Flood Vulnerability Modelling Factors of Nafada Town, Gombe State, Nigeria Using Remote Sensing and GIS Techniques
M.I. Muhammad a , * , U. Wali a , M.A. Modibbo a
a Department of Surveying and Geoinformatics, Abubakar Tafawa Balewa University, Bauchi, Nigeria
* Corresponding author
E-mail addresses: (M.I. Muhammad)
This study employs the integrated approach of Remote Sensing and Geographic Information Systems (GIS) techniques in flood management with the goal of deriving flood vulnerability modelling factors. Flood vulnerability studies have become more efficient in recent years because of the availability of advanced computational facilities and use of GIS. Almost every year, Nafada Town has been experiencing repeated flooding during the rainy season (July to September). As a consequence, properties are lost or destroyed and sometimes lives are lost. The aim of this research is to develop factors that could be used in flood vulnerability modelling of terrain features that favored the incidence of the floods as part of the solution to the problem. The objectives were to process Shuttle Radar Topographic Mission (SRTM) Scene 186/052 with a resolution of 90m·90m which covered the study area, downloaded from United State Geological Surveys (USGS) and the factors were obtained. These fetors were fill sink (elevation), terrain wetness index, proximity to river and overland flow length using the Integrated Land and water information system (ILWIS 3.3) Software, the factors were then classified using Natural breaks extension of ArcGIS 9.3 software. Hence, GIS techniques were proved to be useful in deriving the flood vulnerability modelling factors in a time and cost effective manner. It is recommended that GIS methods should be incorporated in planning and management of floods in the study area and further study should be conducted to combine these factors to develop a flood vulnerability model of the area.
Keywords: Flood, Vulnerability, GIS, Remote Sensing, Mission, Nafada Town, Modelling, Proximity, Overland, Terrain wetness Index.
In simple terms, flood is defined as temporary covering of land by water as a result of surface water escaping from their natural confines or as a result of heavy precipitation (Opolot, 2013). Perhaps, in contemporary times, it is the most consistent serious natural disaster affecting most countries of the world. For instance, Asian countries have been at the frontline of the incidence and severity of flooding in the world. It is estimated that the countries experienced 1/3rd of the 1562 floods that occurred in the world between 1994 and 2004 (Uddin et al., 2013; Bhatt et al., 2014). In Europe, flooding was reported in countries like Italy, Russia, Romania etc. (Ebi et al., 2003). It is even forecasted that the incidence of floods in Europe will double by 2050 while annual economic losses resulting from them will increase five folds (Conner, 2014). Thirty-two major floods occurred in the United States in the 20th Century (Perry, 2000).
2. Study area
3. Materials and methods
The Shuttle Radar Topographical Mission (SRTM) Digital Elevation Model (DEM), Scene 186/052 with a resolution of 90 m·90 m which covered the study area was obtained from (USGS, 2008). The ILWIS 3.3 was used for data processing. The flow chart in Fig. 2 describe how the DEM was processed to achieve the purpose of the study.
The SRTM DEM was imported into the ILWIS 3.3 environment and was process and the flood vulnerability criteria (fill sink/elevation, terrain wetness index, proximity, overland flow length) were obtained.
Classification is based on natural breaks using ArcGIS 9.3, classes are based on natural groupings inherent in the data. ArcMap identifies break points by picking the class breaks that best group similar values and maximize the differences between classes. The features are divided into classes whose boundaries are set where there are relatively big jumps in the data values. It is typical to use this type of thematic classification on continuous phenomena, such as slope, distance, or suitability, where you want to classify the range into a small number of classes and assign colors to those classes.
4. Results and discussion
The results obtained from the data processing described above are presented below.
The graphical representation of the elevation values of the study area is shown in figures 3A and 3B. Fig. 3A show that the average geodetic height of the study area ranges from 246 m (lowest) to 499 m (highest elevation). Fig. 3B show that elevation is lowest (depicted in green) around the River and increases outwards to the height of about 499 m above sea level. This suggests a difference of 53 m between the lowest and highest elevations. This difference is large enough to ensure that in line with the law of gravity, the low lying river and its immediate vicinity is the destination of runoff from surrounding higher elevations.
5. Conclusion and recommendations
Nafada town and its environment has been experiencing flooding over the years, this according to the research has been attributed to many factors amongst which are excess stage discharge, vulnerability, nature and rate of the Terrain Wetness Index, Proximity to the river and Geodetic Height of the area. High Terrain Wetness Index is recorded in areas around river Nafada, significant percentage of the area is low-lying, larger percentages of the people lives very close to the river, hence with close proximity to the river Nafada, the vulnerability and susceptibility of the people to flooding is very high. Hence, the application of this method (RS and GIS) in Nafada to developed flood vulnerability factors like Terrain Wetness Index, DEM, Proximity to the river and overland flow length, it is in no doubt a holistic approach in flood management in the Nafada town and its surroundings. This study was conducted under major constraint of limited data availability. Therefore, the following recommendations are made for the further studies in the future.
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