers in communication. In many respects, gully erosion is more dangerous and destructive than either sheet or rill erosion (Ogbonna, 2012).

The most devastating gully erosion in Nigeria is found in South Eastern Nigeria, in the densely populated Anambra, Imo, Enugu and Abia States. The incidence and persistence of gully erosion in these states, and other parts of Nigeria, have been explained in terms of the fragile geological formation, the high intense tropical rainstorm that lasts up to eight months in the year, the long history of settlement, deforestation, geotechnical and hydro geochemical characteristics as well as with regards to poor land use practices (Ofomata, 1984; Egboka and Nwankwo, 1985; Igbokwe et al., 2008).

Gully erosion is a serious geo-environmental issue in the recent decades; and so, in developing a sustainable remediation procedure, an assessment of gully erosion through a spatial mapping of the areas affected and vulnerable to gully formation is necessary. This therefore requires the use of Geographic Information System (GIS)

as the basic tool for gully erosion mapping. Geospatial information technology and gully erosion Viewing the earth from space is now crucial to the understanding of the influence of man’s activities on his natural resources base over time. Over the past years, data from earth sensing satellites have become vital in mapping the earth’s features and infrastructures, managing natural resources and studying environmental changes (Ssewalu, 2008).

Geospatial information is spatially referenced information that shows the geographical location of earth surface features and defines their physical characteristics. Remote Sensing and Geographical Information Systems are the key components of the geospatial information technology. The collection of remotely sensed data facilitates the synoptic analysis of earth systems function, patterning and change at local, regional and global scales over time.

The possibility of using aerial photography for erosion mapping has been recognized for a long time (Goosen, 1967). Commonly, aerial photographs were used to support conventional geomorphologic methods (Stronquist, 1990) and for direct identification of sheet, rill and gully erosions (Stronsquist et al., 1985). The extension of the modern geospatial information technologies such as Geographic Information Systems and Remote Sensing have created new possibilities for research into improved methods of erosion mapping for monitoring and modeling (Martinez-Cassanovas, 2003; Ali and Behzad, 2012), with speed and economy (Roofi et al., 2004).

Successful mapping of gullies depends on knowing gully characteristics to define the appropriate mapping technique (King, 2002). Gullies can be characterized in various dimensions. Hudson (1980) characterized them as geomorphic features that do not allow for normal ploughing. The shape of gully cross-sections and soil material in which a gully develops have also been used to characterize gullies, with V- and U-shaped gully cross-sections subdivided according to the type of sedimentary material present (Imeson and Kwaed, 1980). Morgan et al. (1997) gave a more landscape-based approach, defining gullies as relatively permanent sleep-sided eroding water courses that are subject to flash floods during rainstorm.

To study the topology of gullies and the effects of gully erosion, and to predict the risk of gully erosion, different approaches have been used. These include: 1. Mapping existing gullies and present erosion activity (Palacio and Lopez, 1994). 2. Characterization of the gully erosion degree on the basis of indices (Williams and Morgan, 1976). 3. Mapping gully erosion hazard in actively eroding

Scholarly J. Sci. Res. and Essay 86 catchments on the basis of the thresholds-contributing-area concept and/or other topographic factors as derived from high-resolution Digital Elevation Models (DEMs) (Williams and Organ, 1976). 4. Mapping of gully retreat rates and quantification of sediment production (Dymond and Hicks, 1986). Improved mapping capabilities of gully distribution and magnitude could lead to enhancements in agricultural production and water resources management as well as, provide more accurate hazard maps through accurately locating severely eroded areas. Changes in the distribution and extent of gullies play an important role in determining the location and resources required for erosion control. Study area The study area is the Jos metropolis, and lies between Latitudes 9°47ʹ00ʺ and 9°53ʹ00ʺ north, and Longitudes 8°49ʹ00ʺ and 8°55ʹ30ʺ east as shown in Figure 1.

Jos is a colonial creation, and its history and early growth is closely tied to tin mining. Though, mineral exploration provides a good source of livelihoods to the people, the activities have adverse impact on land use and land cover. In the area, there is extensive loss of vegetative cover by the aggressive miners. The area is characterized by abandoned mining ditches, mine ponds, mine dumps and mounds. Besides mining, Jos was a popular recreational and holiday town for the colonial officials due to its climate weather and appealing natural environment. The town has grown from several mining settlements and camps which have over the years merged to form the present metropolis.

The impacts of mining activities on the study area are immense. Erosion by water is the most common form of soil degradation, causing loss of soil nutrients, organic matter and damage to soil physical properties and standing crops. The tin mining landscape of the Jos Plateau is characterized by mined ponds, pilot ponds, reservoirs, mine dumps and mounds, and these (with other natural factors) have facilitated the incidence and persistence of gully erosion in the area. This study, therefore, attempts to map out the gully erosion areas in Jos metropolis in Plateau State, Nigeria, using Geospatial information technology. MATERIALS AND METHODS The materials used for this study include: - Global Positioning System (GPS): This was used to obtain the coordinates of gully erosion sites, and were input into Excel Microsoft 2007 and imported into ArcGIS 9.3 software.

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Figure 1. Map of Plateau showing the study area

- Administrative map of Plateau State showing local government areas at scale of 1: 500,000. - High resolution satellite image (Quick Bird) of 0.67 m resolution (Figure 5). - Downloaded Aster data, used to generate contour data at about 50 m interval. The data acquired were processed, and this involved georeferencing, sub-mapping, buffering, and digitization through an on-screen digitizing mode. This gave rise to an inter-active topographic and land use/land cover data. The digitized map of the gully erosion sites was produced, as well as a vector-to-raster conversion to produce raster data of gully erosion sites. The work flow of the methodology is shown in Figure 2.

The structural model of the layers was developed to show their entity relations. The logical design was done to enable easy representation of the data structure when implemented using the software. The various entities are shown in layers and their attributes are stored in the database. In a relational data model, geospatial data are stored in tables indicated by rows and columns. The

logical decision is done for the database showing names of layer/table and other attributes. The entity relational diagram is shown in Figure 3. Spatial analysis The vector layers created were in UTM coordinate system projection, and enabled the calculation of area, length, buffering and overlay (Figure 4). RESULTS AND DISCUSSION Mapping of the spatial spread of the gully erosion The major phenomenon in the study area is the mining ponds. However, from the satellite imagery used, apart from the mining ponds identified, areas along streams and Ngyel River which have high run-off of water, with the soil texture permeable to erosion have severe effects due to massive transportation of the loose soil in the

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Figure 2. Work flow methodology.

area. The metric and geometric relationships of the spatial spread of these gullies are mapped out. Contour generation In Jos, topographic changes are visible and well pronounced from contours drawn and DEM produced, as

shown in Figures 6, 7 and 8 and this is a clear indication of land degradation. In all, 38 gully erosion sites were identified in the study area, as shown in Table 1. Analysis of 3D digital elevation model The DEM of the study area showed slopes that appeared

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Figure 3. Entity relational diagram.

Figure 4. The study area showing spatial entities.

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Figure 5. Image of Jos Bukuru, 2005 for the study area.

steep. Also, the slope shapes are dominantly convex which implies that the flow direction of water generated from all sides of the slope goes down to the low-lying areas. Due to loss of vegetative cover, resulting mainly from mining activities, and coupled with the poor soil compactness, erosion has become pronounced in the study area.

The analysis of the buffered area for the eroded areas (150 m) along the stream (Figure 8) showed that several cultural features, including residential, official and commercial buildings fall within the vulnerable zone. This indicates danger for all the occupants at the rate that the erosion is advancing. From the DEM, the percentages of the areas covered by 5 identified features are shown in

Figure 8, 9 and 10. It is observed that eroded lands occupy the greatest (4.06%), followed by mining ponds (2.92%). Effect of gully erosion in the area This study has shown that gully erosion has reduced the available land for agriculture in the area. It has also reduced the quality of soil fertility through the washing of the top soil which is a key for arable farming. Even cultivated crops are washed away. All these led to repeated cultivation of the available lands without fallowing, and these resulted in low yields, affecting the

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Figure 6. Location of gullies in Jos Bukuru study area.

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Figure 7. DEM showing vulnerability to erosion along a stream.

livelihoods of the farmers. Gully erosion also affects infrastructure like roads, streets and buildings, and has socio-economic implications for the people.

The findings of this study has revealed that gullies and mining ponds are more pronounced in the study area, with a continual downward slope of the terrain undulation

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Figure 8. Bar chart for the land use in the study area.

Table 1. Location of gully erosion sites in the study area.

S/No. Locations Number of sites

1 Sabon Barki 3

2 Bukuru low-cost bridge 1

3 Jossy Royal Hotel Area 4

4 Railway area 14

5 Railway bridge 1

6 Sabon Barki 13

7 Bukuru express way 1

8 Sabon Barki junction 1

Total 38

from the South Eastern part towards the centre of the study area. The general steepness of the terrain are high from the periphery and descending towards the center indicating that large volume of run-off water are discharged towards the centre of the city.

There are several abandoned mining ponds, as well as, flooded areas in the Jos Plateau. The action of rain which results into run-offs, and facilitated by the uncontrolled mining activities, causes the land surface to be eroded, with deposited sands that block the roads. Furthermore, good lands for arable farming are devastated by erosion,

and this condition has serious implications for food security in the State in particular and the country in general. Conclusion The foregoing results have shown that gully erosion exacerbated by human factor of mining, have greatly affected the landscape of the Jos Plateau. Using the geospatial information technology for gully erosion

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Figure 9. Abandoned mining pond within a residential area in Jos.

Figure 10. Abandoned mining pond with erosion destroying surrounding farmlands.

Ogwuche and Bulus 95 mapping has helped to bring an appreciation of the geo- visualization of the spatial distribution of human contributions to land degradation, especially, gully erosion in the area. Recommendations This study makes the following recommendations: i) There should be a comprehensive environmental planning of the Jos metropolis so as to disaggregate the land use into residential, commercial, industrial and mining purposes. ii) All the abandoned mine sites should be landscaped to bring about the aesthetic beauty of the ex-mining environments. iii) All the abandoned mining ponds should be used as dams for dry season irrigation farming. iv) The areas affected and threatened by gully erosion should be declared disaster zones, and people restricted from building within such areas, and commercial or agricultural activities restricted. v) There should be a legal and regulatory framework for the design and operation of mining activities in the area. REFERENCES Ali, M.T. and Behzad, K. (2012). Accuracy and Precision of Same

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