GEOINFORMATION ASSESSMENT of DAM FAILURE VULNERABILITY in NIGERIA *Salamatu, L
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GEOINFORMATION ASSESSMENT OF DAM FAILURE VULNERABILITY IN NIGERIA *Salamatu, L. A1, Hauwa, .M.A1, Mahmud,U1, Oluwafemi, O.A1, Adepoju, K.2, 1Centre for Geodesy and Geodynamic (CGG), Toro, Bauchi State, Nigeria. 2Obafemi Awolowo University, Ile-Ife Osun state. E-mail:[email protected] Abstract: Dam has become a widely distributed and devastating disaster that has caused significant damages both economically and socially in Nigeria. Dam failure has caused more harm than good, Dam failure are caused by flood event, geological/foundation weakness (earthquake), storms and other human activity. Flooding originated from different levels of human environmental system which can lead to Dam failure. Flood event in Nigeria have pushed rivers over their banks and submerged hundreds of kilometers of urban and rural lands. Flash flood are common features in Nigeria during the raining season. This study therefore aims at creating a database and mapping of vulnerable area to dam failure using geospatial techniques. SRTM DEM was developed with ARCGIS 9.3 to identify vulnerable areas in both Towns/Villages as well as LGAs, the DEM was reclassified to highly vulnerable, moderately vulnerable and low vulnerable, using interval of less than 50m, 100m, 200m elevation from Dam 500m Buffer and River 300m Buffer. The study shows that 17 LGAs in Nigeria are vulnerable to dam failure after the buffering analysis was carried out and a total of 33 states are vulnerable to event of Dam failure. KEYWORD: Flooding, Vulnerability, Dam failure, Disaster, Nigeria 1 INTRODUCTION The earth is a combination of different natural systems which occurred uninterrupted before the existence of human beings. Geophysical events such as earthquakes, volcanic eruptions, landslides, spread and retreat of water along the river plains took place as a part of natural systems. Pandey, (2009)Natural hazards are the events or natural phenomenon that threatens or act disastrously in different space and time. When the natural hazards affects the environment and leads to financial environmental or human losses then it is called natural disasters. Natural disasters can be associated with many phenomenon such as the movement of the earth surface (earthquakes, mass movement), water (floods, tsunamis, storms) and fire (wild fire) Gillespie et al, (2007).Water resources in Africa seems abundant, Average annual flow is over 4000 billion m3, and includes the world’s longest river (the Nile) and it’s second largest in terms of basin and flow is the Congo. The wet equatorial zone produces 95 per cent of Africa total flow, while the semi-arid and arid zones produces only 5 per cent .Floods are of many types which includes flash flooding, flooding due to rising ground water Gruntfest and Handmer,( 2001), coastal flooding, and flooding due to the opening or breaking of dams or reservoir Forkuo,( 2011). Flash flood can occur within minutes or hours of excessive rainfall or a dam or levee failure or sudden release Jeyaseelan (1999). Dams which are constructed for a number of purposes such as provision of drinking water, recreation, irrigation and hydropower. If any outbreaks causes loss of life and affects agricultural products seker et al (2001). Dams and reservoirs provide important water storage for human and agricultural consumption and use, flood control, hydroelectric production, navigation, and recreation. However, along with the benefits, dam can also pose serious risk for the downstream river basin, agricultural land, historical sites, wildlife habitat and communities in the event of a catastrophic dam failure (breach). Whether caused by natural forces or terrorist attack, a catastrophic event like a dam failure is of great concern to local government officials in 2 terms of community preparedness and response. Dam failures happen. There are many reasons why a dam may breach: geological/foundation weakness (example: earthquakes), extreme storms which cause dam to overtop, structural problems, old age, terrorism, etc. Aim: The aim of this study is to assess the human vulnerability to Dam Failure hazard in Nigeria with a view of providing policy makers a framework for monitoring and responding to environmental hazard. Objectives The objective of the study are to: The specific objectives includes: To create a Geographic Information System (GIS) Database for Dam location in Nigeria; To examine the vulnerability level of each community where the Dams are located; To create public awareness and increased public participation in land use planning. Study Area Nigeria, officially the Federal Republic of Nigeria, is a federal constitutional comprising 36 states and its Federal Capital Territory, Abuja. The country is located in West Africa and shares land borders with the Republic of Benin in the west, Chad and Cameroon inthe east, and Niger in the north. Its coast in the south lies on the Gulf of Guinea in the Atlantic Ocean. Its cover a total Area of 923,768km2 /356, 667, sq. mi. Nigeria has a lot of Rivers and Dams which serve as means of hydropower, drinkable water, conservation area, recreational area, Transportation, Tourism and irrigation. Some of which includes the kainji dam, shiroro dam, Gubi dam, Eleyele dam, Doma dam, Bosso Dam etc. 3 Figure 1.1The Study Area Source: Salamatu (2014) 4 MATERIALS AND METHODS Data Types and sources In other to achieve the objective of the study both primary and secondary data which contains both spatial and non-spatial (attribute) were used. The data used includes: 1. TheAdminstrative Map of Nigeria showing the states 2. Local government map showing villages and Towns 3. Digital Elevation Model (DEM) of Nigeria at 30m resolution sourced from www.srtdem.org` 4. Google earth pro Data Processing and Preparation Google Earth Using Google earth, locating the Map of Nigeria the Dams were digitized with the required coordinates, and each of the Dams digitized was exported into the ArcGIS 9.3 version environment, the digitized Dams was formally in the format of KMZ. In the ArcGIS 9.3 version the Dams digitized was converted into shape-files after being exported. The digitized Dams was overlaid on the DEM of Nigeria as well as the administrative boundary of Nigeria. AdministrativeMap of Nigeria Using ArcGIS 9.3 version software the maps was imported using the Geo-tiff format from the C:\ drive, The map was Geo-reference and digitized, together with the 36 states and the federal capital territory Abuja as well as the drainage, The shape-files of the villages/towns and the 5 Local government area was also imported into the ArcGIS 9.3 version environment and the layer added to the Map of Nigeria. Methodology to Achieve Each Objective Objectives 1: To map out the Drainage and Dam Using ArcGIS 9.3 version the drainage was digitized on the map of Nigeria and the dams where digitized from Google earth which was converted to shape-file and then overlaid on the map of Nigeria. The criterion used for mapping out was based on proximity analysis in which the Buffer tool was used to Buffer River at 300m and Dams at 500m radius Objectives 2: To delineate and map out the vulnerability of villages and towns to Dam failure The Dam vulnerability area are areas that are likely to be flooded when the river overflow its banks, which leads to dam break or dam failure. The delineation and mapping of the vulnerable villages and towns is crucial for vulnerability assessments. The vulnerable areas was extracted from the DEM which was generated from the digitized contours of the shuttle Radar Topography Mission (SRTM). The dams where digitized from Google Earth and exported to ArcGIS 9.3 version and overlaid on the Map of Nigeria as well as the DEM. Triangular irregular Networks (TIN) was also generated from the contours extracted from the SRTM. The criterion used for delineating the flood vulnerable area was based on proximity analysis in which the Buffer tool was used for the delineation and also height (elevation) and this was achieved using the DEM which was therefore categorized into very highly vulnerable, highly vulnerable, moderately vulnerable, low vulnerable and very low vulnerable to dam break/ flood, the delineated criterion includes 6 1. Villages/Towns within 500m buffer of a dam 2. Villages/Towns within elevation less than 50m within 500m buffer of a dam 3. Towns within river dam buffer zones Objectives 3: To delineate and map out the vulnerability of the Local government areas (LGAS) Using ArcGIS 9.3 version, the map of Nigeria was digitized and the shape-file of the LGAS was overlaid, the dam 500m buffer was overlaid as well as the river 300m buffer which shows LGAS that falls within the buffer zones of the dam. Buffers are usually used to delineate protected zones around features or to show areas of influence, buffer can be used to select features in another feature class or they can be combined with other features using an overlay tool to find parts of features that fall in the buffer areas. The river and the dam was buffered. The output result shows the LGAS that are within river and dam buffer. RESULTS & DISCUSSION Results The results of the study includes the production of thematic map of Dams location and Drainage, Towns and Villages vulnerable to Dam failure as well as LGAs and states in which the Towns and Villages are located. The results located also includes proximity analysis (Buffering) to determine settlements that are vulnerable Dam failure and identifying locations that are prone to Dam failure within the study area. 7 Drainage and Dam (Objective