REMOTE SENSING AND GIS ASSESSMENT OF FLOOD VULNERABILITY OF NIGERIA S CONFLUENCE TOWN

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1 REMOTE SENSING AND GIS ASSESSMENT OF FLOOD VULNERABILITY OF NIGERIA S CONFLUENCE TOWN Abstract J. J. Dukiya Department of Urban and Regional Planning, Federal University of Technology, Minna duksat2000@futminna.edu.ng Lokoja, the Kogi state capital, is located at the Niger-Benue confluence. Hazards erupt when human activities in the confluence area are not properly managed. This article uses the Remote Sensing and GIS technique to assess the flood vulnerability zones of the town using the bench mark minimum and maximum water level from the year 1995 to Land-use/land-cover and flood vulnerability maps were generated from the satellite imageries of Landsat (TM/ETM) of 1987, 1992, 2001 and Nigeria Sat 1 of The orthophoto map and the image drape generated clearly shows that development along the marine road and the new Filele mini-dual carriage road are within the floodable areas of the river confluence. The study recommended an integrated approach in managing the confluence zone. In addition, major development activities should be concentrated on the South-western part of Lokoja. Keywords: Confluence, remote sensing, urbanization, vulnerability Introduction It has been observed that the more accessible the parts of drainage basin and river courses are, the more severe the conflict between lands uses types than the erstwhile remote areas. This is exactly the case of the Niger-Benue rivers right from their sources outside Nigeria down to the delta area on the Atlantic Ocean in Nigeria. The Niger-Benue river confluence is of major interest in this study as it relate to urbanization activities in Lokoja town and river encroachment. Nigeria is well endowed with water resources, both surface and underground water abound in the country. The total annual surface water of Nigeria has been estimated to be 193 X 10 9 of cubic meters, or about 6,120 cubic meters per second. Others have, however, estimated it to be about 10, 000 cubic meters per second or about 315 X 10 9 cubic meters per annum (UNDP, 1996). River confluence areas all over the world are known to offer spectacular environmental attractions to people and have therefore been the focus of varied aspects of human activities. This is one of the major reasons why the former colonial administrator, Lord Lugard, had to locate his administrative headquarter at Lokoja. But that the founding and growth of cities rest on physical resources is axiomatic, and so the rise and development of a city depend not only on the natural resources of its site and environs but also on the regional framework of its physiographic which either aids or hinders its internal and external functional efficiency, Obateru (2004). 123

2 In the last seven years, urbanization activities has become complex in Lokoja town which can be attributed to her Kogi state capital status in 1991 with much pressure on the available land spaces. More so, the core area of the town is sandwiched between the Niger River valley and the elongated Patti Hill to the west. But Obateru (2004) opine that topography of the site and environs of a capital should not be rough or rugged, or else there would be insufficient building space which would result in high land values and inhibit efficient land use organization and economical provision of social infrastructure and public utilities system. The study specifically assesses the urbanization pattern and its effect on the shoreline area of the river confluence environment and the flood vulnerability of the developed areas bordering the river bank. The aim of this study is to assess the effect of Lokoja s urbanization growth on the Niger-Benue confluence area and the vulnerability level to flooding activities. Study area Lokoja town is located between Latitude: N N and Longitude: E E with a total land coverage of about sq.km. The town is about 170 km from the Federal Capital Territory (FCT), Abuja (Fig. 1). Methodological approach After the selection and defining of the study area in term of spatial coverage, three major sources of data sets were identified, that is, ancillary data, satellite data, and ground truthing information. The satellite images used for this study are the Landsat TM/ETM/MSS and the Nigeria Sat.1 as shown in 124 Table 1, and this was subjected to Digital image processing and analysis. Three topographical maps also used for this project are Lokoja sheet no. 147 NW, 147 SW and 147 SE. Also acquired for the study is the ten (10) year water discharge and height gauge of River Niger obtained from National Inland Waterways Authority (NIWA), Lokoja. The georeferencing and co-ordinate system was carried out

3 using Geographical Positioning System (GPS) Garmin 76 model. Table 1: Data sources and their characteristics Data Type Date Scale Identification Acquisition source Landsat (TM), Path 189 row 055 GLCF online Landsat (TM) 1992 Mosaic extraction NRSC, Jos, Nigeria. Landsat(ETM) 1/9/2001 Path 324 row 036 GLCF online Nigeria Sat Mosaic extraction Topographical 1968/69 1: 50,000 Lokoja1 sheet map 147 S.W Topographical map Topographical map Niger volumetric discharge gauges data /69 1: 50,000 Lokoja sheet 147 N.W 1968/69 1: 50,000 Lokoja sheet 147 S.E NRSC, Jos, Nigeria. Kogi state ministry of land and survey, Minna, Nigeria. Federal surveys Kaduna, Nigeria. Federal survey Kaduna, Nigeria. National Inland Waterways Authority (NIWA), Lokoja, Nigeria. To further analyze the general drainage pattern and the terrain configuration of this confluence area, the Digital Terrain Model (DTM) was developed using the contour based network with Lokoja Topographical map sheet 147 N.W. Grid lines were super-imposed on the sheet and the co-ordinate of each grid inter-sections (Grid nodes) and their approximate heights were computed using the Latlon WGS84 in ILWIS 3.0 Academic co-ordinate transformer. A total of 1,172 grid nodes resulted from the Topographical surface gridding for the spread sheet (X,Y,Z) grid-node co-ordinate were extracted using the principle of Lat-long gradient slope distance departure. Trend in the Niger River discharge and the encroachment activities The water discharge of river Niger is highly dependent on the rainfall of other West African countries through which the river flows. The Benue River also is not totally free from other countries 1

4 contribution since it originated from Cameroon Mountain. The major issue discussed here is the continuous modification of the river course particularly around the confluence area which is more of human induced than natural forces. Flooding activities is not an annual event in most rivers regime, a detail survey of the rivers regime gives better understanding of human interaction and modification of such river, Laboryrie, et al (2001). At one of the recording station at the confluence area as shown in Table 2, the year 1998 and 1999 had the highest water discharge which is not unconnected to the activities of the large dams at the upper parts of the river including Kainji and Shiroro dams. Table 2 Yearly discharge record of Niger River, reading at Niger km. years Minimum Discharge in m3/s Maximum Discharge in m3/s Range Discharge in m3/s (March) (October) 1 Mean water level (m) Source: Extracted from NIWA s gauge record in Lokoja Elevation of gauge zero above datum =13.40m Elevation of gauge zero above Mean Sea level (M.S.L) =32.37 Generation of co-ordinate database in arcview GIS In the generation of the DTM based contour map feature, about 1,172 spot heights were digitized as indicated in Fig. 5. The elevation value (H) and the planimetric co-ordinate (EN) of the study area were contoured on the attribute table. This is then imported into Surfer software for conversion into surface grid for surface vector DTM generation. From the vector point figure, it is obvious that some areas is as low as 5.86m above sea level while other is as high as at the Patti ridge summit. Classification and mapping of flood vulnerable areas The spot heighten numerical data generated over the area reveals the minimum and maximum height which was interpolated on the numerical yearly water level gauge (1995 to 2005) acquired from NIWA to develop the potential vulnerability zones. The spot heighten numerical data generated shows that some areas are within 8.023m above sea level and at the same time the Niger River water level in the year 1998 and 1999 in particular was as high as 10m above sea level as presented in table 2 earlier. Findings

5 The following major challenging issues were found out in the course of the study. (i) Lokoja town sandwiching of between the River Niger and the Patti hill actually directly or indirectly supports the spatial development currently spreading toward Kabba and Ganaja roads as shown in this study. (ii) There is general expurgation of many first and second order river channels which under natural conditions, played major role in keeping both sediment and runoff among many small channels which also plays its part in delaying movement of flood peak. Developmental activities all around the catchments areas of River Mimi and even that of the stream at the northern parts of the town changes the river regime and the shape of the river courses. (ix) The DTM generated and the image drape clearly shows that Lokoja town is not only a river side settlement but also a hill side settlement. Also it is clear that new development activities are growing along the river banks that are unstable. (x) On the issue of flooding, it become obvious in this study that newly developed areas along the Niger River are flood prone as indicated in the mapped image analysis. Recommendations To ameliorate the obvious latent problems in the area: The state urban development board and the ministry should withdraw their control of land matters within the 100m either side of the Niger River as entrenched in the NIWA gazette in order to avoid the abuse of the Niger River bank within Lokoja and its environ if the dredging of the Niger and revitalization of the Baro port will not be a mere dream. This is in agreement with scholars like Aroh 2000 in his paper titled Dredging the Lower River Niger -- A Wrong Start So Far. The Niger-Benue confluence is a national pride and should not be seen as Kogi state affair but rather be accorded federal status like any other national parks. Moreover, the Mississippi and Missouri River confluence is national pride in America and it is highly harnessed for national interest. The state government should call a spade-a-spade and relocate all the major governmental activities to the new secretariat area. Also the development control laws in the state should be more stringent so that apart from generating more revenue for the state, physical planning objectives can be realized particularly with the new master plan in place. Apart from relocating the major public institutions to the western side of Patti hill, the new market should be relocated to the same direction even because of the new Abuja road dualization. Human capacity building should be one of the states priorities if the environment is to be sustained. Most of the staffs in the ministry of land, survey and town planning are not computer literate not to talk of manning a RS and GIS work stations. The fact that planning activities has moved away from the traditional, rudimental and labour intensive activities to the modern day computer aided technology was fully demonstrated in the work of Ferreira, J. and Wiggins, L. (1993). References Adefolalu, D.O., (2006). Weather events, climate variability and change in relation to NEEDs and MDGS; problems and prospect of the Nigeria Economy, 9 th inaugural lecture of the Federal University of Technology, Minna, Nigeria, p.56. Drescher, A. W. and Iaquinta, D. T. (2002). Urbanization Linking Development across the Changing Landscape. Final Draft. Rome. January 18, Ferreira, J. and Wiggins, L. (1993). Computing Technology for Land Use and Regional Planning, in R. E. Klosterman and S. P French (Editors) Third International Conference on Computers in Urban Planning and Urban Management, Georgia Institute of Technology, Atlanta, GA, pp

6 Hope Sr., K.R. and Lekorwe, M.H. (1999). Holmen (2004). Food system and biodiversity in Africa, Urbanization and the Environment in Southern Africa: Current issues in international Towards A Managed Framework for the Sustainability of Cities. Rural Development. Pub. Swedes University. Hoggan, H.O., (1989). Computer Assisted Floodplain UNDP (1996). Human Development Report Hydrology &Hydraulics, featuring the U.S Oxford: Oxford University Press. Army corps of Engineers HEC-1 & HEC-2 software system McGraw Hill Inc, pp1-71. Appendix LOKOJA TOWN ON LANDSAT (TM BANDS 2, 4, 5) AS AT Source: Authors laboratory analysis. GPS reading points for the ground truthing survey. S/N Descriptions of locations GPS co ordinate Reading Remarks 1 NIWA duck water site N , E This at the river bank of the Inland waterways 128

7 2 Lokoja Beach Hotel N , E This is at final point of the confluence 3 Mimi bridge across Ganaja road N , E This is the bridge of ganaja road on Mimi river 4 General post office N , E Mollys store ltd, beach N , E 0060 road Filele junction on Abuja N , E 0060 road Source: Researchers field survey, This is the central administrative area of the town along IBB road. This is a T-junctions road point beside the beach road market. This is a T-junctions road point at the new market on Abuja road. 128